In this work, an approach which is essentially experimental is proposed. In the first part, results are presented which were obtained by synchronized fast camera imaging and electrical measurements. These concern the study of the transition between copper electrodes in air and in argon, and between tungsten electrodes in argon for gas pressure in the range 100 mbar – 1 bar. In no case was the transition to arc been observed without the quasi-total constriction of the positive column. Considering tungsten electrodes in argon, the propagation speed of the filamentary part of the positive column from the anode to the cathode was found to be dependent on the gas pressure and the discharge current intensity. During spontaneous transition, the transition duration has been linearly correlated to the electrode gap, suggesting a propagative mechanism with a constant speed. The higher the pressure, the longer is the total transition duration. For a constant pressure and discharge current, the duration of spontaneous transition decreases with decreasing gap distance toward a limiting value, which corresponds to the constant duration of the structural change of the cathode root from diffuse to spot. In the second part, heating of copper anodes and copper cathodes submitted to electric arcs in air and in argon and for various current intensity values (from 30A to 120 A) is considered. Two measurement methods are used. Finally, the surface temperature measurements are used to purpose two models of the electrode surface power balance (heat flux). One model only considers the heating due to the arc spot and the second one considers a supplementary heating from the arc column.
