Processing factors influencing the free carbon contents in boron carbide powder by rapid carbothermal reduction

Abstract

High quality boron carbide powder without free carbon is desired for many applications. In this study, the factors that influence free carbon content in boron carbide powders synthesized by rapid carbothermal reduction reaction were evaluated. The dominant factors affecting free carbon contents in boron carbide powder were reaction temperature, precursor homogeneity, the particle size of reactants, and excess boron reactant amount. The reaction temperature at 1850°C was sufficient to synthesize boron carbide with low free carbon content. Depending on process conditions, precursor homogeneity was also affected by the calcination temperature and time. Smaller particle size of reactants contributed to less carbon content and more uniformity in synthesized boron carbide. Excess boric acid effectively compensated for B2O3 volatilization. In the optimal sample, using 80mol% excess nano boric acid and calcined at 500°C, the free carbon in the synthesized boron carbide was negligible (0.048wt.%).