Solid state sintering of ceramics: pore microstructure models, densification equations and applications

The stability of closed pores in two and three dimensions has been discusse d and it is found that the stability of pores in two dimension can be deter mined mathematically from their particle coordination number and dihedral a ngle; while those in three dimension can be approximately determined by a s pherical pore model. This model is set up by first excluding the effect of interface tension, so the pore was supposed to be spherical, and then the t ensile stress arising from the interface tension was allowed to act on this hypothesized spherical pore. On the basis of the spherical pore model, por e microstructure models for real powder compacts were set up and the densif ication equations for the intermediate and final stages of sintering were d erived. The criterion for pore shrinkage, and the effect of pore size distr ibution and green density were discussed according to the derived equations . The densification equations for pressureless solid state sintering can be easily extended to describe the densification behaviour during hot-pressin g or hot-isostatic-pressing. Densification characteristics in liquid state sintering were also considered from the result of solid state sintering. (C ) 1999 Kluwer Academic Publishers.