Structure of Mg- and Mg/Ca aluminosilicate glasses: 27Al NMR and Raman spectroscopy investigations

The structure and properties of glasses and melts in the MgO-Al2O3-SiO2 (MAS) and CaO-MgO-Al2O3-SiO2 (CMAS) systems play an important role in Earth and material sciences. Aluminum has a crucial influence in these systems, and its environment is still questioned. In this paper, we present new results using Raman spectroscopy and Al-27 nuclear magnetic resonance on MAS and CMAS glasses. We propose an Al/Si tetrahedral distribution in the glass network in different Q(n) species for silicon and essentially in Q(4) and Al-V for aluminum. For the CMAS glasses, an increase of Al-V and Al-VI is clearly visible as a function of the increase of Mg/Ca ratio in the (Ca,Mg)(3)Al2Si3O12 (garnet) and (Ca,Mg)AlSi2O8 (anorthite) glass compositions. In the MAS system, the proportion of Al-V and Al-VI increases with decreasing SiO2 and, similarly with calcium aluminosilicate glasses, the maximum of Al-V is located in the center of the ternary system.