Direct Nitridation Synthesis of Quasi-Spherical β-SiN Powders with CaF Additive.

In this work, the quasi-spherical β-SiN powders were synthesized via an efficient direct nitridation strategy with CaF as the catalytic material under NH atmosphere. The effect of CaF on phase composition and crystalline morphology was studied. CaF additive can accelerate the nitridation of silicon powders, and the particles of nitridation products tend to have an equiaxed structure with the CaF additive increasing. When 4 wt% CaF additive or more was added, submicron β-SiN particles with quasi-spherical morphology and eminent crystal integrity were obtained. In contrast, irregular α-SiN particles appear as the main phase with less than 4 wt% CaF additive. The growth mechanism of SiN particles was also discussed. CaxSiyOz liquid phase is crucial in the nitridation of silicon powders with CaF additive.