Abstract
Hollandite materials, as a class of crystalline nuclear waste forms, are promising candidates for the immobilization of radioactive elements, such as Cs, Ba, as well as a variety of lanthanide and transition-metal fission products. In this study, three Ga-doped titanate hollandite-type phases, Ba 1.33 Ga 2.67 Ti 5.33 O 16 , Ba 0.667 Cs 0.667 Ga 2 Ti 6 O 16 , and Cs 1.33 Ga 1.33 Ti 6.67 O 16 , were synthesized using a solid-state reaction route. All synthesized phases adopted a single phase tetragonal structure, as determined by powder X-ray diffraction (XRD), and elemental analysis confirmed the measured stoichiometries were close to targeted compositions. Extended X-ray absorption fine structure spectroscopy (EXAFS) was used to determine the local structural features for the framework of octahedrally coordinated cations. EXAFS data indicated that Cs 1.33 Ga 1.33 Ti 6.67 O 16 possessed the most disordered local structure centered around the Ga dopant. The enthalpies of formation of all three hollandite phases measured using high-temperature oxide melt solution calorimetry were found to be negative, indicating enthalpies of formation of these hollandites from oxides are thermodynamically stable with respect to their constituent oxides. Furthermore, the formation enthalpies were more negative and hence more favorable with increased Cs content. Finally, aqueous leaching tests revealed that high Cs content hollandite phases exhibited greater Cs retention as compared to low Cs content hollandite. While preliminary in nature, this work draws attention to the links between the capacity for radionuclide retention, atomistic level structural features and bulk thermodynamic properties of materials.
| Original language | English |
|---|---|
| Pages (from-to) | 4314-4324 |
| Number of pages | 11 |
| Journal | Journal of the American Ceramic Society |
| Volume | 102 |
| Issue number | 7 |
| DOIs | |
| State | Published - Jul 2019 |
| Externally published | Yes |
Funding
KSB, YX, and LSN gratefully acknowledge financial support from the DOE‐EPSCoR Project Number: DE‐ SC0012530, “Radionuclide Waste Disposal: Development of Multi‐scale Experimental and Modeling Capabilities” for support of modelling and EXAFS studies. KSB and MZ acknowledge support of thermodynamic measurements as part of the Center for Hierarchical Waste Form Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award No. DE‐SC0016574. AIF and YL acknowledge support of EXAFS data analysis by the U.S. Department of Energy, Office of Basic Energy Sciences under Grant No. DE‐FG02‐03ER15476. The calorimetric experiments carried out at University of California, Davis were supported as part of the Materials Science of Actinides, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award Number DE‐SC0001089. JA acknowledges the support of durability testing by the U.S. Department of Energy, Office of Nuclear Energy, Fuel Cycle Technology, Materials Recovery and Waste Form Development Campaign. Work conducted at Savannah River National Laboratory was supported by the U.S. Department of Energy under contract number DE‐AC09‐08SR22470.
| Funders | Funder number |
|---|---|
| DOE‐EPSCoR | DE‐ SC0012530 |
| Office of Basic Energy Sciences | DE‐AC09‐08SR22470, DE‐SC0001089 |
| U.S. Department of Energy | |
| Office of Science | |
| Basic Energy Sciences |
