Synthesis and sintering of SiC under high pressure and high temperature

Starting from elemental powders, simultaneous synthesis and compaction of SiC were conducted at 3 GPa pressure and temperatures in the range 2100-2900 K. The sintered compacts were characterized by x-ray diffraction, microhardness measurements, and microscopic studies. The efficiency of formation of SiC was dependent on the particle size of the silicon powder, crystallinity of the reactant carbon, molar ratio of silicon and carbon, and synthesis temperature and time. Carbon in excess of the stoichiometric amount was required to obtain compacts free from residual silicon. The SiC samples, with a Si:C molar ratio 1:1.05, prepared at 2100 K for 300 shad a density and hardness of 3.21 g/cm(3) (98.8% of theoretical density) and 22 GPa, respectively. The crystal structure of the SiC depended on the synthesis temperature. Pure beta-SiC in the temperature range 2100-2500 K, and a mixture of alpha- and beta-SiC above 2500 K were obtained. The beta-SIC was highly crystalline and nearly defect-free.