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Strain potentials of copper wire in : I. cupric sulfate II. cupric chloride Elliott, Rodney

Abstract

The effect of stress on the electrode potential of copper in aerated cupric sulphate and in aerated cupric chloride solutions was studied. The influence of the variables time, temperature, concentration, magnitude of stress, mechanical condition of the metal, and pH was considered. The potential difference between two size #22B&S copper wires was continuously recorded on a type G speedomax automatic recorder. Weights were added to one of the wires and the change in the potential difference between the two wires from the pre-stress potential difference value was taken as the strain potential. At least six runs, using fresh pairs of wire for each run, were carried out to illustrate each specific point and to show the results have statistical significance and are reproducible. The following results were obtained: (A) Electronegative strain potentials have been obtained for copper metal in copper sulfate solution; these changes achieve a maximum at the instants of stressing and then decay with time. The magnitude of the electronegative strain potential for a given stress increased exponentially with the absolute temperature and decreased significantly for concentration changes from 0.0005 N to 0.500 N. (B) Experimental evidences were obtained to support the postulate that strain potentials of copper metal in copper sulfate solution and their time dependence parallel film rupture and repair. (C) Both electronegative and electropositive strain.potentials were obtained with size #22B&S soft copper wire in cupric chloride solution; the sign of the strain potential was negative for a concentration of 0.500 N and the sign of the strain potential was positive for concentrations of 0.100, 0.050, and 0.005. The magnitude of the strain potential did not vary with concentration as for the case of copper wire in copper sulfate solution. The electronegative change, obtained in 0.500 N cupric chloride lasted for less than three seconds whereupon the change in the potential difference between the two wires shifted rapidly to a positive value. An attempt was made to explain these results on the basis of the stability of Cu₂O and CuCl films using potential-pH diagrams. The magnitude of the strain potential for a given stress was found to vary exponentially with the absolute temperature between the range 298°K to 338°K.

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