Potentiodynamic Studies of Antimony in Acidic and Alkaline Solutions

Potentiodynamic polarization of antimony in acidic and alkaline solutions has been investigated. In acidic solutions, two transition potentials were observed at about the equilibrium potentials of the Sb/Sb₂O₃ and the Sb₂O₃/Sb₂O₅ reactions. Both anodic and cathodic Tafel behavior was observed for these reactions. The anodic and cathodic Tafel slopes are 100 and 150 mV/decade, respectively, for the Sb₂O₃/Sb₂O₅ reaction. For the latter, the cathodic reaction is first order and the anodic reaction is zero order with respect to the hydrogen ion concentration. A mechanism for the Sb₂O₃/Sb₂O₅ reaction is proposed which is consistent with the experimental kinetic data. In alkaline solutions, only the Sb/Sb₂O₃ reaction was observed. In both acidic and alkaline solutions the differential capacitance of active antimony is substantially larger than the differential capacitance of passive antimony.