JPS59131509A - Preparation of silicon carbide - Google Patents

Abstract

PURPOSE:In thermal decomposition of a silane compound by plasma flame in a gaseous phase, to prepare finely divided particles of beta-type silicon carbide in high reactivity in high formation rate, by introducing a raw material gas into the central part of the plamsa flame. CONSTITUTION:(A) A gas of an organosilane shown by the formula I [R is H or monofunctional hydrocarbon group (at least one is monofunctional hydrocarbon group); n is 1-4], and/or (B) a mixed gas of a silane shown by the formula II(m is 0-4) and a volatile hydrocarbon compound is used as a raw material gas. Namely, argon is introduced from the plasma inlet pipe 2 to the reaction pipe 5, high-frequency power (about 0.5-10MHz, about 1-100kW) is applied to the high-frequency work coil 6 to generate the plasma flame 9. The raw material gas is introduced from the pipe 1 to the central part of the plasma flame 9 (flow velocity: about 1-4m/sec.), and finely divided particles of silicon carbide are dropped into the particle collecting part 7.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing silicon carbide, particularly finely divided silicon carbide.

Silicon carbide is a sintered body that exhibits excellent properties such as oxidation resistance, impact resistance, and high-temperature strength, and is also highly hard, so it has been used for traditional purposes such as refractories and abrasives. It is also attracting attention as a high-temperature structural material. There are two known sintering methods for obtaining this silicon carbide sintered sheath as a high-temperature structural material, including the one-reaction sintering method, the hot press method and the atmospheric pressure sintering method. In order to obtain a high-strength sintered body, it is necessary to make this starting material, silicon carbide, into a powder as fine as possible.

On the other hand, regarding the manufacturing method of this silicon carbide fine powder, 1)
Although methods such as carbonization and thermal decomposition produced by the Acheson method are known, mechanical pulverization in method 1) has a certain limit in pulverization, and method 2) In addition to requiring a sieving step because it consists of a coexistence of relatively coarse particles and fine particles, this method also has the disadvantage of containing a large amount of sintered MJ and sulfuric acid. On the other hand, in method 3), the product becomes fine silicon carbide, and especially when a plasma flame is used as the heat source, C2 has the advantage that the particles become very fine and there is no contamination with impurities. Although it has
This method has problems with the stability of the plasma flame, and also has the disadvantage that the reaction tube is damaged due to adhesion of reactants to the inner wall of the reaction tube, so it has not yet been put into practical use.

That is, the production of silicon carbide powder by vapor phase thermal decomposition of these organosilanes (for example, JP-A-56-32
Publication No. 316, British Patent No. 1134872, etc. are known; in the former method, a raw material gas such as organosilane is mixed with a plasma working gas in advance, and this is introduced into a plasma flame. Therefore, increasing the feed rate of raw material gas will reduce the stability of the plasma flame, and the reaction products that have flowed at the top of the plasma flame will adhere to and accumulate on the inner wall of the reaction tube, which will be heated by high-frequency induction. ,
There is a disadvantage that the reaction tube may be damaged in some cases, and in this latter method, the raw material gas is supplied from the outside of the plasma flame to the plasma flame tail, resulting in insufficient mixing of the raw material gas and the plasma gas. There was a drawback that the reaction rate decreased.

The present invention relates to a method for producing silicon carbide which solves any disadvantages, and which has the general formula Rn510t4-
n (where R is a hydrogen atom or a monovalent hydrocarbon group, at least one of which is a hydrocarbon group, and n is a positive number from 1 to 4)
High-frequency induced plasma flame, which is a gaseous organosilane represented by Hirojin in the center of the city.

It is characterized by thermal decomposition within this plasma flame.

To explain this, the present inventors have studied various methods for producing silicon carbide by a gas phase pyrolysis method that utilizes high-frequency induced plasma of organosilanes. If the raw material gas is supplied so as to penetrate into the plasma, the electrical influence on the high-frequency induced plasma will be slight even if the supply of raw material gas is increased, and the plasma flame will be maintained stably. As the heat received from Proceed,
The present invention has been completed.

The silane used as the starting material in the method of the present invention is represented by the above-mentioned general formula R5iOL4-n, which generates carbide silane ('5in) by thermal decomposition. , must contain at least one carbon atom and one silicon atom in its molecule. Therefore, one of the atoms in the above general formula is a hydrocarbon group such as a methyl group, an ethyl group, or a phenyl group, and various organosilanes containing these hydrocarbon groups are used. Among them, methyltricry
o silane, dimethyldichlorosilane, trimethyldichlorosilane, methyldichlorosilane, tetramethylsilane,
Methylphenyldiglorosilane and trimethylsilane are preferred because they are cheap and easy to handle by one person. Organosilane is also preferred because it forms a large amount of crystals during the manufacturing process of polycarbosilane, which is the main raw material for silicon carbide fibers.

In addition, these silanes have the general formula HmSiOt4-m
Silanes of the formula % can also be used - in this case used as a gas mixture with hydrocarbon compounds as a carbon source to form silicon carbide or with chlorinated hydrocarbon compounds of the general formula %). These hydrocarbon compounds include methane, ethane, propane, ethylene, propylene, acetylene, etc., and the chlorinated hydrocarbons include methyl glolide, ethyl glolide, carbon tetrachloride-methyl glolide, etc.
An example is Holm. Furthermore, if these silanes contain more carbon atoms than silicon atoms in their molecules, carbon may be generated and mixed into the intended silicon carbide. However, if necessary, silicon tetrachloride, which does not contain carbon atoms, is added to the reaction system.
What is necessary is to mix a gaseous substance of a silicon compound such as trig-sigma silane.

Incidentally, the silanes or the silane and hydrocarbon compound as the initiator may be introduced into the plasma flame in the form of a carrier gas. , xenon, radon, argon, etc. are used.

Argon, which is industrially inexpensive, may be used.

Next, the method of the present invention will be explained based on the attached drawings. Figure 1 shows the longitudinal cross-sectional factors of the reactor used in the method of the present invention. It is composed of a plasma reaction tube 5 having an inner tube 3 having an entry tube 2, a cooling gas introduction tube 4 at its head, and a high frequency work coil 6 attached to the plasma reaction tube 5. is the particle collection part 7 and the gas discharge port 8
is provided. To carry out the method of the present invention, first, argon gas is introduced into the reaction tube 5 from the plasma gas introduction tube 2, and then crystal frequency power is applied to the high frequency work coil 6. Gummy in the light trail of tube 3
When a discharge occurs.

This gummy discharge serves as a pilot flame to generate a plasma flame 9 in the reaction tube 5, so after the generation of this plasma flame, silane gas and/or silane gas and hydrocarbon compounds are released from the raw material gas introduction tube 1. Depending on the situation, a silicon compound may be introduced to start the reaction. If the frequency of this frequency control wave power is lower than 0.5 MHz, it will be difficult to generate plasma, and if the frequency is higher than 10 MHz, accidental sparks due to high frequency will easily occur, so this is 0.5 MHz.
It is best to have a power cycle of ~10 MHz - this may also be on the order of 1-100 KW.

In addition to argon gas as the working gas during plasma flame generation, adding a gas that does not inhibit this reaction, such as hydrogen gas, is effective when the input to the plasma flame increases and only argon gas is used as the working gas. This is an effective means to prevent the fluctuation of the generated plasma flame, and it is best to do this within a range where the plasma flame can be generated stably.

The method of the present invention involves introducing the raw material gas into the center of the plasma flame 9 so that the raw material gas flow is completely surrounded by plasma within the plasma flame, thereby absorbing the heat from the plasma flame to the center of the plasma flame 9. This is because it promotes the formation reaction of carbonized silicon in conjunction with gas.

The central axis of the raw material gas introduction pipe 1 described above is the plasma flame 9.
It is necessary to install the raw material gas so that it is aligned with the central axis of the
2. Therefore, it is only necessary to feed the plasma to the top of the flame. In addition, if the flow rate of the rice raw material gas is slow, there is a risk that the jet stream will not penetrate the plasma flame 9 and will flow along the outer edge of the plasma flame 9, and if it is too fast, the plasma flame 9 will be blown out. This is preferably 50 crn/paper or more, preferably in the range of 1 to 4 m/sec. The gas flow rate can be controlled by adjusting the amount of raw material gas and carrier gas introduced here, or by adjusting the amount of pigment gas. The inner diameter of the tip of the introduction tube 1 may be adjusted.

The silane or the mixed gas of silane and a hydrocarbon compound penetrated into the center of the plasma flame as described above.

Heating from this plasma flame reaches a temperature of about 2,000℃, which undergoes gas phase thermal decomposition to form β-type silicon carbide, but most of the silicon carbide produced is 111 m or less. It becomes a fine powder, which is also obtained without the contamination of undesirable impurities, and in this case, there is no reaction outside the plasma flame, so the silicon carbide generated in this case is absorbed into the reaction tube near the plasma flame. There is no possibility that it will stick to the wall.

Since the particles fall into the particle collecting section 7 along with the exhaust gas discharged from the gas outlet 8 provided at the lower part of the reaction tube, they can be easily collected.

In summary, 1. The method of the present invention is a gas-phase pyrolysis method using a plasma flame for silane compounds, and is characterized by penetrating the raw material gas into the center of the plasma flame. The plasma flame does not become unstable even if the supply rate is increased, and the raw material gas is heated extremely effectively by the plasma flame, making it possible to obtain silicon carbide at a high reaction rate and high production rate. In addition to its advantages, the silicon carbide obtained is extremely fine β-type silicon carbide particles, making it useful as a material for forming sintered bodies as ceramic materials. This provides an industrial advantage.

Next, examples of the present invention will be given.

Example A quartz tube with a diameter of 3'7 m + nφ was used as a plasma reaction tube, and as shown in Fig. 1, a four-person source gas tube, a plasma gas center tube, and a cooling gas introduction tube were attached to this. After nine people used the working gas shown in the table, a high frequency power of 3.6MHz-10KW was applied to the high frequency work coil and a gummy discharge was generated using one ignition, and a plasma flame was generated inside the tube. Therefore, the raw material gases shown in Table 1 were introduced into the reactor to start the reaction.

In this case, the flow rate of the raw material gas and the working gas was adjusted as shown in Table 1, and the raw material gas was adjusted to the center of the plasma flame, as shown in Table 1. The result is obtained.

When the particle size of the obtained silicon carbide powder was measured by centrifugal sedimentation method, as shown in Table 1, there were 9 particles of 1 μm or less.
There were sections 7-98.

For comparison, the above case and the case where the raw material gas is mixed with the working gas (Comparative Example 1) and the case where the raw material gas is supplied not to the center of the plasma flame but to the tail of the plasma flame (Comparative Example 2) are shown. When treated under the same conditions, in this case, as shown in Table 1, the yield of silicon carbide decreased and the amount of free silicon and carbon increased.

[Brief explanation of the drawing]

Figure 1 shows a vertical view of a plasma reactor for carrying out the method of the present invention.
■It shows the outline of the area. 1... Raw material gas 8 inlet pipe 2... Plasma gas inlet pipe 3... Inside 1 4... Cooling gas inlet pipe 5
...Plasma reaction tube 6...High frequency work coil 7...Particle collection section 8...Gas outlet 9...
・Plasma flame patent applicant Shin-Etsu Chemical Co., Ltd. No. 11-1

Claims (1)

[Claims] 1. General formula Rn5iOt4-n (where R is a hydrogen atom or a monovalent hydrocarbon group, at least one of which is a monovalent hydrocarbon group, and n is a positive number from 1 to 4). The gaseous organosilane shown and/or the general formula Hm81Ct4-m
One person places a mixed gas of silane and a volatile hydrocarbon compound (where m is a positive number between 0 and 4) in the center of a high-frequency induction plasma flame, and thermally decomposes it within the plasma flame. Characteristic method for producing finely divided silicon carbide 2, using aluminum as a working gas for high-frequency induced plasma flame