JPH0313166B2 - - Google Patents

Description

[Detailed description of the invention]

[Objective of the invention] (Industrial application field) The present invention relates to a method for producing β-type silicon carbide powder, and in particular to a method for producing β-type silicon carbide powder using a mixed powder of silica powder, carbon powder, and silicon carbide powder. Involved in improvements. (Prior Art) Silicon carbide is a material with various properties such as high temperature stability, high strength, and high thermal conductivity, and is widely used in nuclear energy materials, chemical equipment, high temperature gas processing, electric heating elements, electronic resistors, etc. It is used. Among these, it is particularly useful as a high-temperature structural material;
Further, it is being developed as a material that plays an important role in energy and resource conservation. In order to obtain a material with better properties, silicon carbide as a raw material needs to have a small particle size and less variation in particle shape and particle size. Conventionally, silicon carbide powder has been produced by carbon reduction of silica or other methods, but in both cases it is difficult to reduce the particle size and the particle size and shape vary, making it difficult to obtain excellent properties. I couldn't get it. In order to improve the above point, the present inventors first added silicon carbide powder to a mixed powder of silica powder or a compound that generates silica powder during the firing process and carbon powder, and fired the mixture in a non-oxidizing atmosphere. A method for producing silicon carbide powder was developed and proposed. However, the grain shape of the obtained silicon carbide powder tends to be polygonal, and it is not possible to make the grain size fine or spread the variation sufficiently, and in addition, the amount of silicon carbide powder used as a raw material is large. However, there were still issues that needed to be improved. (Problems to be Solved by the Invention) The present invention has discovered that, especially in the case of β-type silicon carbide powder, its properties are greatly affected by the properties of the silicon carbide powder that is an additive component, and By adding β-type silicon carbide powder that has a diameter, β-type carbide has a highly pure spherical shape with a fine particle size and less variation, and also reduces the amount of silicon carbide added and improves economic efficiency. The present invention aims to provide a method for producing silicon powder. [Structure of the Invention] (Means for Solving the Problems) The present invention provides silica powder with an average particle size of 0.5 μm or less, or a compound that produces silica powder with the same average particle size in a firing process, and a compound with an average particle size of 0.5 μm or less. It is characterized by adding crystalline β-type silicon carbide powder with an average particle size of 0.5 μm or less to carbon powder of μm or less or a mixed powder with a compound that generates carbon at high temperatures, and firing the mixture in a non-oxidizing atmosphere. This is a method for producing β-type silicon carbide powder. Examples of compounds that generate silica powder during the firing process include trimethylsilane (CH ₃ SiCl ₄ ),
_Examples include tetramethoxysilane (Si( _C2H5O ) ₄ ) and sodium silicate (NaO- _SiO2 ). Examples of the carbon powder include carbon black and graphite, and examples of compounds that produce carbon powder at high temperatures include various resin-based substances. The silica powder, carbon powder, and crystalline β-type silicon carbide powder preferably have a purity of 99% or more. The reason for limiting the average particle size of the silica powder, carbon powder, and crystalline β-type silicon carbide powder is as follows:
This is because if it exceeds 0.5 μm, it becomes impossible to produce fine β-type silicon carbide powder. The composition of the raw material powder is 1 part by weight of silica powder, 0.5 to 4.0 parts by weight of carbon powder, more preferably 0.6 to 2.0 parts by weight, and 0.01 to 0.2 parts by weight of crystalline β-type silicon carbide powder. Preferably 0.01-0.05
It is preferable to use parts by weight. The reason for limiting the composition to this range is as follows. When the carbon powder is less than 0.5 parts by weight,
Silica tends to remain unreacted in the β-type silicon carbide powder, and on the other hand, if the amount exceeds 4.0 parts by weight, the yield of the β-type silicon carbide powder may decrease. If the amount of the crystalline β-type silicon carbide powder is less than 0.01 part by weight, it will be difficult to fully achieve the effect of addition, while if the amount exceeds 0.2 part by weight, the effect of addition will not change and the economy will be poor. be damaged. In particular, by using a crystalline β-type silicon carbide powder, a sufficient effect can be achieved with a small addition amount of 0.2 parts by weight. The amounts of the compound that generates silica powder and the compound that generates carbon powder in the firing process are determined so that the product falls within the above range. The firing is performed in a non-oxidizing atmosphere, such as an atmosphere of nitrogen, hydrocarbon, carbon monoxide, argon, ammonia gas, hydrogen, etc., preferably in an atmosphere of carbon monoxide or argon at 1350 to 1850 °C (however, For nitrogen and ammonia gas, the temperature is 1550 to 1850°C), more preferably 1400 to 1700°C. Firing temperature
If the firing temperature is lower than 1350°C, it will be difficult to produce β-type silicon carbide powder, while if the firing temperature exceeds 1850°C, grains will grow too much and it will be difficult to produce fine β-type silicon carbide powder. Furthermore, when the non-oxidizing atmosphere is nitrogen or ammonia gas, silicon nitrogen is generated if the temperature is lower than 1550°C, so it is necessary to perform firing at a temperature higher than that temperature. (Function) The reaction in the method of the present invention proceeds with silicon carbide produced by carbon reduction of silica using crystalline β-type silicon carbide with an average particle size of 0.5 μm or less as a nucleus, which has been added in advance. It is possible to produce uniform β-type silicon carbide powder with a high particle size, a spherical shape, and a particle size of 1 μm or less with little variation in particle size. In the above reaction, if amorphous silicon carbide powder is used as the added silicon carbide, it is unstable at high temperatures and may release gas or decompose. As a result, although the detailed mechanism is not clear, the grains of the obtained silicon carbide powder become coarse, deformed, and vary in particle size, and the added silicon carbide powder cannot be used effectively. In contrast, in the present invention, crystalline β-type silicon carbide powder with a specific average particle size is added, which prevents gas release and decomposition during the reaction process and maintains a stable nuclear state. . As a result, the grown silicon carbide powder becomes spherical without becoming coarse, and the grain size is fine with little variation, and β-type silicon carbide powder can be produced. Moreover, the crystalline β-type silicon carbide powder added The amount added can be significantly reduced compared to conventional methods. In addition, in the above reaction, it is possible to achieve some effect by using a silicon carbide source that produces crystalline silicon carbide powder in the temperature range up to 1350°C where the reduction reaction of silica begins, but if the silicon carbide source has a predetermined average particle size By adding crystalline β-type silicon carbide powder, it is possible to produce a β-type silicon carbide powder that has the above-mentioned properties. Further, if carbon powder is added in excess, the carbon powder remains during the reaction process, but it can also be removed by oxidizing the carbon at 600 to 850° C. in an oxidizing atmosphere after firing. (Example) Examples of the present invention will be described in detail below. Example 1 1 part by weight of silica powder with an average particle size of 0.01 μm, 2 parts by weight of carbon powder with an average particle size of 0.05 μm, average particle size of 0.1 μm
100 g of a mixed powder consisting of 0.04 parts by weight of the following fine crystalline β-type silicon carbide powder was placed in a carbon container, and heated under an argon stream (flow rate: 2/min) at 1600 g.
The reaction was carried out at ℃ for 5 hours. This product was heated to 700℃ for 2
Residual carbon was removed by air oxidation for hours to obtain silicon carbide powder. When the obtained silicon carbide powder was subjected to X-ray diffraction, it was confirmed that it had β-type crystallinity. Further, when observed using an electron micrograph, it was found that the particles were almost spherical in shape, and the average particle size was 0.2 μm, and the particle size variation was uniform, with 91% of the particles falling within ±10% of the average. Examples 2 to 8 Silica powder with an average particle size of 0.01 μm, average particle size
After reacting in the same manner as in Example 1 under the conditions shown in Table 1 below using 0.03 μm α carbon powder and crystalline β-type silicon carbide powder with an average particle size of 0.2 μm, the reaction was carried out in air.
The remaining carbon was oxidized and removed by heating at 700°C for 5 hours. The properties of the obtained silicon carbide powder are also listed in Table 1 below. In the characteristics of the produced powder shown in Table 1, the variation in particle size indicates the proportion of particles within ±10% of the average particle size. In Example 7, tetraethoxysilane was used as the silica source, and the raw material component ratio was determined with the silica content as 1.

【table】

[Table] Example 9 Trimethylchlorosilane (CH ₃ SiCl ₄ ) was used as a silica source, and it was hydrolyzed in advance.
CH ₃ SiO _3/2 was used. As for the raw material composition, CH ₃ SiO _3/2 is converted to 1 as SiO ₂ , plus 1 part by weight of carbon powder with an average particle size of 0.01 μm or less, and 0.04 parts by weight of crystalline β-type silicon carbide powder with an average particle size of 0.2 μm. A mixed powder obtained by mixing parts by weight was reacted under the same conditions as in Example 1. When the obtained silicon carbide powder was subjected to X-ray diffraction, it was confirmed that it had β-type crystallinity. Further, when observed by electron micrograph, it was found that the particles were almost spherical in shape, and the average particle size was 0.4 μm, and the proportion of particles with variation in particle diameter within ±10% of the average was 92%, which was uniform. [Effects of the Invention] As detailed above, according to the present invention, it is possible to produce uniform β-type silicon carbide powder with high β-type purity, spherical shape, fine particle size, and little variation in particle size. Moreover, it has remarkable effects such as being able to suppress the amount of added crystalline β-type silicon carbide powder to improve economic efficiency.

Claims (1)

[Scope of Claims] 1. Silica powder with an average particle size of 0.5 μm or less, or a compound that produces silica powder with the same average particle size during the firing process, and carbon powder with an average particle size of 0.5 μm or less, or a compound that produces carbon at high temperatures. The average particle size of the mixed powder with the compound
A method for producing β-type silicon carbide powder, which comprises adding crystalline β-type silicon carbide powder of 0.5 μm or less and firing in a non-oxidizing atmosphere. 2 0.5 parts of carbon powder per 1 part by weight of silica powder
~4.0 parts by weight of crystalline β-type silicon carbide powder
The method for producing β-type silicon carbide powder according to claim 1, wherein 0.01 to 0.2 parts by weight is added. 3 Crystalline β-type silicon carbide powder is silica powder 1
3. The method for producing β-type silicon carbide powder according to claim 2, wherein the amount is added in an amount of 0.01 to 0.05 parts by weight. 4. The method for producing β-type silicon carbide powder according to claim 1, wherein the firing temperature is 1350 to 1850°C.