JPS61168540A - Production of quartz glass - Google Patents

Abstract

PURPOSE:To enable the production of a large-sized quartz glass having high quality at a low cost, by detecting the temperature in a drying vessel, thereby controlling the rate of drying of a gel produced from an alkyl silicate and ultrafine silica powder. CONSTITUTION:Ultrafine silica powder is added to a sol produced by the hydrolysis of an alkyl silicate, and the pH of the mixture is properly adjusted to obtain a gel. The gel is dried and sintered to produce quartz glass. In the above process, the dried state of the gel is detected by the humidity in the drying vessel, and the drying rate is controlled by controlling the heating temperature, rate of air flow, etc. The end point of the drying of the gel is also judged by the humidity. The cracking of the dry gel during production and sintering can be prevented, and a large-sized quartz glass can be produced in high yield at a low cost.

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 and board diffusion furnaces during the IC manufacturing process, and its usefulness has been recognized.Furthermore, with the development of glass with fewer hydroxyl groups and with good optical uniformity, various types of quartz glass have been used. Recently, silica glass fibers have been attracting attention, especially for optical communications.

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 the high price has become a problem. A sol-gel method has been attempted as a method for manufacturing inexpensive, high-quality quartz glass.

As a method for obtaining large-sized quartz glass with good yield using the sol-gel method, ultrafine powdered silica is added completely to a sol prepared by hydrolyzing alkyl silicate, dispersed by ultrasonic waves, etc., and further P
After adjusting K to 3 to 6, drying and sintering at 50 to 90°C is a method that simultaneously solves the problem of cracking during the production of O dry gel and the problem of cracking and crack formation during sintering. Yes, quite large quartz glass (41 nchφ or more)
can now be manufactured at low cost.

A common method for producing a dry gel is to pour the sol into a drying container, cover the container with a pinhole lid, and gradually remove the solvent in a dryer. A method of detecting and controlling the dry state based on the size or weight of the gel is shown.

〔problem〕

However, conventional techniques that check dryness based on size and weight are not only difficult to measure, but also cannot detect short-term changes, making them not very effective methods.

In addition, there is almost no change in the size or weight of the gel at the stage when it is finished drying, and if the gel is misjudged when the drying is finished and a sudden change in temperature is applied, the gel will crack. The conventional technology has a problem in that it cannot provide any effective information regarding the completion of gel drying.

Therefore, the present invention is intended to solve these problems, and its purpose is to be able to sequentially detect the dry state of the gel,
By providing a method that provides clear information regarding the completion of drying, the yield of dry gel production can be significantly improved.

[hands]

The method for producing quartz glass of the present invention is a method for producing quartz glass by a sol-gel method using at least alkyl silicate and ultrafine powder silica as raw materials, in which the dry state of the gel is detected by the humidity in the drying container, and the drying rate is [Operation] The drying speed is determined by the heating temperature Φ air humidity and air speed. The heating temperature and air velocity can be controlled by the set temperature and exhaust volume of the dryer. The dry state can be detected by checking the humidity inside the drying container, which provides useful information when adjusting the set temperature and exhaust volume.◇Easy to measure and highly sensitive.

In addition, since the humidity drops rapidly at the end of gel drying,
It is easy to judge when drying is complete.

〔Example〕

FIG. 1 shows changes over time in each parameter when the gel was dried under the conditions described in Example 1. ■Cracking of the gel can be prevented by keeping the humidity high during the first stage of drying. The end point of drying is also clear. ■ is the length ratio of the gel, and ■ is the weight ratio. ■ and ■ indicate that even if drastic changes in drying conditions occur as shown in Example 2 and below,
doesn't change much. Furthermore, it is difficult to determine when drying is complete.

The present invention will be explained in detail below.

Example 1 4.4 J of ethyl silicate and 3.61 J of a 0.05N aqueous hydrochloric acid solution were vigorously stirred to obtain a colorless and transparent homogeneous solution.

Ultrafine powder silica (Aeroail 0X-50)
1.5 kg'i was gradually added and thoroughly stirred. This sol was irradiated with ultrasonic waves of 28 arsenic for 2 hours while being kept at 20° C., and centrifugal force of 1500 Q was further applied for 10 minutes.

The resulting highly homogeneous sol was adjusted to pH 4.2 with 0.1 N ammonia water, and then placed in a polypropylene drying container (width 20 cIn x 20 crrL x height 10 crrL).
The amount was injected into 20 cells to a depth of 1 crrL. Opening ratio 1
The containers were placed in a dryer with a lid on, and a humidity sensor (made of ceramics) was fixed in one of the containers at a depth of 7 m to 5 m.

The temperature inside the dryer was set at 60° C., and the exhaust volume was adjusted so that the humidity inside the drying container was maintained at 80% or higher. If drying was continued under the same conditions, the humidity began to decrease from the 7th day and fell below 20% on the 100th day. When I took the drying container out of the dryer, I found that the gel had finished drying.
There were no cracks caused by the rapid temperature drop. Furthermore, no cracking of the gel was observed in all 20 containers.

The dry gel had a side of 14 CIFl, a thickness of 0.7 cm, and a weight of 12'Of.

When the dry gel thus produced at a yield of 100 cm was heated to 51,300° C. using an appropriate heating program, colorless and transparent quartz glass was produced. The size is 10
The weight of X10X0.5cit was 110t.

Example 2 After starting drying in the same manner as in Example 1, when the temperature was raised to 80°C on the second day, the humidity decreased to 50°C and
It dropped to less than 10% on the first day. When removed from the dryer, the dry gel production yield was 20%.

On the other hand, when the temperature was raised to 80°C and the exhaust volume was reduced so that the humidity was 80% or higher, the humidity became 10°C or lower on the 8th day. Dry gel production yield is 80%
was.

Example 3 After drying was started in the same manner as in Example 1, the exhaust volume was gradually increased from the 5th day while being careful not to cause a sudden decrease in humidity. On the 8th day, the humidity fell below 20 degrees, so we stopped drying and the dry gel production yield was 90 degrees.
%was.

Example 4 The opening ratio i of the drying container was reduced to 0.5%, and the opening ratio i of the drying container was reduced to 0.5%.
When drying was started in the same manner as above, the humidity began to decrease from the 10th day and reached 20-1 or less on the 15th day.

When the drying container was removed from the dryer, the gel had completely dried and there was no cracking due to the sudden temperature drop.

The dry gel production yield was 100%.

Although the explanation has been given using a flat plate as an example, the same effect can be obtained even if the gel shape is a tube or a rod. The present invention can also be applied to large-sized drying containers that dry many gels at the same time.

〔Effect of the invention〕

As described above, according to the present invention, a sol made of at least alkyl silicate and ultrafine powder silica is used.
In a method for manufacturing quartz glass using the gel method, the drying state of the gel is detected by the humidity in the drying container and the drying rate is controlled, which has the effect of significantly improving the production yield of dry gel. In addition, since the completion of drying is clearly indicated, cracks due to insufficient drying and excessive drying time can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing changes in the gel during the drying process. ■Humidity inside the drying container ■Gel length ratio ■Gel weight ratio

Claims (1)

[Claims] 1) In a method for producing quartz glass by a sol-gel method using at least alkyl silicate and ultrafine powder silica as raw materials, the drying state of the gel is detected by the humidity in the drying container, and the drying rate is determined. A method for producing quartz glass characterized by controlling. 2) The method for producing quartz glass according to claim 1, wherein completion of drying of the gel is also confirmed by checking the humidity in the drying container.