JPH0465322A - Production of glass - 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 provides a method particularly suitable for producing large pieces of glass.

[Prior Art] A so-called sol-gel method is known in which glass is produced by hydrolyzing a metal alkoxide to form a gel, and drying and sintering the gel. Several patents have been reported as a method for producing large-sized glass without cracks using this method. It describes a method of controlling the speed.
In 83 [], in order to produce a reasonable dry gel,
A method of drying the gel under reduced pressure is described.

However, with these methods, it is difficult to completely prevent the gel from cracking during drying, and it is difficult to produce glass lumps of the desired shape with a high yield.
There was a problem that fine bubbles with a diameter of m tend to remain.

In addition, in recent years, in order to prevent the gel from cracking during drying, for example, for large quartz glass, two types of sols, an acid catalyst and an ammonia catalyst, are mixed, or ultrafine silica powder is mixed. Method [JP-A-60-131833],
A method for preventing cracking during drying by adding dimethylamide [JP-A-63-112429] has been proposed.

However, with all methods, volumetric shrinkage of the gel occurs during drying. The volume usually decreases by as much as 50%, and cracks in the gel cannot be completely avoided due to this large volume change.

On the other hand, methods for producing large monolithic silica aerogels using supercritical conditions are also available, for example,
Reported in 209817. Although it is possible to produce relatively large quartz glass with this method,
Due to the need for a large autoclave and the limited manufacturing conditions that do not cause cracks during drying, the examples investigated have been limited to quartz glass, and a practical method for manufacturing glass has not yet been achieved.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems of the prior art, and controls the volume shrinkage of the gel during drying to almost no, thereby preventing cracks and breakage during production. Provided is a method for producing glass by a sol-gel method that eliminates the use of the sol-gel method.

[Means to solve the problem]]

The present invention involves preparing a reaction solution containing a metal alkoxide or its oligomer and an acidic aqueous solution, an additive solvent, or an organic polymer, and creating a gel by hydrolyzing and polymerizing the metal alkoxide or its oligomer in the solution, After washing and removing the organic components in the gel, acidic or alkaline external water/8
A method in which a mixture of liquids or alcohols thereof is immersed for 7 nights to age, then dried and fired to vitrify, and the metal alkoxide polymer is phase-separated in a dispersed state during the hydrolysis/polymerization process. The present invention provides a method for producing glass in which a porous body with a refined pore size is formed by gelling, and the glass is made non-porous by further heat treatment.

The present invention reduces the volume change during drying by 1 by creating a porous body with a uniform pore diameter in the range of 500 Å or more.
By keeping it within 0%, cracks during drying can be completely eliminated, and at the same time, a homogeneous transparent glass body can be manufactured without leaving any bubbles or unsintered areas.

One method for producing a porous body suitable for this process utilizes the phenomenon in which uniformly dissolved organic polymers undergo phase separation during the hydrolysis/polymerization process of metal alkoxides or their oligomers.

Such organic polymers have compatibility to uniformly dissolve in a solution generated by hydrolysis of a metal alkoxide or its oligomer, and phase separation occurs during the hydrolysis process.
In addition, those that do not cause precipitation are used.

Examples of organic polymers having such characteristics include water-soluble organic polymers that can be made into an aqueous solution of an appropriate concentration, and are alcohol-containing liquids that are generated by hydrolysis of alkoxides or oligomers thereof, which are generated by hydrolysis of metal alkoxides or oligomers thereof. Any material that can be uniformly dissolved in the water may be used.

Specifically, sodium or potassium salts of polystyrene sulfonic acid, which are polymeric metal salts, polyacrylic acid, which is a polymeric acid that dissociates to form polyanions, and polymeric bases, which generate polycations in aqueous solution. Preferred are polyallylamine, polyethyleneimine, etc., or neutral polymers such as polyethylene oxide having an ether bond in the main chain, and polyvinylpyrrolidone having a cyclic amide in the side chain. The metal of the metal alkoxide includes the metal of the oxide that will be finally formed, such as Si, Ti, Zr.
, Al are used.

This metal may be one type or two or more types. On the other hand, the oligomer may be any oligomer as long as it can be uniformly dissolved and dispersed in alcohol, and specifically up to about a decamer can be used.

As the metal alkoxide or its oligomer, those having a small number of carbon atoms such as methoxy group, ethoxy group, propoxy group, etc. are preferable. The mixing of the organic polymer and the metal alkoxide or its oligomer is not particularly limited, but it can be achieved by dissolving the organic polymer in an acidic water droplet and stirring this solution and the metal alkoxide or its oligomer. Ru. The organic polymer may be added after mixing the acidic aqueous solution and the metal alkoxide or its oligomer, or the organic polymer may be added after the metal alkoxide or its oligomer is partially hydrolyzed and polymerized. The acidic aqueous solution used at this time is usually hydrochloric acid,
Minerals such as nitric acid with MO of 0.001 or higher are preferred.

For hydrolysis, place the solution in a closed container,
This is achieved by maintaining the temperature at a room temperature of 40 to 60°C for 0.5 to 5 hours. Hydrolysis involves a process in which an initially transparent solution becomes cloudy, undergoes phase separation with the organic polymer, and finally gels.

During this hydrolysis process, the organic polymer or its polymer is in a dispersed state and substantially no precipitation occurs.

The thus gelled product is left to mature at 40 to 80° C. for several days, and then washed with water or alcohol or a mixed solution of these at various pH levels to remove organic polymers.

The three-dimensional pore structure of the target product produced by the above method depends on the temperature and pH value of the reaction system, the molecular weight and content of the organic polymer,
It also varies depending on various conditions that affect the reactivity of the metal alkoxide or its oligomer. Therefore, it is difficult to uniformly describe a method for controlling the pore three-dimensional structure, but as long as the above-mentioned conditions are the same, it is possible to provide a target product with substantially the same pore diameter etc. with good reproducibility.

Further, the desired porous body can also be produced by the following method. The metal alkoxide or its oligomer is hydrolyzed and polymerized in a sol-gel reaction solution containing the metal alkoxide or its oligomer, acidic water/8 liquid, and an additive solvent. In the above-mentioned hydrolysis/polymerization process, the metal alkoxide polymer is dispersed and phase-separated to form a gel. The metal alkoxide or oligomer thereof used preferably has a methoxy group or an ethoxy group. For example, tetramethoxysilane, tetraethoxysilane, etc. are most suitable. Note that a metal alkoxide having a propoxy group or an alkoxyl group having more carbon atoms is not preferred because it becomes difficult to change the polarity of the reaction solution by adding formamide.

Further, as the metal of the metal alkoxide, the metal of the oxide that is finally formed, for example, Si.

Ti, Zr and Al are used. This metal may be one type or two or more types. The typical ones are
Examples include silicon alkoxides.

On the other hand, the metal alkoxide oligomer may be one that can be homogeneously stored or dispersed in the solvent used.
Specifically, up to about 10 mer can be used.

In the above reaction solution, together with the metal alkoxide or its oligomer, the polarity of the sol-gel reaction solution is adjusted with an inorganic acid such as nitric acid or hydrochloric acid that acts as a catalyst for the hydrolysis reaction of the metal alkoxide, and water necessary for the hydrolysis reaction. Contains formamide as an added solvent for The above inorganic acid is added as an acidic aqueous solution. Its concentration is 0,001
It is preferable to have a normality of at least 0.5 to 1.5, particularly 0.5 to 1.5 normal.

Note that the pore diameter of the porous glass can be adjusted by adjusting the normality of the acidic aqueous solution. For example, when the nitric acid concentration is changed from 0.7 to 1.4 normal, the pore diameter can be changed from about 0.1 μm to 5 μm.

In addition, the amount of water in the reaction solution is set so that the oligomer produced by hydrolysis of the metal alkoxide grows into a hydrophobic polymer containing a relatively large amount of alkoxyl groups.
1.4 to 1.8 in molar ratio per mol of metal alkoxide
limited to twice the range. If the amount of water is less than 14 times, the polymer and solvent will undergo liquid-liquid separation, which is undesirable as it will not result in a homogeneous product, and if it exceeds 1.8 times, the gel will have only pores of several tens of nanometers or less. is generated, which is not desirable. Note that the proportion of this water depends on the type of metal alkoxide, for example, in the case of tetraethoxysilane, the molar ratio is 1.7 to 1.8 times, and in the case of tetramethoxysilane, the molar ratio is 1.4 times. A range of ~16 times is appropriate.

Further, formamide as the above-mentioned additive solvent has the function of increasing the dielectric constant of the sol-gel reaction solution and accelerating the polymerization of the generated oligomer, and is optimal for fixing phase separation. The dielectric constant of this formamide is about 11
0, which is higher than water (75-80), methanol, ethanol (20-30), etc., making it possible to make the sol-gel reaction solution highly polar, and also being compatible with water, making it ideal. It is. Such formamide is added in a molar ratio of 2.0 to 3.2 times per mole of metal alkoxide. If this ratio is lower than 20, a gel having only pores of several tens of nanometers will be produced, which is undesirable, and if it exceeds 3.2, polydisperse particle aggregates of micron order will be formed, which is undesirable. The addition ratio depends on the type of metal alkoxide; for example, in the case of tetraethoxysilane, the molar ratio is 3.0 to 3.2 times, and in the case of tetramethoxysilane, the molar ratio is 2. 0 to 3.0 times is appropriate.

Furthermore, as the proportion of formamide added increases, the pores of the resulting porous glass tend to become coarser.

In addition, the hydrolysis/polymerization reaction temperature of the sol-gel reaction solution is 0°C.
~The boiling point of the reaction solution is optimal.

If this temperature is lower than 0° C., it is undesirable, and if it is higher than the boiling point of the reaction liquid, low-boiling components will diffuse, which is undesirable.

Note that this reaction temperature also depends on the type of metal alkoxide; for example, in the case of tetraethoxysilane, it is about 40 to
A range of 60°C is optimal, and in the case of tetramethoxysilane a range of about 40 to 80°C is optimal. Furthermore, the higher the reaction temperature, the smaller the pore diameter tends to be.

Although there are no particular limitations on the preparation of a sol-gel reaction solution containing a metal alkoxide or its oligomer, formamide, and an acidic aqueous solution as a hydrolysis catalyst, the acidic aqueous solution and formamide are mixed first, and then this solution is prepared. Most preferably, the metal alkoxide or its oligomer is added to the mixture and stirred, but formamide may be added after mixing the acidic aqueous solution and the metal alkoxide or its oligomer.

Hydrolysis is achieved by placing the sol-gel reaction solution in a predetermined sealed container and maintaining it at a room temperature of 14°C to 80°C for 0.5 to 5 hours. Hydrolysis involves a process in which an initially transparent solution becomes cloudy, phase separation occurs, and finally gels.

The thus gelled product is left to mature at 40 to 80°C for several hours to several tens of hours, and then treated with an acidic aqueous solution such as a nitric acid aqueous solution to complete the hydrolysis reaction of unreacted alkoxyl groups on the gel surface. and then rinse with water if necessary.

The pore structure of the target product produced by the above method depends on various conditions that influence the proportion of water and formamide after the sol-gel reaction, the temperature and pH value of the reaction system, and the type of metal alkoxide. change. Therefore, it is difficult to uniformly describe a method for controlling the pore three-dimensional structure, but as long as the above-mentioned conditions are the same, it is possible to provide a target product with substantially the same pore diameter etc. with good reproducibility.

Next, the process moves to the ripening step, which is very important in the present invention. Here, the prepared gel is immersed in an alkanoic aqueous solution or an alcoholic mixture thereof, and left to mature for about two days. Examples of the acid used in this case include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid, and examples of the alkali include ammonia, and the pH of the solution is preferably 1 or less or 10 or more.

This step is very important in the present invention. That is, during this aging period, the bonds between the siloxane particles forming the continuous skeleton become stronger, and the entire skeleton is strengthened.

The gel has large pores of 500 Å or more formed by phase separation and micropores of several 100 Å or less in the gel skeleton. In the drying process, a large capillary force acts on the micropores of several hundred angstroms or less, but the skeleton reinforcement achieved by the above treatment makes it possible to produce a dry gel body without cracks or destruction. At this time, the volume change of the gel can be suppressed to within 10%.

After drying, the dry gel is vitrified by heat treatment using the usual method. For example, as a result of examining 5i (h) 100% silica gel, if the pore size is 10,000 Å or less, it can be heated in air or in an oxygen/nitrogen mixed gas. By firing in medium or helium gas, it does not crystallize.
It has been found that it can be made non-porous at temperatures below 1400°C.

Although not particularly limited, in order to achieve the substantial effect of the present invention and to achieve pore-free formation at a lower temperature, the diameter of the pores created by phase separation is desirably 2.000 Å or less. In this range,
Complete non-porous formation is possible at 1,300°C.

[Example] (Example 1) Polyacrylic acid (average molecular weight 8000.40% aqueous solution,
(manufactured by Toagosei) 41.3g and 50.3ml of ion exchange water
105 ml of ethyl silicate was added to a solution of 5.85 ml of concentrated nitric acid (61 wt%) and mixed with stirring. After stirring at room temperature for about 10 minutes, the mixture was transferred to a gelling container, sealed and kept at 60°C, and gelatinized in about 1 hour. After being left as it is for 2 days to ripen, it was washed with a mixed solution of ethanol and water to remove the polyacrylic acid. The obtained porous gel was immersed in IN nitric acid water to perform solvent replacement, and then dried. By the above operation, a gel with a dry gel volume of 200 cm or less, for example, a diameter of 23 cm when dried.
A disc-shaped product with a thickness of 0.5 cm and a thickness of 0.5 cm was able to be produced. Furthermore, it is now possible to fabricate a thin one with a thickness of 0.3 cm, which was previously difficult to fabricate due to the problem of warping. The average pore diameter of the obtained porous gel was 2000
It was a person. By heating this dried gel at 1300° C., it was possible to form a non-porous homogeneous glass.

(Example 2) A porous gel was produced in the same manner as in Example 1, except that the solution to be immersed after gelation was changed to the following.

10. Nitric acid, hydrochloric acid or sulfuric acid aqueous solution of IN or more, or alcohol mixed solution.

20.1N or higher ammonia aqueous solution or alcohol mixed solution.

(Example 3) To 15.0 g of polyacrylic acid (average molecular weight 10,000.40% aqueous solution, manufactured by Toagosei Co., Ltd.), 66 m of ion-exchanged water was added.
105 ml of ethyl silicate was added to a solution of 5.85 ml of concentrated nitric acid (61 wt%) and mixed with stirring.

A porous gel was produced in the same manner as in Example 1. The average pore size of the resulting porous gel was 10,000 pores. By heating this dry gel at 1400° C., it was possible to form a non-porous homogeneous glass.

(Example 4) Tetramethoxysilane, formamide and 1N HNO3
The molar ratio of the aqueous solution (No. 1) is tetramethoxysilane:formamide;water=1:2.
3:1.5 (No, 2) Tetramethoxysilane, formamide:water = 1:2
．． 4 + 1.5 (NQ, 3) Tetramethoxysilane:formamide:water = 1:2
．． 5:1.5 (No, 4) Tetramethoxysilane:formamide:water=l:2.
Mix and stir so that the ratio is 6:1.5 to make it homogeneous, and
Four types, 1 to NG, and 4, were prepared.

Each of these solutions was placed in a sealed container and maintained at 40°C to form a gel. The obtained gel was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then immersed in the solution shown in (Example 2), heated to 60° C., and left for 2 days. The gel was immersed in an ethanol solution, the solvent was replaced, and then dried.

The average pore diameters of the dry gels obtained from the reaction solutions No. 1.2 and 3.4 were about 0.5, 1.23 μm, respectively.

(Comparative Example 1) When a porous gel was produced in the same manner as in Example 1 except that the solution to be immersed after gelation was ethanol, a shrinkage of about 35% in volume change occurred during drying. In this case, it was difficult to produce a porous gel with a diameter of 50+ nm and a thickness of 5 mm or more without cracking or destruction.

[Effects of the Invention] According to the present invention, a gel can be dried with almost no change in volume, thereby preventing cracks and destruction, and producing a large porous gel in a short time with a high yield. be able to. Further, by subsequently performing heat treatment at a high temperature, a homogeneous glass that is made non-porous can be produced.

Claims (5)

[Claims] (1) Prepare a reaction solution containing a metal alkoxide or its oligomer and an acidic aqueous solution, an additive solvent, or an organic polymer, and create a gel by hydrolyzing and polymerizing the metal alkoxide or its oligomer in the solution. After washing and removing the organic components in the gel, it is immersed in an acidic or alkaline aqueous solution or an alcoholic mixture of these and aged.
A method of vitrification by drying and firing, in which a metal alkoxide polymer is dispersed and phase-separated in the hydrolysis/polymerization step to form a gel, thereby producing a porous body with a controlled pore size. A method of manufacturing glass that becomes non-porous through further heat treatment. (2) The reaction solution consists of a metal alkoxide or its oligomer, an acidic aqueous solution, and an organic polymer, and the organic polymer includes sodium polystyrene sulfonate, potassium polystyrene sulfonate, polyacrylic acid, polyallylamine, polyethyleneimine, and polyethylene oxide. The method for producing glass according to claim 1, wherein the glass is polyvinylpyrrolidone. (3) The reaction solution is composed of a metal alkoxide or its oligomer, an acidic aqueous solution, and formamide, and the molar ratio of water to 1 mole of metal alkoxide is 1.4 to 1.8, and the molar ratio of formamide is 2.0 to 1.8. 3.2. The method for producing glass according to claim 1. (4) In the washing/aging step, the organic components are removed from the gel by thorough washing with water or alcohol at various pHs or a mixed solution thereof, and then,
2. The method for producing glass according to claim 1, wherein the gel is sufficiently hydrolyzed and polymerized by immersing it in an acidic or alkaline aqueous solution or an alcoholic mixed solution thereof and heating it to a temperature below the boiling point of the immersion liquid. (5) A porous gel with a uniform pore diameter of 500 Å or more and 10,000 Å or less produced by the phase separation in the porous gel, and a homogeneous glass that is made completely non-porous by heating at 1400° C. or less. 1. The method for manufacturing the glass described in 1.