JPH0556292B2 - - Google Patents

Description

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

[Prior Art] When producing glass by the sol-gel method, one or more metal alcoholates are
In the sol solution obtained by dissolving in water and alcohol,
Generally employed is a method in which a sol solution is hydrolyzed and gelled at a temperature of room temperature to 80° C. with stirring in addition to an acid or alkali catalyst, and the resulting gel is dried and then calcined.

In such a sol-gel method, bubbles are generated during hydrolysis of the metal alcoholate, and these bubbles are known to have a negative effect on the quality of the glass product. The generation of bubbles is particularly noticeable when the amount of alcohol used is small, but if these bubbles occur during the initial stage of gelation, it may be necessary to remove them by using a spatula or by transferring the sol solution to another container. A method of removing it using means is used.

[Problems to be Solved by the Invention] However, if the above-mentioned method is adopted at the stage when gelation has progressed and the viscosity of the liquid has increased, the uniformity of the liquid will be impaired. The bubbles cannot be completely removed.

However, the generation of bubbles can be reduced to some extent by increasing the amount of alcohol used, but in this case there is a disadvantage that it takes a long time of one week or more to complete gelation.

[Means for Solving the Problems] An object of the present invention is to provide a means for easily removing air bubbles generated during hydrolysis without particularly increasing the amount of alcohol used. Specifically, by carrying out the hydrolysis of the metal alcoholate solution (sol solution) under reduced pressure, the homogeneity of the solution can be maintained at both the early and late stages of the gelation process. The aim is to remove air bubbles and produce high-quality glass.

That is, the present invention is characterized in that, in a method for producing glass by a sol-gel method, at least a part of the hydrolysis of a metal alcoholate sol solution is carried out under reduced pressure.

In the present invention, the metal alcoholate includes:
_Si ( _OCH3 ) ₄ , Si( _OC2H5 ) ₄ , Al(i _{- OC3H7} ) ₃ ,
One or two of Ti(OC ₄ H ₉ ) ₄ , Zr(OC ₂ H ₅ ) ₄ , etc.
More than one species can be used. Furthermore, as the alcohol, any alcohol commonly used in the sol-gel process, such as methanol or ethanol, can be used, and as a catalyst, acids or alkalis commonly used in the art can be used.

According to the present invention, a sol solution obtained by dissolving one or more metal alcoholates in water and alcohol and adding an acid or alkali to the solution is subjected to hydrolysis under reduced pressure. In this case, the reduced pressure conditions do not necessarily need to be maintained throughout the entire period of hydrolysis. As a device for hydrolyzing a sol solution under reduced pressure, for example, a vacuum desiccator, a vacuum furnace, an evaporator, etc. can be used, and as a means for reducing the pressure in these devices, an aspirator,
A vacuum pump or the like is used.

The degree of vacuum of the device for hydrolyzing the sol solution is approximately 10 to 10% when the sol solution is not contained.
The pressure may be 70 mmHg, and the degree of vacuum decreases as the alcohol evaporates when the sol solution is contained, but it is preferably in the range of 150 to 750 mmHg. If the temperature exceeds 750 mmHg, the defoaming effect cannot be expected much, and if the temperature falls below 150 mmHg, components other than the by-product alcohol will evaporate.

[Function] Taking tetramethoxysilane Si(OCH ₃ ) ₄ as an example of a metal alcoholate in the sol-gel method, its hydrolysis reaction is shown by the reaction formula: becomes. As is clear from this reaction formula, tetramethoxysilane produces methanol as a by-product through a hydrolysis reaction, and this methanol causes bubbles generated during the gelation process. In the present invention, since the hydrolysis reaction is carried out under reduced pressure, methanol bubbles generated in the sol solution are successively removed from the solution and substantially do not remain in the solution. Since the by-product alcohol is removed from the system, the time required for gelation can also be shortened.

[Examples] Example 1 A solution was prepared by mixing 20 g of tetramethoxysilane, 23 g of water, 1 g of methanol, and 0.01 g of hydrochloric acid. On the other hand, the vacuum desiccator was depressurized with an aspirator to bring the pressure inside the system to 26 mmHg, and the above solution was placed therein and stirred for 30 minutes while operating the aspirator. After 30 minutes, stirring was stopped, and gelation was continued at room temperature for 5 hours to obtain a wet gel containing no air bubbles.

After heating this wet gel at 60℃ for 24 hours,
Remove the gel from the container and heat it at 40°C, 60°C, 80°C.
The mixture was heated at 100°C and 120°C for 12 hours, and then naturally cooled to obtain a dry gel. Next, this dry gel was heated to 1100 °C at a heating rate of 10 °C/hour.
After raising the temperature to .degree. C., the glass was kept at this temperature for 3 hours to obtain a transparent glass without bubbles or cracks.

For comparison, when the above solution was left at room temperature under atmospheric pressure, it took 10 hours to complete gelation, and the resulting wet gel contained many air bubbles. Furthermore, if the operation of the aspirator was continued without stopping after 30 minutes, gelation could be completed in one hour.

Example 2 20 g of tetraethoxysilane, 25 g of water, 5 g of ethanol, and 0.01 g of hydrochloric acid were mixed and the same procedure as in Example 1 was performed to obtain a transparent glass free of bubbles and cracks.

Example 3 Solution A was prepared by mixing 20 g of tetraethoxysilane, 20 g of water, 10 g of methanol, and 0.01 g of hydrochloric acid.
Further, 2 g of aluminum isopropoxide, 2 g of zirconium tetraethylate, 2 g of titanium tetrabutoxide, 2 g of water, and 10 g of methanol were mixed and stirred for 3 hours to prepare solution B. Mix the above solution A and solution B without adding the solution.
To the evaporator adjusted to 24mmHg,
The above mixture was added and stirred under reduced pressure for 20 minutes.

Next, the above solution was placed in a shearley and left to stand at room temperature for 5 hours to obtain a bubble-free wet gel. By drying and firing this gel under the same conditions as in Example 1, a transparent glass free of bubbles and cracks could be obtained.

[Effect of the invention] As demonstrated in Example 1 above, when the metal alcoholate is gelled by the usual method,
Numerous bubbles form in the wet gel, which are dried and
Although there are many bubbles in fired glass, according to the method of the present invention, the bubbles are removed before gelation occurs, so by drying and firing the glass, glass containing almost no bubbles can be obtained. be able to.

Furthermore, in the normal method, until the gelation is completed,
Although it takes a long time of 10 hours or more, according to the method of the present invention, the time required for gelation can be shortened to about 1 hour.

Claims (1)

[Claims] 1. A method for producing glass by a sol-gel method, characterized in that at least a part of the hydrolysis of a metal alcoholate sol solution is carried out under reduced pressure.