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_3~-, SO_4~(2-) and Cl~-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_4~(2-)]/[OH~-], [SO_4~(2-)]/[HCO_3~-] and [Cl~-]/[HCO_3~-] ratios lower pitting potentials while an increase in alkalinity improves passivity and raises pitting potentials. HCO_3~-/CO_3~(2-) can protect copper surfaces by forming carbonate containing minerals. However, carbonated species are less beneficial towards passivity compared to OH~- 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 HCO3", Cl~- and SO_4~(2-) content. The origins of the trends with water chemistry variables are discussed.