Structure–property relations of sodium iron phosphate nuclear waste glasses: Effects of iron redox ratio and glass composition
Iron phosphate glasses, known for their exceptional chemical durability and potential applicability in nuclear waste management, have gained significant attention over the years. The structures of these glasses are complicated by the coexistence of Fe3+ and Fe2+, which plays a crucial role in determining their structures and properties. Here, this work uses molecular dynamics simulations to study the structural changes in Na2O–Fe2O3–P2O5 glasses with varying glass composition and Fe2+/Fe3+ redox ratio. It was found that the redox ratio and modifier contents significantly affected the short-range and medium-range orders in the glasses. Significant changes in the local environments around P5+ and Fe3+ were observed, as reflected by the bond distances and coordination numbers. Na+ cations are found to preferentially associate with Fe3+ (rather than Fe2+), whereas Fe2+ has stronger association with P5+ than Na+, confirming the structural role of Fe2+ as a glass modifier. The disruptions in P–O–P linkages upon increasing FeO suggest that FeO causes glass depolymerization. These glasses achieved higher connectivity with increasing Fe3+ / (Fe3+ + Fe2+) ratios, conerting phosphorous Q2 to Q3 units and iron Q5 units to Q4 units. The decrease of nonbridging oxygen fractions with increasing Fe3+ / (Fe3+ + Fe2+) ratios, through creating P–O–Fe linkages, is the main reason of enhanced network connectivity. Quantitative structure–property relationship analyses with different structural descriptors were used to correlate with measured properties. The analyses provided valuable insights into structure–property relationships, emphasizing the importance of choosing relevant energy parameters and defining glass network connectivity, particularly in Fnet descriptors. It was found the Fe–O–P linkage density exhibits strong correlations to measured dissolution rates, supporting the importance of these linkages in improving the chemical durability in iron phosphate glasses.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE Advanced Research Projects Agency - Energy (ARPA-E)
- Grant/Contract Number:
- AC05-76RL01830; AR0001613
- OSTI ID:
- 2513899
- Report Number(s):
- PNNL-SA--199255
- Journal Information:
- Journal of the American Ceramic Society, Journal Name: Journal of the American Ceramic Society Journal Issue: 2 Vol. 108; ISSN 0002-7820
- Publisher:
- American Ceramic SocietyCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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