An investigation into the surface layers formed on oxidised copper exposed to SO2 in humid air under hypoxic conditions

Abstract Preoxidised Cu surfaces and powdery Cu oxides were exposed to SO 2 vapour in an oxygen-deprived humid atmosphere. The reaction products were investigated by XRD and SEM-EDX. Chevreul’s salt, Cu 2 SO 4 ·CuSO 4 ·2H 2 O results to be the only stable product. Cu(0) is detected in experiments on Cu(I) oxide. Based on the competition between Cu(I) disproportionation and Cu(II) reduction by SO 2 , a reaction pathway is proposed. Initially formed Chevreul’s salt exhibits orthorhombic symmetry and a phase transformation to the stable monoclinic structure occurs upon ageing at room temperature. A mechanistic analogy with bronze disease of archaeological artefacts has been pointed out.