JPS61236617A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To obtain a high-quality quartz glass having no bubble in it by carrying out the sintering of dried gel in the atmosphere of He in a low temperature synthesis of quartz glass by a sol-gel method. CONSTITUTION:The dried gel is made from a sol whose main raw material is alkylsilicate and ultrafine powder silica. This dried gel is put into a furnace in He atmosphere and is sintered at about 900-1,400 deg.C temperature range. Even though the closed holes are formed at the time of sintering, the holes contract and vanish, because the gas present in said holes is He and He has a large permeability to gases. By this method, the quartz glass having good transparency, no bubble in it and optically high-quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing quartz glass by a sol-gel method.

[Summary of the invention]

The present invention is a method for producing quartz glass by the sol-gel method, in which the dry gel is sintered in a helium atmosphere, thereby eliminating the generation of air bubbles in the quartz glass.

[Conventional technology]

Silica glass has recently been attracting attention as a material for glass fibers for optical communications and substrates for photomasks, but its high manufacturing cost has become a problem. The sol-gel method has been attempted as a method for producing high-quality quartz glass at low cost.

As a method for manufacturing large-sized quartz glass with good yield using the sol-gel method, ultrafine powdered silica is added to a sol obtained by hydrolyzing alkyl silicate, dispersed by ultrasonic waves, etc., and the pH is further adjusted to 3 to 2. After that, dry at 50-90℃,
There is a method of sintering. This solution simultaneously solves the problem of cracking during dry gel production and the problem of cracking and cracking during sintering.

Quartz rods and tubes with an outer diameter of 5 cm and a length of 75 crn,
A 41-inch square quartz plate can now be manufactured at low cost.

[Problems and Objects to be Solved by the Invention] However, the above-mentioned prior art has the problem that air bubbles are generated when the dry gel becomes transparent, so it cannot be used for optical purposes. The present invention is intended to solve these problems, and its purpose is to provide a method for producing optically high-quality quartz glass without bubbles.

[Failure to solve the problem]

The method for producing quartz glass of the present invention is characterized in that a dry gel is sintered in a helium atmosphere in a low-temperature synthesis method of quartz glass by a sol-gel method using at least an alkyl silicate and ultrafine powdered silica as raw materials.

[For production]

A dry gel produced using alkyl silicate and ultrafine powder silica as raw materials undergoes sintering in a temperature range of 900 to 1400°C, and close pores are formed. If the gas inside the closed pore is helium, the gas permeability is high, so the closed pore shrinks and disappears.

In the case of gases other than helium, the closed pores will expand and become bubbles.

If the atmosphere during the formation of closed pores is helium, the gas inside the closed pores will be helium, and silica glass without bubbles can be produced.

〔Example〕

The sintering method will be explained with reference to comparative examples. Here are some examples of cases in which the mixing ratio of alkyl silicate and ultrafine silica powder is changed.

Example 1゜ethyl silica) 4.41 and 005N hydrochloric acid aqueous solution 5
-6t was vigorously stirred to obtain a colorless and transparent homogeneous solution. There, ultrafine powdered silica (Aθrosil OX-50
) 1.5 Kji was gradually added and stirred thoroughly.

While keeping this sol at 20℃, 28KH2 ultrasonic waves were applied to it for 2 hours.
After irradiation for a time and further applying a centrifugal force of 1500 ( ) for 10 minutes, the sample was passed through a 1 μm filter.

The resulting highly homogeneous sol was adjusted to pH 4.2 with 0.1 molar aqueous ammonia, and then placed in a polyglopylene fissure vessel (
Width 20 sub x 20 crn x height 10 cm) and depth 1
The amount of cIn was injected. Close the lid with an aperture ratio of 1, and
After drying at ℃ for 7 days, a dry gel with -side 14/'ff + thickness 07 crn was prepared.

The dry gel was placed in a gas exchange furnace, and the temperature was raised to 900°C at a rate of 60°C/hr. Pure helium gas 'Q starts to flow into the furnace from 900°C at a flow rate of 0.5 t/h, and is heated to 1400°C at a rate of 30°C/h, r.
It was held at 1400°C for 1 hour. Planarization and transparency have been completed, and the obtained quartz glass is 10x10xo, 5.
), and there were no bubbles with a diameter of 10 μm or more.

Since it is difficult to observe using microcasting for particles smaller than 10 μm, we optically polished them to a thickness of 20,000 yen and then evaluated them using a condensing lamp. The transparency was very good, and there were no light spots due to inclusions.

Comparative Example 1゜A dry gel prepared in the same manner as in Example 1 was placed in a gas replacement furnace, and the same heat treatment was performed without introducing helium gas.

Many bubbles with a diameter of 20 μm or more were generated in the obtained quartz glass.

Comparative Example 2 A dry gel prepared in the same manner as in Example 1 was placed in a gas replacement furnace and heated to 900°C at a rate of 60°C/hr. The temperature was raised to 1300° C. at a rate of 30° C./hr without introducing helium gas, and the temperature was maintained at 1300° C. for 1 FjFF. Flattening and transparency were completed, but the diameter was 1
A few bubbles of about 0 μm were observed.

After optically polishing it to a thickness of 2m111, it was evaluated using a condensing lamp, and the overall transparency was not good. A relatively large spot of light was still visible.

Example 2 A dry gel prepared in the same manner as in Example 1 was placed in a gas exchange furnace, and the temperature was raised to 1000°C at a rate of 60°C/hr. Pure helium gas started to flow into the furnace from 1000℃ at a flow rate of 0.5t/-, and the flow rate was 125t/hr at a rate of 30℃/hr.
The temperature was raised to 0°C and held at 1250°C for 1 hour. The almost transparent sintered body was transferred to a box-shaped furnace and heated at 1400℃ in the atmosphere.
It was held for 1 hour. Flattening and transparency were completed, and no bubbles with a diameter of 10 μm or more were present.

Since it is difficult to observe with a microscope at a thickness of 10 μm or less, the film was optically polished to a thickness of 2 mm and then evaluated using a condensing lamp. The transparency was very good, and there were no light spots due to inclusions. Also, Example 10
There was almost no difference between it and quartz glass.

Comparative Example 5 A dry gel tabulated in the same manner as in Example 1 was placed in a gas exchange furnace and heated to 1150° C. with a reed at a rate of 60° C./hr. 0.5 t of pure helium gas from 1150℃ /
It started flowing into the furnace at a flow rate of =+, the temperature was raised to 1250°C 1 at a rate of 30°C/hr, and the temperature was maintained at 1250°C for 1 hour. The sintered body, which had become almost transparent, was transferred to a box-shaped furnace and maintained at 1400° C. for 1 hour in the atmosphere. Bubbles with a diameter of about 20 μm were generated in the obtained quartz glass.

Comparative Example 4 A dry gel prepared in the same manner as in Example 1 was placed in a gas replacement furnace, and the temperature was raised to 1000°C at a rate of 60°C/hr. Pure helium gas started to flow into the furnace at a flow rate of 0.517 m from 1000°C, and the flow rate increased to 11 m at a rate of 30°C/hr.
The temperature was raised to 50°C. The white opaque sintered body was transferred to a box furnace and held at 1400° C. for 1 hour in the atmosphere. Bubbles with a diameter of about 20 μm were generated in the obtained quartz glass.

Example 6゜Ethyl silica) 4.41 and 005N hydrochloric acid aqueous solution 1
．． 81 was stirred vigorously to obtain a colorless and transparent homogeneous solution. 0.5 kg of ultrafine powdered silica was gradually added thereto and thoroughly stirred. 28KHz while keeping this sol at 20℃
Ultrasonic waves were applied for 2 hours, and centrifugal force of 1500G was applied for 1 hour.
After 0 minutes, it was passed through a 1 μm filter.

The resulting highly homogeneous sol was adjusted to pH 4.2 with 01N ammonia water, and then poured into a polyglobylene container (width 20 crn x 20 crn x height 10 cm) in an amount to a depth of 1 crn. Close the lid with an opening ratio of 1 inch.

After drying at 60° C. for 7 days, a dry gel with a negative side of 14ffi and a thickness of 0.7 crn was produced.

The dry gel was placed in a gas exchange furnace, and the temperature was raised to 900°C at a rate of 60°C/hr. Pure helium gas started flowing into the furnace at a flow rate of 0.5 l/im from 900°C.
The temperature was raised at 1250°C 1 at a rate of 60°C/hr, and 1250°C
It was kept at ℃ for 1 hour. Planarization and transparency were completed, and the obtained quartz glass had a size of 10×10×O, 5 crn. There were no bubbles with a diameter of 10 μm or more.

After optically polishing it to a thickness of 2B, it was evaluated using a condensing lamp, and the transparency was extremely good. Furthermore, no light spots were observed.

Example 4 Ethyl silicate 441 and 005 normal hydrochloric acid aqueous solution 5.4
) was stirred vigorously to obtain a colorless and transparent homogeneous solution. 2.8 kg of ultrafine powdered silica was gradually added thereto and thoroughly stirred. The same treatments as in Examples 1 and 5 were carried out to produce dry gels with a negative side of 14 crn and a thickness of 0.7 crn.

The dry gel was placed in a gas exchange furnace and the temperature was raised to 1100°C at a rate of 60°C/hr. Pure helium gas at 1100°C began to flow into the furnace at a flow rate of o, 5t7 = r,
The temperature was raised to 1400°C at a rate of 1°C/hr and held at 1400°C for 1 hour. Planarization and transparency were completed, and the obtained quartz glass had a size of 1 oxioxo and 5 crn. There were no bubbles with a diameter of 10 μm or more. 'After optically polishing to a thickness of 2w+1, the transparency was found to be extremely good when evaluated using a condensing lamp. I wore it, and I couldn't see any light spots.

〔Effect of the invention〕

As described above, according to the present invention, air bubbles are eliminated by sintering dry gel in a helium atmosphere in the low-temperature joining method of quartz glass using a sol-gel method using at least alkyl silicate and ultrafine powder silica as raw materials. It is possible to produce optically high-quality silica glass that does not exist before.

As mentioned in the examples, depending on the content of ultrafine silica powder,
The temperature at which closed pores form differs slightly.

When a helium atmosphere is applied in the temperature range of 900 to 1400°C, all dry gels have a temperature of 1.2. be effective.

Although the Heisei era was used as an example, the same effect can be obtained with tubes or rods. Possible applications include quartz substrates for industrial O-masks and support tubes for 51m fibers.

that's all

Claims (1)

[Claims] 1) Production of quartz glass characterized by sintering dry gel in a helium atmosphere in a low-temperature synthesis method of quartz glass by a sol-gel method using at least alkyl silicate and ultrafine powder silica as raw materials. Method. 2) Temperature range for helium atmosphere is 900-1400℃
A method for manufacturing quartz glass according to claim 1, characterized in that: