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

A phenomenon of the temperature dependent structural change of xNa2O · (50 − x)B2O3 · 50SiO2 glasses was observed by use of 11B and 29Si NMR and Raman spectroscopies. The 11B NMR measurement showed that a small fraction of BO4 units transformed into BO3 units below x = 17 (Na2O/B2O3 < 0.51) after the glasses were heat treated at 600 °C for 50 h; an opposite transformation occurred above x = 18; namely BO3 units converted into BO4 units. Raman and 29Si MAS–NMR spectra also showed the effect of the heat treatment on the structure of the glass.