A multinuclear NMR study of hydrous aluminosilicate glasses: Crystalline versus glassy structures.

摘要

Water is the most common volatile in aluminosilicate melts on Earth, and the physical properties of aluminosilicate melts are dependent upon water content. In order to fully understand the reasons for the changes in the physical properties the changes in aluminosilicate melt structure with the addition of water need to be determined. Solid state nuclear magnetic resonance spectroscopy (NMR) is nucleus specific and provides information about local environments of the atoms selected. This dissertation covers recent 1H, 17O, 27Al, and 29Si NMR studies of hydrous calcium, sodium and potassium aluminosilicate glasses.; A data set of 1H to 29Si cross-polarization MAS NMR parameters for crystalline mineral samples with silanol (Si-OH) groups was compiled and correlated to their known Si to H distances. Then NMR parameters were determined for hydrous aluminosilicate glasses and compared with those for the mineral data set. The glasses were found to have Si to H distances similar to those in the silanol-group mineral structures.; The 17O NMR spectra for a synthetic crystalline compound, potassium hydrogen disilicate, were collected and the parameters for its silanol oxygen determined. This site is similar in width to other non-bridging oxygen sites, and should be fully visible in the spectra for the hydrous aluminosilicate glasses. This type of peak is neither seen in the spectra for sanidine nor those for granitic glasses, and thus this type of site is not part of the hydrous aluminosilicate glass structure.; Major differences are seen in the 17O and 27Al NMR spectra for calcium aluminosilicate glasses. The 17O spectrum for the hydrous glass loses the non-bridging oxygen peak and intensity on the high frequency side of the bridging oxygen peak upon hydration but gains a shoulder on the low frequency side of the bridging oxygen peak. In addition, the 27Al spectrum shows narrowing due a reduction in the spread of chemical shifts. The intensity loss to the main 17O peak upon hydration is probably due to the destruction of Al-O-Al sites upon hydration, and the new shoulder arises from the presence of H₂O oxygen sites.