Electrochemical behavior of copper in drinking water: evaluation of dissolution process at low anodic overpotential

Abstract

O comportamento eletroquímico do cobre em água potável foi estudado por polarização potenciodinâmica e espectroscopia de impedância eletroquímica em até quatro dias depois de imersão em condições hidrodinâmicas diferentes. Os resultados de impedância foram interpretados usando modelos de circuito equivalente, os quais mostraram um aumento da espessura do filme com o tempo, que impede a difusão de espécies de cobre através da camada de óxido de cobre formada. Essa camada de óxido é maior em condição de estagnação. A baixos sobrepotenciais anódicos, os diagramas de impedância apresentam pelo menos quatro constantes de tempo que poderiam ser explicadas pela existência de diferentes pocessos faradaicos, a adsorção/dessorção de espécies intermediárias, processos de difusão e a formação de uma camada de óxido na superfície de cobre. Na região anódica, a resistência total à corrosão diminui, possivelmente devido à dissolução das espécies de cobre e ao aumento da difusão através da camada de óxido, principalmente sob condições hidrodinâmicas.The electrochemical behavior of copper in near-neutral aerated tap water was studied by potentiodynamic polarization and electrochemical impedance spectroscopy up to four days of immersion under different hydrodynamic conditions. The impedance results were interpreted by equivalent circuit that showed an increasing film thickness with time that hinders the diffusion of copper species across the oxide layer, which is larger in stagnating condition. At low anodic overpotential, copper impedance presents at least four time constants that could be explained by faradaic processes, adsorption/desorption of intermediate species, diffusion controlled process and oxide layer formation on copper surface. In the anodic region, the overall corrosion resistance decreases possibly due to the dissolution of copper species and the increase of diffusion across the oxide layer, mainly under hydrodynamic condition.

In Situ Electrochemical Impedance Spectroscopy Measurements and their Interpretation for the Diagnostic of Metallic Cultural Heritage: A Review

“…The oxide layer structure and composition cannot be derived from the XPS results presented, as it is not possible to distinguish between copper products using only the photoemission peak, being necessary to resort to the Auger peaks, which not included in their work . Rios et al . observed three time constants in much shorter immersion times and assigned the additional time constant, at higher frequencies, to the oxide layer on the surface, being the medium and low frequency time constants related to the copper corrosion mechanism already described.…”

A Study on Corrosion Behavior of Vacuum Brazed OFE Copper Joints of Industrial Accelerator

“…Copper, when exposed to neutral or slightly alkaline water, is known to develop a protective oxide layer. This protective layer comprises of cuprous species with other copper products like cupric oxide, cupric hydroxide and possibly cupric carbonate [7]. Grazing angle XRD performed on OFE copper as well as "BVAg-8 braze filler" specimens, exposed to stagnant process water, demonstrated that the surface film was comprised of Cu 2 O and CuO, as shown in Fig.…”

“…However, with further exposure the conductivity of process water used in "flowing condition" recorded much larger increase with respect to its counterpart used in "stagnant condition. Possible contributing factors for the increase in water conductivity are believed to be increase in dissolved oxygen and carbon dioxide content and release of copper species from the oxides [7,8].…”

“…Rios et al have also reported that under stagnant condition film formation on copper substrate takes place in the initial hours of its immersion. An increase in the thickness of oxide film thickness is associated with corresponding increase in its polarization which hinders diffusion of copper species across the oxide layer resulting in reduced corrosion rate [7]. On the other hand, immersion testing of copper specimens under flowing process water resulted in significantly reduced thickness of oxide film which should yield smaller polarization resistance and therefore relatively higher corrosion rate [7], which was reflected in larger rise in the conductivity of process water.…”

“…An increase in the thickness of oxide film thickness is associated with corresponding increase in its polarization which hinders diffusion of copper species across the oxide layer resulting in reduced corrosion rate [7]. On the other hand, immersion testing of copper specimens under flowing process water resulted in significantly reduced thickness of oxide film which should yield smaller polarization resistance and therefore relatively higher corrosion rate [7], which was reflected in larger rise in the conductivity of process water. It has been reported that corrosion of copper in water (with dissolved oxygen content) proceeds under cathodic diffusion control and as a result an increase in agitation or flow velocity causes corresponding increase in corrosion rate [4].…”