SiC-B₄C composite powders were synthesized by the carbothermal reduction method under an argon atmosphere using different kinds of carbon sources (carbon black and starch) and silica sol and boric acid as the precursor raw materials. Based on thermodynamic analysis and calculation, the effects of different carbon sources and reaction temperatures on the mass loss rate, phase composition, and microstructure of SiC-B₄C ultrafine composite powders were comparatively studied. Results showed that the optimum conditions for synthesizing SiC-B₄C composite powders with carbon black as the carbon source were 1550 ºC for 2 h, whereas the optimum conditions for synthesizing SiC-B₄C composite powders with starch as the carbon source were 1450 ºC-1550 ºC for 2 h. The powder samples synthesized with carbon black as the carbon source at 1550 ºC were mainly composed of flaky, columnar-like, spherical, and irregular polyhedral particles (about 100-200 nm in diameter). Mutual cohesion or agglomeration between particles was minimal. In the powder samples synthesized at 1550 ºC with an excess of 10 wt% starch, in addition to a certain amount of flaky, spherical, and other irregular structure particles, a certain amount of uniform, slender whiskers (about 50-100 nm in diameter) and a certain phenomenon of lap and winding between the whiskers were noted. The powder samples synthesized at 1550 ºC with an excess of 20 wt% starch had no whisker-like substance

Keywords: carbon black, starch, SiC-B₄C, composite powders, synthesis