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High-resolution, magic-angle-spinning (MAS),  29 Si NMR spectra have been obtained for a sodium silicate glass and liquid (60 mol% SiO 2 ) to temperatures over 600 °C. Crystallization was monitored in situ, and motional averaging of the peaks for distinct silicate anionic species (Q 2  and Q 3  species) in the liquid was observed. Modeling of the spectra yielded species exchange frequencies. The inverses of these exchange frequencies are slightly longer than shear relaxation times calculated from bulk viscosity using the Maxwell relation; viscosities calculated from the NMR data using an Eyring model are close to, but slightly less than, measured viscosities. These results are similar to those obtained for Q 3  - Q 4  exchange in K 2 Si 4 O 9  liquid, indicating that local Si-O bond breaking occurs on a time scale consistent with it being the primary control on viscous flow even in lower silica liquids.

Letters. Silicate species exchange, viscosity, and crystallization in a low-silica melt: In situ high-temperature MAS NMR spectroscopy