Effect of grain contiguity on the thermal diffusivity of aluminum nitride

Thermal diffusivity of AlN-based ceramics was studied as a function of seco nd-phase amount and heat-treatment time, The Y2O3. Al2O3 contents varied ov er the range of 13-31 vol%, The thermal diffusivity decreased as the amount of second phase increased. After sintering at 1850 degrees C,the AlN ceram ics consisted of rounded, largely isolated grains. Heat treatment of these samples for 5-50 h at 1800 degrees C resulted in microstructures that consi sted of largely contiguous AlN grains. There was a substantial increase in the thermal diffusivity after the heat-treatment step, and the incremental improvement was essentially constant for the three compositions that have b een studied. The amount of second phase was unchanged during heat treatment ; therefore,the increase in thermal diffusivity is assumed to be a direct r esult of the enhanced contiguity of AlN grains.