Studies on the Al2OC mesophase in synthesized AlN powder and its effects on properties of AlN ceramic substrates

A mesophase of Al₂OC was first determined in AlN powder synthesized in batch quantities via a carbothermal reduction nitridation (CRN) process. The formation and elimination mechanisms of the mesophase were investigated. Effects of the mesophase on properties of the AlN ceramic substrates were evaluated via bending strength and thermal conductivity tests of the substrates fabricated with AlN powder of different O contents. At the conditions of the synthetic furnace, i.e. T = 1700 °C, P_N2 = 10^?5 kPa, and P_CO = 10^?0.008–10^0.973 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. The properties of the AlN substrates depend on the O content of the AlN powder. The thermal conductivity/bending strength of the AlN substrates increase or decrease, accordingly, based the O content of the reduced AlN powder. AlN substrates made of AlN powder with 0.84 wt% oxygen content show a thermal conductivity and bending strength of 176.3 W/(m·K) and 421.3 MPa, respectively.