Galvanic corrosion of copper/silver contacts in electrical switches

AbstractAbstractThe galvanic corrosion of copper/silver contacts in electrical switches and relays in humid atmospheres was simulated in a model cell involving total immersion. The potential drop (∆E) between two identical calomel electrodes, one stationed at the end of a copper/silver/copper wire, the other sliding along it, was measured. Various cathode (silver wire) lengths, anode/cathode area ratios, and environments (distilled and tap water, natural and synthetic sea water of various compositions, and sulphuric acid solutions of varying strengths) were studied. The ∆E-distance curves were invariably bell shaped, with peaks corresponding to the centre of the silver cathode. The shape and height of the curves depended on the geometry of the galvanic couple, the nature and concentration of the electrolyte, the time of equilibrium in solution, the polarisability of the two metals, and the nature of the cathodic reaction. Corrosion currents were calculated from the AE values and solution conductivities for natural sea water and sulphuric acid solutions. Large currents prevailed at the bimetallic junctions, decreasing with distance from the junction. The currents increased with increasing solution concentration and were higher in acid than in neutral media. Recommendations to prevent galvanic corrosion in switches or to reduce its intensity are given.