HR: 0800h
AN: H11B-0480    [Abstracts]
TI: Long-term Alteration of Fractured Glass Blocks in Seawater
AU: * Verney-Carron, A
EM: aurelie.verney-carron@cea.fr
AF: Commissariat à l'Energie Atomique DEN/DTCD/SECM/LCLT, BP17171, Bagnols sur Cèze, 30207, France
AU: Gin, S
EM: stephane.gin@cea.fr
AF: Commissariat à l'Energie Atomique DEN/DTCD/SECM/LCLT, BP17171, Bagnols sur Cèze, 30207, France
AU: Libourel, G
EM: libou@crpg.cnrs-nancy.fr
AF: Centre de Recerches Pétrographiques et Géochimiques, 15, rue Notre-Dame des Pauvres, Vandoeuvre les Nancy, 54501, France
AB: Fractured archaeological glass blocks, altered in seawater over 1800 years, are studied because of their morphological analogy with the industrial nuclear glass blocks. They represent a striking example of altered fractured glass on a representative timescale in the prospect of a deep geological repository. Thus, they may contribute to the validation of models devoted to assess the long-term behaviour of high-level waste glass. Here, we present results concerning the alteration mechanisms within the cracks and the influence of seawater transport parameters on these mechanisms.
A detailed study of the morphology, mineralogy and chemistry of these blocks allows to see that the alteration thicknesses of internal cracks are thinner than the alteration at the periphery of blocks (1 or 2 orders of magnitude). It suggests that the contribution of internal cracks to global alteration is quite low and that alteration processes depend on the renewal rate of the solution within cracks, so on the aperture and the accessibility to water.
We also show that two mechanisms are involved in the glass alteration: i) interdiffusion between glass alkalis and protons of the solution leading to an amorphous gel layer, and ii) glass network dissolution followed by precipitation of less soluble elements of the glass (Si, Al) and some elements of the seawater (Mg) resulting in the formation of a secondary phases layer (smectites) in the middle of the crack.
It is of note that the influence of transport parameters causes differences in the contribution of both mechanisms and in their respective kinetics. Indeed, at the periphery of blocks, alteration layers are thick and composed mainly of secondary products, because dissolution is maximal when solution is highly renewed. On the contrary, in cracks, where transport is slow, local equilibrium of saturation (Si) seems to be established quickly, creating favourable conditions to a drop in the dissolution rate. It causes a relative increase of the contribution of interdiffusion. Besides, the sealing due to the precipitation of secondary phases accentuates this influence of transport in cracks.
To understand the coupling between chemistry and transport better, mainly the influence of parameters, such as aperture or S/V ratio, on the alteration kinetics, experiments have been carried out. Results show that thinner the fracture, higher pH, which reduces the diffusion coefficient of alkalis, and faster the chemical saturation is reached. These experimental data aim at parametering a model of a fractured glass block alteration.
DE: 1039 Alteration and weathering processes (3617)
DE: 1858 Rocks: chemical properties
SC: Hydrology [H]
MN: 2007 Fall Meeting