JPS60200812A - Production of composite fine powder consisting of silicon nitride and silicon carbide - Google Patents

Abstract

PURPOSE:To produce composite fine powder consisting of silicon nitride and silicon carbide and giving a composite sintered body having superior characteristics at high temp. by bringing an organosilicon compound not contg. halogen and contg. Si and one or more CN groups into a vapor phase reaction. CONSTITUTION:An organosilicon compound represented by the formula such as H3SiCN or (CH3)3SiCN is gasified once, carried with a nonoxidizing gas such as NH3, H2 or N2, and brought into a vapor phase reaction. The particle pressure of the gaseous starting material in the reaction zone is 0.001 - several atm., the reaction time is generally 120-0.05sec, and the reaction temp. is generally 600-1,600 deg.C, preferably 800-1,500 deg.C. The resulting gas cong. formed silicon nitride and silicon carbide is cooled and introduced into a proper capturing apparatus to capture composite fine powder. This powder has >=1mum particle size and a uniform particle size distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a fine composite powder of silicon nitride and silicon carbide. For more details, the general formula is 7? Outside S:
t, Ccy)-<wherein the middle edge of the formula represents hydrogen, an alkyl group, an allyl group, or a phenyl group, and n-0 to 3゜m = 4-n) is reacted in a gas phase. This invention relates to a method for producing a composite fine powder of silicon nitride and silicon carbide, characterized in that:

Non-oxide ceramics such as silicon nitride and silicon carbide have superior high-temperature properties such as high-temperature strength and thermal shock resistance compared to oxide ceramics, mainly alumina, so research on their manufacturing methods and their applications is ongoing. Recently, it has been widely used, and its application is opening up to high-temperature materials such as heat-resistant structural materials for gas turbines, diesel engines, heat exchangers, etc. that operate at high temperatures.

Silicon carbide as a high-temperature material has excellent oxidation resistance, strength properties, and thermal conductivity at high temperatures. Silicon nitride also has excellent thermal shock resistance, thermal expansion coefficient, fracture toughness, and the like. For this reason, the development of composite ceramics as a new material that incorporates the advantages of both has been progressing recently.

Silicon nitride and silicon carbide are mainly processed and formed by sintering, but the composition and purity of the starting materials are important factors in obtaining high-density sintered bodies.

Examples include crystal type 1 particle i flea 1 particle shape.

Non-oxidizing silicon-based ceramics are generally difficult to sinter, and therefore, raw material powder with excellent sintering properties is particularly required to have submicron-level particle diameters and be uniform.

Conventionally, the following methods are known as main methods for producing single silicon nitride products.

(1) A method of nitriding metal silicon powder by heating it to a high temperature in nitrogen or ammonia gas.

(2) A method of simultaneously reducing and nitriding a mixture of silicon powder and carbon by heating it to a high temperature in nitrogen.

(3) An amide or imide thermal decomposition method in which silicon tetrachloride and ammonia are reacted at room temperature or low temperature, the resulting silicon amide or silicon imide is separated, and then heated to a high temperature in a nitrogen or ammonia atmosphere.

(4) A method of causing a gas phase reaction between silicon tetrachloride and ammonia at high temperature.

However, each of these methods has the following problems that must be solved.

(Regarding No. 7, this method is currently used industrially, but it is difficult to obtain fine powder with this method.

The product obtained in this way requires grinding for a long time. Therefore, Re contained in the raw material Si.

Impurities such as Ca, AI, etc. may remain after nitriding, or may be mixed in during the grinding process.

In method (2), not only is it necessary to use sufficiently refined silica powder and carbon powder as raw materials, but also the resulting products are α-type Si3N4 and β-type Si3N4.

It is a mixture of silicon oxynitride, etc., and it is difficult to reduce the variation in particle size and particle size.

Method (3) includes a liquid phase method and a gas phase method, but in both methods, a large amount of ammonium chloride is produced as a by-product along with silicon amide and silicon imide. For this reason, impurities are likely to be mixed in due to corrosion or the use of solvents during product separation and removal of ammonium chloride in the thermal decomposition process.

Furthermore, there are limits to the particle size and crystal type of powder obtained by thermally decomposing silicon amide or silicon imide, making it possible to form fine particles or regular equiaxed granules.

Among these, the gas phase method (4) is said to yield high quality products. However, since the reaction between silicon tetrachloride and ammonia is fast, the reaction also occurs at the outlet of each raw material gas supply pipe, and the outlet is blocked, which not only makes it impossible to continuously operate the kumoe, but also causes side effects similar to method i3). It is difficult to remove the ammonium chloride that is generated, and measures must be taken to prevent corrosion of the equipment.

Furthermore, even if ammonium chloride is completely removed, trace amounts of chlorine are difficult to remove, and in the subsequent crystallization process, silicon nitride may become eight products, or the crystal shape may become needle-like, which may cause problems during sintering. It will no longer have any negative effects.

Furthermore, the following method is known as the main method for producing silicon carbide 31 monomer.

(1) A method in which silica (Si02) and coke (C) are mixed and heated in an Acheson furnace.

(2) Solid phase reaction method of metal silicon powder and carbon powder.

(3) Solid phase reaction method between silica powder and carbon-15) powder.

However, in both methods, since the raw materials contain non-volatile metal impurities, it is difficult to concentrate and accumulate in the product, and it is difficult to reduce the variation in particle size. There was a drawback.

The individual powders of silicon nitride and silicon carbide obtained by the above-mentioned manufacturing method are prepared using a commonly known hot press.

Although it is formed and sintered by various methods such as pressureless sintering and one-reaction sintering, various methods for manufacturing composite sintered bodies that incorporate the advantages of both silicon nitride and silicon carbide have been investigated [8]. Tori 1
For example, the following manufacturing method is known.

(1) A method in which silicon nitride and silicon carbide powder are mechanically mixed, molded using a real press, and then sintered.

(2) Using a reaction sintering method, after molding a mixture of silicon carbide and silicon, a nitriding reaction is performed to generate silicon nitride, or after molding a mixture of silicon nitride and carbon,
A method of infiltrating silicon to produce silicon carbide.

(3) A method in which an organic silicon polymer is used as a raw material, silicon powder is added thereto, the polymer is molded directly or after heat treatment, and a nitriding reaction is performed to produce silicon carbide and silicon nitride.

However, in these attempts, there is a limit to the ability to sufficiently control particle characteristics such as particle size and shape as well as the degree of mixing and uniformly mix each component by using ordinary raw material powder. Mechanical crushing.

This is preferable because impurities are likely to be mixed in by mixing), which has the disadvantage that the sintered body cannot be IQed. In addition, even with a single two-reaction sintering method, there are drawbacks such as increased porosity, complicated processes and drying, and the inability to obtain a desirable sintered body due to limitations in compositional uniformity. .

The present inventors have conducted extensive research on various methods for synthesizing fine powders of silicon nitride and silicon carbide in order to obtain a composite sintered body of silicon nitride and silicon carbide with excellent high-temperature properties.

As a result, by controlling the reaction conditions when reacting a specific organosilicon compound in the gas phase to obtain a fine composite powder of silicon nitride and silicon carbide, we were able to obtain a sintered powder with excellent high-temperature properties as described above. The present invention was completed by discovering that solids could be obtained.

That is, the present invention relates to a method for producing a composite fine powder of silicon nitride and silicon carbide, which is characterized by reacting an organic silicon compound that does not contain halogen and contains Si and CN groups in a gas phase.

According to the method of the present invention, a fine composite powder containing silicon nitride and silicon carbide uniformly on the order of fine particles of 1 micron or less can be easily obtained.

Next, the present invention will be explained in detail.

In the present invention, it does not contain halogen used as a raw material,
Examples of organic silicon compounds containing Si and CN groups include:
Hs SiC7J, (CH3)JSnC/J, (
CH3) + 31 (CJ), a.

(c+4.-cH) CHJ 5i (CA/%, CC
6Hr)a SbC'1(CbHt-)asQ(C')
, etc.

Represented by the general formula R1S (C~) (in the formula, R represents hydrogen, a substituent of hydrocarbons such as an alkyl group, an allyl group, a phenyl group, and n-0 to 3.m=4 n) It is a compound that is These raw materials may be used as a mixture of two or more types, and hydrocarbons may also be used together.

When these raw materials are in a liquid or solid state at room temperature, these raw materials are supplied to the reaction zone by means such as appropriate indirect heating in order to quickly carry out a uniform reaction and obtain the desired composite powder. It is important to do this after it has been gasified.

In addition, as shown in the examples, the raw material was N11.3. Il...
By entraining non-oxidizing gases such as N, 2°Ar, Ile, etc., it is possible not only to adjust the raw material partial pressure and control the supply rate, but also to entrain Nl+,...
Il,, N,? The composition of the produced powder (SiC, S
i, Ny ratio) can be arbitrarily controlled.

For example, if you want to increase the proportion of 5i3N)c, NH
The partial pressure and reaction time of the raw material gas entering the J reaction zone are determined by the particle size, shape, STY, etc. of the product, but for example, the partial pressure is 0.001 to several atm, preferably 0.01 to 0.
5 ATM.

Reaction time 6.1 Generally 120-0.05 sec, preferably 60-0.1 sec.

If the reaction partial pressure is smaller than these values or the distance between the two reaction ribs is longer, the two reactors will become unnecessarily large and this will be disadvantageous from an industrial perspective. If the length is too short, the reaction may not substantially proceed, which is not preferable.

Further, the reaction temperature is generally in the range of 600 to 1600°C, preferably 800 to 1500°C. If the temperature is lower than 600°C, the reaction will not proceed sufficiently and the production rate of silicon nitrides and carbides will be low; if the temperature is higher than 1600°C, a large amount of energy will be required, which is not economical.

As a specific means of carrying out this reaction, 1. For example, the organic silicon compound as a raw material is scumified in advance, and if necessary, it is thoroughly and uniformly mixed with ammonia and non-oxidizing gases such as n, N2+, etc. , an external force is introduced into the type I reaction tube.

The reaction tube used is a flow type, such as an empty column or a packed column, but it is important to have a structure that prevents the gas flow from becoming pulsating or turbulent and maintains thermal uniformity. Important for powder uniformity.

The produced gas containing silicon nitrides and carbides is cooled and introduced into the collection device.2 The collector used in the present invention is not particularly limited, and can be used in commonly used charging or filtering formats. Dust collector, electric dust machine.

Zyc 1'' etc. can be used as appropriate, but since the generated gas does not contain hydrogen chloride, which is a corrosive gas, or ammonium chloride, which becomes solid and precipitates when cooled to below 500 °C, Since it does not require the use of high-grade materials or processing equipment to remove ammonium chloride, an economical collection method can be selected.

(As the photographs in the drawings show, the resulting composite fine powders all have a particle size of 1 micron or less.

Moreover, it has a uniform particle size distribution.

The present invention will be explained in more detail with reference to examples below.
The present invention is not limited to these examples.

Examples 1 to 5 A device consisting of a 1 part 6 purity alumina reaction tube with an inner diameter of 25mm and a length of 700mm installed in an electric oven and a reaction product collector attached to the reaction part was prepared. The reaction temperature was maintained at the specified temperature.

After the organosilicon compound containing a cyan group was gasified, it was thoroughly mixed with ammonia and a non-oxidizing gas such as N2 or I+ gas, and a reaction was carried out by blowing from 1 part of the compound into a pre-reaction mixture.

All of the fine powders collected in the collector were equiaxed, uniform fine particles with a particle size of 1 micron or less. A scanning electron micrograph of the collected fine particles obtained in Example 1 (A) is shown on the figure.

Next, this product was packed into a high-purity alumina tube under an inert atmosphere, and heat-treated for 2 hours in an electric furnace IP heated at 1500°C (1500°C) under an alcon atmosphere. The analysis results of the powder obtained are shown in Table 1, and both were found to be β-3iC and α-Si by X-ray.

There were only nearby ingredients. Also, impurities were measured using fluorescent X-ray analysis! The contents of 'e, 8l, a, and K are each 10 ppm or less, and the content of C1 is 4J:
1100pp or less -C Table 1

[Brief explanation of the drawing]

The drawing shows the composite i"+' obtained by the method of Example 1 of the present invention.
A scanning micrograph of the end of k13) is shown. q Applicant Yusashi Gas Kagaku Co., Ltd. Representative Nagano Kazuko procedural amendment (spontaneous) July 30, 1980 Commissioner of the Japan Patent Office 1 Indication of the case 1988 Patent Application No. 55172 2, Title of the invention: Process for producing a composite fine powder of silicon nitride and silicon carbide 3; Relationship with the case of the person making the amendment Patent applicant address: 2-5-2 Marunouchi, Chiyoda-ku, Tokyo Specification 5; Contents of the amendment

Claims (1)

[Claims] Is the general formula 7? ,, 5 (cuLt (in the formula, R is hydrogen,
Indicates an alkyl group, an allyl group, and a phenyl group. n=o~3. A method for producing a composite fine powder of silicon nitride and silicon carbide, characterized by reacting an organosilicon compound represented by m = 4-n in a gas phase.