Influence of fluoride and chromium(VI) ions on corrosion mechanisms of Pb-3wt%sn-0.5wt%Ag anode

A mix solution of fluorine and chromium ions (Cr-F solution) for applications in chromium plating field has a characteristic of strong corrosion and oxidation, promoting lead alloys anode degraded rapidly. The present study explores the time dependence on corrosion mechanisms of lead alloys anode oxidised in Cr-F solution under conditions of high current density. Scanning electron microscopy (SEM) with an energy dispersive X-ray spectroscopy (EDX) shows a double-layer oxide film is electrochemically developed on lead alloys anode after oxidation for above 0.5h. The outer layer is primarily PbO and PbO2, and the inner layer contains PbCrO4 and PbF2, followed by PbO. In the initial oxidation stage (oxidation time below 60s) of lead alloys anode, the Raman peaks of PbCrO4 and PbF2 are clearly shown by the Raman spectrascanning. With increasing reaction time, Raman peaks intensity for PbO is strengthened. Cyclic voltammetry reveals thateffect of fluorine ions on the electrode potential for lead alloys anode change among Pb, PbO, PbCrO4, PbO1+x (0