Effects of SiC@Al2O3 Nanoparticles on the Nonlinear Conductivity of Epoxy Composites

Nonlinear conductivity enables an insulating material to self-homogenize its electric field distribution, which can be regulated by the core-shell method. In this study, the effects of SiC@A12O3 on nonlinear conductivity are investigated. First, SiC@A12O3 nanoparticles are fabricated. Subsequently, 3 wt%, 7 wt%, and 10 wt% SiC@A12O3/epoxy and SiC/epoxy composites are prepared. The microstructures of the SiC@A12O3 nanoparticles are characterized using transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. The dielectric spectra, breakdown strengths, and conductivities of the epoxy composites are investigated. The experimental results show that a 2-nm-thickness Al2O3 shell is formed around the SiC nanoparticles. Compared with the raw SiC nanoparticles, the SiC@Al2O3 nanoparticles not only reduced the relative permittivity and loss tangent of the composite but also enhanced its breakdown strength. All of the SiC/epoxy composites exhibited nonlinear conductivity, whereas only the 7 wt% and 10 wt% SiC@Al2O3/epoxy composites exhibited nonlinear conductivity. Moreover, the SiC@Al2O3/epoxy composites had a higher switching electric field (i.e., the initial electric field for nonlinear conductivity) than the SiC/epoxy composites. The results demonstrate the possibility of using nonlinear resistive field grading material in high-electric-field applications.