The correlation between surface chemical elements of solid insulating materials and their flashover characteristics in vacuum

The X-ray photoelectron spectroscopy (XPS) technique was employed to analyze the surface chemical elements of alumina ceramic and polytetrafluoroethylene (PTFE) in a high vacuum, respectively. On the surface of alumina samples, there were Al, Si, C and O elements, and C with a maximum percentage of 57.78%. For PTFE samples, F, C, K and O elements were detected, and F showed a remarkable atomic ratio of 73.30%. Obviously, the surface chemical elements assignment disagreed with their chemical formula, respectively. We attributed the high percentage of F to quantities of F atoms existing on the surface of PTFE due to its molecular chain with C atoms surrounded by F atoms spirally. The chemical distortion on a solid surface would result in the alter of surface electron structure and subsequently the adjustment of surface energy distribution. Thus, the solid surface serves as a weak part in a compound dielectric system, which results in the flashover phenomena occurring across the surface/interface region at a low applied electric field.