JPH03285833A - Manufacture of porous glass - Google Patents

Abstract

PURPOSE:To easily obtain porous glass having pore size of submicron to micron order and having a narrow pore size distribution, in the method for manufacturing by a sol-gel process, by specifying the quantity of a solvent to be added and that of water in a reaction soln. CONSTITUTION:In a sol-gel reaction soln. contg. metallic alkoxide or its origomer, an acid water soln. and a solvent to be added, the metallic alkoxide or origomer is hydrolyzed and polymerized to prepare a gel. Next, in the stage of manufacturing glass by baking this gel, as the above solvent to be added, formamide is used by 2.0 to 3.2 molar ratio, e.g. to the metallic alkoxide. At this time, a polyhydric alcohol may be used jointly. Then, the ratio of water in the sol-gel reaction soln. is regulated, by molar ratio, to 1.4 to 1.8 to 1 molar of the metallic alkoxide, and hydrolysis and polymerization are executed. At this time, the polymers of the metallic alkoxide undergo phase separation so that an entangling structure with a soln. phase can be formed and is gelatinized and then this gel is baked.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a porous material that can be used in a wide range of applications where pores on the order of submicrons to microns are required, such as catalyst carriers, enzyme carriers, and separation membrane materials. The present invention relates to a method for producing quality glass by a sol-gel method.

[Prior art] Among conventional porous ceramics, those with ultrafine pore diameters of submicrons or less mainly utilize the phase separation phenomenon caused by heat treatment of borosilicate glass to form an entangled phase separation structure. It is made by eluting one phase with acid.

On the other hand, those with pore diameters of microns or more are made by calcining and thermally decomposing ceramic raw material powder to create particles or open pores between particles, and then sintering under appropriate conditions. However, with these methods, it is difficult to produce porous ceramics with uniform pore diameters ranging from submicrons to several tens of microns. Furthermore, it has the disadvantage that it is difficult to produce membrane-like or fibrous products required depending on the application. For these reasons, recently, the sol-gel method, which can produce ceramics in any shape such as bulk, membrane, or fiber, has been applied to the production of porous ceramics.

However, the sol-gel method using colloidal silica as a starting material can only produce porous materials with pores of submicron size or smaller, and furthermore, because a relatively high concentration of alkali coexists in the starting solution, There was a drawback that the step of eluting this prior to the final heat treatment required time.

In addition, a porous gel body prepared by the above method of hydrolyzing and polymerizing silicon alkoxide in an organic solvent such as alcohol to gel the reaction solution system, and then firing the generated porous gel. The pore diameter is extremely small, 2 to 30 nanometers or less. Attempts have therefore been made to add a large amount of hydrochloric acid to hydrolyze the pores in order to reduce them to micron order, but this has resulted in the problem of widening the pore size distribution.

[Problems to be Solved by the Invention] The present invention solves the above-mentioned problems of the prior art, and provides a porous glass whose pore diameter is on the order of submicrons to microns and whose pore diameter distribution is narrow. It is an object of the present invention to provide a method for producing porous glass that does not use highly toxic starting materials and is easy to handle.

[Means for Solving the Problems] The present invention creates a gel by hydrolyzing and polymerizing the metal alkoxide or its oligomer in a sol-gel reaction solution containing the metal alkoxide or its oligomer, an acidic aqueous solution, and an added solvent. Then, when this gel is fired to produce glass, formamide is used as the additive solvent, and the molar ratio of water in the sol-gel reaction solution to 1 mole of metal alkoxide is 1.4 to 1. In the hydrolysis/polymerization process, the metal alkoxide polymer is phase-separated and gelled to form an entangled structure with the solvent phase, and then this gel is fired. The present invention provides a method for producing porous glass.

The present invention also provides a method of hydrolyzing and polymerizing the metal alkoxide or its oligomer in a sol-gel reaction solution containing the metal alkoxide or its oligomer, an acidic aqueous solution, and an added solvent to create a gel, and then calcining this gel. In producing glass, a mixture of formamide and polyhydric alcohol is used as the additive solvent, and the molar ratio of water in the sol-gel reaction solution to 1 mole of metal alkoxide is 1.4 to 1. .Adjust the ratio to 8 times and phase separate the metal alkoxide polymer in the above hydrolysis/polymerization process to form an entangled structure with the solvent phase to form a gel, and then sinter this gel. The present invention provides a method for producing characteristic porous glass.

The metal alkoxide or oligomer thereof used in the present invention preferably has a methoxy group or an ethoxy group. For example, tetramethoxysilane, tetraethoxysilane, etc. are most suitable. In addition, propoxy group,
A metal alkoxide having an alkoxyl group having a carbon number of 1.5 or more carbon atoms is not preferred because it becomes difficult to significantly 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, AI 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 any oligomer as long as it can be uniformly dissolved or dispersed in the solvent of the present invention.
Specifically, it can be used up to about 10 mer.

In the sol-gel reaction solution of the present invention, together with the metal alkoxide or its oligomer, 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 and sol necessary for the hydrolysis reaction. - The inorganic acid is added as an acidic aqueous solution, including formamide as an added solvent to adjust the polarity of the gel reaction solution. Its concentration is 0.001 normal or more, especially 0.5 to 1.
5 standard is preferred. Note that the pore diameter of the porous glass can be adjusted by adjusting the normality of the acidic aqueous solution. For example, when only the nitric acid concentration is changed from 0.7 to 1.4 normal under a constant solution composition, the pore diameter can be changed from about 0.111 m to 5 μm.

In addition, the amount of water in the sol-gel reaction solution is set at a molar ratio per 1 mole of metal alkoxide so that the oligomer produced by hydrolysis of the metal alkoxide grows as a hydrophobic polymer containing a relatively large amount of alkoxyl groups. 1.4~
The range is limited to 1.8 times. If the amount of water is less than 1.4, the polymer and solvent will undergo liquid-liquid separation, which is undesirable because a homogeneous product will not be obtained. This is undesirable because a gel with only 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, and in the case of tetramethoxysilane, the molar ratio is 1.4 to 1.8. A range of 1.6 is appropriate.

In addition, formamide or a mixture of formamide and polyhydric alcohol 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, thereby preventing the fixation of phase separation. Perfect for carrying out. The dielectric constant of this formamide is about 110, and water (75-80), methanol, ethanol (2
0 to 30), it is possible to make the sol-gel reaction solution highly polar, and it is also compatible with water, so it is optimal.

Such formamide is added in a molar ratio of 2.0 to 3.2 per mole of metal alkoxide. If this ratio is lower than 2.0, 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. In addition,
This addition ratio depends on the type of metal alkoxide; for example, in the case of tetraethoxysilane, the molar ratio is 3.0.
~3.2, and in the case of tetramethoxysilane, a molar ratio of 2.0 to 3.0 is appropriate.

As the polyhydric alcohol mixed with formamide in the additive solvent, glycerin is most suitable, but other polyhydric alcohols can be used as well. Such a polyhydric alcohol may be used as a single type mixed with formamide, or a plurality of types of polyhydric alcohols may be used in combination and mixed with formamide.

When using formamide or a mixture of formamide and polyhydric alcohol as an additive solvent, the pores of the resulting porous glass tend to become coarser as the proportion of formamide added increases.

In addition, the hydrolysis/polymerization reaction temperature of the sol-gel reaction solution is ○℃
A temperature range of ~about the boiling point of the reaction solution or less is optimal. If this temperature is lower than 0° C., it is not preferable for the hydrolysis/polymerization reaction, and if it is higher than the boiling point of the reaction solution, low-boiling components will volatilize, which is not preferable.

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. In addition, when creating a sol-gel reaction solution containing a metal alkoxide or its oligomer whose pore diameter tends to become smaller as the reaction temperature is raised, formamide, and an acidic aqueous solution as a hydrolysis catalyst, there are no particular limitations. Most preferably, the acidic aqueous solution and the formamide are mixed in advance, and the metal alkoxide or its oligomer is added to this solution and stirred. However, after mixing the acidic aqueous solution and the metal alkoxide or its oligomer, formamide is May be added.

In the hydrolysis/polymerization reaction, the sol-gel reaction solution is placed in a predetermined sealed container and heated to 0.
．． This is achieved by holding for 5 to 5 hours. During the hydrolysis/polymerization reaction, the initially transparent solution becomes cloudy and phase separation occurs.
Finally, it goes through the process of gelling. At this time, the metal alkoxide polymer undergoes phase separation and gelation to form an entangled structure with the solvent phase.

The thus gelled product is aged by leaving it 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 wash with water if necessary, 8
The porous glass is obtained by firing at about 00 to 1000°C for several hours.

The pore three-dimensional structure of the object of the present invention changes depending on various conditions that influence the proportion of water and formamide in the sol-gel reaction solution, the temperature and pH value of the reaction system, and the type of metal alkoxide. 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.

If the above-mentioned porous gel is fired without removing unreacted organic components, the substances generated due to the decomposition of the organic components will cause problems such as lowering the purity of SiO□.

Therefore, the organic components from the porous gel can be removed by washing the pre-dried gel with water, but the gel must be heated for a sufficiently long time after the washing process to the extent that the organic components are further decomposed or burned. Organic components can be completely removed. By firing after such treatment, a porous material with improved mechanical strength can be obtained.

[Example] The present invention will be explained in detail below.

Example 1 As a sol-gel reaction solution, tetramethoxysilane, formamide, and a 1N nitric acid (HNO) aqueous solution were used in a molar ratio (No, 1): tetramethoxysilane:formamide:water=1:2
．． 3:1.5 (No, 2) Tetramethoxysilane:formamide:water=1:2
．． 4:1.5 (No, 3) Tetramethoxysilane:formamide:water=l:2.
5:1.5 (No, 4) Tetramethoxysilane:formamide:water=1:2.
Mix and stir so that the ratio is 6:1.5 to make it homogeneous.
~No.4 types were prepared.

10 ml of each of the sol-gel reaction solutions was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction solution was maintained at 40° C. for 2 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60"C for 10 hours, heated to 1000°C at a temperature increase rate of 100°C/hour, and then dried at 1000°C for 2 hours.
Heat treated for hours.

The pores obtained using No.1 sol-gel reaction solution have uniform pores of about 0.5 μm, and those obtained using No. 002 sol-gel reaction solution have pores of about 1 μm. Uniform pores of about 2 μm were obtained using the sol-gel reaction solution of No. 3, and pores of approximately 2 μm were obtained using the sol-gel reaction solution of No. 4. A porous glass was obtained in which pores of approximately 3 μm in size existed in an intertwined structure.

Example 2 As a sol-gel reaction solution, tetramethoxysilane, formamide, and 1N nitric acid aqueous solution were used in a molar ratio (No, 5). Tetramethoxysilane:formamide:water=1
: 2.5 : 1.45 (No, 6) Tetramethoxysilane: Formamide: Water = 1
: 2.5 : 1.50 (No, 7) Tetramethoxysilane:Formamide:Water=l
: 2.5 : 1.55 (No, 8) Tetramethoxysilane:formamide:water=1:
Mix and stir to make the mixture uniform at a ratio of 2.6:1.55.
Four types, 5 to No. 8, were prepared.

10 ml of each of the sol-gel reaction solutions was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction solution was maintained at 40° C. for 2 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and then heated at 1000°C for 2 hours. Heat treated.

The sol-gel reaction solution No. 5 had uniform pores of about 5 μm, and the sol-gel reaction solution No. 6 had uniform pores of about 5 μm.
The one obtained using the gel reaction solution has uniform pores of about 2 μm, and the one obtained using No. 7 sol-gel reaction solution has uniform pores of about 0.1 μm. The porous glass obtained by using the sol-gel reaction solution No. 8 had a structure in which pores of about 0.2 μm were entangled.

Example 3 Tetramethoxysilane, formamide, and 1N nitric acid aqueous solution were used as a sol-gel reaction solution in a molar ratio of tetramethoxysilane:formamide:water=1:2.5:1.5
Mix and stir to homogenize the ratio of No.
Samples No. 9 to No. 10 were prepared.

As in Example 1, this sol-gel reaction solution 1.

ml of each into a sealed container, put this container into a constant temperature bath, and set the reaction temperature of the sol-gel reaction solution to 40"C1No for samples No. 9 and 40"C1No. for the sol-gel reaction solution for sample No. 10. The reaction temperature was maintained at 60° C. for 2 hours to carry out hydrolysis/polycondensation reactions and solidify.

This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, and then dried at 60°C for 10 hours.
Heating to 1000°C at a temperature increase rate of 100°C/hour,
Heat treatment was performed at 1000°C for 2 hours.

The pores obtained using the sol-gel reaction solution No. 9 had uniform pores of about 2 μm, and the pores obtained using the sol-gel reaction solution No. 10 had uniform pores of about 0.5 μm. A porous glass in which pores of uniform size existed in an entangled structure was obtained.

Example 4 As a sol-gel reaction solution, tetramethoxysilane, formamide, and nitric acid aqueous solution were mixed and stirred uniformly so that the molar ratio was tetramethoxysilane:formamide:water=1=2.571.5. , No, 11~No,
13 types were prepared. No. 11 is a nitric acid aqueous solution of 0.7 normal, and No. 12 is 1.0 normal.
No. 13 used a 1.4N nitric acid aqueous solution.

In the same manner as in Example 1, 10 ml of this sol-gel reaction solution was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction solution was set at 40°C and maintained for 2 hours to perform hydrolysis.・Performed a polycondensation reaction and solidified it.

This solidified sample was washed with a 1N nitric acid aqueous solution, further immersed at room temperature for 1 day, then dried at 60°C for 10 hours, and then heated to 1000°C at a heating rate of 100°C/hour.
and heat-treated at 1000° C. for 2 hours.

The pores obtained using the sol-gel reaction solution No. 11 had uniform pores of about 0.5 μm, and the pores obtained using the sol-gel reaction solution No. 12 had uniform pores of about 2 μm. Porous glass was obtained in which pores of uniform size were present in an entangled structure, and pores of uniform size of about 5 μm were obtained using the sol-gel reaction solution No. 13.

Example 5 Tetraethoxysilane, formamide, and 1N nitric acid aqueous solution were used as a sol-gel reaction solution in a molar ratio (No, 14): tetraethoxysilane:formamide:water=1:
2.9: 1.77 (No, 15) Tetraethoxysilane: Formamide: Water: 1:
3.0: 1.77 (No, 16) Tetraethoxysilane:formamide:water=1:
3. Mix and stir to make the mixture uniform at a ratio of 1:1.77.
14. No, 15. Three types, No. 16, were prepared.

10 ml of each of the sol-gel reaction liquids was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction liquid was maintained at 60°C for 3 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and then heated at 1000°C for 2 hours. Heat treated.

The sol-gel reaction solution of No. 14 had uniform pores of about 0.5 μm.

What was obtained using the sol-gel reaction solution of 15 was 2
A porous glass was obtained in which the pores had a uniform size of about 5 μm, and in the case of using the sol-gel reaction solution No. 16, the pores had a uniform size of about 5 μm in an intertwined structure.

Example 6 As a sol-gel reaction solution, tetraethoxysilane, formamide, and 1N nitric acid aqueous solution were used in a molar ratio (No. 17): tetraethoxysilane:formamide:water=1:
3.0: 1.75 (No, 18) Tetraethoxysilane:formamide:water=1
: 3.0: , 1.77 (No, 191 Tetraethoxysilane:formamide:water=1:
3.0 + 1.78 (No, 20) Tetraethoxysilane: Formamide: Water = 1:
Mix and stir to make the mixture uniform at a ratio of 3.0:1.80.
Four types, 7 to No. 20, were prepared.

10 ml of each of the sol-gel reaction liquids was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction liquid was maintained at 60°C for 3 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and then heated at 1000°C for 2 hours. Heat treated.

In the case of No. 17 obtained using the sol-gel reaction solution, a porous glass having a skeleton consisting of uniform spherical particles of about 5 μm was obtained.

The one obtained using the sol-gel reaction solution of 18 is 2μ
The pores with a uniform size of about 0.5 μm were obtained using the sol-gel reaction solution No. 19, whereas the pores with a uniform size of about 0.5 μm were obtained using the sol-gel reaction solution No. 20. The obtained porous glass had uniform pores of about 0.1 μm existing in an entangled structure.

Example 7 As a sol-gel reaction solution, tetraethoxysilane, formamide, and 1N nitric acid aqueous solution were used in a molar ratio of tetraethoxysilane:formamide:water=1:3.0:
Mix and stir to make the mixture uniform at a ratio of 1.77,
Samples No. 21 to No. 22 were prepared.

In the same manner as in Example 1, 10 ml of this sol-gel reaction solution was placed in each airtight container, the containers were placed in a constant temperature bath, and N
o. For sample No. 21, the reaction temperature of the sol-gel reaction solution was set at 60°C, and for sample No. 22, the reaction temperature of the sol-gel reaction solution was set at 80°C and held for 3 hours to conduct hydrolysis/condensation polymerization. The reaction was carried out and solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, and then dried at 60°C for 10 hours.
Heating to 1000℃ at a heating rate of 0℃/hour,
Heat treatment was performed at 00°C for 2 hours.

The one obtained using the sol-gel reaction solution No. 21 has uniform pores of about 2 μm, and the one obtained using the sol-gel reaction solution No. 22 has pores of about 0.2 μm. A porous glass was obtained in which pores of uniform degree were entwined and existed in a mating structure.

Example 8 As a sol-gel reaction solution, tetraethoxysilane, formamide, and an aqueous nitric acid solution were mixed and stirred at a molar ratio of tetraethoxysilane:formamide:water=1:3.0:1.77. to homogenize, No. 2
Three types, 3 to No. 25, were prepared. No.23 is HN
O, 0.7N as an aqueous solution, and No. 24
No. 1.0 standard, and No. 25 use 1.5 standard.

In the same manner as in Example 1, 10 ml of this sol-gel reaction solution was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction solution was set at 60°C and maintained for 3 hours to perform hydrolysis.・Performed a polycondensation reaction and solidified it.

This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, and then dried at 60°C for 10 hours.
Heating to 1000°C at a temperature increase rate of 100°C/hour,
Heat treatment was performed at 1000°C for 2 hours.

No. 23 was obtained using the sol-gel reaction solution, and a porous glass with a skeleton consisting of uniform spherical particles of about 5 μm was obtained.

The one obtained using the sol-gel reaction solution of 24 is 2μ
Pores with a uniform size of about m are also No.

0.25 was obtained using the sol-gel reaction solution.
A porous glass was obtained in which pores of approximately 5 μm in diameter existed in an entangled structure.

Example 9 The pore size distribution of the porous glass prepared according to Example 1 using the sol-gel reaction solution No. 3 was measured by mercury porosimetry, and the results are shown in FIG. As is clear from the figure, it can be seen that the pore diameters are distributed in a narrow range. The porosity calculated from this pore volume was about 70%.

Example 10 As a sol-gel reaction solution, tetramethoxysilane, formamide, glycerin, and 1N nitric acid aqueous solution were used in a molar ratio of tetramethoxysilane: formamide: glycerin: water = 1: 1.25: 1.25: 1.5 The mixture was mixed and stirred to be homogenized so that the ratio was as follows, and sample No. 26 was prepared.

Put 10 ml of this sol-gel reaction solution into a sealed container, put this container into a constant temperature bath, and maintain the reaction temperature of the sol-gel reaction solution at 40°C for 1 hour to perform hydrolysis/polymerization reaction and solidify. I let it happen. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, and then heated at a heating rate of 100°C/hour for 1 day.
The sample was heated to 000°C and heat treated at 1000°C for 2 hours.

From the sample obtained using the sol-gel reaction solution of No. 26, porous glass was obtained in which pores of about 0.05 μm (500 people) existed in an entangled structure.

Comparative Example 1 As a sol-gel reaction solution, tetramethoxysilane, formamide, and 1N nitric acid aqueous solution were used in a molar ratio (No, 27): tetramethoxysilane:formamide:water==1:1.
5:1.5 (No, 28) Tetramethoxysilane:formamide:water=1:3.
Mix and stir so that the ratio is 5:1.5 to make it homogeneous, and then
Two types, 7 to No. 28, were prepared.

10 ml of each of the sol-gel reaction solutions was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction solution was maintained at 40° C. for 2 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and then heated at 1000°C for 2 hours. Heat treated.

No. 27 has only pores of several tens of nanometers or less, and N
No. 28 was formed into an aggregate of spherical particles and no porous glass was obtained.

Comparative Example 2 As a sol-gel reaction solution, tetramethoxysilane, formamide, and 1N nitric acid aqueous solution were used in a molar ratio (No. 29): tetramethoxysilane:formamide:water=1:2.
5:0.5 (No, 30) Tetramethoxysilane:formamide:water=l:2
．． Mix and stir so that the ratio is 5:2.5 to make it homogeneous, and then
Two types, 9 to No. 30, were prepared.

10 ml of each of the sol-gel reaction solutions was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction solution was maintained at 40° C. for 2 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and heated at 1000°C for 2 hours. Heat treated for hours.

In No. 29, the reaction solution separated into two liquids, and in No. 30, it became a solid having only pores of several tens of nanometers or less, and the desired porous glass could not be obtained.

Comparative Example 3 As a sol-gel reaction solution, tetraethoxysilane, formamide, and 1N nitric acid aqueous solution were used in molar ratio (No, 31) Tetraethoxysilane:formamide:water=1
+ 2.0: 1.77 (No, 32) Tetraethoxysilane: Formamide: Water == 1:
Mix and stir to make the mixture uniform at a ratio of 3.5:1.77.
Two types, 1 to No. 32, were prepared.

10 ml of each of the sol-gel reaction liquids was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction liquid was maintained at 60°C for 3 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and then heated at 1000°C for 2 hours. Heat treated.

No. 31 had only pores of 2 to 30 nanometers or less, and No. 32 had aggregates of spherical particles, and the desired porous glass could not be obtained.

Comparative Example 4 As a sol-gel reaction solution, tetraethoxysilane, formamide, and 0.1 N nitric acid aqueous solution were used in a molar ratio (No. 33) Tetraethoxysilane diformamide:water = 1
:'3.0: 0.8 (No, 34) Tetraethoxysilane:formamide:water=1:3.
Mix and stir so that the ratio is 0:3.0 to make it homogeneous.
Two types, 3 to No. 34, were prepared.

10 ml of each of the sol-gel reaction liquids was placed in a sealed container, and each container was placed in a constant temperature bath, and the reaction temperature of the sol-gel reaction liquid was maintained at 60°C for 3 hours to carry out hydrolysis and polycondensation reactions. , solidified. This solidified sample was immersed in a 1N nitric acid aqueous solution at room temperature for 1 day, then dried at 60°C for 10 hours, heated to 1000°C at a heating rate of 100°C/hour, and then heated at 1000°C for 2 hours. Heat treated.

In No. 33, the reaction solution is separated into two liquids, and in No. 34, ~
The resulting solid had only pores of 30 nanometers or less, and the desired porous glass could not be obtained.

In the above comparative examples, the two liquids separated were not subjected to heat treatment.

[Function/Effect] According to the present invention, the silica oligomer produced by hydrolysis/polymerization of metal alkoxide has a molar ratio of 1.4 to 1.4 to 1 mole of metal alkoxide.
1.8, it grows as a hydrophobic polymer containing an alkoxyl group. At this time, in the present invention,
Since the dielectric constant of the solvent is increased by adding formamide or formamide and a polyhydric alcohol such as glycerin as an additive solvent, the polymerization of the silica oligomer is accelerated and the phase separation proceeds by a nucleation/growth mechanism, resulting in a metastable state. Since it occurs in an unstable region rather than a region, both phases form a modulation structure in which they are entangled with each other. However, this structure grows over time, causing so-called coarsening in which phases with strong surface tension separate into spherical shapes and minor phases disperse due to percolation-cluster transition. If the modulated structure in which both phases are entangled with each other is fixed by gelation before the coarsening process progresses, a gel structure with a uniform period reflecting the phase separation structure can be obtained, and after firing such a gel, Porous glass having pore diameters on the order of submicrons to microns can be obtained.

[Effects of the Invention] According to the present invention, porous ceramics having uniform pore diameters ranging from submicrons to several tens of microns can be easily provided. Further, according to the present invention, it is possible to obtain a porous glass with high strength, which can be drilled with a metal drill or the like, and which can be easily cut.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the pore size distribution diagram of the porous glass obtained according to Example I No. 3. Procedural formalities (method) July 1990 LQ date

Claims (7)

[Claims] (1) The metal alkoxide or its oligomer is hydrolyzed and polymerized in a sol-gel reaction solution containing the metal alkoxide or its oligomer, an acidic aqueous solution, and an added solvent to create a gel, and then this gel is fired to form a glass. In producing the above, formamide is used as the additive solvent, and the water in the sol-gel reaction solution is adjusted to a molar ratio of 1.4 to 1.8 times per mole of metal alkoxide. A method for producing porous glass, which comprises phase-separating and gelling a metal alkoxide polymer to form an entangled structure with a solvent phase during a hydrolysis/polymerization process, and then firing this gel. (2) The molar ratio of water in the sol-gel reaction solution to 1 mole of metal alkoxide is 1.4 to 1.8, and the molar ratio of formamide to 1 mole of metal alkoxide is 2.0 to 3. 2. The method for producing porous glass according to claim 1, wherein the ratio is adjusted to .2. (3) Hydrolyze and polymerize the metal alkoxide or its oligomer in a sol-gel reaction solution containing the metal alkoxide or its oligomer, an acidic aqueous solution, and an additive solvent to create a gel, and then bake this gel to create a glass. In producing the above, a mixture of formamide and polyhydric alcohol is used as the above-mentioned additive solvent, and water in the above-mentioned sol-gel reaction solution is mixed with metal alkoxide 1
Adjust the molar ratio to 1.4 to 1.8 times the molar ratio and phase-separate the metal alkoxide polymer to form an entangled structure with the solvent phase in the above hydrolysis/polymerization process. A method for producing porous glass, which comprises gelling and then firing the gel. (4) The molar ratio of water in the sol-gel reaction solution to 1 mol of metal alkoxide is 1.4 to 1.8, and the total amount of formamide and polyhydric alcohol is 1 mol to 1 mol of metal alkoxide. 4. The method for producing porous glass according to claim 3, wherein the ratio is adjusted to a ratio of 2.0 to 3.2. (5) The method for producing porous glass according to claim 3, wherein the polyhydric alcohol is glycerin. (6) The method for producing porous glass according to claim 1 or 3, wherein a nitric acid aqueous solution is used as the acidic aqueous solution. (7) In claim 1 or 3, the metal alkoxide polymer is phase-separated and gelled to form an entangled structure with the solvent phase, and then the gel is treated with an acidic aqueous solution. A method for producing porous glass, characterized in that the hydrolysis reaction of alkoxyl groups remaining on the surface of the gel is completed.