Structural studies of ThO2 containing barium borosilicate glasses

Barium borosilicate glasses containing as much as 18.6 wt% ThO2 have been prepared by a conventional melt-quench method and characterized by Si-29 and B-11 magic angle spinning nuclear magnetic resonance (MAS NMR), Infrared (IR) absorption and differential thermal analysis (DTA) techniques for their structural features. Based on Si-29 and B-11 MAS NMR and IR investigations, it has been established that the borosilicate network is not affected by such a large ThO2 incorporation. Whereas Si exists as Q(3) and Q(2) structural units in the ratio of similar to 0.7, boron exists in both trigonal (BO3) and tetrahedral (BO4) configurations and their relative concentrations are not affected by ThO2 incorporation in these glasses. The higher extent of ThO2 incorporation in barium borosilicate glasses compared to borosilicate glasses has been attributed to the increased number of non-bridging oxygen atoms present in the barium borosilicate glasses. Based on DTA measurements it has been shown that there is neither any change in the glass transition temperature nor the occurrence of any crystallization up to 1000 degrees C, for ThO2 incorporation up to 18.6 wt% in these glasses. For higher concentrations of ThO2, there is phase separation during glass formation and fine crystallites of ThO2 are formed as revealed by XRD. These findings are of significance for the nuclear waste management related to thorium fuel cycle. (c) 2006 Elsevier B.V. All rights reserved.