Anodic behavior of tin, indium, and tin-indium alloys in oxalic acid solution

The anodic behavior of tin, indium, and tin-indium alloys was studied in oxalic acid solution using potentiodynamic technique and characterized by X-ray diffraction and scanning electron microscopy. The E/I curves showed that the anodic behavior of all investigated electrodes exhibits active/passive transition. In the case of tin, the active dissolution region involves two anodic peaks (I and II) prior to permanent passive region. On the other hand, the active dissolution of indium involves four peaks (I-IV) prior to permanent passive region. The first (I) can be associated with the active dissolution of indium to InOOH, the second peak (II) to the formation of In(OH)(3), the third peak (III) to partially dehydration of In(OH)(3), and the peak (IV) to complete dehydration of In(OH)(3) to In2O3. When the surface is entirely covered with In2O3 film, the anodic current falls to a small value (I (pass)) indicating the onset of passivation. The active dissolution potential region of the first three tin-indium alloys involves a net anodic contribution peak, and this is followed by a passive region. It is expected that the investigated peak is related to the formation of In2O3 and SnO (mixed oxides). When the formation of oxides (the oxides of In and Sn) exceeds its dissolution rate, the current drops, indicating the onset of passivation precipitation of In2O3/SnO and SnO2 on the surface which blocks the dissolution of active sites. The alloys IV and V showed small second peak at about -620 mV which may be related to oxidation of In to In2O3 due to high In content in the two examined alloys. The active dissolution and passive current are increase with increasing temperature for all investigated metals and their alloys.