JPS5879809A - Preparation of silicon carbide powder - Google Patents

Abstract

PURPOSE:To enable easily the preparation of fine powder of high-purity beta type silicon carbide having uniform particle size, by heating a fine mixture of a nitrogen-containing silane compound and high-purity carbon under nonoxidizing atmosphere at high temperature. CONSTITUTION:Fine powder of a nitrogen-containing silane compound such as Si(NH)2, Si2N3H, etc. having an average particle diameter of <=0.5mum is blended with fine powder of carbon having a purity of >=99.9wt% and an average particle diameter of <=0.5mum in a molar ratio of carbon to Si in the nitrogen-containing silane compound of 1.2-2 to 1. The mixture is heated in an inert gas atmosphere such as Ar, He, etc. or in vacuum at 1,750-1,950 deg.C for 5-120min, to give high-purity type silicon carbide having an average particle diameter of <=1mum and a beta phase content of >=95%, which is usable as a raw material for a various kinds of sintered members required to have high hardness, oxidation resistance, corrosion resistance, thermal shock resistance, mechanical strength, and thermal conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing β-type substituted silicon by heating.

Silicon carbide and its sintered body have high hardness, -1 hardness, oxidation resistance, and corrosion resistance. Thermal shock resistance and excellent mechanical strength,
Towing, gas turbine parts, heating elements, and tools with good thermal conductivity and low coefficient of thermal expansion.

It is attracting attention as a material for a wide range of wear-resistant parts.

Such silicon carbide sintered bodies contain aluminum as a sintering aid. It is obtained by pressure sintering silicon carbide powder mixed with powder, but silicon carbide is a crucial element for the properties such as density and strength of the sintered body obtained. Average particle size of powder. These are the characteristics of the powder itself, such as particle size distribution, particle shape, and purity. In other words, the silicon carbide powder used as a raw material for the high-strength, high-strength silicon carbide sintered bodies used in the above-mentioned applications is a granular powder with a small average particle size, uniform particle size, and high purity. It is desirable that this is the case.

Conventionally, methods for producing silicon carbide include 1) a method in which silicon and carbon are directly reacted, 3) a method in which silica is heated in a hydrogen atmosphere and reacted with carbon, and 3) a method in which silicon halide is reacted with hydrogen such as methane. A gas phase synthesis method in which a mixed gas is reacted at a temperature of t-too0C or higher is known.

However, method 1) makes it difficult to obtain high-purity, fine, whole silicon, and method 2) does not provide a product with a uniform particle size, and also contains solid solution of oxygen and nitrogen, making it difficult to obtain high-purity silicon. powder is difficult to obtain. Shu's method yields fine, high-purity powder, but requires large amounts of gas for the reactants, making the equipment large.
, not suitable for mass production.

In view of the above points, the present inventors have conducted intensive research to develop a manufacturing method for easily and efficiently obtaining high-purity, fine silicon carbide powder, and have developed a method that satisfies these requirements. They found a manufacturing method and completed the present invention.

That is, the production method of the present invention heats a mixed powder of nitrogen-containing silica/compound and carbon to react with each other to obtain silicon carbide. According to this method, fine β-type silicon carbide with 4i+ purity is obtained. can be obtained extremely easily without any complicated operations.

The present invention will be explained in detail below.

The nitrogen-containing silane compound used as a raw material in the present invention is obtained by washing a mixture of chloride mide (St(MH)*), which is a reaction product of silicon halide and ammonia, and ammonium 7-halogenide with liquid ammonia. The obtained sl (Ml
N), or silicon diimide, ammonium norogenide is heated in 11 or ammonia to produce 9 decomposition products, namely 81. M, H, amorphous or crystalline silicon nitride powder.

It is preferable that these powders have a fine particle size (for example, 1 μm or less) to eliminate impurities such as metals and acids, but powders with an average particle size of 15 μm or less are particularly preferable in order to obtain fine products. .

Further, it is desirable that the carbon powder, which is another raw material of the present invention, has a high purity of 999 or higher. In addition, the particle size is preferably as fine as possible, and in particular, α5 m or less is desirable in order to obtain a refractory or fine product.

In the present invention, the above-mentioned nitrogen-containing silane compound and carbon powder are used in a uniform mixture, and the mixing ratio at that time is determined by the type of nitrogen-containing silane compound, the particles of the NL material powder, the firing temperature, etc.
1 Although it changes somewhat, silicon X in the nitrogen-containing silane compound
Approximately 2 to 2 moles of carbon t is used per 1 mole.

The mixture may be obtained by mixing a nitrogen-containing silane compound prepared in advance and the Km elementary powder, but it can also be obtained by the following method.

That is, a nitrogen-containing silane compound is filled into a furnace and heated to 1000°C.
~ About 5 minutes while heating to a temperature range of csao℃ ~
An aspect ratio hydrogen gas such as methane or ethane is passed through the tank for 120 minutes. According to such a method, the above-mentioned aspect ratio hydrogen gas diffuses into the nitrogen-containing silane compound, decomposes there, and fine carbon powder is precipitated in the nitrogen-containing silane compound. A homogeneous mixture of nitrogen-containing silica/compound and extremely fine carbon powder is obtained.

In the present invention, a mixed powder of a nitrogen-containing silane compound and carbon is heated and reacted in a non-oxidizing atmosphere. The heating temperature at that time is preferably t750°C to t950°C. t75
If the firing temperature is less than 0° C. and the firing temperature is 1M, the reaction between the nitrogen-containing silane compound and carbon may not proceed sufficiently, and silicon nitride may remain in the product, although it depends on the firing atmosphere. Furthermore, firing at a temperature lower than t950° C. is not preferable because α-type silicon carbide is produced. A heating time of 5 minutes to 120 minutes is sufficient.

Any non-oxidizing atmosphere can be used as the firing atmosphere in the present invention, but if these When nitrogen gas is mixed in the gas, a gas with a lower nitrogen partial pressure is more effective in promoting the reaction between the nitrogen-containing silane compound and carbon. but,
Even in a nitrogen atmosphere, for example, 11w1 at a temperature of 1.800℃ or higher
It reacts sufficiently by firing at aA degree. Also, after the reaction.

500-90 in an air stream to remove unreacted ridges.
It is desirable to heat to 0°C.

The reason why highly purified and extremely fine β-type silicon carbide powder can be obtained by the above method is thought to be as follows.

That is, the nitrogen-containing silane compound that is the starting material is originally very fine (usually 1 pm or less), and when it decomposes and reacts with carbon to form silicon carbide, the reactants are the cause of grain growth. The reaction proceeds in the solid phase without passing through the liquid or gas phase, which results in rounding 5. In the end, the formed silicon carbide preserves the shape of the initial nitrogen-containing silane compound well, and therefore a fine product is obtained. It is considered that the

In addition, the nitrogen-containing silica/compound used in the present invention can be easily obtained as a fine product with daytime purity and uniform particle size by reacting silicon halide with ammonia.
Mixing such a nitrogen-containing silane compound and carbon powder,
The present invention obtains fine silicon carbide simply by heating.
It can be said that this is an advantageous method that does not require complicated operations such as particle size adjustment, and therefore has very little risk of contamination with impurities.

As described above, by the method of the present invention in which a mixed powder of a nitrogen-containing silane compound and a return nest is heated in a non-oxidizing atmosphere to cause the two to react, a powder having an average particle size of Ipm or less and a β phase content of 95% can be obtained. One or more highly purified silicon carbide can be obtained very easily. Therefore, when this is used as a raw material to make a silica sintered body, the sintered body is chemically and physically stable and exhibits high strength If.

It is useful as a raw material powder for sintering high-temperature, high-stress materials.

Next, the present invention will be further described in Examples.

Example 1 A reaction product obtained by reacting silicon tetrachloride with ammonia was charged into a tubular furnace made of quartz, and while ammonia was being drawn in, 1. A white amorphous powder (average particle size α1μ) was obtained by holding 10 #6jkl at a temperature of aaa°C [']. Chemical analysis revealed that the composition of this powder was 5 itN, H.

Next, add the powder obtained by the above method to 20 to 100%;
% in a molybdenum boat, and maintained at a temperature of 200°C for 15 minutes while flowing methane gas at a current of 300° per minute in a tube furnace to obtain a mixed powder of Si, N3H, and carbon. This mixed powder was heated to 1,800° C. in a mixed atmosphere using a high frequency induction furnace and held for α5 hours.

Powder 1 obtained as above was added to 800 ml of powder in air.
The mixture was kept at a temperature of 0.degree. C. for 2 hours, and all unreacted carbon was removed with carbon dioxide. The obtained powder has a green color and % xH
β-type silicon carbide and lW1 were added by powder (b) folding. The specific surface area of this silicon carbide powder was 2-5w17f.

Further, an electron micrograph (5000x magnification) of this powder is shown in FIG. From the photograph, it was found that the average particle size of the product silicon carbide was one grain.

Example 2 Obtained fC81(NH), , N in the same manner as Example 1
The H4Cl mixed powder was washed with liquid ammonia at about -70°C to remove the %M++ formed 11rH4Ct, and
<NH)t powder (average particle size (11 tones) IIL#l
It was.

Next, the powder 109 obtained by the above method and 4 tons of carbon powder with a purity of 99% and an average particle size of α5P or less were mixed uniformly, and the mixed powder was heated in a high frequency induction furnace at t750°C in a nitrogen atmosphere for 15 hours. , reacted.

The powder obtained as above was further heated to 800°C in air.
The mixture was maintained at a temperature of 2°C for 2 hours, and all unreacted carbon was removed as carbon dioxide. The resulting powder #'j exhibited a green color and was rotated with β-type silicon carbide by two-line powder diffraction. The specific surface area of this silicon carbide powder was 6JII, and the result was 2.8rrp/r.
Met.

Example 5 A lk composite powder of 5i2N Tsuji and Chlorine obtained in the same manner as in Example 1 was filled into a jofi molypude/sea bream boat and held at a temperature of %400°C for 5 hours under argon gas flow in a tube furnace. did. The flow rate of argon gas is 300m/! / minute.

The powder obtained as above was heated to 800°C in air.
The mixture was maintained at a temperature of 2 ##f, and unreacted carbon was removed as carbon oxide. Samurai Ramuta powder was completely green in color and was identified as β-type silicon plate by X-ray powder diffraction. This silicon carbide ratio III product? The measured result was 4.5 m''#.

[Brief explanation of the drawing]

FIG. 1 is an electron micrograph (3000x magnification) of silicon carbide powder obtained in Example 1 of the present invention. Patent applicant Tol$ Kaiun Kogyo Co., Ltd.

Claims (1)

[Claims] A method for producing silicon carbide powder, which comprises heating a mixed powder of a nitrogen-containing silane compound and carbon in a completely non-oxidizing atmosphere.