New Technique Of Manufacturing Zinc Oxide Varistors

To improve the microstructure uniformity and surge current absorption capability ofthe ZnO varistor is the main purpose in this paper. On the basis of analyzingmicrostructure of the ZnO ceramic and the characterization of crystal, solution andcolloid, chemical coprecipitation process is adopted. After the careful study of theeffects of some precipitants, two inorganic precipitants, which can coprecipitate all themetal ions in groups very well, and the suitable condition are obtained. Fine and activeZnO varistor powders are prepared by coprecipitation. The microstructure of varistorsprepared by coprecipitation powders is more uniform than that of varistors preparedwith conventionally powders by mixed oxide technique. By comparing the performanceof the components made-up by the two methods (chemical and physical) respectively, itis testified that the component produced by chemical method is much superior to that byphysical method. A ZnO varistor manufactured by the chemical method with diameterof 7mm is tested. The results show that its surge current absorption capability is higherthan 1400A, and the small current character is also improved. In addition, it reaches thecriterion of the National Co. By studying performance of the component, which issintered in different temperatures, the conclusion is drawn that 10800 C is theappropnate temperature of sintering. The surge current absorption capability can beenhanced obviously by a process of slow-cooling mid-temperature heat treatment.Considering the widely using of manganese in electronic ceramics, the phasetransformation of manganese in the course of calcine is also researched in-depth in thispaper.