JPS6086036A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To manufacture a quartz glass plate having excellent flatness, in the production of a quartz glass by a sol-gel process, by gelatinizing the raw material sol for a definite time interval in a closed state, and drying and sintering the product. CONSTITUTION:An alkyl silicate (e.g. ethyl silicate) is mixed with an aqueous solution of hydrochloric acid under vigorous agitation, and a specific amount of silica fine powder is dispersed in the resultant homogeneous solution. The pH of the dispersion is adjusted to 3-6 with an aqueous solution of ammonia. The obtained raw material sol is put into a vessel having flat bottom, sealed, and maintained at 0-40 deg.C for >=1 day to effect the gelatinization (formation of the network structure of silica by the dehydrative condensation reaction of tetrahydrosilane). The obtained gel is thermally dried in an opened state, and sintered to obtain a quartz glass plate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses alkyl silicate and finely powdered silica as raw materials in a low-temperature synthesis method of silica glass using a sol-gel method in which PK is adjusted to 3 to 6.
This invention relates to a method of manufacturing with good flatness.

Quartz glass began to be used in crucibles, boards, diffusion furnaces, etc. during the C manufacturing process, and its usefulness was recognized, and with the development of products with fewer hydroxyl groups and better optical uniformity, Silica glass fibers have come to be used for various optical applications, and in particular, quartz glass fibers for optical communications have recently attracted attention.

As described above, quartz glass is used in various fields, and the scope of its use is expanding. However, the manufacturing cost of quartz glass is high, and the high price has become a problem. A sol-gel method has been attempted as a method for manufacturing inexpensive, high-quality quartz glass.

As a method to obtain large-sized quartz glass with good yield using the sol-gel method, ultrafine powdered silica is added to a sol prepared by hydrolyzing alkyl silicate, and the pH is further adjusted to 3 to 6. A
After conditioning, there is a method of drying at 50 to 90°C and sintering. This solution simultaneously solved the problem of cracks during dry gel production and the problems of cracks and cracks during sintering, and it became possible to manufacture fairly large quartz glass (41 nchφ or more) at low cost.

However, when manufacturing large quartz glass, warping occurs during the drying and shrinking process of the gel, and the warping cannot be completely eliminated. Furthermore, even if the drying conditions are precisely controlled and a flat dry gel is produced over a long period of time, there is a strong tendency for warping to occur during sintering.

Even if large quartz glass can be produced, unless it can be made into a shape that can be held in place (for example, a flat plate), its application will be limited to a very small area. Considering that it is used for quartz substrates and boards for industrial use, it is extremely important to obtain quartz glass with good flatness.

The purpose of the present invention is to solve the problem of warpage caused by the conventional sol-gel method, and to produce quartz glass with good flatness, and more specifically, to produce quartz glass that maintains its shape during gelation. did.

Next, an outline of the present invention will be described.

The basic operation of the present invention is to gel the gel in a short time by adjusting the pH to 4 to 5, and then keep it sealed at room temperature for 2 hours.
It is held for ~4 days, and then dried and sintered.

The cause of warping is uneven drying. In a plate-shaped gel, the rate of solvent evaporation differs between the top surface and the bottom surface that is in contact with the container, resulting in partially different shrinkage rates. Furthermore, since a concentration gradient occurs, mass transfer of tetrahydroxysilane as well as the solvent occurs, resulting in partial differences in silica tightness. Sintering the dry gel prepared in this manner does not yield flat quartz glass, and not only warps but also cracks may occur during the drying and sintering process.

The sol whose pH is adjusted to 3 to 3 gels in a short period of time, and then rapidly shrinks while extruding the solvent. Therefore, the gel is kept immersed in the solvent, and there are large differences in the drying speed of the gel.

From a molecular perspective, the process of shrinking and becoming a dry gel after gelation involves a dehydration condensation reaction of tetrahydroxysilane. A silica network structure is formed and becomes denser. Once the polycondensation reaction has progressed to a certain extent and the molecular arrangement has been determined, no mass transfer will occur and shrinkage due to drying and sintering will proceed evenly.

The reaction rate of the dehydration condensation reaction of tetrahydroxysilane is determined by the tetrahydroxysilane concentration, water concentration, hydrogen ion concentration, and temperature. If these factors can be uniformly controlled, the reaction will proceed uniformly. In the sol state, chemical uniformity can be controlled.

Therefore, we propose to keep the sol in closed conditions for a period of time until the network structure is formed, and then fill it with supersaturated steam to prevent the evaporation of the solvent, allowing the polycondensation reaction to proceed uniformly, and then drying and sintering. .

The dry gel prepared based on this method had extremely high flatness and maintained its flatness even after passing the gel. Although the dry gel warped when dried very rapidly, it became flat when sintered.

Example 1 The present invention will be explained in detail based on Examples below.
560 ml of a 0.1 N hydrochloric acid water bath and 440 mA of ethyl silica were vigorously stirred to obtain a colorless and transparent homogeneous solution. Add silica fine powder (jero811ox-
50) After gradually adding 150S' and stirring thoroughly,
Dispersion was performed using ultrasound. Furthermore, a 01N ammonia aqueous solution was added dropwise to adjust the pH to 4.5.
0y was transferred to a flat-bottomed container with an inner diameter of 20 crII and sealed.

When the temperature was maintained at 20° C., it gelled after about 1 hour, and then gradually shrunk while maintaining its flatness. After 2 days, the gel had shrunk by about 10%, and the lid was replaced with a lid with 20 holes of 5 mm in diameter, and the temperature was gradually raised to 60°C and maintained. The subsequent shrinkage proceeded smoothly, and a dry gel with a diameter of 14 ann and very good flatness was obtained.

This dry gel was heated to 125°C at a heating rate of 180°C/hr.
When heated to 0°C, colorless and transparent quartz glass with a diameter of 1 ocrn could be produced. The flatness was extremely good.

Example 2゜The sol prepared in the same manner as in Example 1 was transferred to a sealed container, and
It was kept at ℃ for 4 days. The gel had shrunk by about 10%. Thereafter, drying and sintering were carried out under the same conditions as in Example 1, and a dry gel and quartz glass with very good flatness were obtained.

Example 5 The sol prepared in the same manner as in Example 1 was transferred to a sealed container, and 2D
After holding in 'C for 2 days, the lid was replaced with a lid with 20 holes of 5 mm in diameter. When the temperature was gradually raised to 80° C. and maintained, shrinkage did not proceed uniformly and the obtained dry gel was warped.

However, when this dry gel was vitrified by heating to 1250° C. at a heating rate of 180° C./hr, the warpage was eliminated and silica glass with very good flatness was obtained.

Example 4゜ A sol prepared in the same manner as in Example 1 was prepared with an inner diameter of 5 tyn.

Height 3[]c! The mixture was transferred to a cylindrical container of size N, and left in a sealed container for 2 days. A pinhole was made in the lid and the gel was dried at 60°C to obtain a rod-shaped dry gel that resembled blood powder.

By heating to 1250° C., a rod-shaped quartz glass with a diameter of 2.5 tyn and a length of 10 m was manufactured. It had a similar shape to the inside of the container, and there was no warpage in the axial direction.

As described above, according to the method of the present invention, plate-shaped quartz glass can be easily manufactured in a state with good flatness, so that it can be used as a quartz substrate or board. In addition, since it maintains the shape of the container during gelation, it is very effective in manufacturing rods and cheeps.

that's all Tagan University Suwa Seikosha Co., Ltd.

Claims (3)

[Claims] (1) In the low-temperature synthesis method of quartz glass by the sol-gel method using at least alkyl silicate and ultrafine powdered silica as raw materials, when producing dry gel, the sol whose pH is adjusted to 3 to 6 is sealed in a container and heated to 0°C. A method for producing quartz glass, which comprises maintaining the temperature at ~40°C for at least one day, and then heating and drying it in a semi-open state. (2) The preferred temperature range in a sealed state is 10-25℃
A method for producing quartz glass according to claim 1. (3) The preferred range of time for keeping in a sealed state is 2~
The method for manufacturing quartz glass according to claim 1 or 2, wherein the manufacturing method is 4 days.