J. Phys. IV France 120 (2004) 429-437
FEM-Simulation of the electrode temperature distribution and crater formation. Part I: Breakdown of an electrical dischargeF. Soldera, A. Lasagni and F. Mücklich
Functional Materials, Department Materials Science, University of Saarland, PO Box 15 11 50, 66041 Saarbrücken, Germany
An electrical discharge causes an energy input into the electrode, which melts and evaporates the metal forming a crater on the cathode surface. The larger part of material loss is produced by the ejection of molten particles from the molten pool. From calorimetric results, the amount of energy delivered to the cathode was estimated. Based on FEM, a model was developed to simulate the local temperature increase in the vicinity of the plasma impact zone. Considering phase transitions, it was possible to define a molten and an evaporated region, whose dimensions were compared with the dimensions of experimental craters. Single sparks were produced on cylindrical samples (Pt, Ir, Ru, Al, Au, Ag, Cu, W, Ni, Sn and Pb) in air and nitrogen with pressures ranging from 1 to 9 bar and electrode gaps of 1 and 2 mm. The volumes of experimental craters lay between the volumes of the simulated regions for 5 and 7 bar. For 1 and 3 bar, the volumes of the evaporated regions were overestimated. The shape of the simulated regions showed a very good agreement with the real craters. The relative volumes of the molten regions showed a very good agreement with the relative volumes of eroded material in the different metals.
© EDP Sciences 2004