Why Do Certain Glasses with a High Dissolution Rate Undergo a Low Degree of Corrosion?

Two series of borosilicate glasses were prepared for studying the influence of the substitution of (i) CaO for Na2O and (ii) ZrO2 for SiO2 on glass durability. They were corroded in buffered aqueous solution at pH 6.9 and pH 8.0. An inverse correlation was found between the initial dissolution rate and the final degree of corrosion in the saturation regime. It was observed as a function of pH for a given glass as well as a function of glass composition at a fixed pH. A ToF-SIMS study of the permeation of foreign ions in the corrosion layer, SAXS characterization of the layer reorganization, and Monte Carlo simulations of the corrosion provide the key to this paradoxical behavior: glasses with a fast dissolution rate undergo a fast restructuring of the corroded layer into a passivating film, which rapidly stops corrosion by porosity closure; on the contrary, the slow restructuring of glasses with a slow dissolution rate leads to a higher degree of corrosion.