Passive Films on 90Cu‐10Ni Alloy: The Mechanism of Breakdown in Chloride Containing Solutions

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Abstract
The complex electrochemical behavior of 90Cu‐10Ni alloy in borate buffer solutions containing chloride ions involves Cu oxide formation, passivity onset, and pitting corrosion. The nature of the processes occurring was studied using electrochemical techniques complemented with SEM and EDXA. The overall process can be described by two competing processes: formation and growth of the duplex oxide passive film and formation of the layer. The layer is poorly protective and when the applied potential exceeds a certain critical value, pitting corrosion takes place. The change in both the kinetics and the morphology indicates that at least three stages should be distinguished in the pitting process: adsorption of Cl− ions, pit nucleation, and pit growth. The physical interpretation of the proposed model of passive film breakdown is consistent with its duplex structure, and is discussed in terms of the various conditions leading to nucleation and growth of pits. Experimental kinetic parameters of the passive film breakdown are presented.

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