Characterization of corrosion products formed on copper in urban, rural/coastal, and hot spring areas

Corrosion products formed on copper plates exposed in urban, rural/coastal, and hot spring areas in Japan were characterized by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and coulometric reduction. The exposure tests were carried out for a month in summer. XRD patterns showed that hydrated copper sulfate [Cu4SO4(OH)(6).H2O, posnjakite] and cuprite Cu2O were formed on copper surfaces exposed in urban and rural/coastal areas. The existence of sulfate salt agrees well with the XPS spectra. Sulfur dioxide and particulate sulfate such as ammonium sulfate and sea salt are both possible origins of this sulfate. In contrast, XRD revealed that the only corrosion product formed on the copper exposed in the hot spring area was cuprite Cu2O, although the amount of sulfur on the surface of this sample was the highest. Coulometric reduction analysis showed that there was copper sulfide Cu2S in corrosion products formed on copper exposed in the hot spring area. Posnjakite Cu4SO4(OH)(6).H2O is initially formed in addition to cuprite Cu2O when copper is exposed in urban and rural/coastal atmospheres. This crystalline phase is located at and near the copper surface. Initially formed posnjakite Cu4SO4(OH)(6).H2O may change to brochantite Cu4SO4(OH)(6), which is a typical patina component that appears after further exposure. (C) 2001 The Electrochemical Society.