29Si MAS NMR studies of the spin-lattice relaxation time and bond-angle distribution in vitreous silica

Abstract

A preliminary investigation, using ²⁹Si magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), of the effect of water content on the spinlattice relaxation time, T ₁, and Si‒O‒Si bond-angle distribution of vitreous silica is reported. The decrease in T ₁ with increase in water content suggests that water acts as a major relaxation centre in vitreous silica and a change in water content is also seen to produce a subtle change in the NMR lineshape. The chemical shift of the ²⁹Si resonance occurs at–111·5 p.p.m. with reference to tetramethylsilane (TMS) and the resulting Si‒O‒Si bond-angle distribution is seen to be asymmetric about a peak at 143· · 1· and is in agreement with the X-ray data of Mozzi and Warren (1969).