An experimental comparison of the erosion in tungsten cathodes doped with different rare-earth elements

Three different types of tungsten-based cathodes (thoriated, lanthanized and ceriated) were used in plasma torches operating at different current intensities ranging from 30 to 210 A. For each one of the current intensities used, the erosion rate was measured for each of the cathode types, thereby obtaining for them the curves describing the dependence of the erosion on the current intensity. The effects of erosion on the cathode surface were explored by scanning electron microscope and energy-dispersive x-ray spectrometer. On each of the types of cathodes studied, the cathodic erosion had a maximum for a critical value I* of the current intensity. The value of this critical current intensity depended on the dopant used. The following values were obtained: ITh*=50 A for thoriated tungsten, ICe*=80 A for ceriated tungsten and ILa*=110 A for lanthanized tungsten. (author)