WO2021013876A1

WO2021013876A1 - Process for preparing a silicone dioxide suspension

Info

Publication number: WO2021013876A1
Application number: PCT/EP2020/070646
Authority: WO
Inventors: Thomas Kayser; Bastian WEISENSEEL; Mirko Wittrin; Markus Wilde
Original assignee: Heraeus Quarzglas Gmbh & Co. Kg
Priority date: 2019-07-24
Filing date: 2020-07-22
Publication date: 2021-01-28
Also published as: EP4003923A1; CN114423710A; TW202126579A; TWI765303B; JP2022541570A; JP7324931B2; CN114423710B

Abstract

The present invention relates to a process for preparing a silicone dioxide suspension containing the following method steps: providing a silicone dioxide powder and a liquid; mixing the silicone dioxide powder with the liquid to obtain a slurry; treating the slurry with ultrasound to obtain a precursor suspension; guiding at least a part of the precursor suspension through a first multi-stage filter device, wherein the first multi-stage filter device comprises at least a first, a second and a third filter stage, each filter stage including at least one filter, wherein the second filter stage is arranged downstream of the first filter stage and the third filter stage is arranged downstream of the second filter stage, the first filter stage having a filter fineness of 5 μm or more, the second filter stage having a filter fineness in a range from 0.5 to 5 μm, the third filter stage having a filter fineness of 1 μm or less, and wherein at least one of the filter stages selected from the first, second and third filter stages has a deposition rate of 99.5 % or more. The invention also relates to a silicone dioxide suspension obtained in this way and to granulates and secondary products that can be produced therefrom.

Description

METHOD OF MANUFACTURING A SILICON OXIDE SUSPENSION

The present invention relates to a method for producing a silicon dioxide suspension, comprising the method steps: providing a silicon dioxide powder and a liquid; Mixing the silica powder with the liquid to obtain a slurry; Ultrasonicating the slurry to obtain a precursor suspension; Passing at least a portion of the precursor suspension through a first multi-stage filter device, the first multi-stage filter device having at least a first, a second and a third filter stage, each filter stage including at least one filter, the second filter stage downstream of the first filter stage and the third filter stage is arranged downstream of the second filter stage, the first filter stage having a filter fineness of 5 μm or more, the second filter stage having a filter fineness in a range from 0.5 to 5 μm, the third filter stage having a filter fineness of 1 μm or less , and wherein at least one of the filter stages selected from the first, second and third filter stage has a separation rate of 99.5% or more, the separation rate being specified in accordance with ISO 16889, in each case based on said filter, and indicating the filter fineness which is the smallest particle size which is retained by said filter. The invention also relates to a silicon dioxide suspension which can be obtained in this way, granulates and secondary products which can be produced therefrom.

Quartz glass, quartz glass products and products containing quartz glass are known. Various methods for producing quartz glass and quartz glass bodies are also already known. Nonetheless, considerable efforts are still being made to show manufacturing processes by means of which quartz glass of even higher purity, that is to say the absence of impurities, can be manufactured. In some areas of application of quartz glass and its processing products, particularly high demands are made, for example with regard to homogeneity and purity. This is the case, among other things, with quartz glass, which is processed into light guides or light sources. Impurities can cause absorption here. This is disadvantageous because it leads to color changes and attenuation of the emitted light. Another example of the use of high-purity quartz glass are production steps in semiconductor manufacturing. Any contamination of the glass body can lead to defects in the semiconductors and thus to rejects in production. The high-purity quartz glass types used for these processes, in particular high-purity synthetic quartz glass types, are therefore very expensive to produce. They are expensive. Furthermore, there is a desire in the market for the high-purity quartz glass already mentioned, in particular high-purity synthetic quartz glass, and products made therefrom at a lower price. Therefore, there is an effort to be able to offer high-purity quartz glass at a lower price than before. In this regard, both cheaper production processes and cheaper raw material sources are sought.

Known methods for producing quartz glass bodies include melting silicon dioxide and shaping it into quartz glass bodies from the melt. Irregularities in a glass body, for example due to the inclusion of gases in the form of bubbles, can lead to failure of the glass body under stress, especially at high temperatures, or preclude its use for a specific purpose. Impurities in the raw material that forms quartz glass can lead to the formation of cracks, bubbles, stripes and discoloration in the quartz glass. When used in processes for the production and treatment of semiconductor components, impurities can also be worked out in the glass body and transferred to the treated semiconductor components. This is the case, for example, with etching processes and then leads to rejects in the semiconductor blanks. A problem that frequently occurs with the known production methods is consequently an inadequate quality of the quartz glass body.

Another aspect concerns raw material efficiency. It appears to be advantageous to use quartz glass and raw materials that arise elsewhere as a by-product for industrial processing into quartz glass products if possible, instead of spending these by-products as filling material, e.g. in building construction, or expensively disposing of them as garbage. These by-products are often separated as fine dust in filters. The fine dust raises further problems, especially with regard to health, occupational safety and handling.

It is an object of the present invention to at least partially overcome one or more of the disadvantages resulting from the prior art.

It is a further object of the invention to provide light guides, lighting means, molded bodies and

To provide coatings with a long service life.

To provide coatings of glass that are bubble-free or low-bubble.

To provide coatings made of glass which have a high degree of transparency. It is a further object of the invention to provide light guides, lighting means, molded bodies and

To provide coatings that have a low opacity.

It is a further object of the invention to provide light guides with low attenuation.

To provide coatings that have a high degree of dimensional accuracy. In particular, it is an object of the invention to provide light guides, lighting means, molded bodies and coatings which do not deform at high temperatures. In particular, it is an object of the invention to provide light guides, illuminants, molded bodies and coatings which are dimensionally stable even when they are large.

To provide coatings that are tear and break resistant.

To provide coatings that can be produced efficiently.

To provide coatings that can be produced inexpensively.

To provide coatings in the production of which long post-treatment steps, for example tempering, can be dispensed with.

To provide coatings that have a high resistance to thermal shock. In particular, it is an object of the invention to provide light guides, lighting means, molded bodies and coatings which have low thermal expansion in the event of strong thermal fluctuations.

To provide coatings that have a high hardness.

To provide coatings that have a high level of purity and low contamination with foreign atoms. Foreign atoms are understood to mean components that were not specifically introduced.

To provide coatings that contain a small amount of dopants.

To provide coatings that have a high degree of homogeneity. A homogeneity one Property or substance is a measure of the uniformity of the distribution of this property or substance in a sample.

In particular, it is an object of the invention to provide light guides, illuminants, molded bodies and coatings which have a high material homogeneity. The homogeneity of the substance is a measure of the uniformity of the distribution of elements and compounds contained in the light guide, illuminant or semiconductor device, in particular OH, chlorine, metals, in particular aluminum, alkaline earth metals, refractory metals and dopants.

Another object of the invention is to provide a quartz glass body which is suitable for use in light guides, lighting means, molded bodies and coatings made of quartz glass and at least partially solves at least one, preferably several of the objects already described.

It is a further object of the invention to provide a quartz glass body which has a rectilinear shape. In particular, it is an object to provide a quartz glass body which has a large bending radius. In particular, it is a further object to provide a quartz glass body which has a high curl parameter.

Another object is to provide a quartz glass body in which the migration of cations is as low as possible.

It is a further object to provide a quartz glass body which has a high degree of homogeneity over the entire length of the quartz glass body.

In particular, it is an object of the invention to provide a quartz glass body which has a high homogeneity of the refractive index over the entire length of the quartz glass body.

In particular, it is an object of the invention to provide a quartz glass body which has a high degree of viscosity homogeneity over the entire length of the quartz glass body.

In particular, it is an object of the invention to provide a quartz glass body which has a high material homogeneity over the entire length of the quartz glass body.

In particular, it is an object of the invention to provide a quartz glass body which has a high optical homogeneity over the entire length of the quartz glass body.

It is another object of the invention to provide a silica powder having a high sintering activity.

It is another object of the invention to provide a silica powder having a low sintering temperature.

Another object of the invention is to provide a silicon dioxide powder from which stable granules can be obtained. It is a further object of the invention to provide a silicon dioxide granulate which is easy to handle.

It is a further object of the invention to provide a silicon dioxide granulate which has a low proportion of fine dust.

It is a further object to provide a silicon dioxide granulate that can be stored, transported and conveyed well.

It is a further object of the invention to provide a silicon dioxide granulate which can form bubble-free quartz glass bodies. It is a further object of the invention to provide a silicon dioxide granulate which, as a bulk material, includes as little gas volume as possible.

It is a further object of the invention to provide an open-pore silicon dioxide granulate.

It is a further object of the invention to provide a method with which

Quartz glass bodies can be produced, by means of which at least some of the objects already described are at least partially achieved.

It is a further object of the invention to provide a method with which

Quartz glass body can be produced more easily.

It is a further object of the invention to provide a method with which

Quartz glass body can be produced continuously.

It is a further object of the invention to provide a method with which

Quartz glass bodies can be produced by a continuous melting and shaping process.

It is a further object of the invention to provide a method with which

Quartz glass bodies can be formed at a higher speed.

It is a further object of the invention to provide a method with which

Quartz glass body can be produced with little waste.

It is a further object of the invention to provide a method with which configurable quartz glass bodies can be produced.

It is a further object of the invention to provide a method for the production of quartz glass bodies in which a silicon dioxide granulate can be processed in a melting furnace without having to be subjected to a specific compression step, e.g. by a temperature treatment of more than 1000 ° C.

In particular, it is an object of the invention to provide a method for producing quartz glass bodies in which a silicon dioxide granulate with a BET of 20 m ² / g or more can be introduced into a melting furnace, melted and processed into a quartz glass body.

It is a further object of the invention to provide an automated method with which quartz glass bodies can be produced.

It is another object of the invention to provide a method of making a

To provide silicon dioxide suspension which, if possible, has no particles different from silicon dioxide with a particle size of more than 1 μm.

It is another object of the invention to provide a method of making a

To provide silicon dioxide suspension in which the silicon dioxide suspension has as few impurities as possible.

It is another object of the invention to provide a method of making a

Provide silicon dioxide suspension, in which the solids content of the

Silicon dioxide suspension only has the atoms Si, O, H, CI and C if possible.

It is another object of the invention to provide a method of making a

Provide silicon dioxide suspension, in which the solids content of the

Silicon dioxide suspension has as few atoms as possible that differ from Si, O, H, CI and C.

It is another object of the invention to provide a method of making a

To provide silicon dioxide suspension from soot powder that is as homogeneous as possible and as stable as possible in storage.

Another object of the invention is to provide a method for producing high-purity quartz glass.

It is a further object of the invention to provide a method for producing quartz glass with as few bubbles as possible

It is a further object of the invention to provide a method for producing quartz glass which is free of particles from metallic impurities.

EMBODIMENTS OF THE INVENTION

A contribution to the at least partial fulfillment of at least one of the aforementioned tasks is made by the subjects of the independent claims. The dependent claims provide preferred embodiments which contribute to at least partially fulfilling at least one of the objects. | 1 | A method for producing a silicon dioxide suspension comprising the process steps:

(i) providing a silicon dioxide powder;

(ii) providing a liquid;

(iii) mixing the silica powder with the liquid to obtain a slurry;

(iv) sonicating the slurry to obtain a precursor suspension;

(v) passing at least part of the precursor suspension through a first multi-stage filter device,

wherein the first multi-stage filter device has at least a first, a second and a third filter stage,

each filter stage contains at least one filter,

wherein the second filter stage is arranged downstream of the first filter stage and the third filter stage is arranged downstream of the second filter stage,

where the first filter stage has a filter fineness of 5 pm or more,

wherein the second filter stage has a filter fineness in a range from 0.5 to 5 pm,

wherein the third filter stage has a filter fineness of 1 μm or less, and wherein at least one of the filter stages selected from the first, second and third filter stages has a separation rate of 99.5% or more,

where the separation rate is specified in accordance with ISO 16889, in each case based on the named filter, and

the fineness of the filter indicating which is the smallest particle size that is retained by said filter.

The silicon dioxide suspension is obtained in step (v) preferably after passing through the multi-stage filter device.

| 2 | The method according to embodiment 1, wherein the first filter device is characterized by at least one of the following features:

(a) the first filter stage has a separation rate of 90% or less;

(b) the first filter stage has a filter fineness in a range from 5 to 15 μm;

(c) the second filter stage has a separation rate of 95% or more; (d) the second filter stage has a filter fineness of 0.5 to 2 μm;

(e) the third filter stage has a separation rate of 99.5% or more;

Or a combination of two or more of them.

| 3 | The method according to one of the previous embodiments, wherein at least one filter that is provided in one of the filter stages of the first filter device selected from the first, second and third filter stages is designed as a depth filter.

| 4 | The method of any preceding embodiment, wherein ultrasonically treating the slurry is for at least 10 seconds.

| 5 | The method according to any one of the previous embodiments, wherein the treatment of the slurry with ultrasound is characterized by a power density of up to 600 W / liter.

| 6 | The method according to any one of the preceding embodiments, wherein the slurry has less than 5% by weight of additives for stabilizing the slurry, the% by weight based on the total weight of the slurry. 1 The method according to one of the preceding embodiments, wherein the silicon dioxide powder can be produced from a compound selected from the group consisting of siloxanes and silicon alkoxides.

| 8 | The method according to one of the previous embodiments, wherein the silicon dioxide powder has at least one of the following features:

a. a carbon content of less than 100 ppm;

b. a chlorine content of less than 500 ppm;

c. an aluminum content of less than 200 ppb;

d. a content of atoms other than Si, O, H, C, CI of less than

5 ppm;

e. at least 70% by weight of the powder particles have a primary particle size in one

Range from 10 to 100 nm;

f. tamped density in a range from 0.001 to 0.3 g / cm ³ ;

G. a residual moisture content of less than 5% by weight;

H. a BET surface area of less than 35 g / m ² ;

or a combination of two or more of the features a. to h .; wherein the wt .-%, ppm and ppb are each based on the total amount of silicon dioxide powder.

| 9 | The method according to one of the preceding embodiments, wherein the slurry is characterized by at least one of the following features: a.) A solids content of at least 20% by weight, based on the dry matter of the slurry;

b.) As a 4% by weight slurry, the slurry has an all-in-one pH

Range from 3 to 8;

c.) At least 90% by weight of the silicon dioxide particles have a particle size in one

Range from 1 nm to <10 pm;

d.) a chlorine atom content of 500 ppm or less; and

e.) a content of 5 ppm or less of atoms other than Si, O, H, C, CI,

f.) the slurry is rheopex;

where the% by weight and ppm are always based on the total solids content of the slurry.

110 | The method according to any one of the previous embodiments, wherein the silicon dioxide suspension has at least one of the following features:

A. rheopex properties at a temperature of less than 45 ° C. and a solids concentration in the range from 20 to 70% by weight, the% by weight based on the total solids present in the suspension;

B. At least 90% by weight of the silicon dioxide particles, based on the total weight of all silicon dioxide particles, have a particle size in a range from 1 nm to <10 μm;

C. As a 4% by weight suspension, the suspension has a pH in a range from 3 to 8, the% by weight being based on the solids content of the suspension;

D. a chlorine content of less than 500 ppm;

E. an aluminum content of less than 200 ppb;

F. a content of atoms other than Si, O, H, C, CI of less than 5ppm;

the ppm and ppb each being based on the total amount of silicon dioxide particles. 1111 The method according to one of the previous embodiments, wherein the service life of the first, multi-stage filter device is at least 250 liters, the liters based on the filtered volume of precursor suspension filter device.

112 | The method according to one of the previous embodiments, wherein at least one further filter device is used downstream of the first, multi-stage filter device.

113 | A silicon dioxide suspension obtainable by a method according to one of the preceding embodiments.

114 | A method for producing a silicon dioxide granulate, wherein the

Silicon dioxide suspension according to embodiment 13, or a silicon dioxide suspension obtainable by a method according to one of embodiments 1 to 12 is processed into silicon dioxide granules, the silicon dioxide granules having a larger particle diameter than the silicon dioxide particles present in the silicon dioxide suspension.

115 | The method of embodiment 14, wherein when processing a

Silicon dioxide granules containing granules is formed, the granules having a spherical morphology.

116 | The method of embodiment 14 or 15, wherein the processing is a

Spray granulating is.

117 | The method according to any one of embodiments 14 to 16, wherein the spray drying is characterized by at least one of the following features:

a] spray granulation in a spray tower;

b] the presence of a pressure of the silicon dioxide suspension at the nozzle of not more than 40 bar, for example in a range from 1.3 to 20 bar from 1.5 to 18 bar or from 2 to 15 bar or from 4 to 13 bar, or particularly preferably in the range from 5 to 12 bar, the pressure being given in absolute terms (in relation to p = 0 hPa); c] a temperature of the droplets on entry into the spray tower in a range from 10 to 50 ° C, preferably in a range from 15 to 30 ° C, particularly preferably in a range from 18 to 25 ° C. d) a temperature on the side of the nozzle facing the spray tower in a range from 100 to 450 ° C, for example in a range from 250 to 440 ° C, particularly preferably from 320 to 430 ° C;

e] a throughput of silicon dioxide suspension through the nozzle in a range from 0.05 to 1 m ³ / h, for example in a range from 0.1 to 0.7 m ³ / h or from 0.2 to 0.5 m ³ / h, particularly preferably in a range from 0.25 to 0.4 m ³ / h;

f] a solids content of the silicon dioxide suspension of at least 40% by weight, for example in a range from 50 to 80% by weight, or in a range from 55 to 75% by weight, particularly preferably in a range from 60 to 70 % By weight, in each case based on the total weight of the silicon dioxide suspension;

g] a gas inflow into the spray tower in a range from 10 to 100 kg / min, for example in a range from 20 to 80 kg / min or from 30 to 70 kg / min, particularly preferably in a range from 40 to 60 kg / min;

h] a temperature of the gas stream on entry into the spray tower in a range from 100 to 450 ° C, for example in a range from 250 to 440 ° C, particularly preferably from 320 to 430 ° C;

i] a temperature of the gas stream at the outlet from the spray tower of less than 170 ° C .;

j] the gas is selected from the group consisting of air, nitrogen and helium, or a combination of two or more thereof; preferably air;

k] a residual moisture content of the granules when they are removed from the spray tower of less than 5% by weight, for example less than 3% by weight or less than 1% by weight or in a range from 0.01 to 0.5% by weight .-%, particularly preferably in a range from 0.1 to 0.3% by weight, in each case based on the total weight of the silicon dioxide granules formed during the spray drying;

L] at least 50% by weight of the spray granulate, based on the total weight of the silicon dioxide granulate formed during spray drying, has a flight time in a range from 1 to 100 s, for example over a period of 10 to 80 s, particularly preferably over a period of time from 25 to 70 s;

m] at least 50% by weight of the spray granulate, based on the total weight of the silicon dioxide granulate formed during spray drying, covers a flight distance of more than 20 m, for example of more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m; n] the spray tower has a cylindrical geometry;

o] a height of the spray tower of more than 10 m, for example more than 15 m or more than 20 m or more than 25 m or more than 30 m or in a range from 10 to 25 m, particularly preferably in a range of 15 to 20 m;

p] Intentions of particles less than 90 µm in size prior to removal of the granules from the spray tower;

q] sieving off particles with a size of more than 500 μm after the granulate has been removed from the spray tower, preferably on a vibrating chute;

r] the exit of the droplets of silicon dioxide suspension from the nozzle takes place at an angle of 30 to 60 degrees counter to the perpendicular direction, particularly preferably at an angle of 45 degrees opposite to the perpendicular direction.

The method according to any one of embodiments 14 to 17, wherein the silicon dioxide granulate has at least one of the following features:

A) an angle of repose in a range of 23 to 26 °;

B) a BET surface area in a range from 20 to 50 m2 / g;

C) a bulk density in a range from 0.5 to 1.2 g / cm3;

D) an average particle size of the silicon dioxide particles in a range from 50 to 500 μm;

E) a carbon content of less than 50 ppm;

F) a chlorine content of less than 500 ppm;

G) an aluminum content of less than 200 ppb;

H) a content of atoms other than Si, O, H, C of less than 5 ppm;

l) a tamped density of the silicon dioxide granulate particles in a range from 0.7 to 1.3 g / cm ³ ;

J) a pore volume of the silicon dioxide granulate particles in a range from 0.1 to 2.5 mL / g;

K) a particle size distribution D10 of the silicon dioxide granulate particles in a range from 50 to 150 μm;

L) a particle size distribution D50 of the silicon dioxide granulate particles in a range from 150 to 300 μm; M) a particle size distribution Dgo of the silicon dioxide granulate particles in a range from 250 to 620 μm;

the ppm and ppb each being based on the total weight of the silica granules.

119 | A method for producing a quartz glass body at least including the method steps:

i.) Providing the silicon dioxide granulate according to one of the embodiments 14 to

18;

ii.) Forming a glass melt from the silicon dioxide granulate; and

iii.) Forming a quartz glass body from at least part of the glass melt.

| 20 | A quartz glass body obtainable by a method according to embodiment 19.

| 21 | The quartz glass body according to embodiment 20, having at least one of the following features:

A] a chlorine content of less than 500 ppm;

B] an aluminum content of less than 200 ppb;

C] a content of atoms other than Si, O, H, C of less than 5 ppm;

D] a viscosity (p = 1013 hPa) in a range from logio (h (1250 ° C) / dPas) = 11.4 to logio (P (1250 ° C) / dPas) = 12.9, or log ₁₀ ( h (1300 ° C) / dPas) = 11.1 to log ₁₀ (h (1300 ° C) / dPas) = 12.2, or logio (h (1350 ° C) / dPas) = 10.5 to logio ( h (1350 ° C) / dPas) = 11.5;

E] a refractive index homogeneity of less than 10 ⁴ ;

F] a cylindrical shape;

G] a tungsten content of less than 5 ppm;

H] a molybdenum content of less than 5 ppm;

whereby the ppb and ppm are each based on the total weight of the quartz glass body.

| 22 | A method of making a light guide including the following steps:

AI providing a quartz glass body according to one of the embodiments 20 or 21, or a quartz glass body obtainable by a method according to the embodiment 19, wherein the quartz glass body is first processed into a hollow body with at least one opening; B / introducing one or more core rods into the hollow body from step AI through the at least one opening to obtain a precursor;

C / Heat drawing the precursor to obtain an optical fiber with one or more cores and a shell M1.

| 23 | A light guide obtainable by a method according to Embodiment 22.

| 24 | A method for manufacturing a light source including the following steps:

(i) providing a quartz glass body according to one of the embodiments 20 or 21, or a quartz glass body obtainable by a method according to the embodiment 19, the quartz glass body first being processed into a hollow body with at least one opening;

(ii) optionally equipping the hollow body with electrodes;

(iii) Filling the hollow body from step (i) with a gas.

| 25 | A lighting means obtainable by a method according to embodiment 24.

| 26 | A method for producing a molded article comprising the following steps:

(1) providing a quartz glass body according to one of the embodiments 20 or 21 or a quartz glass body obtainable by a method according to the embodiment 19; and

(2) Molding the quartz glass body to obtain a molded body.

| 27 | A molded article obtainable by a method according to embodiment 26.

| 28 | A method of making a coating on a substrate, including the following steps:

| A | Providing a silicon dioxide suspension obtainable by a method of embodiments 1 to 12 and a substrate;

| B | Applying a layer of the silicon dioxide suspension on the substrate. GENERAL

In the present description, range specifications also include the values specified as limits. An indication of the type “in the range from X to Y” in relation to a variable A means that A can assume the values X, Y and values between X and Y. Areas delimited on one side of the type “up to Y” for a size A mean values Y and less than Y.

DETAILED DESCRIPTION OF THE INVENTION

A contribution to at least partial fulfillment of at least one of the aforementioned tasks is made by the independent claims. The dependent claims provide preferred embodiments which contribute to at least partially fulfilling at least one of the objects.

A first object of the invention is a method for producing a silicon dioxide suspension comprising the method steps:

(i) providing a silicon dioxide powder;

(ii) providing a liquid;

(iii) mixing the silica powder with the liquid to obtain a slurry;

(iv) sonicating the slurry to obtain a precursor suspension;

each filter stage contains at least one filter,

wherein the second filter stage is arranged downstream of the first filter stage and the third filter stage is arranged downstream of the second filter stage, the first filter stage having a filter fineness of 5 μm or more,

wherein the third filter stage has a filter fineness of 1 μm or less, and wherein at least one of the filter stages selected from the first, second and third filter stage has a separation rate of 99.5% or more,

Silicon dioxide powder

In the context of the present invention it is possible in principle to obtain silicon dioxide powder from naturally occurring or synthetically produced silicon dioxide. Synthetic silicon dioxide powder is preferably used. Pyrogenically produced silicon dioxide powder is particularly preferably used.

The silica powder can be any silica powder that has at least two particles. Any method that is familiar to the person skilled in the art and appears to be suitable for the present purpose can be considered as the production method.

According to one embodiment of the present invention, the silicon dioxide powder is produced as a by-product in the production of quartz glass, in particular in the production of soot bodies. Silicon dioxide of this origin is often referred to as "soot dust".

A suitable source for the silicon dioxide powder are silicon dioxide particles which are obtained in the synthetic production of soot bodies using flame hydrolysis burners. During the production of a soot body, a rotating support tube, which has a cylinder jacket surface, is moved back and forth in a reversing manner along a row of burners. The flame hydrolysis burners can be supplied with oxygen and hydrogen as burner gases as well as the starting materials for the formation of primary silicon dioxide particles. The silicon dioxide primary particles preferably have a primary particle size of up to 100 nm. The primary silicon dioxide particles generated by flame hydrolysis aggregate or agglomerate to form silicon dioxide particles with particle sizes of around 9 μm (DIN ISO 13320: 2009-1). In the silicon dioxide particles, the shape of the primary silicon dioxide particles can be recognized by scanning electron microscopy and the primary particle size can be determined. Some of the silicon dioxide particles are deposited on the cylinder jacket surface of the support tube rotating about its longitudinal axis. So the soot body becomes layer by layer built up. Another part of the silicon dioxide particles is not deposited on the cylinder jacket surface of the carrier tube, but accumulates as dust, for example in a filter system. This other part of silicon dioxide particles forms the silicon dioxide powder, often also referred to as “soot dust”. As a rule, the part of silicon dioxide particles deposited on the carrier tube is larger than the part of silicon dioxide particles that accumulates as soot dust in the context of the soot body production, based on the total weight of the silicon dioxide particles.

Nowadays, soot dust is usually disposed of as waste in a complex and cost-intensive manner, or it is used as filler with no added value, e.g. in road construction, as additives in the dye industry, as raw material for tile production and for the production of hexafluorosilicic acid, which is used to renovate building foundations. In the case of the present invention, it is suitable as a starting material and can be processed into a high-quality product.

Silica made by flame hydrolysis is commonly referred to as fumed silica. Pyrogenic silicon dioxide is usually in the form of amorphous silicon dioxide primary particles or silicon dioxide particles.

According to one embodiment, the silicon dioxide powder can be produced from a gas mixture by flame hydrolysis. In this case, the silicon dioxide particles are also formed in the flame hydrolysis and removed as silicon dioxide powder before agglomerates or aggregates form. The main product here is silicon dioxide powder, previously known as soot dust.

Siloxanes, silicon alkoxides and inorganic silicon compounds are preferably suitable as starting materials for the formation of the silicon dioxide powder. Siloxanes are understood to mean linear and cyclic polyalkylsiloxanes. Polyalkylsiloxanes preferably have the general formula

Si _p O _p R _2p,

where p is an integer of at least 2, preferably from 2 to 10, particularly preferably from 3 to 5, and

R is an alkyl group with 1 to 8 carbon atoms, preferably with 1 to 4 carbon atoms, particularly preferably a methyl group

is. Particularly preferred are siloxanes selected from the group consisting of hexamethyldisiloxane, hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5) or a combination of two or more thereof. If the siloxane comprises D3, D4 and D5, D4 is preferably the main component. The main component is preferably at least 70% by weight, preferably at least 80% by weight, for example at least 90% by weight or at least 94% by weight, particularly preferably at least 98% by weight %, each based on the total amount of silicon dioxide powder. Preferred silicon alkoxides are tetramethoxysilane and methyltrimethoxysilane. Preferred inorganic silicon compounds as starting materials for silicon dioxide powder are silicon halides, silicates, silicon carbide and silicon nitride. Silicon tetrachloride and trichlorosilane are particularly preferred as inorganic silicon compounds as starting materials for silicon dioxide powder.

According to one embodiment, the silicon dioxide powder can be produced from a compound selected from the group consisting of siloxanes, silicon alkoxides and silicon halides.

The silicon dioxide powder can preferably be produced from a compound selected from the group consisting of hexamethyldisiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane, tetramethoxysilane and methyltrimethoxysilane, silicon tetrachloride, and, for example, silicon tetrachloride and trichlorosetroxylcyclotylane, particularly preferably two or more of them, octotasilasetroxylotylane, and, for example, more preferably octametroxetroxylotyl, and, for example, octamethylcyclotethyl, for example, and preferably more octamethylcyclotrisiloxane.

Various parameters are important for the formation of silicon dioxide from silicon tetrachloride by flame hydrolysis. A preferred composition of a suitable gas mixture contains a proportion of oxygen in the flame hydrolysis in a range from 25 to 40% by volume. The proportion of hydrogen can be in a range from 45 to 60% by volume. The proportion of silicon tetrachloride is preferably 5 to 30% by volume, all of the aforementioned% by volume based on the total volume of the gas stream. A combination of the aforementioned volume fractions for oxygen, hydrogen and SiCl4 is also preferred. The flame in the flame hydrolysis preferably has a temperature in a range from 1500 to 2500 ° C, for example in a range from 1600 to 2400 ° C, particularly preferably in a range from 1700 to 2300 ° C. The silicon dioxide primary particles formed in the flame hydrolysis are preferably removed as silicon dioxide powder before agglomerates or aggregates form. The silicon dioxide powder can have at least one, for example at least two or at least three or at least four, preferably at least five of the following features:

i. a BET surface area in a range of less than 35 m ² / g, for example from 25 to 35 m ² / g, or from 25 to 30 m ² / g, and

ii. a bulk density of 0.01 to 0.3 g / cm ³ , for example in the range from 0.02 to 0.2 g / cm ³ , preferably in the range from 0.03 to 0.15 g / cm ³ , more preferably im Range from 0.1 to 0.2 g / cm ³ or in the range from 0.05 to 0.1 g / cm ³ .

iii. a carbon content of less than 100 ppm, for example less than 50 ppm or less 30 ppm, particularly preferably in a range from 1 ppb to 20 ppm;

iv. a chlorine content of less than 500 ppm, for example of less than 300 ppm or less than 150 ppm, particularly preferably in a range from 1 ppb to 80 ppm;

v. an aluminum content of less than 200 ppb, for example in the range from 1 to 100 ppb, more preferably in the range from 1 to 80 ppb;

vi. a total content of atoms other than Si, O, H, C, CI of less than 5 ppm, for example less than 2 ppm, particularly preferably in a range from 1 ppb to 1 ppm;

vii. at least 70% by weight of the powder particles have a primary particle size in a range from 10 to 100 nm, for example in the range from 15 to less than 100 nm, particularly preferably in the range from 20 to less than 100 nm;

viii. a tamped density in a range from 0.001 to 0.3 g / cm ³ , for example in the range from 0.002 to 0.2 g / cm ³ or from 0.005 to 0.1 g / cm ³ , preferably in the range from 0.01 to 0.06 g / cm ³ , also preferably in the range from 0.1 to 0.2 g / cm ³ , or in the range from 0.15 to 0.2 g / cm ³ ;

ix. a residual moisture content of less than 5% by weight, for example in the range from 0.25 to 3% by weight, particularly preferably in the range from 0.5 to 2% by weight;

wherein the wt .-%, ppm and ppb are each based on the total weight of the silicon dioxide powder.

The silicon dioxide powder contains silicon dioxide. The silicon dioxide powder preferably contains silicon dioxide in an amount of more than 95% by weight, for example in an amount of more than 98% by weight, or of more than 99% by weight, or of more than 99.9% by weight. -%, each based on the total weight of the silicon dioxide powder. It particularly preferably contains Silicon dioxide powder Silicon dioxide in an amount of more than 99.99% by weight, based on the total weight of the silicon dioxide powder.

The silicon dioxide powder preferably has a content of atoms other than Si, O, H, C, CI of less than 5 ppm, for example less than 2 ppm, particularly preferably less than 1 ppm, in each case based on the total weight of the silicon dioxide powder . However, the silicon dioxide powder often has a content of atoms other than Si, O, H, C, Cl in an amount of at least 1 ppb. The atoms other than Si, O, H, C, CI can be present, for example, as an element, as an ion, or as part of a molecule or an ion or a complex.

Preferably at least 70% of the powder particles of the silicon dioxide powder, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range from 10 to 100 nm or from 15 to 100 nm, and particularly preferably in the range from 20 to 100 nm. The primary particle size is determined by dynamic light scattering according to ISO 13320: 2009-10.

Preferably at least 75% of the powder particles of the silicon dioxide powder, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range from 10 to 100 nm or from 15 to 100 nm, and particularly preferably in the range from 20 to 100 nm.

Preferably at least 80% of the powder particles of the silicon dioxide powder, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range from 10 to 100 nm or from 15 to 100 nm, and particularly preferably in the range from 20 to 100 nm.

Preferably at least 85% of the powder particles of the silicon dioxide powder, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range from 10 to 100 nm or from 15 to 100 nm, and particularly preferably in the range from 20 to 100 nm.

Preferably, at least 90% of the powder particles of the silicon dioxide powder, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range from 10 to 100 nm or from 15 to 100 nm, and particularly preferably in the range from 20 to 100 nm.

Preferably at least 95% of the powder particles of the silicon dioxide powder, based on the number of powder particles, have a primary particle size of less than 100 nm, for example in the range from 10 to 100 nm or from 15 to 100 nm, and particularly preferably in the range from 20 to 100 nm.

The silicon dioxide powder preferably has a specific surface area (BET surface area) in a range from 20 to 35 m ² / g, for example from 25 to 35 m ² / g, or from 25 to 30 m ² / g. The BET surface area is determined by the Brunauer, Emmet and Teller (BET) method using DIN 66132 and is based on gas absorption at the surface to be measured.

The silicon dioxide powder preferably has a pH value of less than 7, for example in the range from 3 to 6.5 or from 3.5 to 6 or from 4 to 5.5, particularly preferably in the range from 4.5 to 5. Der The pH value can be determined using a combination electrode (4% silicon dioxide powder in water).

The silicon dioxide powder preferably has the combination of features a./b./c. or a./b./f. or a./b./g. on, further preferred the combination of features a./b./c./f. or a./b./c./g. or a./b./f./g. , particularly preferably the combination of features a./b./c./f./g.

The silicon dioxide powder preferably has the combination of features a./b./c. The BET surface area is in a range from 20 to 35 m ² / g, the bulk density is in a range from 0.05 to 0.3 g / ml_ and the carbon content is less than 35 ppm.

The silicon dioxide powder preferably has the combination of features a./b./f. where the BET surface area is in a range from 20 to 35 m ² / g, the bulk density is in a range from 0.05 to 0.3 g / ml_ and the total content of metals other than aluminum is in a range from 1 ppb to 1 ppm.

The silicon dioxide powder preferably has the combination of features a./b./g. with the BET surface area in a range from 20 to 35 m ² / g, the bulk density in a range from 0.05 to 0.3 g / ml_ and at least 70% by weight of the powder particles having a primary particle size in one Range from 20 to less than 100 nm. The silicon dioxide powder further preferably has the combination of features a./b./c./f. The BET surface area is in a range from 20 to 35 m ² / g, the bulk density is in a range from 0.05 to 0.3 g / ml_, the carbon content is less than 40 ppm and the total content of metals other than aluminum ranges from 1 ppb to 1 ppm.

The silicon dioxide powder further preferably has the combination of features a./b./c./g. the BET surface area is in a range from 20 to 35 m ² / g, the bulk density is in a range from 0.05 to 0.3 g / ml_, the carbon content is less than 40 ppm and at least 70 wt. -% of the powder particles have a primary particle size in a range from 20 to less than 100 nm.

The silicon dioxide powder further preferably has the combination of features a./b./f./g. , the BET surface area being in a range from 20 to 35 m ² / g, the bulk density being in a range from 0.05 to 0.3 g / ml_, the total content of metals other than aluminum in is in a range from 1 ppb to 1 ppm and at least 70% by weight of the powder particles have a primary particle size in a range from 20 to less than 100 nm.

The silicon dioxide powder particularly preferably has the combination of features a./b./c./f./g. The BET surface area is in a range from 20 to 35 m ² / g, the bulk density is in a range from 0.05 to 0.3 g / ml_, the carbon content is less than 40 ppm, the total content of metals Other than aluminum, is in a range from 1 ppb to 1 ppm and at least 70% by weight of the powder particles have a primary particle size in a range from 20 to less than 100 nm.

Steps (i) - (v) of the first item are:

(i) providing a silicon dioxide powder;

(ii) providing a liquid;

(iii) mixing the silica powder with the liquid to obtain a slurry;

(iv) sonicating the slurry to obtain a precursor suspension;

(v) passing at least part of the precursor suspension through a first multi-stage filter device, wherein the first multi-stage filter device has at least a first, a second and a third filter stage,

each filter stage contains at least one filter,

Further filter stages can be provided between the filter stages referred to as the first, second and third filter stages.

In the context of the present invention, a liquid is understood to be a substance or a mixture of substances that is liquid at a pressure of 1013 hPa and a temperature of 20 ° C.

A “slurry” in the context of the present invention means a mixture of at least two substances, the mixture having at least one liquid and at least one solid under the conditions present when considered. During the process, a slurry and a precursor suspension are formed. The precursor suspension is also a slurry, but this was treated with ultrasound according to step (iv). Unless a “slurry” or “precursor suspension” is expressly designated in the following, that is to say in general terms of a “slurry”, what is described in this way can in principle apply to the slurry, or to the precursor suspension, or to both the slurry and the precursor suspension . This can be justified in such a way that, when the slurry is treated to obtain the precursor suspension, not each of the characteristics described below is changed by the treatment, or that a characteristic changes, but remains within the generally described characteristic. In principle, all substances and mixtures of substances known to the person skilled in the art and appearing to be suitable for the intended use are suitable as the liquid. The liquid is preferably selected from the group consisting of organic liquids and water. The silicon dioxide powder is preferably soluble in the liquid in an amount of less than 0.5 g / L, preferably in an amount of less than 0.25 g / L, particularly preferably in an amount of less than 0.1 g / L, the g / L are given as g silicon dioxide powder per liter of liquid.

Polar solvents are preferably suitable as the liquid. This can be organic liquids or water. The liquid is preferably selected from the group consisting of water, methanol, ethanol, n-propanol, iso-propanol, n-butanol, tert-butanol and mixtures of more than one thereof. The liquid water is particularly preferred. The liquid particularly preferably contains distilled or deionized water, for example also “ultra-pure” water. This has an electrical conductivity of <0.2 me / a.

The silicon dioxide powder is preferably processed into a slurry. The silica powder is almost insoluble in the liquid at room temperature, but it can be incorporated into the liquid in large proportions by weight to obtain the slurry.

The silicon dioxide powder and the liquid can be mixed in any manner. For example, the silicon dioxide powder can be added to the liquid, or the liquid can be added to the silicon dioxide powder. The mixture can be agitated during the addition or after the addition. The mixture is particularly preferably agitated during and after the addition. Examples of agitation are shaking and stirring, or a combination of both. The silicon dioxide powder can preferably be added to the liquid with stirring. More preferably, part of the silicon dioxide powder can be added to the liquid, the mixture thus obtained being agitated and the mixture then being mixed with the remaining part of the silicon dioxide powder. Part of the liquid can also be added to the silicon dioxide powder, the mixture thus obtained being agitated, and the mixture then being mixed with the remaining part of the liquid.

A slurry is obtained by mixing the silica powder and the liquid. The slurry is preferably a suspension in which the silicon dioxide powder is uniformly distributed in the liquid. By "uniform" it is meant that the density and composition of the slurry at any point do not differ by more than 10% average density and composition differ, each based on the total amount of slurry. A uniform distribution of the silicon dioxide powder in the liquid can be produced or obtained by agitation as already described above, or both. The precursor suspension is also such a suspension with the properties just described.

The slurry, like the precursor suspension, preferably has a liter weight in the range from 1000 to 2000 g / L, for example in the range from 1200 to 1900 g / L or from 1300 to 1800 g / L, particularly preferably in the range from 1400 to 1700 g / L. The liter weight is determined by weighing a volume-calibrated container.

According to one embodiment, at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features apply to the slurry:

a.) The slurry has a solids content of at least 20% by weight, for example in a range from 20 to 70% by weight, or in a range from 30 to 50% by weight, or in a range from 55 to 75% by weight, particularly preferably in a range from 60 to 70% by weight, each based on the total weight of the slurry;

b.) the slurry has a pH in a range of 3 or more, for example more than 4 or a pH in the range from 4.5 to 8 or from 4.5 to 7, the pH Value is determined on a 4% by weight slurry;

c.) at least 90% of the silica particles in the slurry have a 4

% By weight slurry has a particle size according to DIN ISO 13320-1 in the range from 1 nm to <10 μm, for example in a range from 200 to 300 nm; d.) a content of 5 ppm or less of atoms other than Si, O, H, C, CI;

e.) the slurry is rheopex;

f.) the slurry is transported into contact with a plastic surface;

g.) the slurry is sheared;

h.) the slurry has a temperature of more than 0 ° C, preferably in one

Range from 5 to 35 ° C;

i.) the slurry has a viscosity according to DIN 53019-1 (5 rpm, 30% by weight) in a range from 500 to 2000 mPas, for example in the range from 600 to 1700 mPas, particularly preferably in the range from 650 to 1350 mPas on; According to another embodiment, at least one, for example at least two or at least three or at least four, particularly preferably at least five of the aforementioned features a.) - j.) Also apply to the precursor suspension.

The silicon dioxide particles in a 4% by weight aqueous slurry preferably have a particle size D10 in a range from 50 to 250 nm, particularly preferably in the range from 100 to 150 nm. The silicon dioxide particles in a 4% by weight aqueous slurry preferably have Slurry has a particle size D50 in a range from 100 to 400 nm, particularly preferably in the range from 200 to 250 nm. The silicon dioxide particles in a 4% by weight aqueous slurry preferably have a particle size D90 in a range from 200 to 600 nm , particularly preferably in a range from 350 to 400 nm. The particle size is determined by means of DIN ISO 13320-1. The information on particle size D10, D50 or D90, or a combination of two or more of them, can also apply to the precursor suspension.

Particle size is understood to mean the size of the particles assembled from the primary particles that are present in a silicon dioxide powder, in a slurry, in a precursor suspension or in a silicon dioxide granulate. The mean particle size is understood as the arithmetic mean of all particle sizes of the substance mentioned. The D 50 value indicates that 50% of the particles, based on the total number of particles, are smaller than the specified value. The Dio value indicates that 10% of the particles, based on the total number of particles, are smaller than the specified value. The Dgo value indicates that 90% of the particles, based on the total number of particles, are smaller than the specified value. The particle size is determined using a dynamic image analysis method according to ISO 13322-2: 2006-11.

The “isolectric point” is understood to mean the pH value at which the zeta potential takes on the value 0. The zeta potential is determined according to ISO 13099-2: 2012.

The pH of the slurry is preferably adjusted to a value in the above-mentioned range. In order to adjust the pH, substances such as NaOH or NH3, for example as an aqueous solution, can preferably be added to the slurry. The slurry is often agitated. The information on the pH of the slurry can also apply to the pH of a precursor suspension. The slurry is treated with ultrasound in the following step (iv) to obtain a precursor suspension. In principle, any method and any ultrasound source that is known to the person skilled in the art and appears suitable for the present application can be selected for the treatment with ultrasound.

Ultrasound in the present context is sound with a peak frequency in the range from 20 to 100 kHz. This can be a monofrequency sound or sound of a bandwidth. In the latter case, at least 60% of the ultrasonic frequencies used in the treatment are in a range spanned by the peak frequency ± 10 Hz.

In a further embodiment, the treatment of the slurry with ultrasound lasts at least 10 seconds, for example at least 20 seconds or at least 40 seconds, or at least 60, 120, 180 or 240 seconds.

In a further embodiment, the treatment of the slurry with ultrasound lasts at most 1000 seconds, for example at most 500 seconds or at most 200 seconds, or at most 100, 50 or 20 seconds.

In a further embodiment, the treatment of the slurry with ultrasound lasts in a range from 10 to 1800 seconds, for example from 30 to 1000 seconds, or from 30 to 600 seconds, or from 40 to 300 seconds.

The power density applied by ultrasound is the electrical power consumption of the ultrasound source divided by the volume of the slurry. In a further embodiment, an ultrasonic generator or an agitator ball mill, or a combination of both, is used as the ultrasonic source.

In a further embodiment, the temperature of the slurry during the ultrasonic treatment is in a range from 5 to 45 ° C, for example between 10 and 40 ° C, or between 15 and 40 ° C.

In another embodiment, the ultrasonic power density applied to the slurry is less than 600 W / liter, for example less than 450 W / liter, or about 300 W / liter, the power density based on the volume of the slurry. A power density of 100 W / liter is usually not fallen below. In one embodiment, the power density by ultrasound is in a range from 400 to 500 W / liter and the treatment time is in a range from 10 to 90 seconds.

In another embodiment, the power density by ultrasound is in a range from 300 to 400 W / liter and the treatment time is in a range from 90 to 250 seconds.

At least part of the precursor suspension is passed through a first multi-stage filter device in the following step (v). The silicon dioxide suspension is obtained as a filtrate after the precursor suspension has passed through the multi-stage filter device. The first multi-stage filter device has at least a first, a second and a third filter stage. The first multi-stage filter device can have further filter stages, such as a fourth, and optionally a fifth, and optionally a sixth filter stage. The filter stages within a multi-stage filter device are arranged in a specific order. They are numbered in the downstream direction. This means that the precursor suspension first flows through the first filter stage, downstream of it the second filter stage and so on. An arrangement of several filters next to one another is also conceivable. In this case, different amounts of suspension would flow through the filters arranged next to one another at approximately the same time. By arranging several filters next to one another within a filter stage, the service life of the filter stage, or the throughput through the filter stage, or both can be increased. Furthermore, further filter stages can be provided between the first and second filter stages already mentioned, or between the second and third filter stages, which are not further described here. In addition, one or more filter stages not described further here can be provided both between the first and the second filter stage and between the second and the third filter stage, independent of one another.

Each of the filter stages contains at least one filter. A single filter can be provided within a filter stage. A plurality of filters can also be provided. These are usually arranged next to one another. In this case, the majority of filters are usually filters with the same characteristic data. As already described, several filters can be arranged next to one another in order to share the flow within the filter stage. The service life of the filter stage or the throughput of the filter stage, or both, is often increased. The first filter stage has a filter fineness of 5 pm or more, for example from 5 pm to 15 pm, or about 10 pm, or about 15 pm.

The second filter stage has a filter fineness in a range from 0.5 to 5 μm, for example in a range from 0.5 to 2 μm, or approximately 1 μm, or approximately 2 μm.

The third filter stage has a filter fineness of 1 pm or less, for example 1 pm or 0.5 pm.

At least one of the filter stages selected from the first, second and third filter stage has a separation rate of 99.5% or more, for example of 99.8%, or of 99.9%.

The filter fineness describes the smallest particle size that a filter can filter out with a certain degree of effectiveness. The filter fineness is also indicated below with x.

The separation rate e _c , also filtration rate) is specified in all cases mentioned in accordance with ISO 16889: 2008. According to this standard, a β _x value is determined as the quotient of N _x and N _h , with N _x = number of particles in front of the filter, N _h = number of particles after the filter and x the filter fineness. The filter fineness is the particle size in pm against which the separation rate was determined. The separation rate, also indicated by e _c , is then (ß _x - 1) / ß _x .

As an example, a separation rate e = 75% means that for a suspension with 400 particles with a particle size of 10 μm or more per unit volume upstream of the filter, this suspension after the filter has a number of 100 particles with a particle size of 10 μm or more per unit volume downstream of the filter. In this example, 75% of particles with a particle size of 10 μm or more were removed from the suspension.

Based on the definition of the separation rate and filter fineness for an individual filter, corresponding information can be made for a filter stage including one or more individual filters. The ranges and preferred configurations given above apply

The first filter device can be characterized by at least one, or more, or all of the following features: (a) the first filter stage has a separation rate of 90% or less, for example 85%, 80% or 75%, or from 80 to 99.9%, or from 80 to 95%;

(b) the first filter stage has a filter fineness in a range of 5 pm or more, from 5 to 25 pm, or 5 to 15 pm, for example 10 pm or 5 pm;

(c) the second filter stage has a separation rate of 80% or more, for example 95% or more, for example 98%, 99%, 99.9% or 99.99%, or in a range from 80 to 99 , 9%, or from 80 to 95%;

(d) the second filter stage has a filter fineness in a range of 0.5 pm or more, for example 5 to 10 pm, or 0.5 to 2 pm, for example 0.5 pm, 1.0 pm, 1.5 pm or 2.0 pm;

(e) the third filter stage has a separation rate of 80% or more, for example 99.5% or more, for example 99.9% or 99.99%, or in a range from 80 to 99.9%, or in a range from 95 to 99.9%;

(f) the third filter stage has a filter fineness in a range of 0.5 μm or more, for example in the range from 0.5 to 10 μm, or from 0.5 to 3 μm, or from 0.5 to 1 μm ; or a combination of two or more of features (a) through (e), each of which

Combination of the values mentioned by way of example with one another is preferred. In a

Embodiment, a combination of all features (a) to (f) is advantageous, for example

Example F1.3 in the following table 1.

In a preferred embodiment, the first filter stage has a filter fineness of 5 μm or more, for example in the range from 5 μm to 25 μm, and a separation rate in the range from 80% to 99.9%, preferably 80% to 95%.

In a further embodiment, the second filter stage has a filter fineness of 0.5 μm or more, for example in the range from 0.5 μm to 10 μm, and a separation rate in the range from 80% to 99.9%, preferably 95% to 99, 9% up.

In a further embodiment, the third filter stage has a filter fineness of 0.5 μm or more, for example in the range from 0.5 μm to 10 μm, and a separation rate in the range from 80% to 99.9%, preferably 95% to 99% .9% up.

According to further examples, the first filter device can be characterized, for example, by the following combinations of features: Table 1

In a further embodiment, the first, multi-stage filter device contains at least one depth filter. In the present context, a depth filter is understood to mean a filter in which the particles to be separated are retained over a distance within the filter. In this case, no filter cake is usually formed during operation of the filter. In contrast, with a surface filter or surface filter, the particles to be deposited are deposited at the interface of the surface filter. A filter cake is built up during operation of the filter. The first multi-stage filter device can further include a plurality of depth filters. It is also possible that all filters used in the first multi-stage filter device are depth filters.

In a further embodiment, at least one further, preferably multi-stage filter device is used downstream of the first, multi-stage filter device. In addition, two, three, four, five and up to 10 or more multistage filter devices arranged downstream in a sequence can be provided.

In a further embodiment, at least the second, multi-stage filter device is provided with depth filters.

In a further embodiment, the second filter stage of the first filter device contains at least one first filter with a separation rate of 90% or less and at least one further filter with a separation rate of 95% or more.

In a further embodiment, the service life of the first, multi-stage filter device is at least 100 liters, for example 150 liters or more, or 250 liters or more, or 500 liters, or 800 liters and more, or 1000 liters and more, each based on liters the volume of precursor suspension filtered by the first multi-stage filter device. In a further embodiment, the service life of the second, optionally multi-stage filter device is at least 100 liters, for example 150 liters or more, or 250 liters or more, or 500 liters, the liters based on the volume of precursor suspension filtered by the second filter device.

In connection with a filter device, the service life means the volume of a suspension that can pass through the filter device before the filter device clogs. The clogging can be recognized on the basis of a pressure increase in front of the filter to at least 1.5 times that of the freshly inserted filter with unchanged pumping power. If the filter is clogged, the work step must be paused and the clogged filter, or the clogged filters, cleaned or replaced.

In a further embodiment, the slurry has less than 5% by weight, less than 2% by weight, for example 0% by weight (none), additives, in particular additives for stabilization, the% by weight based on the Total weight of the slurry. Often times the slurry has at least 0.1% by weight of additives, for example in a range from 0.1 to 5% by weight, the% by weight based on the total weight of the slurry. The content of additives usually does not change in the course of a filtration, or at most hardly changes. Accordingly, the precursor suspension, as well as the silicon dioxide suspension obtainable according to the process, has a content of additives for stabilization as indicated for the slurry.

According to a further embodiment, at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features apply to the silicon dioxide suspension obtainable by the method:

A. the silica suspension is rheopex under the test conditions mentioned in;

B. at least 90% of the silicon dioxide particles in the silicon dioxide suspension in a 4% by weight slurry have a particle size according to DIN ISO 13320-1 in the range from 1 nm to <10 μm, for example in a range from 200 to 300 nm ;

C. the silica suspension has a pH in a range of 3 or more, for example more than 4, or a pH in the range from 4.5 to 8 or from 4.5 to 7, the pH is determined on a 4% strength by weight slurry;

D. a content of chlorine in the solid fraction of the silica suspension of 500 ppm or less, 350 ppm or less, or 200 ppm or less, the ppm based on the total amount of solid in the silica suspension. E. an aluminum content of less than 200 ppb, for example in the range from 1 to 100 ppb, particularly preferably in the range from 1 to 80 ppb, the ppm based on the total amount of solids in the silicon dioxide suspension ..;

F. a content of 5 ppm or less of atoms other than Si, O, H, C, CI;

G. the silicon dioxide suspension has a solids content of at least 20% by weight, for example in a range from 20 to 70% by weight, or in a range from 30 to 50% by weight, or in a range from 55 to 75% % By weight, particularly preferably in a range from 60 to 70% by weight, in each case based on the total weight of the slurry;

H. the silicon dioxide suspension has a temperature of more than 0 ° C, preferably in a range from 5 to 35 ° C;

I. the silicon dioxide suspension has a viscosity according to DIN 53019-1 (5 rpm, 30 wt.

%) in a range from 500 to 2000 mPas, for example in the range from 600 to 1700 mPas, particularly preferably in the range from 650 to 1350 mPas.

A second subject of the invention is a silicon dioxide suspension obtainable by a method according to the first subject. Embodiments described in this context are also possible.

A third object of the invention is a method for producing a silicon dioxide granulate, wherein the silicon dioxide suspension according to the second object or a silicon dioxide suspension that was produced by a method according to the first object, in particular by performing method steps (i) to (v), to a Silicon dioxide granulate is processed.

The silicon dioxide granulate has a larger particle diameter than the silicon dioxide particles present in the silicon dioxide suspension. Embodiments described in connection with the first and second subject matter relating to the production and features of the silicon dioxide suspension are likewise embodiments of the third subject matter. In principle, all methods known to the person skilled in the art, by means of which an increase in the particle diameter is achieved, are suitable for producing the silicon dioxide granulate.

A silicon dioxide granulate has a larger particle diameter than a silicon dioxide powder, and likewise than the silicon dioxide particles contained in the silicon dioxide suspension described above.

The silicon dioxide granulate has a particle diameter which is larger than the particle diameter of the silicon dioxide powder. The particle diameter of the silicon dioxide granulate is preferably in a range from 500 to 50,000 times larger than the particle diameter of the silicon dioxide powder, for example 1,000 to 10,000 times larger, particularly preferably 2,000 to 8,000 times larger.

Preferably at least 90% of the silicon dioxide granulate provided in step i.) Are formed from pyrogenically produced silicon dioxide powder, for example at least 95% by weight or at least 98% by weight, particularly preferably at least 99% by weight or more, in each case based on the Total weight of the silica granules.

A silicon dioxide granulate with granules is preferably formed during processing, the granules having a spherical morphology; more preferably, the processing includes spray granulation or roller granulation.

A powder is understood to mean particles of dry solid substances with a primary particle size in the range from 1 to less than 100 nm.

The silica granules can be obtained by granulating silica powder. A silicon dioxide granulate generally has a BET surface area of 3 m ² / g or more and a density of less than 1.5 g / cm ³ . Granulating is the process of converting powder particles into granules. During granulation, agglomerations of several silicon dioxide powder particles form, i.e. larger agglomerates, which are referred to as "silicon dioxide granules". These are often referred to as "silica granulate particles" or "granulate particles". In their entirety, granules form a granulate, for example the silicon dioxide granules a “silicon dioxide granulate”. The silicon dioxide granulate has a larger particle diameter than the silicon dioxide powder. The process of granulating to convert a powder into granules will be explained in more detail later.

In the present context, silicon dioxide grains are understood to mean silicon dioxide particles which can be obtained by comminuting a silicon dioxide body, in particular a quartz glass body. A silicon dioxide grain generally has a density of more than 1.2 g / cm ³ , for example in a range from 1.2 to 2.2 g / cm ³ , and particularly preferably about 2.2 g / cm ³ . More preferably, the BET surface area of a silicon dioxide grain is generally less than 1 m ² / g, determined in accordance with DIN ISO 9277: 2014-01.

In principle, all silicon dioxide particles suitable to the person skilled in the art come into consideration as silicon dioxide particles. Silicon dioxide granules and silicon dioxide granules are preferably selected.

A particle diameter or a particle size is understood to mean the diameter of a particle which results as “area equivalent circular diameter X _A I” according to the formula x _Ai = ^, where Ai denotes the area of the considered particle in an image analysis. Suitable methods for the determination are, for example, ISO 13322-1: 2014 or ISO 13322-2: 2009. Comparative information such as “larger particle diameter” always means that the related values were determined using the same method.

The granules of the silicon dioxide granulate preferably have a spherical morphology. A spherical morphology is understood to mean a round to oval shape of the particles. The granules of the silicon dioxide granulate preferably have an average sphericity in a range from 0.7 to 1.3 SPHT3, for example an average sphericity in a range from 0.8 to 1.2 SPHT3, particularly preferably an average sphericity in a range of 0 .85 to 1.1 SPHT3. The SPHT3 feature is described in the test methods.

Furthermore, the granules of the silicon dioxide granulate preferably have an average symmetry in a range from 0.7 to 1.3 symmetry, for example an average symmetry in a range from 0.8 to 1.2 symmetry, particularly preferably an average symmetry in a range of 0.85 to 1.1 symm3. The characteristic of the mean symmetry Symm3 is described in the test methods. granulation

The silica granules are obtained by granulating silica powder. Granulating is the process of converting powder particles into granules. During granulation, larger agglomerates, which are referred to as "silicon dioxide granules", form due to the agglomeration of several silicon dioxide powder particles. These are often referred to as "silicon dioxide particles", "silicon dioxide granulate particles" or "granulate particles". In their entirety, granules form a granulate, e.g. the silicon dioxide granules a "silicon dioxide granulate".

In the present case, in principle, any granulation process can be selected which is known to the person skilled in the art and appears suitable for granulating silicon dioxide powder. In the granulation process, a distinction can be made between build-up granulation and press granulation, and further between wet and dry granulation processes. Known methods are roller granulation in a granulating plate, spray granulation, centrifugal atomization, fluidized bed granulation, freeze granulation, as well as granulation processes using a granulating mill, compacting, roller pressing, briquetting, production of slugs or extrusion.

During processing, a silicon dioxide granulate is preferably formed with granules which have a spherical morphology; the processing further preferably being carried out by spray granulation or roller granulation. More preferably, a silicon dioxide granulate with granules which have a spherical morphology contains at most 50% granules, preferably at most 40% granules, more preferably at most 20% granules, more preferably between 0 and 50%, between 0 and 40% or between 0 and 20 %, or between 10 and 50%, between 10 and 40% or between 10 and 20% granules that do not have a spherical morphology, the percentage in each case based on the total number of granules in the granules. The granules with a spherical morphology have the SPHT3 values already mentioned in this description.

Spray drying

According to an embodiment of the third subject matter, silica granules are obtained by spray granulating the slurry. Spray granulation is also known as spray drying. The spray drying is preferably carried out in a spray tower. For spray drying, the silicon dioxide suspension is put under pressure at an elevated temperature. The pressurized silicon dioxide suspension is then released through a nozzle and thus sprayed into the spray tower. As a result, droplets are formed which dry immediately and initially form small dry particles (“germs”). The tiny particles together with a gas flow acting on the particles form a fluidized bed. In this way, they are kept in suspension and can form a surface for drying further droplets.

The nozzle through which the silicon dioxide suspension is sprayed into the spray tower preferably forms an inlet into the interior of the spray tower.

When spraying, the nozzle preferably has a contact surface with the silicon dioxide suspension. The “contact area” is understood to mean the area of the nozzle that comes into contact with the silicon dioxide suspension during spraying. Often at least part of the nozzle is shaped as a tube through which the silicon dioxide suspension is passed during spraying, so that the inside of the hollow tube comes into contact with the silicon dioxide suspension.

The contact surface preferably contains a glass, a plastic or a combination thereof. The contact surface preferably contains a glass, particularly preferably quartz glass. The contact surface preferably contains a plastic. In principle, all plastics known to the person skilled in the art are suitable which are stable at the process temperatures and do not give off any foreign atoms to the silicon dioxide suspension. Preferred plastics are polyolefins, for example homopolymers or copolymers containing at least one olefin, particularly preferably homopolymers or copolymers containing polypropylene, polyethylene, polybutadiene or combinations of two or more thereof. The contact surface preferably consists of a glass, a plastic or a combination thereof, for example selected from the group consisting of quartz glass and polyolefins, particularly preferably selected from the group consisting of quartz glass and homopolymers or copolymers containing polypropylene, polyethylene, polybutadiene or combinations of two or more of them. The contact surface preferably does not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium and manganese.

In principle, it is possible for the contact surface and the other parts of the nozzle to consist of the same or different materials. The other parts of the nozzle preferably contain the same material as the contact surface. It is also possible that the further Parts of the nozzle contain a material different from the contact surface. For example, the contact surface can be coated with a suitable material, for example a glass or a plastic.

The nozzle is preferably more than 70% by weight, based on the total weight of the nozzle, formed from an element selected from the group consisting of glass, plastic or a combination of glass and plastic, for example more than 75% by weight. % or more than 80% by weight or more than 85% by weight or more than 90% by weight or more than 95% by weight, particularly preferably more than 99% by weight.

The nozzle preferably comprises a nozzle plate. The nozzle plate is preferably made of glass, plastic or a combination of glass and plastic. The nozzle plate is preferably formed from glass, particularly preferably quartz glass. The nozzle plate is preferably made of plastic. Preferred plastics are polyolefins, for example homopolymers or copolymers containing at least one olefin, particularly preferably homopolymers or copolymers containing polypropylene, polyethylene, polybutadiene or combinations of two or more thereof. The nozzle plate preferably does not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium and manganese.

The nozzle preferably comprises a twist screw. The twisting screw is preferably made of glass, plastic or a combination of glass and plastic. The twisting screw is preferably made of glass, particularly preferably quartz glass. The twist screw is preferably made of plastic. Preferred plastics are polyolefins, for example homopolymers or copolymers containing at least one olefin, particularly preferably homopolymers or copolymers containing polypropylene, polyethylene, polybutadiene or combinations of two or more thereof. The helical screw preferably does not contain any metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium and manganese.

The nozzle can also comprise further components. Preferred further components are a nozzle body; a nozzle body surrounding the swirl screw and the nozzle plate, a cross piece and a baffle plate are particularly preferred. A nozzle preferably comprises one or more, particularly preferably all, of the further components. The further components, independently of one another, can in principle consist of any material known to the person skilled in the art and suitable for this purpose, for example from a metal-containing material, from glass or from a plastic. The nozzle body is preferably formed from glass, especially prefers quartz glass. The further components are preferably made of plastic. Preferred plastics are polyolefins, for example homopolymers or copolymers containing at least one olefin, particularly preferably homopolymers or copolymers containing polypropylene, polyethylene, polybutadiene or combinations of two or more thereof. The further components preferably contain no metals, in particular no tungsten, titanium, tantalum, chromium, cobalt, nickel, iron, vanadium, zirconium and manganese.

The spray tower preferably has a gas inlet and a gas outlet. Gas can be introduced into the interior of the spray tower through the gas inlet and it can be discharged through the gas outlet. It is also possible to introduce gas into the spray tower via the nozzle. Gas can also be discharged through the outlet of the spray tower. Furthermore, gas can preferably be supplied via the nozzle and a gas inlet of the spray tower, and discharged via the outlet of the spray tower and a gas outlet of the spray tower.

An atmosphere selected from air, an inert gas, at least two inert gases or a combination of air with at least one inert gas, preferably at least two inert gases, is preferably present in the interior of the spray tower. Inert gases are preferably selected from the list consisting of nitrogen, helium, neon, argon, krypton and xenon. For example, air, nitrogen or argon is present in the interior of the spray tower, particularly preferably air.

The atmosphere present in the spray tower is more preferably part of a gas stream. The gas stream is preferably introduced into the spray tower via a gas inlet and discharged via a gas outlet. It is also possible to introduce parts of the gas flow via the nozzle and to discharge parts of the gas flow via a solids outlet. The gas stream can absorb further components in the spray tower. During spray drying, these can originate from the silicon dioxide suspension and merge into the gas flow.

A dry gas stream is preferably fed to the spray tower. A dry gas stream is understood to mean a gas or a gas mixture whose relative humidity is below the condensation point at the temperature set in the spray tower. A relative humidity of 100% corresponds to an amount of water of 17.5 g / m ³ at 20 ° C. The gas is preferably preheated to a temperature in a range from 150 to 450 ° C, for example from 200 to 420 ° C or from 300 to 400 ° C, particularly preferably from 320 to 400 ° C. The interior of the spray tower can preferably be temperature controlled. The temperature in the interior of the spray tower is preferably up to 550 ° C, for example 300 to 500 ° C, particularly preferably 320 to 450 ° C.

At the gas inlet, the gas stream preferably has a temperature in a range from 150 to 450 ° C, for example from 200 to 420 ° C or from 300 to 400 ° C, particularly preferably from 320 to 400 ° C.

At the solids outlet, the gas outlet or at both locations, the discharged gas stream preferably has a temperature of less than 170.degree. C., for example from 50 to 150.degree. C., particularly preferably from 100 to 130.degree.

More preferably, the difference between the temperature of the gas flow during introduction and the gas flow during discharge is in a range from 100 to 330.degree. C., for example from 150 to 300.degree.

The silicon dioxide granules obtained in this way are in the form of an agglomerate of individual particles of silicon dioxide powder. The individual particles of the silicon dioxide powder can still be seen in the agglomerate. The mean particle size of the particles of the silicon dioxide powder is preferably in the range from 10 to 1000 nm, for example in the range from 20 to 500 nm or from 30 to 250 nm or from 35 to 200 nm or from 40 to 150 nm, or particularly preferably in the range from 50 to 100 nm. The mean particle size of these particles is determined in accordance with DIN ISO 13320-1.

Spray drying can be carried out in the presence of auxiliaries. In principle, all substances can be used as auxiliaries which are known to the person skilled in the art and appear suitable for the intended use at hand. So-called binders, for example, come into consideration as auxiliary substances. Examples of suitable binders are metal oxides such as calcium oxide, metal carbonates such as calcium carbonate and polysaccharides such as cellulose, cellulose ethers, starch and starch derivatives.

In the context of the present invention, spray drying is particularly preferably carried out without auxiliaries.

Preferably, a part of it is separated off before, after or before and after the silicon dioxide granulate is removed from the spray tower. All of them come to the expert to separate them known and seemingly suitable processes. The separation is preferably carried out by sifting or sieving.

Before removing the silicon dioxide granulate formed by spray drying from the spray tower, particles with a particle size of less than 50 μm, for example with a particle size of less than 70 μm, particularly preferably with a particle size of less than 90 μm, are separated by sifting. The sifting is preferably carried out by a cyclone, which is preferably arranged in the lower region of the spray tower, particularly preferably above the outlet of the spray tower.

After removing the silicon dioxide granulate from the spray tower, particles with a particle size of more than 1000 μm, for example with a particle size of more than 700 μm, particularly preferably with a particle size of more than 500 μm, are separated by sieving. The particles can in principle be sieved by any method known to the person skilled in the art and suitable for this purpose. Sieving is preferably carried out by means of a vibrating chute.

According to one embodiment, the spray drying of the silicon dioxide suspension through a nozzle into a spray tower is characterized by at least one, for example two or three, particularly preferably all of the following features:

a] spray granulation in a spray tower;

b] the presence of a pressure of the silicon dioxide suspension at the nozzle of not more than 40 bar, for example in a range from 1.3 to 20 bar from 1.5 to 18 bar or from 2 to 15 bar or from 4 to 13 bar, or particularly preferably in the range from 5 to 12 bar, the pressure being given in absolute terms (in relation to p = 0 hPa);

c] a temperature of the droplets on entry into the spray tower in a range from 10 to 50 ° C, preferably in a range from 15 to 30 ° C, particularly preferably in a range from 18 to 25 ° C.

d) a temperature on the side of the nozzle facing the spray tower in a range from 100 to 450 ° C, for example in a range from 250 to 440 ° C, particularly preferably from 320 to 430 ° C;

f] a solids content of the silicon dioxide suspension of at least 40% by weight, for example in a range from 50 to 80% by weight, or in a range from 55 to 75% % By weight, particularly preferably in a range from 60 to 70% by weight, in each case based on the total weight of the silicon dioxide suspension;

k] a residual moisture content of the granulate on removal from the spray tower of less than 5% by weight, for example less than 3% by weight or less than 1% by weight or in a range from 0.01 to 0, 5% by weight, particularly preferably in a range from 0.1 to 0.3% by weight, in each case based on the total weight of the silicon dioxide granules formed during the spray drying;

m] at least 50% by weight of the spray granulate, based on the total weight of the silicon dioxide granulate formed during spray drying, covers a flight distance of more than 20 m, for example of more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m.

n] the spray tower has a cylindrical geometry;

q] sieving off particles with a size of more than 500 μm after the granulate has been removed from the spray tower, preferably on a vibrating chute; r] the exit of the droplets of silicon dioxide suspension from the nozzle takes place at an angle of 30 to 60 degrees counter to the perpendicular direction, particularly preferably at an angle of 45 degrees opposite to the perpendicular direction.

The direction of the gravity vector is understood as the perpendicular direction.

The flight distance means the distance that a droplet of the silicon dioxide suspension travels from the exit from the nozzle in the gas space of the spray tower to form a granule until the flight and fall process is completed. The flight and fall process regularly ends when the granules hit the floor of the spray tower or when the granules hit other granules already lying on the floor of the spray tower, whichever occurs first.

The flight time is the duration that a granule needs to cover the flight path in the spray tower. The granules in the spray tower preferably have a helical trajectory.

Preferably, at least 60% by weight of the spray granules, based on the total weight of the silicon dioxide granules formed during the spray drying, cover an average flight distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m.

Preferably at least 70% by weight of the spray granules, based on the total weight of the silicon dioxide granules formed during the spray drying, cover an average flight distance of more than 20 m, for example more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m.

Preferably at least 80% by weight of the spray granules, based on the total weight of the silicon dioxide granules formed during the spray drying, cover an average flight distance of more than 20 m, for example of more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m. Preferably at least 90% by weight of the spray granulate, based on the total weight of the silicon dioxide granulate formed during the spray drying, cover an average flight distance of more than 20 m, for example of more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m.

Roll granulation

According to another embodiment of the first subject matter, silicon dioxide granules are obtained by roll granulating the silicon dioxide suspension.

Roll granulation is carried out by stirring the silicon dioxide suspension in the presence of a gas at an elevated temperature. Roll granulation is preferably carried out in a stirred tank equipped with a stirring tool. The stirred tank preferably rotates in the opposite direction to the stirring tool. The stirred container also preferably has an inlet through which silicon dioxide powder can be introduced into the stirred container, an outlet through which silicon dioxide granulate can be removed, a gas inlet and a gas outlet.

A pen vortex is preferably used to stir the silicon dioxide suspension. A pin vortex is understood to mean a stirring tool which is provided with a plurality of elongated pins, the longitudinal axis of which runs coaxially to the axis of rotation of the stirring tool. The sequence of movements of the pins preferably describes coaxial circles around the axis of rotation.

The silicon dioxide suspension is preferably adjusted to a pH value of less than 7, for example to a pH value in the range from 2 to 6.5, particularly preferably to a pH value in a range from 4 to 6. To adjust the pH Value, an inorganic acid is preferably used, for example an acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, particularly preferably hydrochloric acid.

An atmosphere selected from air, an inert gas, at least two inert gases or a combination of air with at least one inert gas, preferably at least two inert gases, is preferably present in the stirred container. Preferred inert gases are selected from the list consisting of nitrogen, helium, neon, argon, krypton and xenon. For example, air, nitrogen or argon is present in the stirred container, particularly preferably air.

The atmosphere present in the stirred tank is more preferably part of a gas flow. The gas flow is preferably introduced into the stirred tank via the gas inlet and discharged via the gas outlet. The gas stream can take up further constituents in the stirred tank. During roll granulation, these can come from the silicon dioxide suspension and merge into the gas flow.

A dry gas stream is preferably fed to the stirred tank. A “dry gas stream” is understood to mean a gas or a gas mixture whose relative humidity is below the condensation point at the temperature set in the stirred tank. The gas is preferably preheated to a temperature in a range from 50 to 300 ° C, for example from 80 to 250 ° C, particularly preferably from 100 to 200 ° C.

Preferably, 10 to 150 m ^{3 of} gas per hour are introduced into the stirred vessel per 1 kg of the silicon dioxide suspension used, for example 20 to 100 m ^{3 of} gas per hour, particularly preferably 30 to 70 m ^{3 of} gas per hour.

The silicon dioxide suspension is dried by the gas flow while stirring with the formation of silicon dioxide granules. The granules formed are removed from the stirring chamber.

The granules removed are preferably dried further. The drying is preferably carried out continuously, for example in a rotary kiln. Preferred temperatures for drying are in a range from 80 to 250.degree. C., for example in a range from 100 to 200.degree. C., particularly preferably in a range from 120 to 180.degree.

In the context of the present invention, continuous means in relation to a method that this can be operated continuously. This means that substances and materials involved in the process can be added and removed continuously while the process is being carried out. It is not necessary to interrupt the procedure for this.

Continuous as an attribute of an object, for example in relation to a “continuous furnace”, means that this object is designed in such a way that a process or process step that takes place in it can be carried out continuously. The granules obtained by rolling granulation can be sieved. Sieving can be done before or after drying. Preference is given to sieving before drying. Granules with a particle size of less than 50 μm, for example with a particle size of less than 80 μm, particularly preferably with a particle size of less than 100 μm, are preferably sieved out. More preferably, granules with a particle size of more than 900 μm, for example with a particle size of more than 700 μm, particularly preferably with a particle size of more than 500 μm, are sieved out. In principle, larger particles can be screened out by any method known to the person skilled in the art and suitable for this purpose. Larger particles are preferably sieved off using a vibrating chute.

According to one embodiment, the roll granulation is characterized by at least one, for example two or three, particularly preferably all of the following features:

[a] the granulation takes place in a rotating stirred tank;

[b] the granulation takes place under a gas flow of 10 to 150 kg of gas per hour and per 1 kg of silicon dioxide suspension;

[c] the gas temperature during introduction is 40 to 200 ° C;

[d] Granules with a particle size of less than 100 μm and of more than 500 μm are sieved off;

[e] the granules formed have a residual moisture content of 15 to 30% by weight;

[f] the granules formed are dried at 80 to 250 ° C., preferably in a continuous drying tube, particularly preferably down to a residual moisture content of less than 1% by weight.

The silicon dioxide granulate obtained by granulation, preferably by spray or roller granulation, is preferably treated before it is processed into quartz glass bodies. This pretreatment can serve various purposes that either facilitate processing into quartz glass bodies or influence the properties of the resulting quartz glass bodies. For example, the silicon dioxide granulate can be compressed, cleaned, surface modified or dried.

According to a further embodiment of the first object, the silicon dioxide granulate has the following features:

A) an angle of repose in a range of 23 to 26 °;

B) a BET surface area in the range from 20 m ² / g to 50 m ² / g; and C) a bulk density in a range from 0.5 to 1.2 g / cm ³ , for example in a range from 0.6 to 1.1 g / cm ³ , particularly preferably in a range from 0.7 to 1, 0 g / cm ³ ;

D) an average particle size in a range from 50 to 500 μm;

E) a carbon content of less than 50 ppm;

F) a chlorine content of less than 500 ppm; for example 350ppm or less, or 200ppm or less;

G) an aluminum content of less than 20 ppb;

H) a tapped density in a range from 0.7 to 1.2 g / cm ³ ;

I) a pore volume in a range from 0.1 to 2.5 ml_ / g, for example in a range from 0.15 to 1.5 ml_ / g; particularly preferably in a range from 0.2 to 0.8 ml / g;

J) an angle of repose in a range of 23 to 26 °;

K) a particle size distribution D ₁₀ in a range from 50 to 150 μm;

L) a particle size distribution D ₅₀ in a range from 150 to 300 μm;

M) a particle size distribution D ₉₀ in a range from 250 to 620 pm,

the ppm and ppb each being based on the total weight of the silica granules.

The silicon dioxide granulate preferably has a metal content of metals other than aluminum of less than 1000 ppb, for example less than 500 ppb, particularly preferably less than 100 ppb, in each case based on the total weight of the silicon dioxide granulate. Often, however, the silicon dioxide granulate has a content of metals other than aluminum in an amount of at least 1 ppb. The silicon dioxide granulate often has a metal content of metals other than aluminum of less than 1 ppm, preferably in a range from 40 to 900 ppb, for example in a range from 50 to 700 ppb, particularly preferably in a range from 60 to 500 ppb, respectively based on the total weight of the silicon dioxide granulate. Such metals are, for example, sodium, lithium, potassium, magnesium, calcium, strontium, germanium, copper, molybdenum, titanium, iron and chromium. These can be present, for example, as an element, as an ion, or as part of a molecule or an ion or a complex.

The silicon dioxide granulate can contain further components, for example in the form of molecules, ions or elements. The silicon dioxide granulate preferably contains less than 5 ppm, for example less than 3 ppm, particularly preferably less than 1 ppm, based in each case on the total weight of the silicon dioxide granulate, of atoms that are composed of Si, O, H, C, CI are different. Often other constituents, expressed as the amount of atoms that are different from Si, O, H, C, CI, are contained in an amount of at least 1 ppb. The further constituents can in particular be selected from the group consisting of carbon, fluoride, iodide, bromide, phosphorus or a mixture of at least two of these.

The silicon dioxide granulate preferably contains less than 10 ppm carbon, for example less than 8 ppm or less than 5 ppm, particularly preferably less than 4 ppm, in each case based on the total weight of the silicon dioxide granulate. Often carbon is contained in the silicon dioxide granulate in an amount of at least 1 ppb.

The silicon dioxide granulate preferably contains less than 100 ppm, for example less than 80 ppm, particularly preferably less than 70 ppm, in each case based on the total weight of the silicon dioxide granulate, of further constituents. Often, however, the other ingredients are included in an amount of at least 1 ppb.

A fourth subject matter of the invention is a method for producing a quartz glass body at least including the process steps: i.) Providing the silicon dioxide granulate by a method as described in the third subject matter or as described in one of the embodiments mentioned in this context;

ii.) Forming a glass melt from the silicon dioxide granulate; and

iii.) Forming a quartz glass body from at least part of the glass melt.

The provision in step i.) Can take place in any manner known to the person skilled in the art and suitable for the present method. This can be, for example, by the method already described for producing a silicon dioxide granulate according to the third subject, for example by spray granulation or roller granulation. The silicon dioxide granulate obtained in this way is fed to a furnace and melted into a glass melt in step ii.). The silicon dioxide granules can be produced by carrying out method steps (i) to (v) of the first subject matter of the invention, and then carrying out the method according to the third subject matter of the invention. The embodiments preferred in both methods are also preferred here. Step ii.)

According to step ii.), A glass melt is formed from the silicon dioxide granulate. Usually the silicon dioxide granulate is heated until a glass melt is obtained. The heating of the silicon dioxide granulate to form a glass melt can in principle take place in any of the ways known to the person skilled in the art for this purpose.

V-train for producing a glass melt

The formation of a glass melt from the silicon dioxide granulate, for example by heating, can be carried out by a continuous process. The silicon dioxide granulate can preferably be introduced continuously into a furnace or the glass melt can be continuously removed from the furnace, or both. More preferably, the silicon dioxide granulate is continuously introduced into the furnace and the glass melt is continuously removed from the furnace.

In principle, a furnace which has at least one inlet and at least one outlet is suitable for this purpose. An inlet is understood to be an opening through which silicon dioxide and possibly other substances can be introduced into the furnace. An outlet is understood to mean an opening through which at least part of the silicon dioxide can be removed from the furnace. The furnace can for example be oriented vertically and horizontally. The furnace is preferably oriented vertically. At least one inlet is preferably located above at least one outlet. In connection with fixtures and features of a furnace, in particular an inlet and outlet, “above” means that the fixtures or the feature that is arranged “above” another is in a higher position above Has normal zero (NN). “Vertical” is understood to mean that the direct connection between the inlet and the outlet of the furnace has a deviation of no more than 30 ° to the perpendicular direction.

According to one embodiment of the first subject, the furnace includes a hanging sheet metal crucible. The silicon dioxide granulate is introduced into the hanging sheet metal crucible and heated to obtain a glass melt. A sheet metal crucible is understood to mean a crucible which contains at least one rolled sheet. A sheet metal crucible preferably has a plurality of rolled sheets. These are connected to one another by suitable connecting means, for example rivets. A hanging sheet metal crucible is understood to mean a sheet metal crucible of the type described above which is arranged hanging in an oven. The hanging sheet metal crucible can in principle consist of all materials known to the person skilled in the art and suitable for melting silicon dioxide. The sheet metal of the hanging sheet metal crucible preferably contains a sintered material, for example a so-called sintered metal. Sintered metals are understood to mean metals or alloys that are obtained by sintering metal powders. A sintered metal can be formed into a sheet, for example by rolling. A sheet crucible made of sintered metal preferably contains two or more, or a plurality of sheets. These sheets can consist of rolled sintered metal.

The sheet metal of the metal crucible preferably contains at least one element selected from the group consisting of refractory metals. Refractory metals are understood to mean the metals of the 4th subgroup (Ti, Zr, Hf), the 5th subgroup (V, Nb, Ta) and the 6th subgroup (Cr, Mo, W).

The sheet metal of the metal crucible preferably contains a sintered metal selected from the group consisting of molybdenum, tungsten or a combination thereof. The sheet metal of the sheet metal crucible further preferably contains at least one further refractory metal, particularly preferably rhenium, osmium, iridium, ruthenium or a combination of two or more thereof.

The sheet metal of the metal crucible preferably contains an alloy of molybdenum with a refractory metal, or tungsten with a refractory metal. Particularly preferred alloy metals are rhenium, osmium, iridium, ruthenium or a combination of two or more thereof. According to a further example, the sheet metal of the metal crucible is an alloy of molybdenum with tungsten, rhenium, osmium, iridium, ruthenium or a combination of two or more thereof. For example, the sheet metal of the tin crucible is an alloy of tungsten with molybdenum, rhenium, osmium, iridium, ruthenium or a combination of two or more thereof.

The previously described sheet metal of the metal crucible can preferably be coated with a refractory metal. According to one example, the sheet metal of the tin crucible is coated with rhenium, osmium, iridium, ruthenium, molybdenum and tungsten, or a combination of two or more thereof.

The sheet metal and the coating preferably have different compositions. For example, a molybdenum sheet is coated with one or more layers of rhenium, osmium, iridium, ruthenium, tungsten, or any combination of two or more thereof. According to another example, a tungsten sheet is coated with one or more layers of rhenium, osmium, iridium, ruthenium, molybdenum or a combination of two or more thereof. According to a further example, the sheet metal of the metal crucible can consist of molybdenum alloyed with rhenium or of tungsten alloyed with rhenium, and be coated on the inside of the crucible with one or more layers containing rhenium, osmium, iridium, ruthenium or a combination of two or more thereof.

The sheet metal of the hanging sheet metal crucible preferably has a density of 95% or more of the theoretical density, for example a density of 95% to 98% or from 96% to 98%. Higher theoretical densities, in particular in the range from 98 to 99.95%, are further preferred. The theoretical density of a material corresponds to the density of a pore-free and 100% dense material. A density of the sheet metal of the sheet metal crucible of more than 95% of the theoretical density can be obtained, for example, by sintering a sintered metal and then compacting the sintered material. A sheet metal crucible is particularly preferably obtainable by sintering a sintered metal, rolling to obtain a sheet metal and processing the sheet metal into a crucible.

The sheet metal crucible preferably has at least one cover, one wall and one base plate. The hanging sheet metal crucible preferably has at least one, for example at least two or at least three or at least four, particularly preferably at least five or all of the following features:

(a) at least one, e.g. more than one or at least two or at least three or at least five, particularly preferably three or four layers of the sheet metal;

(b) at least one sheet, e.g. at least three or at least four or at least six or at least eight or at least twelve or at least 15 or at least 16 or at least 20 sheets, particularly preferably twelve or 16 sheets;

(c) at least one connection of two pieces of sheet metal, e.g. at least two or at least five or at least ten or at least 18 or at least 24 or at least 36 or at least 48 or at least 60 or at least 72 or at least 48 or at least 96 or at least 120 or at least 160, particularly preferably 36 or 48 connections of two identical or several different sheet metal pieces of the hanging sheet metal crucible;

(d) the sheet metal pieces of the hanging sheet metal crucible are riveted, for example to at least one connection, by deep drawing, for example by a combination of deep drawing with sheet metal attachment, or connected by countersinking, screwed or welded, e.g. by Electron beam welding and sintering of the welds, particularly preferably riveted;

(e) the sheet metal of the hanging sheet metal crucible can be obtained by a deformation step which is associated with an increase in the physical density, preferably by deformation of a sintered metal or a sintered alloy; further preferably the forming is a rolling;

(f) a suspension made of copper, aluminum, steel, iron, nickel or a

Refractory metal, e.g. from the crucible material, preferably a water-cooled one

Suspension made of copper or steel;

(g) a nozzle, preferably a nozzle firmly connected to the crucible;

(h) a mandrel, for example a mandrel attached to the nozzle with bars, or a mandrel attached to the lid with a support rod, or a mandrel connected to a support rod from below the crucible;

(i) at least one gas inlet, e.g. in the form of a filling tube or as a separate inlet;

(j) at least one gas outlet, e.g. as a separate outlet on the lid or in the wall of the crucible;

(k) a cooled jacket, preferably a water-cooled jacket;

(L) an insulation from the outside, preferably an insulation from the outside made of zirconium oxide.

The hanging sheet metal crucible can in principle be heated in any manner known to the person skilled in the art and which appears suitable for this purpose. The hanging sheet metal crucible can be heated, for example, by means of electrical heating elements (resistive) or by induction. With resistive heating, the solid surface of the metal crucible is heated from the outside and releases the energy from there to the inside. With inductive heating, the energy is coupled directly into the side wall of the crucible by coils and from there it is released to the inside of the crucible. In the case of resistive heating, the energy is coupled in by radiation, the solid surface being heated from the outside and the energy being released from there on the inside. The crucible is preferably heated inductively.

According to one embodiment of the present invention, the energy input into the crucible, in particular for melting a material to be melted, does not take place by heating the crucible, or a material present therein, or both, by means of a flame, such as one in the crucible or on the crucible directed burner flame. According to a further embodiment, no burners are provided for melting the material to be melted. Due to the hanging arrangement, the hanging sheet metal crucible can be moved in the furnace. The crucible can preferably be at least partially moved into and out of the furnace. If there are different heating zones in the furnace, their temperature profiles are transferred to the crucible in the furnace. By changing the position of the crucible in the furnace, several heating zones, varying heating zones or several varying heating zones can be implemented in the crucible.

The tin crucible has a nozzle. The nozzle is formed from a nozzle material. The nozzle material preferably contains a pre-compressed material, for example with a density in a range of more than 95%, for example from 98 to 100%, particularly preferably from 99 to 99.999%, in each case based on the theoretical density of the nozzle material. The nozzle material preferably contains a refractory metal, for example molybdenum, tungsten or a combination thereof with a further refractory metal. Molybdenum is particularly preferred as the nozzle material. A nozzle containing molybdenum can preferably have a density of 100% of the theoretical density.

The base plate contained in a metal crucible is preferably thicker than the sides of the metal crucible. The base plate is preferably made of the same material as the sides of the sheet metal crucible. The base plate of the metal crucible is preferably not a rolled sheet. The base plate is, for example, 1.1 to 5000 times thicker or 2 to 1000 times thicker or 4 to 500 times thicker, particularly preferably 5 to 50 times thicker, in each case with respect to a wall of the sheet metal crucible.

According to one embodiment of the first object, the furnace includes a hanging or a standing sintered crucible. The silicon dioxide granulate is introduced into the hanging or standing sintered crucible and heated to obtain a glass melt.

A sintered crucible is understood to mean a crucible which is made from a sintered material which contains at least one sintered metal and has a density of not more than 96% of the theoretical density of the metal. Sintered metals are understood to mean metals or alloys that are obtained by sintering metal powders. The sintered material and the sintered metal in a sintered crucible are not rolled. The sintered material of the sintered crucible preferably has a density of 85% or more of the theoretical density of the sintered material, for example a density of 85% to 95% or from 90% to 94%, particularly preferably from 91% to 93%.

The sintered material can in principle consist of all materials known to the person skilled in the art and suitable for melting silicon dioxide. The sintered material is preferably made from at least one of the elements selected from the group consisting of refractory metals, graphite or materials lined with graphite foil.

The sintered material preferably contains a first sintered metal selected from the group consisting of molybdenum, tungsten and a combination thereof. The sintered material also preferably contains at least one further refractory metal that is different from the first sintered metal, particularly preferably selected from the group consisting of molybdenum, tungsten, rhenium, osmium, iridium, ruthenium or a combination of two or more thereof.

The sintered material preferably contains an alloy of molybdenum with a refractory metal, or tungsten with a refractory metal. Rhenium, osmium, iridium, ruthenium or a combination of two or more thereof are particularly preferred as alloy metals. According to another example, the sintered material includes an alloy of molybdenum with tungsten, rhenium, osmium, iridium, ruthenium, or a combination of two or more thereof. For example, the sintered material includes an alloy of tungsten with molybdenum, rhenium, osmium, iridium, ruthenium, or a combination of two or more thereof.

According to a further embodiment, the sintered material described above can contain a coating that contains a refractory metal, in particular rhenium, osmium, iridium, ruthenium or a combination of two or more thereof. In one example, the coating includes rhenium, osmium, iridium, ruthenium, molybdenum, and tungsten, or a combination of two or more thereof.

The sintered material and its coating preferably have different compositions. For example, a sintered material including molybdenum is coated with one or more layers of rhenium, osmium, iridium, ruthenium, tungsten, or any combination of two or more thereof. According to another example, a sintered material including tungsten with one or more layers of rhenium, osmium, Iridium, ruthenium, molybdenum or any combination of two or more thereof are coated. According to a further example, the sintered material can consist of molybdenum alloyed with rhenium or of tungsten alloyed with rhenium, and can be coated on the inside of the crucible with one or more layers containing rhenium, osmium, iridium, ruthenium or a combination of two or more thereof.

A sintering crucible is preferably manufactured by sintering the sintered material in a mold. The sintering crucible can be manufactured as a whole in a mold. It is also possible for individual parts of the sintered crucible to be manufactured in a mold and then processed into the sintered crucible. The crucible is preferably made from more than one part, for example from a base plate and one or more side parts. The side parts are preferably made in one piece based on the circumference of the crucible. The sintered crucible can preferably be manufactured from several side parts arranged one above the other. The side parts of the sintered crucible are preferably sealed by screwing or by a tongue and groove connection. A screwing is preferably done by manufacturing side parts that have a thread at the edges. In the case of a tongue and groove connection, two side parts to be connected each have a groove at the edges, into which a tongue is inserted as a connecting third part, so that a positive connection is formed perpendicular to the crucible wall plane. A sintering crucible is particularly preferably made from more than one side part, for example from two or more side parts, particularly preferably from three or more side parts. The parts of the hanging sintered crucible are particularly preferably screwed together. The parts of the upright sintered crucible are particularly preferably connected by means of a tongue and groove connection.

The base plate can in principle be connected to the crucible wall by any means known to the person skilled in the art and suitable for this purpose. According to one embodiment, the base plate is provided with an external thread and is connected to the crucible wall by screwing the base plate into the crucible wall. According to a further embodiment, the base plate is connected to the crucible wall with the aid of screws. According to a further embodiment, the base plate is suspended in the sintered crucible, for example by placing the base plate on an inner collar of the crucible wall. According to a further embodiment, at least a part of the crucible wall and a thickened base plate are sintered in one piece. The base plate and the crucible wall of the hanging sintered crucible are particularly preferably screwed together. The bottom plate and the crucible wall of the standing sintered crucible are particularly preferably connected by means of a tongue and groove connection. The base plate contained in a sintered crucible is preferably thicker than the sides, for example 1.1 to 20 times thicker or 1.2 to 10 times thicker or 1.5 to 7 times thicker, particularly preferably 2 to 5 times thicker. The sides preferably have a constant wall thickness over the circumference and over the height of the sintered crucible.

The sintering crucible has a nozzle. The nozzle is formed from a nozzle material. The nozzle material preferably contains a pre-compressed material, for example with a density in a range of more than 95%, for example from 98 to 100%, particularly preferably from 99 to 99.999%, in each case based on the theoretical density of the nozzle material. The nozzle material preferably contains a refractory metal, for example molybdenum, tungsten or a combination thereof with a refractory metal. Molybdenum is particularly preferred as the nozzle material. A nozzle containing molybdenum can preferably have a density of 100% of the theoretical density.

The hanging sintered crucible can in principle be heated in any manner familiar to the person skilled in the art and appearing suitable for this purpose. The hanging sintered crucible can be heated inductively or resistively, for example. In the case of inductive heating, the energy is coupled directly into the side wall of the sintered crucible by coils and from there released to the inside of the crucible. With resistive heating, the energy is coupled in by radiation, with the solid surface being heated from the outside and the energy being released from there on the inside. The sintered crucible is preferably heated inductively. In the case of resistive heating, the energy is coupled in by radiation, the solid surface being heated from the outside and the energy being released from there on the inside. The crucible is preferably heated inductively.

According to one embodiment of the present invention, the energy input into the crucible, in particular for melting a material to be melted, does not take place by heating the crucible, or a material present therein, or both, by means of a flame, such as one in the crucible or on the crucible directed burner flame.

The sintered crucible preferably has one or more than one heating zone, for example one or two or three or more than three heating zones, preferably one or two or three heating zones, particularly preferably one heating zone. The heating zones of the sintered crucible can be brought to the same or different temperatures. For example, all heating zones can be set to one temperature or all heating zones can be set to different temperatures or two or more heating zones be brought to different temperatures independently of one another on one and one or more heating zones. All heating zones are preferably brought to different temperatures, for example the temperature of the heating zones increases in the direction of the material transport of the silicon dioxide granulate.

A hanging sintering crucible is understood to mean a sintering crucible of the type described above which is arranged hanging in a furnace.

The hanging sintered crucible preferably has at least one, for example at least two or at least three or at least four, particularly preferably all of the following features:

{a} a suspension, preferably a height-adjustable suspension;

{b} at least two sealed rings as side parts, preferably at least two rings screwed together as side parts;

{c} a nozzle, preferably a nozzle firmly connected to the crucible;

{d} a mandrel, for example a mandrel attached to the nozzle with bars or a mandrel attached to the lid with a support rod or a mandrel connected to a support rod from below the crucible;

{e} at least one gas inlet, e.g. in the form of a filling pipe or as a separate inlet, particularly preferably in the form of a filling pipe;

{f} at least one gas outlet, e.g. on the lid or in the wall of the crucible.

{g} a cooled jacket, particularly preferably a water-cooled jacket;

{h} an insulation on the outside of the crucible, for example on the outside of the cooled jacket, preferably an insulation layer made of zirconium oxide.

The preferred suspension is a suspension attached during manufacture of the hanging sintered crucible, for example a suspension provided as an integral part of the crucible, particularly preferably a suspension made of the sintered material provided as an integral part of the crucible. Another preferred suspension is a suspension attached to the sintered crucible made of a material different from the sintered material, for example aluminum, steel, iron, nickel or copper, preferably made of copper, particularly preferably a cooled one, for example a water-cooled one attached to the sintered crucible Suspension made of copper.

Due to the hanging arrangement, the hanging sintering crucible can be moved in the furnace. The crucible can preferably be at least partially moved into and out of the furnace. If there are different heating zones in the furnace, their temperature profiles are transferred to the crucible in the furnace. By changing the position of the crucible in the furnace, several heating zones, varying heating zones or several varying heating zones can be implemented in the crucible.

A standing sintered crucible is understood to mean a sintered crucible of the type described above which is arranged upright in a furnace.

The standing sintered crucible preferably has at least one, for example at least two or at least three or at least four, particularly preferably all of the following features:

/ a / an area shaped as a standing surface, preferably an area shaped as a standing surface on the bottom of the crucible, more preferably an area shaped as a standing surface in the base plate of the crucible, particularly preferably an area shaped as a standing surface on the outer edge of the bottom of the crucible;

/ b / at least two sealed rings as side parts, preferably at least two rings sealed by a tongue and groove connection as side parts;

Id a nozzle, preferably a nozzle firmly connected to the crucible, particularly preferably a region of the bottom of the crucible that is not shaped as a standing surface;

/ d / a mandrel, for example a mandrel attached to the nozzle with bars or a mandrel attached to the cover with bars or a mandrel connected to a holding rod from below the crucible;

lei at least one gas inlet, e.g. in the form of a filling pipe or as a separate inlet; / f / at least one gas outlet, e.g. as a separate outlet on the lid or in the wall of the crucible;

lg / a lid.

The upright sintering crucible preferably has a separation of the gas spaces in the furnace and in the area below the furnace. The area below the furnace is understood to mean the area below the nozzle in which the removed glass melt is located. The gas spaces are preferably separated by the surface on which the crucible stands. Gas that is in the gas space of the furnace between the inner wall of the furnace and the outer wall of the crucible cannot escape down into the area below the furnace. The removed glass melt has no contact with the gases from the gas space of the furnace. Preferably, glass melts removed from a furnace with an upright sintered crucible and quartz glass bodies formed therefrom have a higher surface purity than glass melts and quartz glass bodies formed from a furnace with a sintered crucible arranged in a suspended manner.

The crucible is preferably connected to the inlet and the outlet of the furnace in such a way that silicon dioxide granulate can enter the crucible through the inlet of the crucible via the inlet of the crucible and molten glass can be removed through the outlet of the crucible and the outlet of the furnace.

In addition to the at least one inlet, the crucible preferably contains at least one opening, preferably several openings, through which gas can be introduced and discharged. The crucible preferably comprises at least two openings, at least one being able to be used as a gas inlet and at least one being used as a gas outlet. The use of at least one opening as a gas inlet and at least one opening as a gas outlet preferably leads to a gas flow in the crucible.

The silicon dioxide granulate is introduced into the crucible through the inlet of the crucible and then heated in the crucible. The heating can be carried out in the presence of a gas or a mixture of two or more gases. When heated, water bound to the silicon dioxide granulate can also pass into the gas phase and thus form another gas. The gas or the mixture of two or more gases is located in the gas space of the crucible. The gas space of the crucible is understood to mean the area inside the crucible that is not occupied by a solid or liquid phase. Suitable gases are, for example, hydrogen, inert gases and two or more of them. Inert gases are understood to mean gases that do not react with the substances provided in the crucible up to a temperature of 2400 ° C. Preferred inert gases are nitrogen, helium, neon, argon, krypton and xenon, particularly preferably argon and helium. The heating is preferably carried out in a reducing atmosphere. This can preferably be provided by hydrogen or a combination of hydrogen and an inert gas, for example by a combination of hydrogen and helium, or of hydrogen and nitrogen, or of hydrogen and argon, particularly preferably a combination of hydrogen and helium.

An at least partial gas exchange of air, oxygen and water for hydrogen, at least one inert gas, or a combination of hydrogen and at least one inert gas is preferably carried out on the silicon dioxide granulate. The at least partial gas exchange is carried out on the silicon dioxide granulate when the silicon dioxide granulate is introduced, or before the heating, or during the heating, or during at least two of the aforementioned activities. The silicon dioxide granulate is preferably heated to melt in a gas stream of hydrogen and at least one inert gas, for example argon or helium.

The furnace, preferably also a crucible located therein, preferably has at least one gas outlet through which gas supplied to the furnace and formed during operation of the furnace is withdrawn. The furnace can also have at least one dedicated gas inlet. Alternatively or additionally, gas can be introduced through the solids feed, also referred to as the solids inlet, for example together with the silicon dioxide particles, or before, after, or by a combination of two or more of the aforementioned possibilities.

The furnace and the gas flow are preferably characterized by the features described in the context of the first subject. The gas flow is preferably formed by introducing a gas through an inlet into the furnace and by discharging a gas from the furnace through an outlet. The “gas exchange rate” is understood to mean the volume of gas that is led out of the furnace through the outlet over time. The gas exchange rate is also referred to as the throughput of the gas flow or the volume throughput.

The gas exchange rate of the gas stream is preferably in a range from 200 to 3000 liters / h, for example from 200 to 2000 liters / h, particularly preferably from 200 to 1000 liters / h.

The furnace temperature for melting the silicon dioxide granulate is preferably in the range from 1700 to 2500 ° C, for example in the range from 1900 to 2400 ° C, particularly preferably in the range from 2100 to 2300 ° C.

The residence time in the oven is preferably in a range from 1 hour to 50 hours, for example 1 to 30 hours, particularly preferably 5 to 20 hours. In the present context, the dwell time means the time which is required in accordance with the method to remove a filling quantity of the melting furnace from the melting furnace in which the glass melt is formed while the method is being carried out. The filling quantity is the total mass of silicon dioxide present in the melting furnace. The silicon dioxide can be present as a solid and as a glass melt. The furnace temperature preferably increases over the length in the direction of the material transport. The furnace temperature preferably increases over the length, in the direction of the material transport, by at least 100 ° C., for example by at least 300 ° C. or by at least 500 ° C. or by at least 700 ° C., particularly preferably by at least 1000 ° C. The highest temperature in the furnace is preferably 1700 to 2500 ° C, for example 1900 to 2400 ° C, particularly preferably 2100 to 2300 ° C. The oven temperature can increase uniformly or according to a temperature profile.

The furnace temperature preferably decreases before the glass melt is removed from the furnace. The furnace temperature preferably decreases by 50 to 500.degree. C., for example by 100.degree. C. or by 400.degree. C., particularly preferably by 150 to 300.degree. C., before the glass melt is removed from the furnace. The temperature of the molten glass during removal is preferably 1750 to 2100 ° C, for example 1850 to 2050 ° C, particularly preferably 1900 to 2000 ° C.

The furnace temperature preferably increases over the length, in the direction of the material transport, and decreases before the glass melt is removed from the furnace. The furnace temperature preferably increases over the length, in the direction of material transport, by at least 100 ° C., for example by at least 300 ° C. or by at least 500 ° C. or by at least 700 ° C., particularly preferably by at least 1000 ° C. The highest temperature in the furnace is preferably 1700 to 2500 ° C, for example 1900 to 2400 ° C, particularly preferably 2100 to 2300 ° C. The furnace temperature preferably decreases by 50 to 500.degree. C., for example by 100.degree. C. or by 400.degree. C., particularly preferably by 150 to 300.degree. C., before the glass melt is removed from the furnace.

Preheating section

The furnace preferably has at least a first and a further chamber connected to one another by a passage, the first and the further chamber having different temperatures, the temperature of the first chamber being lower than the temperature of the further chamber. In the further chamber, a glass melt is formed from the silicon dioxide granulate. This chamber is referred to below as the melting chamber. A chamber connected to the melting chamber via a material guide, but located upstream, is also referred to as a preheating section. It is, for example, the one in which at least one outlet is directly connected to an inlet of the melting chamber. The aforementioned arrangement can also be designed in independent ovens. Then the melting chamber is a melting furnace. With regard to the further description, however, the melting furnace can be synonymous with Melting chamber are understood. Accordingly, the comments on the melting furnace also apply to the melting chamber, and vice versa. The concept of the preheating section is the same for both approaches.

The silicon dioxide granulate preferably has a temperature in a range from 20 to 1300 ° C. on entering the furnace.

According to a first embodiment, the silicon dioxide granulate is not tempered before it enters the melting chamber. For example, when entering the furnace, the silicon dioxide granulate has a temperature in a range from 20 to 40 ° C, particularly preferably from 20 to 30 ° C. If silicon dioxide granulate II is provided according to step i.), It preferably has a temperature in a range from 20 to 40 ° C., particularly preferably from 20 to 30 ° C., when it enters the furnace.

According to another embodiment, the silicon dioxide granulate is tempered to a temperature in a range from 40 to 1300 ° C. before entering the furnace. Tempering means setting the temperature to a selected value. The temperature control can in principle take place in any of the ways known to the person skilled in the art and known for temperature control of silicon dioxide granules. For example, the temperature control can take place in a furnace that is arranged separately from the melting chamber or in a furnace that is connected to the melting chamber.

The temperature control preferably takes place in a chamber connected to the melting chamber. The furnace therefore preferably comprises a preheating section in which the silicon dioxide can be tempered. The preheating section itself is preferably a continuous furnace, particularly preferably a rotary kiln. A continuous furnace is understood to mean a heated chamber which, during operation, causes the silicon dioxide to move from an inlet of the continuous furnace to an outlet of the continuous furnace. The outlet is preferably connected directly to the inlet of the melting furnace. In this way, the silicon dioxide granulate can get into the melting furnace from the preheating section without further intermediate steps or measures.

It is further preferred that the preheating section comprises at least one gas inlet and at least one gas outlet. Gas can enter the interior space, the gas space of the preheating section, through the gas inlet, and it can be discharged through the gas outlet. It is also possible to introduce gas into the preheating section via the inlet for the silicon dioxide granulate of the preheating section. Gas can also be discharged via the outlet of the preheating section and then separated from the silica granules. Furthermore, gas can preferably be supplied to the preheating section via the inlet for the silicon dioxide granulate and a gas inlet, and discharged via the outlet of the preheating section and a gas outlet of the preheating section.

A gas flow is preferably formed in the preheating section by using the gas inlet and the gas outlet. Suitable gases are, for example, hydrogen, inert gases and two or more of them. Preferred inert gases are nitrogen, helium, neon, argon, krypton and xenon, particularly preferably nitrogen and helium. A reducing atmosphere is preferably present in the preheating section. This can preferably be provided by hydrogen or a combination of hydrogen and an inert gas, for example by a combination of hydrogen and helium or by hydrogen and nitrogen, particularly preferably by a combination of hydrogen and helium. More preferably, there is an oxidizing atmosphere in the preheating section. This can preferably be provided by oxygen or a combination of oxygen and one or more further gases; air is particularly preferred. It is furthermore possible to control the temperature of the silicon dioxide in the preheating section at reduced pressure.

For example, when entering the furnace, the silica granules have a temperature in a range from 100 to 1100 ° C or from 300 to 1000 or from 600 to 900 ° C.

According to one embodiment of the first subject matter, the furnace includes at least two chambers. The furnace preferably includes a first and at least one further chamber. The first and the further chamber are connected to one another by a passage.

The at least two chambers can in principle be arranged as desired in the furnace, preferably vertically or horizontally, particularly preferably vertically. The chambers in the furnace are preferably arranged in such a way that when the method according to the first object is carried out, silicon dioxide granulate passes through the first chamber and is then heated in the further chamber to obtain a glass melt. The further chamber preferably has the above-described features of the melting furnace and the crucible arranged therein.

Preferably each of the chambers contains an inlet and an outlet. The inlet of the furnace is preferably connected to the inlet of the first chamber by a passage. The outlet of the furnace is preferably connected to the outlet of the further chamber through a passage. The outlet of the first chamber is preferably connected to the inlet of the further chamber through a passage.

The chambers are preferably arranged in the furnace in such a way that the silicon dioxide granulate can pass through the inlet of the furnace into the first chamber. The chambers are preferably arranged in the furnace in such a way that a silicon dioxide glass melt can be removed from the further chamber through the outlet of the furnace. Particularly preferably, the silicon dioxide granulate can get into the first chamber through the inlet of the furnace and a silicon dioxide glass melt can be removed from a further chamber through the outlet of the furnace.

The silicon dioxide can pass through the passage in the form of granules or powder in the direction of material transport specified by the method from a first into a further chamber. Chambers connected by a passage include arrangements in which further intermediate elements are arranged in the direction of material transport between a first and a further chamber. In principle, gases, liquids and solids can pass through the passage. Silicon dioxide powder, suspensions of silicon dioxide powder and silicon dioxide granulate can preferably pass the transition between a first and a further chamber. While the method according to the invention is being carried out, all of the substances introduced into the first chamber can reach the further chamber via the passage between the first and the further chamber. Preferably only silicon dioxide in the form of granules or powder reaches the further chamber via the passage between the first and further chambers. The passage between the first and the further chamber is preferably closed by the silicon dioxide, so that the gas space of the first and the further chamber are separated from each other, preferably so that different gases or gas mixtures, different pressures or both can be present in the gas spaces. According to another embodiment, the passage is formed by a lock, preferably by a rotary valve.

The first chamber of the furnace preferably has at least one gas inlet and at least one gas outlet. The gas inlet can in principle have any shape known to the person skilled in the art and suitable for introducing a gas, for example a nozzle, a valve or a pipe. The gas outlet can in principle have any shape known to the person skilled in the art and suitable for discharging a gas, for example a nozzle, a valve or a pipe. Preferably, silicon dioxide granulate is introduced into the first chamber through the inlet of the furnace and heated. The heating can be carried out in the presence of one gas or a combination of two or more gases. For this purpose, the gas or the combination of two or more gases is present in the gas space of the first chamber. The gas space of the first chamber is understood to mean the area of the first chamber that is not occupied by a solid or liquid phase. Suitable gases are, for example, hydrogen, oxygen, inert gases and two or more of them. Preferred inert gases are nitrogen, helium, neon, argon, krypton and xenon, nitrogen, helium and a combination thereof are particularly preferred. The heating is preferably carried out in a reducing atmosphere. This can preferably be provided by hydrogen or a combination of hydrogen and helium. Preferably, the silicon dioxide granulate is heated in the first chamber in a stream of the gas or the combination of two or more gases.

It is further preferred that the silicon dioxide granulate in the first chamber is heated at reduced pressure, for example at a pressure of less than 500 mbar or less than 300 mbar, for example 200 mbar or less.

The first chamber is preferably provided with at least one device with which the silicon dioxide granulate is moved. In principle, all devices can be selected which are known to the person skilled in the art and appear suitable for this purpose. Stirring, pouring or swiveling devices are particularly suitable.

According to one embodiment of the first subject, the temperatures in the first and in the further chamber are different. The temperature in the first chamber is preferably lower than the temperature in the further chamber. The temperature difference between the first and the further chamber is preferably in a range from 600 to 2400 ° C., for example in a range from 1000 to 2000 ° C. or from 1200 to 1800 ° C., particularly preferably in a range from 1500 to 1700 ° C. The temperature in the first chamber is more preferably 600 to 2400 ° C., for example 1000 to 2000 ° C. or 1200 to 1800 ° C., particularly preferably 1500 to 1700 ° C. lower than the temperature in the further chamber.

According to one embodiment, the first chamber of the furnace is a preheating section, particularly preferably a preheating section as described above, which has the features described above. The preheating section is preferably connected to the further chamber through a passage. Preferably, silicon dioxide passes from the preheating section via a passage into the further chamber. The passage between the preheating section and the further chamber can be closed so that no gases introduced into the preheating section can pass through the opening into the further chamber. The passage between the preheating section and the further chamber is preferably closed so that the silicon dioxide does not come into contact with water. The passage between the preheating section and the further chamber can be closed so that the gas space of the preheating section and the first chamber are separated from one another in such a way that different gases or gas mixtures, different pressures or both can be present in the gas spaces. The configurations described above are preferably suitable as the passage.

According to a further embodiment, the first chamber of the furnace is not a preheating section. For example, the first chamber is an equalization chamber. A compensation chamber is understood to be a chamber of the furnace in which throughput variations in an upstream preheating section or throughput differences between a preheating section and the further chamber are compensated. For example, a rotary kiln can be connected upstream of the first chamber as described above. This usually has a throughput that can vary by up to 6% of the average throughput. Preferably, silicon dioxide is kept in a compensation chamber at the temperature at which it enters the compensation chamber.

It is also possible for the furnace to have a first chamber and more than one further chamber, for example two further chambers or three further chambers or four further chambers or five further chambers or more than five further chambers, particularly preferably two further chambers. If the furnace has two further chambers, the first chamber is preferably a preheating section, the first of the further chambers is an equalization chamber and the second of the further chambers is the melting chamber, based on the direction of material transport.

According to a further embodiment, an additive is present in the first chamber. The additive is preferably selected from the group consisting of halogens, inert gases, bases, oxygen or a combination of two or more thereof.

In principle, halogens in elemental form and halogen compounds are suitable as additives. Preferred halogens are selected from the group consisting of chlorine, fluorine, chlorine-containing compounds and fluorine-containing compounds. Elemental chlorine and hydrogen chloride are particularly preferred. In principle, all inert gases and mixtures of two or more thereof are suitable as additives. Preferred inert gases are nitrogen, helium or a combination thereof.

Bases are in principle also suitable as additives. Preferred bases as additives are inorganic and organic bases.

Oxygen is also suitable as an additive. The oxygen is preferably present as an oxygen-containing atmosphere, for example in combination with an inert gas or a mixture of two or more inert gases, particularly preferably in combination with nitrogen, helium or nitrogen and helium.

The first chamber can in principle contain any material that is known to the person skilled in the art and is suitable for heating silicon dioxide. The first chamber preferably contains at least one element selected from the group consisting of quartz glass, a refractory metal, aluminum and a combination of two or more thereof, particularly preferably the first chamber contains quartz glass or aluminum.

The temperature in the first chamber preferably does not exceed 600 ° C. if the first chamber contains a polymer or aluminum. The temperature in the first chamber is preferably 100 to 1100 ° C. if the first chamber contains quartz glass. The first chamber preferably contains essentially quartz glass.

When the silicon dioxide is transported from the first chamber to the further chamber through the passage between the first and the further chamber, the silicon dioxide can in principle be in any desired state. The silicon dioxide is preferably in the form of a solid, for example as particles, powder or granules. According to one embodiment of the first object, the silicon dioxide is transported from the first to the further chamber as granules.

According to a further embodiment, the further chamber is a crucible made of a sheet metal or a sintered material which contains a sintered metal, the sheet metal or the sintered metal being selected from the group consisting of molybdenum, tungsten and a combination thereof.

The glass melt is withdrawn from the furnace through the outlet, preferably via a nozzle. Step iii.)

A quartz glass body is formed from at least part of the glass melt. For this purpose, at least part of the glass melt produced in step ii) is preferably removed and the quartz glass body is formed therefrom.

A portion of the glass melt produced in step ii) can in principle be removed continuously from the melting furnace or the melting chamber, or after the glass melt has been produced. Part of the glass melt is preferably removed continuously. The glass melt is removed through the outlet from the furnace or the outlet from the melting chamber, in each case preferably via a nozzle.

The glass melt can be cooled before, during or after removal to a temperature which enables the glass melt to be shaped. As the glass melt cools down, the viscosity of the glass melt increases. The molten glass is preferably cooled to such an extent that the shape formed is retained during molding and, at the same time, the molding can be carried out as quickly, reliably and with little effort as possible. The person skilled in the art can easily determine the viscosity of the glass melt for molding by varying the temperature of the glass melt on the mold. The molten glass preferably has a temperature in the range from 1750 to 2100 ° C., for example 1850 to 2050 ° C., particularly preferably 1900 to 2000 ° C., when it is removed. After removal, the molten glass is preferably at a temperature of less than 500 ° C., for example less than 200 ° C. or less than 100 ° C. or less than 50 ° C., particularly preferably to a temperature in the range from 20 to 30 ° C cooled.

The formed quartz glass body can be a solid body or a hollow body. A solid body is understood to mean a body which consists essentially of a single material. Nevertheless, a solid body can have one or more inclusions, for example gas bubbles. Such inclusions in a solid body often have a size of 65 mm ³ or less, for example less than 40 mm ³ , or less than 20 mm ³ , or less than 5 mm ³ , or less than 2 mm ³ , particularly preferably less than 0.5 mm ³ . A solid body preferably contains less than 0.02% by volume of its volume, for example less than 0.01% by volume or less than 0.001% by volume, of inclusions, in each case based on the total volume of the solid body. The quartz glass body has an external shape. The outer shape is understood to mean the shape of the outer edge of the cross section of the quartz glass body. The external shape of the quartz glass body is preferably round, elliptical or polygonal in cross section with three or more corners, for example 4, 5, 6, 7 or 8 corners; the quartz glass body is particularly preferably round.

The quartz glass body preferably has a length in the range from 100 to 10000 mm, for example from 1000 to 4000 mm, particularly preferably from 1200 to 3000 mm.

The quartz glass body preferably has an external diameter in the range from 1 to 500 mm, for example in a range from 2 to 400 mm, particularly preferably in a range from 5 to 300 mm.

The quartz glass body is shaped using a nozzle. To do this, the glass melt is passed through the nozzle. The outer shape of a quartz glass body formed by the nozzle is determined by the shape of the opening of the nozzle. If the opening of the nozzle is round, a cylinder is formed when the quartz glass body is formed. If the opening of the nozzle has a structure, this structure is transferred to the outer shape of the quartz glass body. A quartz glass body, which is formed by means of a nozzle with structures at the opening, has an image of the structures in the longitudinal direction on the glass strand.

The nozzle is integrated in the melting furnace. It is preferably integrated into the melting furnace as part of the crucible, particularly preferably as part of the outlet of the crucible.

The at least part of the glass melt is preferably removed through the nozzle. The outer shape of the quartz glass body is formed by removing at least part of the glass melt through the nozzle.

The quartz glass body is preferably cooled after it has been formed in order to retain its shape. After molding, the quartz glass body is preferably cooled to a temperature which is at least 1000 ° C below the temperature of the glass melt during molding, for example at least 1500 ° C or at least 1800 ° C, particularly preferably 1900 to 1950 ° C. The quartz glass body is preferably cooled to a temperature of less than 500 ° C., for example less than 200 ° C. or less than 100 ° C. or less than 50 ° C., particularly preferably to a temperature in the range from 20 to 30 ° C. According to one embodiment of the first object, the quartz glass body obtained can be treated with at least one measure selected from the group consisting of chemical, thermal or mechanical treatment.

The quartz glass body is preferably chemically aftertreated. Post-treatment concerns the treatment of a quartz glass body that has already been formed. Chemical aftertreatment of the quartz glass body is understood in principle to mean any measure that is known to the person skilled in the art and appears suitable for changing the chemical structure or the composition of the surface of the quartz glass body, or both, through the use of substances. The chemical aftertreatment preferably comprises at least one measure selected from the group consisting of treatment with fluorine compounds and ultrasonic cleaning.

Particularly suitable fluorine compounds are hydrogen fluoride and fluorine-containing acids, for example hydrofluoric acid. The liquid preferably has a content of fluorine compounds in a range from 35 to 55% by weight, preferably in a range from 35 to 45% by weight, the% by weight in each case based on the total amount of liquid. The remainder to 100% by weight is usually water. Deionized or deionized water is preferably selected as the water.

Ultrasonic cleaning is preferably carried out in a liquid bath, particularly preferably in the presence of detergents. In the case of ultrasonic cleaning, no fluorine compounds, for example hydrofluoric acid or hydrogen fluoride, are generally used.

The ultrasonic cleaning of the quartz glass body is preferably carried out under at least one, for example at least two or at least three or at least four or at least five, particularly preferably all of the following conditions:

Ultrasonic cleaning takes place in a continuous process.

The system for ultrasonic cleaning has six chambers connected to one another by pipes.

The residence time of the quartz glass body in each chamber can be adjusted. The residence time of the quartz glass body in each chamber is preferably the same. The residence time in each chamber is preferably in a range from 1 to 120 minutes, for example from less than 5 minutes or from 1 to 5 minutes or from 2 to 4 minutes or from less than 60 minutes or from 10 to 60 minutes or from 20 minutes to 50 min, particularly preferably in a range from 5 to 60 min. The first chamber comprises a basic medium, preferably containing water and a base, and an ultrasonic cleaner.

The third chamber comprises an acidic medium, preferably containing water and an acid, and an ultrasonic cleaner.

In the second chamber and in the fourth to sixth chamber, the quartz glass body is cleaned with water, preferably demineralized water.

The fourth to sixth chambers are operated as a cascade with water, preferably desalinated water. The water is preferably only introduced into the sixth chamber and runs from the sixth into the fifth and from the fifth into the fourth chamber.

The quartz glass body is preferably thermally post-treated. Thermal aftertreatment of the quartz glass body is understood in principle to mean any measure that is known to the person skilled in the art and appears suitable for changing the shape or structure of the quartz glass body or both by the action of temperature. The thermal aftertreatment preferably comprises at least one measure selected from the group consisting of tempering, upsetting, inflating, pulling out, welding and a combination of two or more thereof. The thermal aftertreatment is preferably carried out without the aim of removing material.

The tempering is preferably carried out by heating the quartz glass body in a furnace, preferably to a temperature in a range from 900 to 1300 ° C., for example in a range from 900 to 1250 ° C. or from 1040 to 1300 ° C., particularly preferably in one range from 1000 to 1050 ° C or from 1200 to 1300 ° C. In the thermal treatment, a temperature of 1300 ° C. is preferably not exceeded for a continuous period of more than 1 hour, particularly preferably a temperature of 1300 ° C. is not exceeded during the entire thermal treatment period. The tempering can in principle take place at reduced pressure, at normal pressure or at elevated pressure, preferably at reduced pressure, particularly preferably in vacuo.

The upsetting is preferably carried out by heating the quartz glass body, preferably to a temperature of about 2100 ° C., and subsequent shaping during a rotating rotary movement, preferably at a rotary speed of about 60 rpm. For example, a quartz glass body in the form of a rod can be formed into a cylinder by upsetting. A quartz glass body can preferably be inflated by blowing a gas into the quartz glass body. For example, a quartz glass body can be blown into a large tube. For this purpose, the quartz glass body is preferably heated, preferably to a temperature of about 2100 ° C., while a rotating rotary movement, preferably at a speed of rotation of about 60 rpm, is carried out and the interior is flushed with a gas, preferably at a defined and regulated Internal pressure up to about 100 mbar. A large pipe is understood to mean a pipe with an outside diameter of at least 500 mm.

A quartz glass body can preferably be drawn out. Pulling out is preferably carried out by heating the quartz glass body, preferably to a temperature of about 2100 ° C., and then drawing at a controlled pulling speed to the desired outer diameter of the quartz glass body. For example, lamp tubes can be formed from quartz glass bodies by drawing them out.

The quartz glass body is preferably post-treated mechanically. Mechanical aftertreatment of the quartz glass body is understood in principle to mean any measure that is known to the person skilled in the art and appears suitable for changing the shape of the quartz glass body by an abrasive measure or dividing the quartz glass body into several pieces. In particular, the mechanical aftertreatment includes at least one measure selected from the group consisting of grinding, drilling, honing, sawing, water jet cutting, laser cutting, roughening by sandblasting, milling and a combination of two or more thereof.

The quartz glass body is preferred with a combination of these measures, for example with a combination of a chemical and a thermal aftertreatment or a chemical and a mechanical aftertreatment or a thermal and a mechanical aftertreatment, particularly preferably with a combination of a chemical, a thermal and a mechanical aftertreatment treated. Furthermore, the quartz glass body can preferably be subjected to several of the aforementioned measures, independently of one another.

According to a further embodiment, the method can contain the following, optional method step:

iv.) Forming a hollow body with at least one opening from the quartz glass body. The hollow body formed has an inner and an outer shape. The internal shape is understood to mean the shape of the inner edge of the hollow body in cross section. The inner and outer shape of the cross section of the hollow body can be the same or different. The inner and outer shape of the hollow body can be round, elliptical or polygonal in cross section with three or more corners, for example 4, 5, 6, 7 or 8 corners.

The outer shape of the cross section preferably corresponds to the inner shape of the cross section of the hollow body. The hollow body particularly preferably has a round inner and a round outer shape in cross section.

In another embodiment, the hollow body can differ in the inner and outer shape. The hollow body preferably has a round outer shape and a polygonal inner shape in cross section. The hollow body particularly preferably has a round outer shape and a hexagonal inner shape in cross section.

The hollow body preferably has a length in the range from 100 to 10000 mm, for example from 1000 to 4000 mm, particularly preferably from 1200 to 2000 mm.

The hollow body preferably has a wall thickness in a range from 0.8 to 50 mm, for example in a range from 1 to 40 mm or from 2 to 30 mm or from 3 to 20 mm, particularly preferably in a range from 4 to 10 mm .

The hollow body preferably has an outside diameter of 2.6 to 400 mm, for example in a range from 3.5 to 450 mm, particularly preferably in a range from 5 to 300 mm.

The hollow body preferably has an inside diameter of 1 to 300 mm, for example in a range from 5 to 280 mm or from 10 to 200 mm, particularly preferably in a range from 20 to 100 mm.

The hollow body contains one or more openings. The hollow body preferably contains an opening. The hollow body preferably contains an even number of openings, for example 2, 4, 6, 8, 10, 12, 14, 16, 18 or 20 openings. The hollow body preferably contains two openings. The hollow body is preferably a tube. This shape of the hollow body is particularly preferred when the light guide contains only one core. The hollow body can have more than two openings contain. The openings are preferably located opposite one another in pairs in the ends of the quartz glass body. For example, each end of the quartz glass body has 2, 3, 4, 5, 6, 7 or more than 7 openings, particularly preferably 5, 6 or 7 openings. Preferred shapes are, for example, tubes, twin tubes, that is to say tubes with two parallel channels, multi-channel rods, that is to say tubes with more than two parallel channels.

The hollow body can in principle be shaped in all ways known to the person skilled in the art. The hollow body is preferably shaped by means of a nozzle. The nozzle preferably contains a device in the center of its opening which diverts the glass melt during molding. A hollow body can be formed from a glass melt.

A hollow body can be formed by using a nozzle and subsequent post-treatment. In principle, all methods known to those skilled in the art for producing a hollow body from a solid body, for example the upsetting of channels, drilling, honing or grinding, are suitable as post-treatment. A preferred post-treatment is to guide the solid body over one or more mandrels, a hollow body being formed. The mandrel can also be introduced into the solid body to form a hollow body. The hollow body is preferably cooled after it has been formed.

After formation, the hollow body is preferably at a temperature of less than 500 ° C., for example less than 200 ° C. or less than 100 ° C. or less than 50 ° C., particularly preferably to a temperature in the range from 20 to 30 ° C cooled.

Precompression

In principle, it is possible to subject the silicon dioxide granulate provided in step i.) To one or more pretreatment steps before it is heated in step ii.) Until a glass melt is obtained. Thermal or mechanical treatment steps, for example, come into consideration as pretreatment steps. For example, the silicon dioxide granulate is compacted prior to heating in step ii.). “Compaction” is understood to mean a reduction in the BET surface area and a reduction in the pore volume.

The silicon dioxide granulate is preferably compacted thermally by heating the silicon dioxide granulate or mechanically by exerting pressure on the silicon dioxide granulate, for example rolling or pressing the silicon dioxide granulate. The silicon dioxide granulate is preferably compacted by heating. The compression of the takes place particularly preferably Silica granulate by heating by means of a connected to the melting furnace

Preheating section.

The silicon dioxide is preferably compressed by heating at a temperature in a range from 800 to 1400 ° C, for example at a temperature in a range from 850 to 1300 ° C, particularly preferably at a temperature in a range from 900 to 1200 ° C.

In one embodiment of the first article, the BET surface area of the

Silica granulate before heating in step ii.) Is not reduced to less than 5 m ² / g, preferably not to less than 7 m ² / g or not to less than 10 m ² / g, particularly preferably not to less than 15 m ² /G. It is further preferred that the BET surface area of the silicon dioxide granulate is not reduced before the heating in step ii.) Compared to the silicon dioxide granulate provided in step i.).

In one embodiment of the first article, the BET surface area of the

Siliziumdioxidgranulats m to less than 20 ² / g reduced, for example to less than 15m ² / g, or less than 10 m ² / g, or to a range of more than 5 to less than 20 m ² / g or of 7 to 15 m ² / g, particularly preferably in a range from 9 to 12 m ² / g. The BET surface area of the silicon dioxide granulate is preferably reduced by less than 40 m ² / g, for example by 1 to 20 m ² / g or by 2 to 10, compared to the silicon dioxide granulate provided in step i.) Before heating in step ii.) m ² / g, particularly preferably around 3 to 8 m ² / g, the BET surface area after compaction being more than 5 m ² / g.

The compacted silicon dioxide granulate preferably has at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features:

A. a BET surface area in a range from more than 5 to less than 40 m ² / g, for example from 10 to 30 m ² / g, particularly preferably in a range from 15 to 25 m ² / g;

B. a particle size D10 in a range from 100 to 300 μm, particularly preferably in a range from 120 to 200 μm;

C. a particle size D50 in a range from 150 to 550 μm, particularly preferably in a range from 200 to 350 μm;

D. a particle size D90 in a range from 300 to 650 μm, particularly preferably in a range from 400 to 500 μm; E. a bulk density in a range from 0.8 to 1.6 g / cm ³ , particularly preferably from 1.0 to 1.4 g / c ³ ;

F. a tamped density in a range from 1.0 to 1.4 g / cm ³ , particularly preferably from 1.15 to 1.35 g / cm ³ ;

G. an amount of carbon of less than 5 ppm, for example less than 4.5 ppm, more preferably less than 4 ppm;

H. a Cl content of less than 500 ppm, particularly preferably from 1 ppb to 200 ppm, the ppm and ppb each being based on the total weight of the compacted silicon dioxide granulate.

The compacted silicon dioxide granulate preferably has the combination of features A./F./G. or A./F./H. or A./G./H. on, particularly preferably the combination of features A./F./G. /H.

The compacted silicon dioxide granulate preferably has the combination of features A./F./G. The BET surface area is in a range from 10 to 30 m ² / g, the tamped density is in a range from 1.15 to 1.35 g / ml_ and the carbon content is less than 4 ppm.

The compacted silicon dioxide granulate preferably has the combination of features A./F./H. The BET surface area is in a range from 10 to 30 m ² / g, the tamped density in a range from 1.15 to 1.35 g / ml_ and the chlorine content in a range from 1 ppb to 200 ppm.

The compacted silicon dioxide granulate preferably has the combination of features A./G./H. where the BET surface area is in a range from 10 to 30 m ² / g, the carbon content is less than 4 ppm and the chlorine content is in a range from 1 ppb to 200 ppm.

The compacted silicon dioxide granulate preferably has the combination of features A./F./G./H. The BET surface area is in a range from 10 to 30 m ² / g, the tamped density is in a range from 1.15 to 1.35 g / ml_, the carbon content is less than 4 ppm and the chlorine content in one Range from 1 ppb to 200 ppm.

In one embodiment of the first article, the melting energy is transferred to the silicon dioxide granulate via a solid surface. The compacted silicon dioxide granulate can be selected as the silicon dioxide granulate, for example. A solid surface is understood to be a surface which is different from the surface of the silicon dioxide granulate and which does not melt or decompose at temperatures to which the silicon dioxide granulate is heated to melt. Suitable materials for the solid surface are, for example, the materials suitable as crucible materials.

The solid surface can in principle be any surface known to the person skilled in the art and suitable for these purposes. For example, the crucible or a separate component that is not the crucible can be used as the solid surface.

In principle, the solid surface can be heated in any way known to the person skilled in the art and suitable for this purpose in order to transfer the melting energy to the silicon dioxide granulate. The solid surface is preferably heated by resistive heating or induction heating. In the case of inductive heating, the energy is coupled directly into the solid surface through coils and released from there to the inside. With resistive heating, the solid surface is heated from the outside and releases the energy from there to the inside. A boiler room gas with a lower heat capacity, for example an argon atmosphere or an atmosphere containing argon, is advantageous. For example, the solid surface can be heated electrically or by externally firing the solid surface with a flame. The solid surface is preferably heated to a temperature which can transfer an amount of energy sufficient to melt the silicon dioxide granules to the silicon dioxide granules and / or to partially melted silicon dioxide granules.

According to one embodiment of the present invention, the energy input into the crucible does not take place by heating the crucible, or a melt material present therein, or both, by means of a flame, such as a burner flame directed into the crucible or onto the crucible.

If a separate component is used as the solid surface, it can be brought into contact with the silicon dioxide granulate in any way, for example by placing the component on the silicon dioxide granulate or by inserting the component between the granules of the silicon dioxide granulate or by pushing the component between the crucible and the silicon dioxide granulate or a combination of two or more thereof. The component can be heated before or during or before and during the transfer of the melt energy. The melting energy is preferably transferred to the silicon dioxide granulate via the inside of the crucible. The crucible is heated to such an extent that the silicon dioxide granulate melts. The crucible is preferably heated resistively or inductively. The heat is transferred from the outside to the inside of the crucible. The solid surface of the inside of the crucible transfers the melting energy to the silicon dioxide granulate.

According to a further embodiment of the present invention, the melting energy is not transferred to the silicon dioxide granulate via a gas space on the silicon dioxide granulate. More preferably, the melting energy is not transferred to the silicon dioxide granulate by firing the silicon dioxide granulate with a flame. Examples of these excluded energy transmission paths are directing one or more burner flames from above into the crucible, or at the silicon dioxide, or both.

A fifth subject of the invention is a quartz glass body obtainable by the method described in the fourth subject. Accordingly, a method for producing a quartz glass body is also preferred, a method according to the first subject matter of the invention, in particular steps (i) to (v) being carried out first, from which a silicon dioxide granulate is formed. A glass melt and finally a quartz glass body are then formed from this, as already described above.

In one embodiment, the quartz glass body has at least one, preferably two or more, up to all of the following features:

A] a chlorine content of less than 1 ppm;

B] an aluminum content of less than 200 ppb;

C] a content of atoms other than Si, O, H, C of less than 5 ppm;

D] a viscosity (p = 1013 hPa) in a range from logio (h (1250 ° C) / dPas) = 1 1, 4 to log ™ (P (1250 ° C) / dPas) = 12.9, or log ₁₀ (h (1300 ° C) / dPas) = 11.1 to log ₁₀ (h (1300 ° C) / dPas) = 12.2, or log ₁₀ (h (1350 ° C) / dPas) = 10.5 up to log ₁₀ (h (1350 ° C) / dPas) = 11.5;

E] a refractive index homogeneity of less than 10 ⁴ ;

F] a cylindrical shape;

G] a tungsten content of less than 5 ppm; H] a molybdenum content of less than 5 ppm;

A sixth object of the present invention is a method for producing a light guide comprising the following steps:

AI providing a quartz glass body according to the fifth subject matter of the invention, or one of its embodiments, or a quartz glass body obtainable by the method according to the fourth subject matter;

wherein the quartz glass body is first processed into a hollow body with at least one opening;

B / introducing one or more core rods into the quartz glass body through the at least one opening while obtaining a precursor;

C / Heat drawing the precursor from step B / to obtain a light guide with one or more cores and a shell M1.

Step A /

The quartz glass body provided in step A / is preferably characterized by the features according to the fourth and / or fifth subject matter of the invention. Furthermore, the quartz glass body can have been shaped into a hollow body with at least one opening by a forming process. The quartz glass body obtainable in this way particularly preferably has the features according to the fifth subject matter.

Step B /

One or more core rods are introduced through the at least one opening in the quartz glass body (step B /). In connection with the present invention, the term core rod denotes an object which is provided to be introduced into a sheath, for example a sheath M1, and processed into a light guide. The core rod has a core made of quartz glass. The core rod preferably contains a core made of quartz glass and a first cladding layer MO surrounding the core.

Each core rod has a shape that is selected so that it fits into the quartz glass body. The outer shape of a core rod preferably corresponds to the shape of an opening in the Quartz glass body. The quartz glass body is particularly preferably a tube and the core rod is a rod with a round cross section.

The diameter of the core rod is smaller than the inner diameter of the hollow body. The diameter of the core rod is preferably 0.1 to 3 mm smaller than the inner diameter of the hollow body, for example 0.3 to 2.5 mm smaller or 0.5 to 2 mm smaller or 0.7 to 1.5 mm smaller, especially preferably 0.8 to 1.2 mm smaller.

The ratio of the inner diameter of the quartz glass body to the diameter of the core rod is preferably in the range from 2: 1 to 1,0001: 1, for example in the range from 1.8: 1 to 1.01: 1 or in the range from 1.6: 1 up to 1.005: 1 or in the range from 1.4: 1 to 1.01: 1, particularly preferably in the range from 1.2: 1 to 1.05: 1.

A region within the quartz glass body that is not filled by the core rod can preferably be filled with at least one further component, for example a silicon dioxide powder or a silicon dioxide granulate.

It is also possible for a core rod already located in at least one further quartz glass body to be inserted into a quartz glass body. The further quartz glass body has an outer diameter that is smaller than the inner diameter of the quartz glass body. The core rod introduced into the quartz glass body can also already be located in two or more further quartz glass bodies, for example in 3 or 4 or 5 or 6 or more further quartz glass bodies.

A quartz glass body which is obtainable in this way and provided with one or more core rods is referred to below as a “precursor”.

Step C /

The precursor is drawn in the heat (step e /). The product obtained in this way is a light guide with one or more cores and at least one shell M1.

The precursor is preferably drawn at a speed in the range from 1 to 100 m / h, for example at a speed in the range from 2 to 50 m / h or from 3 to 30 m / h. The quartz glass body is particularly preferably drawn at a speed in the range from 5 to 25 m / h. The hot drawing is preferably carried out at a temperature of up to 2500 ° C., for example at a temperature in the range from 1700 to 2400 ° C., particularly preferably at a temperature in the range from 2100 to 2300 ° C.

The precursor is preferably passed through an oven which heats the precursor from the outside.

The precursor is preferably elongated until the desired thickness of the light guide is achieved. The precursor is preferably elongated to 1,000 to 6,000,000 times the length, for example to 10,000 to 500,000 times the length or to 30,000 to 200,000 times the length, in each case based on the length of the quartz glass body provided in step AI. The precursor is particularly preferably elongated to 100,000 to 10,000,000 times the length, for example to 150,000 to 5,800,000 times the length or to 160,000 to 640,000 times the length or to 1,440,000 to 5,760,000 times the length or to 1,440,000 to 2,560,000 times the length, each based on the length of the quartz glass body provided in step AI.

The diameter of the precursor is preferably reduced by the elongation by a factor in a range from 100 to 3,500, for example in a range from 300 to 3,000 or from 400 to 800 or from 1,200 to 2,400 or from 1,200 to 1,600, each based on the diameter of the quartz glass body provided in step AI.

The light guide, also referred to as light wave guide, can contain any material that is suitable for guiding or guiding electromagnetic radiation, in particular light.

Conducting or guiding radiation denotes the extension of the radiation over the longitudinal extension of the light guide without any substantial hindrance or attenuation of the intensity of the radiation. The radiation is coupled into the conductor via one end of the light guide. The light guide preferably conducts electromagnetic radiation in a wavelength range from 170 to 5000 nm. The attenuation of the radiation by the light guide in the respective wavelength range is preferably in a range from 0.1 to 10 dB / km. The light guide preferably has a transmission rate of up to 50 Tbit / s.

The light guide preferably has a curl parameter of more than 6 m. In the present context, the curl parameter is the bending radius of a fiber, for example a light guide or a sheath M1, understood, which adjusts itself to a freely movable fiber without the action of external force.

The light guide is preferably designed to be flexible. Bendable in the context of the invention means that the light guide is characterized by a bending radius of 20 mm or less, for example 10 mm or less, particularly preferably less than 5 mm or less. A bending radius is the narrowest radius that can be formed without breaking the light guide and without impairing the ability of the light guide to conduct radiation. An impairment occurs when the light transmitted through a bend in the light guide is attenuated by more than 0.1 dB. The attenuation is preferably given at a reference wavelength of 1550 nm.

The quartz preferably consists of silicon dioxide with less than 1% by weight of other substances, for example with less than 0.5% by weight of other substances, particularly preferably with less than 0.3% by weight of other substances, each based on the total weight of the quartz. More preferably, the quartz contains at least 99% by weight silicon dioxide, based on the total weight of the quartz.

The light guide preferably has an elongated shape. The shape of the light guide is defined by its length L and its cross section Q. The light guide preferably has a round outer wall along its longitudinal extent L. A cross section Q of the light guide is always determined in a plane that is perpendicular to the outer wall of the light guide. If the light guide is curved in the longitudinal extent L, the cross section Q is determined perpendicular to the tangent at a point on the light guide outer wall. The light guide preferably has a diameter di _. in a range from 0.04 to 1.5 mm. The light guide preferably has a length in a range from 1 m to 100 km.

The light guide can have one or more cores, for example one core or two cores or three cores or four cores or five cores or six cores or seven cores or more than seven cores, particularly preferably one core. More than 90%, for example more than 95%, particularly preferably more than 98% of the electromagnetic radiation that is guided through the light guide is preferably guided in the cores. For the transport of light in the cores, the wavelength ranges mentioned as preferred that have already been specified for the light guide apply. The material of the cores is preferably selected from the group consisting of glass or quartz glass, or a combination of the two, particularly preferred Quartz glass. The cores can be made of the same material or different materials, independently of one another. All cores are preferably made of the same material, particularly preferably made of quartz glass.

Each core has a, preferably round, cross section QK and has an elongated shape with the length LK. The cross section QK of a core is independent of the cross section QK of each further core. The cross sections QK of the cores can be the same or different. The cross sections QK of all cores are preferably the same. A cross section QK of a core is always determined in a plane that is perpendicular to the outer wall of the core or the light guide outer wall. If a core is curved in the longitudinal extension, the cross-section QK is determined perpendicular to the tangent at a point on the outer wall of this core. The length LK of a core is independent of the length LK of each further core. The lengths LK of the cores can be the same or different. The lengths LK of all cores are preferably the same. Each core preferably has a length LK in a range from 1 m to 100 km. Each core has a diameter d _K. The diameter d _{K of} a core is independent of the diameter d _{K of} each further core. The diameter d _{K of} the cores can be the same or different. The diameters d _{K of} all cores are preferably the same. The diameter d _{K of} each core is preferably in a range from 0.1 to 1000 μm, for example from 0.2 to 100 μm or from 0.5 to 50 μm, particularly preferably from 1 to 30 μm.

Each core has at least one refractive index profile perpendicular to the maximum core extension. “Refractive index profile” means that the refractive index perpendicular to the maximum core extension is constant or changes. The preferred refractive index profile corresponds to a concentric refractive index profile, for example a concentric refractive index profile in which a first area with the maximum refractive index is located in the center of the core, followed by a further area with a lower refractive index. Each core preferably has only one refractive index profile over its length LK. The refractive index profile of a core is independent of the refractive index profile of each further core. The refractive index curves of the cores can be the same or different. The refractive index curves of all cores are preferably the same. In principle, it is also possible for a core to have a large number of different refractive index profiles.

Each refractive index profile perpendicular to the maximum core extension has a maximum refractive index hk. Each refractive index profile perpendicular to the maximum core extension can also have other lower refractive indices. The lowest refractive index of the refractive index profile is preferably not less than 0.5 less than the maximum refractive index hk of the refractive index profile. The lowest refractive index of the refractive index profile is preferably from 0.0001 to 0.15, for example from 0.0002 to 0.1, particularly preferably from 0.0003 to 0.05 lower than the maximum refractive index hk of the refractive index profile.

The core preferably has a refractive index hk in a range from 1.40 to 1.60, for example in a range from 1.41 to 1.59, particularly preferably in a range from 1.42 to 1.58, each determined at a reference wavelength of l _G = 589 nm (sodium D line), at a temperature of 20 ° C and at normal pressure (p = 1013 hPa). For more information, see the Test Methods section. The refractive index hk of a core is independent of the refractive index hk of each further core. The refractive indices hk of the cores can be the same or different. The refractive indices hk of all nuclei are preferably the same.

Each core of the light guide preferably has a density in a range from 1.9 to 2.5 g / cm ³ , for example in a range from 2.0 to 2.4 g / cm ³ , particularly preferably in a range from 2, 1 to 2.3 g / cm ³ . The cores preferably have a residual moisture content of less than 100 ppb, for example less than 20 ppb or less than 5 ppb, particularly preferably less than 1 ppb, in each case based on the total weight of the core. The density of a core is independent of the density of any other core. The densities of the cores can be the same or different. The densities of all cores are preferably the same.

If a light guide contains more than one core, each core is characterized by the above features regardless of the other cores. It is preferred that all cores have the same characteristics.

According to the invention, the cores are surrounded by at least one shell M1. The shell M1 surrounds the cores preferably over the entire length of the cores. The shell M1 preferably surrounds the cores to at least 95%, for example at least 98% or at least 99%, particularly preferably 100% of the outer surface, that is to say the entire outer wall, of the cores. Often the cores are completely surrounded by the shell M1, except for the ends (the last 1-5 cm in each case). This serves to protect the cores from mechanical damage. The cladding M1 can contain any material, including silicon dioxide, which has a lower refractive index than at least one point P in the course of the cross section QK of the core. This at least one point in the course of the cross section QK of the core is preferably the point which lies in the center of the core. Furthermore, the point P in the course of the cross section QK of the core is preferably the point which has a maximum of the refractive index ri _Kmax in the core. The shell M1 preferably has a refractive index PMI which is at least 0.0001 lower than the refractive index of the core hk at the at least one point in the course of the cross section Q of the core. The shell M1 preferably has a refractive index PMI which is in a range from 0.0001 to 0.5, for example in a range from 0.0002 to 0.4, particularly preferably in a range from 0.0003 to 0.3 is less than the refractive index of the core Pk

The shell M1 preferably has a refractive index PMI in a range from 0.9 to 1.599, for example in a range from 1.30 to 1.59, particularly preferably in a range from 1.40 to 1.57. The envelope M1 preferably now forms a region of the light guide with a constant refractive index. A range with a constant refractive index is understood to mean a range in which the refractive index does not deviate by more than 0.0001 from the mean value of the refractive index PMI in this range.

In principle, the light guide can contain further covers. Particularly preferably, at least one of the further sheaths, preferably several or all of them, has a refractive index which is lower than the refractive index hk of each core. The light guide preferably has one or two or three or four or more than four further sheaths which surround the sheath M1. The further envelopes surrounding the envelope M1 preferably have a refractive index which is lower than the refractive index PMI of the envelope M1.

The light guide preferably has one or two or three or four or more than four further sheaths which surround the cores and are surrounded by the sheath M1, that is to say lie between the cores and the sheath M1. Furthermore, the further shells lying between the cores and the shell M1 preferably have a refractive index which is higher than the refractive index PMI of the shell M1.

The refractive index preferably decreases from the core of the light guide towards the outermost shell. The decrease in the refractive index from the core to the outermost cladding can be gradual or continuous. The decrease in the refractive index can have various sections. More preferably, the refractive index can be gradual and in at least one section steadily decrease in at least one other section. The levels can be the same or different. It is entirely possible to provide sections with an increasing refractive index between sections with a decreasing refractive index.

The different refractive indices of the various shells can be set, for example, by doping the shell M1, the further shells and / or the cores.

Depending on the type of production of a core, a core can already have a first cladding layer MO after its production. This cladding layer MO, which is directly adjacent to the core, is sometimes also referred to as an integral cladding layer. The cladding layer MO is closer to the core center point than the shell M1 and, if contained, the further shells. The cladding layer MO is generally not used to guide light or to guide radiation. Rather, the cladding layer MO contributes to the fact that the radiation remains within the core and is transported there. The radiation guided in the core is therefore preferably reflected at the transition from the core to the cladding layer MO. This transition from the core to the cladding layer MO is preferably characterized by a change in the refractive index. The refractive index of the cladding layer MO is preferably smaller than the refractive index hk of the core. The cladding layer MO preferably contains the same material as the core, but has a lower refractive index than the core due to doping or additives.

At least the shell M1 is preferably made of silicon dioxide and has at least one, preferably several or all of the following features:

a) an OH content of less than 5 ppm, particularly preferably less than 1 ppm;

b) a chlorine content of less than 200 ppm, preferably less than 100 ppm, for example less than 80 ppm, particularly preferably less than 60 ppm; c) an aluminum content of less than 200 ppb, preferably less than 100 ppb, for example less than 80 ppb, particularly preferably less than 60 ppb; d) an ODC level of less than 5 10 ¹⁵ / cm ^3, for example in a range of 0, 1 10 ¹⁵ to 3 10 ¹⁵ / cm ^3, more preferably in a range from 0.5 to 10 ¹⁵ 2.0-10 ¹⁵ / cm ³ ;

e) a metal content of metals other than aluminum of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm; f) a viscosity (p = 1013 hPa) in a range from logio (h (1250 ° C) / dPas) = 11.4 to logio (P (1250 ° C) / dPas) = 12.9 and / or log ₁₀ (h (1300 ° C) / dPas) = 1 1, 1 to log ₁₀ (h (1300 ° C) / dPas) = 12.2 and / or logio (h (1350 ° C) / dPas) = 10.5 until logio (h (1350 ° C) / dPas) = 11.5;

g) a curl parameter greater than 6 m;

h) a homogeneity of the refractive index of less than 1 - 10 ⁴ ;

i) a transformation point Tg in a range from 1150 to 1250 ° C, particularly preferably in a range from 1180 to 1220 ° C,

whereby the ppb and ppm are each based on the total weight of the casing M1.

The shell preferably has a homogeneity of the refractive index of less than T 10 ⁴ . The homogeneity of the refractive index denotes the maximum deviation of the refractive index at any point on a sample, for example a shell M1 or a quartz glass body, based on the mean value of all the refractive indices determined on the sample. To determine the mean value, the refractive index is determined at at least seven measuring points.

The shell M1 preferably has a metal content of metals other than aluminum of less than 1000 ppb, for example less than 500 ppb, particularly preferably less than 100 ppb, based in each case on the total weight of the shell M1. However, the shell M1 often has a content of metals other than aluminum in an amount of at least 1 ppb. Such metals are, for example, sodium, lithium, potassium, magnesium, calcium, strontium, germanium, copper, molybdenum, titanium, iron and chromium. These can be present, for example, as an element, as an ion, or as part of a molecule or an ion or a complex.

The shell M1 can contain further components. The shell M1 preferably contains less than 5 ppm, for example less than 45 ppm, particularly preferably less than 4 ppm, further constituents, the ppm in each case being based on the total weight of the shell M1. Carbon, fluorine, iodine, bromine and phosphorus can be considered as further constituents. These can be present, for example, as an element, as an ion, or as part of a molecule or an ion or a complex. However, the shell M1 often has a content of atoms other than Si, O, H, C, CI in an amount of at least 1 ppb.

The shell M1 preferably contains less than 5 ppm of carbon, for example less than 4 ppm or less than 3 ppm, particularly preferably less than 2 ppm, in each case based on on the total weight of the shell M1. However, the shell M1 often has a carbon content in an amount of at least 1 ppb.

The shell M1 preferably has a homogeneously distributed amount of OH, amount of Cl or amount of Al.

In one embodiment of the light guide, the envelope M1 has a weight fraction of at least 80% by weight. for example at least 85% by weight, particularly preferably at least 90% by weight, based in each case on the total weight of the shell M1 and the cores. The shell M1 preferably has a weight fraction of at least 80% by weight. for example at least 85% by weight, particularly preferably at least 90% by weight, in each case based on the total weight of the shell M1, the cores and the further shells lying between the shell M1 and the cores. The casing M1 preferably has a weight fraction of at least 80% by weight. for example at least 85% by weight, particularly preferably at least 90% by weight, in each case based on the total weight of the light guide.

The envelope M1 preferably has a density in a range from 2.1 to 2.3 g / cm ³ , particularly preferably in a range from 2.18 to 2.22 g / cm ³ .

Another aspect relates to a light guide, obtainable by a method comprising the following steps:

AI providing a quartz glass body according to the fifth subject matter of the invention, or a quartz glass body obtainable by the method according to the fourth subject matter, the quartz glass body first being processed into a hollow body with at least one opening;

Steps A /, B / and C / are preferably characterized by the features described in the context of the fourth subject matter.

The light guide is preferably characterized by the features described in the context of the sixth subject. A seventh subject matter of the present invention relates to a method for producing a luminous means including the following steps:

(i) providing a quartz glass body according to the fifth subject matter of the invention,

, or a quartz glass body obtainable by the method according to the fourth subject matter, the quartz glass body first being processed into a hollow body;

(ii) optionally equipping the hollow body with electrodes;

(iii) filling the hollow body with a gas.

Step (i)

In step (i) a quartz glass body is provided. The quartz glass body provided in step (i) is first processed into a hollow body containing at least one opening, for example one opening or two openings or three openings or four openings, particularly preferably one opening or two openings.

A quartz glass body obtainable by a method according to the fifth subject is preferably provided for step (i), or obtained by a method according to the fourth subject. The quartz glass body preferably has the features described in the context of the fourth or fifth subject.

For processing a quartz glass body according to the seventh object into a hollow body, several possibilities come into consideration.

The processing of the quartz glass body to form a hollow body with an opening can in principle be carried out by means of all methods known to the person skilled in the art and suitable for the production of hollow glass bodies with an opening. For example, methods including pressing, blowing, sucking or combinations thereof are suitable. It is also possible to form a hollow body with one opening from a hollow body with two openings by closing one opening, for example by melting it together.

The hollow body consists of a material that contains silicon dioxide, preferably in an amount in a range from 98 to 100% by weight, for example in a range from 99.9 to 100% by weight, particularly preferably 100% by weight , each based on the total weight of the hollow body. The material from which the hollow body is made preferably has at least one, preferably several, for example two, or preferably all of the following features:

HK1. a silicon dioxide content of preferably more than 95% by weight, for example more than 97% by weight, particularly preferably more than 99% by weight, based on the total weight of the material;

HK2. a density in a range from 2.1 to 2.3 g / cm ³ , particularly preferably in a range from 2.18 to 2.22 g / cm ³ ;

HK3. a light transmission at at least one wavelength in the visible range from 350 to 750 nm in a range from 10 to 100%, for example in a range from 30 to 99.99%, particularly preferably in a range from 50 to 99.9%, based on the amount of light generated within the hollow body;

HK4. an OH content of less than 500 ppm, for example less than 400 ppm, particularly preferably less than 300 ppm;

HK5. a chlorine content of less than 200 ppm, preferably less than 100 ppm, for example less than 80 ppm, particularly preferably less than 60 ppm;

HK6. an aluminum content of less than 200 ppb, for example less than 100 ppb, more preferably less than 80 ppb;

HK7. a carbon content of less than 5 ppm, for example less than 4.5 ppm, particularly preferably less than 4 ppm;

HK8. an ODC level of less than 5-10 ¹⁵ / cm ³ ;

HK9. a metal content of metals other than aluminum of less than 1 ppm, for example less than 0.5 ppm, particularly preferably less than 0.1 ppm;

HK10. a viscosity (p = 1013 hPa) in a range from logio h (1250 ° C) = 1 1, 4 to logio h (1250 ° C) = 12.4 and / or logio h (1300 ° C) = 11.1 to logio h (1350 ° C) = 11.7 and / or log ₁₀ h (1350 ° C) = 10.5 to log ₁₀ h (1350 ° C) = 1 1, 1;

HK1 1. a transformation point Tg in a range from 1150 to 1250 ° C, particularly preferably in a range from 1180 to 1220 ° C;

the ppm and ppb each being based on the total weight of the hollow body. Step (ii)

The hollow body from step (i) is preferably equipped with electrodes, preferably two electrodes, before being filled with a gas. The electrodes are preferably connected to an electrical power supply. The electrodes are preferably connected to a lamp base.

The material of the electrodes is preferably selected from the group of metals. In principle, any metal can be selected as electrode material that does not oxidize, corrode, melt or otherwise impair its shape or conductivity as an electrode during the operating conditions of the lamp. The electrode material is preferably selected from the group consisting of iron, molybdenum, copper, tungsten, rhenium, gold and platinum or at least two of them, with tungsten, molybdenum or rhenium being preferred.

Step (iii)

The hollow body provided in step (i) and optionally equipped with electrodes in step (ii) is filled with a gas.

Filling can be carried out using any method known to the person skilled in the art and suitable for filling. A gas is preferably passed through the at least one opening into the hollow body.

The hollow body is preferably evacuated with a gas before filling, preferably to a pressure of less than 2 mbar. The hollow body is filled with the gas by subsequently introducing a gas. These steps can be repeated in order to minimize contamination with air, especially with oxygen. These steps are preferably repeated at least twice, for example at least three times or at least four times, particularly preferably at least five times, until the amount of contamination with other gases such as air, in particular oxygen, is sufficiently low. This procedure is particularly preferred for filling hollow bodies with an opening.

If a hollow body contains two or more openings, the hollow body is preferably filled through one of the openings. The air in the hollow body prior to filling with the gas can exit through the at least one wider opening. The gas is passed through the hollow body until the amount of contamination with other gases such as air, in particular oxygen, is sufficiently low. The hollow body is preferably filled with an inert gas or a combination of two or more inert gases, for example with nitrogen, helium, neon, argon, krypton, xenon or a combination of two or more thereof, particularly preferably with krypton, xenon or a combination of Nitrogen and argon. Further preferred fillers for hollow bodies of illuminants are deuterium and mercury.

The hollow body is preferably closed after filling with a gas, so that the gas does not escape during further processing, so that no air enters from the outside during further processing, or both. The closure can be done by melting or by putting on a closure. Suitable closures are, for example, quartz glass closures, which are melted onto the hollow body, for example, or lamp bases. The hollow body is preferably closed by melting.

The illuminant contains a hollow body and possibly electrodes. The lighting means preferably has at least one, for example at least two or at least three or at least four, particularly preferably at least five of the following features:

I.) a volume in a range from 0.1 cm ³ to 10 m ³ , for example in a range from 0.3 cm ³ to 8 m ³ , particularly preferably in a range from 0.5 cm ³ to 5 m ³ ;

II.) A length in a range from 1 mm to 100 m, for example in a range of

3 mm to 80 m, particularly preferably in a range from 5 mm to 50 m;

III.) A radiation angle in a range from 2 to 360 °, for example in a range from 10 to 360 °, particularly preferably in a range from 30 to 360 °;

IV.) An emission of light in a wavelength range from 145 to 4000 nm, for example in a range from 150 to 450 nm, or from 800 to 4000 nm, particularly preferably in a range from 160 to 280 nm;

V.) a power in a range from 1 mW to 100 kW, particularly preferably in one

Range from 1 kW to 100 kW, or in a range from 1 to 100 watt.

Another aspect relates to a lighting means, obtainable by a method comprising the following steps:

(i) providing a quartz glass body in accordance with the fifth subject matter of the invention or a quartz glass body obtainable by a method in accordance with the fourth subject matter, the quartz glass body first being processed into a hollow body; (ii) optionally equipping the hollow body with electrodes;

(iii) filling the hollow body with a gas.

Steps (i), (ii) and (iii) are preferably characterized by the features described in the context of the seventh subject matter.

The lighting means is preferably characterized by the features described in the context of the seventh subject.

An eighth subject of the present invention relates to a method for producing a molded body comprising the following steps:

(1) providing a quartz glass body in accordance with the fifth subject matter of the invention or a quartz glass body obtainable by a method in accordance with the fourth subject matter;

(2) Molding the quartz glass body to obtain the molded body.

The quartz glass body provided in step (1) is a quartz glass body in accordance with the fifth subject matter or obtainable by a method in accordance with the fourth subject matter of the invention. The quartz glass body provided preferably has the features of the first or fifth object.

Step 2)

In principle, all methods known to the person skilled in the art and suitable for the shaping of quartz glass can be used to shape the quartz glass body provided in step (1). The quartz glass body is preferably shaped into a shaped body as described in the context of the first, fourth and fifth subject matter. More preferably, the shaped body can be formed by means of known glass blowing techniques.

The shaped body can in principle assume any shape that can be formed from quartz glass. Preferred moldings are, for example:

Hollow bodies with at least one opening such as round bottom flasks and flat bottom flasks,

Attachments and closures for such hollow bodies,

Open items such as bowls and boats (carrier racks for wafers),

Crucibles, both open and lockable, Panels and windows,

Cuvettes,

Tubes and hollow cylinders, e.g. reaction tubes, profile tubes, rectangular chambers,

Rods, bars and blocks, for example in round or square, symmetrical or asymmetrical design,

tubes and hollow cylinders closed on one or both sides,

Domes and bells,

Flanges,

Lenses and prisms,

welded parts,

curved parts, for example convex or concave surfaces and plates, curved rods and tubes.

According to one embodiment, the shaped body can be treated after the molding. In principle, all of the methods described in the context of the first subject that are suitable for reworking the quartz glass body come into consideration here. The shaped body can preferably be processed mechanically, for example by drilling, honing, external grinding, comminuting or drawing.

Another aspect relates to a molded body obtainable by a method comprising the following steps:

(1) Providing a quartz glass body according to the fifth subject matter of the invention, or one

Quartz glass body obtainable by the method according to the fourth subject matter of the invention;

(2) Molding the quartz glass body to obtain the molded body.

Steps (1) and (2) are preferably characterized by the features described in the context of the eighth subject.

The shaped body is preferably characterized by the features described in the context of the eighth subject. A ninth object of the invention is a method for producing a coating on a substrate, comprising the following steps:

| A | Providing a silicon dioxide suspension obtainable according to the first subject matter or one of its embodiments and a substrate;

| B | Applying a layer of the silicon dioxide suspension on the substrate;

thereby forming a coating on the substrate.

The in step | A | The silicon dioxide suspension provided is obtainable by a method according to the first aspect of the invention. The silicon dioxide suspension can have further features corresponding to the embodiments described in connection with the first subject matter.

For the application in step | B | In principle, all methods known to the person skilled in the art and suitable for producing a coating come into consideration. At least part of the substrate is covered with the silicon dioxide suspension.

In a further embodiment, the application can be laying down the silicon dioxide suspension on the substrate or dipping the substrate into the silicon dioxide suspension or a combination of both forms. The application by depositing the silicon dioxide suspension can, for. B. by spin coating, impregnation, pouring, dripping, spraying, spraying, knife coating, brushing or printing, for example via a metering pump or inkjet, screen, gravure, offset or pad printing on the substrate. The silicon dioxide suspension can be applied with a wet film thickness in a range from 0.01 μm to 250 μm, for example in a range from 0.1 μm to 50 μm.

Depositing is also understood to mean that the silicon dioxide suspension used for the application is applied to the substrate by means of an aid. This can be done using different aids. Thus, the silicon dioxide suspension used for application can be sprayed onto the substrate through a nozzle, injected or deposited through a slot nozzle. Other possible methods are curtain casting and spin coating. In addition, the silicon dioxide suspension can be applied to the surface of the substrate, for example via a roller or cylinder. For example, micro-dosing or digital printing via a nozzle are known as spraying processes. In this case, the silicon dioxide suspension used for application can be applied or the silicon dioxide suspension is simply applied dropwise to the substrate. During dipping, the substrate can be drawn through a bath in the silicon dioxide suspension. If the substrate is only to be partially coated, only the surface to be coated can optionally be dipped into the silicon dioxide suspension and pulled out again, as is done, for example, with dip coating. By dipping several times, different layer thicknesses can be achieved. In addition, the thickness of the layer can be adjusted through the viscosity and the solids content of the silicon dioxide suspension. In this way, wet layer thicknesses of the silicon dioxide suspension can be achieved during application in a range between 0.5 to 1000 μm, preferably in a range from 5 to 250 μm, particularly preferably in a range from 10 to 100 μm.

Optionally, but not necessarily, a step [C] follows, reducing the liquid content of the coating. The step | C | is carried out until the liquid content of the coating, based on the total weight of the coating, reaches or falls below a target value. This target value can be, for example, 10% by weight, 5% by weight, 2% by weight or even 0.2% by weight, the% by weight in each case based on the total weight of the coating. In principle, all methods known to the person skilled in the art and appearing suitable for reducing the liquid content of a layer can be considered, in particular at least one selected from the group consisting of: drying under heat, drying by painting over the coating with a gas or gas mixture, evaporation of liquid at reduced ambient pressure, stimulating the movement of molecules in the liquid, in the case of water, for example with microwaves, and so on. A combination of two or more of the methods mentioned is also possible. The combination can be designed spatially and / or temporally simultaneously, spatially and / or temporally successive, or spatially and / or temporally overlapping. In the present context, overlapping means that a first method has not yet been completed when a subsequent method has already started.

The invention is illustrated by way of example below by means of figures. The figures are not to scale and are not intended to limit the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows schematically the method steps for producing a silicon dioxide suspension according to the first subject. Figure 2 shows a first filter arrangement with three filter stages, a 12th and 3rd filter stage.

Figure 3 shows another arrangement of filters.

FIG. 4 shows schematically a method for producing a quartz glass body.

FIG. 5 shows by way of example a) the particle size distribution of the slurry, b) the

Precursor suspension after dispersing.

FIG. 6 shows 3 hot quartz glass bodies: a) many bubbles, b) hardly any bubbles, c) very many bubbles (foam glass).

FIG. 7 shows comparative photographs of a glass body, granules formed from a) unfiltered silicon dioxide suspension being used as the melt material; b) a glass body, granules of silicon dioxide suspension filtered according to the invention being used as melting material.

DETAILED DESCRIPTION OF THE FIGURES

In FIG. 1, a method for producing a silicon dioxide suspension is shown schematically, including at least the following steps (i) providing a silicon dioxide powder 101; (ii) providing a liquid 102; (iii) mixing the silica powder with the liquid to obtain a slurry 103; (iv) sonicating the slurry to obtain a precursor suspension 104; and (v) passing at least a portion of the precursor suspension through a first multi-stage filter device 105.

FIG. 2 schematically shows a filter arrangement comprising three filter stages, each with a first filter 211, a second filter 212 and a third filter 213. These are arranged downstream.

FIG. 3 schematically shows a further filter arrangement comprising three filter stages. After a silicon dioxide suspension has passed through a first filter stage with a filter 311, the suspension is divided on the way to a second filter stage. This causes part of the suspension to pass through a filter A 312 of the second filter stage and another part of the suspension passed through a filter B 313. The suspension is then combined again and fed to a third filter stage with a filter 314.

FIG. 4 schematically shows a method for producing a quartz glass body including method steps 411, 412 and 413. In step i.) 411 silicon dioxide granulate is provided. In step ii.) 412 a glass melt is formed from the silicon dioxide granulate. In step iii.) 413 a quartz glass body is formed from at least a part of the glass melt.

In graph a) FIG. 5 shows, by way of example, the particle size distribution of a slurry of silicon dioxide powder in water, as the present method is based on. This graphic shows a lot of well-dispersed particles with a particle size of less than 1 pm, but also a number of agglomerates in the range from 1 to 5 pm and 10 to 100 pm. Graph b) shows the particle size distribution of a silicon dioxide suspension obtained by dispersing a silicon dioxide slurry according to graph a). All particles are now dispersed. No particle sizes of silicon dioxide particles greater than 1 μm were detected. A subsequent filtration maintains the particle size distribution from FIG. 5 b) relating to the silicon dioxide particles. However, particles other than silicon dioxide are deposited.

FIG. 6 shows comparative images of (hot) glass bodies approx. 1 m after they have been withdrawn from the crucible, granules formed from a) unfiltered silicon dioxide suspension being used as the melt material; b) a glass body, whereby a granulate of silicon dioxide suspension filtered according to the invention was used as melt material, c) a glass body, where granulate material as in Example 15-4 was used as melt material, that is, the suspension of pyrogenic silica was made with a ball mill (zirconium oxide balls and beakers coated with polyurethane) before filtering.

Two different cooled quartz glass bodies are shown in FIG. The quartz glass body in Figure a) was produced from a suspension of silicon dioxide particles that was not treated according to the present invention. It contains plenty of larger bubbles. The quartz glass body in Figure b) was produced based on a silicon dioxide suspension treated according to the invention. There are just barely any bubbles. TEST METHODS a. OH content

The OH content of the glass is determined by infrared spectroscopy. The method specified by DM Dodd & DM Fraser “Optical Determinations of OH in Fused Silica” (JAP 37, 3991 (1966)) is used. Instead of the device specified therein, an FTIR spectrometer (Fourier transform infrared spectrometer, currently System 2000 from Perkin Elmer) is used. The analysis of the spectra can in principle be carried out both on the absorption band at approx. 3670 cm ^-1 and on the absorption band at approx. 7200 cm ^-1 . The band used is selected according to the rule that the transmission loss due to OH absorption is between 10 and 90%. b. Oxygen Deficiency Centers (ODCs)

For quantitative detection, the ODC (l) absorption at 165 nm is determined by means of a transmission measurement on a sample between 1-2 mm thick using a vacuum UV spectrometer, model VUVAS 2000, from McPherson, Inc. (USA).

Then:

N = a / o with

N = defect concentration [1 / cm ³ ]

a = optical absorption [1 / cm, base e] of the ODC (I) band

o = effective cross section [cm ² ] where o = 7.5 IO ¹⁷ cm ^{2 is} used (from L. Skuja, "Color Centers and Their Transformations in Glassy S1O2", Lectures of the summer school "Photosensitivity in optical Waveguides and glasses ", July 13-18 1998, Vitznau, Switzerland). c. Elemental analysis

c-1) Massive samples are shattered. For cleaning, approx. 20 g of the sample are then placed in an HF-resistant vessel, completely covered with HF and thermally treated at 100 ° C. for one hour. After cooling, the acid is discarded and the sample rinsed several times with ultrapure water. The vessel with the sample is then dried in the drying cabinet.

Then approx. 2 g of the solid sample (broken material, cleaned as above; dust etc. without pretreatment directly) are weighed into an HF-resistant digestion container and mixed with 15 ml HF (50% by weight). The digestion container is closed and thermally treated at 100 ° C until the solid sample is completely dissolved. The digestion container is then opened and further thermally treated at 100 ° C. until the solution has completely evaporated. Meanwhile, the digestion tank is filled 3x with 15ml ultrapure water. 1 ml of HNO _{3 is} added to the digestion container in order to dissolve deposited impurities and made up to 15 ml with ultrapure water. The measurement solution is now ready. c-2) Measurement of ICP-MS / ICP-OES

Whether OES or MS is used depends on the expected element concentration. Typical limits of quantification for MS are 1 ppb, for OES 10 ppb (each related to the weighed sample amount). The element concentration is determined with the measuring devices in accordance with the specifications of the device manufacturers (ICP-MS: Agilent 7500ce; ICP-OES: Perkin Elmer 7300 DV) and using certified reference liquids for calibration. The element concentration in the solution (15ml) determined by the devices is then converted to the original weight of the sample (2g).

Note: It is important to ensure that the acid, the vessels, the water and the devices are of sufficient purity to be able to determine the element concentrations to be detected. This is checked by digesting a blank sample without quartz glass.

The following elements are determined in this way: Li, Na, Mg, K, Ca, Fe, Ni, Cr, Hf, Zr, Ti, (Ta), V, Nb, W, Mo, Al. c-3) Samples in liquid form are determined as described above, the sample preparation according to step c-1) being omitted. 15 ml of the liquid sample are added to the decomposition vessel. There is no need to convert to an original weight. d. Determining the density of a liquid

To determine the density of a liquid, a precisely defined volume of the liquid is weighed into a measuring vessel that is inert to the liquid and its components, the empty weight and the weight of the filled vessel being measured. The density results from the difference between the two weight measurements divided by the volume of the liquid introduced. e. Detection of fluoride

15 g of a quartz glass sample are crushed and treated in nitric acid for cleaning at a temperature of 70 ° C. The sample is then rinsed several times with ultrapure water and then dried. Of this, ₂ g of the sample are weighed into a nickel crucible and covered with 10 g of Na ₂ CO ₃ and 0.5 g of ZnO. The crucible is closed with a Ni lid and annealed at 1000 ° C. for one hour. Then the nickel crucible is filled with water and boiled until the melting cake has completely dissolved. The solution is transferred to a 200 ml volumetric flask and made up to 200 ml with ultrapure water. After undissolved constituents have settled, 30 ml are removed and transferred to a 100 ml volumetric flask, 0.75 ml glacial acetic acid and 60 ml TISAB are added and topped up with ultrapure water. The measurement solution is transferred to a 150 ml beaker.

The fluoride content of the measurement solution is determined by means of an ion-sensitive (fluoride) electrode, suitable for the expected concentration range, and display device according to the manufacturer's specifications, here a fluoride ion-selective electrode and reference electrode F-500 with R503 / D on a pMX 3000 / pH / ION of the company Wissenschaftlich-Technische Werkstätten GmbH. With the fluoride concentration in the solution, the dilution factor and the initial weight, the fluoride concentration in the quartz glass is calculated. f. Detection of chlorine (> = 50 ppm)

15g of a quartz glass sample are crushed and treated in nitric acid for cleaning at approx. 70 ° C. The sample is then rinsed several times with ultrapure water and then dried. Of this, 2 g of the sample are filled into a PTFE insert of a pressure vessel, 15 ml NaOH (c = 10 mol / l) are added, closed with a PTFE lid and placed in the pressure vessel. This is closed and thermally treated at approx. 155 ° C for 24 hours. After cooling, the PTFE insert is removed and the solution is completely transferred into a 100 ml volumetric flask. There 10 ml HNO3 (65% by weight) and 15 ml acetate buffer are added, allowed to cool and made up to 100 ml with ultrapure water. The The measurement solution is transferred to a 150ml beaker. The measuring solution has a pH value in the range between 5 and 7.

The determination of the chloride content in the measurement solution is carried out using an ion-sensitive (chloride) electrode, suitable for the expected concentration range, and a display device according to the manufacturer's specifications, here an electrode type CI-500 and reference electrode type R-503 / D on a pMX 3000 / pH / ION the company Wissenschaftlich-Technische Werkstätten GmbH. G. Chlorine content (<50 ppm)

Chlorine contents <50 ppm up to 0.1 ppm in quartz glass are determined by means of

Neutron Activation Analysis (NAA) determined. For this purpose, 3 booblets, each 3 mm in diameter and 1 cm in length, are drawn from the quartz glass body to be examined. These are submitted to a research institute for analysis, in this case the Institute for Nuclear Chemistry at Johannes Gutenberg University in Mainz. In order to rule out contamination of the samples with chlorine, it is agreed with the research institute to thoroughly clean the samples in an HF bath on site and only immediately before the measurement. Each Böhrling is measured several times. The research institute then sends back the results and the troubles. H. Optical properties

The transmission of quartz glass samples is determined with commercial grating or FTIR spectrometers from Perkin Elmer (Lambda 900 [190-3000nm] or System 2000 [1000-5000nm]). The choice depends on the required measuring range.

To determine the absolute transmission, the specimens are polished plane-parallel (surface roughness RMS <0.5 nm) and the surface is freed of all residues after polishing by means of an ultrasonic treatment. The sample thickness is 1 cm. In the case of expected, strong transmission loss due to contamination, doping, etc., a thicker or thinner sample can also be selected in order to remain in the measuring range of the device. A sample thickness (measuring length) is selected at which only minor artifacts occur due to the radiation passing through the sample and at the same time a sufficiently detectable effect is measured. To measure the opacity, the sample is placed in front of an Ulbrich sphere in the beam path. The opacity is calculated on the basis of the thus measured transmission value T according to the formula: O = 1 / T = ₀ l / li refractive index and refractive index distribution on a pipe or rod

The refractive index distribution of tubes / rods can be determined by means of a York Technology Ltd. Preform Profiler P102 or P104 can be characterized. To do this, the rod is placed horizontally in the measuring chamber and sealed tightly. The measuring chamber is then filled with an immersion oil that has a refractive index at the test wavelength of 633 nm, which is very similar to the outermost glass layer at 633 nm. The laser beam then goes through the measuring chamber. A detector is mounted behind the measuring chamber (in the direction of the beam), which determines the deflection angle (beam entry in versus beam exit from the measuring chamber). Assuming the radial symmetry of the refractive index distribution of the rod, the diametrical refractive index curve can be reconstructed by means of an inverse Abel transformation. These calculations are carried out by the software of the device manufacturer York.

The refractive index of a sample is determined using the York Technology Ltd. Preform Profiler P104 intended. In the case of isotropic samples, even when measuring the refractive index distribution, there is only one value, the refractive index. j. Carbon content

The quantitative determination of the surface carbon content of silicon dioxide granulate and silicon dioxide powder is carried out on an RC612 carbon analyzer from Leco Corporation, USA, through the complete oxidation of all surface carbon contaminations (except SiC) with oxygen to carbon dioxide. For this purpose, 4.0 g of a sample are weighed out and placed in a quartz glass boat in the carbon analyzer. The sample is flushed with pure oxygen and heated to 900 ° C for 180 seconds. The C0 _{2 formed} is detected by the infrared detector of the carbon analyzer. Under these measurement conditions the detection limit is <1 ppm (weight ppm) carbon.

A quartz glass boat suitable for this analysis on the above-mentioned carbon analyzer is available as a consumable for LECO analyzer with the LECO number 781-335 in laboratory supplies, in this case from Deslis Laborhandel, Flurstrasse 21, D-40235 Düsseldorf (Germany), Deslis- No. LQ-130XL. Such a shuttle has the dimensions of width / length / height of approx. 25mm / 60mm / 15mm. The Quartz glass boat is filled halfway up with sample material. For silicon dioxide powder, a weight of 1.0 g of sample material can be achieved. The lower detection limit is then <1 ppm by weight of carbon. A weight of 4 g of a silicon dioxide granulate is achieved in the same quartz glass boat with the same filling level (mean particle size in the range from 50 to 500 μm). The lower detection limit is then around 0.1 ppm by weight of carbon. The lower detection limit is reached when the measuring surface integral of the sample is not greater than three times the measuring surface integral of a blank sample (blank sample = procedure as above, but with an empty quartz glass boat). k. Curl parameters

The curl parameter (also called: “fiber curl”) is determined in accordance with DIN EN 60793-1-34: 2007-01 (German version of the standard IEC 60793-1-34: 2006). Measurements are made according to the method described in Annex A in Sections A.2.1, A.3.2 and A.4.1 (“extrema technique”).

L. damping

The attenuation is determined in accordance with DIN EN 60793-1-40: 2001 (German version of IEC 60793-1-40: 2001). Measurements are made according to the method described in the annex (“cut back method”) at a wavelength l = 1550 nm with the viscosity of slurries or suspensions

The slurry is adjusted to a concentration of 30% by weight solids content with demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MQcm). The viscosity is then measured on an MCR102 from Anton-Paar. For this purpose, the viscosity is measured at 5 revolutions / minute (rpm). It is measured at a temperature of 23 ° C and an air pressure of 1013 hPa. The procedure for a suspension is exactly the same. n. Thixotropy & Rheopexy

- n1. Thixotropy

The slurry or suspension is adjusted to a concentration of 30% by weight solids content using demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MQcm). The thixotropy is then determined with an MCR102 from Anton-Paar with a cone-plate arrangement. For this purpose, the viscosity is measured at 5 and 50 revolutions / minute (rpm). The quotient of the first and the second value gives the thixotropy index. The measurement is taken at a temperature of 23 ° C.

- n2. Rheopexy

The slurry or suspension is adjusted to a concentration of 60% by weight solids content with demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MQcm). The viscosity of the slurry or suspension heated to 25 ° C. is then measured using a Kinexus pro + rheometer with paddle stirrer from Malvern Panalytical Ltd. determined over a period of 15 minutes at a constant shear rate of 25 / s or 100 / s. o. Zeta potential of the slurry or suspension

A zeta potential measuring cell (Flow Cell, Beckman Coulter) is used for zeta potential measurements. The sample is dissolved in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MQcm) to obtain a 20 mL solution with a concentration of 1 g / L. The pH is brought to 7 by adding HN0 ₃ solutions with concentrations of 0.1 mol / L and 1 mol / L and an NaOH solution with a concentration of 0.1 mol / L. It is measured at a temperature of 23 ° C. p. Isoelectric point of the slurry or suspension

A zeta potential measuring cell (Flow Cell, Beckman Coulter) and an autotitrator (DelsaNano AT, Beckman Coulter) are used for the isoelectric point. The sample is dissolved in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MQcm) in order to obtain a 20 ml solution with a concentration of 1 g / L. The pH is varied by adding HNQr solutions with concentrations of 0.1 mol / L and 1 mol / L and an NaOH solution with a concentration of 0.1 mol / L. The isoelectric point is the pH value at which the zeta potential is equal to 0. It is measured at a temperature of 23 ° C. q. pH of the slurry or suspension

The pH of the slurry is measured using a WTW 3210 from Wissenschaftlich-Technische-Werkstätten GmbH. The pH 3210 Set 3 from WTW is used as the electrode. It is measured at a temperature of 23 ° C. r. Solids content

An initial weight of a sample of the slurry or suspension is heated to 500 ° C. for 4 hours and, after cooling, weighed again (rri2). The solids content w results from m ₂ / ml * 100 [wt. %]. see bulk density

The bulk density of a bulk material is determined in accordance with the standard DIN ISO 697: 1984-01 using an SMG 697 from Powtec. The bulk material (silicon dioxide powder or granulate) does not form lumps. t. Tamped density

The tamped density of a bulk material is measured in accordance with the DIN ISO 787: 1995-10 standard. In the present case, silicon dioxide powder or silicon dioxide granules are particularly suitable as bulk goods. and determination of the pore size distribution

The pore size distribution is determined in accordance with DIN 66133 (with a surface tension of 480 mN / m and a contact angle of 140 °). The Pascal 400 from Porotec is used to measure pore sizes smaller than 3.7 nm. The Pascal 140 from Porotec is used to measure pore sizes from 3.7 nm to 100 μm. The sample is subjected to a pressure treatment before the measurement. A manual hydraulic press is used for this purpose (order no. 15011 from Specac Ltd., River House, 97 Cray Avenue, Orpington, Kent BR5 4HE, U.K.). A “pellet die” with an inner diameter of 13 mm from Specac Ltd. 250 mg sample material weighed in and loaded with 1 t according to the display. This load is held for 5 s and readjusted if necessary. The sample is then relaxed and dried for 4 h at 105 ± 2 ° C. in a circulating air drying cabinet.

The weight of the sample in the type 10 penetrometer is accurate to 0.001 g and is selected for good reproducibility of the measurement so that the "stem volume used", i.e. the percentage of Hg volume used to fill the penetrometer, is between 20% up to 40% of the total Hg volume. The penetrometer is then slowly evacuated to 50 μm Hg and left at this pressure for 5 minutes. The following parameters are specified directly by the software of the measuring devices: total pore volume, total pore surface (assumption pores cylindrical), Average pore radius, modal pore radius (most common pore radius), peak n. 2 pore radius (pm). v. Primary particle size

The primary particle size is measured using a Zeiss Ultra 55 scanning electron microscope (SEM). The sample is suspended in demineralized water (Direct-Q 3UV, Millipore, water quality: 18.2 MWah) in order to obtain an extremely dilute suspension. The suspension is treated with an ultrasound probe (UW 2070, Bandelin electronic, 70 W, 20 kHz) for 1 min and then applied to a carbon adhesive pad. w. Average particle size in suspension

The particle size and grain size of the solid are measured using a Bluewave wet with a measuring cell, available from Microtac GmbH, 47807 Krefeld, Germany in accordance with their operating instructions. The Bluewave wet contains a sample dosing system and a wet dispersion module. To carry out the measurement, the solid is suspended in demineralized water and the suspension is introduced drop by drop into the measuring device. The concentration of the suspension to be measured and the amount of suspension to be added to the device are automatically set by the measuring device through automated dilution up to the optimum particle size and material-dependent measurement window. The preparation of the suspension to be measured takes place with a view to a translucent appearance of the suspension before it is introduced drop by drop into the measuring device. The measurement parameters are set according to the operating instructions based on the solid matter to be measured in suspension (particle shape, optical properties). The Bluewave wet outputs the D10, D50 and D90 values for a sample. The suspension is treated with the ultrasonic probe (UW 2070, Bandelin electronic, 70 W, 20 kHz) for 1 min. x. Particle size and grain size of the solid

The particle size and grain size of the solid are measured using a Camsizer XT, available from Retsch Technology GmbH, Germany in accordance with their operating instructions. The software outputs the D10, D50 and D90 values for a sample. y. BET measurement

The static volumetric BET method according to DIN ISO 9277: 2010 is used to measure the specific surface area. For the BET measurement, a “NOVA 3000” or a “Quadrasorb” (available from Quantachrome), which according to the SMART Method ("Sorption Method with Adaptive dosing Rate") works, applied. The micropore analysis is carried out using the t-plot method (p / pO = 0.1-0.3) and the mesopore analysis using the MBET method (p / pO = 0.0-0.3). The standards Alumina SARM-13 and SARM-214, available from Quantachrome, are used as reference material. The tare weight of the measuring cells used (clean and dry) is weighed. The type of measuring cell is chosen so that the sample material and filler rod supplied fill the measuring cell as much as possible and the dead space is reduced to a minimum. The sample material is brought into the measuring cell. The amount of sample material is selected so that the expected measured value corresponds to 10-20 m ² / g. The measuring cells are fixed in the heating stations of the BET measuring device (without filler rod) and evacuated to <200 mbar. The evacuation speed is set so that no material escapes from the measuring cell. In this state, heating is carried out at 200 ° C. for 1 h. After cooling, the measuring cell filled with the sample is weighed (gross). Then the tare weight is subtracted from the gross weight = net weight = weight of the sample. Now the filler rod is inserted into the measuring cell and this in turn is fixed in the measuring station of the BET measuring device. Before starting the measurement, the sample name and sample weight are entered in the software. The measurement is started. The saturation pressure of the nitrogen gas (N2 4.0) is measured. The measuring cell is evacuated and is cooled down to 77 K using a nitrogen bath. The dead space is measured using helium gas (He 4.6). It is evacuated again. A multi-point analysis with at least 5 measuring points is carried out. N2 4.0 is used as an adsorptive. The specific surface is given in m ² / g. z. Viscosity of vitreous bodies

The viscosity of the glass is measured with the help of the bar bending viscometer type 401 - from TA Instruments with the manufacturer's software WinTA (currently version 9.0) under Windows 10 according to the standard DIN ISO 7884-4: 1998-02. The span between the supports is 45mm. Test sticks with a rectangular cross-section are cut from areas of homogeneous material (sample top and bottom with fine grinding of at least 1000 grit). The sample surfaces after processing have grain size = 9pm & RA = 0.15pm. The test sticks have the following dimensions: length = 50mm, width = 5mm & height = 3mm (allocation length, width, height as in the standard). Three samples are measured and the mean value is calculated. The sample temperature is measured by a thermocouple close to the sample surface. The following parameters are used: heating rate = 25 K to a maximum of 1500 ° C, load weight = 100 g, maximum deflection = 3000 pm (in deviation from the norm). za. Residual moisture

The residual moisture of a sample of silicon dioxide granulate is determined with the aid of a Moisture Analyzer HX204 from Mettler Toledo. The device works on the principle of thermogravimetry. The HX204 is equipped with a halogen lamp as a heating element. The drying temperature is 220 ° C. The starting weight of the sample is 10 g ± 10%. The "Standard" measurement method is selected. The drying is continued until the weight change does not exceed 1 mg / 140 s. The residual moisture results from the difference between the starting weight of the sample and the final weight of the sample, divided by the starting weight of the sample.

The residual moisture content of silicon dioxide powder is determined in accordance with DIN EN ISO 787-2: 1995 (2h, 105 ° C.).

EXAMPLES

The invention is further illustrated by examples below. The invention is not limited to the examples.

E. 1. Manufacture of silicon dioxide granules from silicon dioxide powder

E15-x: A suspension of pyrogenic silica (BET = 30 m ² / g, mean particle size in suspension = 100 nm) was introduced into deionized water (L = 0.1 pS / cm) in a mixer with a stirrer / paddle geometry and homogenized. The solids content of the homogenized mixture was 55% by weight. In cases E15-2, E15-3, the suspension was then treated by means of an ultrasonic generator in accordance with the information in Table 2. All suspensions E15-x were then passed through a filter arrangement. The particle size and elemental analysis before filtration is given in Table 3.

For examples E15-1 to E15-4, a filter arrangement with three filters No. 1 to 3 (sequence downstream from 1 to 2 to 3) was selected. This was as follows:

1. Filter: Acura Multiflow® (PP multilayer depth filter), filter fineness 10 μm, separation rate 80%; 2. Filter: Acura Promelt® (PP depth filter), filter fineness 1 μm, separation rate 99.9%;

3. Filter: Acura Multiflow® (PP multilayer depth filter), filter fineness 0.5 μm, separation rate 80%.

Example E15-1 was produced as before, but no ultrasound treatment was carried out.

For E15-2 an ultrasonic generator type UIP 1000 hdT-230 (Fa. Hielscher Ultrasonics GmbH, Teltow (Germany), with titanium probe BS4d55 with booster B4-1.2 and a flow cell FC100L1 K-1S was used. A power density of 950 W / Liters and a flow rate of 180 liters / h.

At E15-3, an ultrasonic generator type vortex reactor block WB 4-1604 from Bandelin (Berlin, (Germany)) with a power density of 550W / liter and a

Selected flow rate of 250 liters / h.

In example E15-4, the procedure given under E-15-x was followed. However, instead of ultrasonic treatment, treatment in a Diskus 20 type ball mill from Netzsch Feinmahltechnik GmbH, Selb (Germany) with the following operating parameters: speed 900 rpm, flow rate 250 liters / h, grinding balls of size 500 μm was carried out before the microfiltration was made.

Table 2

Table 3

* Here the metal ion content (sum of lines 9 of table 3) is given as the quotient of examples E15-2 to E15-4 with the metal ion content of E15-2 to E15-4 before dispersing (line 3, table 2).

A comparison of Example 15-1 with the other Examples E15-2 to E15-4 shows that after a dispersion step the average particle size in a suspension is significantly lower and the particle size distribution is significantly narrower than in a comparison suspension that was not additionally dispersed.

Dispersion with ultrasound with a power density of 950 W / liter shows good homogenization with small average particle sizes, but in analytical evidence an increased content of elements that are different from Si, O, H, C and CI, in particular of metal atoms. In the further processing into quartz glass, these mean either insoluble particles or the formation of gas bubbles. These particles are only partially retained in the filter arrangement. A comparable, even more pronounced finding is observed when using a ball mill for dispersing. Examples E15-2 and E-15-3 according to the invention show good and uniform dispersion and a low content of elements other than Si, O, H, C and CI. Most of the particles, which contain elements other than Si, O, H, C and CI, are retained in the filter assembly.

The filter arrangement in Examples E15-3 and E15-4 has an operating time (service life of the filter arrangement) that is at least 8 times longer than that in Example E15-1. In E15-4, however, the input of metal ions is considerably higher than in E15-3 due to the dispersion step with a ball mill.

As a result, a purer silicon dioxide suspension is obtained with a long service life of the filter arrangement.

The entry of metal ions (Ca, Co, Cr, Cu, Fe, Ge, Hf, K, Li, Mg, Mn, Mo, Na, Nb, Ni, Ti, V, W, Zn, Zr) is when dispersing with a Ball mill considerably higher than when dispersing with ultrasound.

2. Different filter combinations in filter arrangement

E16-x: A slurry of pyrogenic silica (BET = 30 m ² / g, mean particle size in suspension = 100 nm) was poured into deionized water (L = 0.1 pS / cm) in a mixer with stirrer / paddle Geometry introduced and homogenized. The solids content of the homogenized mixture was 63% by weight. All slurries were then treated by means of an ultrasonic generator (power: 550 W / L, flow rate: 250 L / h, treatment duration 30 s). All suspensions E16-x were then passed through a filter arrangement. The filter arrangement was configured with three filters No. 1 to 3 (order downstream from 1 to 2 to 3). The following filters were used (Table 4):

Table 4

The multiflow filters are available from Fuhr GmbH, 55270 Klein-Winternheim (Germany). They were used in the following configuration: Height: 20 (20 inches), material polypropylene, gradation 4 (four-ply), adapter F3 (222 adapter with fin).

The Promelt filters are also available from Fuhr GmbH. They were used in the following configuration: Height: 20 (20 inches), material polypropylene, gradation 1 (ß-rate = 1000) (four-ply), adapter F3 (222 adapter with fin).

The amaPure TS filter is available from Filtration Group GmbH, Schleifbachweg 45, 74613 Öhringen (Germany) (formerly Mahle Industriefiltration). It was used in the following configuration: Overall height: 20 inches (50.8 cm), material polypropylene, design: X8.

The combinations of the three filters in each case in a filter arrangement are given in Table 5.

Observations:

i. The granulability of the suspensions obtained in E16-1 to E16-8 was found to be “good.” “Good” means that all suspensions were suitable for granulation.

ii. The bubbling of a quartz glass produced from the respective granulate was “good” for Examples E16-1 to E-16-3 and E16-7 and E16-8. “Good” means a quartz glass quality that is acceptable for sale with hardly any bubbles. Such a quartz glass is shown in Figure 7, b). The bubbles of Examples E16-4 to E16-6 were rated “medium.” “Medium” means a quartz glass quality with a larger amount of bubbles, which can only be regarded as salable with restrictions.

iii. The metal ion input was consistently low, the particle size distribution, expressed as the ratio of D90 to D10, low.

iv. Depending on the filter arrangement, shorter service lives (<1000 liters) and longer service lives (> 1000 liters) were observed. Table 5

* Here the metal ion content (sum of lines 9 of table 3) is given as the quotient of examples E15-2 to E15-4 with the metal ion content of E15-2 to E15-4 before dispersion (line 3, table 2).; * * FF = filter fineness; *** AR = separation rate.

Ultrasound treatment

E17-x: A slurry of fumed silica (BET = 30 m ² / g, mean particle size in suspension = 100 nm) was poured into deionized water (L = 0.1 pS / cm) in a mixer with a stirrer / paddle Geometry introduced homogenized. The solids content of the homogenized mixture was 63% by weight. All slurries were then treated with an ultrasonic generator. The parameters of the ultrasound treatment are listed in Table 6. All suspensions E17-x were then passed through the same filter arrangement as in Examples E15-x.

Observations:

i. With high ultrasonic power, the mean particle size in suspension before filtering is slightly lower than with lower ultrasonic power. At the same time, the content of metal ions and (as a result) of ions other than Si, O, H, C and Cl is significantly higher.

ii. With the same treatment duration (10s), the metal ion input is significantly lower with an ultrasonic power of 550 W / L than with 950 W / L. The

Particle size distribution D10 and D90 differ only slightly. If you double the treatment time at 550 W / L to 20s, particle sizes and distributions comparable to the treatment with 950 W / L and 10s are achieved, with a significantly lower metal ion concentration due to the ultrasound treatment.

iii. The metal ion concentration increases with longer treatment times.

Table 6

REFERENCE LIST

Step (i)

Step (ii)

Step (iii)

Step (iv)

Step (v)

First filter

Second filter

Third filter

First filter stage with filter Second filter stage, filter A Second filter stage, filter B Third filter stage with filter Step i.)

Step ii.)

Step iii.)

Claims

EXPECTATIONS

1. A method for producing a silicon dioxide suspension comprising the process steps:

(i) providing a silicon dioxide powder;

(ii) providing a liquid;

(iii) mixing the silica powder with the liquid to obtain a slurry;

(iv) sonicating the slurry to obtain a precursor suspension;

each filter stage contains at least one filter,

the second filter stage being arranged downstream of the first filter stage and the third filter stage being arranged downstream of the second filter stage, the first filter stage having a filter fineness of 5 μm or more,

2. The method according to claim 1, wherein the silicon dioxide suspension is obtained in step (v) after passing through the multi-stage filter device.

3. The method according to claim 1 or 2, wherein the first filter device is characterized by at least one of the following features:

(a) the first filter stage has a separation rate of 90% or less;

(b) the first filter stage has a filter fineness in a range from 5 to 15 μm; (c) the second filter stage has a separation rate of 95% or more;

(d) the second filter stage has a filter fineness of 0.5 to 2 μm;

(e) the third filter stage has a separation rate of 99.5% or more;

Or a combination of two or more of them.

4. The method according to any one of the preceding claims, wherein at least one filter which is provided in one of the filter stages of the first filter device selected from the first, second and third filter stages, is designed as a depth filter.

5. The method of any preceding claim, wherein the ultrasound treatment of the slurry lasts for at least 10 seconds.

6. The method according to any one of the preceding claims, wherein the treatment of the slurry with ultrasound is characterized by a power density of up to 600 W / liter.

7. The method according to any one of the preceding claims, wherein the slurry has less than 5 wt .-% of additives for stabilizing the slurry, the wt .-% based on the total weight of the slurry.

8. The method according to any one of the preceding claims, wherein the silicon dioxide powder can be produced from a compound selected from the group consisting of siloxanes and silicon alkoxides.

9. The method according to any one of the preceding claims, wherein the silicon dioxide powder has at least one of the following features:

a. a carbon content of less than 100 ppm;

b. a chlorine content of less than 500 ppm;

c. an aluminum content of less than 200 ppb;

d. a content of atoms other than Si, O, H, C, CI of less than

5 ppm;

Range from 10 to 100 nm;

f. tamped density in a range from 0.001 to 0.3 g / cm ³ ;

G. a residual moisture content of less than 5% by weight;

H. a BET surface area of less than 35 g / m ² ; or a combination of two or more of the features a. to h .; wherein the wt .-%, ppm and ppb are each based on the total amount of silicon dioxide powder.

10. The method according to any one of the preceding claims, wherein the slurry is characterized by at least one of the following features:

a.) a solids content of at least 20% by weight, based on the dry mass of the slurry;

b.) As a 4% by weight slurry, the slurry has an all-in-one pH

Range from 3 to 8;

Range from 1 nm to <10 pm;

d.) a content of 5 ppm or less of atoms other than Si, O, H, C, CI,

e.) the slurry is rheopex;

where the% by weight and ppm are always based on the total solids content of the

Slurry are related.

11. The method according to any one of the preceding claims, wherein the silicon dioxide suspension has at least one of the following features:

A. rheopex properties at a temperature of less than 45 ° C and a solids concentration in the range from 20 to 70% by weight, the% by weight based on the total solids present in the suspension ;;

D. a chlorine content of less than 500 ppm;

E. an aluminum content of less than 200 ppb;

F. a content of atoms other than Si, O, H, C, CI of less than 5ppm;

the ppm and ppb each being based on the total amount of silicon dioxide particles.

12. A silicon dioxide suspension obtainable by a method according to one of the preceding claims.

13. A method for producing a silicon dioxide granulate, wherein the silicon dioxide suspension according to claim 12, or a silicon dioxide suspension obtainable by a method according to one of claims 1 to 11 is processed into silicon dioxide granulate, the silicon dioxide granulate having a larger particle diameter than the silicon dioxide particles present in the silicon dioxide suspension .

14. The method according to claim 13, wherein the spray drying is characterized by at least one of the following features:

a] spray granulation in a spray tower;

b] the presence of a pressure of the silicon dioxide suspension at the nozzle of not more than 40 bar, for example in a range from 1.3 to 20 bar from 1.5 to 18 bar or from 2 to 15 bar or from 4 to 13 bar, or particularly preferably in the range from 5 to 12 bar, the pressure being given in absolute terms (in relation to p = 0 hPa); c] a temperature of the droplets on entry into the spray tower in a range from 10 to 50 ° C, preferably in a range from 15 to 30 ° C, particularly preferably in a range from 18 to 25 ° C.

h] a temperature of the gas stream on entry into the spray tower in a range from 100 to 450 ° C, for example in a range from 250 to 440 ° C, particularly preferably from 320 to 430 ° C; i] a temperature of the gas stream at the outlet from the spray tower of less than 170 ° C .;

j] the gas is selected from the group consisting of air, nitrogen and helium, or a combination of two or more thereof; preferably air; k] a residual moisture content of the granules when they are removed from the spray tower of less than 5% by weight, for example less than 3% by weight or less than 1% by weight or in a range from 0.01 to 0.5% by weight .-%, particularly preferably in a range from 0.1 to 0.3% by weight, in each case based on the total weight of the silicon dioxide granules formed during the spray drying;

m] at least 50% by weight of the spray granules, based on the total weight of the silicon dioxide granules formed during spray drying, covers a flight distance of more than 20 m, for example of more than 30 or more than 50 or more than 70 or from more than 100 or more than 150 or more than 200 or in a range from 20 to 200 m or from 10 to 150 or from 20 to 100, particularly preferably in a range from 30 to 80 m; n] the spray tower has a cylindrical geometry;

15. The method according to any one of claims 13 or 14, wherein the silicon dioxide granulate has at least one of the following features:

A) an angle of repose in a range of 23 to 26 °; B) a BET surface area in a range from 20 to 50 m2 / g;

C) a bulk density in a range from 0.5 to 1.2 g / cm3;

E) a carbon content of less than 50 ppm;

F) a chlorine content of less than 500 ppm;

G) an aluminum content of less than 200 ppb;

H) a content of atoms other than Si, O, H, C of less than 5 ppm;

L) a particle size distribution D50 of the silicon dioxide granulate particles in a range from 150 to 300 μm;

M) a particle size distribution D90 of the silicon dioxide granulate particles in a range from 250 to 620 μm;

the ppm and ppb each being based on the total weight of the silica granules.

16. A method for producing a quartz glass body at least including the method steps:

i.) providing the silicon dioxide granulate according to one of claims 13 to 15; ii.) Forming a glass melt from the silicon dioxide granulate; and

iii.) Forming a quartz glass body from at least part of the glass melt.

17. A quartz glass body obtainable by a method according to claim 16.

18. The quartz glass body according to claim 17, having at least one of the following features:

A] a chlorine content of less than 500 ppm;

B] an aluminum content of less than 200 ppb;

C] a content of atoms other than Si, O, H, C of less than 5 ppm; D] a viscosity (p = 1013 hPa) in a range from logio (h (1250 ° C) / dPas) = 11.4 to logio (P (1250 ° C) / dPas) = 12.9, or log ₁₀ ( h (1300 ° C) / dPas) = 11.1 to log ₁₀ (h (1300 ° C) / dPas) = 12.2, or logio (h (1350 ° C) / dPas) = 10.5 to logio ( h (1350 ° C) / dPas) = 11.5;

E] a refractive index homogeneity of less than 10 ⁴ ;

F] a cylindrical shape;

G] a tungsten content of less than 5 ppm;

H] a molybdenum content of less than 5 ppm;

19. A method of making a light guide including the following steps:

AI providing a quartz glass body according to one of claims 17 or 18, or a quartz glass body obtainable by a method according to one of claims 16, wherein the quartz glass body is first processed into a hollow body with at least one opening;

B / introducing one or more core rods into the hollow body from step AI through the at least one opening to obtain a precursor;

20. A method for manufacturing a light source including the following steps:

(i) providing a quartz glass body according to one of claims 17 or 18, or a quartz glass body obtainable by a method according to one of claims 16, wherein the quartz glass body is first processed into a hollow body with at least one opening;

(ii) optionally equipping the hollow body with electrodes;

(iii) Filling the hollow body from step (i) with a gas.

21. A method for producing a molded article comprising the following steps:

(1) providing a quartz glass body according to one of claims 17 or 18 or a quartz glass body obtainable by a method according to one of claims 16; and

(2) Molding the quartz glass body to obtain a molded body.