A theory for the cathode mechanism in lowcurrent vacuum arcs, with application to the calculation of erosion rate

The erosion of palladium contacts due to gas breakdown arcs in air and in an activating environment (naphthalene vapour) has been studied. The rate of erosion in air was not constant with arc energy but increased almost linearly from about 0·1 to 1·5 cm3 erg−1 over an energy range of about 100 to 500 erg per discharge. Beyond this energy range a slower increase was observed. Under the activated conditions the erosion rate was much lower than in air (eg at 2000 erg the erosion rate in air was 1·65×10−14 cm3 erg−1 and with naphthalene activation the rate was 1·1×10−14 cm3 erg−1); however, a variation in the erosion rate with energy was also observed. The variation with energy is considered to be caused by part of the available erosion energy being used up in surface film decomposition.

Articles you may be interested inEnhanced hydrogenation and reduced lattice distortion in size selected Pd-Ag and Pd-Cu alloy nanoparticles Summary Abstract: Calculation of the surface segregation of Pd-Cu, Pd-Ag, and Pd-Au alloys J. Vac. Sci. Technol. A 5, 889 (1987); 10.1116/1.574336 Arc durations as a function of contact metal and exposure to organic contaminantsWe report the existence of a region within which enhanced arcing (activation) exists for palladium and palladium/silver contacts, as a function of arc current and of exposure to organic vapors. The current range where activation exists is from ~ 0.1 to ~ 1.2 A, where the range of exposures (partial pressure times time) used for diethyl phthalate was from ~ 10 -J to ~ 10 Pas. At very low organic exposure levels (depending upon the organic vapor and the electrode metal), arc-duration statistics show an exponential behavior. Under moderate to high organic exposure levels, arc-duration show a log-normal distribution similar to that obtained under clean conditions when the arc current exceeds the minimum arc-sustaining current. At sufficiently high currents arc-duration statistics become independent of organic exposure. The envelope of the activated curves is predicted by the activation theory of Gray, Uhrig, and Hohnstreiter.

Articles you may be interested inAn ultra-low leakage current single carbon nanotube diode with split-gate and asymmetric contact geometry Appl.The ,tatistical distributions of break-arc durations have been examined as functions of arc current and number of operations under both "clean" and contaminated conditions. Exponential distributions were found for arcs between clean palladium electrodes operating below 0.9 A. At higher currents a Gaussian-(normal) type distribution was observed. Under highly contaminated condition;, the Gaussian distribution was observed at all current levels examined. These distributions have been discussed in terms of the "ionic-burst" mechanism and thermionic emission. A model for the so-called activation or arc-duration enhancement of arcs is presented.

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