Surface Flashover Characteristics in Polyimide/ZnO Nanocomposite under dc Voltage in Vacuum

It is well known that the solid materials flashover phenomenon is very complicated and influenced by many factors, such as surface conditions, electrodes and traps, etc. In this paper, dc flashover experiments of polyimide (PI) and PI/ZnO nano-composite are studied in vacuum to reveal the surface flashover mechanism. The trap levels and space charge distributions were obtained by thermally stimulated current (TSC) and pulsed electro-acoustic (PEA) methods respectively. Further researches on surface states of flashover tested sample, such as observation by scanning electron microscopy (SEM), and measurement of secondary electron emission (SEE) coefficient, were carried out as well. Experimental results showed that the dc surface flashover voltage of PI/ZnO nano-composite is significantly enhanced compared to that of pure PI. The experiments results can be explained as that the doped ZnO nano-particles introduced deeper traps, which can reduce the level of charge carrier mobility, secondary electron emission and space charge accumulation. Meanwhile, the gas desorption efficiency of nano-composite is much lower than that of pure PI. It suggests that the doped ZnO nano-particles plays a critical role in affecting the surface flashover performance under dc voltage in vacuum.