Sintering of silicon carbide and theory of sintering

Abstract

The three important aspects of sintering of SiC, that is, powder processing, sintering additives and sintering theory, are reviewed in this paper. First, in order to obtain sinterable SiC powder, the carbothermic reduction of SiO2 was investigated using a precursor derived from liquid sources, β(3C)-SiC powder free from any residual carbon was synthesized. The powder did not need a purification process and could be sintered with C and a small amount of B additives. Second, low-temperature sintering of α(6H)-SiC powder by AlB2 and C additives was developed. AlB2 addition enabled the sintering of SiC powder at around 1900°C. Al atoms from the additives dissolved into SiC and promoted elongation of grains during sintering. The fracture toughness of sintered SiC increased with the aspect ratio of the grains. Third, to understand the sintering behavior of SiC powder, new sintering models and a theory were proposed. In the theory, it was assumed that total excess energy in a system drove mass transport for sintering and grain growth. From the rate equations of sintering and grain growth, the surface energy and the grain boundary energy were found to play an important role in both processes.