Densification of ceramics containing entrapped gases

Abstract

Limits to the shrinkage of isolated pores and to the densification of powder compacts have been calculated for various sintering conditions. The impeding effect of an entrapped gas diminishes with lower gas pressure in the sintering atmosphere, with higher solid-gas interfacial tension, with smaller initial pore size, and with higher dihedral angle. Over 99·5% relative density can be achieved under conventional conditions when sintering fine powders with a pore size of less than a few micrometres. In contrast, the final density can be much reduced in coarse powder compacts and under high initial atmospheric pressures. The effect of entrapped gas on the driving force and on the rate of densification during sintering is also calculated. The effect of pore coalescence due to grain growth on the bloating of compacts is discussed. © 1989.