Nanodiamond-filled high-temperature vulcanized silicon rubber composite for high-voltage insulator applications

Nanodiamond particles with various filling ratios were added into the commercial high-temperature vulcanized silicon rubber composites, which were originally designed for high-voltage outdoor insulators. Their microstructures and electrical, thermal, mechanical, dielectric, and hydrophobic properties were systematically studied. Our results show that the nanodiamond filler improved slightly the electrical breakdown strength, i.e., from 16.2 kV/mm for the unfilled sample to 17.1 kV/mm for 0.9 vol%-filled sample, and the thermal conductivity was increased from 0.45 W/m K for the unfilled sample to 0.50 W/m K for 1.8 vol%-filled sample. Moreover, the hydrophobic properties were also improved with the contact angle at room temperature increased from 91.2° for the unfilled sample to 102.6^° for the 1.8 vol%-filled sample. However, the mechanical properties were deteriorated by these fillers, i.e., decrease of the tensile strength, tear strength, etc. The dielectric constants were found to increase first with the filling fraction and then decrease. Possible mechanisms responsible for the improvement or deterioration for specific properties of the composites are discussed. Our results show that with delicate control of the filling fraction, nanodiamond fillers are helpful for the silicon rubber-based outdoor high-voltage composite insulators.