Effects of refining methods and time on suspension, microstructure, and electrical properties of ZnO varistors

The effects of the refining methods including roller ball milling, the vertical stirring milling, and high-pressure micro jet homogenization on the suspension, the microstructure, and the electrical properties of the ZnO varistors were investigated in the way of comparison. For the first time, the high-pressure micro jet homogenizer was employed in the preparation of the varistors to improve the homogeneity of the microstructure of the varistor ceramics. When the homogenization process was carried out for 5 min after the vertical stirring milling, the particle size distribution range of the suspension was narrowed, and the grain size of the sintered ZnO varistor ceramics was more uniform, resulting in an excellent electrical comprehensive performance, with breakdown voltage gradient of 234.7 V/mm, nonlinear coefficient of 38.9, residual voltage ratio of 1.69, and current withstand capacity of 450 A against 18 times of 2 ms square waveform impulses.