JPH0259441A - Production of silica glass - Google Patents

Abstract

PURPOSE:To easily obtain large-sized silica glass free from cracks and crazes by using a specified solvent and adding hydroxyalkylcellulose in a sol preparing stage when silica glass is produced by a sol-gel process. CONSTITUTION:Silicon alkoxide is hydrolyzed to prepare silica sol, this sol is converted into gel and dried and the resulting dry gel is sintered to produce silica glass. In the hydrolyzing stage, a solvent contg. morpholine and/or N- ethylmorpholine is used as a solvent for the silicon alkoxide and hydroxyalkylcellulose is added. The solvent used in combination with the morpholine and/or N-ethylmorpholine may be alcohols, ethers, ketones or esters.

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 uses are rapidly expanding.

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. Target,
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 i (OR) 4 (R: alkyl group) (including its polycondensate in the present invention. For example, (RO)3St・(O31
(OR)z) , ・O3i (OR)s, (n=0~
8. R: Alkyl group)) to water (pH with alkali or acid)
may be adjusted) and hydrolyzed to produce silica hydrosil (referred to as silica sol in the present invention). At this time, an appropriate alcohol is generally added as a solvent so that the silicon 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 fractures are likely to occur in the gel, making it difficult to produce a monolithic large-sized dry gel without cracks and fractures 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 provides a method for producing silica glass using a sol-gel method, in which a solvent containing morpholine and/or N-ethylmorpholine is used as a solvent for silicon alkoxide during sol preparation. It is characterized by the addition of hydroxyalkyl cellulose.

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.

As the hydroxyalkylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxybutylcellulose, hydroxybutylmethylcellulose, etc. can be used.

The molecular weight of these hydroxyalkylcelluloses is not particularly limited in the present invention, but 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 morpholine and/or N-ethylmorpholine 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 fine silica particles in the sol. Solvent components used with morpholine and/or N-ethylmorpholine include alcohols such as methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, and butyl alcohol, ethers such as dimethyl ether, acetone, and ethyl methyl ketone. At least one kind of ketones such as esters such as ethyl acetate and esters such as ethyl acetate can be used.

Silica glass is produced by transferring the silica sol prepared as described above to a container such as a petri dish, gelling it by keeping it at room temperature to 70°C, then drying it at a temperature above room temperature for several weeks to form a dry gel, and then using a known method. , e.g. 1000-1 in air
It is obtained by raising the temperature to 400°C and sintering it.

(Function) Although the details of why gel cracking that occurs during the drying process is prevented by using a solvent containing morpholine and/or N-ethylmorpholine are unknown, morpholine and/or N-ethylmorpholine It is involved in the production and growth control of silica fine particles in the sol together with hydroxyalkyl cellulose, and also has a boiling point of 128 to 130.
°C (morpholine), 138 °C (N-ethylmorpholine)
It is thought that this is because the evaporation rate during the drying process is lower than that of water and other solvents such as alcohol, contributing to the relaxation of stress generated in the gel, making it possible to make the gel larger. It will be done.

Example 0.01M choline aqueous solution 47g 1 methyl alcohol 67g
g and 21 g of morpholine were mixed, and 2 g of hydroxypropyl cellulose (average molecular weight: 300,000) was added and dissolved. 99 g of tetramethylsiloxane was added to the resulting solution.
was added slowly and mixed thoroughly to obtain a silica sol. This was placed in a Teflon-coated Petri dish with a diameter of 200 mm, sealed with aluminum foil, and gelatinized at room temperature. After that, a hole was made in the lid and it was dried for 2 weeks in a constant temperature oven at 60℃, and then 1
The temperature was raised to 70° C. and dried for one day to obtain a dry gel. The dry gel thus obtained had no cracks or breaks. When the obtained dry gel was heated and sintered in air to 1300°C, transparent silica glass without cracks or cracks was obtained.

(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)

[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 morpholine and/or N-ethylmorpholine is used as a solvent for silicon alkoxide, and hydroxyalkyl cellulose is added.