Direct current arc has been used in a wide industrial field. Reducing in cathode erosion is an important issue for process cost reduction, however the erosion mechanism under molecular gas as plasma supporting gas has not been clarified yet. The purpose of this research is to elucidate the erosion mechanism of tungsten based cathodes in atmospheric pressure Ar-N 2 DC arc. The metal vapor generated from the cathode surface was successfully visualized by a high speed camera system with a pair of band pass filters. Combing the visualization with the cahtode temperature measurements provides the tungsten vapor evaporation mechanism; tungsten vapor was generated not from the high temperature part of the cathode tip but from the peripheral part. The arc temperature measurement confirmed that ionization of tungsten atoms in the high-temperature region of the arc caused to this characteristic distribution of tungsten vapor. These findings advance the understanding of such electrode phenomena leading to increased use time of the electrode, and as a result the industrial use of N 2 arcs is expected to expand.

Cathode erosion is an important issue in the industrial applications of the direct-current arc. However, the mechanism of erosion under molecular gas has not been well clarified. The purpose of this study is to elucidate the erosion mechanism of tungsten-based cathodes in atmospheric pressure Ar-N 2 DC arcs. Tungsten electrodes doped with various metal oxides as electron emitters were investigated. The metal vapor from the cathode was successfully visualized by an optical system that combined a high-speed camera with bandpass filters. The difference in the electrode temperature distribution due to the additives is explained with two factors. The first is the thermal factor that the high melting point additive is difficult to spread on the cathode surface. The second is the chemical factor that the emitter is reduced by nitrogen radicals. Advances in the understanding of such electrode phenomena are expected to lead to expanded applications of nitrogen arcs.