JPH02217323A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To reduce OH group content and prevent bubbles and foreign materials from contaminating quartz glass by hydrolyzing an alkoxysilane, converting the resultant sol into a wet gel, then treating the gel with an aqueous solution of HCl, drying and calcining the treated gel. CONSTITUTION:An alkoxysilane (e.g. tetramethoxysilane) is hydrolyzed to provide a sol, which is then converted into a wet gel. The resultant gel is subsequently treated with a 0.01-12 N aqueous solution of HCl in an amount of about 2 pts.vol. based on 1 pt.vol. wet gel at ambient temperature to 60 deg.C for >=1hr, then dried at 50-70 deg.C for about 10 days and calcined at 1000-1400 deg.C to afford quartz glass with <=50ppm OH group content.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a method for producing quartz glass, and in particular, the OH group content is 50 pp- or less and there are no bubbles or foreign substances, so it can be used for optical glass, optical fiber, The present invention relates to a method for manufacturing silica glass, which is useful for single crystal pulling crucibles, semiconductor diffusion furnaces, etc., by a sol-gel method.

[Prior art 1] A method for producing quartz glass is a method in which silica sol is produced by hydrolyzing alkoxysilane, and this sol is gelled, dried, and sintered to obtain quartz glass (Japanese Patent Publication No. 59
This method is known as the sol-gel method, and according to this method, silicon compounds such as silicon tetrachloride are The Oq method involves hydrolyzing with a hydrogen flame to create silica and directly melting and vitrifying it on a carrier, and the soot method involves depositing soot to form a porous silica base material, which is then melted and sintered to create quartz glass. It is also known that quartz glass can be obtained at a lower cost.

However, since the silica glass obtained by this sol-gel method has a high content of hydroxyl groups, it is inconvenient as a product. Various methods have been proposed to control this OH group content. ) a method of adjusting the particle size of silica fine particles in a suspension of a mixture of an acidic hydrolyzed solution of alkoxysilane and silica fine particles and/or a mixing ratio with the acidic hydrolyzed liquid; 2) a method of adjusting sintering conditions; 3) A method of contacting with a gas such as C12, 5OC12 during heat treatment, 4) A method of contacting a wet gel with a liquid or gas containing water to replace alkoxy groups in the gel with hydroxyl groups,
Methods such as heating or reacting with a base are known.

[Problems to be Solved by the Invention] However, in the above-described method l), increasing the particle size of colloidal silica increases the pore closing temperature during sintering and increases the dehydration rate. Although the OH group content of the particles decreases, in this case, even if the particle size is increased to about 3,000 particles, the OH group concentration remains at 3,000 particles.
It is said that the limit is to reduce the OH group concentration to 00 PPM, and it is not possible to reduce the OH group concentration further than this, and if the mixing ratio of colloidal particles is increased, the pore closing temperature during sintering can be increased. Therefore, although the OH group content can be lowered, the lower limit of the concentration is set at 300 ppm even with this method. Next, in method 2), if the holding temperature is kept below the pore-closing temperature for a long time and if the vacuum is used, the dehydration rate becomes faster, so the OH group value can be further reduced, but the lower limit is still about 150 ppm. However, it is still considered to be insufficient for reducing OH groups.

In addition, in the method 3) described above, the OH group content is reduced to 50 ppm.
The CI2 used here can be:
, 5OII:12 and the like are corrosive and highly toxic, there are disadvantages in that the materials for the furnace material are limited, it takes time and effort, and the equipment investment is large. Using this method, it is possible to obtain quartz glass that does not substantially contain OH groups, but such special OH removal method is necessary.
A sol-gel method for freeing OH groups without performing group treatment has not been reported, nor has a method for reducing the OH group content to 50 ppm or less, and as described in 4) above.
Regarding the method described above, the OH group content cannot be reduced by heat treatment alone, and when a base is used, it remains inside the glass, resulting in a problem that the physical properties of the resulting quartz glass are adversely affected.

[Means for Solving the Problems] The present invention relates to a method for producing quartz glass that overcomes these disadvantages, and involves forming a sol obtained by hydrolyzing alkoxysilane into a wet gel, and then adding hydrogen chloride to the sol. After treatment with a solution, it is dried and sintered to have an OH group content of 50p.
This method is characterized by obtaining quartz glass having a particle diameter of pm or less.

That is, the present inventors conducted various studies on how to obtain quartz glass having an OH group content of 50 ppm or less by the sol-gel method. Afterwards, they discovered that by treating this gel with a hydrogen chloride solution, drying it, and sintering it, silica glass with a 0 group content of 50 ppm or less could be obtained. Proceeding with research, this hydrogen chloride solution was found to be 0.0
The concentration should be 1N or more, preferably 1N or more, and it was confirmed that the higher the concentration, the lower the OH group content, and that appropriate treatment time and temperature should be used for the treatment method. The present invention was completed.

This will be explained in further detail below.

[Function] The present invention relates to a method for producing quartz glass by the sol-gel method, which involves hydrolyzing alkoxysilane to make a sol, making it a wet gel, and then drying and sintering this gel. This step may be performed using a conventionally known method.

Therefore, the alkoxysilane used as the starting material here may be tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, methoxytriethoxysilane, dimethoxyjethoxysilane, or trimethoxyethoxysilane. From the viewpoint of hydrolytic reactivity, availability, and price, tetramethoxysilane or tetraethoxysilane may be used.

The hydrolysis of this alkoxysilane is alkoxysilane 1
2 to 30 moles of water, an acidic catalyst such as hydrochloric acid or sulfuric acid, or a basic catalyst such as ammonia water 0.
1 to 10 mol and 0 to 5 mol under atmospheric pressure or under pressure in the presence of 0 to 30 mol of an alcohol such as methanol, ethanol, propatool, butanol added as necessary.
This hydrolysis can be carried out by stirring at 0°C, and transparent, translucent, or opaque silica sol can be obtained, but in order to form this silica sol into a wet gel, heating and pH adjustment are required.

If it is left sealed at room temperature, it will be obtained as a wet gel.

In order to obtain high quality quartz glass, the starting material used here is preferably one of high purity such as purified distillate or semiconductor grade.

In the method of the present invention, the silica wet gel thus obtained is treated with an aqueous hydrogen chloride solution, then dried and sintered to form quartz glass.The method using tetramethoxysilane as a starting material will be explained below. do.

Tetramethoxysilane as a raw material is hydrolyzed by adding methanol, an aqueous hydrogen chloride solution or aqueous ammonia to produce a silica sol, and this sol is subjected to temperature or pH adjustment to form a wet gel.

This wet gel can then be placed in a container made of polyethylene, polypropylene, tetrafluoroethylene, etc., which is a material that will not be contaminated by an aqueous hydrogen chloride solution, and treated with an aqueous hydrogen chloride solution, but this wet gel is a three-dimensional network. If it is incomplete, cracks will occur during subsequent operations, so this is a hydrogen chloride aqueous solution 1! It is best to leave it for a certain period of time in a sealed state at room temperature before washing, but if you leave it for too long, the shrinkage will progress and the subsequent diffusion of the hydrogen chloride aqueous solution will be slow, which will reduce the effectiveness of the OH removal treatment. , the pores shrink and H5i-OH! 5t-O
Since the conversion of R into a siloxane bond is incomplete, this may be left for about two days.

To treat this wet gel with an aqueous hydrogen chloride solution, it is sufficient to add about 2 parts by volume of a 0.01 to 12 N aqueous hydrogen chloride solution to 1 part by volume of this wet gel, but syneresis of the wet gel has already occurred in this container. There may be syneresis water generated by this process, which may or may not be removed.Addition of this aqueous hydrogen chloride solution will reduce the OH groups contained in this wet gel, resulting in The advantage is that the target hydroxyl group content in the quartz glass is 50 pp or less.

This means that the hydroxyl and alkoxy groups in the wet gel are MSt-O
H+ HO-5i'iii! → Mi5i-0-5i Mi+H
20゜mi 5l-OH+ RO-5lia→E 5l-0
This reaction is thought to be due to the siloxane bonds being formed by -5iW + ROH for 8 times, but this reaction also proceeds in the drying step after treatment with an aqueous hydrogen chloride solution, resulting in a dry gel with fewer hydroxyl groups after the drying step.

The aqueous hydrogen chloride solution used here may be commercially available hydrochloric acid (35% by weight) diluted with water;
It may be used in the range of 1N to 12N, but in order to reduce the hydroxyl group and prevent the generation of bubbles, it is better to use a higher concentration.For example, if a 12N aqueous hydrogen chloride solution is used, The hydroxyl group in quartz glass can be reduced to IOPPM or less, and depending on conditions, it can be reduced to Oppm. In addition, if this treatment temperature is too low, the progress of the above-mentioned reaction will be slow, and if it is set higher than 60°C, the volatilization of HCl will become a problem. If the reaction time is too short, the hydrogen chloride aqueous solution will not diffuse sufficiently into the gel, and the effect of reducing OH groups cannot be expected. Therefore, it is better to make the reaction time longer; However, since the diffusion situation of the aqueous hydrogen chloride solution varies depending on the type of alkoxysilane, the reaction conditions, the shape of the gel, etc., it is best to determine the treatment time experimentally for each individual case.

For wet gel treated in this way, the hydrogen chloride aqueous solution added here is discarded, a pinhole is made in the lid of this container, and
If it is gradually dried at about 50 to 70°C, it can be made into a dry gel for about 10 days.
The desired quartz glass (can be obtained by heat treatment at ~1,400°C and sintering, but this glass has a hydroxyl group content of 50 ppIm or less and does not generate bubbles, so it can be used as is. It can be used in various directions.

In addition, the quartz glass synthesized by treating the wet gel with an aqueous hydrogen chloride solution has a temperature of 2,000 ml at normal pressure.
No foaming occurred even after treatment at 0° C. for 10 minutes.

〔Example] Next, examples of the present invention will be given.

Example 1 Tetramethoxysilane and 1) H-10 aqueous ammonia and methanol were mixed in a ratio of 1:4:4C molar ratio) and hydrolyzed, and the obtained silica sol was mixed with 40IIIlφx
The mixture was placed in a 5 hmL polypropylene container to a height of ioms, and a wet gel was formed at room temperature in a sealed container.

Next, 12 N, 6 N, and 2 N are added to 1 volume part of this wet gel.
Add 3 parts by volume of 1N hydrogen chloride aqueous solution,
After treating at 60°C for 2 days, the hydrogen chloride aqueous solution was removed, a pinhole with a diameter of 1 + u+ was made in the lid of this container, and it was dried at 60°C for 10 days to form a dry gel. When fired at ℃, quartz glass was obtained, and the hydroxyl group content of this material was measured.
Depending on the concentration of the hydrogen chloride aqueous solution used above, the results shown in Table 1 were obtained, and when observed with an optical microscope, it was found that No air bubbles were detected, confirming that these were high quality bulk glasses.

Table 1 Example 2 Tetramethoxysilane, ethanol, NH4OH.

Water 1:25:1. [Mixed at a ratio of l:24 (mole ratio) and hydrolyzed to make a spherical silica sol, and at the same time, 4 moles of a 0.01 N aqueous hydrogen chloride solution and 2.7 moles of ethanol were added to 1 mole of tetramethoxysilane. , which was hydrolyzed to produce a transparent hydrolyzed sol.

Next, this spherical silica sol was concentrated until the silica concentration was 36% by weight, and the transparent hydrolyzed sol obtained above was mixed therewith at a volume ratio of 1:0.6. (2) The mixture was placed in a tetrafluoroethylene container with a diameter of 50 mm + L so that the height was 20 mm, and a wet gel was formed at room temperature while the container was closed.

Next, 3 parts by volume of 12N, 6N, 2N, and 1N hydrogen chloride aqueous solutions were added to 1 part by volume of this wet gel, and the mixture was heated at 25°C.
After treating for 5 days, the hydrogen chloride aqueous solution was removed, a hole with a diameter of 1 mm was made in the lid of this container, and the gel was dried at 60°C for 10 days, and the gel was fired at 1,400°C to form quartz glass. When the hydroxyl group content of this product was measured, the results shown in Table 2 were obtained depending on the concentration of the hydrogen chloride aqueous solution used above, and when this product was observed with an optical microscope, both of these were found to be No air bubbles were detected, confirming that the quartz glass was of high quality.

Table 2 [Effects of the Invention] The present invention relates to a method for producing quartz glass in which a wet gel obtained by the sol-gel method is treated with an aqueous hydrogen chloride solution, then dried and sintered. For example, the hydroxyl groups and alkoxy groups in the wet gel are converted into siloxane bonds by treatment with an aqueous hydrogen chloride solution, so the resulting quartz glass has a hydroxyl group content of 50 ppm or less,
This provides an industrial advantage in that no bubbles are generated.

Claims (1)

[Claims] 1. The sol obtained by hydrolyzing alkoxysilane is turned into a wet gel, which is treated with an aqueous hydrogen chloride solution and then dried.
A method for producing quartz glass, which comprises sintering to obtain quartz glass having an OH group content of 50 ppm or less.