Hollandite materials are represented by the general formula A2B8O16 where the A site is either a mono or divalent element and B site is either a di, tri or tetravalent element. In this study, the A site consisted of Ba and Cs with a wide range of B site dopants including Zn, Ga, Fe and Al which were incorporated into the hollandite structure via a solid-state reaction method. Each of these compositions was found to form single-phase hollandite across the A-site compositional range from the pure Ba end member to the pure Cs end member. The enthalpies of formation of the hollandite phases measured using high temperature oxide melt solution calorimetry were found to be negative, indicating these hollandites are thermodynamically stable with respect to their constituent oxides. Furthermore, the formation enthalpies were more negative and hence more favourable with increased Cs content across a wide range of B site dopants. In addition to formation energy measurements, select monolithic an powder-based aqueous leaching tests indicated that the hollandite phase with higher Cs-loading enhanced Cs retention. The impact of atomistic level structural features on the bulk thermodynamic properties of hollandite and Cs retention capacity will be discussed.

Framework dopant effects in tunnel-structured hollandite waste forms for Cs-immobilization

2019 Spring National Meeting

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