Preparation of Zinc Oxide Varistors With Cerium Oxide

Abstract

Mixtures of ZnO and Ce6O11 as additive were prepared by solid-state reaction from the calcined oxides with the following Proportions: 0.03, 0.08, 0.1, 0.2 and 0.4 mole. Disc specimens 1.2 cm, 5cm in diameter and 0.3 cm thickness were processed under a force of 70 KN fired at 1150°C/30 minutes XRD revealed the presence of limited solid solution of cerium in ZnO, as evident from the shift in the peaks [ 0.03-0.04 A] up to 0.1 mole addition and remains constant . SEM revealed the presence of inter-granular phase. EDAX showed it to be a mixture of ZnO and Ce6O11 .Also cerium was detected in the ZnO grains confirming the XRD results RCL circuit was used to measure the capacitance and resistance at different frequencies at room temperature. The dielectric constant and conductivity were calculated. The microstructure of Ce-doped ZnO cermics, revealed the presence of a liquid phase between cermic and ZnO .An inter-granular phase rich in ceium is made from this liquid, occurs at grain corners. The addition of 0.25 mol% of each Co and Cr2O3 and / or 0.5 mol% Bi2O3 participated and inceased the formation of this liquid phase as indicated by EDAX. Cerium was detected partly with in the ZnO grains and mainly in this intergraular phase togather with ZnO alone and Cr2O3 and or Bi2O3 .The liquid phase enhanced the preferential grain growth of the ZnO grains.