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-N2 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.
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