13775-06-9Relevant academic research and scientific papers
Optical spectrum and crystal-field analysis of uranium trifluoride
Karbowiak,Drozdzyński
, p. 187 - 196 (2007)
The first low temperature absorption spectrum and crystal-field analysis of uranium trifluoride are presented. The measurements have been performed on a polycrystalline sample in the 4000-30,000 cm-1 range at 4.2 K. One may notice the largest crystal-field splitting of SLJ multiplets among all so far reported data for uranium(III) as well as in polycrystalline samples and U3+ doped single crystals. In the presented analysis 94 experimental crystal-field levels, observed in 0-24,116 cm-1 energy range, have been identified and fitted to a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions at the C2 site symmetry. In order to exclude a possible influence of inaccuracy in the description of the free-ion multiplets on crystal-field parameters a number of additional freely varied parameters associated with the centroids of the free-ion multiplets were introduced. In the final step of the fitting procedure eight free-ion and 14 CF parameters were freely varied giving B02 = - 833 (45), Re B22 = 272 (36), B04 = 1817 (89), Re B24 = 186 (106), Im B24 = 776 (82), Re B44 = 523 (104), Im B44 = + 1460 (58), B06 = 1081 (105), Re B26 = - 841 (89), Im B26 = - 2459 (74), Re B46 = - 665 (88), Im B46 = - 1024 (74), Re B66 = 1416 (56), Im B66 = - 1682 (93) and r.m.s. = 24 cm-1. The performed calculation procedure enabled the determination of good starting values, reliable crystal-field parameters and a small r.m.s. deviation.
Studies on (2UF4 + H2 = 2UF3 + 2HF) and vapour pressure of UF3
Roy, K. N.,Prasad, Rajendra,Venugopal, V.,Singh, Ziley,Sood, D. D.
, p. 389 - 394 (1982)
Equilibrium constants for 2UF4(s) + H2(g) = 2UF3(s) + 2HF(g) have been measured in the temperature range 967 to 1120 K.The results can be expressed in the form: log10K = (6.35 +/- 0.17)-(12270 +/- 78)(K/T).The results have been tr
Reduction process of uranium(IV) and uranium(III) in molten fluorides
Hamel,Chamelot,Laplace,Walle,Dugne,Taxil
, p. 3995 - 4003 (2007)
This study focused on the electroreduction process of uranium cations in molten fluorides. It involved cyclic voltammetry, chronopotentiometry with and without current reversal, and square wave voltammetry. The results indicate a two-step reduction process for uranium(IV). The first step U(IV)/U(III) exchanging one electron corresponds to a soluble/soluble system and is limited by U(IV) diffusion with DU(IV) = 1.25 ± 0.35 × 10-5 cm2 s-1 in LiF-NaF at 720 °C. In order to perform a thorough study of the second step U(III)/U(0) in the reduction process, the melt was chemically reduced in U(III) with U metal as reducing agent. Alternatively to the use of LiF-NaF where U metal is unstable at 720 °C, the chemical reduction of U(IV) in U(III) was performed in a LiF-CaF2-UF4 solution containing U metal at 810 °C. It has been confirmed that the reduction of U(III) proceeds in one step exchanging three electrons and by a diffusion controlled process with DU(III) = 2.2 ± 0.7 × 10-5 cm2 s-1 in LiF-CaF2 at 810 °C.
Spectroscopic properties of K5Li2UF10
Karbowiak,Gajek,Drozdzyński
, p. 239 - 248 (2008/10/09)
A new uranium (III) fluoro-complex of the formula K5Li 2UF10 has been synthesised and characterised by X-ray powder diffraction and electronic absorption spectra measurements. The compound crystallises in the orthorhombic system, space group Pnma, with a = 20.723, b = 7.809, c = 6.932 ?, V = 1121.89 ?3, Z = 4 and is isostructural with its K5Li2NdF10 and K 5Li2LaF10 analogous. The absorption spectrum of a polycrystalline sample of K5Li2UF10 was recorded at 4.2 K in the 3500-45,000 cm-1 range and is discussed. The observed crystal-field levels were assigned and fitted to parameters of the simplified angular overlap model (AOM) and next to those of a semi-empirical Hamiltonian, which was representing the combined atomic and one-electron crystal-field interactions. The starting values of the AOM parameters were obtained from ab initio calculations. The analysis of the spectra enabled the assignment of 71 crystal-field levels of U3+ with a relatively small r.m.s. deviation of 37 cm-1. The total splitting of 714 cm -1 was calculated for the 4I9/2 ground multiplet.
Matrix IR spectra of the products from F2, ClF, and Cl2 reactions with pulsed-laser evaporated uranium atoms
Hunt, Rodney D.,Thompson, Craig,Hassanzadeh, Parviz,Andrews, Lester
, p. 388 - 391 (2008/10/08)
Pulsed Nd:YAG laser ablated uranium atoms were codeposited with F2 and excess Ar onto a CsI window at 12 K. Infrared spectra revealed the presence of several uranium fluorides including the previously characterized UF4, UF5, and UF6. Lower laser energy favored new absorptions at 400, 446, 496, and 561 cm-1. These product absorptions increased stepwise during annealings which permitted diffusion and reaction of the fluorine. Similar studies with ClF produced the above absorptions plus a new band at 554 cm-1 which is tentatively assigned to ClF2-. The first bands appearing at 400 and 446 cm-1 are assigned to UF and UF2, respectively. The 496- and 561-cm-1 bands are tentatively assigned to UF3 and F3-, respectively. Finally, uranium atoms were reacted with Cl2. In addition to several absorptions due to UCl4, a new doublet at 312 and 308 cm-1 is assigned to UCl2.
Thermochemical properties of the gaseous lower valent fluorides of uranium
Lau, K. H.,Hildenbrand, D. L.
, p. 2646 - 2652 (2007/10/02)
High temperature gaseous equilibria involving the lower-valent uranium fluorides UF, UF2, UF3, and UF4 were studied by mass spectrometry, and reaction enthalpies and entropies with estimated uncertainties of +/-2 kcal/mol and +/-2 cal/deg mol were derived solely from the temperature coefficients of reaction equilibrium constants.These results yield the following bond dissociation energies at 298 K in kcal/mol: Do(F3U-F) = 148.2; Do(F2U-F) = 149.0; Do(FU-F) = 136.5; and Do(U-F) = 157.5.The sum of these values is compatible with the heat of atomization of UF4(g) evaluated from independent source.A value of Do(F3U-F) derived from electron impact measurements agrees well with the equilibrium data.The reaction entropy data indicate that the electronic entropies of UF, UF2, and UF3 are comparable to that of atomic uranium in the same temperature range, and provide a basis for estimating the total thermodynamic functions of these species.Experimental entropies obtained for UF4 indicate the likelihood of a distorted tetrahedral structure of effective C2v symmetry.The results provide sufficient information for predicting the equilibrium composition of the gaseous U-F system over a wide temperature range.
Standard enthalpies of formation of uranium compounds VII. UF3 and UF4 (by solution calorimetry)
Cordfunke, E. H. P.,Ouweltjes, W.
, p. 193 - 198 (2007/10/02)
Enthalpies of solution of UF3 and UF4 in a mixed aqueous solvent containing sulphuric acid, boric acid, and ceric sulphate have been measured calorimetrically.Together with measurements of the enthalpy of solution of γ-UO3 and U3O8 in the same solution, the standard enthalpies of formation of solid UF3 and UF4 have been derived: SDH0f(UF3, s, 298.15 K) = -(1508.5 +/- 5.5) kJ mol-1; SDH0f(UF4, s, 298.15 K) = -(1920.0 +/- 3.7) kJ mol-1.The values differ considerably from literature values.
Interaction of uranium and its alloys with alkali metal fluorides
NOVOSELOV GP,KASHCHEEV IN,DOGAEV YUD
, p. 48. (2008/10/08)
The results of an investigation of uranium interaction with alkali metal fluorides at 1273 K and above under nonequilibrium conditions are presented. The processes are accompanied by evaluation of alkali metal vapors and formation of uranium tetra and tri
