Kinetics of charge transfer at mechanically strained copper electrodes—I. Anodic dissolution

• Published in: Electrochimica acta 1970-10, Vol.15 (10), p.1623-1636
• Main Authors: Devanathan, M.A.V., Fernando, M.J.
• Format: Article
• Language: English
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/0013-4686(70)80084-6

A technique is described which permits a recording of mechano-electrochemical dissolution current at constant pre-determined strain rates for the Cu/aq. CuSO 4 system under potentiostatic control. Studies have been carried out in the range 2.5–15 mV with strain rate ranging from 0.047 to 0.9105 strain/min. The increase in current is proportional to the square root of the corrected strain ε at constant overpotential η, the gradient being dependent on η. At high strains, a slight departure from linearity has been observed: this deviation is greater, the lower the strain rate. The results are interpreted on the slow surface diffusion model. The variation of dislocation density consequent on straining shortens the surface diffusion path, thereby enhancing the dissolution current. An equation is derived which connects the dissolution current with ε 1 2 , η, a factor G ▪ A the constant of proportionality between the density of dislocations N and the corrected strain ε, D the surface diffusion constant for ad-atoms and the usual electrodes kinetic-parameters. This equation is strictly valid as a limiting law and departures at high strains are due to relaxation effects. These have been quantitatively accounted for a healing factor h. An equation which takes into account the strain rate is derived and verified. Using published values for the electrode kinetic parameters for the Cu reaction, the value of A is calculated from the graphs and found to be in excellent agreement with that reported from etch-pit counts. The results provide quantitative support for the validity of the slow surface-diffusion model for copper dissolution at low overpotential. Description d'une technique mécanique permettant en électrochimie d'obtenir un courant de dissolution pour des vitesses de contrainte prédéterminées et constantes dans le systéme Cu/CuSO 4aq sous contrôle potentiostatique. Ces études ont été effectuées dans un domaine de surtension anodique compris entre 2,5 et 15 mV et pour une vitesse de contrainte allant de 0,047 à 0,9105 unité/minute. L'accroissement du courant est proportionnel à la racine carrée de la tension corrigée pour une surtension ε constante, le gradiant dépendant de η. Pour de fortes contraintes on observe un faible écart par rapport à la linéarité: cette déviation est d'autant plus grande que la vitesse de contrainte est plus faible. Les résultats sont interprétés suivant le modèle d'une lente diffusion superficielle. La variation de la densité de disloc