Microstructural Features of the ZnO-Bi_2O_3 Binary System

摘要

Grain growth in ZnO with Bi_2O_3 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 735 °C, high density (> 90%) was not achieved at all Bi_2O_3 contents; this finding was contradictory to the well-known liquid-phase sintering. At 800 °C, rapid improvement in sintering occurred when increasing the content of Bi_2O_3 from 0.125mol% to 0.25mol%. Schematic study on weight loss also demonstrated an insignificant level of Bi_2O_3 volatilization under certain content. Analysis of the grain growth kinetics from isothermal sintering (900 °C - 1,000 °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 μm). 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.