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.