Surface dielectric properties of Cu-evaporated alumina insulators in vacuum and air

Metal evaporated on a nonideally smooth surface of ceramic insulators constitutes a discontinuous layer. Thus, the dielectric properties of the ceramic material are preserved, but at the same time one can observe a great change in these properties. The authors present a comparative analysis of some selected surface dielectric properties of alumina insulators on which a copper layer is deposited. The following relations were investigated in air and in vacuum: the dependence of surface resistivity on the amount of deposited copper, the dependence of surface resistivity on voltage, and flashover voltage as a function of surface resistivity. Coating the insulator with copper may cause both an increase (176%) and a decrease (59%) of flashover voltage in vacuum, whereas in air the influence of surface resistivity within the range of 10⁸-10²⁰ Ω-cm/cm was not observed