Growth of cubic and hexagonal BN particles by using BBr3, NH4Br and metallic Na as reactants

Hexagonal BN (h-BN) particles were prepared by using BBr3, NH4Br and metallic Na as reactants in stainless steel autoclaves at 450ºC for 24h; When the target temperature was set in the range of 500–600ºC, cubic BN (c-BN) particles that co-existed with h-BN were obtained. It is found that 600ºC and a molar ratio of BBr3 to NH4Br of 1:3 are the optimal reaction parameters for the highest yield production of c-BN particles. c-BN powder with controllable content has been synthesized through a one-step method in the absence of solvents. The as-obtained samples that contain pure h-BN and the mixture of c-BN and h-BN have high thermal stabilities in ambient atmosphere below 920 and 1100ºC, respectively.