Anodic Behaviour of Antimony and Antimony-Tin Alloys in Alkaline Solutions

The electrochemical and corrosive behaviour of antimony and antimony-tin alloys (Alloy No./Sb(wt. %); I/90, II/80, III/65, IV/50) as anodes in various aqueous concentrations of KOH have been investigated using galvanostatic, potentiodynamic and potentiostatic techniques. Galvanostatic potential–time curves at 4 mA cm^-2 revealed that passivation of both antimony and antimony tin alloys is inhibited by an increase in KOH concentration. The opposite effect was observed with an increase in Sn content in the alloy. At high Sn content and low [OH^-] a pseudo passivation potential was observed. (Abnormal early passivation occurring in the active anodic region due to the formation of tin oxides, which dissolve in alkali. Then, potential decreases.) The alloy with 50% Sn exhibited immediate passivation. The potentiodynamic curves were swept from Eo.c up to +1000 mV vs SCE. The results showed an increase in the peak current (Ip) for antimony and its alloys with increasing [OH^-] on the oxide film. The first three alloys showed two anodic peaks at -780 and -450 mV, but the forth traced a third peak at -940 mV. X-ray diffraction and SEM micrographs detailed the electrochemical results and morphology of the electrode surface.