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Étude des mécanismes de déchloruration d'objets archéologiques ferreux corrodés en milieu marin. Cas des traitements en solutions alcalines aérée et désaérée

Florian Kergourlay 1, 2 
1 LAPA - UMR 3685 - Laboratoire Archéomatériaux et Prévision de l'Altération
NIMBE UMR 3685 - Nanosciences et Innovation pour les Matériaux, la Biomédecine et l'Energie (ex SIS2M)
Abstract : Archaeological iron artefacts, when excavated, undergo degradations if they are not readily stored and treated. Artefacts from underwater excavations contain unstable chlorine-containing phases which accelerate corrosion phenomena. To limit damages and stabilize the objects, it is necessary to remove chloride ions trapped in the corrosion layers. Various dechlorination treatments have been developed by conservation workshops (immersion in alkaline solutions, cathodic polarization, hydrogen plasma, subcritical fluid...). Despite a genuine efficiency, these treatments need to be optimized (processing time, reliability, reproducibility ...) by a better understanding of dechlorination mechanisms (structural evolution of corrosion pattern during treatment, transport phenomena in the layer, kinetics of chlorides extraction...). The objectives of this study are multiple. The characterisation of the corrosion pattern developed in the marine environment and then left in oxidise environment were performed using multiscale tech- niques on an experimental corpus consisting of wrought iron ingots from Gallo-Roman shipwrecks submerged for over 2000 years and discovered off the Saintes-Maries-de-la-Mer (Bouches-du-Rhone, France). It was established that the corrosion pattern of a freshly excavated object is mainly composed of the ferrous hydroxychloride β-Fe2(OH)3Cl, chlorinated phase containing about 20 wt% chlorine. Then the evolution of the corrosion pattern was monitored during the treatment steps : treatment step, strictly speaking, which consists of the circulation of an aerated or deaerated NaOH solution and washing and drying steps. First, the in situ monitoring of the corrosion layer's evo- lution during the treatment step was carried out under synchrotron radiation by micro X-ray diffraction coupled to the determination of chloride ions in solution extracts. Then, at the end of washing and drying steps, the corrosion pattern was characterized ex situ, elementarily and structurally. The whole data allowed us to refine dechlorination mechanisms occurring within the corrosion layer at each stage and also discuss models of chloride extraction proposed in the literature.
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Submitted on : Thursday, July 26, 2012 - 5:17:10 PM
Last modification on : Monday, January 10, 2022 - 10:16:06 AM
Long-term archiving on: : Friday, December 16, 2016 - 3:31:47 AM

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Florian Kergourlay. Étude des mécanismes de déchloruration d'objets archéologiques ferreux corrodés en milieu marin. Cas des traitements en solutions alcalines aérée et désaérée. Matériaux. Université Paris-Est, 2012. Français. ⟨NNT : ⟩. ⟨tel-00721176v1⟩

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