Effects of SiO₂ and B₂O₃ Content on Structure of Simulated High-Level Waste Glasses

Borosilicate glass has been widely used as a basal frit for the solidification of high-level waste due to its excellent chemical stability, good thermal stability, and high glass tolerance for radioactive waste properties. There is inherent dependence relationship between the structure of waste glass solidified bodies and its composition, which will have impact on the properties of waste glass. The contents of waste glass composition are considered as variables that will give rise to the change of certain structural characteristics of waste glass solidified bodies, which is an internal thread to explore the influence on the performance of high-level waste glass solidified bodies. The aim of this study is to obtain the influence rule of the content of waste glass composition on its structural feature parameters(such as the fraction of non-bridging oxygen) and to estimate the properties of waste glass solidified body, and then to provide a guidance for designing an optimal formula of waste glass for highly efficient disposal of high-level waste. In this study, a series of waste glass samples were prepared on the basis of the formula for certain simulated high-level waste glass solidified body, but the glass composition was changed as a function of SiO₂ or B₂O₃ content. Furthermore, the Raman spectroscopy is applied for analysis of the silicate networks structure unit(Qn, where Q and n represents the tetrahedral unit and the number of bridging oxygen per tetrahedron, respectively) of the waste glasses. And the influence of the content of SiO₂ and B₂O₃ on the network structure of the waste glass solidified bodies was discussed. The results show that an increase of the fraction of bridging oxygen with increase of SiO₂ content(mass ratio of SiO₂ to that of all the other oxides) from 0.721 to 1.037 and in the meantime silicate network polymerization degree(N) as indicated by the ratio of non-bridging oxygen/bridging oxygen decrease. However, the fraction of bridging oxygen first decreases with B₂O₃ content(mass ratio of B₂O₃ to that of all the other oxides) reaching to 0.143 from 0.117 and then increases with further increase of B₂O₃ content to 0.176. The density determinations have shown close results and no crystallization are observed on the waste glass solidified bodies within our scope of the experiments.