Abstract
Uranium tetrafluoride is an important intermediate in the nuclear fuel cycle. Facile synthesis of its hydrate, uranium tetrafluoride hydrate (UF4·2.5H2O), has recently been reported. The hydrate forms by contacting anhydrous UF4with neat H2O at room temperature for 24 h or by exposing anhydrous UF4to high relative humidity (>90%) conditions for several weeks. These pathways are of clear environmental relevance. Further understanding of the structure and optical spectra of UF4·2.5H2O, especially of the water molecules, is therefore necessary. Herein, the structure of UF4·2.5H2O was probed using time-of-flight neutron powder diffraction to improve understanding of the crystalline water environments in the structure. The complete structure was elucidated and compared to a previously reported partial structure for UF4·2.5H2O and a predicted complete structure from density functional theory. The crystalline structure exhibits three distinct water environments: two of the three water sites are bound to uranium, and the third water is unbound or "free". Furthermore, the completed structure reveals an extensive hydrogen bonding network involving water-fluorine and water-water interactions. One bound water site participates in hydrogen bonding with nearby fluoride ligands (O-H···F-U), and the second bound water site participates in hydrogen bonding with the unbound water (O-H···O) and a nearby fluoride ligand (O-H···F-U); the unbound water participates in hydrogen bonding with bound water (O-H···O-U). Low-temperature experiments and thermal analysis indicate UF4·2.5H2O is thermally stable from 10 to 358 K, undergoes dehydration at higher temperatures, and is nearly dehydrated at 473 K. Structural measurements provide foundational understanding and will inform future investigations of the thermal and environmental stability of UF4·2.5H2O.
Original language | English |
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Pages (from-to) | 13256-13267 |
Number of pages | 12 |
Journal | Journal of Physical Chemistry C |
Volume | 126 |
Issue number | 31 |
DOIs | |
State | Published - Aug 11 2022 |
Funding
J.C.S. and K.J.P. acknowledge support from Department of Energy/National Nuclear Security Administration under Award Number DE-NA0003921. A portion of this work was sponsored by the Department of Energy, National Nuclear Security Administration Office. A portion of this research used resources at the Spallation Neutron Source (IPTS 26154), a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. A portion of this research used resources of the Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. A portion of this research used resources of the Oak Ridge Leadership Computing Facility at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. A portion of this work was produced by Battelle Savannah River Alliance, LLC under Contract No. 89303321CEM000080 with the U.S. Department of Energy. Publisher acknowledges the U.S. Government license to provide public access under the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). We thank Michael Sanders at the Colorado School of Mines for assistance with the TGA/DSC experiments. The views and conclusions expressed in this document are those of the authors and do not reflect the official policy or position of the United States Air Force, or the Department of Defense.