Properties and microstructure of AlN prepared using alumina crucible and MoSi2 heating element

Thermal conductivity, electrical, and mechanical properties of aluminum nitride (AlN) ceramics doped with Y2O3 and CaO and using a conventional MoSi2 heating element furnace were investigated. Relative densities of over 98% of the theoretical values show that the critical sintering temperature for AlN densification may be as low as 1650 °C. An AlN ceramic with 1 wt.% Y2O3 and 1 wt.% CaO fired at 1700 °C for 3 h has a thermal conductivity of 110 W m−1 K−1 and a Vicker's hardness of 1053 kg mm−2. Its dielectric constant and loss factor are 9.97 and 1.1 × 10−3 at 1 MHz, respectively. Microprobe observations of the test samples reveal that the thermal conductivities are related to the secondary phase composition and elemental distribution at grain boundaries and the oxygen content of sintered AlN.