Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2010

ACL
doi

C.Martineau, V.K.Michaelis, S.Schuller, S.Kroeker, 'Liquid-Liquid Phase Separation in Model Nuclear Waste Glasses: A Solid-State Double-Resonance NMR Study', Chem. Mat. (2010) doi:10.1021/cm1006058

Double-resonance nuclear magnetic resonance (NMR) techniques are used in addition to single resonance NMR experiments to probe the degree of mixing between network-forming cations Si and B, along with the modifier cations Cs+ and Na+ in two molybdenum-bearing model nuclear waste glasses. The double-resonance experiments involving 29Si in natural abundance are made possible by the implementation of a CPMG pulse-train during the acquisition period of the usual REDOR experiments. For the glass with lower Mo content, the NMR results show a high degree of Si-B mixing, as well as an homogeneous distribution of the cations within the borosilicate network, characteristic of a non-phase-separated glass. For the higher-Mo glass, a decrease of B-Si(Q4) mixing is observed, indicating phase separation. 23Na and 133Cs NMR results show that although the Cs+ cations, which do not seem to be influenced by the molybdenum content, are spread within the borate network, there is a clustering of the Na+ cations, very likely around the molybdate units. The segregation of a Mo-rich region with Na+ cations appears to shift the bulk borosilicate glass composition toward the metastable liquid-liquid immiscibility region and induce additional phase separation. Although no crystallization is observed in the present case, this liquid-liquid phase separation is likely to be the first stage of crystallization that can occur at higher Mo loadings or be driven by heat-treatment. From this study emerges a consistent picture of the nature and extent of such phase separation phenomena in Mo-bearing glasses, and demonstrates the potential of doubleresonance NMR methods for the investigation of phase separation in amorphous materials.