Cyclic Voltammetric Studies on Selected Tin-Silver Binary Alloys in Sodium Hydroxide Solution

Abstract

Abstract The electrochemical corrosion and passivation behavior of four selected tin-silver alloys, xSn-Ag (x = 26, 50, 70, and 96.5 wt%) (II through V), in addition to their pure metallic components, Ag(I) and Sn(VI), were investigated in aqueous sodium hydroxide (NaOH) solution. The techniques used are linear sweep cyclic voltammetry and electrochemical impedance spectroscopy (EIS). In general, for all studied samples, the cyclic voltammograms show that increasing the scan rate shifts the passivation peak potential (Ep,a) positively and the reduction peak potential (Ep,c) negatively with a concomitant increase in both the passivation peak current density (ip,a) and the reduction peak current density (ip,c). EIS results investigate that the total resistance (RT) and the relative thickness (1/C) of the passive layers on the six tested electrodes are both found to increase with time of immersion, being more pronounced for sample II. Although this silver-rich alloy (74 wt%) has the most protectiveness among the tested specimens, the relative thickness of its passive film is much lower than that for the pure silver. After any immersion period the passivation sequence of the six samples can be arranged in the following order:II ≫ I > IV > III > V > VI.