Abstract
Two kinds of silicon carbide powders prepared from different synthesizing process were classified and decarbonated to investigate the particle size dependence of powder properties. Influence of the particle size on the sintering behavior was studied by dilatometry and microstructural observations. A powder synthesized from metallic silicon and carbon in solid state has a broad primary particle size distribution. This powder was also characteristic in having large amounts of unreacted carbon and impurity oxygen in the fine fraction of classified powder. The densification with boron and carbon additives progressed initially with equiaxial grain growth, and then, with formation of plate-like grains at high temperatures. The free carbon contained in the fine fraction promoted the densification remarkably at the initial stage sintering, while the coarse fraction reduced the densification rates. Inhomogeous sintered bodies were obtained from the powder consisted of the fine fraction with the large amount of free carbon and poorly sinterable coarse fraction. On the contrary, the other powder synthesized from tetrachlorosilane and heavy oil in gas phase had a narrow size distribution. In this case, the classified and decarbonated fractions showed almost the same densification behavior producing sintered bodies with homogeneous microstructure. The starting powder have to be homogeneous in chemical composition especially in fine fractions in addition to the reduced fraction of coarse particles.
