Enhanced arcing as a function of organic exposure and arc current for Pd and Pd/Ag electrodes

We report the existence of a region within which enhanced arcing (activation) exists for palladium and palladium/silver contacts, as a function of arc current and of exposure to organic vapors. The current range where activation exists is from ∼0.1 to ∼1.2 A, where the range of exposures (partial pressure times time) used for diethyl phthalate was from ∼10−3 to ∼10 Pa s. At very low organic exposure levels (depending upon the organic vapor and the electrode metal), arc-duration statistics show an exponential behavior. Under moderate to high organic exposure levels, arc-duration show a log-normal distribution similar to that obtained under clean conditions when the arc current exceeds the minimum arc-sustaining current. At sufficiently high currents arc-duration statistics become independent of organic exposure. The envelope of the activated curves is predicted by the activation theory of Gray, Uhrig, and Hohnstreiter.