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 (ZrB2) 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-ZrB2 composite powders were investigated. The results showed that when the amount of H3BO3 added was the theoretical amount (i.e., 0 wt. % in excess) or 10 wt. % in excess, SiC-ZrB2 composite powders containing a certain amount of graphite could be prepared by holding at 1550 - 1650 degrees C for 2 h. When the amount of boric acid was 20 wt. % in excess, SiC-ZrB2 composite powders with a high purity were obtained at a calcination temperature of1650 degrees C. When the amount of boric acid was 30 wt. % in excess, SiC-ZrB2 composite powders with a high purity were successfully prepared at a calcination teperature higher than 1600 degrees 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 degrees C formed a diverse microstructure consisting of flaky, spherical, and columnar particles and whisker-like substances.