Investigation of alumino-silicate glasses by coupling experiments and simulations: Part I - Structures

A set of alumino-silicate glasses with SiO2-Al2O3-Na2O-CaO compositions was investigated using Raman and NMR spectroscopy techniques and by classical molecular dynamics, in order to study the structural modifications which occur when CaO progressively replaces Na2O and when Al2O3 progressively replaces SiO2. The effect of a gradual increase in the Al2O3 content was also studied. Al was always 4 coordinated for all the compositions studied, including the peraluminous glasses. An increase in the number of Al-O-Al bonds was found when the Al2O3 or CaO content increases. The study confirmed that AlO4 groupings are preferentially compensated by Na rather than by Ca, and that there are non-bridging oxygens surrounded by mixed environments containing both Na and Ca. Combining the information given by the Raman and NMR spectroscopy results enabled the attribution of the Raman band at 570cm-1 to the Si-O-Al bonds. It confirmed that the band at 510cm-1 can be attributed to the Al-O-Al bonds, while that at 985cm-1 can be attributed to the Q4-Al entities. Lastly, it was demonstrated that the classical molecular dynamics potentials of Deng et al., specifically developed for this type of glasses, permit the reproduction of a large number of the experimental results quantitatively or sometimes simply qualitatively.