Evolution of pore morphology in sintering powder compacts

Abstract

In this paper, the effects of heating rates and green densities on the pore morphology of powder compacts are evaluated. For low green density specimens sintered at a low heating rate, the Ostwald ripening process might be very important in the evolution of pore morphology, principally because of surface diffusion that occurs at the lower sintering temperatures. At deliberately lower green densities, the observed kinetic responses as well as the microstructural development were strongly influenced by green states of powder compacts. For undoped Al 2O 3 compacts with high green densities ( D 0 > 0·64), the experimentally observed activation energy during the later stages of sintering (to D f > 0·992) was ∼ 629 kJ/mole, a value consistent with the volume diffusion of Al ions. The main principles for selecting a kinetically and morphologically optimized firing schedule are established and discussed. Even for the usually difficult case of undoped alumina ceramics, these principles are shown to be very effective in producing sintered specimens with high density, fine grains and minimal pore entrapment.