Synthesis of AlN Powder by Carbothermal Reduction-Nitridation of Various Al_2O_3 Powders with CaF_2

摘要

The effect of Al_2O_3, properties on the synthesis of AlN powder by the carbothermal reduction-nitridation method with CaF_2 addition was investigated. Four types of Al_2O_3 powders, one type prepared by the Bayer method and three types prepared by the Alkoxide methods, were compared in this work. An Al_2O_3/C molar ratio of 0.29 was selected. The amount of CaF_2 powder added was adjusted to 3wt%. The carbothermal reduction-nitridation was carried out at 1400 and 1450°C in N_2 flow. Nitridation rate tended to increase with decreasing particle size of raw Al_2O_3, and also to depend on synthesizing method of Al_2O_3. The raw Al_2O_3 powder made by the Bayer method was confirmed to form CaF_25·Al_2O_3, as an intermediate. In contrast the intermediates could not be detected by XRD in powders made by the Alkoxide method. The reason is not clear. Particle sizes of the products increased somewhat with increasing reaction temperatures. However, even though different particle sizes of Al_2O_3 powders were used, AlN powders synthesized under the same condition showed nearly equal particle size with round shape and narrow size distribution. This phenomenon suggests that the controlling step determining the size and shape is in the reduction -nitridation process of the intermediate compounds.