X-ray photoelectron spectroscopy study of passive layers formed on Pb-Sn and Pb-Sb alloys
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I. INTRODUCTION
LEAD alloys currently are the main grid materials for lead-acid batteries. Grids made by Pb-Sb alloys have good mechanical and casting properties and are easy to process. The Pb-Sn alloy has a low casting temperature and high mechanical strength. Moreover, alloying Sn improves the deep-cycle charging-discharging property of lead-acid batteries. Alloying Sn or Sb helps to form a passive film between the grid and the active materials pasted on plates (mainly positive plates). This passive film protects the grid from corrosion in the acid surroundings. The property of passive film is decided by its composition and structure. Extensive work has been done, and some instructive results have come up.[1–6] Among them, the double-layer structure mode was very popular.[6,7,8] In terms of the relationship between the content of alloying elements and film conductivity, investigations were done in an alkali environment (pH 9).[5] However, the practical working environment of the grid is sulfuric acid; the composition and character of formed films in an acid environment are inevitably quite different from those in an alkali one. No research, though, has been performed in this area before. In this article, X-ray photoelectron spectroscopy (XPS) was used to study the passive films grown on the surface of Pb-Sn and Pb-Sb alloys in sulfuric acid. The compositions and microstructures were studied, and the influence of the JING XU, Ph.D. Student, is with the Mechanical and Aerospace Egneinering Depatment, West Virginia Universtiy, Morgantown, WV 26506, and the Corrosion and Protection Center, Key Lab for Corrosion and Erosion, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] XIAOGANG LI, Professor, is with the Corrosion and Protection Center, Key Lab for Corrosion and Erosion, University of Science and Technology Beijing, and the State Key Lab for Corrosion and Protection, Shenyang 110016, P.R. China. XINGBO LIU, Research Assistant Professor, NATHANIEL DEEM, Master Student, and EVER BARBERO, Chairman, are with the Mechanical and Aerospace Egneinering Depatment, West Virginia Universtiy, Morgantown, WV 26506. CHAOFANG DONG, Lecturer, is with the Corrosion and Protection Center, Key Lab for Corrosion and Erosion, University of Science and Technology Beijing. Manuscript submitted September 18, 2003. METALLURGICAL AND MATERIALS TRANSACTIONS A
alloying elements on the passive films was also discussed. It was useful for further optimizing the properties of grids in Pb acid batteries. Simultaneously, it could also benefit the batteries’ lifetimes in deep-cycle service by preventing grids from being corroded in the severe service environment. II. EXPERIMENT The electrolyte was a 4.0 mol/L H2SO4 solution prepared from analytical reagent (AR)-grade sulfuric acid and distilled water. Four Pb-Sn alloys and three Pb-Sb alloys with different compositions were used as the working electrodes. The alloys were cast from Pb (99.99 pct) and Sb (99.99 pct) or Sn (99.9 pct). The
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