JPH0259444A - Production of silica glass - Google Patents

Abstract

PURPOSE:To obtain silica glass not causing cracking or crazing by adding polyvinyl acetate to a solvent contg. furfuryl alcohol, hydrolyzing silicon alkoxide in the solvent, converting the resulting silica sol into gel, drying and sintering the gel. CONSTITUTION:Polyvinyl acetate is added to a solvent (e.g., methanol) contg. furfuryl alcohol and silicon alkoxide having a group such as methyl or ethyl is hydrolyzed in the solvent in the presence of a catalyst, preferably a base catalyst. The resulting silica sol is quickly poured into other vessel and allowed to stand at 0-100 deg.C for several min to several ten days to form silica gel. This gel is allowed to stand at room temp. to 200 deg.C for several hr to several ten days until it is dried and the dry gel is sintered by heating to 1,000-1,400 deg.C at 50-400 deg.C/hr heating rate in a proper atmosphere to obtain silica glass. This silica glass is obtd. at a low cost and can be used in various fields of optics, semiconductor industry, electronic industry, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing silica glass used for optical applications, semiconductor industry, electronic industry, physical and chemical applications, etc.

(Prior art) 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 for optical fibers, photomask substrates for IC manufacturing, TPT substrates, etc. It has been used for many years, and its applications are expanding more and more.

Conventional methods for producing silica glass include a method in which natural quartz is melted in an electric furnace or an oxyhydrogen flame, or a method in which silicon tetrachloride is oxidized and melted at high temperature in an oxyhydrogen flame or a plasma flame. Since the manufacturing process requires high temperatures of 2000℃ or higher, it consumes a large amount of energy, and materials that can withstand such high temperatures are required during manufacturing, and it is difficult to obtain high purity materials, making it economical.
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 represented by the general formula S L (OR)a (R: alkyl group) (in the present invention, 0 containing its polycondensate, for example (R0)ss i. (O31
(OR)z)-・O3i (OR)s, (n-0~8
, R; alkyl group)) is added with water (the pH may be adjusted with an alkaline earth metal) and hydrolyzed to form silica hydrosil (referred to as silica sol in the present invention). At this time, silicon An appropriate alcohol is generally added as a solvent so that the alkoxide and water 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 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 uses a solvent containing furfuryl alcohol as a solvent for silicon alkoxide and polyacetic It is characterized by the addition of vinyl.

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. Furthermore, partially polymerized silicon alkoxides can also be used.

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.

The molecular weight of polyvinyl acetate is not particularly limited in the present invention, but it is selected depending on the solubility in water and solvents and the degree of growth of silica fine particles in the sol. The amount of furfuryl alcohol used as a solvent for silicon alkoxide is not particularly limited in the present invention, but is selected depending on the degree of growth of silica fine particles in the sol.

Solvent components used with (furfuryl) alcohol include alcohols such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, butyl alcohol, ethers such as dimethyl ether, ketones such as acetone and ethyl methyl ketone, At least one type of ester such as ethyl acetate can be used.

The silicon alkoxide, polyvinyl acetate, solvent, and water are thoroughly mixed using a Stark or the like to make the resulting sol as uniform as possible.

Further, ultrasonic waves may be irradiated, and silica fine particles may be added during sol preparation.

The generated sol solution is quickly transferred to another container and allowed to gel. During gelation, it is preferable to seal the container to prevent the solvent from escaping from the generated gel, and the temperature during gelation is preferably 0° C. or higher.

In the drying process, instead of using a lid with holes, the gel is dried and shrunk and solidified in an appropriate atmosphere to form a dry gel.

Thereafter, silica glass is manufactured by sintering using a gel-sol method.

Generally used conditions are used for the gelling step, drying step, and sintering step. For example, each
Leave at 100℃ for a few minutes to several 10 days, leave at room temperature to 200℃ for several hours to several 10 days, 1000 to 140 in an appropriate atmosphere
For example, heating to 0° C. at a heating rate of 50 to 400° C. for 7 hours.

(Function) Although the effects of furfuryl alcohol and polyvinyl acetate are unknown, they contribute to the generation and growth of silica particles in the sol, to the relaxation of stress generated in the gel during the drying process, and to increase the size of the gel. It is thought that it became possible to take shape.

Example 1 Silicon tetramethoxide: furfuryl alcohol = 1
= 1 molar ratio, add methanol in the same amount as furfuryl alcohol and stir, and then add polyvinyl acetate to 100 parts by weight of silicon tetramethoxide.
0 parts by weight was added to form a homogeneous solution. This solution has a concentration of 0.
0.01 mol/1 choline aqueous solution was added in an amount of 4 mol to 1 mol of silicon tetramethoxide and thoroughly mixed to obtain a silica sol.

The obtained sol was placed in a Teflon-coated glass Petri dish with a diameter of 200 m to a depth of 10 days, sealed and gelatinized at room temperature. 60℃ instead of a lid with a gelled afterfill.
The gel was dried for 14 days, and then heated to 170°C for 7 days at 30°C to obtain a dry gel without any cracks or cracks. This dried gel was heated in air to 1300° C. at a rate of 60° C./hour to obtain silica glass without cracks or foaming. This silica glass has no devitrification or bubbles and is of high quality. Further, as a result of analysis, the properties of this silica glass matched those of commercially available silica glass.

Example 2 Silicon tetramethoxide: furfuryl alcohol-t
il molar ratio, add half of methanol to furfuryl alcohol, stir, and add polyvinyl acetate to 100 parts by weight of silicon tetramethoxide.
0 parts by weight was added to form a homogeneous solution. This solution has a concentration of 0.
01 mol/II of choline aqueous solution was added in an amount of 4 mol to 1 mol of silicon tetramethoxide and thoroughly mixed to obtain a silica sol.

Thereafter, the same operation as in Example 1 was performed to obtain silica glass. This silica glass has no devitrification or bubbles and is of high quality. Further, as a result of analysis, the properties of this silica glass matched those of commercially available silica glass.

Comparative Example The same operation as in Example 1 was performed except that furfuryl alcohol was not used as the solvent and only methanol was used. As a result, the gel was prone to cracks and cracks during drying.

(Effects of the Invention) According to the present invention, large-sized silica glass can be easily manufactured by the sol-gel method without causing cracks or cracks. There are basically no restrictions on its size, and its shape is not limited to plate-like ones, but also rod-like and tubular ones, which can be manufactured at a lower cost than in the past.

Claims (1)

[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, at the step of hydrolyzing silicon alkoxide to form silica sol, A method for producing silica glass, characterized in that a solvent containing furfuryl alcohol is used as a solvent for silicon alkoxide, and polyvinyl acetate is added.