JPS59102833A - Preparation of quartz glass - Google Patents

Abstract

PURPOSE:To prepare large-sized void-free dry gel for the preparation of quartz glass, in a short time, in high yield, by hydrolyzing an alkoxysilane using an acid as a catalyst, adjusting the pH of the product within a proper range with a base, and gelatinizing the product. CONSTITUTION:An alkoxysilane is hydrolyzed at a high rate of hydrolysis using an acid as a catlayst, and adjusted to 3-6pH with a base to increase the rate of polymerization and to effect the gelatinization at room temperature. The gel is put into a vessel, and dried in a semi-closed state by raising the temperature to obtain a large-sized void-free dry gel having low cracking defects, easily, in high yield, in a short time. The dry gel can be vitrified at a low temperature of about 950-1,000 deg.C to obtain colorless transparent quartz glass.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing quartz glass using a sol-gel method, in which alkoxysilane is hydrolyzed with an acid, then a base is completely added thereto, and the mixture is gelled at pH 5 to 6.

The sol-gel method is a non-bath melting glass manufacturing method in which a metal alkoxide is hydrolyzed and gelled, and the resulting dry gel is heated. When Kanahashi alkoxide is used as a starting material, 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 breaks down during the gelling shrinkage process after hydrolysis or during heating of the dry gel.

Although quartz glass is a frequently used and useful material, it is currently manufactured by bath melting at around 2000° C., making it very expensive. Although the sol-gel method is considered promising because it has characteristics such as high purity, low cost, and energy saving, silica glass having a diameter of 5t7n or more has not been obtained. This is because dry gel cannot be produced.

Cracking during the gelation shrinkage process is largely due to the internal structure and drying conditions.

In order to hydrolyze alcoquine 7ran and turn it into a gel,
There are methods using a base such as ammonia as a catalyst and methods using an acid such as hydrochloric acid as a catalyst.

When used as a base catalyst, the hydrolysis rate is slow and the polymerization rate is fast, so the dried gel obtained has a coarse structure with thick particles. Due to the weak binding force between particles, dry gels with a diameter of 2 cnI or more do not emit light.

When an acid is used as a catalyst, the water decomposition rate is fast and the polymerization rate is slow, so grain growth does not occur. It is believed that tetrahydroxysilane forms dimers to tetramers.

The bonding strength is strong, and the cracking appears to be caused by the drying conditions.

Dry gels with a diameter of 7 cm have been announced, but as the gel gets larger, it becomes difficult to control drying.

Therefore, it is currently impossible to produce large-sized dry gels at a high rate.

It has drawbacks such as being stiff, containing air bubbles because it is gelled by heating to 50 to 70°C, and cannot be produced in a short time because of the need to maintain high humidity.

The present invention eliminates the disadvantages of 1). After hydrolysis using an acid as a catalyst, a base is added to increase the polymerization rate.
By gelling at room temperature and then drying in a semi-open air condition at elevated temperature, it is possible to obtain a large, bubble-free dry gel in a high yield and in a short period of time.

Hereinafter, the present invention will be explained in detail based on a case study.

In order to obtain a large dry gel, it can be seen from the example of ammonia and hydrochloric acid that it is advantageous to form a network structure. For this purpose, it is necessary to perform complete hydrolysis with an acid so that the monomer is uniformly dispersed. The polymerization rate depends on temperature, tetrahydroxysilane concentration, and hydrogen ion concentration. The previous two points are being studied, including drying conditions and concentration. We conducted all experiments focusing on hydrogen ion concentration.

Example 1 10 times the molar amount of water relative to ethyl orthosilicate was added as a 0.1 molar hydrochloric acid bath solution, and stirred for 1 hour under water cooling to obtain a uniform transparent solution (hereinafter referred to as bath solution A). While stirring, gradually swirl 0.1 N ammonia water into bath liquid A until the pH is 4,
It was set at 6. When left at room temperature, the colorless and transparent 11 gelled after about 30 minutes. Thereafter, the shrinkage progressed rapidly while extruding all of the bath medium.

Gel is a sword that is cheap even when opened.

After gelling in a polytetrafluoroethylene container with a diameter of 10 m and a height of 5 crn, cover all 20 holes with a diameter of 3 mm, hold at 60°C for 1 day, and gradually raise the temperature to 90°C in a box. trap. Drying at 90°C for 2 days yielded a dry gel with a diameter of 4.5 cm.

Vitrification occurs at 950°C to 1000°C, and colorless and transparent quartz glass is obtained.

Example 2 Gradually drop 01 normal ammonia water into bath liquid A to P H4
, 4, it took #J2 hours for gelation. Thereafter, in the same manner as in Example 1, quartz glass was obtained.

Example: 0.1N ammonia water was gradually added dropwise to bath solution A to pH 5.
When the above procedure was carried out, gelation occurred in several tens of seconds.

The dried gel was colorless and transparent, and silica glass was obtained by sintering.

Example 4 When 0.5N ammonia water was gradually added dropwise to the bath solution A, the solution remained colorless and transparent, and solidification proceeded. After gelation, silica glass was obtained by sintering.

Example 5 Bath liquid hf tetrahydroxysilane d degree 40 cqt%
The mixture was concentrated to 1,000 liters, and gradually poured with 1 normal aqueous ammonia with stirring. As in Example 1, the mixture gelatinized after about 3 minutes at pH 4.6 and shrunk to produce a dry gel with a diameter of 5.0 cm.

Vitrification occurred at 950°C to 1000°C, yielding colorless and transparent quartz glass.

Example 6 After setting the pH to 4.6 in the same manner as in Example 1, gelation was performed in a container with a diameter of 30σ. It was dried at 60° C. for 2 days and at 90° C. for 3 days, and a dried gel with a diameter of 13.5 Crn was prepared. After sintering, quartz glass was obtained.

As described above, according to the present invention, the following effects are exhibited. First, it gels at room temperature, so the circular part does not contain any air bubbles. ``Also, the gelation time can be manipulated.
Dry gel can be prepared in a very short time.

The biggest feature is that it is extremely resistant to cracking during the shrinkage process.
This means that it is easy to prepare large-sized dry gels.

The invention is a very important means in producing stone-glass gold using the sol-gel method.

that's all Applicant: Suwa Kozue Kogo Co., Ltd.

Claims (1)

[Claims] In the production of quartz glass using the sol-gel method, [alkoxysilane is used as a catalyst?] A method for producing quartz glass, which is characterized in that after hydrolysis, a base is added and the pH is adjusted to a range of 3 to 2, and then gelation occurs.