Sintering of Ultrafine Silicon Carbide Powders by Using Boron and Carbon as Sintering Aids

Abstract

The sinterability of ultrafine 8-SiC powders with the average particle size of 0.01-0.05, μm obtained by three kinds of vapor phase reactions, (CH₃)₄Si-H₂ system at 1200-1300°C, SiH₄, CH₄, -H₂, system at 1400°C and CH₃SiCl₃-H₂ system using plasma jet method, was compared in the presence of boron and/or carbon as sintering aids at 1400-2050°C. The effects of the sintering aids on the grain growth of SiC were also investigated to elucidate the function of the aids in densification of SiC. The following results were obtained.
(1) The sinterability of SiC powders hardly varied with their synthesis methods, except SiC powder consisting of hollow particles produced by the SiH₄ system the sintered bodies with the relative density of above 90% were obtained by the pressureless-sintering in the presence of boron and/or carbon at 2050°C. The crystallinity of SiC powders did not affect the sinterability to observable extent.
(2) The addition of boron or carbon suppressed the grain growth of SiC. This effect was remarkably enhanced by simultaneous addition of boron and carbon. The coexistence of them, which was essential for the densification of SiC, was characterized by the suppression of grain growth in the course of heating up to sintering temperatures.