ECN-measurements at copper in artificial tap water - Investigation of anion-effects

Electrochemical noise analysis was succesfully applied to study anion effec ts in the first 20 h starting period of copper corrosion in tap water. The influence of chloride, sulfate and bicarbonate as single anions and the int eractions between them in three anion solutions were characterized in terms of standard deviation and PSD(I) data as well as interaction coefficients obtained from the evaluation of a set of experiments designed according to a statistical 2(3)-factorial plan. The results let conclude that sulfate ha s an activating and chloride a passivating effect. Bicarbonate seems to act as a buffering agent. It is obviously the combination of the presence of a ll three anions in a narrow range of concentration ratios which finally lea ds to pitting corrosion. The relevance of these results from short term exp osure for the long term performance of copper in tap water and the likeliho od of pitting corrosion should now be investigated in long term exposure te sts.