Iron XAS spectra for different spots of the images (100*100 µm2) where the elemental repartitions of Cl and Fe are displayed.
Synchrotron based micro X-ray Absorption Spectroscopy was used to obtain micro scale chemical information such as coordination and oxidation state of phases constituting corrosion products within archaeological iron artefacts buried in soil. The knowledge about iron corrosion process related to the presence of chlorine, is particularly important for restoration and conservation of the metallic artefacts. The samples available for X-ray microprobe analyses are cross sections from iron corroded objects coming from different archaeological excavation sites dating from 12th to 16th century AD. Previously, several analytical techniques such MEB-EDS, µRaman and µXRD have been employed to reveal morphological, compositional and structural information of corrosion products. X-ray Absorption Near Edge Structure (µXANES) was used to determine the spatial variation of the predominant Fe oxidation state and the corresponding crystallographic phase. The micro-XAS and imaging experiments were conducted on the ID21 beamline at ESRF and on the LUCIA beamline at SLS. Analyses performed at Fe and Cl K-edge (µXANES) revealed the correlation between the Fe2+ and Fe3+ distribution in the corrosion products, and the evolution of the chlorine concentration. In addition to the presence of the well-known beta iron hydroxide βFeOOH: akaganeite, in iron corrosion product, we highlight the presence of an other important phase, the βFe2(OH)3Cl hydroxychloride. This result is particularly interesting because, to our knowledge, this phase has never been identified in archaeological artefacts corrosion products. These findings help to gain new insights concerning the influence of such phases in iron corrosion mechanism within their precise characterisation. *LURE and SLS