Preparation of ZnO varistors by solution nano-coating technique

This paper introduces a new method to produce nano-composite powder for the preparation of high performance ZnO varistors. ZnO particles were coated with Bi2O3, Sb2O3, Co2O3, Cr2O3 and other additives via liquid nano-coating technique. Then the prepared powder was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermal gravity and differential scanning calorimetry (TG-DSC) and particle size distribution. The results showed that the ZnO composite powder is homogeneously coated and ultrafine. The densification, phase composition and microstructure of ZnO varistors was studied by linear shrinkage, X-ray diffraction (XRD) and SEM, respectively. The preliminary electrical parameters of ZnO varistors showed that the breakdown voltage Vb (1 mA/cm2) and nonlinear coefficient α is 5400 V/cm and 50, respectively, much higher than that of conventional ball milling method. This result shows that nano-coating is a promising route to prepare ZnO varistors.