GRAIN-GROWTH OF ZNO DURING BI2O3 LIQUID-PHASE SINTERING

Grain growth of ZnO during the liquid-phase sintering of binary ZnO-Bi2O3 ceramics has been studied for Bi2O3 contents from 3 to 12 wt% and sintering from 900-degrees to 1400-degrees-C. The results are considered in combination with previously published studies of ZnO grain growth in the ZnO-Bi2O3 system. For the Bi2O3 contents of the present study, the rate of ZnO grain growth is found to decrease with increasing Bi2O3. Activation analysis, when combined with the results of similar analyses of the previous studies, reveals a change in the rate-controlling mechanism for ZnO grain growth. Following a low-Bi2O3-content region of nearly constant activation energy values of about 150 kj/mol, further Bi2O3 additions cause an increase of the activation energy to about 270 kJ/mol. Consistent with accepted models of liquid-phase sintering, it is concluded that the rate-controlling mechanism of ZnO grain growth during liquid-phase sintering in the presence of Bi2O3 changes from one of a phase-boundary reaction at low Bi2O3 levels to one of diffusion through the liquid phase at about the 5 to 6 wt% Bi2O3 level and above.