Evidence of a Nonphotochemical Mechanism for the Solid-State Formation of Uranyl Peroxide

Kirkegaard, Marie C.; Miskowiec, Andrew; Ambrogio, Michael W.; Anderson, Brian B.

doi:10.1021/acs.inorgchem.8b00512

Cited by 15 publications

(31 citation statements)

References 41 publications

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“…In Table 1 we identify two peaks at 109 and 112 meV associated with the symmetric stretching mode of the uranyl ion. Raman spectra of the same vibrational mode consistently show a similar two peak decomposition, always with a redshift shoulder 1,4,44 . For the symmetric mode, the vibrational frequency is proportional to the square root of the oscillator mass (16 amu for O).…”

Section: Water Couplingmentioning

confidence: 63%

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

Miskowiec

Niedziela

Kirkegaard

et al. 2019

Sci Rep

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Inelastic neutron scattering (INS) is uniquely sensitive to hydrogen due to its comparatively large thermal neutron scattering cross-section (82 b). Consequently, the inclusion of water in real samples presents significant challenges to INS data analysis due directly to the scattering strength of hydrogen. Here, we investigate uranyl fluoride (UO 2 F 2 ) with inelastic neutron scattering. UO 2 F 2 is the hydrolysis product of uranium hexafluoride (UF 6 ), and is a hygroscopic, uranyl-ion containing particulate. Raman spectral signatures are commonly used for inferential understanding of the chemical environment for the uranyl ion in UO 2 F 2 , but no direct measurement of the influence of absorbed water molecules on the overall lattice dynamics has been performed until now. To deconvolute the influence of waters on the observed INS spectra, we use density functional theory with full spectral modeling to separate lattice motion from water coupling. In particular, we present a careful and novel analysis of the Q-dependent Debye–Waller factor, allowing us to separate spectral contributions by mass, which reveals preferential water coupling to the uranyl stretching vibrations. Coupled with the detailed partial phonon densities of states calculated via DFT, we infer the probable adsorption locations of interlayer waters. We explain that a common spectral feature in Raman spectra of uranyl fluoride originates from the interaction of water molecules with the uranyl ion based on this analysis. The Debye–Waller analysis is applicable to all INS spectra and could be used to identify light element contributions in other systems.

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Section: Water Couplingmentioning

confidence: 63%

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

Miskowiec

Niedziela

Kirkegaard

et al. 2019

Sci Rep

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“…Understanding the structure and reactivity of nuclear materials is a primary scientific goal for nuclear forensics, environmental stewardship, and fuel cycle science. − In both industrial and environmental settings, water is present as a common reactant; therefore, understanding the reactivity, solubility, and bond strength of water with nuclear materials is clearly important for addressing questions in environmental and industrial contexts. In addition to the formation of unique crystal structures, the interaction of water with fluorinated materials, especially, produces distinct hydrolysis products. − …”

Section: Introductionmentioning

confidence: 99%

Inelastic Neutron Spectra of Uranium Tetrafluoride Hydrate, UF₄(H₂O)_2.5

et al. 2021

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Uranium tetrafluoride hydrate (UFH) is formed by immersing anhydrous UF4 under water for 12 h. UFH is therefore clearly a chemical species of environmental concern, as anhydrous UF4 is an intermediate uranium form in the nuclear fuel cycle. We use inelastic neutron scattering (INS) to probe the full vibrational spectra of UFH and its deuterated analogue in an effort to improve the fundamental understanding of its vibrational spectra. Coupled with density functional theory (DFT) calculations, the first for this compound, and full spectral modeling, we generate the complete vibrational spectra of UFH and compare them to prior optical spectroscopic results. In particular, the combination of DFT with INS allows us to identify multiple distinct chemical environments in the water bending and OH stretching regions. Whereas the water molecules directly bound to the U atoms execute OH stretching around 3600 cm–1, a second class of H-bonded waters vibrate below 3000 cm–1, an indicator of strong H bonding. In addition, a class of librational water modes are observed between 400 and 900 cm–1, which themselves can be separated in energy according to their chemical environments. Measurements presented herein directly assist in the assignment of certain spectral features in the infrared spectrum and will inform future investigations of UFH for environmental or forensics purposes.

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“…Accordingly, these phases are observed as alteration products on UO 2 fuel under aqueous conditions subsequent to peroxide generation by way of α-radiolysis of water. − In the presence of neptunium, studtite is observed as an alteration product of the uranyl hydroxide hydrate mineral metaschoepite [(UO 2 ) 8 (OH) 12 ·4H 2 O] . Recently, uranyl peroxide was observed as a degradation product of UO 2 F 2 and an intermediate in the conversion of uranyl fluoride to uranyl hydroxide under humid conditions. , Consequently, the presence of uranyl peroxides may provide insight into the age and storage conditions of both natural and technogenic uranyl fluoride and uranium oxide materials.…”

Section: Introductionmentioning

confidence: 99%

“…15 Recently, uranyl peroxide was observed as a degradation product of UO 2 F 2 and an intermediate in the conversion of uranyl fluoride to uranyl hydroxide under humid conditions. 16,17 Consequently, the presence of uranyl peroxides may provide insight into the age and storage conditions of both natural and technogenic uranyl fluoride and uranium oxide materials.…”

Section: ■ Introductionmentioning

confidence: 99%

Structural, Spectroscopic, and Kinetic Insight into the Heating Rate Dependence of Studtite and Metastudtite Dehydration

et al. 2020

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Uranyl peroxide minerals studtite (UO 2 O 2 •4H 2 O) and metastudtite (UO 2 O 2 •2H 2 O) are important materials in the nuclear fuel cycle. When heated, they dehydrate and transform to amorphous uranium oxides (UO x ), yet phase stability and heating rate dependence of these transformations are poorly understood. This information is critical to proper management of fuel cycle materials. In this work, we use in situ powder X-ray diffraction (PXRD), Raman spectroscopy, and thermogravimetric analysis (TGA) to monitor the dehydration of studtite and metastudtite. Strong linear correlation between the heating rate and phase transition temperature is observed. Geometric contraction and diffusion-related kinetic models describe studtite dehydration at slow heating rates, whereas Avrami−Erofeev or reaction order models become more accurate for faster thermal treatments. A second order model describes the transition from metastudtite to UO x regardless of the heating rate. Water retention during studtite dehydration is indicated by PXRD, Raman spectroscopy, and TGA. We observe mixed-phase UO x dehydration products of metastudtite with a likely formation mechanism involving conversion of some uranyl centers from hexagonal to pentagonal bipyramidal coordination units via peroxide liberation. Our observations clarify over 100 years of measurements on these materials and represent an advancement in understanding the chemical behavior of nuclear fuel cycle materials.

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Evidence of a Nonphotochemical Mechanism for the Solid-State Formation of Uranyl Peroxide

Cited by 15 publications

References 41 publications

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

Inelastic Neutron Spectra of Uranium Tetrafluoride Hydrate, UF₄(H₂O)_2.5

Structural, Spectroscopic, and Kinetic Insight into the Heating Rate Dependence of Studtite and Metastudtite Dehydration

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Evidence of a Nonphotochemical Mechanism for the Solid-State Formation of Uranyl Peroxide

Cited by 15 publications

References 41 publications

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

Analysis of Water Coupling in Inelastic Neutron Spectra of Uranyl Fluoride

Inelastic Neutron Spectra of Uranium Tetrafluoride Hydrate, UF4(H2O)2.5

Structural, Spectroscopic, and Kinetic Insight into the Heating Rate Dependence of Studtite and Metastudtite Dehydration

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Inelastic Neutron Spectra of Uranium Tetrafluoride Hydrate, UF₄(H₂O)_2.5