Improvement of DC Flashover of Particle-filled Composite Liquid Silicone Rubber by Direct Fluorination

At 0.1 MPa and 85 ℃, the composite liquid silicone rubber samples containing 18 phr fumed silica and 15 phr melamine cyanurate are directly fluorinated using F₂/N₂ mixture with 12.5% F₂ volume. The DC flashover performance of the fluorinated samples is evaluated by using the finger electrode/sheet sample configuration. The experimental results show that the flashover voltage of composite liquid silicone rubber sample is increased by 30.6%. Attenuated total reflection infrared analysis（ATR-IR） shows that C—F bond existed in the fluorinated layer, and X-ray photoelectron spectroscopy（XPS） shows that direct fluorination not only formed C—F bond, but also Si—F bond and N—F bond. Scanning electron microscopy（SEM） reveals that fluorination makes the surface of composite silicone rubber nano-structured, forming a fluorinated layer with a thickness of micron. The results of surface conductivity and surface potential decay measurements show that fluorination significantly improves the surface conductivity of composite liquid silicone rubber, making it difficult for charge to accumulate on the surface of the sample, which is the main reason why fluorination improves the DC flashover property of the sample.