Multisecular corrosion behaviour of low carbon steel in anoxic soils: Characterisation of corrosion system on archaeological artefacts (original) (raw)
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Corrosion of iron archaeological artefacts in soil: characterisation of the corrosion system
Corrosion Science, 2005
This paper presents a study made on 40 iron archaeological artefacts buried in soil during several centuries. Samples were taken with the adhering soil and cross-sections were made. The used characterisation techniques are optical and electronic microscopies, EDS coupled to SEM, EPMA, micro-XRD under synchrotron radiation, micro-Raman spectrometry. A specific vocabulary is proposed to describe the corrosion layout. The most identified corrosion layout is made of several ten micrometers zones of magnetite and/or maghemite embedded in a goethite matrix. A corrosion mechanism is proposed in order to explain this profile. When the soil water contains more chlorine or carbonates, some specific corrosion product appear as akaganeite, oxychlorides and siderite.
Applied Geochemistry
This article is part of an ongoing study on the long-term corrosion behaviour of ferrous archaeological artefacts. The aim of this study is to correlate the corrosion products formed on ancient artefacts in an anoxic medium to the environmental data using thermodynamic modelling. For this purpose, measurement campaigns have been conducted on the archaeological site of Glinet (16th century, High Normandy (Seine-Maritime), France) where the evolution of the pore water chemistry has been recorded for a period of one year. Three evolution steps have been distinguished after the oxidizing perturbation which was induced by the piezometers installation. The first step was related to an oxidizing environment in which pore water was in equilibrium with a Fe(III) precipitated phase: ferrihydrite (FeOOH·0.4 H2O). The second step was considered as an intermediate step and Fe speciation had evolved; equilibrium was achieved between ferrihydrite and a Fe(II) carbonate phase: siderite (Fe(II)CO3)....
Journal of Raman Spectroscopy, 35, 739-745, 2004
The description and identification of corrosion products formed on archaeological iron artefacts need various approaches at different observation scales. For this study, samples from five sites were prepared using two techniques. The first consists in cutting cross-sections perpendicular to corrosion layers. This allows local observations and analysis of the corrosion layer stratigraphy at different levels. The second consists in performing manual grinding or abrading of the corrosion layers starting from the current surface of the excavated artefact to the metal core. It allows the description of the successive layers and is well adapted for the analysis on a larger scale. In addition to these two observation scales, the identification of the iron oxides formed needs the coupling of several complementary techniques. Elementary compositions were determined by scanning electron microscopy–energy-dispersive x-ray (SEM–EDX) analysis and electron probe microanalysis (EPMA). Structural identification was performed by x-ray micro-diffraction under synchrotron radiation (µXRD) and micro-Raman spectroscopy. These analyses were performed on the same samples with both x-ray diffraction and Raman spectroscopy in order to ensure a reliable characterization. In some cases there are some ambiguities or overlapping between signatures of different phases by µXRD (such as maghaemite–magnetite) or Raman spectroscopy (such as goethite–magnetite) which can be overcome by the association of the two methods. The final aim is to set up an analytical methodology that will be optimal for the study of ancient iron corrosion products. It is the first step in the study of long-term mechanisms of iron in soil.
Study of archaeological artefacts to refine the model of iron long-term indoor atmospheric corrosion
Journal of Nuclear Materials, 2008
The study of long-term indoor atmospheric corrosion is involved in the field of the interim storage of nuclear wastes. Indeed study of archaeological artefacts is one of the only mean to gather information on very long periods. Concerning ancient items, due to the complexity of the system, it is necessary to couple many analytical techniques from the macro to the microscopic scale. This enables to propose a description of the Amiens cathedral chain rust layers, made of a matrix of goethite, with lepidocrocite and akaganeite locally present and marbling of a poor crystallized phase associated to ferrihydrite. Electrochemical measurements permit to study the reduction capacity of the rust layer and to draw reduction mechanisms of the so-called active phases, by in situ experiments coupled with X-ray diffraction and X-ray absorption spectroscopy.