AWWA ACE93141

Copper passivation was examined in simple solutions that contained bicarbonate, chloride, perchlorate, nitrate or sulfate at pH 5.5, 7.0, 8.5 and 10. Copper corrosion rates increased with aging in the presence of sulfate, nitrate and perchlorate at all pHs, whereas copper passivated in the presence of chloride at pH greater than 7.0. Bicarbonate ion was discovered to have a dual nature that was pH dependent, causing activation (increased corrosion rates) after aging at pH less than 7.0 and passivation at pH greater than 8.5. Activation in the presence of bicarbonate was due to catalysis of oxygen reduction (cathodic) reactions, while sulfate, nitrate, and perchlorate increased the copper oxidation (anodic) reaction rates after aging. Under the conditions tested, copper exhibited a natural tendency towards activation that was countered only by the presence of chloride or bicarbonate within certain pH ranges.