The effect of the PbO addition on the sintering of ZnO

The microstructural evolution and densification for the ZnO-PbO system were studied. Specimens were prepared. by the mixed oxide route, and sintered at temperatures in the range of 1000-1300degreesC. The bulk densities of the PbO-added ZnO samples increased from 1000 to 1100degreesC. In sinterings above 1100degreesC, the bulk density was decreased almost linearly due to lead oxide evaporation except in 2.5 mol% PbO-added ZnO samples. The ZnO-PbO ceramics have a two phase microstructure comprising ZnO grains and a Pb-rich phase at the grain boundaries. The average grain size of ZnO increases with the PbO addition up to 7.5 mol% PbO addition but, the excess PbO addition decreases the grain size. This is due to the change in the grain growth mechanism from the solution precipitation in the liquid-phase to that of an ion diffusion mechanism in a thicker layer of liquid.