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

Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115, U.S.A.

Correspondence: ^* E-mail: jvo{at}pangea.stanford.edu

One-pulse magic angle spinning (MAS) ²⁹Si and ¹H-²⁹Si 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 be compared with the cross-polarization time constants (_SiH) and the proton spin-relaxation times in the rotating frame [₁(H)], and a rough correspondence exists between a mineral’s shortest Si-H distance and its _SiH value. Also, fast [₁(H)] values correspond to large bulk H 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 _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.

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