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1.
Inorg Chem ; 62(45): 18724-18731, 2023 Nov 13.
Article in English | MEDLINE | ID: mdl-37917811

ABSTRACT

Uranium trichloride (UCl3) has received growing interest for its use in uranium-fueled molten salt reactors and in the pyrochemical processing of used fuel. In this paper, we report for the first time the experimentally determined Raman spectra of UCl3, at both ambient condition and in situ high temperatures up to 871 K. The frequencies of five of the Raman-active vibrational modes (vi) of UCl3 exhibit a negative temperature derivative ((∂νi/∂T)P) with increasing temperature. This red-shift behavior is likely due to the elongation of U-Cl bonds. The average isobaric mode Grüneisen parameter (γiP = 0.91 ± 0.02) of UCl3 was determined through use of the coefficient of thermal expansion published in Vogel et al. (2021) and the (∂νi/∂T)P values determined in this study. These results are in general agreement with those calculated here by density functional theory (DFT+U). Finally, a comparison of the ambient band positions of UCl3 to those of isostructural lanthanide (La-Eu) and actinide chlorides (Am-Cf) has been made.

2.
Anal Chem ; 94(19): 7084-7091, 2022 May 17.
Article in English | MEDLINE | ID: mdl-35512178

ABSTRACT

Small-particle analysis is a highly promising emerging forensic tool for analysis of interdicted special nuclear materials. Integration of microstructural, morphological, compositional, and molecular impurity signatures could provide significant advancements in forensic capabilities. We have applied rapid, high-sensitivity, hard X-ray synchrotron chemical imaging to analyze impurity signatures in two differently fabricated fuel pellets from the 5th Collaborative Materials Exercise (CMX5) of the IAEA Nuclear Forensics International Working Group. The spatial distributions, chemical compositions, and morphological and molecular characteristics of impurities were evaluated using X-ray absorption near-edge structure (XANES) and X-ray fluorescence chemical imaging to discover principal impurities, their granularity, particle sizes, modes of occurrence (distinct grains vs incorporation in the UO2 lattice), and sources and mechanisms of incorporation. Differences in UO2+x stoichiometry were detected at the microscale in nominally identical UO2 ceramics (CMX5-A and CMX5-B), implying the presence of multiple UO2 host phases with characteristic microstructures and feedstock compositions. Al, Fe, Ni, W, and Zr impurities and integrated impurity signature analysis identified distinctly different pellet synthesis and processing methods. For example, two different Al, W, and Zr populations in the CMX5-B sample indicated a more complex processing history than the CMX5-A sample. K-edge XANES measurements reveal both metallic and oxide forms of Fe and Ni but with different proportions between each sample. Altogether, these observations suggest multiple sources of impurities, including fabrication (e.g., force-sieving) and feedstock (mineral oxides). This study demonstrates the potential of synchrotron techniques to integrate different signatures across length scales (angstrom to micrometer) to detect and differentiate between contrasting UO2 fuel fabrication techniques.

3.
Inorg Chem ; 57(15): 9504-9514, 2018 Aug 06.
Article in English | MEDLINE | ID: mdl-30009590

ABSTRACT

The tetracyanoplatinate ligand was employed in synthesizing the first neptunyl cyanoplatinate complexes. Results indicate in situ oxidation of Pt(II) by Np(V/VI) to form mixed-valent Pt-Pt stacked columnar chains linked by cation-cation interaction induced chains of Np(V) polyhedra into a two-dimensional sheet structure. The Pt-Pt stacking distances of 3.04-3.05 Å are the longest reported columnar platinophilic interactions among mixed-valent tetracyanoplatinate structures. These complexes further illustrate the marked chemical differences and structural diversity of solid-state Np(V) coordination complexes with regard to Np(VI) and U(VI).

4.
Chem Commun (Camb) ; 53(69): 9550-9553, 2017 Aug 24.
Article in English | MEDLINE | ID: mdl-28808712

ABSTRACT

The interplay between aqueous alkaline earth (Ca, Sr, Ba) polycationic speciation and uranyl-peroxide polyoxometalate self-assembly and evolution is described here using solution (Raman and X-ray scattering) and solid-state (microscopy, X-ray diffraction) characterization. Supramolecular assembly of Sr-encapsulated and decorated polyanions and polycations yields the fourth largest inorganic unit cell reported from single-crystal X-ray diffraction.

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