Abstract: ²⁹Si, ¹¹B, ²³Na MAS NMR were employed to study the structure change of the Na₂O-B₂O₃-SiO₂ glass in the process of
thermal treatment of phase separation. The results show that oxygen atoms are deleted among the [SiO₄] structure units and the aggregation degree of Si
increases in the process of phase separation. In the meantime, the structure of boron atoms in silicon-rich phase is transformed gradually from [BO₃] to
[BO₄] and [BO₄] units enter into sodium-boron rich phase. The difference between the compositions of the two phases gradually increases. The phase separation
is the result of diffusion and mass transfer. Moreover, the glass has a more rapid structure adjustment rate at a higher temperature of thermal treatment,
thus can get to the equilibrium state faster.

Key words: sodium borosilicate, phase separation, NMR