1 Department of Chemistry and Bioscience, The Faculty of Engineering and Science, Aalborg University, VBN2 Section of Chemistry, The Faculty of Engineering and Science, Aalborg University, VBN3 The Faculty of Engineering and Science, Aalborg University, VBN4 Inorganic Amorphous Materials, The Faculty of Engineering and Science, Aalborg University, VBN5 Oxide Glass Chemistry, The Faculty of Engineering and Science, Aalborg University, VBN6 Corning Incorporated7 Rensselaer Polytechnic Institute8 Corning Incorporated9 Rensselaer Polytechnic Institute
While the mixed alkali effect has received significant attention in the glass literature, the mixed alkaline earth effect has not been thoroughly studied. Here, we investigate the latter effect by partial substitution of magnesium for calcium in sodium aluminosilicate glasses. We use Raman and NMR spectroscopies to obtain insights into the structural and topological features of these glasses, and hence into the mixed alkaline earth effect. We demonstrate that the mixed alkaline earth effect manifests itself as a maximum in the amount of bonded tetrahedral units and as a minimum in liquid fragility index, glass transition temperature, Vickers microhardness, and isokomtemperatures (viz., the temperatures atη=10^13.5 and 10^12.2 Pa s). The observed min-ima in fragility, glass transition temperature, and isokom temperature are ascribed to bond weakening in the local structural environment around the network modifiers. We suggest that, since the elastic properties of the investi-gated system are compositionally independent, the minimum in Vickers microhardness is closely correlated to the minimum in isokom temperatures. Both of these properties are related to plasticflow and the translational motion of structural units, and hence both may be relatedto the same underlying topological constraints. This indicates that there might not be any significant difference in the onset of the rigid sub-Tgconstraints for the inves-tigated compositions.
Journal of Non-crystalline Solids, 2013, Vol 369, p. 61-68