Influence of Mn2 + on the performance of Pb-Ag anodes in fluoride/chloride-containing H2SO4 solutions

Abstract

In this study, surface morphology, inner structure and phase composition of anodic layers on Pb-Ag anode in fluoride/chloride-containing H2SO4 solutions were investigated in the presence/absence of Mn2+. Additionally, corrosion morphology of metallic substrate and anodic potential variation of Pb-Ag anodes were studied as well. The influence of Mn2+ on the anodic layer property and corrosion behavior of Pb-Ag anodes in fluoride/chloride-containing H2SO4 solutions was then clarified. The results revealed that in the presence of Mn2+, anodic layer consisted of an external layer in MnO2/PbO2-PbSO4/MnO2 structure and an inner layer adhering to the metallic substrate. Due to the coverage of an external layer, the corrosion of metallic substrate was relieved by the presence of Mn2+ in fluoride/chloride-containing H2SO4 solution. As was demonstrated, Mn2+ decreased PbO2 concentration in the inner layer, especially in fluoride-containing solution. In the presence of Mn2+, the anodic potential was higher than that in solutions without Mn2+ due to larger thickness and resistance of anodic layer. In addition, the anodic potential was characterized by oscillation in Mn2+-containing solution, indicating low stability of anodic layer. Comparatively, the anodic layer formed in the presence of Mn2+ and chloride ion was more stable than that in solutions containing Mn2+ and fluoride ion.