Abstract
Erosion that occurred during arc shut down was investigated. The arc current was 200 A; the cathode was made of hafnium. Different gases were used: oxygen, nitrogen, and noble gases (argon, helium, and hydrogen–argon mixture). The gas pressure was 3 atm. It was shown that erosion in noble gases is higher compared to gases that create chemical compounds with hafnium (oxygen and nitrogen). The following model of arc-off erosion is suggested. An amount of plasma gas is diluted in the molten tip of the cathode. When the arc is terminated, the gas pressure in the cathode vicinity drops down. The diluted gas then leaves the molten puddle and carries some liquid material with it.
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