Synthesis of AIN Powder by Carbothermal Reduction-Nitridation of Various AI2O3 Powders with CaF2

摘要

The synthesis of AIN powders by carbothermal reduction-nitridation of various types of AI2O3 powders, which were prepared by Bayer method and alkoxide method, was investigated. Calcium fluoride (CaF,) was added as a catalyst to promote the reaction. An AI2O3/C molar ratio of 0.29 and CaF, of 3wt were fixed in advance. The reduction-nitridation was performed at 1400 to 1450 deg. C in an N2 flow. The nitridation rates tended to increase with decreasing particle size of raw AI2O3 powder, and also depended on the synthesizing method of Al2O3 powder. The powder made by the Bayer method reacted with CaF2, to form CaF2, , 5Al2O3 as an intermediate. Equiaxed AIN particles with uniform size and shape were obtained through this process. The particle size of AIN products increased somewhat with increasing reaction temperature. It is most meaningful that different conditions yielded almost the same particle size with equiaxed shape and narrow size distributions. This phenomenon suggests that the controlling step determining the size and shape is in the reduction-nitridation process of the intermediate .