Grain Growth in Sintered ZnO and ZnO‐Bi2O3 Ceramics

Grain growth in a high‐purity ZnO and for the same ZnO with Bi 2 O 3 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: G n — G n 0 = K 0 t 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 Zn 2+ lattice diffusion mechanism. Additions of Bi 2 O 3 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 Bi 2 O 3 content. The preexponential term K 0 was also independent of Bi 2 O 3 content. It is concluded that the grain growth of ZnO in liquid‐phase‐sintered ZnO‐Bi 2 O 3 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Bi 2 O 3 ‐rich liquid phase.