Effect of oxide additives on the morphology of fine-particle silicon carbide

Silicon carbide powders were prepared from pelletized mixtures of fine-particle SiO2 and petroleum coke with CaO, Fe2O3, and Al2O3 additions at temperatures from 1770 to 1870 K and atmospheric pressure. The Si loss in the form of SiO and the SiC:yield were measured. The materials with CaO additions consisted of needlelike crystallites and a small amount of submicron-sized particles. The materials containing Fe2O3 consisted of roughly equal amounts of needlelike crystallites and submicron-sized particles. The introduction of CaO-Fe2O3 (10-66% Fe2O3) combined additions resulted in materials consisting mainly of submicron-sized particles. In the presence of Al2O3, needlelike crystallites did not grow.