A comparative study on the structural aspects of sodium borosilicate glasses and barium borosilicate glasses: Effect of Al2O3 addition

• Sodium and barium borosilicate glasses are being used for immobilization of high level radioactive liquid waste.
• Aluminum will be one of the component in high level radioactive liquid waste arising from reprocessing of thoria based spent fuels.
• Al exists in the glass only as AlO4− structural units and interacts with silica structural units forming Si-O-Al linkages.
• The relative concentrations of BO3 and BO4− units evaluated match with that predicted by Dell and Bray model.

Sodium borosilicate and barium borosilicate glasses containing different amounts of Al2O3 were prepared by conventional melt-quench method and their structural information was obtained by 29Si, 11B and 27Al Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) technique. By employing the Dell and Bray model, different types of boron and silicon structural units present in the glass have been identified. The relative concentrations of BO3 and BO4− structural units evaluated from the 11B MAS NMR patterns match (within experimental errors) with that predicted by Dell and Bray model. Al3 + ion exists only as AlO4− structural units with Si-O-Al type of linkages in the glass. Higher glass transition temperature of barium borosilicate glass compared to sodium borosilicate glass has been attributed to the formation of relatively more connected BO4– structural units at the expense of less connected BO3 structural units in the former glass.