Densification kinetics during isothermal sintering of 8YSZ

The densification behavior during the isothermal sintering of 8YSZ was examined in the initial and intermediate stages of sintering. In the initial stage, a difficulty in evaluating the densification behavior arises from the transition of the stable pore structure and the limitation of the theoretical two-sphere model. In the intermediate stage, a linear relationship with a slope of -1/2 is observed between the densification rate and the time. An empirical equation of the densification kinetics is proposed and found to be valid in a wide density range. At a relative density of 0.6-0.73, the activation energy is 688 kJ/mol. Rapid grain growth is observed at a relative density of 0.73-0.8 and >0.9 for the isothermal sintering at 1200-1300 °C and 1400-1500 °C, respectively. The rapid grain growth reduced significantly the densification rate. The densification mechanism and grain growth behavior are also discussed.