Effect and corresponding mechanism of NaCl additive on boron carbide powder synthesis via carbothermal reduction

Abstract The demand of high-quality boron carbide (B 4 C) is enormous for various application, while its yield is quite low (40–50%) that needs to be improved. In this study, the effects of sodium chloride (NaCl) additive on the quality and yield of B 4 C synthesized by carbothermal reduction from an H 3 BO 3 –C powder mixture were investigated in detail. Under the optimal amount of 4 wt% NaCl additive, the purity, yield, and average particle size of B 4 C increase from 93.54% to 96.28%, 88.82% to 93.56%, and 24.2 to 43.3 μm, as compared to the case without additive. Furthermore, the underlying effect mechanism of the NaCl additive was comprehensively analyzed. The NaCl additive promotes the depolymerisation of the complex network structure of B 2 O 3 reactant and effectively decreases its viscosity by about 73%. This facilitates the mass transfer and improves the reaction kinetic, and thereby increases B 4 C yield. Additionally, the lower viscosity improves the kinetic condition of B 4 C crystal formation and promotes the growth of crystal, thus increasing the particle size. This study may imply a feasible route for the large-scale production of high-quality B 4 C.