JPH10152332A - Opaque silica glass and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily producing opaque silica glass with uniformly dispraised bubbles excellent in high-temperature viscosity and heat- insulating ability. SOLUTION: This opaque silica glass is 1.7 to 2.1g/cm<3> in apparent, 10 to 100μm in average bubble diameter, 3×10<5> to 5×10<6> pieces/cm<3> in bubble amount and 10 to 40cm<2> /cm<3> in the total sectional area of bubbles. In the above glass, the linear transitivity is <=3% when the glass >=1mm thick is irradiated with a light beam 300 to 900nm in wavelength. The concentration of elemental nitrogen in the silica glass base is 1 to 50ppm. The method for producing the glass comprises filling a starting material wherein silicon nitride powder is blended dispersedly with silica powder having an average particle diameter of 10 to 500μm into an intricatedly shaped heat-resistant mold and heating the starting material to a temperature at or higher than its melting point but up to 1900 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an opaque quartz glass, and more particularly to an opaque quartz glass excellent in heat insulation and bonding to a transparent quartz glass, and a method for producing the same.

[0002]

2. Description of the Related Art A conventional method for producing opaque quartz glass is as follows.
It is a method of heating and melting the siliceous raw material powder to vitrify,
As a method of heating and melting, argon-oxygen plasma flame, Bernoulli method of melting in a flame such as oxyhydrogen flame,
Alternatively, there is a vacuum melting method of heating and melting silica filled in a container under a high vacuum. As a raw material of the opaque quartz glass, natural quartz or low-grade quartz has been used. These raw materials contain many fine bubbles, and when the raw materials are melted, the bubbles remain as they are, and opaque quartz glass is obtained. However, in recent years, with the progress of high integration of LSIs in the semiconductor field, the demand for high purity of raw materials to be used has become severe, and high purity products have been demanded even in fields where low purity products were conventionally used. I started. A typical field is a flange material, and supply of opaque and high-purity quartz glass, that is, high-purity opaque quartz glass is desired. However, the conventional natural raw materials for producing opaque quartz glass contain a large amount of impurities together with fine bubbles. It is said that it is extremely difficult to remove these impurities, and high purification by purification is impossible. On the other hand, relatively high-purity quartz has a small amount of bubbles present in the crystal, particularly fine bubbles, so that the opacity does not increase even when it is melted, and the obtained quartz glass becomes translucent. Not just.

As an improvement method, the content of each element of alkali (earth) metal, Fe and Al is low, a large number of fine bubbles are included, and silanol groups as vaporizable components are uniformly contained in a specific range of concentration. A method has been proposed in which the contained high-purity amorphous silica is flame-melted (JP-A-6-24771).

However, according to this method, only a quartz glass product having a simple shape such as a silica filler for an IC encapsulant or a base material ingot for producing a silica glass powder can be directly produced, and a flange-like, cylindrical, To manufacture quartz glass products having complicated shapes such as hollow prismatic shapes, screw shapes, turbocharger shapes, square water tanks and troughs, a large amount of post-processing such as shaving is required, and the use of quartz glass is required. Rate decreases, resulting in increased manufacturing costs.

[0005] As another new opaque quartz glass, a highly purified crystalline quartz powder is heated in an ammonia atmosphere to form an ammonia, and then heated and melted in an inert gas atmosphere to reduce the bubble diameter. However, opaque quartz glass having improved heat resistance by increasing the number of bubbles and increasing the total bubble cross-sectional area per unit volume of the opaque quartz glass has been proposed (JP-A-7-61827 and JP-A-7-61827). -300341). However, in this method,
The density, bubble diameter, and bubble amount of opaque quartz glass are very sensitive to the particle size, particle size distribution of the raw material powder, and the state of filling when filled in a melting vessel, so it is not easy to control bubbles with good reproducibility. However, there is a problem that the bubble diameter and the bubble amount are largely different between the surface and the inside. In addition, when the nitrogen content in the quartz glass is large and flame processing is performed for repairing the defective portion of the quartz glass, nitrogen gas is released as bubbles from the glass substrate, and the repaired part becomes uneven, or the repaired part is Unfavorable situations occur in dimensional accuracy and appearance, such as opacity different from other places. Furthermore, when flame joining is performed with a transparent quartz glass member, the nitrogen element-containing concentrations of the two greatly differ, and joining is not successful.

As another method for producing opaque quartz glass, there is a method of adding a fine powder such as carbon or silicon nitride as a foaming agent to a siliceous raw material powder such as silica stone, silica sand, α-quartz, cristobalite and heating and melting. It has been proposed (for example, JP-A-4-65328). However, in this method, although problems such as those described above can be avoided, the glass obtained by melting with an oxyhydrogen flame easily incorporates OH groups, the viscosity at high temperatures decreases, and the glass is used for a long time at high temperatures. It is disadvantageous for applications such as jigs for semiconductor manufacturing. In addition, mixing of solid particles, solid-phase reaction / decomposition reaction, and the like are involved, and it is difficult to control so that fine bubbles are uniformly dispersed in a melt. Further, in the flame melting method, it is difficult to complete the reaction because the residence time of the fine particles in the flame is extremely short, and the added foaming agent may remain as a foreign substance in the melt. Further, there is a problem that a phenomenon in which the siliceous raw material reacts with the foaming agent to color the melt occurs.

As described above, each of the prior patents has a problem which has not been solved yet.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in order to solve these problems, and it is possible to easily prepare an opaque quartz glass in which bubbles are uniformly dispersed, and which has excellent high-temperature viscosity and heat insulation. It is to provide a manufacturing method. In addition, this opaque quartz glass can directly produce complicated shapes such as a flange shape, a cylindrical shape, a hollow prismatic shape, a screw shape, a turbocharger shape, a square water tank shape, or a "tub shape". In addition, when the content of nitrogen element in quartz glass is reduced and flame processing is performed to repair the defective part of quartz glass, nitrogen gas is not released as bubbles from the glass substrate, and the outer surface of the repaired part is smooth. It is also an object of the present invention to provide a novel opaque quartz glass that can be joined successfully by flame joining with a transparent quartz glass member because the two elements have similar nitrogen element concentrations.

[0009]

As a production method, a fine powder such as carbon or silicon nitride is added as a foaming agent to a siliceous raw material powder such as silica stone, silica sand, α-quartz, cristobalite, etc., followed by heating and melting. Method (JP-A-4-653)
No. 28 gazette) and an average particle diameter of 10
A starting material powder obtained by mixing and dispersing silicon nitride powder in relatively inexpensive coarse silica powder of about 500 μm and 0.001 to 0.05 parts by weight of silicon nitride powder with respect to 100 parts by weight of silica powder has a complicated shape. Filled into a heat-resistant mold having
Heat in an electric furnace under a vacuum atmosphere to 400 ° C. or higher and lower than the melting temperature of the starting raw material powder, and then, in a vacuum atmosphere or an inert gas atmosphere, up to a temperature at which the raw material can be melted to 1900 ° C. or lower. By adopting a manufacturing method of heating in an electric furnace and generating bubbles by vitrification and foaming, the bubbles are uniformly dispersed, not only excellent in high-temperature viscosity and heat insulation, but also complicated in casting such as casting. Without powder molding, the shape of the heat-resistant mold is appropriately selected from flange-shaped, cylindrical, hollow prismatic, screw-shaped, turbocharger-shaped, square-shaped aquarium-shaped or trough-shaped, as appropriate. By doing so, it is possible to directly produce a glass body close to the final product, and even if post-processing is required, it is simple.

Hereinafter, the present invention will be described in more detail.

[1] Starting Material The starting material is a mixed powder obtained from silica powder and silicon nitride powder.

(A) Silica Powder As the silica powder used in the present invention, Na, K, Mg, Ca, and Fe are each independently contained as metal impurities.
It is preferable to use a high-purity crystalline or amorphous silica powder of not more than ppm. The reason for this is that when the opaque quartz glass obtained by the method of the present invention is heated, impurities having a low vapor pressure tend to be scattered, and the opaque quartz glass itself is partially crystallized to be easily broken or colored. This is in order to avoid being lost. Such high-purity silica powder can be obtained by a synthesis method or by purifying a natural raw material. For example, in order to obtain amorphous silica powder by a synthesis method, a method in which an alkali metal silicate aqueous solution (water glass) is reacted with an acid to remove an alkali metal to obtain silica, and a method in which SiCl ₄ is hydrolyzed. Examples of the method include a method for producing silica and a method for hydrolyzing silicon alkoxide to produce silica. For production on an industrial scale, an aqueous solution of an alkali metal silicate comprising an alkali metal such as Na, K, and Li and silicon dioxide ( Those obtained by a method of reacting (water glass) with an inorganic acid such as sulfuric acid, nitric acid and hydrochloric acid are preferred. In order to obtain crystalline silica powder from a natural raw material, it can be obtained by a method of treating natural quartz with hydrofluoric acid.

The average particle diameter of the silica powder is preferably 10 to provide fluidity so that it can be easily filled in a heat-resistant mold.
The range is 500 μm. When the average particle diameter is less than 10 μm, the fluidity of the powder is reduced, and it is difficult to uniformly fill the powder. It is not preferable because it causes bubbles to be generated.

Since the bubble diameter in the opaque quartz glass obtained by the method of the present invention depends on the average particle diameter of the silica powder, the bubble diameter can be controlled by adjusting the average particle diameter.
That is, a powder made of fine particles is used when finer bubbles are obtained, and a powder made of coarse particles is used when coarse bubbles are obtained.

(B) Silicon Nitride Powder As silicon nitride powder, it is preferable to use silicon tetrachloride, silicon, silica or the like as a raw material and use a high-purity powder obtained by nitriding them. The reason is that impurities are scattered from the opaque quartz glass obtained by the method of the present invention, or the opaque quartz glass itself is partially crystallized to be easily damaged or to avoid being colored. It is.

The amount of the silicon nitride powder is from 0.001 to 100 parts by weight of the silica powder.
0.05 parts by weight. If the amount is less than 0.001 part by weight, the amount of bubbles generated by foaming becomes small, and a sufficient heat barrier property cannot be obtained, which is not preferable. If the amount exceeds 0.05 parts by weight, the amount of bubbles generated by foaming increases, and the mechanical strength of the obtained opaque quartz glass deteriorates. Another reason is that if it exceeds 0.05 parts by weight, the concentration of nitrogen element contained in the quartz glass substrate becomes 50 ppm or more, and nitrogen gas is released from the quartz glass substrate when the obtained glass is reheated by flame processing or the like. However, since the bubble amount and the bubble diameter increase, the whiteness of the opaque quartz glass changes. Also, as the average particle size of the silicon nitride powder,
0.1 to 1 μm, preferably 0.1 to 0.5
More preferably, it is μm. The reason for this is that if the average particle size is in this range, bubbles will not be coarsened or the amount of bubbles will not be drastically reduced, and furthermore, the powder will aggregate and cannot be mixed uniformly with the silica powder. To avoid.

[2] Mixed dispersion The degree of dispersion of the silicon nitride powder in the raw material powder composed of silica powder and silicon nitride powder affects the bubble diameter and its distribution during foaming, so that the silicon nitride powder does not agglomerate. Need to be mixed. The equipment used for mixing is not particularly limited as long as the silicon nitride powder can be dispersed, and examples thereof include a mortar and a ball mill.
Further, in order to improve the dispersion of the silicon nitride powder, a wet method using a dispersion medium is preferably used. Examples of the dispersion medium include water and alcohol.

[3] Filling into Container Next, the obtained mixed powder is filled into a heat-resistant mold. The material and shape of the heat-resistant mold used here are not particularly limited as long as the object of the present invention can be achieved. For example, as a material, carbon, boron nitride, silicon carbide, or the like having a property of hardly reacting with silica is preferably used. Further, in order to improve the slip between the inner surface of the heat resistant mold and the mixed powder, it is preferable to perform filling and heating using carbon felt or carbon paper. The packing density of the mixed powder is preferably from 0.7 to 1.8 g / cm ^{3 in} order to uniformly fill the heat-resistant mold, and it is also preferable that the packing density is uniform in order to uniformly foam. Is preferred. The shape of the heat resistant mold is
Since the shape of the glass after vitrification and bubble generation is substantially the same as the shape of the heat-resistant mold, it can be arbitrarily selected so as to obtain an opaque quartz glass having a desired shape.

[4] Vitrification and Bubble Formation In order to sufficiently decompose the silicon nitride component in the silicon nitride powder and bring the quartz glass into a nearly perfect glass state after the formation of bubbles by foaming, a mixture filled in a heat-resistant mold is used. Heat the powder. The heating device used in this heat treatment is not particularly limited as long as it has a heating ability required to bring the raw material powder into a glassy state, but an electric furnace or the like can be exemplified. The mixed powder is heated in the heating device at a temperature not lower than the temperature at which the raw materials can be melted and not higher than 1900 ° C. The temperature at which the raw material can be melted is 1713 ° C. at normal pressure through cristobalite when using amorphous silica powder as the raw material, but it is difficult to pass through cristobalite when using crystalline quartz powder as the raw material. , The melting temperature will be lower than this temperature.

When the raw material is heated at a temperature lower than a temperature at which the raw material can be melted, the raw material does not melt. When amorphous silica powder is used as the raw material, a part or all of the raw material is heated during heating. Is converted from amorphous silica to cristobalite, which is crystalline, which is not preferable because cristobalite remains without being completely melted and glass is easily broken. Also, 1
Heating at a temperature exceeding 900 ° C. is not preferable because the density of the obtained glass is reduced due to the coarsening of the bubbles, and the mechanical strength required for machining into a predetermined shape and size cannot be obtained. The time of the heat treatment is not particularly limited as long as the entire amount of the raw material can be melted and vitrified. The time is not fixed depending on the heating temperature, but usually 1 hour is sufficient.

In the heating and heating process, it is preferable to maintain a vacuum atmosphere until the powder filler changes from an open pore state to a closed pore state. Subsequently, a vacuum atmosphere can be used until the powder filling in a closed pore state is transformed into glass. The degree of vacuum is preferably 10 mmHg or less in absolute pressure. The reason for this is that only the desorption gas and decomposition gas of the nitrogen element, which are generated by the reaction of the silicon nitride component and the silica component in the raw material powder and solid-dissolve in the quartz glass, are present in the closed cells, so that the entire glass is produced. This is because the distribution of bubbles can be made uniform.

The vacuum atmosphere is released when the powder filling, which has been in the open pore state, changes to the closed pore state or when it is transformed into glass, and an inert gas is introduced. As the inert gas, a heat-resistant type used in the method of the present invention, a raw material, can be used without particular limitation as long as it does not substantially react with the product. For example, nitrogen,
Argon, helium, etc. can be used. Particularly, nitrogen and argon are preferably used in consideration of economy and airtightness.
As the pressure of the inert gas to be introduced, normal pressure is usually used to prevent unstable behavior such as expansion and contraction of bubbles in the glass when the obtained glass is reheated by flame processing, etc. It can be done even if it is done. If desired, the pressure may be slightly reduced.

[5] Opaque quartz glass The properties of the opaque quartz glass obtained in the above steps are as follows.
In order to increase the mechanical strength and the workability or to improve the accuracy of the glass surface, the apparent density is 1.7 to 2.1 g / cm.
^{3. The} average bubble diameter is preferably 10 to 100 μm.

In the method for producing opaque quartz glass of the present invention, factors controlling the diameter and amount of closed cells contained in the glass include the addition amount of silicon nitride powder, the particle diameter and distribution of silica powder, melting temperature, Introduced gas pressure. For example, the apparent density is 1.95 to 2.05 g / c.
m ³ , average bubble diameter 50-70 μm, bubble amount 7 × 10 ⁵ -8
In order to obtain an opaque quartz glass having an excellent thermal barrier property having × 10 ⁵ pieces / cm ³ , the amount of the added silicon nitride powder is 0.01 to
0.02 parts by weight (based on 100 parts by weight of silica powder),
Average particle size of silica powder 100 to 200 μm (particle size distribution: 10 to 600 μm), melting temperature 1800 to 1850
C. and an introduced gas pressure of 1.0 to 2.0 kgf / cm ² . Furthermore, an apparent density of 2.05 to 2.12 g / c, which can provide a smooth surface at the same time as high thermal insulation.
m ³ , average bubble diameter 30-50 μm, bubble volume 1-2 × 10 ⁶
In order to obtain an opaque quartz glass having particles / cm ³ , the addition amount of silicon nitride powder is 0.005 to 0.02 parts by weight (based on 100 parts by weight of silica powder), and the average particle diameter of silica powder is 50 to 100 μm (particles). Diameter distribution: 10 to 200 μm),
Melting temperature 1750-1850 ° C, introduced gas pressure 1.0-
It is preferable to select a range of 2.0 kgf / cm ² . The largest factor that governs the bubbles is the particle size of the silica powder, and by using silica powder having a finer particle size, it is possible to obtain an opaque quartz glass having a small bubble diameter and a large amount of bubbles, and having excellent thermal barrier properties. .

The opaque quartz glass obtained in this manner is not particularly limited as long as it has a white appearance, but it has a characteristic that bubbles are uniformly dispersed, for example, a wavelength of 300 to 900 nm. It can be confirmed that opacity is caused by a decrease in linear transmittance when light is applied. The linear transmittance is 300 to 90 when the thickness of the glass is 1 mm or more in order to secure the thermal barrier property.
The linear transmittance when irradiated with light of 0 nm is preferably 3% or less.

The opaque quartz glass having such a linear transmittance has low thermal conductivity of the glass due to the presence of bubbles, and its effect is amplified by scattering heat rays. Therefore, an opaque quartz glass having excellent heat shielding properties can be obtained by lowering the linear transmittance, that is, by facilitating scattering of heat rays.

In addition, the method of the present invention does not incorporate OH groups into the glass in the raw material and in the melting step, so that an excellent opaque quartz glass having high viscosity at high temperatures can be obtained.

[0028]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto. The analysis of impurities and the like were performed as follows.

Analysis of Impurities Crystalline silica powder was analyzed by ICP method.

~ X-ray diffraction ~ An opaque quartz glass is cut into 20 mm x 10 mm using a cutting machine.
It was cut into a size of × 2 mm (thickness) to obtain a measurement sample. The glass state of the sample was observed using an X-ray diffractometer (model: MXP3, manufactured by Mac Science). The glass state was confirmed by the presence or absence of a diffraction peak due to crystals such as quartz and cristobalite in the obtained diffraction pattern.

-Apparent density-Transparent opaque quartz glass is cut into 30 mm x 30 mm using a cutting machine.
It was cut into a size of × 10 mm (thickness) to obtain a measurement sample. An electronic balance (manufactured by Mettler, model: AT2
61) and the apparent density was measured by the Archimedes method.

[Average Cell Diameter and Cell Volume] An opaque quartz glass is cut into a size of 30 mm × 10 mm using a cutting machine.
It was a measurement sample having a size of 0.3 mm (thickness). Using a polarizing microscope (Model: BH-2, manufactured by Olympus Corporation) having a graduated lens, the bubble diameter and bubble amount in the sample were measured. Regarding the average bubble diameter, the counted bubbles were regarded as a perfect sphere and the total volume was calculated. The total volume was calculated by dividing the total volume by the number of bubbles, and the average diameter was further calculated.

-Particle Size- The particle size distribution and average particle size of the powder are determined by the laser diffraction scattering method COULTER LS-130 (COULTER E).
LECTRONICS). -Packing Density-The packing density of the powder was determined by filling a predetermined weight of powder into a heat-resistant mold, measuring the volume occupied by the powder, and dividing the powder weight by the volume.

-Confirmation of Cavity- The glass was cut using a cutting machine, and the cut surface was visually observed.

Light Transmittance Quartz glass is cut using a cutting machine, and both surfaces in the thickness direction are polished with # 1200 alumina abrasive grains to obtain 30 mm ×
A measurement sample having a size of 10 mm × 1 mm (thickness) was used. Using a spectrophotometer (manufactured by Hitachi, Ltd., model: double beam spectrophotometer 220), the linear transmittance when irradiating light of wavelengths of 300, 500, 700, and 900 nm in the thickness direction of the sample was measured. It was measured.

-Concentration of nitrogen element in glass substrate-Quartz glass was sufficiently pulverized using a mortar to obtain a powder. This was decomposed under pressure using nitric acid-hydrofluoric acid and sulfuric acid, separated by distillation, and measured by ion chromatography.

-Total bubble cross-sectional area- Assuming that a bubble is a perfect sphere, it is defined by the sum of the areas of the circles including the diameter thereof. The average bubble cross-sectional area is calculated from the average bubble diameter, and this is multiplied by the bubble amount. Was calculated.

Example 1 Natural quartz powder having an average particle diameter of 300 μm and a particle diameter distribution in the range of 30 to 500 μm (manufactured by UMININ, trade name: I
OTA-5) was purified by a known method of hydrofluoric acid treatment (hereinafter referred to as quartz powder) and used as a raw material powder. Silicon nitride powder obtained from silicon tetrachloride by a known ammonia treatment method (Ube Industries,
(Trade name: SN-E10, average particle size 0.5 μm) was weighed out so as to be 0.01 part by weight with respect to 100 parts by weight of quartz powder, and 50 parts by weight of ethanol with respect to 100 parts by weight of quartz powder. Then, ultrasonic vibration was applied simultaneously with stirring to sufficiently disperse. Quartz powder was added to the obtained silicon nitride dispersion liquid, sufficiently stirred and mixed. Next, ethanol was removed using a vacuum evaporator and dried to obtain a mixed powder of quartz powder and silicon nitride powder (hereinafter referred to as a mixed powder). 300 g of the mixed powder was applied to a carbon crucible having a 2 mm-thick carbon felt attached to the inner surface (outer diameter:
130 mm, inner diameter: 100 mm, depth: 50 mm). The packing density at this time was 1.4 g / cm ³ . After placing the crucible in an electric furnace and creating a vacuum atmosphere of 1 × 10 ⁻³ mmHg, the temperature was increased from room temperature to 1800 ° C. at 300 ° C. /
The temperature was raised at the rate of time. After holding at 1800 ° C. for 10 minutes, nitrogen gas was introduced until the pressure in the electric furnace reached normal pressure (1 kgf / cm ² ), and the heating was terminated. The opaque quartz glass thus obtained was confirmed to be in a glass state by X-ray diffraction. This glass was evaluated by the method described above, and as a result, the apparent density, average cell diameter, and cell volume were shown in Table 1, and the total cell cross-sectional area and light transmittance were shown in Table 2.
It was shown to. Table 3 shows the nitrogen element concentration in the glass substrate.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

Example 2 The quartz powder in Example 1 was pulverized using a dry ball mill, and the particle size was adjusted by sieving to obtain a powder having an average particle size of 50 μm and a particle size distribution in the range of 10 to 200 μm. . Using this quartz powder, the mixed amount of the silicon nitride powder was 0.03 parts by weight based on 100 parts by weight of the quartz powder to obtain a mixed powder. 300 g of this mixed powder is
The same carbon crucible as in Example 1 was filled. The packing density at this time was 1.4 g / cm ³ . This was heated under the same conditions as in Example 1 to obtain opaque quartz glass. The opaque quartz glass was confirmed to be in a glass state by X-ray diffraction. This glass was evaluated by the method described above. As a result, the apparent density, average cell diameter, and cell volume are shown in Table 1, and the total cell cross-sectional area and light transmittance are shown in Table 2.
Table 3 shows the nitrogen element concentration in the glass substrate.

Example 3 The quartz powder in Example 1 was pulverized using a dry ball mill, and the particle size was adjusted by sieving. The average particle diameter was 50 μm and the particle diameter distribution was in the range of 10 to 200 μm. Using this quartz powder, a mixed powder was produced under the same conditions as in Example 1.

300 g of the mixed powder was filled in the same crucible made of carbon as in Example 1. The packing density at this time was 1.2 g / cm ³ . This was heated under the conditions of Example 1 to obtain opaque quartz glass. The opaque quartz glass was confirmed to be in a glass state by X-ray diffraction.
This glass was evaluated by the method described above. As a result, the apparent density, average cell diameter, and cell volume are shown in Table 1, and the total cell cross-sectional area and light transmittance are shown in Table 2. Table 3 shows the nitrogen element concentration in the glass substrate.

Example 4 Example 4 was carried out under the same conditions as in Example 1 except that the heating temperature was 1850 ° C. It was confirmed that the obtained opaque quartz glass was in a glass state by X-ray diffraction. This glass was evaluated by the method described above. As a result, the apparent density, average cell diameter, and cell volume are shown in Table 1, and the total cell cross-sectional area and light transmittance are shown in Table 2. Table 3 shows the nitrogen element concentration in the glass substrate.

Example 5 The same procedure as in Example 1 was carried out except that after heating at 1800 ° C. for 10 minutes, nitrogen gas was introduced until the pressure in the electric furnace reached 2.0 kgf / cm ² to complete the heating. It carried out on condition of. It was confirmed that the obtained opaque quartz glass was in a glass state by X-ray diffraction. This glass was evaluated by the method described above. As a result, the apparent density, average cell diameter, and cell volume are shown in Table 1, and the total cell cross-sectional area and light transmittance are shown in Table 2. Table 3 shows the nitrogen element concentration in the glass substrate.

Example 6 An amorphous silica powder having an average particle diameter of 300 μm and a particle diameter distribution in the range of 50 to 1000 μm obtained by reacting sodium silicate with an acid and then heat-treating (manufactured by Nitto Chemical Industry Co., Ltd.) Product name: Silica Ace A) is pulverized using a dry ball mill, and classified by sieving to have an average particle size of 18
A powder having a particle size distribution of 0 to 10 μm in a range of 10 to 600 μm was obtained and used as a raw material powder. Silicon nitride powder obtained from silicon tetrachloride by a known method of ammonia treatment (product name: SN-E10, manufactured by Ube Industries, Ltd.)
An average particle diameter of 0.5 μm) was weighed out so as to be 0.01 part by weight with respect to 100 parts by weight of the amorphous silica powder, and was added to 50 parts by weight of ethanol with respect to 100 parts by weight of the amorphous silica powder. After charging, ultrasonic vibration was applied simultaneously with stirring to sufficiently disperse. Amorphous silica powder was added to the obtained silicon nitride dispersion liquid, sufficiently stirred and mixed. Next, ethanol was removed using a vacuum evaporator and dried to obtain a mixed powder of amorphous silica powder and silicon nitride powder (hereinafter, referred to as a mixed powder). A carbon crucible having a 2 mm-thick carbon felt attached to the inner surface thereof (300 g of the mixed powder) (outer diameter: 130 mm, inner diameter: 100 mm, depth: 50 m)
m). The packing density at this time is 0.81 g / c.
m ³ . Put the crucible in the electric furnace, 1 × 10 ^-3 m
After a vacuum atmosphere of mHg, the temperature was raised from room temperature to 1800 ° C. at a rate of 300 ° C./hour. After holding at 1800 ° C. for 10 minutes, the pressure in the electric furnace was reduced to normal pressure (1 kgf / cm).
Heating was terminated by introducing nitrogen gas until ² ) was reached. The opaque quartz glass thus obtained was confirmed to be in a glass state by X-ray diffraction. The glass was evaluated by the method described above, and as a result, apparent density,
Table 1 shows the average bubble diameter and the bubble amount, and Table 2 shows the total bubble cross-sectional area and light transmittance. Table 3 shows the nitrogen element concentration in the glass substrate.

Example 7 A mixed powder was obtained by setting the mixing amount of the silicon nitride powder to the amorphous silica raw material powder in Example 6 to 0.02 parts by weight based on 100 parts by weight of the amorphous silica powder. 300 g of this mixed powder was filled in the same carbon crucible as in Example 1. At this time, the packing density was 0.81 g / cm ³ . This was heated under the same conditions as in Example 1 to obtain opaque quartz glass. The opaque quartz glass was confirmed to be in a glass state by X-ray diffraction. The glass was evaluated by the method described above, and as a result, apparent density,
Table 1 shows the average bubble diameter and the bubble amount, and Table 2 shows the total bubble cross-sectional area and light transmittance. Table 3 shows the nitrogen element concentration in the glass substrate.

Example 8 The raw material powder of amorphous silica in Example 6 had an average particle diameter of 250 μm and a particle diameter distribution in the range of 10 to 800 μm. 300 g of the obtained mixed powder was filled in the same crucible made of carbon as in Example 1. At this time, the packing density was 0.79 g / cm ³ . Example 1
And opaque quartz glass was obtained. The opaque quartz glass was confirmed to be in a glass state by X-ray diffraction. The glass was evaluated by the method described above,
As a result, the apparent density, average bubble diameter, and bubble amount are shown in Table 1.
Table 2 shows the total cross-sectional area of the bubbles and the light transmittance. Also,
Table 3 shows the nitrogen element concentration in the glass substrate.

Example 9 An amorphous silica powder having an average particle size of 170 μm and a particle size distribution in the range of 30 to 400 μm obtained by reacting silicon alkoxide with water and then heat-treating the product (manufactured by Mitsubishi Chemical Corporation; (MKC silica PS300L) was used as a raw material powder. The mixing amount of the silicon nitride powder (product name: SN-E10, manufactured by Ube Industries, 0.5 μm in average particle size) with respect to the amorphous silica powder is 0.01 part by weight with respect to 100 parts by weight of the silica powder. And mixed powder was obtained in the same manner as in Example 1. 300 g of the mixed powder was filled in the same carbon crucible as in Example 1. At this time, the packing density was 0.81 g / cm ³ . This was heated under the same conditions as in Example 1 to obtain opaque quartz glass. The opaque quartz glass thus obtained was confirmed to be in a glass state by X-ray diffraction. The glass was evaluated by the method described above, and as a result, apparent density,
Table 1 shows the average bubble diameter and the bubble amount, and Table 2 shows the total bubble cross-sectional area and light transmittance. Table 3 shows the nitrogen element concentration in the glass substrate.

When the opaque quartz glass obtained in Examples 1 to 9 was sliced and observed with a microscope, it was found that bubbles were uniformly dispersed. Also,
These glasses were placed in an electric furnace, and were subjected to normal pressure (1 k
gf / cm ² ) and a heat treatment at 1800 ° C. for 10 minutes. When the glass after the heat treatment was sliced and observed under a microscope, the state of bubbles was not different from that before the heat treatment.

Comparative Example 1 The quartz powder in Example 1 was pulverized using a dry ball mill, and further dispersed in ethanol to adjust the particle size by the difference in sedimentation speed. The average particle size was 5 μm and 1 to 10 μm. Having a particle size distribution in the range of
Using this quartz powder, a mixed powder was produced under the same conditions as in Example 1.

[0053] 300 g of the obtained mixed powder was filled in the same carbon crucible as in Example 1. The packing density at this time was 0.9 g / cm ³ . This was heated under the same conditions as in Example 1 to obtain quartz glass. This quartz glass is X
It was confirmed that the glass was in a glass state by line diffraction. However, the apparent density of this glass is as low as 1.2 g / cm ^3.
Some cavities were scattered.

Comparative Example 2 The amorphous silica raw material powder in Example 6 was used with an average particle diameter of 700 μm and a particle diameter distribution in the range of 500 to 1000 μm. Obtained mixed powder 30
0 g was filled in the same carbon crucible as in Example 1. The packing density at this time was 0.78 g / cm ³ .
This was heated under the same conditions as in Example 1 to obtain quartz glass. The quartz glass was confirmed to be in a glass state by X-ray diffraction. However, the apparent density of this glass was as low as 1.4 g / cm ^3, and the inside diameter of the glass was 0.5 g / cm ^3.
Cavities of about 1 mm were scattered.

Comparative Example 3 An experiment was carried out under the same conditions as in Example 6 except that the heating temperature was changed to 1950 ° C. It was confirmed that the obtained quartz glass was in a glass state by X-ray diffraction. However, the apparent density of this glass was as low as 1.5 g / cm ³ , the average cell diameter reached 200 μm, and it was a very brittle glass.

Comparative Example 4 Example 1 was carried out under the same conditions as in Example 1, except that the mixing amount of the silicon nitride powder was changed to 0.06 parts by weight with respect to 100 parts by weight of the quartz powder. It was confirmed that the obtained quartz glass was in a glass state by X-ray diffraction. The apparent density of this glass was 1.7 g / cm ³ . Table 3 shows the nitrogen element concentration in the glass substrate.

The glass was placed in an electric furnace and heated at 1800 ° C. for 10 minutes while maintaining the atmosphere at normal pressure (1 kgf / cm ² ) with nitrogen gas. The glass after the heat treatment had a higher whiteness than before the heat treatment. When this was sliced and observed with a microscope, both the amount of bubbles and the diameter of bubbles were larger than those before the heat treatment.

[0058]

The opaque quartz glass of the present invention is obtained by adding silicon nitride powder to silica powder and heating the mixture to cause vitrification of the silica powder and foaming by decomposition of the silicon nitride powder. Of impurities can be prevented. Further, by adjusting the particle size of the silica powder, the amount of the silicon nitride powder mixed, and the heating temperature, the bubble diameter and apparent density of the obtained opaque quartz glass can be controlled. In addition, since a glass having a shape substantially similar to the shape of the heat-resistant mold can be obtained, the raw material powder is filled in a heat-resistant mold having a shape similar to a desired shape, and vitrification is performed. It becomes possible to greatly reduce the machining process such as grinding to be performed. Further, since the nitrogen element concentration in the glass substrate is low, even if reheating treatment such as flame processing is performed, a change in whiteness of the opaque quartz glass due to refoaming can be suppressed.

Further, when the transparent quartz glass member is joined by flame processing, since the nitrogen element concentration is close, both glasses in the vicinity of the joint are not deteriorated, and good joining is possible without fear of cracking.

Claims (5)

[Claims] 1. An apparent density of 1.7 to 2.1 g / cm ³ , an average cell diameter of 10 to 100 μm, and a cell volume of 3 × 10
^{5 to} 5 × 10 ⁶ cells / cm ³ , and the total bubble cross-sectional area is 10 to 10.
Opaque quartz glass characterized by being 40 cm ² / cm ³ . 2. When the thickness is 1 mm or more, a wavelength of 300 to
2. The opaque quartz glass according to claim 1, wherein the linear transmittance when irradiated with light of 900 nm is 3% or less. 3. The method according to claim 1, wherein the concentration of nitrogen element in the quartz glass substrate is 1-5.
The opaque quartz glass according to claim 1, wherein the opaque quartz glass is 0 ppm. 4. A starting material powder obtained by mixing and dispersing silicon nitride powder in silica powder having an average particle diameter of 10 to 500 μm and 0.001 to 0.05 parts by weight of silicon nitride powder per 100 parts by weight of silica powder. Filled in a heat-resistant mold having a complicated shape, and heated under a vacuum atmosphere to a temperature not lower than the melting point of the starting material and not higher than 1900 ° C., or under a vacuum atmosphere, the temperature of the starting material is not lower than 1400 ° C. Heating to a temperature lower than the melting temperature, and then heating to a temperature not lower than the melting point of the starting material and not higher than 1900 ° C. in an inert gas atmosphere to generate bubbles by vitrification and foaming. 4. The method for producing opaque quartz glass according to any one of 1 to 3. 5. The method for producing opaque quartz glass according to claim 4, wherein the heat-resistant mold having a complicated shape is a flange, a cylinder, a hollow prism, a screw, or the like.
A method for producing opaque quartz glass, which is in the shape of a turbocharger, a square water tank or a trough.