On the kinetics of chromium electrodeposition on copper electrodes

In a previous work, we observed that, during cyclic potentiodynamic curves of cathodic polarisation (from 0.00 to - 1.25 V/SCE, 5 mV s(-1)) in chromic acid solution of industrial composition, ARMCO iron undergoes a pitting corrosion, while carbon steels undergo a selective ferritic corrosion. Blisters of pure iron were also observed on ARMCO iron electrodes surface. These occurrences suggest a direct participation of the metal substrate to the overall reaction of reduction of the chromic acid to chromium metal. Therefore, the chemical nature of the electrode metal has been changed, in order to pl avc that the chromium reduction goes on through an ECE mechanism involving a fast chemical reaction between unstable intermediate chromium reduction goes and the metal substrate. Cathodic potentiodynamic polarisation curves were performed on copper electrodes and the scans were stopped at four different potentials (-0.90, - 1.00, -1.10 and -1.25 V/SCE). The copper surface undergoes a severe corrosion in all the experimental conditions. The morphology of the attack depends on the polarisation potential and on the presence of additives in solution, like iron sulphate. (C) 2001 Elsevier Science B.V. All rights reserved