POTASSIUM HYDROGEN DISILICATE: A POSSIBLE MODEL COMPOUND FOR 17O NMR SPECTRA OF HYDROUS SILICATE GLASSES

Abstract

Oxygen-17 magic angle spinning, non-spinning, 1H-decoupled, 1H-17O cross-polarization, and triple-quantum magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy experiments were performed at two different magnetic fields on crystalline potassium hydrogen disilicate (KHSi2O5) and hydrous and anhydrous potassium tetrasilicate (K2Si4O9), sanidine (KAlSi3O8), and haplogranite (KAlSi3O8-NaAlSi3O8-SiO2) glasses. Crystalline KHSi2O5 has two bridging oxygen sites and one non-bridging oxygen site, and the NMR parameters for these two types of sites have been determined. The non-bridging oxygen (silanol) site is well-resolved and observed in a crystalline compound with an isotropic chemical shift (δiso) of 60 ppm, a quadrupolar coupling constant (CQ) of 3.5 MHz, and an asymmetry parameter (η) of 0.35. Knowledge of the non-bridging-oxygen site parameters allows for comparisons to glassy or other materials that might have silanol-type structures. A similar peak can be found in the hydrous potassium silicate spectrum but not in the hydrous potassium aluminosilicate glass spectrum.