THE BEHAVIOR OF TITANIUM, STAINLESS-STEEL, AND COPPER-NICKEL-ALLOYS AS PLASMA TORCH CATHODES

Cathode erosion continues to be a problem hindering the widespread app lication of plasma technology. In this work, cathode erosion was studi ed on titanium, stainless steel 314, copper-nickel 10% and 30%, and co pper 122 for magnetically rotated arcs operating in argon, nitrogen, a nd argon/hydrogen mixtures at a constant magnetic flux density of 0.1 T. Titanium and stainless steel gave very low erosion rates in argon ( 0.2 and 0.3 mu g/C respectively). Cupronickels were shown to be suitab le for nitrogen and hydrogen plasmas. The slope of hydrogen solubility versus temperature in the cathode material was found to be important in determining hydrogen plasma erasion characteristics. When the plasm a gas has a high solubility in the cathode material, or can react with the cathode, a negative erosion rate may result. When gas solubility in the cathode is low, oxide stability and mode of electron emission m ay govern the erosion rate. A high gas solubility in the cathode mater ial, as with hydrogen, can result in mechanical erosion due to micro-e xplosions near the cathode surface.