OXYGEN SPECIATION IN HYDROUS SILICATE-GLASSES - AN O-17 NMR-STUDY

The structural roles of H2O and OH in hydrous Na2Si4O9 (sodium tetrasi lcate, NTS) and NaAlSi3O8 (''albite'') glasses have been investigated with O-17, one-dimensional fast magic-angle spinning (MAS), static, an d cross-polarization (CP), and two-dimensional triple quantum MAS (3QM AS) NMR techniques. Silica gel and crystalline analcime (NaAlSi2O6. H2 O) were also studied as model compounds. Peaks for molecular H2O are c learly identified in the analcime and in the hydrous glasses in one-di mensional, partial saturation experiments. Bridging and nonbridging ox ygen sites are clearly resolvable in the 3QMAS spectra, as is a featur e related to SiOH in hydrous NTS glass. This feature may also be prese nt in the hydrous albite glass, although, lacking further characteriza tion of other site types (e.g., NaOH, AlOH, Si-OH-Al), this assignment remains tentative. H-1-O-17 CP experiments with short contact times r eveal a peak that is similar in both hydrous glasses and silica gel, a gain possibly related toSiOH groups.