Sintering of aluminium nitride: Particle size dependence of sintering kinetics

Abstract

The effect of particle size (0.78 ∼ 4.4 μm) on the sintering kinetics of AIN powder was investigated in the temperature range from 1600 to 2000° C and the results were analysed on the basis of vacancy diffusion models. The mechanisms of sintering are discussed. Fractional shrinkage is proportional to the nth power of soaking time with n = 0.20 for 4.4 μm and 1.5 μm powders and 0.33 for 0.78 μm powder. For the 0.78 μm powder at 1900° C, however, n decreases gradually as grain growth proceeds. The experimental activation energy for sintering is between 92 kcal/mole for 4.4 μm and 129 kcal/mole for 0.78 μm powder. Unlike this activated energy, the rate of sintering and the diffusion constant calculated from it increase drastically with decrease of particle size; the derived diffusion constant for 1.5 μm powder is 101 to 102 times larger than that of 4.4 μm powder, and for 0.78 μm powder the diffusion constant is estimated to be still higher. The particle-size dependence of parameter n and the diffusion constant seems to be caused by a variation in predominant diffusion mechanisms; namely, bulk diffusion in coarse powder and surface or grain-boundary diffusion in fine powder.