The effect of carbon coating of AIN powder on sintering behavior and thermal conductivity

High thermal conductive AlN ceramics doped with Y2O3 were produced by sintering the powders obtained after applying a carbon coating to the surface of AlN powder grains. During sintering at 1800 degrees C for 1 hour, the carbon reacts with the surface of the AlN grains by carbothermal-reduction of Al2O3, and also with the Al2Y4O9 intermediate phase to form AlN, Y2O3 and CO. By adding 0.56 mass% of carbon, almost all the Al2Y4O9 is reacted and the thermal conductivity increases from 184 W/(m . K) to 224 W/(m . K). Further carbon addition decreases the thermal conductivity and also the final sintered density. (C) 1999 Kluwer Academic Publishers.