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Altération des vitraux médiévaux. Contribution à l'étude du comportement à long terme des verres de confinement

Abstract : In this manuscript, the alteration of glasses has been studied by two coupled approaches: i) the study of the alteration of medieval stained-glasses and, ii) the experimental leaching of model glasses. The medieval stained-glasses are mainly composed of oxygen, silicon, calcium and alkalis and can be divided in two chemical families (sodic or potassic) according to the nature of the flux used. Altered on windows or buried in the ground, they show three different modes of alteration: i) by waters of condensation and, ii) by atmospheric agents for the stained-glasses on windows; iii) by groundwaters and humic acids for glasses excavated from archaeological sites. The study of altered layers reveal that mechanisms and the kinetics of alteration are very dependent on the chemical composition of the glass and to the conditions of alteration. In the case of an alteration by meteoric waters, a network of micro-cracks develops within the film controlling the progress of the alteration. Archaeological glasses present on the other hand a continuous layer devoid of cracks, suggesting diffusion processes. Furthermore, a chemical study of altered zones shows a strong dissolution of network modifying cations and a preferential incorporation of network forming elements in the altered layer. The behaviour of transition elements, heavy metals and rare earth elements is also documented. In parallel, an experimental approach has been developed to study the alteration of model glasses. Two vitrified wastes and a potassic glass whose composition is similar to that of medieval stained-glasses have been altered in static mode, under different pH (1 to 10), temperatures (20 to 80°C) and durations (from 12 hours to 6 months). These experiments reveal different alteration mechanisms as a function of the pH of the solution and the chemical composition of the glass. At pH=1, network modifying cations are strongly leached while the network formers show a behaviour which is a function of their ionic radii, suggesting the presence of condensation phenomena in the altered layer. At neutral to basic pH, saturation of a large number of elements is rapidly reached in the solution, implying a mineralogical and chemical composition of the altered layer very different compared to that found under acid pH. Under these conditions, transition elements and heavy metals, because of their weak solubility, are strongly incorporated in the alteration products. These experiments also show that the more a glass is polymerised, the less it is leached. Finally, the observation of alteration under experimental and natural conditions shows the necessity to study natural analogues to predict the long term behaviour of vitrified wastes. Therefore, medieval stained glasses provide an excellent model for following the behaviour of glasses under natural conditions of alteration and over times ranging from several hundred years to more than a millennium.
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https://tel.archives-ouvertes.fr/tel-00007665
Contributor : Jérôme Sterpenich <>
Submitted on : Tuesday, December 7, 2004 - 10:13:44 AM
Last modification on : Thursday, February 25, 2021 - 9:46:09 AM
Long-term archiving on: : Thursday, September 13, 2012 - 1:25:34 PM

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  • HAL Id : tel-00007665, version 1

Citation

Jérôme Sterpenich. Altération des vitraux médiévaux. Contribution à l'étude du comportement à long terme des verres de confinement. Géochimie. Université Henri Poincaré - Nancy I, 1998. Français. ⟨tel-00007665⟩

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