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

Abstract

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