Abstract
The copper corrosion was studied for 30 days in two alkaline electrolytes: saturated Ca(OH)2 and cement extract, employed to simulate concrete-pore environments. Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry were carried out at the open circuit potential (OCP), and potentiodynamic polarization (PDP) curves were performed for comparative purposes. Electrochemical current fluctuations, considered as electrochemical noise (EN), were employed as non-destructive methods. The tests revealed that sat. Ca(OH)2 is the less aggressive to the Cu surface, mainly because of the lower in one order pH. In consequence, the OCP values of Cu were more positive, the polarization resistance values were higher by one order of magnitude, and the anodic currents of Cu were lower than those in the cement extract. The analyzed EN indicated that the initial corrosion attacks on the Cu surface are quasi-uniform, resulting from the stationary persistent corrosion process occurring in both model solutions. XPS analysis and X-ray diffraction (XRD) patterns revealed that in sat. Ca(OH)2, a Cu2O/CuO corrosion layer was formed, which effectively protects the metallic Cu-surface. We present evidence for the sequential oxidation of Cu to the (+1) and (+2) species, its impact on the corrosion layer, and also its protective properties.
Highlights
Concrete-embedded metals corrode in fresh and humid concrete, where the direct metal oxidation in the pore alkaline environment leads to changes at the metal interface during the curing time.The corrosion process can stop when a protective oxide film is formed on the metal surface, the so-called passive layer
In order to evaluate the damage on the copper surface, the corrosion products formed were removed from the surface of the samples exposed for 720 h, submerged them in a sulfuric acid solution during 2 min at 21 ◦ C, according to the cleaning procedure recommended by ASTM G1 standard [42]
The XPS determined the existence of a native copper oxide layer, which was not possible to detect by X-ray diffraction (XRD)
Summary
Concrete-embedded metals corrode in fresh and humid concrete, where the direct metal oxidation in the pore alkaline environment leads to changes at the metal interface during the curing time. The corrosion could proceed later in the hardened concrete when its pores, capillaries and cavities contain humidity, and dissolved ionic ingredients extracted from the cement are aggressive against metal in the presence of oxygen diffused at the metal surface (except for aluminum, for example) [1] This internal electrolyte increases the electrical conductivity of concrete, which raises the rate of the electrochemical anodic process that in turn accelerates the corrosion process [2]. In view of the advantages of model solutions, it is appropriate to study the corrosion behavior of copper in this type of environment, because it allows comparative results to be obtained, and some testing parameters to be controlled, which are difficult to achieve in the non-homogeneous internal surface of concrete samples. Some authors have used a few of these techniques to characterize the attack suffered by steels in concrete [37,38] or in solutions that simulate concrete [16,35,39], as well as to determine the corrosion products that are formed during the process
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