Synthesis of AlN powder by carbothermal reduction-nitridation of various Al2O3 powders with CaF2

We investigated the effect of characteristics of raw Al2O3 powder on the sy nthesis of AlN by the carbothermal reduction-nitridation method, in which C aF2 was added as a catalytic material. Four types of Al2O3 powders were sel ected. 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 conduc ted from 1350 degrees to 1450 degrees C in N-2 flow. The nitridation rate t ended to increase with decreasing particle size of raw Al2O3 and was found to depend on the Al2O3 synthesizing method. The particle sizes of the synth esized AlN increased somewhat with increasing reaction temperatures. Howeve r, even though different particle sizes of Al2O3 powders were used, AlN pow ders synthesized under the same conditions exhibited almost the same partic le 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 mec hanism of AlN powder by carhothermaI reduction-nitridation of Al2O3 with Ca F2 addition was the nitridation of the intermediate compounds through the l iquid phase of the system CaF2-CaO . 6Al(2)O(3)-CaO . 2Al(2)O(3).