JPH0121090B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing ultrafine β-type polycrystalline silicon carbide having a spherical shape. In recent years, silicon carbide powder has been attracting attention as a raw material for forming heat-resistant ceramics, and with the development of applications for electronic materials, there is a demand for higher purity as well as improvements in sinterability and other physical properties. has been done. Therefore, methods for producing silicon carbide include methods of thermally decomposing methylchlorosilanes and hydrogen gas, silicon tetrachloride or monosilane and a hydrocarbon compound and hydrogen gas, or tetramethylsilane and hydrogen gas at high temperatures. However, methods using chlorosilanes such as methylchlorosilane and silicon tetrachloride have slow decomposition rates and problems in removing the by-product hydrochloric acid, and when monosilane is used, It has the disadvantages of being dangerous to handle and, like tetramethylsilane, very expensive, and the sinterability of silicon carbide obtained by these methods is not as good as that produced by conventional electric furnace methods. Similarly, there was a disadvantage that it was not necessarily satisfactory. The present invention relates to a method for producing silicon carbide that solves these disadvantages, and is based on the general formula (CH ₃ ) _a Si _b H _c (where b=1 to 3, 2b+1≧a,
At least one methylhydrodiene silane compound represented by a≧b, 2b+1≧c≧1, a+c=2b+2) is contained in a carrier gas at a concentration of 40% by volume or less, and this is added to a reaction zone at 750 to 1600°C. The crystallite size is 50.
It is characterized by obtaining spherical silicon carbide with an average particle size of aggregates of 0.01 to 1 μm at a particle diameter of 0.01 μm to 1 μm. To explain this, the present inventors first found that the molecule contains at least one ≡SiH bond, but ≡SiX bond (X is a halogen atom or an oxygen atom).
Developed a method for producing fine silicon carbide powder by thermally decomposing organic silicon compounds that do not contain carbon dioxide at temperatures above 1000°C (see Japanese Patent Application No. 147342-1982), which also
It was confirmed that the same effect could be obtained at temperatures below 1000℃, but after further research on this and examining the starting material and gas phase thermal decomposition conditions, we found that the above-mentioned methylhydrodiene silane By using the compound as a starting material and subjecting it to gas-phase pyrolysis under the reaction conditions described above, silicon carbide can be obtained in the form of spherical crystals with crystallites of 50 Å or less and an average particle size of the aggregates of 0.01 to 1 μ. Upon discovering this, we investigated its physical properties and found that it has particularly excellent sintering properties and can be easily sintered without the addition of sintering aids, which have conventionally been considered unavoidable in the sintering of this type of silicon carbide. The present invention was completed by confirming that it could be molded to high density and sintered. The methylhydrodiene silane compound used as the starting material in the method of the present invention has the above general formula (CH ₃ ) _a
It is represented by Si _b H _c , which includes
_{CH3SiH3 ,} ( _CH3 ) _{2SiH2 ,} ( _CH3 ) _3SiH ,
_{CH3H2SiSiH2CH3 ,} ( _CH3 ) _{2HSiSiH ( CH3} ) _{2 ,}
(CH ₃ ) ₂ HSi―SiH(CH ₃ )―SiH(CH ₃ ) ₂ ,
(CH ₃ ) ₂ HSi—Si(CH ₃ ) ₂ —SiH(CH ₃ ) ₂ is exemplified, and these are used either singly or as a mixture of two or more of them. The product obtained by thermal decomposition as described above or by reduction of methylchlorodisilanes produced as a by-product during the synthesis of methylchlorosilanes by the reaction of metal silicon and methyl chloride, which is called the direct method. Available. In the method of the present invention, the above-mentioned methylhydrodiene silane compound is introduced into a vertical or horizontal tube furnace together with a carrier gas and pyrolyzed in the gas phase at 750 to 1600°C.The concentration of this silane compound is 40% by volume. In this case, the yield decreases due to the adhesion of silicon carbide to the reaction tube wall, and the size of the crystallites of this silicon carbide increases, and the particle size distribution of the aggregate becomes wider, resulting in sintering. The concentration of this silane compound in the carrier gas should be less than 40% by volume, preferably less than 30% by volume, since this has the disadvantage of reduced properties. There is no particular lower limit to the concentration of the silane compound in this mixed gas, but if it is too low, the productivity of silicon carbide will be excessively low.
This is preferably 0.2% by volume or more, preferably 1% by volume or more. In addition, if the thermal decomposition temperature is set below 750°C, the thermal decomposition reaction will not occur sufficiently and an oily polymer will form on the tube wall, resulting in a rapid decrease in yield, whereas if it is set above 1600°C, this The decomposition of CH ₄ produced by decomposition is promoted and carbon is produced.
Since this will be mixed in the target silicon carbide, it is necessary to keep it in the range of 750 to 1600°C, preferably 800 to 1500°C. Note that this thermal decomposition reaction is performed by increasing the concentration of the silane compound as described above.
It needs to be 40% by volume or less, and as a carrier gas to dilute it, an inert gas such as hydrogen gas, helium, argon, or nitrogen gas, or a mixture of these gases may be used.
Preferred is hydrogen gas or hydrogen gas to which nitrogen gas, helium, or argon is added. According to the method of the present invention, as described above, when the crystallite size is 50 Å or less, the average particle size of the aggregate is
Ultrafine silicon carbide particles with a spherical shape of 0.01 to 1μ can be obtained, but this can be obtained by easily refining the methylhydrodiene silane compound as a starting material to a high purity by distillation. It can be obtained as a high-purity product with extremely few impurities, and this is also because the product obtained by thermal decomposition is a spherical body with a uniform particle size with a very narrow particle size distribution. There is no need for any process, and the particle size can be freely adjusted by changing the concentration of the silane compound mentioned above and the reaction conditions for thermal decomposition. The advantage is that ultrafine silicon carbide of any particle size can be easily obtained. Next, examples of the method of the present invention will be given. Example 1 An alumina reaction tube with an inner diameter of 52 mm and a length of 1000 mm was installed in a horizontal reactor, the temperature at the center was maintained at 1150°C, and tetramethyldisilane [(CH ₃ ) ₂ HSi
- Hydrogen gas containing 3% by volume of SiH (CH ₃ ) ₂ ]400
ml/min for 8 hours for gas phase pyrolysis, 15.5 g of brown ultrafine silicon carbide powder (yield 75
%)was gotten. Next, chemical analysis of this powder revealed that it was high purity silicon carbide with Si = 69.9% and C = 29.4%, and that Al, Cr, Cu, and
The amounts of impurities such as Fe, Mg, Mn, Ni, Ti, and V were all 10 ppm or less. In addition, regarding this, bright field images of electron microscopy (Fig. 1) and β-SiC
(111) A dark-field image (Figure 2) was created by diffraction, and the size and grain size of the crystallites were measured based on this image. The size of the crystallites was less than 20 Å, and the average aggregate size was A spherical shape with a particle size of 0.1-0.2μ was observed. This is also a centrifugal automatic particle size distribution analyzer (CA manufactured by Horiba, Ltd.).
The measurement results using the PA500 model confirmed that there were no particles smaller than 0.08 μm or larger than 0.5 μm, and that 88.3% of the particles were spherical in size from 0.1 to 0.3 μm. Furthermore, when this powder was subjected to X-ray diffraction,
This becomes as shown in Figure 3, which is the β type.
It was confirmed that it was SiC, but the specific surface area of this material measured by the Betts method was 26.8 m ² /g.
The infrared absorption measured by the KBr method was as shown in Figure 4. Examples 2 to 7 In the method of Example 1, the concentration of tetramethyldisilane, the type of carrier gas, and its hydrogen gas concentration were changed as shown in Table 1, and the materials were treated in the same manner as in Example 1 to cause a thermal decomposition reaction. As a result, the results shown in Table 1 were obtained.
In addition, in the comparative example, the reaction time was 4 hours, but in this case SiC thickly adhered inside the reaction tube and was damaged during cooling.

[Table] Examples 8 to 17 In Example 1, the type and concentration of the methylhydrodiene silane compound, the composition and amount of carrier gas introduced, and the reaction temperature were changed as shown in Table 2, and the same procedure as in Example 1 was carried out. As a result of the treatment, the desired ultrafine silicon carbide powder was obtained with a yield of 70% or more in all cases. Next, the physical properties of the silicon carbide powder thus obtained were measured using the same method as in Example 1, and the results shown in Table 3 were obtained. They were molded in a hot press carbon mold without any additives, and then heated and sintered at 1900°C for 0.5 hours in an argon gas atmosphere. The result was a sintered body with a density of %).

【table】

[Table] %, which was rather poor.

[Brief explanation of drawings]

Figure 1 shows a bright-field electron microscope image of ultrafine particulate carbon obtained by the method of the present invention, and Figure 2 shows its β
-Dark field image of SiC (111) diffraction, Figure 3 is its X-ray diffraction diagram, and Figure 4 is the image of this silicon carbide.
This shows infrared absorption by the KBr method.

Claims (1)

[Claims] 1 General formula (CH ₃ ) _a Si _b H _c (here b = 1 to 3, 2b
+1≧a, a≧b, 2b+1≧c≧1, a+c=
At least one methylhydrodiene silane compound represented by 2b+2) is contained in a carrier gas at a concentration of 40% by volume or less, and the mixture is heated at 750°C.
Gas-phase pyrolysis is performed in a reaction zone at ~1600°C, and the crystallite size is less than 50 Å and the average particle size of the aggregates is
A method for producing ultrafine silicon carbide, characterized by obtaining silicon carbide in the form of spherical bodies of 0.01 to 1 μm.