NMR study of structural changes of alkali borosilicate glasses with heat treatment

A phenomenon of the temperature dependent structural change of xNa 2 O . (50 - x)B 2 O 3 . 50SiO 2 glasses was observed by use of 11 B and 29 Si NMR and Raman spectroscopies. The B NMR measurement showed that a small fraction of BO 4 units transformed into BO 3 units below x = 17 (Na 2 O/B 2 O 3 < 0.51) after the glasses were heat treated at 600°C for 50h; an opposite transformation occurred above x = 18; namely BO 3 units converted into BO 4 units. Raman and 29 Si MAS-NMR spectra also showed the effect of the heat treatment on the structure of the glass.