THE CORROSION BEHAVIOR OF COPPER IN NEUTRAL TAP WATER .1. CORROSION MECHANISMS

The corrosion behaviour of copper in neutral aerated simulated tap wat er is investigated using electrochemical methods and XPS. Semi-infinit e diffusion behaviour is found in electrochemical impedance spectrosco py (EIS) from intermediate to low frequency. Polarization resistance ( R(p)) obtained at very low frequency (0.0005 Hz) increases with immers ion time, which coincides with the growth of oxide film on copper. The growth of oxide film with immersion time has little effect on the cat hodic process, but considerably reduces the anodic dissolution current . The observed results suggest that the diffusion of copper ions in ox ide film controls the overall corrosion rate. Under rotating condition s polarization resistance decreases and anodic current increases, whic h was caused by the decrease of the oxide film thickness. The phenomen a of the mixed diffusion of copper ion in oxide film and in solution h as been observed at a low pH of 5. Passivation is found when pH = 10. XPS spectra show that the oxide film formed is composed mainly of cupr ous oxide. An equivalent circuit representing the corroding interface is proposed with a discussion of theoretical approaches to the calcula tion of diffusion impedance and polarization resistance.