Abstract
The effect of additives on carbothermal reduction-nitridation was investigated for the preparation of AlN powders from the Al2O3-C-N2 system. According to the role of additives in nitridation, they were divided into three categories: “promote”, “have no effect” and “disturb”. In particular, CaF2 was an excellent nitridation promoter providing spherical AlN particles. The apparent activation energy of nitridation for CaF2 addition was 190kJ/mol, while those for Y2O3, Yb2O3 and without additive were around 250kJ/mol. CaF2, Y2O3, Yb2O3 and transition metal compounds strongly affected AlN grain morphologies, supplying spherical and rod-like shapes of AlN. It was estimated that the reduction-nitridation proceeds through the formation of intermediates like CaF2⋅5Al2O3 and Y-aluminates.
