Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

摘要

The electrochemical pitting behavior of UNS C11000 copper was investigated in a synthetic potable water found to cause pitting. Tests were also conducted in several other (HCO{sub}3){sup}-, (SO{sub}4){sup}(2-) and Cl{sup}-containing-waters. Studies of the effect of water chemistry on passivity, uniform corrosion, and pitting were accomplished using the cyclic voltammetry method. Certain water chemistry concentrations promote pitting. High [(SO{sub}4){sup}(2-)]/[OH{sup}-], [(SO{sub}4){sup}(2-)]/[(HCO{sub}3){sup}-] and [Cl{sup}-]/[(HCO{sub}3){sup}-] ratios lower pitting potentials while an increase in alkalinity improves passivity and raises pitting potentials. (HCO{sub}3){sup}-/(CO{sub}3){sup}(2-) can protect copper surfaces by forming carbonate containing minerals. However, carbonated species are less beneficial towards passivity compared to OH{sup}- with respect to passivation efficiency. Empirical equations that forecast pitting and repassivation potentials as a function of selected water chemistry variables were developed by linear regression analysis based on experimental pitting and repassivation potential trends with (HCO{sub}3){sup}-, Cl{sup}- and (SO{sub}4){sup}(2-) content. The origins of the trends with water chemistry variables are discussed.