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 rotati onal echo double resonance (REDOR). The comparison of the results obtained for sodium tetrasilicate and phonolite glasses suggests that the water inco rporation mechanisms are qualitatively similar for these two compositions. From proton NMR experiments, we observe no evidence of proton clustering an d a wide range of chemical shifts ranging from 0 to 16 ppm, even for the al uminosilicate phonolite glass, identifying at least three types of hydroxyl (OH) protons in addition to molecular H2O. This variety of OH groups can b e discussed in terms of hydrogen bonding strength. For both compositions, t he results indicate some depolymerization of the tetrahedral network, but t he picture cannot be so simple as to completely exclude any of the differen t previously proposed models for water incorporation in silicate glasses. ( C) 2001 Elsevier Science B.V. All rights reserved.