Al and Sr environment in tectosilicate glasses and melts: Viscosity, Raman and NMR investigation

Abstract : Structure and properties of SrO-Al$_2$O$_3$-SiO$_2$ glasses and melts were investigated along the tectosilicate join (SrO/Al$_2$O$_3$ = 1), varying the amount of silica. The structure of the glasses was studied by means of various spectroscopic techniques: Raman, $^{27}$Al NMR and XAS at the Sr K-edge. Raman spectroscopy revealed that the fraction of high-membered tetrahedral rings diminishes upon substitution of SiO$_2$ by SrAl$_2$O$_4$ favouring the formation of low-membered rings. Sr K-edge XANES shows that the strontium coordination number is around 9, based on the spectrum similarity with the one obtained for crystalline strontianite. $^{27}$Al NMR spectroscopy indicates the presence of four- and five-coordinated aluminium the latter being found in small quantities (< 5%), i.e. smaller than for analogous Mg- and Ca-based aluminosilicate glasses. A minimum in $T_g$ is found when the AlO$_5$ content is maximum, both in Sr and Ca aluminosilicates. This fact indicates the importance of minor species such as five-fold aluminium in activating viscous flow, similarly to what has been proposed for five-fold silicon by Farnan and Stebbins (1994). Increase of $T_g$ at low silica content was correlated to a decrease in AlO$_5$ content as well as to a decrease of a number of different structural units and, as a consequence, an ordering of the system.
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Alexey Novikov, Daniel R. Neuville, Louis Hennet, Yann Gueguen, Dominique Thiaudière, et al.. Al and Sr environment in tectosilicate glasses and melts: Viscosity, Raman and NMR investigation. Chemical Geology, Elsevier, 2017, 461, pp.115-127. 〈http://www.sciencedirect.com/science/article/pii/S000925411630626X〉. 〈10.1016/j.chemgeo.2016.11.023〉. 〈cea-01478247〉

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