Abstract
A comparative study has been made of characteristics of Gas-Tungsten-Arc cathodes, consisting of tungsten mixed with a small quantity of lanthanum, yttrium, cerium, thorium oxides respectively. Through observation of oxide contained in electrode after arcing, the change in electrode properties are discussed. The oxide changes its shape and distribution during arcing by the melting of oxide itself, and consequently disappears from the surface layer, which is the reason why arc starting loses the normal behavior. The introducing oxygen into shielding gas promotes intensely the electrode consumption and resulted in forming the "rim" at the periphery just behind the cathode area. It gives serious problems in durability of electrode and the stability of arc.
