Surface charge decay of direct-fluorinated RTV silicone rubber/SiO2 nanocomposites

Silicone rubber (SiR) is a kind of basic insulating material and is widely used to coat porcelain and glass high voltage insulators. In HVDC transmission lines, corona could occur occasionally, which can markedly inject the charges into insulators surface and damage the insulators. The existence of surface charge has a great effect on insulation degradation and plays an important role on dielectric flashover. Fluorination is a method to change the chemical structure of the surface layer of polymers, which could induce the corresponding change in electrical properties of the surface layer thus influencing the charge decay when they are used as an insulator. Nanoparticles also can influence the electrical properties of the composite material. This paper tries to study the effect of fluorination time and nanoparticle adding rate on surface charge accumulation and decay of the fluorinated SiR nanocomposites. Samples were prepared by dispersing nano-SiO₂ into SiR with weight percent of 1 wt%. Then the samples were direct-fluorinated in a reaction vessel at about 298K (25 °C) using a F₂/N₂ mixture with 12.5% F₂ by volume and 0.05 MPa (500 mbar) for respectively 5, 10, 15 and 20 minutes. The decay curve of surface potential under dc voltage was obtained at 25 °C with a relative humidity of ~40%. Obtained results show the dependence of the surface potential as well as the dissipation time upon the fluorination time. It is suggested that the direct fluorination can significantly improve the decay rate of the surface charge.