A B-11 AND LI-7 MAS-NMR STUDY OF SOL-GEL LITHIUM TRIBORATE GLASS SUBJECTED TO THERMAL DENSIFICATION

The effects of thermal densification on a sol-gel lithium triborate gl ass have been studied by B-11 and Li-7 NMR both static and at the magi c angle (MAS). B-11 spectra show that the boron average coordination i s similar in sol-gel and melt-quenched samples and it does not change upon annealing. Li-7 T-1 is shorter (similar to 8.5 s) in sol-gel glas s as prepared than in its melt-quenched counterpart (similar to 13 s) due to dipolar-dipolar Li-H interaction. Li-7 longitudinal relaxation behavior captures a part of a complex devitrification process which is driven by the loss of both residual solvent and moisture. (C) 1997 El sevier Science Ltd.