Process of phase separation in sodium borosilicate glass as studied by NMR

Si-29, B-11, Na-23 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.