Study On The Preparation Of Nanometer ZnO Varistor And Aqueous Tape Casting Processing

This article has outlined the characteristic of the nanometer ZnO and the performance of use as varistor. The recent developments on the research of the ZnO varistors are also reviewed in this paper, which contain the theory of conduction, aging, nonlinear additive and manufacturing technique. The ZnO particles with nano-meter size are synthesized by the mechanochemical processing and characterized by using DTS, XRD, IR, and TEM in this paper. According to the work above, results of analysis indicate that the particle sizes of ZnO are about 60-80 nm by special decentralized processing; and the phases of the samples crystallize is hexagonal ZnO structure, which have high purity, fine crystallinity and large adsorption capacity. Preparation of varistors with different doped amount of Br₂O₃, Sb₂O₃, TiO₂, which sintered at different temperatures, is also carried out. Base on the experiments, the conclusion can be drawn below: the doping prescription volume is 2.0%; the sintering temperature is 1150℃. The optimization experiments reveal the facts that the ZnO varistors prepared by uncaicined powder sintered at 800°C have better properties such as shrinkage rate trends, leakage current, breakdown voltage of unit thickness, dissipation factor, dielectric constant and so on. The best result of the former experiment: the shrinkage rate can reach 18.2%, leakage current is 1.8μA, the breakdown voltage of unit thickness, dissipation factor and dielectric constant are 951V/mm, 3711 kΩ·m, 4.3×10⁵ respectively; the result of calcined powders is worse than the uncaicined sample, the lowest leakage current can reach 19μA, dissipation factor is 0.2, the breakdown voltage of unit thickness reach its maximum of 879 V/mm, dielectric constant is better than former's, which is 1.46×10⁷. The best varistor property ZnO powders have successfully produced the green tapes, which have smooth surface, homogeneous microstructure, good flexibility and high strength through aqueous tape-casting processing with Styrene acrylic emulsion as binders. The multilayer varistors body is got by the lamination technology with aqueous tape-casting processing. After sintered the ZnO multilayer body, the largest relative density can reach 99.85%, the breakdown voltage of unit thickness is 1247 V/mm, the minimum of leakage current is 0.3μA. This study has a good theoretical guidance on varistor materials and ZnO devices, particularly in the exploration of processing of aqueous tape casting to preparation of chip resistors.