The correlation between surge energy capability and Bi2O3 volatilization in ZnO varistors

This study investigated the correlation between the surge energy capability and Bi2O3 volatilization in ZnO varistors by analyzing the volatilization phenomenon of Bi2O3. A ZnO varistor is composed mainly of Sb2O3, Bi2O3. Bi2O3 has the lowest vapor pressure among these components. Bi2O3 play an important role, moreover, in forming it grain boundaries. These grain boundaries have low conductivity in the leakage current region, but, becomes higher in the region. It also determines the surge energy capability of the varistors. Bismuth oxide has four phases, each with intrinsic ion-conductivity. Formation of the bismuth oxide phase depends on the amount of bismuth at the grain boundary. Volatilization of Bi2O3 should therefore be prevented when developing ZnO varistors was conducted using with high energy capabilities. Analysis of the volatilization phenomenon of Bi2O3 X-ray analysis methods such as X-ray fluorescence, X-ray photoelectron spectroscopy and X-ray diffraction. The results confirmed a close correlation among them. Sealed sintering methods were proposed to prevent the volatilization of Bi2O3 by ZnO varistors. (C) 2018 The Ceramic Society of Japan. All rights reserved.