Si-29 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 mi nerals with OH groups and on hydrous aluminosilicate glass samples. The sil anol-group samples used were krauskopfite, rosenhahnite, thaumasite, ussing ite, and KHSi2O5 with known Si to H distances and ellenbergerite, the proto n positions of which are not as well defined. The Si-H distances from the m inerals 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 distan ce and its rsi, value. Also, fast [tau(1p)(H)] values correspond to large b ulk Ii densities. The CP spectra of the hydrous aluminosilicate glass sampl es were fitted with two peaks, representing two different Si environments w ithin the glass structure. The contact-time curves of the higher frequency peak imply tau(SiH) similar to the mineral samples with short Si-H distance s, and this suggests that the glasses could contain a large fraction of eit her Si-OH groups or protonated bridging O atoms.