Microstructural Features of the ZnO-Bi2O3 Binary System

Grain growth in ZnO with Bi2O3 addition of up to 1 mol% was examined in great detail for sintering in air. The results are analyzed and compared with previous reports in the context of the simplified phenomenological grain growth kinetics equation along with the physical properties of the sintered ceramics. In spite of the eutectic temperature at 73 degrees C, high density (> 90%) was not achieved at all Bi2O3 contents; this finding was contradictory to the well-known liquid-phase sintering. At 800 degrees C, rapid improvement in sintering occurred when increasing the content of Bi2O3 from 0.125mo1% to 0.25mo1%. Schematic study on weight loss also demonstrated an insignificant level of Bi2O3 volatilization under certain content. Analysis of the grain growth kinetics from isothermal sintering (900 degrees C - 1,000 degrees C) revealed strikingly different results in both grain growth exponent (n) and activation energy previously reported in literature. The n values ranged from 3.2 to 5.6 whereas the activation energy from 335 to 598 kJ/mol. Such large disparities were believed to be associated with various mass transport processes. The grain sizes in this study were much smaller than those published in literature (> 10 mu m). This size difference, along with other microstructural features, was discussed and correlated in order to explain such anomalies and new findings obtained from the grain growth kinetics results.