JPH0222133A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To obtain a dried gel without cracking in a shorter drying time by dipping a wet gel consisting of silica in a mixture solution of an alcohol and silicone oil and drying the gel. CONSTITUTION:A wet gel, consisting of aerosil prepared by a vapor method or silica obtained by hydrolyzing a silicon alkoxide is dipped in a mixture solution of an alcohol, such as methanol or ethanol, and a silicone oil, such as alcohol-soluble higher fatty acid-modified silicone oil, dried and calcined to afford quartz glass.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing quartz glass, particularly a method for producing quartz glass by a sol-gel method.

[Prior art] In the production of quartz glass using the sol-gel method, first,
A sol, which is a fluid colloidal solution, is prepared by dissolving or dispersing silicon alkoxide, silica powder, or a mixture of both as the silica component in water or a mixture of water and alcohol. This sol is then poured into a mold and solidified to produce a jelly-like wet gel containing a large amount of water or water and alcohol inside. After that, this wet gel is dried to remove the water and alcohol contained inside and become a dry gel, which is a dry porous body.
The dry gel is heated to 500 to 600°C in an oxygen atmosphere to remove residual organic matter, and then heated to 1200 to 1500°C in a helium atmosphere to obtain transparent quartz glass.

[Problems to be Solved by the Invention] One of the major drawbacks of this prior art is that cracks tend to occur during the drying process of the wet gel, which contains a large amount of water and alcohol. Drying had to be carried out extremely slowly, and this was one of the major factors hindering industrial production.

An object of the present invention is to provide a method for producing quartz glass by obtaining a crack-free dry gel in a short drying time and firing the dry gel.

[Means and effects for solving the problems] The gist of the present invention is to provide a method for producing silica glass by producing a wet gel made of silica, then drying and firing the wet gel. After being immersed in a silicone oil mixture, it is dried and fired.
First, to create a wet gel, silicon alkoxide, silica powder, or a mixture of both is dissolved or dispersed in water or a mixture of water and alcohol to create a sol, which is a fluid colloidal solution. The mixture is poured into a mold and solidified to form a jelly-like wet gel.6 As the silicon alkoxide, methoxy, ethoxy, propoxy, butoxysilane, etc. can be used.

As the silica powder, it is possible to use Aerosil produced by a gas phase method or an alkoxide-mediated silica powder obtained by drying a colloid/8 liquid produced by hydrolysis of silicon alkoxide.

Alcohols include methanol and ethanol.

Globanol, butanol, etc. can be used.

As the silicone oil, alcohol-soluble higher fatty acid-modified silicone oil or silicone polyether copolymer can be used.

By immersing this wet gel in an alcohol-silicone oil mixture and then drying it, the silicone oil alleviates the distortion of the gel due to vaporization of water and alcohol during drying, and the drying time is significantly shortened. Also, by heating, the carbon and water components in the silicone oil are removed, and the remaining silicon becomes equivalent to gel components during the firing process, forming a solid silica glass.

[Example] Specific examples of the present invention will be described below.

(Example 1) Silicon ethoxide and water with a pH of 9 in a molar ratio of 1 = 4
The mixed solution was placed in a cylindrical plastic container and allowed to gel at room temperature to produce 10 wet gels each having a diameter of 3011 mm and a length of 3001111 mm. Five of these wet gels were mixed into 1 oo of a mixture of ethanol and alcohol-soluble silicone oil in a molar ratio of 2=1.

These wet gels were soaked for 24 hours in ml.
When we put 0 gels in a dryer and raised the temperature from 70°C to 140°C at a rate of 40°C per day for 3 days to dry them, we found that all 5 wet gels without immersion treatment were much larger. However, only one of the five wet gels subjected to the immersion treatment had cracks, and the other four had no cracks, resulting in dry gels with a diameter of 15111 mm and a length of 15 axes. These crack-free dry gels were heated in an oxygen atmosphere in an electric furnace for 60 minutes.
It was heated to 0° C. and then heated to 1250° C. in a helium atmosphere to obtain a transparent quartz glass rod with a diameter of 1011 and a length of 100111.

The reason why the wet gel subjected to the ethanol-silicone oil immersion treatment was difficult to crack is that the silicone oil acts to alleviate the strain that occurs in the wet gel due to the vaporization of water and alcohol when heated at 140'Cd. It's for a reason. 6 in an oxygen atmosphere following further drying treatment.
The carbon and hydrogen components of the silicone oil are removed from the gel by heat treatment up to 00°C, and the silicon component becomes SiO□, which is equivalent to the gel component, and during the sintering process, the Si derived from the gel
It is thought that it becomes integrated with O2 to form quartz glass.

(Example 2) Instead of a quartz rod, a quartz tube was made using a concentric plastic container with an outer diameter of 30 Ill and an inner diameter of 2011 Ill.
A wet gel with a length of 300 inches was prepared.

This tubular wet gel was treated with a mixed solution of ethanol and alcohol-soluble silicone oil in the same manner as the rod-shaped wet gel, then dried and sintered to obtain a quartz tube with an outer diameter of 10 nn, an inner diameter of 61 m11, and a length of 100111 mm. In this case as well, when tubular wet gels without any treatment were dried for comparison, all of them had numerous cracks.

[Effects of the invention] According to the present invention, the following excellent effects are exhibited.

(1) When drying a wet gel immersed in a mixture of alcohol and alcohol-soluble silicone oil, the silicone oil acts to alleviate the strain that occurs in the wet gel due to the vaporization of water and alcohol, so the wet gel dries. It can save a lot of time.

(2) In the production of quartz glass using the sol-gel method, the long drying process that was required can be significantly shortened, leading to cost reductions in terms of energy savings and time savings.

(3) It is also possible to produce large-sized quartz glass, which was previously difficult to produce because the drying time was too long.

Claims (1)

[Claims] 1. After producing a wet gel made of silica, the wet gel is dried and fired to produce quartz glass, in which the wet gel is immersed in an alcohol-silicon oil mixture, then dried and fired. A method for producing quartz glass characterized by: