An in-situ X-ray absorption spectroelectrochemistry study of the response of artificial chloride corrosion layers on copper to remedial treatment

Abstract

In the experiments described in this study, we make use of X-ray absorption spectroscopy (XAS) at the K-edge of copper for monitoring the surface–solution interface of corroded metals in-situ in a sodium sesquicarbonate solution. We show conclusively that, unlike previously published XRD measurements, the XAS spectra are almost wholly characteristic of the contaminated solution and not the corroded surface, in cases where the sesquicarbonate is effective at removing chlorides. This is true even when there is only ∼125 µm of fluid over the sample, which demonstrates that there is very effective absorption of the Cu Kα radiation from the surface by copper in solution. As a function of time we observe a rising intensity in the XANES and EXAFS regions which is accompanied by a proportional increase in the degree of EXAFS modulation. The latter is due to the fact that a significant proportion of the corrosion product goes into solution, rather than being converted to a stable compound on the surface. Moreover, the spectra show that the local atomic environment of the copper in solution is extremely similar to that in the surface. Overall from both XAS and previously performed XRD data we can conclude that the chlorine containing corrosion products become detached from the surface and go partly into solution, while a thin cuprite layer forms (or is already present at) at the original metal surface.