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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 similar to 125 mu m of fluid over the sample, which demonstrates that there is very effective absorption of the Cu K alpha 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

The characterization of materials constituting cultural artefacts is a challenging step in their conservation, due to the object’s uniqueness and the reduced number of conservation institutes able to supply non-destructive analysis. We propose an alternative analytical tool, which combines accessibility (low cost and portable) and high sensitivity, based on electrochemical linear sweep voltammetry (LSV) with paraffin impregnated graphite electrode (PIGE). To investigate the composition of “white alloys” that certainly have been used as decoration on copper-based Roman fibulae, sampling was done very locally by gently rubbing the selected areas with the PIGE. LSV results evidence the presence of silver, lead, and tin, supporting the argument provided by typological analysis that these metals were used for decoration

The focus of this study consists of examining how corrosion potential measurements can contribute in providing information on the effectiveness of storage and stabilization treatments of copper alloys in aqueous solutions. We report on the electrochemical behavior of artificial copper alloy coupons (covered or not with corrosion layers), simulating the behavior of real artifacts, immersed in sodium sesquicarbonate solutions. Particular attention is given to the transformation of the corrosion layer as a function of time. In addition, synchrotron radiation X-ray diffraction measurements are performed before and after the treatment in order to understand the reactions that take place during the immersion processes.Copper alloys recovered from marine environments can be heavily contaminated with chloride ions. While cuprous chloride (nantokite) may lie dormant in the existing corrosion layer, a reaction with moisture and oxygen causes this unstable compound to expand in volume on conversion to one of the copper trihydroxychlorides (atacamite, paratacamite). This creates physical stress within the object affected, resulting in cracking or fragmentation. Ultimately this behavior, often called bronze disease, can reduce an apparently solid object into a heap of powder. For this reason, archaeological copper alloys recovered from wet saline environments should not be exposed directly to the atmosphere, as the metal will then corrode at an accelerated rate in the oxygen-rich air. 1-3 Alternatively, the contamination will have to be treated if the copper alloys are to be stabilized against continuing corrosion.Copper-based objects are therefore usually stored and stabilized (i.e., chloride ions are being leached from the corrosion layer) in a solution using either tap water or diluted sodium sesquicarbonate (equimolar mixture of sodium hydrogen carbonate and carbonate). 2,4-6 Several other methods for stabilizing corroded copper alloys are in practice as well, such as washing the objects in alkaline dithionite, in citric acid inhibited with thiourea, or in aqueous acetonitrile; however, the use of tap water or a sodium sesquicarbonate solution remains the most commonly used, since this procedure proves to be the least damaging to the patina. 2,5 Nevertheless, results often show a certain instability of the artifacts in solution, such as the chemical transformation of the natural patina. Examples include the formation of tenorite (CuO) 7 or chalconatronite (Na 2 Cu(CuO 3 ) 2 ‚3H 2 O). 8 The occurrence of these side effects means that monitoring of the storage and stabilization treatments remains necessary.A literature search shows that storage and stabilization processes are mainly monitored by analyzing the chloride concentration of the solution at regular time intervals. [5][6]9 This is very useful to monitor the chloride removal from the corrosion layer but does not provide information with regard to possible side effects taking place at the metal surface, such as the modification of the natural patina or the develop...