JPS643811B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing quartz glass in which alkoxysilanes are separately hydrolyzed using acidic and basic catalysts and then thoroughly mixed to form a gel in a sol-gel method.

The sol-gel method is a non-melting glass manufacturing method in which a metal alkoxide is hydrolyzed, gelled, and the resulting dry gel is heated. When metal alkoxides are used as starting materials, homogeneous glass can be produced at relatively low temperatures even with compositions that are difficult to produce by melting. However, it generally has the disadvantage that it tends to break during the gelling shrinkage process after hydrolysis or during heating of the dry gel.

To prevent fracture during the sintering process, the thickness of 50 to 80 Å is
It is necessary to create a dry gel that contains a large amount of relatively large pores.

To hydrolyze and gel alkoxysilane, there are two methods: a method using a base such as ammonia as a catalyst, and a method using an acid such as hydrochloric acid as a catalyst.

When a base such as ammonia is used as a catalyst, the dried gel produced contains a large number of pores larger than 50 Å, so there are no cracks during sintering. However, it is extremely difficult to create a dried gel in the desired shape, and no examples have been published in which a dried gel with a diameter of 2 cm or more has been obtained.

When an acid such as hydrochloric acid is used as a catalyst, dry gels can be easily produced, and dry gels with a maximum diameter of 7 cm have been published. However, it is prone to cracking during the sintering process, and it fractures violently especially at temperatures above 700°C. Even if the temperature increase rate is slowed to 0.5°C/min, this can hardly be prevented. This is because the dried gel contains only micropores of around 20 Å. If it is gelled at a temperature of 60°C or higher, it will contain pores of 50 to 80 Å, which can prevent cracking during the sintering process to some extent. However, this method alone is incomplete.

As mentioned above, it has a structure that does not crack during the sintering process.
Large-scale dry gels have not yet been produced and the method has not been established. Dry gel preparation methods using ammonia and hydrochloric acid as catalysts have advantages and disadvantages, and neither method has yielded satisfactory results.

The present invention aims to compensate for each other's shortcomings and to produce large-sized quartz glass without cracking during gelation shrinkage and sintering processes.

The method for producing quartz glass of the present invention is a method for producing quartz glass using a sol-gel method, in which a sol obtained by hydrolyzing an alkoxysilane using a base as a catalyst and a sol obtained by hydrolyzing an alkoxysilane using an acid as a catalyst are used. It is characterized in that it is mixed uniformly and then gelled.

That is, in the present invention, fine particles grown to various sizes after hydrolysis with ammonia are uniformly dispersed in various proportions in the fine structure of tetrahydroxysilane that has been hydrolyzed with hydrochloric acid, and then gelled. and achieve the above objectives.

Hereinafter, the present invention will be explained in detail based on experimental examples.

Experimental Example 1 Si(OC ₂ H ₅ ) ₄ :H ₂ O:C ₂ H ₅ OH was mixed at a molar ratio of 1:10:8 to form a homogeneous solution. A 0.1N ammonia aqueous solution was used as the water, and the tube was sealed tightly and allowed to stand at room temperature for 3 days to allow hydrolysis and grain growth. The white translucent solution was concentrated to a silica concentration of 25 mt% using a rotary evaporator. (Hereinafter, this will be referred to as sol A.) When concentrated more than this, gelation occurred instantly.

Meanwhile, stirring was continued for 1 hour under ice cooling at a molar ratio of Si(OC ₂ H ₅ ) ₄ :H ₂ O=1:10. A 0.1N aqueous hydrochloric acid solution was used as water to obtain a colorless and transparent homogeneous solution. This solution was concentrated to the same silica concentration as Sol A. (Hereinafter, this will be referred to as sol B.) Considering tetrahydroxysilane, it is 40 mt%.

Sol A and Sol B, which were prepared separately in this way, were thoroughly mixed at a volume ratio of 1:1.

Since it was an aqueous solution in which ammonium chloride was generated by neutralization, it was dissolved, and a uniform white translucent sol was obtained. This mixed sol exhibited a pH of 3, probably because ammonia was removed during the concentration process. A dry gel with a diameter of 4 cm was prepared by heating to 70°C. This dry gel
Even when magnified 10,000 times, no particles were observed and the surface was smooth, but when the pore size distribution was measured, it contained a large amount of pores of 40 to 80 Å. Therefore, it did not crack at all even when the temperature was raised at 5°C/min, and it became colorless and transparent quartz glass at 1150°C.

Ammonium chloride contained in the dried gel was completely decomposed and removed at temperatures below 650°C, and no adverse effects on sintering were observed.

Experimental example 2 When sol A and sol B are mixed at a volume ratio of 1:2.
The pH was 1, and the degree of white turbidity was stronger than when the ratio was 1:1. By selecting sealed conditions and heating to 70°C, a dry gel with a diameter of 6 cm was obtained. 40-80 compared to 1:1
Vitrification occurred at around 1050°C, probably due to a decrease in the number of Å pores. Even at a mixing ratio of 1:2, the temperature is 5℃/
It withstood a temperature increase rate of min. without cracking.

As described above, the sol obtained by hydrolyzing alkoxysilane with a basic catalyst and the sol obtained by hydrolyzing it with an acidic catalyst are uniformly mixed and then gelled. By adjusting the particle size of the silica that makes up the sol, it is possible to arbitrarily increase or decrease the particle size of the silica, and by adjusting the amount of sol that has been hydrolyzed by an acidic catalyst to be mixed. Since the decomposed sol can have any combination of particle sizes from large to small, when it is made into a sol, it tends to form a strongly bonded structure, and the sol does not break at all or have cracks in it during the drying process. Furthermore, it is possible to produce large quartz glass without cracks or cracks even during sintering.

(2) All raw materials are alkoxysilanes, so
Not only can it be purified, but since it is a liquid operation, it can easily prevent impurities from eluting from the container etc. during the manufacturing process, and it can also prevent contamination with impurities during the shrinking and drying processes of the gel. This can be easily prevented by modifying the container, making it possible to produce large, crack-free quartz glass with high purity.

Since the quartz glass produced by this production method has good purity, it is possible to obtain large quartz glass that is superior to, but not inferior to, meltable quartz glass in terms of density, refractive index, Vickers hardness, coefficient of thermal expansion, etc. be able to.

Claims (1)

[Claims] 1. In the production of quartz glass using the sol-gel method, a sol obtained by hydrolyzing alkoxysilane using a base as a catalyst and a sol obtained by hydrolyzing using an acid as a catalyst are uniformly mixed and then gelled. Characteristic manufacturing method of quartz glass.