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

Abstract

The electrochemical and passivation properties of three selected binary xSn-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.

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“…3, consists of two circuits in series from R 1 C 1 and R 2 C 2 parallel combination and the two are in series with R s . In this way C 1 is related to contribution from the capacitance of the outer layer and the faradaic reaction therein and C 2 pertains to the inner layer, while R 1 and R 2 are the respective resistances of the outer and inner layers constituting the surface film, respectively [28,29]. Analysis of the experimental spectra was made by best fitting to the corresponding equivalent circuit using Thales software provided with the workstation where the dispersion formula suitable to each model was used [30].…”

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