An experimental study of the dependence on the current intensity of the erosion of thoriated tungsten cathodes in plasma arcs

The erosion occurring in thoriated tungsten cathodes used in transferred plasma torches operating with current intensities ranging from 30 to 210 A has been experimentally investigated. The cathode erosion rate was determined by measuring the cathode's weight loss after arcing, and the eroded cathode surface was explored by a scanning electron microscope and an energy dispersive X-ray spectrometer. It has been discovered that a critical current intensity, I/sub CR/ /spl sim/ 50 A, exists for which the cathode erosion rate becomes maximum.