Structural characterization of water-bearing silicate and aluminosilicate glasses by high-resolution solid-state NMR

Various one- and two-dimensional high-resolution solid-state NMR techniques have been applied to hydrous silicate and aluminosilicate glasses: simple acquisition, cross-polarization (CP-MAS), heteronuclear correlation (HETCOR), dipolar dephasing, spin counting, double-quantum correlation, and rotational echo double resonance (REDOR). The comparison of the results obtained for sodium tetrasilicate and phonolite glasses suggests that the water incorporation mechanisms are qualitatively similar for these two compositions. From proton NMR experiments, we observe no evidence of proton clustering and a wide range of chemical shifts ranging from 0 to 16 ppm, even for the aluminosilicate phonolite glass, identifying at least three types of hydroxyl (OH) protons in addition to molecular H2O. This variety of OH groups can be discussed in terms of hydrogen bonding strength. For both compositions, the results indicate some depolymerization of the tetrahedral network, but the picture cannot be so simple as to completely exclude any of the different previously proposed models for water incorporation in silicate glasses.