International Journal of Electrochemical Science (Jan 2008)
Pitting Corrosion of Tin by Acetate Anion in Acidic Media
Abstract
The corrosion behaviour of tin is studied in acetate buffer solutions (pH 4.5). The potentiodynamic anodic polarization curve in 0.1M acetate solution exhibits two anodic peaks A1 and A2 prior to the passive layer formation region which is followed by pitting corrosion. A1 and A2 are attributed to stannous and stannic species formation. The effect of scan rate on the potentiodynamic behaviour of tin in this solution was studied. It showed that the corrosion process in the potential range of peaks A1 and A2 is mass transport controlled. Pitting corrosion is confirmed by light microscope images. The negative going scans of the cyclic voltammograms show three cathodic peaks C1, C2 and C3. The potentiostatic current time transients, at different electrolyte concentrations and applied potentials (around the pitting potential) involve three stages. The first stage, in which current decreases rapidly with time till reaching a minimum value im at the incubation time ti . The second and third stages, where current increases again linearly with time at two different slopes, are correlated to the pit nucleation and growth respectively. The nucleation rate (ti-1) was found to increase with increasing the electrolyte concentration and the anodic applied potential. The impedance spectra, at potentials of passive layer and pitting formations, exhibit a high frequency conductive semicircle and a low frequency inductive loop. The results showed a decrease in the electrode impedance as the applied potential approached the pitting potential.
