JPS598625A - Preparation of quartz glass - Google Patents

Abstract

PURPOSE:To prepare a dried gel for preparing a quartz glass, having a low shrinkage, and not easily crushable safely and efficiently at a low cost by the sol-gel method, by violently agitating an alkoxysilane and water in two layers, and hydrolyzing the alkoxysilane. CONSTITUTION:Water is added to an alkoxysilane, e.g. ethyl orthosilicate, at about 5-15 molar ratio between the water and the alkoxysilane and an adequate amount of hydrochloric acid as a catalyst for the hydrolytic reaction is added thereto. The resultant two layers are agitated vigorously at room temperature without adding ethanol as a solvent. The mixture changes into a transparent homogeneous system in a short time of about 5min, and the temperature is increased to about 40 deg.C or above. Thus, the hydrolytic reaction is clearly completed. A dried gel is prepared from the resultant Si(OH)4 sol and then sintered at about 1,000 deg.C or below to give the aimed quartz glass. The dried gel can be obtained safely without cracking in shrinkage by reducing the amount of the ethanol in the hydrolytic reaction solution, and increasing the concentration of Si(OH)4 according to the above-mentioned method.

Description

Detailed Description of the Invention The present invention uses a sol-gel method to hydrolyze alkoxysilane in a two-component system with water without adding alcohol as a solvent. This is a non-melting glass manufacturing method in which alkoxides are hydrolyzed and the resulting dry gel is heated. When a metal alkoxide is used as a starting material, it is easy to purify the raw material, and homogeneous glass can be produced at a relatively low temperature even if the composition is difficult to produce by a melting method. When producing quartz glass by the melting method, it is difficult to adjust the raw materials and the purity is low, 1700~2
Although a high temperature of 1,000°C is required, when the sol-gel method is used, vitrification occurs at a temperature of 1,000°C or lower and quartz glass can be obtained. However, in order to prevent cracking during the gelation shrinkage process after hydrolysis, or during the gelation shrinkage process, which has the disadvantage that it tends to break during the heating of the dry gel, it is necessary to have a small shrinkage rate. A high concentration of tetrahydroxysilane is required. Further, in order to prevent the dried gel from being crushed during heating, it is necessary to completely hydrolyze the gel. It is desirable that the reaction be quick and that completion can be easily confirmed.

Conventionally, the hydrolysis reaction of alkoxysilane has been carried out homogeneously by adding alcohol as a solvent. Since a considerable amount of alcohol is required to dissolve the alkoxysilane and water, gelation is slow, and the shrinkage rate after gelation is large, resulting in cracking and loosening. Furthermore, since the reaction is a homogeneous system, the reaction progresses slowly and it is not possible to determine how much hydrolysis has been completed, so stirring had to be continued for a longer time than necessary. Alcohol accounts for a large proportion of the raw material cost, and a large amount of alcohol evaporates during drying, which is dangerous. In the case of mass production, the amount of alcohol in the hydrolysis reaction solution used for gelation should be small in order to aim for low cost and safety.

The present invention eliminates this drawback, and by vigorously stirring the alkoxysilane and water in two layers, the hydrolysis reaction is completed in a short time. The completion of the process can be confirmed by the system generating heat and becoming a homogeneous solution. By reducing the amount of alcohol in the hydrolysis reaction solution and increasing the concentration of tetrahydroxysilane, it was possible to obtain a dry gel safely and without cracking due to shrinkage.

The present invention will be described in detail below based on experimental examples. 1. When producing bulk quartz glass by the sol-gel method, the molar ratio of water to ethyl orthosilicate (H2O) /
Hydrolysis is carried out under conditions such that (5BoazHs)4) is 5 to 15. The reaction is shown by formulas (1) and (2).

n5i(002H6)4+4nH20→n5i(OH)
4102-1-2nH20・(g nSi(oH) 4 →m5102-1-2nH20・
-(2) If the amount of water is less than 5 times the mole, sufficient hydrolysis will not occur, and even if the dried gel is subsequently heated at a high temperature, it will become black and difficult to become transparent. Moreover, water in an amount of 15 times the mole or more is meaningless and is unnecessary because it only delays the gelation time.

Ethyl orthosilicate 22 ml (0.1 mot)
10 times the molar amount of water 18 m t (i, Omot)
When added, it was completely divided into 21 meters. To make this a homogeneous system, add 36 ml of ethanol (0.6 ml).
) is required, and the volume will approximately double. Therefore, hydrochloric acid was used as a catalyst for the hydrolysis reaction (Hal) / (
sl(oc+as)4] is 0.02,
The two layers were vigorously stirred at room temperature without adding any ethanol (etham as a solvent). After about 5 minutes, the yarn turned into a transparent homogeneous system and generated heat, raising the temperature of the yarn to over 40°C.

Liquid chromatography analysis confirmed that the raw material ethyl orthosilicate had disappeared and ethanol had been produced. This (0-4 mOL reaction resulted in 23 mt (0-4 mOL)
) ethanol was produced ~ Even if the dry gel obtained by hydrolysis without using ethanol as a solvent is sintered, silica glass can be similarly obtained at the same temperature below 1000°C. Ta. No difference was observed between the two in the analysis results of specific gravity, Vickers hardness, refractive index, near-infrared absorption spectrum, etc. It has been found that there is no effect on the production of quartz glass even if the hydrolysis reaction is not carried out in a homogeneous system.

As mentioned above, in order to homogeneously hydrolyze 0.1 mole of ethyl orthosilicate, more than a6 mole of ethanol is required, and after the reaction is completed, it is eventually removed along with the 0.4 mole of ethanol produced. There must be. If hydrolysis is carried out using only ethyl orthosilicate and an aqueous hydrochloric acid solution, not only will the cost of ethanol be eliminated, but the volume will be reduced to about half, making it easier to operate. Furthermore, since the amount of ethanol to be removed is reduced, the gelation time is shortened, and the volumetric shrinkage rate during the drying shrinkage process is reduced. Furthermore, drying time is shortened, increasing work efficiency.

As described above, the present invention has the characteristics of reducing costs, improving safety and work efficiency, and improving dry gel production conditions by performing hydrolysis without adding alcohol.

that's all

Claims (1)

[Claims] (1) A quartz glass manufacturing method using a sol-gel method, characterized in that a dry gel is produced by vigorously stirring alkoxysilane and water in two layers to cause a hydrolysis reaction. manufacturing method.