THE ANODIC BEHAVIOR OF SB AND PB-SB EUTECTIC IN SULFURIC-ACID-SOLUTIONS

Ring-disc voltammetric experiments on antimony in H2SO4 solutions show that a partly passivating oxide layer is formed on the metal surface preventing oxygen evolution. Due to the ionic conductivity and/or porosity of the layer the dissolution of the metal proceeds through the layer, and its rate is controlled by diffusion in the layer. Antimony is dissolved mainly in the trivalent state. Based on the determinations of the Tafel coefficient the mechanism of dissolution is dependent on the acid concentration. In the case of the lead-antimony eutectic the formation of a semipermeable lead sulphate membrane retards the rate of dissolution. ac Impedance measurements on antimony show features of a simple passivation process, eg a negative polarization resistance after the maximum in the current. The effect of mass transfer through the oxide layer is also observed. Thus the ac impedance measurements confirm the interpretation given above. © 1990.