A corrosion study of the ferrous medieval reinforcement of the Amiens cathedral. Phase characterisation and localisation by various microprobes techniques

International audienceRaman structural imaging can extract original information in order to answer new questions raised in the recent studies on iron and low alloy steel corrosion. Up to now, this technique has allowed the extraction of the qualitative distribution of the compounds constituting the corrosion product layers. We propose here a methodology to extract quantitative parameters from Raman hyperspectral maps, executed by a home-developed software: LADIR-CAT. Specifically developed for iron corrosion quantitative component imaging, the approach and program operation are described. The LADIR-CAT is applied on ancient corroded iron samples originating from the Amiens cathedral (France) to establish the description and the composition of the corrosion system through quantitative compound imaging

Section: Application To Iron Indoor Atmospheric Corrosion Products: Cmentioning

confidence: 99%

Section: Application To Iron Indoor Atmospheric Corrosion Products: Cmentioning

confidence: 99%

Section: Studied Samples: Ancient Artefacts and Reference Phasesmentioning

confidence: 99%

Section: Quantification Of Amiens' Cathedral Corrosion Productsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A methodology for Raman structural quantification imaging and its application to iron indoor atmospheric corrosion products

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Protective ability index measurement through Raman quantification imaging to diagnose the conservation state of weathering steel structures

Aramendia

Gómez‐Nubla

Bellot‐Gurlet

et al. 2014

Weathering steel was designed to resist against the atmospheric impact due to the development of a characteristic rust layer that protects the metal by reducing the corrosion rate. This rust layer is formed by different iron (oxy‐hydr)oxides that acts as a barrier and provides the protective ability. In order to check the conservation state trough the protective capability, it is necessary to calculate the so‐called protective ability index (PAI). It mainly takes into account the ratio (α/γ) between the mass of goethite (α‐FeOOH) and lepidocrocite (γ‐FeOOH), present in the rust layer of weathering steel. Raman spectroscopy, apart from a qualitative technique, is recently becoming a semi quantitative approach. Therefore, it is a valuable tool for the calculation of the mentioned index. This paper is a widening of a previous work in which it was uncovered a problem in different weathering steel sculptures which are exposed to a Cl− and SO2‐rich urban atmosphere because they present different esthetical problems on their surfaces, such as detachments of steel chips, discolorations and irregularities. In order to relate these problems on the surface and the rust layer composition, PAI calculations were performed from the phase identification obtained from Raman imaging and using spectra decomposition to quantify each compounds. Although goethite and lepidocrocite were the most commonly detected compounds, hematite, akaganeite and magnetite were also identified. Hematite is a sub product formed in rich SO2 atmospheres; therefore, a PAI with its content is proposed. Protective indexes obtained for the different artworks exposed in different places provide quantitative clues for the conservation diagnosis of weathering steel structures. Copyright © 2014 John Wiley & Sons, Ltd.

Investigation of atmospheric corrosion layers on historic iron nails by micro‐Raman spectroscopy

Yucel

Kalkanlı

Caner-Saltık

2016

In this study, some Ottoman low carbon steel nails from a 16th century brick masonry dome of Kiliç Ali Pasha Bath in Istanbul and from a 19th century stone dwelling in Phocaea Izmir were studied for their long term corrosion characteristics. Their corrosion layers were examined with a Senterra Bruker micro‐Raman spectrometer and Tescan Vega model Scanning Electron Microscopy (SEM) with Inca X‐Stream 2 Energy‐Dispersive X‐ray spectroscopy (EDX). Powdered samples scraped from the corrosion layers were studied by X‐ray powder diffraction and Fourier transform infrared spectroscopy. The corrosion layer consisted of two main sub‐layers, namely an ‘inner corrosion layer’ including a ‘reaction front’ and a ‘transformed medium’ which included the depositions from the surrounding media. Peak intensities of X‐ray powder diffraction traces were not proportional to the abundance of oxides and oxyhydroxides in the corrosion layer, most probably because of their partly amorphous and nano‐size nature. Inner corrosion layer and transformed medium layers were studied in detail by micro Raman spectroscopy at 532 nm, 0.2 mW, 200 s. The Protective Ability Index (PAI) of the corrosion layers were expressed as the ratio of isotropic goethite band thickness to the thickness of reaction front composed of other oxides and oxyhydroxides being magnetite, maghemite, hematite, lepidocrocite, distinguished by micro‐Raman which is a unique method for phase identification. PAI was then estimated to be ~6–10 for 16th century nails and ~3 for 19th century nails. Corrosion mechanisms and PAI were concluded to be affected by compositional characteristics of artefacts and their atmospheric conditions. Copyright © 2016 John Wiley & Sons, Ltd.