SYNTHESIS AND CHARACTERISATION OF SiC-ZrB₂ COMPOSITE POWDERS BY CARBOTHERMAL/BOROTHERMAL REDUCTION REACTION

Four raw materials, namely, zirconium silicate, silica sol, boric acid, and graphite, were slected as precursor materials.Silicon carbide (SiC)-zirconium borate (ZrB 2 ) ceramic composite powders were prepared via carbothermal/borothermal reduction in a high-temperature tube furnace under an argon atmosphere.The effects of the boric acid dosage and calcination temperature on the phase composition and microstructure of the SiC-ZrB 2 composite powders were investigated.The results showed that when the amount of H 3 BO 3 added was the theoretical amount (i.e., 0 wt.% in excess) or 10 wt.% in excess, SiC-ZrB 2 composite powders containing a certain amount of graphite could be prepared by holding at 1550 -1650 C for 2 h.When the amount of boric acid was 20 wt.% in excess, SiC-ZrB 2 composite powders with a high purity were obtained at a calcination temperature of 1650 C.When the amount of boric acid was 30 wt. % in excess, SiC-ZrB 2 composite powders with a high purity were successfully prepared at a calcination teperature higher than 1600 C.In addition, when the amount of boric acid was 20 wt.% in excess, a large amount of bamboo-like whisker materials with a diameter of approximately 50 -200 nm appeared in the poder samples.These materials overlapped and were wound together.When the amount of boric acid was 30 wt. % in excess, the powder samples prepared at 1600 -1650 C formed a diverse microstructure consisting of flaky, spherical, and columnar particles and whisker-like substances.