Synthesis of Nano Zno Powder and Study of Its Varistor Behavior at Different Temperatures

Abstract

Commercial ZnO varistor ceramics are multi-component, with minor amounts of added oxides that play important roles, both in electrical sense and to control microstructure. The emphasis of this paper is mainly on improving the electrical properties and the effect of nano ZnO powder on varistor behavior. Ultra fine ZnO powders with crystallite size 3-10nm have been prepared by sol-gel auto combustion method. The synthesized powders characterized by X-ray diffraction (XRD), differential thermal analysis (DTA)/thermogravimetry analysis (TGA), transmission electron microscopy (TEM) and surface area using Brunauer-Emmett-Teller (BET) method. Different valance state elements in oxide form are additively doped with nano ZnO powder for fabrication of varistors. Sintering is performed at 850 to 1150°C with 4h soaking time. The varistor is characterized with respect to phase identification, crystallite size determination using X-ray Diffraction. The densification and microstructure analysis using scanning electron microscope (SEM) are also investigated. It is shown that the varistor is mainly consisting of ZnO, Zn 7 Sb 2 O 12 spinel and Bi 2 O 3-rich phases. It can be produced having a sintered density ~99% of its theoretical density with grain size ~5-7m and a maximum breakdown voltage 292 V/mm.