Abstract:Raman spectroscopy is one of the most useful techniques for studying the structure of UO 2 and changes due to specific defects caused by doping, changes in stoichiometry, irradiation, or heating under oxidizing conditions. In this paper, we illustrate several aspects of the application of Raman techniques to the study of UO 2 , including the use of wavelength-dependent excitation (455, 532, and 785 nm) to assess the effects of doping (Nd, Th, and Zr), ion irradiation, and in situ heating and oxidation (UO 2 t… Show more
“…This was evident, as there are no U–O vibrational modes present in any of the spectra that were recorded between 300 and 1000 cm –1 ; in uranium oxychloride (UO 2 Cl 2 ), there is a strong temperature-dependent vibrational band located between 700 and 760 cm –1 . Additionally, there are no vibrational features near 450 cm –1 , which occurs in uranium dioxide [(U 4+ O 2 ) 0 ], and near 775 cm –1 , which occurs in uranyl [(U 6+ O 2 ) 2+ ] hydrates and oyxhydrates. − …”
Uranium trichloride (UCl 3 ) 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 UCl 3 , at both ambient condition and in situ high temperatures up to 871 K. The frequencies of five of the Raman-active vibrational modes (v i ) of UCl 3 exhibit a negative temperature derivative ((∂ν i / ∂T) P ) with increasing temperature. This red-shift behavior is likely due to the elongation of U−Cl bonds. The average isobaric mode Gruneisen parameter (γ iP = 0.91 ± 0.02) of UCl 3 was determined through use of the coefficient of thermal expansion published in Vogel et al. (2021) and the (∂ν i /∂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 UCl 3 to those of isostructural lanthanide (La−Eu) and actinide chlorides (Am−Cf) has been made.
“…This was evident, as there are no U–O vibrational modes present in any of the spectra that were recorded between 300 and 1000 cm –1 ; in uranium oxychloride (UO 2 Cl 2 ), there is a strong temperature-dependent vibrational band located between 700 and 760 cm –1 . Additionally, there are no vibrational features near 450 cm –1 , which occurs in uranium dioxide [(U 4+ O 2 ) 0 ], and near 775 cm –1 , which occurs in uranyl [(U 6+ O 2 ) 2+ ] hydrates and oyxhydrates. − …”
Uranium trichloride (UCl 3 ) 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 UCl 3 , at both ambient condition and in situ high temperatures up to 871 K. The frequencies of five of the Raman-active vibrational modes (v i ) of UCl 3 exhibit a negative temperature derivative ((∂ν i / ∂T) P ) with increasing temperature. This red-shift behavior is likely due to the elongation of U−Cl bonds. The average isobaric mode Gruneisen parameter (γ iP = 0.91 ± 0.02) of UCl 3 was determined through use of the coefficient of thermal expansion published in Vogel et al. (2021) and the (∂ν i /∂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 UCl 3 to those of isostructural lanthanide (La−Eu) and actinide chlorides (Am−Cf) has been made.
“…This may be because some of the metallic U only oxidized to UO 2 , U 3 O 7 , or U 4 O 9 . [41][42][43][44] Also, other oxidized and hydrolyzed species like La oxides/hydroxides or tungsten oxides/ hydroxides may have been detected and included in the overall oxygen signal in each region observed.…”
Electrochemical recovery of dilute concentrations of actinides from spent nuclear fuel would reduce the longevity of storing high-level nuclear waste. Electrochemical deposition with redox replacement (EDRR) is used in a molten salt medium for the selective electrochemical recovery of uranium in the presence of excess concentrations of lanthanum. In each EDRR cycle, after a short electrodeposition pulse, the deposited lanthanum is spontaneously replaced by uranium at open circuit. After repeated cycles, uranium metal was obtained on a tungsten electrode immersed in LiCl-KCl melt that contained 1 wt.% lanthanum chloride – 0.15 wt.% uranium4+ chloride. Scanning electron microscopy and energy dispersive X-ray spectroscopy analysis revealed uranium particles approximately 0.5 - 1 μm with well-defined rectangular shapes; and with 20 – 60 times more uranium recovered on the surface of the electrode than lanthanum.
“…The temperature and sensitivity of the instrument were calibrated by heating indium, tin, lead, zinc, aluminium, silver, and gold across their fusion point repeatedly at temperature change rates of 5, 10, 15, and 20 °C min −1 . 92,96–100…”
Nanocrystalline pyrochlore materials have been investigated for their enhanced radiation tolerance as ceramic nuclear waste hosts. In this work, we study the thermodynamic driving force of nano-scale materials for radiation...
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