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Morizet, Y., Paris, M., Gaillard, F. & Scaillet, B. (2014) Carbon dioxide in silica-undersaturated melt Part II: Effect of CO2 on quenched glass structure. Geochim. Cosmochim. Acta, 144 202–216.
Added by: Laurent Cournède (2016-03-10 21:01:54) |
| Type de référence: Article DOI: 10.1016/j.gca.2014.08.034 Numéro d'identification (ISBN etc.): 0016-7037 Clé BibTeX: Morizet2014 Voir tous les détails bibliographiques  |
Catégories: IMN Mots-clés: al-27 mas nmr, angle-spinning nmr, dissolution mechanisms, high-pressure, high-resolution si-29, hydrous aluminosilicate glasses, nuclear magnetic-resonance, solid-state NMR, solubility mechanisms, water speciation Créateurs: Gaillard, Morizet, Paris, Scaillet Collection: Geochim. Cosmochim. Acta |
Consultations : 1/560
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| Résumé |
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Despite CO2 is the second most abundant volatile species implied in magmatic systems, its impact on the molecular structure of aluminosilicate glasses in complex systems is currently not well-constrained. Inasmuch, whether CO2 induces an increase in glass polymerization or not is yet not clear for complex glass compositions. Using the set of nephelinite glass samples investigated in Part I (Morizet et al., 2014), in which the CO2 solubility and speciation have been constrained as a function of the \#K (molar K2O/K2O + Na2O), we have conducted a thorough investigation of the change in the silicate network structure associated to CO2 dissolution. The change in silicate structure has been studied as a function of volatiles solubility (CO2 up to 4.5 wt.\%, H2O up to 3 wt.\%) as well as a function of the \#K (between 0 and 0.75) of the glasses. We used Si-29 Solid-State NMR for probing the silicon local environment in the quenched glasses. We observe that in such depolymerized nephelinite compositions the exchange between Na and K in volatile-free glasses induces a change in the glass structure attributed to the Mixed Alkali Effect (MAE) invoked in previous works. The observed changes might be related to geometric changes in the glass structure (change in network species bond lengths or angles). The addition of H2O only produces a negligible change in the degree of polymerization being probed by the constant NBO/T (Non-Bridging Oxygen per Tetrahedron) as H2O is added to volatile-free glasses. In contrast, we observed that the addition of CO2 induces a strong change in the glass structure which might be interpreted as an increase in polymerization. Alternatively, considering the identified CO2 dissolution mechanism (mostly as non-bridging carbonates units), the glass structure changes might reflect an apparent glass polymerization through the creation of Si-O-C bonds rather a true polymerization through the creation of Si-O-Si bonds. (C) 2014 Elsevier Ltd. All rights reserved.
Added by: Laurent Cournède |