Effect of nano-fillers on nonlinear conduction and DC breakdown characteristics of epoxy composites

In order to improve the nonlinear conduction ang dc breakdown strength, the influences of nano-fillers on epoxy nano-composites are studied. The epoxy nano-composites are prepared by regulating the shape factor of the semiconductor filling phase, with separate doping or two phase co-doping. The crystal structure and morphology of the composites and nano-fillers are analyzed by X ray diffraction and scanning electron microscopy. The conductivity and dc breakdown strength of the nano-composites are measured. The results show that the surface treated nano-fillers are well dispersed in the epoxy matrix. Compared with pure epoxy and epoxy nano-composites with lower filler loading of ZnO particles, the ones with higher filler loading of ZnO particles and lower filler loading of ZnO sheets exhibit a distinct nonlinear conduction character, but their breakdown strength is significantly reduced. By contrast, the breakdown strength of BN/epoxy nano-composites with low filler loading is significantly increased, and the 3 wt% BN/epoxy nano-composite behaves the highest breakdown strength. Based on 3 wt% BN nano-sheet, ZnO–BN epoxy nano-composites are prepared by two phase co-doping. Compared with single doping, the two phase co-doping nano-composites can not only improve the nonlinear conductivity, but also alleviate the problem of the serious deterioration of dc breakdown performance. The nonlinear conduction and dc breakdown properties of the studied nano-composites are related to the interaction zone of nano-filler in polymer matrix.