Inorganic Anions and Copper Pitting

1 May 1994

journal article
Published by Association for Materials Protection and Performance (AMPP) in Corrosion

Vol. 50 (5) , 366-372
https://doi.org/10.5006/1.3294345

Abstract

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.

Keywords

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