Mechanical behaviour of highly porous glasses

The mechanical behaviour of highly porous glassy materials (pore volume higher than 85%) is investigated using Hg porosimetry. Because of the small pore size of these materials, Hg liquid cannot enter their porous network and consequently induces an isostatic pressure. Due to the high compliance of the solid network of these materials, compression results in the sample shrinkage. The experiments described in this paper show that an isostatic pressure applied to highly porous glasses induces an irreversible volume shrinkage which can be associated with an unexpected plastic behaviour and structure strengthening. The magnitude of the plastic shrinkage and the increase of the associated mechanical properties depend on the starting bulk density. The irreversible compaction can be explained by siloxane bond formation between clusters constituting the porous glasses, retaining the strained structure. This densification process could offer a new way to synthesise glasses at room temperature.