Long-Term Behavior of Embiez Archaeological Glass: Results after 1800 Years of Alteration in a Marine Environment
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Long-Term Behavior of Embiez Archaeological Glass: Results after 1800 Years of Alteration in a Marine Environment Stéphane Gin1, Jean-Louis Chouchan1, Danièle Foy2 1 2
CEA Valrhô, DTCD/SECM/LCLT BP 17171, 30207 Bagnols-sur-Cèze Cedex, France CNRS, Laboratoire d’Archéologie Médiévale Méditerranéenne, UMR 6572, Aix en Provence, France
ABSTRACT An archaeological glass initially fractured and altered for 1800 years in a marine environment is now being examined by the CEA because of its strong morphological similarity to the nuclear glasses used for immobilization of long-lived radionuclides (i.e. the presence of fractures and cracks formed during cooling, which significantly increase the surface area accessible to water). The issue concerns glass alteration by water, and in particular the different behavior of the external surfaces in contact with a solution highly renewed and the internal surfaces, which constitute a much more confined medium. The preliminary results of this study are discussed. The cracks in the archaeological glass have been filled by crystallized alteration products formed jointly by elements from the glass and elements dissolved in seawater. The glass is distinctly less altered (by a factor of 10 to 100) on the internal surfaces generated by the cracks than on the external surfaces. The forward glass dissolution rate was measured at different temperatures on pristine glass samples and under conditions that allowed us to estimate the dissolution rate of the external surfaces under realistic conditions at about 200 µm in 1800 years. The implications of this study are then discussed. INTRODUCTION Studying natural and archaeological analogs is a key step in evaluating the long-term behavior of HLW glass [1]. The CEA has recently been working with archaeological glass samples discovered in the Mediterranean Sea near the French island of Embiez. The blocks, some of which weigh more than 10 kg, show morphological similarities with nuclear glasses fabricated to immobilize long-lived radionuclides. They were fractured as the molten glass cooled and, unlike other natural analogs, they have been altered for 1800 years under known physical and chemical conditions that have remained constant over time [2]. The use of analogs to validate predictive models of the long-term behavior of nuclear glass consists here in examining the capability of the models to account for observations: contribution of internal cracks and fractures to the overall alteration of the blocks, description of newly-formed mineral phases, role of these phases in the glass dissolution kinetics, etc. This paper describes the first phase of the study and discusses the physical and chemical characteristics of the altered glass blocks. ORIGIN OF THE GLASS Manufacturing and trading of glass in the ancient Roman world have been documented by numerous studies, mainly from a historical standpoint. Large quantities of primary glass (not subjected to secondary processing like annealing) were produced near the sites where raw
materials were extracte
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