Characterization of the patina formed on a low tin bronze exposed to aqueous hydrogen sulfide

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The dark gray corrosion layer (patina) formed on the surface of a polished low tin bronze alloy following exposure to a deoxygenated and saturated aqueous solutions of H 2 S has been characterized by X‐ray photoelectron spectroscopy, scanning electron microscopy‐energy dispersive spectroscopy and X‐ray diffraction. The system represents a model for bronze corrosion in reducing conditions where sulfate‐reducing bacteria in soils or deoxygenated seawater may generate H 2 S during respiration. The initial surface was dominated by metallic copper together with Sn, Pb and Zn oxides and hydroxides. Surface enrichment of Pb and Zn was noted because of a smearing effect during polishing. At least some of the lead was crystalline. In contrast, the corrosion layer formed by H 2 S(aq) exposure was dominated by polycrystalline Cu 2 S (low and high chalcocite) and smaller concentrations of CuSO 4 · n H 2 O. This surface was enriched with Zn as Zn(OH) 2 . Lead was present as redeposited PbS (galena) crystallites in at least two different morphologies. Unlike bronzes exposed to oxidizing conditions, which develop protective SnO 2 layers, the H 2 S(aq)‐exposed surface was considerably depleted in Sn.