Globally reinforced mechanical, electrical, and thermal properties of nonlinear conductivity composites by surface treatment of varistor microspheres

The composite filled with zinc oxide (ZnO) varistor microspheres display promising nonlinear conductivity properties and can be used for grading electric field in electrical equipment. However, the mechanical properties of composites containing ZnO varistor microspheres are seriously degraded, so how to balance the mechanical and electrical performances of electric field grading materials is a key issue for practical applications. In this work, concurrent reinforcement effect of surface-treated ZnO varistor microspheres on the mechanical, electrical, and thermal properties of silicone rubber (SR) composites are studied. 3-Aminopropyltriethoxysilane, a silane coupling agent, is used for surface functionalization of ZnO varistor microspheres, which are then used as a filler in SR to prepare an electric field grading material. Mechanical tensile tests reveal that the tensile strength and initial modulus of the composite incorporated with surface-treated filler are markedly improved and the thermal conductivity of this composite is also increased compared with a composite with untreated filler. Meanwhile, the composites with surface-treated filler displays more stable nonlinear electrical properties under mechanical deformation than those with untreated filler. This method would lead to electric field grading composite materials with excellent comprehensive properties towards practical applications in cable insulation, insulators, terminal accessories, etc.