Solid-state NMR insight into cation-modulated network structure and chemical durability of phosphate nuclear waste glasses

Abstract

Phosphate glasses are extensively explored for nuclear waste vitrification. However, a full, systematic understanding of the mechanisms controlling their chemical durability is still lacking. Based on the similar ionic radii and matching valence states of Zn 2+ /Ga 3+ and Fe 2+ /Fe 3+ , this study adopted a strategy of substituting Fe ions with Zn 2+ /Ga 3+ and selected three phosphate glass systems with similar O/P ratios, namely Fe 2 O 3 -NaPO 3 (FPx), ZnO-Ga 2 O 3 -NaPO 3 (ZGPx), and Na 2 O-Al 2 O 3 -NaPO 3 (NAPx), to systematically investigate the effects of different cation systems on the microscopic structure and chemical durability of phosphate glasses. Solid-state nuclear magnetic resonance (SSNMR) was employed to characterize the glass network structures of the ZGPx and NAPx systems at the atomic scale, while deionized water immersion tests were conducted to evaluate the ion leaching behavior of each glass system with different O/P ratios. The results show that Zn 2+ /Ga 3+ can effectively serve as structural surrogates for Fe 2+ /Fe 3+ and are suitable for elucidating the structural evolution and chemical durability mechanism of iron phosphate glasses. Furthermore, the results show that, apart from the conventional O/P ratio, the chemical characteristics of glass modifier and intermediate cations also play an important role in the polymerization state of the glass network.