| ZnO varistors have been widely used in the field of voltage stabilizer and over-voltageprotection for its excellent nonlinear voltage-current properties, surge current adoptioncapacity and high working stability. Bismuth-based ZnO varistors, mainly doped withBi2O3and Sb2O3, have obtained much attention from many researchers for its lowproduction cost, quick response time and long service time, and seize the dominant placein the varistor market. However, this field is still expecting to improve the surge currentwithstanding capability as well as voltage-gradient. This paper mainly aims to produce highvoltage-gradient varistor with high surge current withstanding capability while maintainingother electrical characteristics.This paper adopts direct doping and pre-synthesis doping to fabricate bismuth-basedZnO varistors and discusses effects of doping amount and other fabrication process on ZnOvaristor characteristics.First of all, fundamental mechanism and fabrication process of zinc oxide varistor areintroduced, effects of different sintering temperature and sintering time on ZnO varistorare studied and discussed from the microstructure. The results show that: as sinteringtemperature and sintering time increases, average grain size increases and breakdownvoltage-gradient decreases, but nonlinear coefficient and surge current withstandingcapacity first increases and decreases later.Then, effects of BiSbO4replacing Bi2O3and Sb2O3on ZnO varistor are discussed, andcontrasts of different temperature at which BiSbO4is synthesized on density, microstruc-ture, sintering mechanism of ZnO varistor can be seen. The results show that: comparedwith traditional direct doping of Bi2O3and Sb2O3, varistors doped with BiSbO4synthesizedunder800°C show higher nonlinear coefficient and capacity of withstanding surge current,breakdown voltage-gradient E1mA=324V/mm, nonlinear coefficient=85, residue voltageratio K5kA=2.3, variation of breakdown voltage after surge current U1mA=3%.At last, effects of SiO2-doping and Zn2SiO4replacing SiO2on ZnO varistor arediscussed from the density, microstructure, sintering mechanism. The results show that:compared with SiO2, varistors doped with Zn2SiO4show higher voltage-gradient andnonlinear coefficient, better withstanding surge current capacity; as Zn2SiO4-dopingamount increases, ZnO grain size decreases, breakdown voltage-gradient, nonlinearcoefficient and surge current withstanding capacity first increases and then decreases. AsZn2SiO4-doping amount is0.75mol%, optimum properties of ZnO varistor can be obtained, breakdown voltage-gradient E1mA=382V/mm, nonlinear coefficient=85, residue voltageratio K5kA=2.0, variation of breakdown voltage after surge current U1mA=5%. |
