Anodic passivation of Pb-Ag-Nd anode in fluoride-containing H₂SO₄ solution

Abstract

An attempt was made to build up a thick and compact oxide layer rapidly by pre-treating the Pb-Ag-Nd anode in fluoride-containing H₂SO₄ solution. The passivation reaction of Pb-Ag-Nd anode during pre-treatment process was investigated using cyclic voltammetry, linear scanning voltammetry, environmental scanning electron microscopy and X-ray diffraction analysis. The results show that PbF₂ and PbSO₄ are formed near the potential of Pb/PbSO₄ couple. The pre-treatment in fluoride-containing H₂SO₄ solution contributes to the formation of a thick, compact and adherent passive film. Furthermore, pre-treatment in fluoride-containing H₂SO₄ solution also facilitates the formation of PbO₂ on the anodic layer, and the reason could be attributed to the formation of more PbF₂ and PbSO₄ during the pre-treatment which tend to transform to PbO₂ during the following electrowinning process. In addition, the anodic layer on anode with pre-treatment in fluoride-containing H₂SO₄ solution is thick and compact, and its predominant composition is β-PbO₂. In summary, the pre-treatment in fluoride-containing H₂SO₄ solution benefits the formation of a desirable protective layer in a short time.)

Keywords

lead-based anode / fluoride / passive film / anodic layer / synergistic effect

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