Electrochemical Behavior of Homogeneous Pb-Tℓ Alloys in 1N H₂ SO₄

The anodic polarization of Pb-Tℓ alloys (solid solutions) in 1N H₂SO₄ was investigated using potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray diffractometry were used in the identification of reaction products. In the potential range from -0.29 to 1.97 V (SHE), three principal film composition regions were distinguished: (1) From -0.29 (the rest potential) to 0.20 V, only PbSO₄ was present. (2) From 0.20 to ca. 1.52 V, PbO_tet was the principal product, although basic lead sulfates, and in some instances α-PbO₂, were present. (3) From 1.52 to 1.97 V, β-PbO₂ was the dominant surface product. Removal of the β-PbO₂ surface layer revealed an interior layer that contained significant quantities of α-PbO₂. The relative amounts of PbO₂ on the surface decreased in this potential region with increasing amounts of Tℓ in the alloy, and PbO_tet became the dominant phase. The presence of Tℓ(III) in the electrolyte indicates that the PbO₂ may have been reduced by the Tℓ(I)/Tℓ(III) redox reaction.