DE2337495A1 - PROCESS FOR THE PRODUCTION OF SILICON DIOXIDE WITH HIGHLY THICKENING AND THIXOTROPIC PROPERTIES - Google Patents

Description

German Andtejewikl

DipL-Ing. Gesthuyitft ** ' ^July

43 B * »en, The» t »tpUM J

LONZA AG, Gampel / Wallis (Management: Basel)

Process for the production of silicon dioxide with strongly thickening and thixotropic properties.

The invention relates to a process for the production of highly dispersed silicon dioxide by reacting coarse-particle silicon dioxide Silicon dioxide or materials containing silicon dioxide with the aid of a plasma torch, with avoidance the formation of silane groups.

It is known (DOS 1 933 291) that highly disperse silicon dioxide is obtained by reacting silicon dioxide Materials with a reducing agent at high temperatures to form a gas stream containing silicon monoxide, Subsequent cooling of the gas stream in the presence of oxidizing gases and separation of the one formed with the cooling highly disperse silicon dioxide from the residual gas, to produce, on the silicon monoxide-containing hot gas stream is before its cooling water vapor with the formation of a highly dispersed intermediate product containing silane and silanol groups for action brought and then subjected the intermediate product to a thermal aftertreatment after separation from the gas stream. This thermal aftertreatment is necessary to remove the silane groups which have a negative impact on the properties of the end product to destroy.

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There is also known a method (Dutch laid-open patent application 67.16766) which involves the production of silica particles describes, characterized in that silicon dioxide is vaporized in a plasma generator and the end flame of the plasma generator, which contains the evaporated silicon dioxide, is extinguished in the presence of a hydrogen-containing compound. Hydrogen-containing compounds include water and ammonia. It is essential in this process that the hydrogen gas containing compound at such a point in the plasma system is introduced that the presence of free hydrogen is ensured during the formation of solid silica particles. *

The object of the present invention is to produce a product with strongly thickening and thixotropic properties. To do this, it is necessary to destroy the silane groups that are formed • or to prevent their formation, but without the Destroying silanol groups or preventing their formation and thus the stated and desired properties of the end products to obtain. In particular, the method should be able to be carried out simply and not over several methods.

According to the invention this is achieved in that the intermediate formed in the plasma jet, off of silicon monoxide existing intermediate product of the area of the plasma jet, pulls, brings to temperatures of 13CX) ⁰ to 1900 K and then

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reoxidized to silicon dioxide with a mixture of steam and a compound of the type N- (R ₁ R ₂ R ₃ ), where R ^ R ₃ R _{3 can be} hydrogen atoms or organic radicals which together contain no more than 6 carbon atoms and scares off. A mixture of steam and ammonia is preferably used. Other compounds of the N- (R ₁ R ₂ R ₃ ) type that are advantageously used are alkylamines, such as methylamines, ethylamines, propylamines, butylamines, alkylamines and hexylamines.

For the reoxidation and quenching, it is expedient to use a steam which contains 1 to 10% by weight, preferably 3 to 5% by weight, of the compound H- (R ^ R ₃ R ₃ ).

The reoxidation is passed advantageously at temperatures of 13OO ° K to 1900 ° K, preferably at 1500 ⁰ K to 19OO ° K _# a. In the method of the invention, a plasma torch is used, which can be gas-stabilized as well as liquid-stabilized. One possible embodiment of such a burner is described in Swiss patent specification 494 517, for example.

Quartz sand is preferably used as the silicon dioxide. For example, a sand that is used to produce Glass is suitable used. The grain size can be kept within fairly wide limits, but it is advisable to use a grain size not to exceed 150 - 200 n £ sh.

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The introduction of silicon dioxide is most expedient in the vicinity of the anode with the aid of a carrier gas, for example directly into the plasma jet. After feeding the silica these granules are carried away by the plasma jet and accelerated in the direction of the anode. On the surface of the When the particles are heated simultaneously, the reduction to gaseous silicon monoxide begins.

The temperature of this gas mixture should preferably be kept above 2300 ° C. by regulating the energy supply to the burner in order to avoid undesirable side reactions, such as the formation of silicon carbide. At the exit of the reaction vessel, a cooling nozzle may be attached, a non-oxidizing gas (such as H2 # N2 # Ar, CO) welphe by supplying the gas stream to a temperature of 13OO to 1900 ⁰ K cools.

After the cooling process, which may be necessary, the reaction mixture is passed into the reoxidation and quenching reactor and _{treated with the mixture of water vapor compound N- (R, R 3} R ₃ ). The desired highly disperse silicon dioxide is now formed, which has excellent properties in terms of thickening effect and thixotropy due to the greatly reduced silane group concentration and the large number of silanol groups.

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Comparative examples

example 1

With the help of a plasma torch, such as in the Swiss Patent 494 517 described, which generates a hydrocarbon pasina, quartz sand was evaporated and carbothermally reduced.

The gaseous SiO formed was drawn off, with H ₂ to 1500

Cooled to 1900 ° K and then with three times the stoichiometric Amount of water vapor oxidized and quenched at the same time.

The product thus obtained turned out to be very finely divided amorphous > 2

2 SiO ₀ with a specific surface area of 120 m 2 / g. On the surface there were 2-3 silane groups per 100 Å and 4.0 silanol groups

o2 "»

per 100 A. A 3% dispersion in dioctyl phthalate resulted in a viscosity of 171 cP and only slight thixotropy.

Example 2 (according to the invention)

As described in Example 1, quartz sand was evaporated in a plasma torch. The gaseous SiO formed was drawn off, _{cooled to 1500-1900 K with H 2} and then quenched with steam to which 2% by weight ammonia gas, based on the steam, was added. A very fine amorphous SiO _{2 was formed} , the silane groups of which had completely disappeared. In contrast, a surface silanol concentration of 6.8 / 100 A could be measured. A 3 % strength dispersion in dioctyl phthalate gave a viscosity of 680 cP and pronounced thixotropy.

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Example 3

It was prepared as described in Example 2, working, but the gaseous SiO is oxidized at a temperature above 2000 ⁰ K and quenched, the finely divided amorphous S1O2 obtained had a specific surface area of 38O m / g and the Sxlanolgruppenkonzentratxon was 3.2 OH groups per 100 Å, but the viscosity of a 3% dispersion in dioctylphthalate was only 195.

Example 1 2 3_

Surface area ra ² / g 120 22O 380

Silane groups Si-H / 100 R 2-3

Silanol groups SiOH / 100 R ² 4 6.8 3.2 Thickening cP 171 68O 195

(3 % SiO ₂ in DOP)

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Example 4

In the same process as described under (1), 5% by weight of ammonia gas, based on the water vapor, was added to the water vapor mixed in. As a result, a product was obtained which was neither analytically nor in its application from the of example (3) differed.

Example 5

In the same process as described under (1), 10% by weight of ammonia gas (based on the water vapor) was added to the water vapor. With the help of the IR spectral analysis it was possible to show that neither NH ₃ (through physical absorption) nor NH 4 groups chemically bonded to the Si atom could be found on the particle surface. Otherwise, the properties of SiO_ were the same as those already listed in Example 3.

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Claims (1)

Claims I). Process for the production of highly dispersed silicon dioxide by reacting coarse silicon dioxide or silicon dioxide-containing materials with the aid of a plasma torch while avoiding the formation of silane groups, so that a product with strongly thickening and thixotropic properties is obtained, characterized in that the intermediate "Silicon monoxide" intermediate product formed in the plasma jet is withdrawn from the area of the plasma jet, brought to temperatures of 1300 to 1900 K and then with a mixture of water vapor and a compound of the type If- (R, RpR_), where ^β 1 ^β 2 ^Ε 3 hydrogen atoms or organic radicals, which together contain no more than 6 carbon atoms, can be reoxidized to silicon dioxide and quenched. 2. The method according to claim 1, characterized in that the compound used is N- (R ^ RpR, -) ammonia. 3. The method according to claim 1, characterized in that steam, which expediently contains 1 to 10 wt. ^ Of the compound N- (R ₁ R ₂ R ^), is used. 4. The method according to claim 1 and 2, characterized in that the reoxidation at temperatures of the intermediate 'product of 1500 to 1900 ⁰ K is initiated. 409813/0782 K / ms4895-4906 The representative: July 16, 1973