COBALT OXIDE AND ANTIMONY OXIDE EFFECTS IN THE ZINC-OXIDE BISMUTH OXIDE SYSTEM

The effects of Co3O4 and Sb2O3 in the ZnO-Bi2O3 sintering process have been studied by several researchers. However, some aspects of their i nfluence on ZnO-Bi2O3 sintering behavior, which are important for the characteristics of ZnO varistors, such as the phase distribution, are still not well understood. Aiming to a better comprehension of the inv olved phenomena, we have studied the thermal and physicochemical behav ior of the ZnO-Bi2O3 system during the sintering process (crystalline phases formed, evaporation and decomposition reactions), by thermograv imetric analysis, scanning electron microscopy and X-ray diffraction. Thermogravimetric analysis shows a weight loss of the samples during t he sintering process. We show that this weight loss is a consequence o f Bi2O3 evporation. Experimental results indicate that the pyrochlore phase restrains the bismuth oxide evaporation. At temperatures higher than 950-degrees-C the pyrochlore reacts with ZnO and then the weight loss and the grain growth rate increase.