Potentiodynamic studies on anodic dissolution and passivation of tin, indium and tin–indium alloys in some fruit acids solutions

The anodic dissolution and passivation of tin, indium and tin–indium alloys were studied in 0.5 M solutions of both malic and citric acids, using potentiodynamic technique and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The E/I curves showed that the anodic behavior of all investigated electrodes exhibits active/passive transition. The active region of tin involves two anodic peaks (I and II) prior to the passive region in both the investigated acids, while indium exhibits two peaks (I and II) in malic and one peak in citric acid. These two peaks (I and II) correspond to the formation of InOOH and In(OH)3/In2O3 system, respectively, but that observed peak in citric acid is to InOOH. The active region for tin–indium alloys (I, II and III) in citric acid showed one peak (I) and shoulders (II). This shoulder predominates with increasing temperature due to little In2O3 formation and its dissolution at higher temperatures. The disappearance of this shoulder for the alloys (IV and V) with high indium percent may be due to the formation of large amounts of In2O3 with tin oxides on the surface.