Time variation in copper cathode erosion rate for long-duration arcs

It has generally been assumed that the erosion rate of arc cathodes is independent of arcing time. Results are given from two different systems which show that this is not true for water-cooled copper cathodes over which 45 and 100 A arcs were rotated for up to one hour in air at atmospheric pressure at several different speeds. In all cases the erosion rate is an increasing function with time and can be represented by a power law. The results seem to support a recent model in which it has been suggested that the erosion of cathodes with relatively thick oxide films occurs by globules leaving submicron-diameter craters with a depth of the order of the oxide thickness.