Electrochemistry action of F ions in the TFS (tin free steel) plating solution was investigated by means of A.C. voltammetry, electrochemical impedance spectrum (EIS) and Mott-Schottky analysis technology. The A.C. voltammetry results showed that F ions have a characteristic of inhibiting the chemical state transition of Cr ions, decreasing the oxide current density of lead alloy and lead oxide anode, and influencing the oxidation and reduction mechanism of lead alloy and lead oxide anode. Polymer for Cr and O ions cluster might be formed under conditions of electric field. In addition, inductive reactance phenomenon was observed on EIS for lead alloy anode in Cr ions solution. The properties of F ions solution were found to eliminate the inductive reactance phenomenon, and increase obviously the conducting ability of Cr ions solution. According to analysis of Mott-Schottky, carrier concentrations of anode materials were increased by being added F ions, and anode of lead alloy and lead oxide exhibited an n-type semiconductive character.

This work examines the change of surface properties and the reaction process of lead alloy anode in CrO3 solution under conditions of high current density, by means of SEM, EDX, XRD, electrochemical test and Raman spectroscopy, for understanding the corrosion mechanism of lead alloy anode. In the initial oxidation stage of lead alloy anode, the diffraction peaks of monoclinic PbCrO4 and PbO are clearly shown in the XRD spectrum of the lead alloy surface. With increasing reaction time, PbCrO4 and PbO diffraction peaks are weakened and those of lead dioxide strengthened. Cyclic voltammetry reveals that the electrode potential change is among Pb, PbO, PbCrO4, PbO1+x (0 < x < 1) and β-PbO2. According to impedance tests, charge transfer and a corrosion product film on lead alloy surface happen under the high and medium frequencies, and chromium-oxide ion clusters are absorbed on free sites of the anode surface for the low frequency. The corrosion products have characteristic of complex semiconducting behavior shown in the Mott–Schottky plots. Raman spectra indicates that Cr2O72− and HCrO4− ions are firstly absorbed on the anode surface, and then PbCrO4 is produced between Cr2O72− and Pb, PbO is reacted from HCrO4−. The mechanism of the anode reaction at the anode/solution interface is discussed using the experimental results.

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