Understanding composition-property-phase relations in high Fe2Q3 Hanford waste glasses.

To support the vitrification efforts at the US Hanford site, three borosilicate glasses were designed and incrementally doped on a pro-rata basis with Fe2O3 from 0 – 14 mol%. The first series was an Na-borosilicate glass, the second introduced CaO, Al2O3, and Li2O into the composition, while the third was derived from a high Fe waste glass composition (known as HLW Ng-Fe2). These three glass sample series were used to investigate how Fe2O3 integrates into borosilicate glass networks of varying complexity. 57Fe Mössbauer and Fe K-edge XANES spectroscopies were used to describe the iron chemistry across all three glass series, while B K-edge XANES, Raman, Si 2p & B 1s spectroscopies were used to describe the glass network. The iron was demonstrated to exist entirely as Fe3+ in all samples, while the coordination of the Fe3+ was shown to be predominantly tetrahedral, with some evidence of higher-coordinated units. The silicate sub-network was shown to be more affected by the increasing Fe2O3 contents in the simplest glass series, but in more complex series, the borate sub-network was shown to be affected more by increasing Fe2O3 content. The boron coordination, as determined by B K-edge XANES spectroscopy, showed no substantial changes as a function of increasing Fe2O3 content. Complex tetrahedral avoidance hierarchies and mixed modifier effects were presented as hypotheses to explain these network effects. The Hanford analogue series was selected for further research on the glass properties. The glasses were split into two sub series – the “Laboratory Produced” and the “Canister Centreline Cooled” series. The latter samples were heat treated to represent the slow cooling in the HLW steel canisters to be used at the Hanford Waste Treatment Plants (WTPs). The glass transition temperature, phase abundances (as measured by Rietveld refinement of XRD patterns), and 7-day chemical durability were studied. It was found that there are very few deviations between the two sub-series in glass transition temperature and chemical durability, but the heat-treated series showed a greater abundance of crystalline phases. All properties were consistent with limits set by the glass reference material (DWPF-EA glass) in literature. However, further work is required to confirm this as no reference material was studied alongside these samples.