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Thermochemistry and Structure of Model Waste Glass Compositions
Published online by Cambridge University Press: 21 February 2011
Abstract
Enthalpies of mixing of major oxide and waste components of proposed DWPF glasses are estimated. Several proposed glass compositions have very similar molar proportions of major structure-related components. Heats of mixing of major components are predicted to be small (glassy reference states), but may be endothermic or exothermic. Lanthanides are likely to form regions in the glasses rich in R-O-Si bonds but relatively depleted in Si-O-Si bonds. Measured enthalpies of solution of simple lanthanide-bearing glasses resemble those of mechanical mixtures of these end-members, with near-zero enthalpies of mixing for fairly large variations in lanthanide concentrations. DWPF glasses have alkalis in excess of those needed to charge-balance all T3+ cations in tetrahedral coordination. Electropositive +4, +5, and +6 cations are expected to use these excess alkalis to stabilize their own coordination polyhedra, forming complexes with effectively constant macroscopic stoichiometric ratios which contribute to enthalpies of solution in direct proportion to their concentration. Therefore, variations in the concentrations of high-valence cations in DWPF waste containment glasses are also predicted to result in near-zero enthalpies of mixing.
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- Copyright © Materials Research Society 1990
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