Effect of initial microstructure on final intergranular phase distribution in liquid-phase-sintered ceramics

The glass-melt penetration of dense TiO₂ polycrystals (where the grains are initially in contact) and the sintering of SiO₂-coated TiO₂ powders (where the grains are initially separated) have been used to investigate the influence of initial particle separation on final microstructures. Grains that were initially in sintered contact resisted penetration by the liquid and retained crystalline boundaries. However, grains that were initially separated by liquid had a tendency to form a final state where they were separated by a glass film ∼1 nm thick. The results imply that crystalline grain boundaries and those that contain a thin amorphous film represent two local thermodynamic minima that are separated by an energy barrier. These observations are in agreement with a thermodynamic model that predicted such a barrier for this system, and these observations show that the stable phase distribution in liquid-phase-sintered ceramics can be dependent on the path.