The influence of specific chemical reactions on microstructural features in ZnO based varistors is reported from a new approach. These reactions are revisited taking into account their effects on the phase distribution in the microstructure. From this reaction, the formation of structures and its characteristics in according to its ability to form heterogeneous or homogeneous characteristics at microstructure were used to classify these oxides. In these analyses ZnO, Bi2O3, Zn2Bi3Sb3O14 and Zn7Sb2O12 were considered. ZnO and Zn2Bi3Sb3O14 oxides were classified as without a direct influence on the microstructural development. The disponibility of the Bi2O3 oxide was considered as a precursor of heterogeneity, while the Zn7Sb2O12 is considered a precursor of homogeneity. In this sense, a ceramic-ceramic composite was prepared through the addition (10 wt.%) of spinel type oxide with stoichiometry Zn4MnCoCrSb2O12± delta to an adequate composition for varistor development. The composite was sintered at 1160 ºC during 2 h, being cooled from the sintering temperature to room temperature. High microstructural homogeneity and excellent electrical properties are developed, since that the number of ZnO twinned grains is increased. The texture of these grains was investigated by digital analysis of the image of the scanning electron microscopy micrograph. The correlation between twinned ZnO grains and the degree of microstructural homogeneity of the composite is discussed.
ceramic processing; composite; varistor; microstructure; twins
