JPH0520364B2 - - Google Patents

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 SiCl ₄ are passed through a flame and deposited on a target, and the resulting glass porous body is sintered to form a glass lump. The method of obtaining is becoming mainstream. 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, Si
A method of obtaining transparent glass by hydrolyzing a metal alkoxide mainly containing silica gel or silica gel containing additive elements, drying the silica gel, and performing a nonporous treatment, etc. is being actively researched.

For example, after a Si alkoxide such as silicon tetramethoxide is thoroughly stirred and mixed with ethanol, water is added and further stirred to hydrolyze it. At this time, it is preferable to add a pH adjuster such as ammonia to the water. As the hydrolysis reaction begins, particles begin to separate out, 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 porosity treatment such as heating in an oxygen-containing He atmosphere to turn it into transparent glass.

This so-called sol-gel method has the advantage that alkoxides can be prepared for many metal elements, and various substances can be easily added.

[Problem that the invention seeks to solve]

However, the above method also has the disadvantage that the gel tends to crack during the sintering process. This cracking during sintering is thought to be due to the small pore diameter of the gel, which causes closed pores to form before water, alcohol, etc. escape during sintering. After closed pores are formed, when they are further heated, the pressure inside the closed pores increases,
Cracks occur. On the other hand, gels with large pore diameters that are difficult to form closed pores are easily sintered. Therefore, in order to stably obtain a glass lump, it is necessary to stably obtain a gel with a large pore size.

The pore diameter can be controlled by controlling the bulk density of the gel, but conventionally it has been difficult to control the bulk density of the gel. The bulk density of a gel is determined by the degree of shrinkage during drying, but the shrinkage force is due to surface tension, and the degree of shrinkage is approximately
It is determined by the particle size and the surface tension of the dispersion medium. Conventionally, it has been difficult to control the bulk density of gels, firstly because it is not possible to control the particle size of the constituent particles, and secondly because it is not possible to select an arbitrary dispersion medium.

Regarding particle size, when particles are generated by hydrolyzing a highly concentrated solution, particles of various sizes are produced, making it difficult to control the particle size. However, by hydrolyzing a dilute solution under appropriate conditions to create a sol, and then drying the sol using a method that makes it easy to control the particle size of the resulting particles, such as spray drying, it is possible to create a narrow particle size distribution for any particle size. particles are obtained. (Reference Stober et al.
COlloid Interface Science, vol. 26 1968
P.62; Ceramics vol.16 NO.10 1981 P.851)
In the past, it was not possible to control the particle size of the particles that make up a gel because if a dilute solution was hydrolyzed, a sol could be formed but it would not gel, so a highly concentrated solution had to be used. be.

As for the dispersion medium, conventionally it was not possible to select anything other than a mixture of water and alcohol. Moreover, if the conditions for hydrolysis are constant, the ratio of water to alcohol is also fixed. Furthermore, since the dispersion medium contains a large amount of alcohol, the freeze-drying method, which is a drying method that allows easy control of bulk density, requires extremely low temperatures and is not practical.

The present invention eliminates the drawbacks of the conventional sol-gel method detailed above, allows easy bulk density control, and stably obtains easily sinterable gels with large pore diameters.
It is an object of the present invention to provide a method for manufacturing glass.

[Means for solving problems]

In view of the current situation, the present inventors conducted intensive research and found that by separating the process of making particles and the process of gelling and drying, the bulk density can be easily controlled and an easily sinterable gel can be stably obtained. We have come up with the idea that the above problems can be solved by doing this.

That is, the present invention provides a method for producing glass by hydrolyzing a metal alkoxide, in which particles obtained by hydrolysis are once separated from a dispersion medium for said hydrolysis, and then mixed with an arbitrary dispersion medium. Provided is a method for producing glass, characterized in that the glass is subsequently dried to obtain a dry gel, which is then subjected to treatment including nonporous treatment.

As a particularly preferred embodiment of the present invention, in the above, the metal alkoxide is Si, B, Ge, P, Al,
Examples include a method for producing a glass that is an alkoxide of at least one element selected from the group consisting of Sb, Ti, Zr, Sn, Y, Pb, and Cs.

In another particularly preferred embodiment of the present invention, B, Ge,
P, Al, Sb, Ti, Zr, Sn, Y, Sr, Pb and
The above-mentioned method for producing glass may also be mentioned, in which at least one element selected from the group consisting of Cs or a compound of the element is added and the element is contained in the glass produced thereby.

In the glass manufacturing method of the present invention, in the step of creating particles, the particle size can be easily controlled without considering the concentration required for gelation, for example, by hydrolyzing a dilute solution and spray drying. Particles are produced by methods such as The particles thus obtained are added to any liquid (dispersion medium) having an appropriate surface tension, and then gradually dried. In this way, an easily sinterable dry gel having a large pore size can be obtained with little variation. Furthermore, by using water as the liquid, freeze-drying, which allows easy control of bulk density, can be performed even at a relatively high temperature of -10°C or higher. Furthermore, by adding an appropriate substance to the dispersion medium, it is possible to add the substance to the glass to change the properties of the glass. For example, by using water as a dispersion medium and adding boric acid to the water, the refractive index of the manufactured glass can be lowered.

Examples of metal alkoxides used in the method of the present invention include Si, B, Ge, P, Al, Sb, Ti,
Examples include methoxides, ethoxides, propoxides, butoxides of Zr, Sn, Y, Pb, and Cs, etc. For example, when producing quartz glass, Si alkoxides or Si alkoxides and one of the above alkoxides below B are used. Hydrolyze the mixture of seeds or more.

The metal alkoxide in the present invention may be hydrolyzed by a conventional method, that is, by mixing alcohol and water to a concentration suitable for the hydrolysis reaction. The alcohol is appropriately selected from methanol, ethanol, propanol, butanol, and the like.

After completion of hydrolysis, the obtained particles can be separated from the dispersion medium for hydrolysis, that is, alcohol and water, by a conventional separation/drying method. For example, the precipitated particles are taken and dried, or the dispersion medium is evaporated to obtain a powder, and the methods generally used for drying the powder include spraying into a high temperature, blowing hot air, vacuum drying, freeze drying, etc. can be used.

The particles thus obtained are again mixed with an arbitrary dispersion medium, but in this case the concentration can be adjusted to a concentration suitable for gelation.

The optional dispersion medium may be any liquid as long as it contains only a small amount of impurities harmful to optical properties such as Fe, Cu, Co, etc., such as water, alcohols, etc.
Examples include, but are not limited to, acetone.

In addition, the above arbitrary dispersion medium contains additives such as B, Ge, P, Al, Sb, Ti, Zr, Sn, Y, Sr,
By adding at least one element or compound selected from the group consisting of Pb and Cs,
The element can be included in the manufactured glass. These elements can be added as salts, alkoxides, etc. in the form of aqueous solutions, mineral acid solutions, etc. By adding such elements, the refractive index of the product glass can be changed.

Dry the gel produced as described above to obtain a dry gel, but if it dries too quickly, the gel may shrink and crack due to distortion, so dry it slowly or
Freeze-drying can avoid this type of cracking.

As mentioned above, if water is used as an optional dispersion medium, freeze-drying, which is advantageous in terms of easy bulk density control, can be performed even at a relatively high temperature of -10°C or higher.

Next, the dried gel is made non-porous, for example, by sintering it in a suitable atmosphere at a temperature lower than the melting point of the components. At
Sintering is performed at a temperature of about 1200-1500℃.

〔Example〕

EXAMPLES The method for manufacturing glass of the present invention will be specifically explained below with reference to Examples.

Example 1 1/8 mole of tetramethyl silicate redistilled immediately before the experiment was added to 3 moles of ethanol and thoroughly mixed with a magnetic stirrer. Thereafter, a mixture of 2 moles of ethanol and 10 ml of saturated aqueous ammonia was added and stirred vigorously. Thereafter, the mixture was kept at room temperature for 3 hours with gentle stirring, and then sprayed in a high temperature of 800°C and dried. The particle size of the powder thus obtained was approximately 0.1 micron with little variation.

1 g of this powder was added to 50 ml of ethanol, dispersed using ultrasonic waves, and concentrated by heating in a water bath. When fluidity became high, heating was stopped and the tubes were transferred to five test tubes with a diameter of 12 mm and a length of 105 mm, each coated with silicone on the inside, capped loosely with aluminum foil, and placed in a constant temperature bath at 60°C. Leave to dry for 5 days, and the diameter will be approximately 8 mm.
Dry silica gel with a length of about 14 mm was obtained. The bulk density of this dry gel is an average of 0.52 g/cm ³ and a standard deviation of 0.01.
g/cm ³ and was sintered at 1300° C. in a He atmosphere to obtain crack-free transparent glass for all five dried gels.

Example 2 1 g of the powder prepared in Example 1 was added to 50 ml of a 0.1% boric acid aqueous solution, dispersed using ultrasonic waves, and then heated and concentrated. When fluidity became high, heating was stopped and the tubes were transferred to the same five test tubes as above, capped loosely with aluminum foil, and placed in a constant temperature bath at 60°C. Let it dry for 2 days, then take it out when it has a length of about 15 mm, slowly cool it in a freezer car (-20℃), freeze it, and then vacuum-dry it while cooling it with ice and sodium chloride cryogen to dry the gel. I got it. The average bulk density of this dry gel is 0.49 g/cm ³ The standard deviation is:
0.01g/ ^cm3 , and this was heated at 1300℃ in a He atmosphere.
A crack-free transparent glass was obtained for all five dried gels.

Comparative example: Mix 1/16 mole of silicon tetramethoxide and 1/4 mole of ethanol using a magnetic stirrer.
After adding 1/2 mole of water to which 3 drops of 13% ammonia water had been added and further mixing, the mixture was transferred to the same five test tubes as above, capped loosely with aluminum foil, and placed in a constant temperature bath at 60°C. After 7 days, it was almost completely dry, with a diameter of about 6 mm and a length of about 11 mm. The average bulk density of this dry gel was 0.78 g/cm ³ and the standard deviation was 0.06 g/cm ³ . When this dried gel was sintered at 1300°C in a He atmosphere, three of the five pieces were cracked and only extremely small pieces of transparent glass were obtained.

〔Effect of the invention〕

As is clear from the results of the above Examples and Comparative Examples, the method of the present invention can produce dry gels with a lower bulk density and a narrower particle size distribution width than those obtained by the conventional method, and the dry gels are easily sinterable. It is.

In addition, once the particles generated by hydrolysis are separated,
Since it gels in any dispersion medium, if water is used as any dispersion medium, it is practically advantageous because it can be freeze-dried at a relatively high temperature compared to the conventional method that contains a large amount of alcohol. .

Therefore, according to the present invention, it is possible to easily control the particle size of the particles constituting the gel, which has been difficult to control in the past, and the bulk density of the dried gel can be easily controlled. As a result, it has the excellent effect of easily obtaining a dry gel that can be sintered without cracking.

Claims (1)

[Claims] 1. In a method for producing glass by hydrolyzing a metal alkoxide, particles obtained by hydrolysis are once separated from a dispersion medium for said hydrolysis, and then mixed with an arbitrary dispersion medium. , and then drying to obtain a dry gel, which is then subjected to a treatment including a nonporous treatment. 2 Metal alkoxide is Si, B, Ge, P, Al,
The method for producing glass according to claim 1, wherein the glass is an alkoxide of at least one element selected from the group consisting of Sb, Ti, Zr, Sn, Y, Pb and Cs. 3 Add B, Ge, P, as additives to any dispersion medium.
Adding at least one element or compound of an element selected from the group consisting of Al, Sb, Ti, Zr, Sn, Y, Sr, Pb, and Cs, thereby causing the glass produced to contain the element. A method for producing glass according to claim 1.