The thermal diffusivity of particulate composites prepared by sintering compacts of Al2O3 with additions of 1-25 mol% AlN under 1-atm nitrogen gas pressure at 1600-1800 degrees C has been measured over the range 25-1000 degrees C using the laser flash method. The diffusivity of reaction-sintered materials decreased on addition of AlN, mainly due to the formation of an AlON phase. This effect was less pronounced with increasing temperature and furthermore, it appeared to be related to the temperature-dependence of thermal resistance. The influence of crystalline phase, microstructure and physical property on the thermal diffusivity of AlON/Al2O3 was characterized. The thermal conductivity of the sintered materials at room temperature behaved in a similar manner to the thermal diffusivity. (C) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.