IN SUPPORT OF A DEPOLYMERIZATION MODEL FOR WATER IN SODIUM ALUMINOSILICATE GLASSES: INFORMATION FROM NMR SPECTROSCOPY

Abstract

A variety of 29Si, 27Al, 23Na, 17O and 1H NMR data are consistent with the formation of Q3 AlOH and SiOH groups upon dissolution of H2O into aluminosilicate glasses. 29Si single-pulse and 1H-29Si CP/MAS data present more direct evidence for the formation of Q3 Si species. A model that involves rupture of Si-O-Si, Al-O-Si, and Al-O-Al linkages, and possibly cation exchange between H+ and Na+ is most consistent with the variety of data available. In this model the water dissolution process involves several reactions that are likely to proceed concurrently throughout the glass compositional space defined by Al/Si ratio and water content. Because the types of reactions do not change with Al/Si ratio, this model predicts smooth variations in hydroxyl and molecular water species abundances throughout compositional space within the system NaAlSiO4-SiO2-H2O.