Optimisation study for making aluminium nitride using an improved carbothermal reduction-nitridation process

In order to obtain a high thermal conductivity, impurities such as oxygen and carbon should be removed from aluminium nitride (AlN) during its synthesis using a carbothermal reduction-nitridation (CRN) process. In this study, AlN powders were prepared under various conditions (1550-1750 degrees C, 0.5-4.0 hrs, nitrogen at 75-399 ml/min) using mixtures of alumina (Al2O3) and carbon black (C) at different molar ratios of 0.28 to 0.40. Residual carbon of the synthesized AlN powder was removed in a decarbonisation step using an electric furnace (600-900 degrees C, 0.5-4.0 hrs). The synthesis of AlN from alumina-carbon black mixtures of Al2O3/C molar ratio of 0.31 (5% excess carbon black) at optimum conditions of 1700 degrees C for 3-4 hrs and air decarbonisation (annealing) at 750 degrees C for 2 hrs produced product containing 385 ppm C and 0.62 wt% O-2, lower than for current commercial products.