Formation mechanism and elimination of mesophase in AlN powder synthesized in a carbothermal reduction nitriding process

Abstract

A mesophase of Al2OC was first determined in the AlN powder synthesized in batch quantities via a carbothermal reduction nitridation (CRN) process. The formation mechanism of the mesophase was described. Finally, the CRN process parameters were optimized to eliminate the mesophase in the AlN powder. The results show that as an incomplete reduction product of Al2O3, Al2OC has a highly similar crystal structure to AlN. The formation of Al2OC depends on the PN2 and PCO in the synthetic furnace. At the conditions of T = 1700 °C, PN2 = 10-5 kPa, and PCO = 10-0.008-100.973 kPa, the formation of Al2OC is thermodynamically favorable. By increasing the flow rate of N2 in the synthetic furnace, the formed Al2OC was unstable and decomposed into AlN. Hence, the C and O contents of the AlN powder synthesized in batch quantities were greatly reduced. It can significantly improve the performance of the AlN ceramics.