Structural and physico-chemical properties of selected glasses in the (Ca _{1- <i>x</i>} Mg _<i>x</i> )O-Al ₂ O ₃ system

Oxide glasses and melts are of interest in many fields of science and technology. The structural and physico-chemical properties of C12A7, C11M1A7, C10M2A7, C9M3A7, and C8M4A7 glasses (C = CaO, M = MgO and A = Al2O3) were studied for the first time. It was shown by Al K-edge XANES spectroscopy that Al is in fourfold coordination in all studied glass samples with increasing Q4/Q2 ratio in the C12A7-C8M4A7 composition range. The coordination number of Ca was found to be between 6 and 7 in all studied glasses by Ca K-edge XANES spectroscopy. From the thermodynamic point of view there is no composition dependence, within experimental uncertainty, of the heat capacity in the C12A7-C8M4A7 composition range. In contrast, the enthalpy of formation from the constituent solid oxides at 298.15 K was found to be greater for C8M4A7 than for C12A7 glasses. A decrease of density, molar volume and glass transition temperature was observed for increasing MgO content. In addition to the experimental investigation, classical molecular dynamics simulations were conducted using a recently optimized Born-Mayer-Huggins potential. It was found that the simulations present a good estimation of the structural properties (local surroundings of Ca and Mg) and some of the thermodynamic properties (heat capacity of glasses and liquids), but overestimate the values of the coordination number of Al and the other thermodynamic properties (density and enthalpy of formation from oxides at 298.15 K).