Treatments based on the immersion of iron artefacts in NaOH or KOH solutions with or without cathodic polarisation of the metal core, used for conservation purposes, were applied to Gallo-Roman iron ingots excavated from the Mediterranean Sea. The transformation of the initial layer of beta-Fe-2(OH)(3)Cl was followed with time. The resulting phases were characterised by a complete set of multi-scale complementary techniques. It could be demonstrated that the main process involved successively the transformation of beta-Fe-2(OH)(3)Cl into Fe(OH)(2) and the oxidation of Fe(OH)(2) into alpha-/delta-FeOOH and magnetite. Cathodic polarisation accelerated, via migration processes, the removal of chloride ions. (C) 2011 Elsevier Ltd. All rights reserved.

To elucidate the origin of armours supposed to be from Lombardy according to art-historians, the very small Slag Inclusions entrapped in the metallic matrix were analysed on the samples taken on armours. This paper presents the analytical protocol, based on the coupling of LA-ICP-MS and confocal SR-µ-XRF (confocal Micro-X-ray fluorescence under Synchrotron Radiation) developed to obtain trace element information from this kind of inclusion. Confocal SR-µ-XRF has been applied to inclusions of ancient iron artefacts for the first time. The reliability and reproducibility of the procedure developed for the trace elements quantifying have been checked by a comparison of the results obtained by LA-ICP-MS and by confocal SR-µ-XRF. Our first results allow us to draw some preliminary observations on the origin of the samples.

In anoxic carbonated environments, the corrosion layer formed on iron is composed of magnetite and ferrous carbonates with different distributions, influencing the electronic properties of the whole layer. This study aims at determining at a micrometric scale the electronic properties of such corrosion layers, with a reaction tracing based on the use of the Cu2+/Cu-(0) redox couple. Experiments reveal that the electrons formed at the metallic interface are available everywhere in the pores of a thick corrosion layer. This result is of importance to elucidate the corrosion mechanisms because it implies a decoupling of the anodic and the cathodic reactions. (C) 2011 Elsevier Ltd. All rights reserved.

An iron ingot immersed during 2000years at 12m depth in the sea has been examined with the help of a combination of microscale techniques. This methodology allowed us to show that the main phase precipitated during the immersion is an iron hydroxychloride (β-Fe2(OH)3Cl) that is characteristic of corrosion in anoxic and chlorinated medium. Moreover locally on the external part of the corrosion products sulphur containing phases have been identified as mackinawite (FeS) in nanocrystalline or slightly oxidised state. The presence of this phase could be explained by the activity of sulphate-reducing bacteria. The presence of β-Fe2(OH)3Cl could be interpreted via a thermodynamic modelling taking into account the environmental conditions.

In the context of nuclear waste storage, archaeological artefacts can be used as analogues for long-term prediction of iron corrosion behaviour. As many studies are based on laboratory simulations, it is necessary to establish a link between short and long-term behaviour. In this study, corrosion product crystalline structures on archaeological artefacts buried in soils and iron coupons immersed in synthetic environments have been compared. The occurrence of carbonated iron (siderite FeCO3 and iron hydroxicarbonate Fe2(OH)2CO3) has been observed on items from both environments using Raman micro-spectroscopy and X-ray micro-diffraction.

The electrochemical reduction of lepidocrocite γ-FeOOH was investigated at 25°C in neutral or slightly alkaline solutions containing chloride, sulphate or bicarbonate anions by means of thin lepidocrocite film electrodeposited on inert gold substrate or graphite/lepidocrocite powder composite electrode. Electrochemical measurements were coupled to in situ electrochemical quartz crystal microbalance (EQCM) and ex situ SEM and FTIR analysis. The reduction of lepidocrocite occurs in all the electrolytes considered here. The initial reduction product is adsorbed ferrous ion, Feads2+. The desorption of Feads2+ is promoted as pH increases, leading to an increase of reduction depth. This promotion is related to the formation of secondary FeII-containing species, as revealed by SEM and FTIR. The comparison of γ-FeOOH reduction potentials and iron corrosion potentials let us state that the galvanic coupling is possible.