Surface and gas phase reactions arising with epoxy exposed to partial discharges

The relative effects of gas phase and surface reaction processes, occurring in air and nitrogen during the partial-discharge-induced degradation of epoxy resin specimens, were investigated. For discharges in both air and nitrogen, ESCA (electron spectroscopy for chemical analysis) surface analyses indicated that the oxygen within the epoxy matrix structure itself contributes markedly to the formation of certain types of degradation products, which in turn cause a transition in the discharge mechanism. The initially occurring large-pulse (short-risetime) discharges (300 to 500 pC) were replaced by small-pulse (long risetime) discharges (1.0 to 0.5 pC) and eventually by true glow discharges when the specimens were tested to sufficiently long exposure times