Abstract: A powdery mixture of a fine silicon carbide powder admixed with boron or a boron compound, e.g. boron carbide, titanium boride and boron oxide, as a sintering aid is compression-molded into a green body which is subjected to a sintering treatment into a sintered body. Different from conventional methods in which the sintering treatment is performed always in an atmosphere of an inert gas, e.g. argon, the sintering treatment in the inventive method is performed in an atmosphere of a rare gas containing 0.005-5% by volume of nitrogen. The sintered body of silicon carbide obtained by this method has an outstandingly high electric volume resistivity of 10.sup.10 to 10.sup.13 ohm.cm and a coefficient of thermal conductivity of 100-220 W/m.K.

Abstract: In place of the conventional silicon source materials used in the prior art method for the preparation of silicon carbide whiskers, the inventive method utilizes a hydrolysis product of a chlorosilane compound R.sub.a SiCl.sub.4-a or a chlorodisilane compound R.sub.b Si.sub.2 Cl.sub.6-b, in which R is a hydrogen atom or a monovalent hydrocarbon group, a is zero to 3 and b is 1 to 5, as the silicon source which is intimately mixed with a powder of carbon and the mixture is heated at 1400.degree. to 1700.degree. C. to give silicon carbide whiskers in a high conversion. Alternatively, the hydrolysis of the chloro(di)silane compound is performed in an aqueous medium in which a powder of carbon is dispersed in advance so that the hydrolysis product as formed is already a mixture with the carbon powder.

Abstract: Sintered bodies of silicon carbide having remarkably increased volume resistivity and thermal conductivity can be obtained by heating a green body shaped of a fine silicon carbide powder admixed with boron or a boron compound, e.g. boron carbide, titanium boride and boron oxide, as a sintering aid at 1800.degree. to 2200.degree. C. in the presence of or in the vicinity of a shaped body of a powdery mixture of a fine silicon carbide powder admixed with boron nitride in the same furnace. The improvements in the volume resistivity and thermal conductivity of the sintered body are particularly remarkable when the fine silicon carbide powder is a pyrolysis product of a methyl hydrogen silane compound such as tetramethyl disilane.

Abstract: The invention provides a method for the preparation of an ultrafine powder of silicon carbide having an extremely fine and uniform particle size distribution of spherical agglomerate particles each formed of crystallites of 5 nm or smaller in size. The silicon carbide powder is prepared by the vapor phase pyrolysis of a specified methyl hydrogen(poly)silane as diluted with a carrier gas, e.g. hydrogen, to give a concentration of 40% by volume or lower at a temperature of 750.degree. to 1600.degree. C. The silicon carbide powder can readily be sintered at a temperature of 1750.degree. to 2500.degree. C. even without addition of a sintering aid to give a sintered body of extremely high density reaching 80% or larger of the theoretical value which can never be obtained of the conventional silicon carbide powders.