Direct Nitridation Synthesis of Quasi-Spherical β-Si(3)N(4) Powders with CaF(2) Additive

In this work, the quasi-spherical β-Si(3)N(4) powders were synthesized via an efficient direct nitridation strategy with CaF(2) as the catalytic material under NH(3) atmosphere. The effect of CaF(2) on phase composition and crystalline morphology was studied. CaF(2) additive can accelerate the nitridation of silicon powders, and the particles of nitridation products tend to have an equiaxed structure with the CaF(2) additive increasing. When 4 wt% CaF(2) additive or more was added, submicron β-Si(3)N(4) particles with quasi-spherical morphology and eminent crystal integrity were obtained. In contrast, irregular α-Si(3)N(4) particles appear as the main phase with less than 4 wt% CaF(2) additive. The growth mechanism of Si(3)N(4) particles was also discussed. CaxSiyOz liquid phase is crucial in the nitridation of silicon powders with CaF(2) additive.