Deterioration of iron archaeological artefacts: micro-Raman investigation on Cl-containing corrosion products

Deterioration after excavation of archaeological iron artefacts buried in soil is often associated with the presence of chlorinated phases in corrosion products, leading to serious problems for conservation of metallic objects of cultural heritage. Therefore, in order to better understand the corrosion process related to the presence of chlorine, some high-resolution techniques of material characterisation are implemented. The analyses are realised on cross sections of corroded iron objects excavated from archaeological sites dated from the 12th to the 16th century A.D. CI-containing phases appear even when the Cl level in the water is low. In addition to the common oxy-hydroxide-containing chloride, akaganeite (beta-FeOOH) often mentioned in the literature, a ferrous hydroxychloride beta-Fe-2(OH)(3)Cl was also found in the corrosion layers. Moreover, part of the study is based on the preparation and desalinisation of pure akaganeite powder in order to characterise the influence of the chloride content on its crystalline structure as characterised by Raman spectroscopy. Copyright (c) 2007 John Wiley & Sons, Ltd.