Corrosion characterization of new tin-silver binary alloys in nitric acid solutions

Electrochemical techniques were used to characterize the corrosion behavior of four new binary alloys xSn-Ag (x = 26, 50, 70 and 96.5 wt%) alloys and their individual metal components in nitric acid solutions. The experimental data were collected by using open-circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Over the concentration range studied (0.075-4.5 M), each of the two corrosion parameters (E-corr, and i(corr)) shows a regular dependency on both the alloy composition and the solution concentration. In general, for all studied samples, especially pure Ag and those with lower Sri contents (26 and 50 wt%), increasing the acid concentration increases I-corr, meanwhile causes a shift of the corresponding E-corr towards more positive values. This is probably due to the increase in the effect of cathodic depolarizer as the nitric acid concentration is increased. EIS results at the free corrosion potential confirmed well this behavior, where at concentrations <= 1.5 M the thickness of the surface film increases while its resistance decreases with increasing tin wt%, indicating formation of less protective thicker film. However, at higher concentrations all samples exhibit identical behavior. (C) 2008 Elsevier Ltd. All rights reserved.