Synthesis and sintering of SiC under high pressure and high temperature

Starting from elemental powders, simultaneous synthesis and compaction of S iC were conducted at 3 GPa pressure and temperatures in the range 2100-2900 K. The sintered compacts were characterized by x-ray diffraction, microhar dness measurements, and microscopic studies. The efficiency of formation of SiC was dependent on the particle size of the silicon powder, crystallinit y of the reactant carbon, molar ratio of silicon and carbon, and synthesis temperature and time. Carbon in excess of the stoichiometric amount was req uired 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 ha rdness of 3.21 g/cm(3) (98.8% of theoretical density) and 22 GPa, respectiv ely. 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 alph a- and beta-SiC above 2500 K were obtained. The beta-SIC was highly crystal line and nearly defect-free.