JPS6186429A - Glass manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing glass, and more particularly to a method for producing glass by a sol-gel method using a metal alkoxide as a raw material.

[Conventional technology]

Currently, methods for producing optical fiber preforms include the 'VAD method, in which glass particles such as 5scz4 are passed through a flame and deposited on a target, and the resulting glass porous body is sintered to form a glass lump. The mainstream method is to obtain This is an excellent method for obtaining high-purity porous glass at a relatively low cost. However, since this method is a gas phase reaction, it has the disadvantage that the substances that can be used as additives are limited to those that can be gasified.

Therefore, in recent years, as a method to compensate for this drawback, metal alkoxides mainly composed of 81 are hydrolyzed to obtain silica gel or silica gel containing additive elements, and after drying the silica gel, a process such as making it non-porous is performed to make transparent glass. How to obtain it is being actively researched.

For example, St such as silicon tetramethoxide
After thoroughly stirring and mixing the alkoxide with ethanol, water is added and further stirred for hydrolysis. At this time, it is preferable to add a pH adjuster such as ammonia to the water. Particles begin to precipitate with the start of the hydrolysis reaction, and the reaction solution is transferred to a container coated with silicone on the inside, covered with aluminum foil or the like to prolong the drying time, and placed in a constant temperature bath at, for example, 60°C. By slowly drying the sol solution, the sol solution is gelled and the gel is dried. The gel shrinks as it dries, and drying is usually completed after several days.

A method is already known in which the gel thus obtained is taken out and subjected to a non-porous treatment such as heating in an oxygen-containing He 2 atmosphere to turn it into transparent glass.

This so-called sol-gel method can produce alkoxides for many metal elements, such as B, Gs, A
I, Sb, Ti, Zr, Sn, Y, Sr
, Pb, CB, and other various elements can be easily added.

[Problem that the invention seeks to solve]

However, the above method has the disadvantage that the gel tends to crack during the drying or sintering process. One of the causes of gel cracking during drying is the generation of air bubbles.

Bubbles may be generated when or after the sol gels. This seems to occur more easily when the rate of alkoxide hydrolysis reaction is increased by reducing the amount of alcohol in the sol solution or increasing the pH.

When bubbles occur, distortion occurs around them, and disc-shaped cracks tend to form around the bubbles.

These cracks grow as the gel dries and the gel breaks.

Therefore, in order to eliminate the drawback of gel cracking, there is a need to establish a method for preventing the generation of bubbles.

[Problem that the invention seeks to solve]

The present invention was made in view of the current situation, and was based on the idea that the generation of air bubbles could be prevented by degassing the sol liquid.

That is, the present invention uses at least one of the raw materials as an alkoxide, obtains a sol solution, gels the sol solution, dries the gel, and sinters the dried gel to produce a glass lump. Provided is a method for producing glass, characterized in that degassing is carried out under a reduced pressure of 1 Torr or more and less than normal pressure.

In a preferred embodiment of the present invention, the pressure during degassing in the above method is lower than the vapor pressure of the sol liquid.

Furthermore, as another preferred embodiment, in the above method, the pressure at which the sol liquid is gelled is set at a pressure higher than the vapor pressure of the sol liquid.

As the alkoxide of the present invention, for example, day! ,B,G
o, P, kl, 8b, Ti, Zr, Sn, Y, Fb
At least one selected from the group consisting of b and CS
Alkoxides of certain elements are preferred, and for example, methoxides, ethoxides, propoxides, butoxides, etc. of the above elements can be used.

In order to obtain a sol solution from a raw material that still contains at least one alkoxide, a normal hydrolysis reaction etc. may be used.
For example, alcohol and water may be mixed to a suitable concentration for the reaction.

The alcohol is appropriately selected from methanol, ethanol, propatool, butanol, and the like. I7 However, the method of the present invention is not limited to this method, and the method of the present invention can be applied to a sol obtained by any method.

It has been proposed in Japanese Patent Publication No. 5B-167436 to subject the sol liquid to a degassing treatment at a pressure of [L I Torr or less, but the present invention degassing the sol liquid at a pressure of I Tar or more and less than normal pressure. It is based on finding something desirable to do.

According to our research, since the sol boils at about several + TOrr, it is usually sufficient to carry out such deaeration treatment at a pressure about the vapor pressure of the sol. However, if the degassing is carried out at a pressure slightly lower than the vapor pressure, the deaeration time can be shortened. The vapor pressure of the sol liquid varies depending on the composition of the raw material, but is approximately several tens of T Or r . Therefore, degassing is I
It is desirable to carry out the process at a pressure of about Torr to several tens of Torr, but even higher pressures are effective as long as they are lower than normal pressure. At this time, by adding vibration, the deaeration effect can be slightly enhanced.

It is technically extremely difficult to reduce the pressure to 0.1 Torr or less because the sol liquid boils violently and the pressure increases. It is difficult and unnecessary to achieve a pressure higher than 0.1 Torr (I Torr), and it is not necessary. Therefore, deaeration is carried out at a pressure of I Torr or more and less than normal pressure, particularly preferably at a pressure of 20 to 60 Torr, or In particular, it is desirable to carry out the process at the vapor pressure of the sol liquid or at a pressure slightly lower than that.

Next, when the sol gels, the pressure needs to be higher than the vapor pressure of the sol so that the sol does not boil. Otherwise, the gel will turn into a gel while it is about to boil, and a gel of the desired shape will not be obtained. The pressure during this gelation may be higher than normal pressure, but it is meaningless to set the pressure higher than normal pressure.

The sol liquid after the deaeration treatment is gelled by a known technique, the gel is dried, and the dried gel is sintered to obtain a transparent glass lump.

〔Example〕

The present invention will be explained below by giving examples.

Example 1 Silicon tetramethoxide 9.5f and ethanol &5
Mix f with a magnetic stirrer and add 13%
Water with 3 drops of ammonia water9. After adding Of and further mixing, the mixture was poured into four test tubes at the 5th minute mark. The test tube had a diameter of 12 cm and a length of 105 cm, and had silicone coated on its inner surface.

Two of these were allowed to gel as they were. The remaining 02 pieces are 6
The sol liquid was degassed at a boiling pressure of about 0 Torr, and then gelled at normal pressure. Both of the tubes that were not degassed contained air bubbles, and both of the tubes that were degassed contained no air bubbles.

Each of the four test tubes was lightly capped with aluminum foil and placed in a constant temperature bath at 60°C. After 7 days the gel was almost dry. The ones that were not degassed were both cracked. Both of the degassed bottles did not crack.

Example 2 Next, silicon tetramethoxide 957 and ethanol a02 were mixed using a magnetic stirrer, and 1
! Water 907 containing 3 drops of 1-thiammonium water was added and further mixed, and the mixture was placed into four test tubes similar to those in Example 1 at the 5th minute mark.

Two of these were allowed to gel as they were. Two leftovers 6
The sol liquid was degassed at a boiling pressure of about 0 Torr, and then gelled at normal pressure. Both of the tubes that were not degassed contained air bubbles, and both of the tubes that were degassed contained no air bubbles.

Each of the four test tubes was lightly wrapped with aluminum foil and placed in a constant temperature bath at 60°C. After 7 days the gel was almost dry. The ones that were not degassed were both cracked. Both of the degassed bottles did not crack.

Example 3 Silicon tetramethoxide 9.59 and ethanol 11
．． Mix 59 with a magnetic stirrer and add 1
5. Water with 5 drops of thiammonia added9. After adding Of and further mixing, the mixture was placed into four test tubes similar to those in Example 1 at the 5th minute mark.

Two of these were allowed to gel as they were. The remaining two are 6
The sol liquid was degassed at a boiling pressure of about 0 Torr, and then gelled at normal pressure. One of the tubes that had not been degassed contained bubbles, and both of the tubes that had been deaerated contained no bubbles.

Each of the four test tubes was lightly capped with aluminum foil and placed in a constant temperature bath at 60°C. After 7 days the gel was almost dry. None of the gels were cracked, but one that was not degassed contained air bubbles within the gel.

The six degassed gels were sintered at a temperature of 1300°C,
A transparent glass was obtained.

Comparative Example 1 When nothing was put into the vacuum container and the vacuum pump was used, the pressure reached about 10-' Torr in a few minutes.

Next, a sol solution with the same composition as in Example 3 was placed in the vacuum container described above and pulled with a vacuum pump, resulting in 1. OTorr.
It began to boil violently at a certain pressure, and it was not possible to reduce the pressure below this level.

Next, the vacuum container containing this sol liquid was cooled to -10°C and pulled with a vacuum pump, but at this temperature, the pressure was 20 Torr.
r It boiled violently at 5 degrees.

In the above experiments, 60 Torr and 20 T
orr is a pressure approximately equal to the vapor pressure of the sol liquid at room temperature and −10° C., and therefore it is very difficult to reduce the pressure to less than I Torr .

〔Effect of the invention〕

According to the present invention, it is possible to easily obtain a gel that does not contain air bubbles and therefore does not crack during drying.

Claims (4)

[Claims] (1) In the method of producing a glass lump by using at least one of the raw materials as an alkoxide, obtaining a sol solution, gelling the sol solution, drying the gel, and sintering the dried gel, the sol solution is heated to 1 Torr. As described above, the method for producing glass is characterized in that the degassing treatment is carried out under reduced pressure below normal pressure. (2) The alkoxide is Si, B, Ge, P, Al
, Sb, Ti, Zr, Sn, Y, Pb and Cs. (3) The method for manufacturing glass according to claim (1), wherein the pressure at which the sol liquid gels is higher than the vapor pressure of the sol liquid. (4) The method for producing glass according to claim (1), wherein the pressure during the degassing treatment is lower than the vapor pressure of the sol liquid.