GRAIN-GROWTH OF ZNO IN ZNO-BI2O3 CERAMICS WITH AL2O3 ADDITIONS

Grain growth of ZnO during liquid-phase sintering of a ZnO-6 wt% Bi2O3 ceramic was investigated for Al2O3 additions from 0.10 to 0.80 wt%. S intering in air for 0.5 to 4 h at 900 degrees to 1400 degrees C was st udied. The Al2O3 reacted with the ZnO to form ZnAl2O4 spinel, which re duced the rate of ZnO grain growth. The ZnO grain-growth exponent was determined to be 4 and the activation energy for ZnO grain growth was estimated to be 400 kJ/mol. These values were compared with the activa tion parameters for ZnO grain growth in other ceramic systems. It was confirmed that the reduced ZnO grain growth was a result of ZnAl2O4 sp inel particles pinning the ZnO grain boundaries and reducing their mob ility, which explained the grain-growth exponent of 4. It was conclude d that the 400 kJ/mol activation energy was related to the transport o f the ZnAl2O4 spinel particles, most probably controlled by the diffus ion of O2- in the ZnAl2O4 spinel structure.