“…Based on actual operating experience of HTV silicone rubber composite insulator, water (from relative humidity, spray, and rain), salt solution (from dissolving of soluble matter in contamination), and nitric acid solution (generated from the discharge around the composite insulator in the presence of water, oxygen, and nitrogen) are three kinds of liquid that HTV silicone rubber composite insulator most commonly encounter during operation [13, 16]. These liquids can permeate into HTV silicone rubber by diffusion process accompanied by chemical interaction and physical dissolution processes, our previous research [13, 17] showed that there was no unified diffusion model (such as Fick diffusion model or Langmuir diffusion model) to describe all these diffusion processes of liquids into HTV silicone rubber due to the fact that chemical reaction and physical dissolution complicated the diffusion processes significantly. Furthermore, the changes of surface chemical properties of HTV silicone rubber caused by liquids diffusion can be characterised from two aspects, one was the change of polymer matrix and the other one was the change of inorganic filler (mainly the ATH filler) beneath and/or on the surface [18].…”