JPH01131008A - Production of ceramics - Google Patents

Abstract

PURPOSE:To obtain in high efficiency a high-quality ceramic consisting of Si3N4 and/or SiC by heating at specified temperature, in an inert or reducible gas, a silicate of guanidine compound. CONSTITUTION:First, a silicate of guanidine compound is prepared by reaction, at 20 to 200 deg.C, between (A) a guanidine compound such as (1-methyl)guanidine, 1-phenylguanidine or 1-methylolguanidine and (B) a silicon oxide such as colloidal silica or a precursor capable of forming a silicon oxide (e.g., (di)silane) in the molar ratio A/B=10-1/1-10. Thence, this compound is heated at >=1200 deg.C for 1 to 6hrs in an inert or reducible gas (e.g., N2, H2, NH3) to be converted into the objective ceramic.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing ceramics. In particular, the present invention relates to a method for manufacturing ceramics made of silicon nitride, silicon carbide, or both. Silicon nitride and silicon carbide are new materials that have high thermal stability and excellent wear resistance, and are expected to be used in a wide range of fields in the future by taking advantage of these properties.

(Prior Art and Problems to be Solved by the Invention) Several methods are conventionally known as industrial methods for producing silicon nitride and silicon carbide. For example, the following two methods are mainstream for manufacturing silicon nitride. That is, one method is to heat a metal silicon powder to a high temperature in the presence of a vapor phase nitriding agent, and the other method is to heat a dispersed mixture of silicon oxide powder and carbon powder to a high temperature in the presence of a vapor phase nitriding agent. This is a method of heating to. However, the silicon nitride powder obtained by these conventional methods is difficult to obtain due to the abnormal temperature rise that often occurs during the reaction in the former method, and the uniform dispersion of silicon oxide powder and carbon powder in the latter method. Both methods have the problem that the particle size distribution tends to be wide and the average particle size tends to be large because of the inability to obtain a sufficient amount of particles. Furthermore, all of these conventional methods involve a pulverization step, and in the latter method in particular, it is difficult to obtain high-purity carbon of sufficient purity at a low cost to increase the purity of silicon nitride in the product. Up until now, it has been quite difficult to economically produce high-purity silicon nitride powder on an industrial scale due to problems such as difficulty in producing silicon carbide. The following two methods are well known: one is to heat silica and carbon to a temperature of 1,600°C or higher in an inert gas atmosphere, and the other is to heat silicon and carbon to a temperature of 1,600°C or higher. This is a method of directly reacting at a temperature of 1400°C or higher.

However, since all of these methods involve reactions between solids, it is necessary to finely pulverize the raw materials silica, silicon, or carbon over a long period of time in order to carry out the reaction sufficiently. - After re-pulverizing the previously obtained silicon carbide, it is necessary to refine it through long steps such as iron removal and silica removal in order to improve the purity, which makes it difficult to manufacture in terms of both labor and energy requirements. At present, it is quite difficult to manufacture it economically on a large scale.

(Means and effects for solving the problems) The present inventors have conducted detailed research to solve these problems. As a result, instead of the conventional method described above, ceramics made of silicon nitride and/or silicon carbide can be efficiently produced by using silicate of a guanidine compound as a raw material and heating it under appropriate conditions. They discovered what they could do and completed the present invention.

That is, the present invention is a method for producing ceramics, which is characterized by heating a silicate of a guanidine compound to a temperature of 1200''C or higher in an inert gas or a reducing gas.

Ceramics mentioned herein means silicon nitride, silicon carbide, or a mixture thereof. In the method of the present invention, the production ratio of silicon nitride and silicon carbide as products can be changed by changing the temperature at which the silicate of the guanidine compound used as a raw material is heated in an inert gas or a reducing gas. Although the production ratio of these depends on the reaction time, the reaction temperature is generally 1200° C. or higher. Especially 1
By setting the temperature to 200 to 1450°C, ceramics containing mainly silicon nitride can be obtained;
By setting the temperature to 2000°C, ceramics containing mainly silicon carbide can be obtained.

Above all, when the temperature is between 1400 and 1500℃,
Ceramics made of a mixture of silicon nitride and silicon carbide can be obtained.

The silicate of a guanidine compound used in the method of the present invention means the following compound or mixture consisting of a guanidine compound and silicic acid. That is, a guanidine compound has the following general formula: ■H R'R'' N-(, -NR3R' (where N is a nitrogen atom, C is a carbon atom, H is a hydrogen atom, and R , R2, R3 and R4 each represent hydrogen, an alkyl group, an aryl group, a cycloalkyl group, an alkylaryl group or a hydroxyalkyl group. Also, R1 may be an amino group. Specific examples include guanidine in which R1 to R4 are all hydrogen, 1-methylguanidine, 1,1-dimethylguanidine, 1.3
-dimethylguanidine, I, L3- trimethylguanidine, 1, L3,3-tetramethylguanidine, 1-ethylguanidine, ■-phenylguanidine, 1-cyclohexylguanidine, ■-benzylguanidine, 1-methylolguanidine, 1- Aminoguanidine, 1,1-
dimethylolguanidine, 1,3-ethylguanidine,
■.

3-diphenylguanidine, 1,3-dicyclohexylguanidine, 1,3-dibenzylguanidine, 1,3-
Examples include dimethylolguanidine and trimethylolguanidine. Among these various guanidine compounds, guanidine, 1-methylguanidine, 1.
1-dimethylguanidine, 1,3-dimethylguanidine, 1-ethylguanidine, 1-methylolguanidine,
1,1-dimethylolguanidine, 1,3-dimethylolguanidine, trimethylolguanidine, 1-phenylguanidine, 1,3-diphenylguanidine, etc. are preferably used.

These silicates of guanidine compounds in the method of the invention are synthesized from the guanidine compounds described above and silicon oxide or a precursor capable of producing silicon oxide. In addition to silica, colloidal silica is a suitable example of silicon oxide.

In particular, from the viewpoint of the quality of the ceramics obtained, colloidal silica having an extremely low content of alkali metals or alkaline earth metals is preferred. Further, examples of precursors capable of producing silicon oxide include silane, disilane, silicon tetrachloride, methyltrichlorosilane, ethyl silicate, isopropyl silicate, and the like. These silicon oxides or precursors capable of producing silicon oxides and the guanidine compound are mixed at a molar ratio of 10:1 to 1:10, and the mixture is heated at a temperature of 2.
A silicate of a guanidine compound can be obtained by stirring at a temperature of 0 to 200 °C, preferably 40 to 100"C, for several minutes to several hours, and in some cases for several days. For example, in the case of a silicate of guanidine, An aqueous solution of colloidal silica was added to an aqueous solution of free guanidine, and the mixture was heated under normal pressure for 6 hours.
The silicate of guanidine can be obtained as a colorless and transparent viscous liquid by thoroughly mixing the mixture under stirring at 0° C. for 2 hours and then evaporating the water under slightly reduced pressure. Also,
If free guanidine is difficult to obtain, use a column filled with a strongly basic anion exchange resin in which an aqueous solution of various guanidine salts, such as guanidine carbonate, guanidine hydrochloride, guanidine sulfamate, or guanidine nitrate, is regenerated into the hydroxyl form. Free guanidine can be obtained in the form of an aqueous solution, such as by passing through the solution. Silicates of other guanidine compounds can also be obtained by applying similar operations. In this case, if the guanidine compound is insoluble in water, it can be synthesized by using other solvents, such as alcohols such as methanol and ethanol, in place of water.

The silicates of these guanidine compounds thus obtained are converted into ceramics by heating to a temperature of 1200° C. or higher in an inert gas or reducing gas atmosphere. As mentioned above, this heating temperature depends on the reaction time, but is preferably in the range of 1200 to 1450°C when obtaining ceramics mainly containing silicon nitride; In order to obtain ceramics containing the above, a temperature range of 1450 to 2000°C is preferable.

Above all, in the temperature range of 1400 to 1500°C, ceramics mainly composed of a mixture of silicon nitride and silicon carbide can be obtained. The heating time depends on the reaction temperature, but
Usually 1 to 6 hours is preferred.

The gas used as the atmosphere is nitrogen as an inert gas,
Examples include helium, neon, or argon, and examples of the reducing gas include ammonia, hydrogen, carbon oxide, or a mixed gas thereof.

When the purpose is to obtain silicon nitride or ceramics containing silicon nitride, it is particularly preferable to use nitrogen or ammonia among these gases from the viewpoint of nitriding efficiency and economy.

The silicate of the guanidine compound used in the method of the present invention can be synthesized with very few impurities if the guanidine compound, silicon oxide, or silicon oxide precursor used as its raw material is purified at the stage.

In addition, when the silicate of the guanidine compound is heated to a high temperature of 900°C or higher, the organic matter completely decomposes and disappears, and what remains as a solid is essentially the product silicon nitride and/or silicon carbide and a small amount of silicon oxide. The content of other impurities is usually extremely small. The amount of silicon oxide contained as an impurity can be reduced by using the guanidine compound in excess of the silicon oxide or silicon oxide precursor when synthesizing the silicate of the guanidine compound. The preferred excess of the guanidine compound to the silicon oxide or silicon oxide precursor is 5% or more of the stoichiometry, particularly preferably 10 to 100%. By employing this method, the method of the present invention enables the production of silicon nitride and/or silicon carbide with extremely few foreign substances.

(Example) Hereinafter, the method of the present invention will be explained in more detail with reference to Examples.

Reference Example 1 (Preparation of free guanidine aqueous solution) Guanidine carbonate (manufactured by Mitsui Toatsu Chemical Co., Ltd.) was recrystallized with water three times at 900°C.
High purity guanidine carbonate with an ignition residue of 10 ppm or less was prepared. Dissolve 200 grams of this high-purity guanidine carbonate in 2 liters of distilled water and pass through a glass column filled with 3 liters of a strong basic anion exchange resin (trade name, Revachit M-600), which has been regenerated into hydroxyl group form, to dissolve the carbonate. Roots removed. When passing through the column, a portion of the initially low concentration flowthrough was separated and only the relatively concentrated portion was collected to form 1.6 liters of an aqueous solution containing 58.3 grams of free guanidine per liter. Obtained.

This free guanidine aqueous solution was stored in a cool and dark place, and was fractionated as needed and used as a raw material for producing a silicate of a guanidine compound.

Example 1 Reagent colloidal silica (manufactured by Kaguchi Kagaku, trade name Snowtex-N1 containing 20.2% by weight of silica) 5'5
．． 2g of guanidine aqueous solution prepared by the method of Reference Example 1
．． After dropping it into 5 liters of water, it was left at 60°C for 13 hours under stirring, and water was evaporated at about 30°C under reduced pressure (about 20 mmHg) to form a guanidine silicate (colorless and transparent) containing some excess guanidine and water. (viscous liquid) approx.
4g was obtained.

Weighed out 10g of the guanidine silicate obtained in this way,
This was heated at 1350° C. for 2 hours under a nitrogen atmosphere. After cooling, the resulting crystal was analyzed by X-ray diffraction and infrared absorption spectrum, and it was confirmed that silicon nitride containing almost no impurities other than a small amount of silica was produced.

Example 2 In the method of Example 1, the silicate of guanidine was added to 135
Instead of heating at 0°C for 2 hours, it was heated at 1700°C for 4 hours.

After cooling, analysis of the obtained crystals by X-ray diffraction and infrared absorption spectrum confirmed that silicon carbide was produced. Almost no impurities other than silica were detected in this crystal.

Example 3 In the method of Example 1, the silicate of guanidine was added to 135
Instead of heating at 0°C for 2 hours, it was heated at 1450°C for 3 hours.

After cooling, the resulting crystal was analyzed by X-ray diffraction and infrared absorption spectrum, and it was confirmed that silicon nitride containing a small amount of silicon carbide was produced.

Example 4 In the method of Reference Example 1, 1-methylguanidine hydrochloride (manufactured by Tokyo Kasei, GR) was used instead of guanidine, and 1
An aqueous solution containing 34.8 g of free 1-methylguanidine per liter was prepared.

Next, in the method of Example 1, a guanidine compound was prepared in the same manner except that 1 liter of this free 1-methylguanidine aqueous solution was used instead of 0.5 liter of the free guanidine aqueous solution prepared by the method of Reference Example 1. The silicate was prepared to obtain about 49 g of 1-methylguanidine silicate containing some 1-methylguanidine and water.

Next, 10 g of the 1-methylguanidine silicate was heated at 1600° C. for 5 hours under a nitrogen atmosphere. After cooling, the resulting crystals were analyzed by X-ray diffraction and infrared absorption spectroscopy, and it was confirmed that highly pure silicon carbide containing almost no impurities other than a small amount of silica was produced.

(Effects of the Invention) The method of the present invention provides a method for producing silicon nitride and/or silicon carbide using a new production route. especially,
The method of the present invention makes it possible to produce silicon nitride and/or silicon carbide of higher quality than conventional methods. Further, the method of the present invention makes it possible to produce silicon nitride and silicon carbide using the same raw materials and the same equipment.

Patent applicant: Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] (1) A method for producing ceramics, which comprises heating a silicate of a guanidine compound to a temperature of 1200° C. or higher in an inert gas or reducing gas. (2) The method according to claim 1, wherein the temperature is 1200 to 1450°C. (3) The method according to claim 1, wherein the temperature is 1450 to 2000°C.