Abstract
The precursor of Co and Pr added zinc oxide varistor was successfully obtained. by a wet chemical method using zinc acetate as a starting material with praseod ymium oxide and cobalt chloride as additives.Changes in crystalline size, compact density, additives distribution, and voltage-current curve were characterized with sintering temperatures from 1200 to 1300°C for the samples prepared by the wet chemical method with or without calcination, and by a ball-mill method for a comparison.
The crystalline size of zinc oxide increased for each sample with the increase in sintering temperature.The distribution is narrower and the average crystalline size is smaller for a sample by a wet chemical method. Cobalt contributed to almost constant value of coefficient of variation for the samples prepared by the wet chemical method in this temperature range.Large value of coefficient of variation was obtained for praseodymium at high temperature, which resulted from segregation to grain boundaries with growth of crystalline. Decreasing tendency was observed of nonlinearity α and break-down voltage with the increase in sintering temperature. Smaller amount of addition of both Co and Pr in the samples prepared by the wet chemical method was effective for improving the varistor characteristics.
