Oxygen sites in hydrous aluminosilicate glasses: the role of Al-O-Al and H2O

We describe here high-field ¹⁷O magic-angle-spinning (MAS) and triple-quantum MAS (3QMAS) NMR spectra for several alkali silicate and Na, K, and Ca aluminosilicate glasses containing up to 10 wt.% water. The H₂O site appears to have a large quadrupolar coupling constant, and its chemical shift increases from Na- to K- glasses, suggesting significant cation-H₂O interactions. In ¹⁷O one-pulse MAS and 3QMAS and ²⁷Al one-pulse NMR experiments, major differences were seen between spectra for anhydrous and hydrous calcium aluminosilicate glasses. The changes in the ¹⁷O MAS spectra can be explained by the addition of an H₂O peak and to the disappearance of an Al-O-Al peak from the ¹⁷O NMR spectrum for the hydrous glass. The ²⁷Al results are consistent with this interpretation.