JPS6366768B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing ultrafine silicon carbide, particularly ultrafine β-type silicon carbide having a uniform spherical shape. Silicon carbide has traditionally been widely used as a fireproof material, abrasive material, and non-metallic heating element, but it has excellent abrasion resistance, oxidation resistance, hot strength, thermal conductivity, and radio wave absorption properties. Because of its excellent physical properties, it has recently been attracting attention as a material for sintered bodies, abrasive materials, molding materials, as well as structural materials and substrate materials for electrically active parts. On the other hand, hot press method, normal pressure sintering method, reaction sintering method, etc. are known as sintering methods for obtaining sintered bodies of silicon carbide, and these sintering methods can improve sintering degree and strength. In order to obtain a sintered body with excellent properties, silicon carbide as a raw material must be made into a powder that has as fine and uniform a particle size as possible and does not contain unnecessary impurities. Silicon carbide, which is obtained by the thermal decomposition method of methylsilane, which is produced by the gas-phase reaction of silicon tetrachloride and hydrocarbon gas using plasma as a heat source, is sintered due to strong mutual agglomerative bonds even if the particles are thin. The disadvantages are that the properties are not necessarily good, the productivity is poor, and there is also a problem in removing the by-product hydrochloric acid. For this reason, the applicant of this patent first decomposed an organic silicon compound containing at least one ≡SiH bond in the molecule but not containing SiX (X is a halogen atom or an oxygen atom) at 750°C or higher in the vapor phase. We developed a method to produce fine silicon carbide powder, and after further research on this, we developed the organosilicon compound with the general formula (CH ₃ ) _a Si _b H _c (b is an integer from 1 to 3, 2b+1≧
a, a≧b, 2b+1≧c≧1, a+c=2b+2)
If the methylhydrodienesilane compound shown by is subjected to gas phase pyrolysis in a heating furnace, the crystallites will consist of silicon carbide aggregates of 50 Å or less, and the average particle size will be
It is possible to obtain high purity silicon carbide fine powder having a uniform spherical shape of 0.01 to 1μ, and
It was discovered that this product has extremely superior sintering properties compared to conventional commercially available products (Patent application No. 58
- see specification No. 155912). However, in this heating furnace-based gas phase pyrolysis method, especially when high temperatures of 1000°C or higher are required, the reaction tube must be made of a magnetic tube such as a quartz tube or an alumina tube, making it difficult to mass-produce. In this case, a small amount of silicon carbide film is deposited on a part of the reaction tube, which may cause the reaction tube to burst. In order to obtain powder, it was necessary to increase the amount of carrier gas and lower the concentration of the methylhydrodiene silane compound as a raw material, which was found to be problematic from an economic standpoint. The present inventors conducted various studies on methods to solve the above-mentioned disadvantages and drawbacks, and as a result, the general formula (CH ₃ ) _a Si _b H _c (b is an integer from 1 to 3, 2b+1≧a,
If a methylhydrodiene silane compound (a≧b, 2b+1≧c≧1, a+c=2b+2) is introduced into the tail of a non-oxidizing high-frequency plasma flame and is thermally decomposed by contact with the plasma flame, it can be formed into a uniform spherical shape. The present invention was completed by confirming that β-type silicon carbide in the form of ultrafine particles can be easily obtained. As mentioned above, the methylhydrodiene silane compound used as the starting material in the method of the present invention is represented by the general formula (CH ₃ ) _a Si _b H _c and contains at least one ≡SiH bond in its molecule, but ≡ Does not contain SiX (X is a halogen atom or an oxygen atom),
These include _{CH3SiH3 ,} ( _{CH3 ) 2SiH2} , ( _CH3 ) _3SiH , _{CH3H2Si - SiH2CH3 ,} ( _CH3 ) _2HSi -SiH( _CH3 ) ₂ , H( Examples include _CH3 ) _2Si - _SiCH3H -Si( _CH3 ) _2H , H( _CH3 ) _2Si -Si( _CH3 ) ₂ -Si( _CH3 ) _2H , etc. Type 1 or 2
Used as a mixture of more than one species. This methylhydrodiene silane compound can be obtained by thermally decomposing polydimethylsilane at 350°C or higher,
It can also be obtained by reducing methylchlorodisilanes, which are by-produced during the synthesis of methylchlorosilanes by the reaction of methyl chloride and metal silicon, which is called the direct method, but these can be easily obtained by distillation. It can be purified to high purity. The method of the present invention is to thermally decompose the above-mentioned methylhydrogensilane compound by contacting it with a high-frequency plasma flame to obtain silicon carbide. Ultrafine silicon carbide particles with a uniform spherical shape and a particle size distribution of 0.01 to 0.2 μm can be easily obtained. This is because the above-mentioned methylhydrodienesilane compound is thermally decomposed more quickly than chlorosilanes such as methyltrichlorosilane, which have traditionally been used to produce silicon carbide through thermal decomposition reactions. The silicon carbide obtained by the method of the present invention also has the advantage of having excellent sinterability, and it does not require the use of sintering aids, which were conventionally considered indispensable for sintering silicon carbide. It can be easily sintered by normal pressure sintering without addition. The high-frequency plasma used as a heat source in the method of the invention may be generated in a high-frequency electromagnetic field of 1 to 10 MHz, and the working gas may be a monoatomic molecular gas, for example a monocomposition gas such as argon gas. The gas may be a gas that does not inhibit the reaction, for example, a mixed gas of hydrogen gas and a monatomic molecular gas, or it may be a composition gas that does not contain any monatomic molecular gas. However, when using a mixture of monatomic molecular gas and other gases as the working gas, the mixing ratio of the two becomes unstable when a gas other than monatomic molecular gas is mixed in when the plasma flame power is low. This is due to the power of the plasma flame, as the plasma flame becomes stable even without mixing monatomic molecular gas when the power of the plasma flame is high enough. However, it is necessary to avoid the mixing of oxidizing gases as this will lead to oxidation of the silicon carbide particles produced. Furthermore, in the method of the present invention, a methylhydrogensilane compound is introduced into the tail of a plasma flame and thermally decomposed.For example, as shown in FIG. 1, a working gas is supplied from a working gas supply port 1, Methylhydrogensilane is supplied from the reaction gas supply pipe 5 provided at the tail of the plasma flame 3 in the reaction tube 4, which generates plasma 3 by being held in a high-frequency electromagnetic field by the high-frequency current flowing through the coil 2. This method involves introducing a compound and thermally decomposing it using the heat of plasma flame, but according to this method, even though the methylhydrogensilane compound has little chance of receiving heat from the plasma, the methylhydrogensilane compound As mentioned above, the diene compound has a very high thermal decomposition rate, so thermal decomposition proceeds easily, and it is also possible to supply a large amount of raw material gas, which improves the productivity of silicon carbide. This gives you the advantage of being able to The methylhydrogensilane compound can be introduced into the reaction tube by mixing the methylhydrogensilane compound into the plasma working gas in advance and supplying it together with the working gas, as shown in FIG. Further, as shown in FIG. 3, a method in which a methylhydrogensilane compound is penetrated into the central axis of the plasma flame is also considered. However, in order to keep the plasma flame stable, the method shown in Figure 2 poses a problem in terms of production because it is necessary to determine the mixing ratio of the methylhydrodiene silane compound depending on the applied voltage. The silicon carbide produced in this process adheres to and accumulates on the inner wall of the reaction tube.
If this becomes excessive, the plasma becomes unstable and the reaction tube becomes red hot, making it impossible to operate for long periods of time. In order to penetrate the plasma, for example, it is necessary to install a gas supply pipe and maintain an appropriate gas ejection speed, which poses difficulties in workability.If this is not done properly, the plasma flame may become unstable or disappear. As a result, there is a problem that productivity becomes unstable, so the method of the present invention, which introduces the methylhydrogensilane compound into the tail of the plasma flame described above, is industrially the most stable and advantageous method. It is considered a method. Next, Examples and Comparative Examples of the method of the present invention and application examples of the ultrafine particulate β-type silicon carbide obtained by the method of the present invention will be shown. Examples 1 to 6, Comparative Examples 1 to 3 An argon plasma flame was generated in a quartz plasma generation tube with an inner diameter of 37 mm using a high frequency current with a high frequency oscillation tube input of 10 KW and an oscillation frequency of 3.6 MHz.
When various methylhydrogensilane compound gases listed in Table 1 were introduced into the plasma flame tail and thermally decomposed to produce ultrafine silicon carbide, the results shown in Table 1 were obtained. Ta. For comparison, a case where methyltrichlorosilane was used as the methylhydrogensilane compound (Comparative Example 1), and a case where the methylhydrogensilane compound was mixed with argon gas as a working gas and introduced from the top of the plasma flame (Comparative Example 2) Furthermore, when silicon carbide was produced in the case where a methylhydrogensilane compound was introduced so as to penetrate the central axis of the plasma flame (Comparative Example 3), the results shown in Table 1 were obtained. Ta. The X-ray diffraction diagram of the ultrafine particulate β-type silicon carbide obtained in Example 2 is shown in Figure 4, and the IR
The chart is as shown in Figure 5. In addition, the average crystallite diameter of the ultrafine silicon carbide shown in Table 1 can be determined from the dark field image of an electron microscope or the X-ray diffraction diagram using the following formula: L=0.9×λ/β×cosθ [L: Average crystallite diameter (Å) λ: X-ray wavelength (Å) β: Half-width of diffraction peak (radians) θ: Black reflection angle] The particle size of the aggregate was measured by electron microscopy and centrifugal sedimentation. It is something.

[Table] Application example 1 15g of ultrafine particulate β-type silicon carbide obtained in Example 2
was placed in a hot press carbon mold with a diameter of 40 mm without adding any sintering aids, degassed under reduced pressure, and placed in an argon gas atmosphere under a pressure of 100 kg/ ^cm2 .
After heating and sintering at 2300°C for 30 minutes and measuring the density after cooling, an excellent sintered body with a density of 2.90 g/CC (91% of the theoretical density) was obtained. Application example 2 15% by weight of the ultrafine β-type silicon carbide obtained in Example 2 was mixed into an epoxy paint, and this was applied to the bonnet of a metal stereo lamp to a thickness of 0.15 mm. When I compared the reproduced sound with an amplifier that did not have this, I found that this one did not muddy the sound at all due to noise, I could listen to transparent reproduced sound, and it had excellent radio wave shielding properties.

[Brief explanation of drawings]

FIG. 1 is a schematic longitudinal cross-sectional view of a silicon carbide manufacturing apparatus according to the method of the present invention, and FIGS. 2 and 3 are longitudinal cross-sectional views of a silicon carbide manufacturing apparatus according to a method of a comparative example. Figure 4 is an X-ray diffraction diagram of ultrafine silicon carbide obtained by the method of the present invention, and Figure 5 is its IR.
This shows the chart. DESCRIPTION OF SYMBOLS 1... Working gas supply port, 2... High frequency work coil, 3... Plasma flame, 4... Reaction tube, 5... Reaction gas supply tube.

Claims (1)

[Claims] 1 General formula (CH ₃ ) _a Si _b H _c (where b is an integer from 1 to 3, 2b+1≧a, a≧b, 2b+1≧c≧1, a
+c=2b+2) A method for producing ultrafine silicon carbide, which comprises introducing at least one methylhydrogensilane compound represented by the following formula into the tail of a high-frequency plasma flame and thermally decomposing it.