Stability of low-current break arcs between palladium contacts

The statistical distributions of break-arc durations have been examined as functions of arc current and number of operations under both ``clean'' and contaminated conditions. Exponential distributions were found for arcs between clean palladium electrodes operating below 0.9 A. At higher currents a Gaussian- (normal) type distribution was observed. Under highly contaminated conditions the Gaussian distribution was observed at all current levels examined. These distributions have been discussed in terms of the ``ionic-burst'' mechanism and thermionic emission. A model for the so-called activation or arc-duration enhancement of arcs is presented.