Synthesis of AlN Powder by Carbothermal Reduction‐Nitridation of Various Al2O3 Powders with CaF2

Abstract

We investigated the effect of characteristics of raw Al2O3 powder on the synthesis of AlN by the carbothermal reduction‐nitridation method, in which CaF2 was added as a catalytic material. Four types of Al2O3 powders were selected. An Al2O3/C molar ratio of 0.29 was fixed, and the amount of CaF2 was varied from 3 to 30 wt%. The carbothermal reduction‐nitridation was conducted from 1350° to 1450°C in N2 flow. The nitridation rate tended to increase with decreasing particle size of raw Al2O3 and was found to depend on the Al2O3 synthesizing method. The particle sizes of the synthesized AlN increased somewhat with increasing reaction temperatures. However, even though different particle sizes of Al2O3 powders were used, AlN powders synthesized under the same conditions exhibited almost the same particle size, round shape, and narrow size distribution. From XRD analysis, CaO·6Al2O3 and CaO·2Al2O3 were identified as intermediate compounds during these reactions. The above phenomena suggest that the synthesis mechanism of AlN powder by carbothermal reduction‐nitridation of Al2O3 with CaF2 addition was the nitridation of the intermediate compounds through the liquid phase of the system CaF2‐CaO·6Al2O3‐CaO·2Al2O3.