GRAIN-GROWTH IN SINTERED ZNO AND ZNO-BI2O3 CERAMICS

Grain growth in a high‐purity ZnO and for the same ZnO with Bi2O3 additions from 0.5 to 4 wt% was studied for sintering from 900° to 1400°C in air. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: Gn—Gn0=K0t exp(—Q/RT). For the pure ZnO, the grain growth exponent or n value was observed to be 3 while the apparent activation energy was 224 ± 16 kJ/mol. These parameters substantiate the Gupta and Coble conclusion of a Zn2+ lattice diffusion mechanism. Additions of Bi2O3 to promote liquidphase sintering increased the ZnO grain size and the grain growth exponent to about 5, but reduced the apparent activation energy to about 150 kJ/mol, independent of Bi2O3 content. The preexponential term K0 was also independent of Bi2O3 content. It is concluded that the grain growth of ZnO in liquid‐phase‐sintered ZnO‐Bi2O3 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Bi2O3‐rich liquid phase. Copyright © 1990, Wiley Blackwell. All rights reserved