Interface analysis of pure Sn, pure Ag and SnAg binary alloys in H2SO4

Abstract The electrochemical and passivation properties of three selected binary x SnAg ( x = 26, 50 and 70 wt%) alloys were studied by means of open‐circuit potential variation, potentiodynamic curves and a.c. impedance spectroscopy techniques.The specimens were polarized between −1.0 and 0.5 V versus saturated calomel electrode (SCE) in naturally oxygenated sulfuric acidsolutions of different concentrations The experimental results indicate that i corr increases with increasing either the acid concentration or the Sn content in the solid phase. Electrochemical impedance spectroscopyresults measured at the free corrosion potential confirm that alloy I (26SnAg) characterizes by thicker passive film with higher protective ability compared to the other two samples richer in tin component. The exponential variation of the relative thickness of the surface film on any of the tested samples assumes an almost constant thickness for a thin barrier layer and a much larger outer porous layer that dominates the total film thickness on the alloy. Copyright © 2010 John Wiley & Sons, Ltd.