JPS61168542A - Production of quartz glass - Google Patents

Abstract

PURPOSE:Dried gel obtained from an alkyl silicate and ultrafine silica powder is sintered in a closed vessel in an appropriate temperature zone for hours to give a quartz glass of low water content and high mechanical strength at elevated temperatures. CONSTITUTION:In the low-temperature synthesis of quartz glass through the sol-gel method where a dried gel obtained at least from an alkyl silicate and an ultrafine silica powder, the sintering temperature is kept in a range from 900-1,300 deg.C over 20hr, preferably the temperature range is divided into several zones or the temperature is gradually raised. Thus, the water formed by dehydrative polymerization is sufficiently diffused to give quartz glass of low water content.

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.

[Conventional technology]

Quartz glass has come to be used in crucibles, board diffusion furnaces, etc. during the IC manufacturing process, and its usefulness has been recognized, and with the development of products with fewer hydroxyl groups and better optical uniformity, various types of quartz glass have been used. In particular, quartz glass 7-eye glass for optical communication has been attracting attention recently.

As described above, quartz glass is used in various fields, and its range of applications is expanding. However, the manufacturing cost of quartz glass is high, and its high price is a problem. A sol-gel method has been attempted as a method for manufacturing inexpensive, high-quality quartz glass.

As a method of obtaining 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 further P
There is a method of adjusting H to 3 to 6, then drying and sintering at 50 to 90°C. This solution simultaneously solves the problem of cracking during dry gel production and the problem of cracks and cracks during sintering.
can now be manufactured at low cost.

In order to produce high-quality quartz glass with few hydroxyl groups and no bubbles, it is very effective to sinter dry gel in a closed container made of a heat-resistant material with a dense structure.

〔problem〕

However, with the conventional technology that simply raises the temperature in a closed container and sinters it, the limit is to reduce the water content of quartz glass to 1100 ppm, and it is impossible to achieve a water content of 300 ppm in fused silica. It affects mechanical strength and requires lower moisture content when used at high temperatures, such as in thin layer transistor (TPT) substrates. Chlorination, which replaces hydroxyl groups with chlorine and lowers the apparent moisture content, does not improve mechanical strength at high temperatures.

The present invention is intended to solve these problems, and its purpose is to reduce the water content (number of hydroxyl groups) of quartz glass and increase its mechanical strength in a high temperature range.

〔means〕

The method for producing quartz glass of the present invention is a low-temperature synthesis method of quartz glass using at least an alkyl silicate and ultrafine powder silica as raw materials, and a sol-gel method in which dry gel is sintered in a closed container made of a heat-resistant material with a dense structure. , 90
It is characterized by being maintained in a temperature range of 0 to 130" for 20 hours or more.

It is more effective to maintain the temperature not at a single temperature, but to divide it into several stages, or to raise the temperature gradually at a low rate.

[Effect]

Sintering of a dry gel made from alkyl silicate and ultrafine powdered silica proceeds in a temperature range of 900 to 1300°C. Unlike ordinary sintering of metal or ceramic powders, water generation occurs in the same temperature range because it involves dehydration polymerization of hydroxyl groups. Therefore, in order to reduce the water content of quartz glass, it is necessary to diffuse the generated water molecules, and it is necessary to hold them for a long time before sintering is completed6.
Even if it is held for a long time at 900° C. or lower, at which sintering does not start, or at 1,300° C. or higher, at which surface seizing ends, there is no effect on lowering the water content. In order to gradually diffuse the water generated while sintering progresses, the temperature should be 900 to 130.
It is effective to keep the temperature in the 0°C temperature range for a long time in several stages, or to gradually raise the temperature.

〔Example〕

The relationship between holding temperature/holding time and moisture content, and the relationship between mechanical strength in a high temperature range will be explained using examples. Also,
Some examples will also be given of cases in which the mixing ratio of alkyl silicate and ultrafine powder silica is changed.

Example 1 Ethyl silica) 4.41 and 005N aqueous hydrochloric acid solution 561 were vigorously stirred to obtain a colorless and transparent homogeneous solution. There, ultrafine powdered silica (Aerosil OX-50
) 9 was gradually added to 1.5 and stirred thoroughly.

While keeping this sol at 20℃, 28KHz ultrasonic waves were applied for 2 hours.
After irradiation for a period of time and further applying a centrifugal force of 1300 G for 10 minutes, the sample was passed through a 1 μm filter.

The obtained highly homogeneous sol was adjusted to pHtz with CL1 normal ammonia water, and then placed in a polypropylene container (width 2
5 (mX 25Ci #LX height 10cm) K was injected in an amount to give a depth of 1 s. Cover with a lid with an opening ratio of 1% and heat at 60°C.
After drying for 0 days, -side 1Bcrrts thickness α7
A CIl+ dry gel was successfully prepared.

Dry gel was placed in a quartz container with a sealed structure, heated to 1100°C at a rate of 90°C/hr, and heated to 110°C.
It was held at 0°C for 50 hours. Thereafter, the temperature was raised to 1300° C. at a rate of 90° C./hr and maintained for 1 hour to make it completely transparent. The obtained quartz glass is I Z5x 12.5x
The size of α5cIIL was 700 ppm. The supporting ratio of ultrafine powder silica in quartz glass is 5
It is 5chi.

Polished to thickness 1.21K, flatness 5μm or less, 1
When placed in a diffusion furnace at 150° C. for 5 hours, the flatness changed to 30 μm. When fused silica of the same size was subjected to the same heat treatment, the flatness was 10.
It was less than μm.

Comparative Example 1 A dry gel prepared in the same manner as in Example 1 was placed in a quartz container, heated to 1300°C at a rate of 90°C/hr, and held for 1 hour, where it became completely transparent. The moisture content of the obtained quartz glass was 1200 ppm. After polishing, it was placed in a diffusion furnace at 1150°C for 5 hours.
The flatness changed from less than 5μ wind to 60μ wind.

Comparative Example 2 The temperature was raised using the same temperature program as Comparative Example 1, but
In the temperature range of ~1000℃, C1z-containing atmosphere, 1000℃
In the temperature range of ~1100℃, 02 containing atmosphere, 1100
In the temperature formula of ~1300°C, sintering was performed in a He atmosphere. The moisture content was measured by IR (infrared absorption spectrum) and was found to be Oppm.

Thickness: 1.2 Dragon, polished to a flatness of 5 μm or less, 4
When the film was stood in a diffusion furnace at 150° C. for ycs, the flatness changed to 60 μm.

Example 2 A dry gel prepared in the same manner as in Example 1 was placed in a quartz container, heated to 1100°C at a rate of 90°C/hr, and held at 1100°C for 80 hours.

Thereafter, the temperature was raised to 1300°C at a rate of 90°C/hr and maintained for 1 hour to make it completely transparent. The moisture content of the obtained quartz glass was 500 ppm.

When the same polishing and heat treatment btS as in Example 1 were carried out, the flatness changed to 20 μm.

Example 3 A dry gel prepared in the same manner as in Example 1 was placed in a quartz container, heated to 11001.1 at a rate of 90°C/hr, and held at 1100°C for 80 hours.

Once cooled to room temperature, the translucent dry gel was taken out of the quartz container and heated again at a rate of 90°C/hr for 13
The temperature was raised to 00° C. and maintained for 1 hour to make it completely transparent. The moisture content of the obtained quartz glass was 5 G Oppm.

When the same polishing and heat treatment as in Example 1 were performed, the flatness changed to 20 μm.

Example 4 A dry gel prepared in the same manner as in Example 1 was placed in a quartz container, heated at a rate of 90°C/hr, and heated to 1050°C.
℃ for 20 hours, 1100℃ for 40 hours, 1150℃ for 2 hours
Each was held for 0 hours. Thereafter, the temperature was raised to 1300°C at a rate of 90°C/hr and maintained for 1 hour to make it completely transparent. The moisture content of the obtained quartz glass is S Q Op
The pm value was almost the same as that of fused silica.

When the same polishing and heat treatment as in Example 1 were performed, the flatness was 10 μm or less.

Example 5 A dry gel prepared in the same manner as in Example 1 was placed in a quartz container, and the temperature was raised to 1000°C at a rate of 90°C/hr. Then 10 at a rate of 2°C/hr up to 1200°C.
The temperature was increased over 0 hours. 13 again at a rate of 90°C/hr.
The temperature was raised to 00° C. and maintained for 1 hour to make it completely transparent. The moisture content of the obtained quartz glass was 300 ppm.

When the same polishing and heat treatment as in Example 1 were performed, the flatness was 10 μm or less.

Example 6 Ethyl silica) 4.41 and 1.8 μm of a 0-05N aqueous hydrochloric acid solution were vigorously stirred to obtain a colorless and transparent homogeneous solution.

Ultrafine powder silica (Aerosil 0X-50)
9 was gradually added to 15' and thoroughly stirred. This sol was irradiated with 28KHz ultrasonic waves for 2 hours while keeping it at 20℃, and then subjected to a centrifugal force of 1300G for 10 minutes.
It was passed through a filter of m.

The resulting highly homogeneous sol was adjusted to pH 4.2 with α1 normal ammonia water, and then poured into a polypropylene container (width 25 cIIL x height 10 cIrL) in an amount to give a depth of 1α. Close the lid with an opening ratio of 1%, and
When dried at 0°C for 10 days, -side 18a1 thickness α
A 7σ dry gel was produced.

A dry gel gold container was placed in a quartz container with a sealed structure, and the temperature was raised at a rate of 90°C/hr, and held at 950°C for 20 hours, 1000°C for 40 hours, and 1050°C for 20 hours. Then 130 at a rate of 90 °C/hr
The temperature was raised to 0°C and the mixture became completely transparent. The obtained quartz glass had a size of IZ5X12.5Xα5 (lffl) and a water content of q500 ppm.The supporting ratio of ultrafine powder silica in the quartz glass was 50%.

When the same polishing and heat treatment as in Example 1 were performed, the 7 lasotoneness changed to 20 μm.

Example 7 Ethyl silica) 4.4 l, Q, 05N aqueous hydrochloric acid solution s, and 41 were vigorously stirred to obtain a colorless and transparent homogeneous solution. There, ultrafine powdered silica (Aerosil 0X-50
) 2.8 units were gradually added and stirred thoroughly. Hereinafter, the same processing as in Example 1 and Example 6 is performed, and -side 18c is
rIL1 thickness 17cr! A dry gel of L was prepared.

Dry gel was placed in a quartz container with a sealed structure, heated at a rate of 90℃/hr, and heated to 1100℃ for 20 minutes.
The temperature was maintained at 1150°C for 40 hours and at 1200°C for 20 hours. Then 1300 at a rate of 90℃/hr
The temperature was raised to 'C' and maintained for 3 hours to make it completely transparent.

The obtained quartz glass had a size of 12.5 x 12.5 x α5 (m) and a water content of 1100 pp. The supporting ratio of ultrafine powder silica in the quartz glass was 70%.

When the same polishing and heat treatment as in Example 1 were performed, the flatness was 5 μm or less.

As mentioned above, the optimum holding temperature varies depending on the content of ultrafine silica powder. Furthermore, the higher the content of ultrafine silica powder, the lower the water content of quartz glass tends to be. This is shown in Figure 1.

The content of ultrafine silica powder is 50% ■, 55% is ■, 70
% is ■. However, in both cases 900 to 130
If the holding time at 0°C is less than 20 hours, the moisture content will increase rapidly.

The thermal strength at 1150°C is shown in Figure 2.

The change in flatness is desirably 50 μm or less, and from this point of view, it is necessary to hold the film for 20 hours or more.

〔Effect of the invention〕

As described above, according to the present invention, there is provided a low-temperature synthesis method of quartz glass using at least alkyl silicate and ultrafine powder silica as raw materials, using a sol-gel method in which dry gel is sintered in a closed container made of a heat-resistant material with a dense structure. In, 90
Holding the glass in the temperature range of 0 to 1300°C for 20 hours or more has the effect of reducing the water content of the quartz glass and increasing its mechanical strength in the high temperature range.

Although the explanation was given using a flat plate as an example, the same effect can be obtained with a tube or a rond, and it can be used as a furnace tube, significantly expanding the range of applications of synthetic quartz.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the change in moisture content with respect to holding time when holding is carried out using an optimal program in the temperature range of 900 to 1300°C. Since the moisture content varies depending on the proportion of ultrafine powdered silica in the quartz glass, five examples are shown: 1...50% 2...55chi 5...70% Figure 2 shows 12.5x I Z5xα12cIIL FIG. 3 is a diagram showing the relationship between moisture content and flatness when a quartz glass plate of 100 is placed in a diffusion furnace at 1150° C. for 5 hours. That's all for now.

Claims (1)

[Scope of Claims] 1) A low-temperature synthesis method of quartz glass using at least an alkyl silicate and ultrafine powder silica as raw materials, using a sol-gel method in which a dry gel is sintered in a closed container made of a heat-resistant material with a dense structure. 20 in the temperature range of ~1300℃
A method for producing quartz glass characterized by holding it for a period of time or more. 2) The method for producing quartz glass according to claim 1, wherein the temperature to be maintained is not a single temperature but divided into several stages, or the temperature is gradually increased at a low rate.