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

Abstract

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 with systematic variations in concentrations of these species. Studies of the effect of water chemistry on passivity, uniform corrosion, and pitting were accomplished using the cyclic voltammetry method complemented by various diagnostic methods. Certain water chemistry concentrations promote pitting. Critical pitting potentials ͑E Pit ͒ for copper pitting are decreased by certain water chemistry variables. High ͓SO 4 2− ͔/͓OH − ͔, ͓SO 4 2− ͔/͓HCO 3 − ͔, and Cl − /͓HCO 3 − ͔ ratios lower pitting potentials while an increase in alkalinity ͑increasing ͓OH − ͔ or ͓HCO 3 − ͔/͓CO 3 2− ͔͒ 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 toward 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 HCO 3 − , Cl − , and SO 4 2− content. The origins of the trends with water chemistry variables are discussed.

Nanoscale surface characterization of aqueous copper corrosion: Effects of immersion interval and orthophosphate concentration

“…Corrosion of the metal can occur uniformly across the surface or it can take place in a localized area (i.e., pitting). Metallic copper can form a thin passivating layer of cuprous oxide (Cu 2 O) [7,8] for protection against degradation [9]. The thickness, porosity and ability of the passivating layer to conduct ions are properties that affect the progression of corrosion [10][11][12].…”

Impact of pH, Dissolved Inorganic Carbon, and Polyphosphates for the Initial Stages of Water Corrosion of Copper Surfaces Investigated by AFM and NEXAFS

“…Corrosion of copper surfaces by water is a process that involves multiple parameters. [27][28][29][30][31] Previously, we studied the effects of phosphates as a function of pH for mitigating the corrosion of copper. 8 Essentially, the previous report provides control experiments as a baseline for designing further studies of different water parameters.…”

Effects of Aluminum Solids on the under Deposit Corrosion of Copper in Synthetic Potable Water: The Arguments for and against a Semi-Permeable Membrane

“…Previous study demonstrates that E Pit decreases with increasing [SO 4 2− ]/[OH − ] ratio. 13 An empirical equation for the pitting potentials of copper in ESDW also indicates that E Pit would decrease with decreasing [OH − ], assuming negligible change of other anion concentrations and without deposits. 13 Therefore, sequestering of OH − and transport of SO 4 2− would shift E Pit according Figure 16.…”

“…Also, consumption of hydroxyl anions will lead to an increase in the [SO 4 2− ]/[OH − ] ratio, which will cause a decrease in the pitting potential according to previous studies. 13 The higher pH at the cathode tends to dissolve any aluminum deposits that form, preventing much deposition there. Thus, on this basis, in a pH 9 water with high concentration of aluminum, pitting might be selfperpetuating under Al(OH) 3 deposits.…”