Dissolution of Oxide Glasses:  A Process Driven by Surface Generation

Grazing incident X-ray scattering (GISAXS) has been used to study in situ the alteration of sodium borosilicate glass monoliths in water. The treatment used to extract the pore volume and the specific surface from the disordered porous media is first introduced and validated by comparing results in other geometries (powders). In the same time, the plane geometry of the GISAXS experiments allows an accurate measurement of the alteration depth. It is shown that the alteration results in the formation of a porous layer, the thickness and porosity of which can be quantitatively assigned to the difference of dissolution between silicon on the one side and boron and sodium on the other. The in situ experiments reveal that a large specific surface develops very rapidly in the layer. No gradient of structure throughout the depth of the altered layer could be observed. Introduction of zirconium promotes a strong increase of the glass durability but increases the specific surface area of the altered layer.