Influence of insoluble elements on the nanostructure of water altered glasses

Borosilicate glasses with increasing amounts of zirconium (0–10% Zr) have been altered in static water. The structure of the altered layer at the nanometer scale has been probed using anomalous small angle X-ray scattering at the K-edge of Zr. The distribution of Zr in the altered layer is found to be homogeneous with no precipitation of ZrO2 nodules. Nevertheless, large effects of Zr are observed on both the kinetics of dissolution and the structure of the altered layer. Above 2% of Zr content, the concentration of Si at saturation decreases and the kinetics of alteration are considerably slowed down. This is linked to a drastic morphological transformation of the altered layer. Indeed, a large increase of the specific surface area as well as of the pore volume in the altered layer is observed. It is also shown that above 2% of Zr, the total volume of the grain (core plus hydrated layer) remains constant and equal to the initial volume of the pristine grain.