Résumé:

Tackling precisely the microscopic properties of minerals and glasses is a very complex multidisciplinary issue: It has been, and continues to be, a subjec t of investigation in many fields of fundamental science, from solid state physics to geochemistry, and of major interest for various applications. Despite this very strong interest from the scientific community, an important number of molecular mechanisms remain unfortunately unclear even for silicates with a simple composition. In this talk, we will present first-principles density functional theory calculations which may be used to better understand two peculiar mechanisms present in silicate glasses. Firstly, we will discuss the structural properties of two (Li/Na) single-alkali silicate glasses with the same cation content. The influence of the network modifier nature on the relevant structural parameters will be further examined in terms on their correlations to the first-principles calculated NMR param eters of our glassy models. This comparative study may be helpful to obtain a precise microscopic insight into one of the unsual properties of oxide glasse s, namely the so-called mixed alkali effect. Secondly, we will provide a description of some initial mechanisms of hydration and hydrolysis of a calcium aluminosilicate glass. It is found that hydrolysis, among all the regular bridging bonds, is only allowed at specific sites. The existence of such reactive sites is likely a general feature of amorphous systems, and it may be used to describe qualitatively some experimental trends common to silicates and aluminosilicates.