Research On Effect Of Bismuth On The Electrochemical Properties And Corrosion Behavior Of Lead Alloys Involved In Lead Acid Battery

The effect of bismuth on the electrochemical behaviors of lead alloys in sulfuric solutions were investigated and the by CV, LSV, CA, CP and AC impedance. The electrode reactions include transformation of PbSO₄? PbO₂, formation of PbO, conversion of Pb? PbSO₄, hydrogen and oxygen evolution, anodic corrosion of lead alloy and following results have been obtained.1. Some irregular redox peaks appear nearby the reduction peak of PbO₂ when the lead electrode potential is cycled from hydrogen evolution potential to oxygen evolution potential. These redox peaks can be ascribed to the sum of reduction current of PbO₂ and oxidation current of lead under oxides.2. Two oxidation peaks are observed when bismuth is anodized in sulfuric acid solution. The first oxidation peak is corresponding to the formation of bismuth sulphate, which follows dissolution-precipitation mechanism and is controlled by ion diffusion in solution. The second oxidation peak is the second oxidation of bismuth under the bismuth sulphate film. The oxidation product is non-crystalline.3,The addition of bismuth accelerated the formation of PbO₂ from PbSO₄ in 1.28g/cm^-3 H₂SO₄ solution. The peak potential of PbO₂ formation decreases, as the bismuth level increases. The SEM result shown that the microstructure of the PbO₂ layers became more loosen and lacunaris, which benefit to the initial capacity of battery. And the XRD result indicated that PbO₂ presented as unshaped dioxide.4,The formation of PbO was inhibited, hence, the resistance of the passive film on the lead-bismuth alloy reduces. The passive film was made up by t-PbO, PbO·PbSO₄ and PbSO₄. And bismuth existed as a-Bi₂O₃,β-Bi₂O₃, BiSO₄ and possibly Bi₂(SO₄)₃.5,Bismuth content lower than 0.112% has no significant effect on corrosion rate. However, the corrosion rate increases quickly when the bismuth amount is over 0.158%. And the corrosion product are composed of irregular-shaped agglomerates that are consists of fine, needle-like crystals, which grow out from the surface of the agglomerates. And the needle-like crystals are interlaced with each other to form the "bridge" of the agglomerates. So the presence of bismuth strengthens the connectivity of the corrosion product. Bismuth addition influences the microstructure of the alloy, which may have effect on the corrosion behaviors. The corrosion occurs firstly at the grain boundaries of lead-bismuth alloys. As the addition of bismuth increases, the grain boundaries become broader.6,Both hydrogen evolution and oxygen evolution on Pb-Ca-Sn-Al alloys are enhanced by addition of bismuth. The presence of bismuth may have beneficial effect on the formation of lead dioxide. But the relationship between the peak current and the amount of bismuth is not linear.7,The service life experiment suggested that negative grids contained bismuth might promoted the hydrogen evolution and deteriorate the sealing reaction efficiency...