Effect of BaO addition on the structural aspects and thermophysical properties of sodium borosilicate glasses

Sodium borosilicate glasses containing different amounts of BaO were prepared by a conventional melt quench method and characterized for their structural aspects by 29Si, 11B NMR and IR spectroscopy. From 29Si MAS NMR studies, it has been inferred that these glasses consist of Q2 and Q3 structural units of silicon and that the addition of BaO results in the marginal conversion of Q3 to Q2 structural units. There is no direct interaction between Ba2+ ions and boron structural units, as revealed by the identical values of the relative concentration of BO3 and BO4 structural units and quadrupolar coupling constant values for the BO3 structural units. The identical values of glass transition temperature and vibrational frequencies corresponding to Si–O–Si/Si–O–B and B–O linkages of all the samples further support this. As the borosilicate network is unaffected, the systematic increase in the values of thermal expansion coefficient with increase in BaO content has been attributed to the increase in the relative concentration of less rigid Ba–O linkages compared to the more rigid Si–O and B–O linkages in the glass. Such studies will be useful for the development of matrices for the management of nuclear waste generated during the reprocessing of the spent fuel from thoria based reactors.