Computer Science
Scientific paper
Nov 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987gecoa..51.2977c&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 51, Issue 11, pp.2977-2990
Computer Science
15
Scientific paper
Basaltic glasses are considered as natural analogues for nuclear waste glasses. Thermodynamic computer codes used to evaluate long term behavior of both nuclear waste and basaltic glasses require the knowledge of the dissolution mechanism of the glass network (congruent dissolution or ion exchange in a residual hydrated structure). The paper presents the results of a series of experiments designed to study the structure and chemical composition of alteration layers formed on the surface of artificial tholeiitic glass altered in artificial seawater. Experiments were performed at 60°C, 1 bar and 350 bars in non-renewed conditions. A natural sample from Palagonia (Sicily) has been studied by electron microscopy and comparison between natural and experimental palagonitic layers is made. The behavior of dissolved silica during experiments, and both the structure and the chemical composition of the palagonitic layers, indicate that they form by precipitation of secondary minerals from solution after a total breakdown of the glassy network, i.e. , congruent dissolution of the glass. Hence the dissolution equation necessary for thermodynamic modelling of basaltic glass dissolution in seawater at low temperature must be written as a simple stoichiometric process. For the first 2.10 5 years of reaction the palagonitic layers do not constitute a diffusional barrier to the mass transfer between the glass and the bulk solution. The growth of these layers is linearly dependent on time. These experiments indicate that the transformation of glass to palagonitic material is not isovolumetric. Hence it is preferable to use Fe or Ti as conservative elements for chemical budget calculations.
Crovisier J. L.
Eberhart J. P.
Honnorez Jose
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