29Si CPMAS NMR investigations of silanol-group minerals and hydrous aluminosilicate glasses

One-pulse magic angle spinning (MAS) Si-29 and H-1-Si-29 cross-polarization (CP) MAS nuclear magnetic resonance (NMR) spectroscopy was performed on minerals with OH groups and on hydrous aluminosilicate glass samples. The silanol-group samples used were krauskopfite, rosenhahnite, thaumasite, ussingite, and KHSi2O5 with known Si to H distances and ellenbergerite, the proton positions of which are not as well defined. The Si-H distances from the minerals can he compared with the cross-polarization time constants (tau(S,H)) and the proton spin-relaxation times in the rotating frame [tau(1p)(H)], and a rough correspondence exists between a mineral's shortest Si-H distance and its rsi, value. Also, fast [tau(1p)(H)] values correspond to large bulk Ii densities. The CP spectra of the hydrous aluminosilicate glass samples were fitted with two peaks, representing two different Si environments within the glass structure. The contact-time curves of the higher frequency peak imply tau(SiH) similar to the mineral samples with short Si-H distances, and this suggests that the glasses could contain a large fraction of either Si-OH groups or protonated bridging O atoms.