INORGANIC ANIONS AND COPPER PITTING

Copper (Cu) pitting was examined in oxygenated solutions containing bicarbonate (HCO3-), chloride (Cl-), nitrate (NO3-), perchlorate (ClO4-), or sulfate (SO42-) ions at pH values of 5.5, 7.0, 8.5, and 10.0. While short-term (a few hours) cyclic polarization experiments at anion concentrations (or ionic strengths) typical of drinking waters were inconclusive, potentiostatic testing provided insight into Cu pitting behavior. Cl- exhibited a time-dependent dual nature, accelerating anodic reactions in the short term and causing passivation over longer periods. Passivation occurred only at pH 10.0 in the systems containing NO3- and ClO4- and did not occur in the presence of SO42-. Results supported the notion that SO42- or NO3- and not Cl-, (as commonly believed), are key to Cu pitting in potable water distribution systems.