JPH03187914A - Production of inorganic oxide - Google Patents

Abstract

PURPOSE:To prevent discoloration and reduction in strength by prewashing a molded article of inorganic oxide consisting essentially of silica produced by sol gel method with organic solvent before burning and removing carbon content to remain after burning. CONSTITUTION:Water glass is reacted with an acid or an alkali in the presence of a surfactant (e.g. polyethylene glycol) to give sol. Or a silicon alkoxide (e.g. silicon tetramethoxide or silicon tetraethoxide) is reacted with an acid or an alkali and water to give sol. Then the sol is formed to give a molded article, which is washed with an organic solvent (propyl alcohol or butyl alcohol) to remove organic substances to remain as carbides after burning. Then the washed molded article is burnt at 500-1,500 deg.C for 1-10 hours to give a molded article of silicate.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to a method for producing an inorganic oxide, in particular to a method for producing an inorganic oxide using a sol-gel method. The present invention relates to a method of eliminating unnecessary coloring by effectively removing the components and obtaining a high-strength inorganic oxide.

(Prior art) Inorganic oxides, especially those containing silica as a main component, have high heat resistance,
It has excellent processability and has a wide range of applications, including granular, plate-like, and fibrous forms.

Examples of methods for producing such inorganic oxides include a method in which a molded body is obtained by hydrolysis and polymerization reaction using a metal alkoxide such as ethyl silicate as a raw material, and a method in which a molded product is obtained by using an inexpensive water glass as a raw material instead of an expensive metal alkoxide and using a surfactant. After preparing an emulsion by vigorously mixing it with an organic solvent in the presence of an organic solvent, granules can be obtained by contacting it with an acid or alkali, or by reacting water glass with propylene carbonate, etc. to obtain a viscous liquid, which is then strained. There are ways to obtain fiber by spinning.

(Problems to be Solved by the Invention) However, in any of these methods, it is necessary to finally perform firing at a relatively high temperature, and the carbon content derived from the surfactant and raw material organic matter is removed after firing. Also remains, which has drawbacks such as coloration black and weakening of silicate bonds, resulting in a decrease in strength and heat resistance.

(Means for Solving the Problems) As a result of various studies and examinations aimed at eliminating these drawbacks of conventional methods, the present inventor discovered that organic substances that can become carbon components after firing are contained in the prepared molded bodies. It has been discovered that the above object can be achieved by sintering the molded body after washing and removing it with an organic solvent in advance, and this is the gist of the present invention.

In the present invention, the means for preparing the molded body before firing is as follows:
The following measures will be adopted:

First, a molded article is obtained from a sol obtained by reacting water glass with an acid or alkali in the presence of an organic solvent and a surfactant.

The water glass used in this case is usually what is called No. 3 silica, but other
No. 1 or No. 1 silica may also be used.

As the acid, for example, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, hydrofluoric acid, etc. can be appropriately employed, and as the alkali, for example, ammonia, urea, acetamide, hexamethyltetraamine, etc. can be appropriately employed.

The reaction ratio of water glass and acid or alkali is usually 0.001 to 0.5 mole of alkali or acid per 1 mole of water glass calculated as NatO.n5iO□. Organic solvents include benzene, hexane, and Freon 113.
etc. may be adopted as appropriate.

Further, as the surfactant to be used, for example, polyethylene glycol, polyethylene glycol monooleyl ether, polyoxyethylene sorbitan monostearate, etc. can be appropriately employed.

The amount of surfactant used is water glass Na2O・n5
0.0 for 1 mole of io□. It is appropriate to employ about 1 to 0.2 mol of O.

If the amount used is less than the above range, an emulsion serving as a precursor of granular silica will not be produced, and if the amount exceeds the above range, the precursor particles may aggregate, so either is preferable. Examples of the form of the molded body that can be produced by such a method include porous or non-porous granular bodies and plate-like bodies.

Next, as another method for preparing a molded body, there is a method of obtaining a molded body from a sol obtained by reacting a silicon alkoxide, an acid or alkali, and water.

As the alkoxide used in this case, for example, silicon tetramethoxide, silicon tetraethoxide, silicon tetraisopropoxide, silicon tetratert-butoxide, etc. can be appropriately employed.

Further, as the acid, for example, hydrochloric acid, sulfuric acid, nitric acid, acetic acid, hydrofluoric acid, etc. can be employed, and as the alkali, for example, ammonia, urea, acetamide, hexamethyltetraamine, etc. can be employed as appropriate.

The reaction ratio of silicon alkoxide, acid or alkali, and water is 0.00% of acid or alkali per mol of silicon alkoxide. It is appropriate to employ 1 to 0.5 moles of O and about 1.0 to 15 moles of water.

The molded article that can be produced by this method can have any shape by controlling the ratio of silicon alkoxide to water. When the proportion of water is small, the sol has viscosity and has particularly good stringability (for this reason, it is particularly suitable for forming fibers, but by increasing the proportion of water, it is also possible to obtain granular or plate-like bodies). I can do it.

Yet another method for preparing a molded body is a method of obtaining a molded body from viscous flUM obtained by reacting water glass with propylene carbonate or butylene carbonate.

When employing this method, the reaction ratio between water glass and propylene carbonate or butylene carbonate is 1 mole of water glass (calculated as Na20nSiO□) to 0.0 of propylene carbonate or butylene carbonate.
It is appropriate to employ 0.01-0.5 mol.

Since such a reaction product is viscous, it is particularly suitable as a molded product in the form of a fiber, but it is also possible to obtain a fine granule or plate-like product.

Since this molded body contains an alkali, by neutralizing it with an acid before firing, it is possible to prevent the strength of the fired body from decreasing and to impart water resistance.

As the acid used, for example, strong acids such as hydrochloric acid, sulfuric acid, and nitric acid can be employed.

In any case, the molded bodies obtained by the above methods are washed with an organic solvent before firing to remove organic substances that may remain as carbides in the molded bodies after firing. urge

The organic solvent to be used may be any organic solvent as long as it can achieve the above-mentioned purpose and does not have a negative effect on the final fired product, but propyl alcohol and butyl alcohol are particularly preferred. .

The reason for this is not clear, but it is thought that the alcohol has a great effect of washing out organic matter in the silicic acid.

The amount of these organic solvents to be used is strictly determined by the type of the solvent used, but in general, it is appropriate to use 100 times or more of the weight of the molded article.

If it deviates from the above usage range, it is not preferable because there is a risk that cleaning and removal of organic matter that may remain as carbide may be incomplete. As specific cleaning means, any appropriate means may be employed, such as simply immersing the molded body in an organic solvent, or using heating or ultrasonic waves in combination.

The molded body washed by
A desired silicic acid molded body can be obtained by firing it for about 1 to 10 hours.

(Example) Example 1 To 20% by weight of No. 3 water glass, 73% by weight of Freon 113 and 2% by weight of polyethylene glycol as a nonionic surfactant were added and mixed with vigorous stirring, and then 5% by weight of 2N hydrochloric acid was added under stirring. A sol of porous silica particles was prepared by adding %. Such silica particles are heated to a temperature of 1
After drying at 00°C for 1 hour, each 1g of the particles was immersed in 100g of butyl alcohol (25°C) for 1 hour, and then further soaked with 2N
Dealalization was carried out by immersing the sample in a nitric acid aqueous solution (25°C) for 1 hour while stirring. Next, porous silica particles with an average particle diameter of 1 μm were obtained by firing at 800° C. for 2 hours. These particles are colorless and transparent and have a residual carbon content of 10
It was less than ppm.

Example 2 Porous silica particles in the form of a sol were obtained by vigorously stirring 30% by weight of ethyl silicate, 60% by weight of ethyl alcohol, 8% by weight of water, and 2% by weight of 2N hydrochloric acid. The particles were mixed with 100 g of propyl alcohol (per 1 g of the particles).
Porous silica particles having an average particle diameter of 0.1 μm were obtained by immersing the particles in 25° C. for 1 hour and then calcining them at 800° C. for 2 hours. These particles are colorless and transparent with a residual carbon content of 5 p.
It was below pm.

Comparative Example 1 The molded product of Example 1 was immediately fired in the same manner as in Example 1 without washing with butyl alcohol, resulting in particles with a mixture of black and white, and the amount of carbon remaining was as much as 1% by weight. is.

Comparative Example 2 The molded product of Example 2 was immediately fired in the same manner as in Example 2 without being washed with propyl alcohol, resulting in particles with a mixture of black and white, and the amount of carbon remaining was as high as 1.5% by weight. I did.

Example 3 10% by weight of butylene carbonate was added to 90% by weight of No. 3 water glass and vigorously stirred to obtain a viscous liquid with stringiness. A fiber precursor having a diameter of 20 μm was obtained from this liquid by dry spinning according to a conventional method. Then set this to 100
After drying by keeping it at ℃ for 1 hour, it was immersed in 100 g of butyl alcohol (25 ℃) per 0.1 g of the precursor for 1 hour, and then immersed in 2N nitric acid aqueous solution (25 ℃) for 1 hour. dealkalization was carried out.

This was held at 800° C. for 2 hours and fired to obtain silica fibers. This fiber is colorless and transparent and has a residual carbon content of 10 ppm.
It was below.

Example 4 5% by weight of propylene carbonate was added to 95% by weight of No. 3 water glass and vigorously stirred to obtain a viscous liquid with stringiness. A fiber precursor having a diameter of 10μ was obtained from this solution by dry spinning according to a conventional method. Then set this to 100
After drying by keeping at ℃ for 1 hour, it was immersed in 100 g of propyl alcohol (25 ℃) per 0.1 g of the precursor for 1 hour, and then immersed in 2N nitric acid aqueous solution (25 ℃) for 1 hour. dealkalization was carried out.

This was held at 800° C. for 2 hours and fired to obtain silica fibers. This fiber is colorless and transparent and has a residual carbon content of 5 ppm.
It was below.

Comparative Example 3 The fiber precursor of Example 3 was immediately fired in the same manner as in Example 3 without being washed with butyl alcohol, resulting in a fiber with a mixture of black and white, and the residual amount of carbon was 1% by weight. It also extended to

Comparative Example 4 The fiber precursor of Example 4 was immediately fired in the same manner as in Example 4 without being washed with 12 propyl alcohol, resulting in a fiber with a mixture of black and white colors and a carbon residue of 0. It reached as much as .5% by weight.

Claims (1)

[Claims] 1. A method for producing an inorganic oxide in which a molded body is obtained from a sol obtained by reacting water glass with an acid or an alkali in the presence of a surfactant, and the molded body is fired. 1. A method for producing an inorganic oxide, which comprises washing a molded body with an organic solvent before firing. 2. In a method for producing an inorganic oxide in which a molded body is obtained from a sol obtained by reacting a silicon alkoxide, an acid or alkali, and water, and the molded body is fired, the molded body is washed with an organic solvent before firing. A method for producing an inorganic oxide, characterized by: 3. A method for producing an inorganic oxide in which a molded body is obtained from a viscous liquid obtained by the reaction of water glass and propylene carbonate or butylene carbonate, and the molded body is fired, in which the molded body is washed with an organic solvent before firing. A method for producing an inorganic oxide, characterized by: 4. The method according to claim (1), (2) or (3), wherein the organic solvent is propyl alcohol or butyl alcohol.