JPS63230508A - Production of silicon nitride-silicon carbide mixed fine powder of silicon nitride fine powder - Google Patents

Abstract

PURPOSE:To efficiently obtain the titled high-purity isometric fine powder of an uniform and fine particle shape, by thermally decomposing a specific organosilicon compound in the vapor phase in a nonoxidizing atmosphere without containing NH3 and heat-treating the resultant amorphous fine powder in an NH3-containing nonoxidizing atmosphere. CONSTITUTION:An organosilicon compound expressed by the formula (R is hydrocarbon group, such as alkyl or allyl; n is 1-3) is previously gasified and thermally decomposed in the vapor phase in a nonoxidizing atmosphere, such as N2, Ar- or H2-containing N2 or Ar, at 800-1,600 deg.C without using NH3 to provide amorphous spherical fine powder of uniform shape having <=0.3mu average particle diameter. The obtained fine powder is then heat-treated at 1,400-1,600 deg.C in a mixed gas atmosphere of 5-100vol.% NH3 and a nonoxidizing gas, such as N2 or Ar for 0.5-24hr.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for producing a silicon nitride-silicon carbide mixed fine powder or a silicon nitride fine powder, and more specifically, a method for producing a silicon nitride-silicon carbide mixed powder or a silicon nitride fine powder by a gas phase reaction method. Regarding the manufacturing method of mixed fine powder or silicon nitride fine powder, in particular, NH3 is not used in the gas phase reaction, and NH3 is not used in the heat treatment process.
The present invention relates to a method for efficiently producing fine powder consisting of equiaxed particles with high purity and uniform particle shape, in which silicon nitride and silicon carbide exist in a desired composition, by performing crystallization in an atmospheric gas containing Z.

[Prior art and its problems]

In recent years, silicon nitride and silicon carbide are being used in a wide range of applications as high-temperature structural materials.

By the way, there are various physical properties required for high-temperature structural materials, but when comparing silicon nitride and silicon carbide, silicon nitride has good thermal shock resistance and fracture toughness, while silicon carbide has good oxidation resistance and high-temperature strength. Each has excellent properties. For this reason, silicon nitride and silicon carbide are being developed in fields that take advantage of their respective characteristics. On the other hand, attempts have been made to develop silicon nitride-silicon carbide composite ceramics in order to take advantage of the advantages of both. Examples of this method include: (1) mechanically mixing silicon nitride powder and silicon carbide powder and sintering the mixture using a hot press or the like; (2) using a reaction sintering method to prepare silicon carbide powder in advance. A method in which a mixture of silicon nitride and carbon is molded and then subjected to nitriding to produce silicon nitride, or a mixture of silicon nitride and carbon is molded and silicon is infiltrated to produce silicon carbide.

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

etc. are known. Among these methods, methods (2) and (3) generally have the advantage of good dimensional stability of the sintered body, but the resulting sintered body tends to be porous, and it is difficult to obtain a dense sintered body. It is difficult to do so.

Therefore, in order to obtain a high-density composite, the above-mentioned (1) is usually required.
method is being used. For example, P, F, Lange.

J, Am, Ceram, Soc, 56,445
(1973), by mixing silicon nitride with silicon carbide and hot-press sintering, a composite with improved thermal conductivity and high-temperature strength was obtained. However, it has been reported that room temperature strength and other properties tend to decrease, and are largely dependent on the particle size of the raw materials used.

As described above, although some physical properties are improved, other physical properties are not improved, and the expected physical properties are not necessarily obtained with this method. This is thought to be due to the particle size and shape of the raw material powder being unsuitable for forming a composite, or to the fact that each component is not mixed uniformly.

That is, if a raw material with a large particle size is used, defects will be introduced into the sintered body, making it impossible to obtain a sintered body with high strength. Furthermore, if the mixture is not uniformly mixed and the dispersion is insufficient, the same result will occur. Furthermore, performing mechanical mixing over a long period of time in order to achieve uniform mixing may cause impurities to be mixed in during the mixing, resulting in undesirable results.

In order to improve these drawbacks of raw material powder, a method has been proposed for producing a mixed powder of silicon nitride and silicon carbide by causing a gas phase reaction between an inorganic silicon halide compound, ammonia, and a carbonaceous material (especially Kaisho 58-91058
), according to this method, silicon nitride and silicon carbide are uniformly mixed in advance, and the specific surface area of the powder after heat treatment is 1.
0 m"/g or more, it is said to be composed of fine particles. However, this method uses separate raw materials for the silicon source and the carbon source, and the thermal decomposition temperatures of each are different. Therefore, it is difficult to say that silicon nitride and silicon carbide are mixed uniformly because they decompose simultaneously during the reaction, and because inorganic halides are used, large amounts of ammonium halides are produced as by-products in the manufacturing process. As seen in the synthesis of silicon nitride powder using silicon chloride, there is a drawback that needle-shaped crystals are likely to be formed in the powder after crystallization, which lowers the density of the molded body and inhibits densification during sintering.

In addition, methods for obtaining fine silicon nitride powder include metal silicon nitriding, silica reduction, imide decomposition, and gas phase methods. Among these methods, the gas phase method can produce fine powder with high purity, but when inorganic halides are used, the reaction is very fast and there is a risk that the reaction will occur in the gas supply section and cause clogging of the supply section. A large amount of ammonium chloride is produced as a by-product during the reaction.

Furthermore, there is a drawback that many needle-shaped crystals are formed during crystallization, which lowers the density of the molded product and inhibits densification.

In order to eliminate these drawbacks, the present inventors have previously developed a method for producing a silicon nitride-silicon carbide mixed fine powder by a gas-phase reaction between an organohalogenated silicon compound and ammonia (Japanese Patent Application Laid-open No.
-200814) or a method for producing silicon nitride fine powder (JP-A-61-63506).

In these methods, since silicon and carbon are already bonded at the raw material stage, a high-purity, fine mixed powder can be obtained in which they are mixed at the molecular level through a thermal decomposition reaction with ammonia. The problem of clogging of the supply section is also solved, and the amount of ammonium chloride produced as a by-product is also extremely small.

However, it has been found that even in these methods, needle-like crystals and metallic silicon are often generated during the heat treatment process of the obtained fine powder.

[Means for solving problems]

In view of the various problems observed in the above-mentioned conventional methods, the present inventors have determined that silicon nitride powder and silicon carbide powder can be mixed uniformly in advance, with high purity and finely divided, without using mechanical mixing means. As a result of research on the synthesis method of silicon nitride-silicon carbide mixed fine powder or silicon nitride fine powder, which consists of particles with uniform particle shape, we found that using an organic silicon compound containing halogen, ammonia can be removed in the gas phase reaction stage. By conducting the reaction in a non-oxidizing atmosphere that does not exist, and carrying out the heat treatment step in a non-oxidizing atmosphere containing Aim 13, with sufficient control of the amount of NH2, reaction temperature, and reaction time, the above-mentioned target microorganism can be achieved. It has been found that a powder can be obtained.

The present invention provides a silicon nitride-silicon carbide mixed fine powder consisting of highly pure, fine, equiaxed particles with a controlled particle shape that does not contain acicular crystals or free silicon, or a high purity, fine, and gelatinized powder. The present invention provides a fine silicon nitride powder consisting of highly equiaxed particles.

That is, the present invention provides general formula R, sic l a-n
(However, in the formula, R represents a hydrocarbon group such as an alkyl group or an allyl group, and n is 1 to 3). , Ar or ■ N containing 2, Ar, etc. to obtain an amorphous fine powder by vapor phase pyrolysis, and the fine powder was heated to 140 ml under a non-oxidizing atmosphere containing NH3.
The present invention relates to a method for producing silicon nitride-silicon carbide mixed fine powder or silicon nitride fine powder, which is characterized by heat treatment at 0 to 1600°C.

When carrying out the method of the present invention, various heating or decomposition means are applied to the gas phase reaction. For example, heating methods such as resistance type or high frequency, plasma method, laser decomposition method, etc. are used, but in practice, the heating furnace method is common, and in this case, the temperature range is usually 800"C to 1600°C. The process is carried out under a non-oxidizing atmosphere such as N, Ar, or N2.Ar containing H2.

Adding H2 to the atmospheric gas is effective in controlling the amount of carbon in the produced powder and discharging chlorine in the raw material as hydrochloric acid.

The organosilicon compound used as a raw material in the present invention is represented by the general formula R,5iCf4- (wherein R represents a hydrocarbon group such as an alkyl group or an allyl group, and n is 1 to 3). , specifically, CHJtCI! , :l
l (CHi)zstcf t + (CH2)ssx
cf + (C1,・C3)SiCf*, (CHI)
(CJs)SiCfz etc. are exemplified.

The specific method of the gas phase reaction in the method of the present invention will be explained using a heating furnace method.The above raw material organosilicon compound is gasified in advance, and N2. Ar
Or N2 containing H2. After thoroughly mixing with a non-oxidizing gas such as 8R, it is supplied to the reaction tube. The reaction proceeds rapidly, and the suspended gaseous substances produced by the reaction are cooled, coagulated, and guided to a collector where they are collected. In this case, a commonly used filter type dust collector, electric precipitator, cyclone, etc. is appropriately used as the collector.

The main product obtained by this method has an average particle size of 0.
It is an amorphous spherical fine powder with a uniform shape and a particle size of 3 μm or less.

The amorphous fine powder thus obtained is subsequently heat treated at a high temperature. In the present invention, this heat treatment step is carried out at N11.
It is essential to carry out under a non-oxidizing atmosphere containing NH
, decomposes into active species such as NH or NH Produces powder. In this case, by appropriately selecting the concentration of NH,i, the content of silicon nitride in the generated fine powder can be selected to a desired amount, and usually 5VolX
It is used in the range of ~100 Volχ, NH alone or N13. And N! It is used by mixing with non-oxidizing gas such as ,^r.

In this case, hydrazine or the like may be used instead of Nlh.

The heat treatment temperature is generally in the range of 1400°C to 1600°C, preferably 1450"C to 1550°C. If the temperature of the heat treatment step is lower than 1400°C, nitrogen will be introduced into the product, but it will not lead to crystallization. It is undesirable because it requires a long time, and at high temperatures exceeding 1600°C, silicon nitride is not produced but only silicon carbide is produced, which is undesirable.The heat treatment time is determined mainly in relation to the heat treatment temperature, and crystallization Usually 0.5 to 2 to complete
Although the duration is 4 hours, longer durations tend to cause particle growth, so shorter durations are preferable, and generally 8 hours or less.

In the method of the present invention, the heat treatment is carried out by holding the material at a required temperature for a required period of time in an air furnace or pusher furnace. .

The fine powder obtained by crystallization using the heat treatment method described above is a mixed fine powder in which silicon nitride and silicon carbide are uniformly distributed, or a fine silicon nitride powder with a high gelatinization rate, and contains needle-like crystals. It consists of equiaxed particles with a uniform particle shape of 3 μm or less.

〔Effect of the invention〕

As described above, according to the method of the present invention, a highly pure, fine, equiaxed fine powder with uniform particle shape suitable for obtaining a silicon nitride-silicon carbide composite sintered body or a silicon nitride sintered body can be obtained. can be obtained.

Examples of the present invention are shown below, but the present invention is not limited to these Examples.

Examples 1 to 4 Inner diameter 25nuw and length 700mm installed in electric furnace
The reaction was carried out using an apparatus consisting of a reaction tube made of high-purity alumina, a floating reaction product aggregator and a product collector attached to the product outlet of the reaction tube.

After holding the reaction tube at 1000°C, it was gasified (
CL), 1SiCf and ^r were introduced into the reaction tube from the raw material inlet. (Organic silicon concentration 11.5 Volχ)
The reaction proceeded immediately, and most of the suspended product gas was coagulated in the condenser, and some of the suspended substances were condensed in the conduit between the condenser and the collector and collected in the collector. The collected fine powder was a submicron-sized spherical amorphous powder.

Next, the fine powder was filled into an alumina container, and heated in a mixed gas atmosphere of NH and N2 at various concentrations shown in Table 1.
Heat treatment was performed at 500°C for 12 hours. Obtained crystals! The fine powder consists of equiaxed particles with a uniform particle shape of 3 μmm or less, and has an X! The composition determined by a-diffraction was as shown in Table 1. In addition, analysis of impurities using fluorescent X-rays revealed Fe, Af, and Ca.

K was 100 ppm or less in all cases. The first SEM photograph of the silicon nitride-silicon carbide mixed fine powder of Example 3 is
Shown as a diagram.

Example 5.6 Using the same apparatus as in the previous example, (CH3)zSiC
l z to Nt(80Volχ), Hg(20Volχ
) was introduced into a reaction tube maintained at 1200°C and reacted to obtain a spherical amorphous fine powder. This fine powder was filled into an alumina container and heat treated under the conditions shown in Table 2 to obtain a silicon nitride-silicon carbide mixed fine powder and a silicon nitride fine powder. The obtained fine powder consisted of equiaxed particles with a uniform particle size of 2 μm or less, and the composition determined by X-ray diffraction was as shown in Table 2.

Table 2

[Brief explanation of drawings]

FIG. 1 is an SEM photograph of a crystalline silicon nitride-silicon carbide mixed fine powder obtained by the method of the present invention. Patent applicant Mitsubishi Gas Chemical Co., Ltd. agent (9070) Patent attorney Sadafumi Kobori Figure 1

Claims (1)

[Claims] General formula R_nSiCl_4_-_n (wherein, R represents a hydrocarbon group such as an alkyl group or an allyl group, and n is 1
~3)), NH_3
A nitriding process characterized by obtaining an amorphous fine powder by vapor phase pyrolysis in a non-oxidizing atmosphere that does not contain NH_3, and heat-treating the fine powder at 1400 to 1600°C in a non-oxidizing atmosphere containing NH_3. A method for producing silicon-silicon carbide mixed fine powder or silicon nitride fine powder.