Corrosion Products Formed on Copper exposed to humid SO 2 ‐containing atmospheres

X‐ray diffraction analyses have been performed on samples of electrolytic copper (min. 99,9% Cu) exposed to humid atmoshperes at SO 2 ‐supplies of 10 and 100μg SO 2 per cm 2 surface area per hour (10 and 100 ppm SO 2 . respectively). During the SO 2 ‐exposures copper (II) sulphate (CuSO 4 · 5 H 2 O) were the only crystalline phases formed in detectable amounts. Interruption of the SO 2 ‐ supply resulted in the formation of copper (I) oxide and antlerite (CuSO 4 ) · 2Cu (OH) 2 . During prolonged exposure brochanite (CuSO 4 · 3Cu(OH) 2 ) and langite (CuSO 4 · 3Cu(OH) 2 ) and langite (CuSO 4 · Cu(OH) 2 · 2H 2 O) were also formed i. E. the Cu:S ratio of the basic copper sulphates increased with time. The formation of antlerite was preceeded by formation of an unidentified intermediate compound, probably a basic copper sulphate with a Cu:S ratio of less than three, and a simultaneous transformation of the copper (II) sulphate and copper (I, II) sulphite formed during the SO 2 ‐exposure.