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

Alexey Novikov (1, 2) , Daniel R. Neuville (1) , Louis Hennet (2) , Yann Gueguen (3) , Dominique Thiaudière (4) , Thibault Charpentier (5) , Pierre Florian (2)

1 IPGP - Institut de Physique du Globe de Paris
2 CEMHTI - Conditions Extrêmes et Matériaux : Haute Température et Irradiation
3 IPR - Institut de Physique de Rennes
4 SSOLEIL - Synchrotron SOLEIL
5 LSDRM - Laboratoire Structure et Dynamique par Résonance Magnétique (LCF)

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.

Keywords: Five-fold aluminium; Structure; Strontium glasses; Aluminosilicates; Viscosity; Configurational entropy

Domains: Material chemistry

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, 2017, 461, pp.115-127. ⟨10.1016/j.chemgeo.2016.11.023⟩. ⟨cea-01478247⟩