JPH01138138A - Production of silica glass - Google Patents

Abstract

PURPOSE:To readily obtain a large-sized silica glass free from cracks and/or fissures, by gelling a silica sol produced by hydrolysis of a silicone alkoxide in the presence of polyacrylamide followed by drying and sintering. CONSTITUTION:A solution prepared by adding an alcohol (e.g., methyl alcohol) to a solution formed by dissolving polyacrylamide in water containing a base is incorporated with a silicone alkoxide of the formula Si(OR)4 (R is alkyl) followed by hydrolysis to produce a silica sol. Thence, this silica sol is transferred to a vessel, being gelled at room temperature - 70 deg.C followed by drying for several weeks at temperatures equal to or higher than room temperature to form a dry gel. This gel is then sintered at 1,000-1,400 deg.C in air, thus obtaining the objective silica glass.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention produces silica glass used for optics, semiconductor industry, electronic industry, physics and chemistry, etc.

(Prior technology) Silica glass has excellent heat resistance, corrosion resistance, and optical properties, so it is an important material indispensable for semiconductor manufacturing, and is also used in optical fibers, photomask substrates for IC manufacturing, TPT substrates, etc. It has been used for many years, and its applications are being expanded more and more.

Conventional methods for manufacturing silica glass include melting natural quartz in an electric furnace or oxyhydrogen flame, or oxidizing and melting silicon tetrachloride at high temperature in an oxyhydrogen flame or plasma flame. Since the manufacturing process requires high temperatures of 2000°C or higher, it consumes a large amount of labor and energy, and materials that can withstand such high temperatures are required during manufacturing, and it is difficult to obtain high-purity materials, making it economically difficult. Target 1
There are some quality issues.

On the other hand, in recent years, a method of synthesizing silica glass at low temperature called the sol-gel method has been attracting attention. The outline will be briefly described below.

Silicon alkoxide (in the present invention, its polycondensate is included) represented by the general formula S i (OR) a (R: alkyl group) 2 For example, (RO)zS dish・(O3i
(OR)21-・O3i(OR)! , (n=o~8
．． R: alkyl group) is added with water (pH may be adjusted with an alkali or acid) and hydrolyzed to form silica hydrosil (referred to as silica sol in the present invention). At this time, silicon alkoxide and water An appropriate alcohol is generally added as a solvent to form a homogeneous system. This silica sol is gelled by standing still, increasing the temperature, adding a gelling agent, etc. Thereafter, the gel is evaporated to dryness to obtain a dry silica gel. Silica glass is obtained by sintering this dried gel in a suitable atmosphere.

(Problems to be Solved by the Invention) However, there are still unresolved problems in the production of silica glass by the sol-gel method.

In particular, during the process of drying the gel, cracks and cracks are likely to occur in the gel, making it difficult to produce a monolithic large-sized dried gel without any cracks or cracks with a good yield.

The present invention provides a method for manufacturing silica glass that does not cause cracks or cracks.

(Means for Solving the Problems) The present invention is characterized in that polyacrylamide is added during sol preparation in a method for producing silica glass by a sol-gel method.

In the present invention, there are no particular restrictions on the alkyl group of silicon alkoxide, but from the viewpoint of ease of hydrolysis and gelation time, silicon alkoxide having a methyl group, ethyl group, propyl group, or butyl group is used. is preferred. When adding water or a mixed solution of water and alcohol to silicon alkoxide and hydrolyzing it to generate silica sol, polyacrylamide is added in advance to the water or mixed solution of water and alcohol and uniformly dissolved.

What is the molecular weight of the polyacrylamide to be added?

The polyacrylamide is selected by adding it to water or a mixed solution of water and alcohol in advance and dissolving it uniformly.

The amount of polyacrylamide added can be adjusted as appropriate depending on the type of silicon alkoxide used and the rate of hydrolysis.

The catalyst added with water is not particularly limited, such as bases and acids, but
From the viewpoint of gelation time and ease of sintering of the resulting dry gel, a base gives more preferable results. There are no particular restrictions on the alcohol added together with water, but from the viewpoint of solubility in both water and alkoxide.

Preferably, alcohols such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol are used.

Silica glass is obtained by transferring the silica sol prepared as described above to a container such as a Petri dish, keeping it at room temperature to 70°C to gel it, and then drying it at a temperature above room temperature for several weeks to form a dry gel.

Further known methods 2, eg too in air.

It is obtained by sintering at a temperature of ~1400°C.

(Effect) Although the details of the cause of the effect of adding polyacrylamide are unknown, it is due to the control of the formation of silica particles in the sol, the bonding between these silica particles in the gel, and the generation of silica particles in the gel during the drying process. It is thought that this contributed to the relaxation of the stress caused by the gel, making it possible to increase the size of the gel.

Example 1 3 moles of water and 0.0005 moles of choline were mixed, 7.6 g of polyacrylamide was added thereto, sufficiently dissolved, and then mixed with 3 moles of methyl alcohol. The resulting solution was mixed with 1 mol of silicon methoxide (Si(OCHz)
n) and mixed thoroughly to obtain a silica sol. This was placed in a Teflon-coated glass Petri dish with a diameter of 150 ns, sealed with aluminum foil, and gelatinized at room temperature. Thereafter, a hole was made in the lid, and the gel was dried for two weeks in a constant temperature bath at 50°C, and then transferred to a constant temperature bath at 120°C and dried for one day, to obtain a dried gel having a diameter of about 120+++m.

The bulk density of the dry gel thus obtained was approximately 0°6 g/c.
J, and there were no cranks or cracks.

When the resulting gel was heated and sintered in air to 1200°C, it had a diameter of approximately 801mm. A transparent silica glass with a thickness of 51 mm and no cracks or cracks was obtained. As a result of analysis, this silica glass matched that of the silica glass.

Example 2 Polyacrylamide 3. Og to 3 moles of water.

After sufficiently dissolving in 0.0005 mol of choline.

Mixed with 3 moles of methyl alcohol.

Thereafter, the same operation as in Example 1 was performed to obtain a dry gel. The dried gel obtained had no cracks or cracks.

Example 3 15.2 g of polyacrylamide in 3 moles of water.

After sufficiently dissolving in o, ooos moles of choline.

Mixed with 3 moles of methyl alcohol. Example 1 below
A dry gel was obtained in the same manner as above. The dried gel obtained had no cracks or cracks.

(Effects of the Invention) According to the present invention, large-sized silica glass without cranks or cracks can be easily produced by the Solcale method. There are basically no restrictions on its size, and it can be manufactured in any shape such as a plate, rod, or tube.

Claims (1)

[Scope of Claims] 1. In a method for producing silica glass in which silicon alkoxide is hydrolyzed to form silica sol, this is gelled, dried to form a dry gel, and then sintered, silicon alkoxide is hydrolyzed. A method for producing silica glass, characterized in that polyacrylamide is added at the step of preparing a silica sol.