Structure and mechanical properties of alkali-alkaline earth-silicate glasses

The elastic and indentation behaviours of silicate glasses with different compositions were investigated and interpreted in the light of structural analysis, using MAS-NMR and neutron diffusion experiments. The coordination numbers as well as the interatomic distances and the number of bridging oxygens per tetrahedron were experimentally determined Largest elastic moduli and hardness values are obtained for the grades which have the lowest silica contents, or in other terms for glasses with a high glass network filling rate in comparison to the open and flexible network of vitreous silica. The silicon content also plays a major role in the indentation behaviour by favouring flow densification beneath the indenter. The lower the Poisson's ratio, or the bulk modulus or the glass compactness, the more anomalous is the glass behaviour A transition in the behaviour of sodalime-silica glasses was observed for a silica content Of about 74 mol%, both in the chemical shift of the Q(3) units in the NMR spectra and in the hardness and crack length/indentation size ratio (cla). This transition is likely to originate from phase separation.