Sintering behavior of two-phase oxide powder compacts

The difference in diffusivity between constituent cations results in Kirkendall and Frenkel effects, which, in turn, lead to expansion of oxide powder compacts, local densification, and formation of porous but rigid skeleton, which prevents obtaining poreless ceramics. It is proposed that, because of the nonequilibrium nature of the process, the energy released during chemical reaction is partially expended for formation of new surfaces in the porous skeleton. The density of resulting ceramics can be increased by bringing the process closer to equilibrium by lowering the heating rate, employing certain additives or nonstoichiometric compositions, and by varying powder particle size.