- Vibrational properties of uranium fluorides
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Multiphase mixtures of the uranium fluoride compounds UFx with x = 3, 4, 4.5, 5, whose local U–F bonding geometry is conserved, may result from UF6 reduction. One method for identifying multiphase mixtures is optical vibrational spectroscopy, b
- Miskowiec, Andrew,Shields, Ashley E.,Niedziela,Cheng, Yongqiang,Taylor, Paul,DelCul, Guillermo,Hunt, Rodney,Spencer, Barry,Langford, John,Abernathy, Douglas
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- Thermochemical properties of the gaseous lower valent fluorides of uranium
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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.
- Lau, K. H.,Hildenbrand, D. L.
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- Uranium tetrafluoride production using the dropping mercury electrode
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This work shows the technical feasibility to obtain uranium tetrafluoride through an electrochemical process using a dropping mercury electrode. This product was obtained from ammonium diuranate, dissolved in hydrofluoric solutions, using concentrations of 50 g/L UO2F2. The system was evaluated with current intensities densities from 1.6 to 6.3 A and temperatures from 25 to 65 °C. The maximum current efficiency achieved was 95 %. The UF4 powders achieved spherical morphology, with diameters between 40–60 μm. This property allows correct compaction for the subsequent production of metallic uranium, which allows reaching high-density UF4 – Mg mixtures, between 3.0–3.5 g/cm3, as it was proven in our previous studies. This technique achieved this result thanks to the electrochemical properties of the mercury, when used as cathode. The impurity levels of this product obtained by electrolysis are only those that come from the initial ammonium diuranate concentrates. This method is an alternative to the classic process of UF4 precipitation in an aqueous medium using reducing agents, as the conventional stannous chloride (SnCl2), which commonly contaminate uranium compounds.
- Dides, Munir,Hernández, José,Olivares, Luis
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- Hydrazinium(+2) and hydroxylammonium hexafluorouranates(V)
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In the reaction between uranium hexafluoride and hydrazinium(+2) fluoride in liquid hydrogen fluoride at room temperature, with excess uranium hexafluoride, the product is hydrazinium(+2) bishexafluorouranate(V), N2H6(UF6)
- Frlec, Boris,Hyman, Herbert H.
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- Preparation and Characterization of the Adduct Uranium Pentafluoride-Arsenic-Pentafluoride (1/1)
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The system UF5-AsF5, UF6-AsF5-UF4, and UF4-AsF5-F2 were studied using anhydrous HF as a solvent.In all cases a dark blue solution results from which blue crystals of composition UF5.AsF5 were isolated at temperatures lower than -30 deg C.At room temperature thermal decomposition of the adduct takes place giving AsF5 vapour, and a solid residue which was identified as β-UF5.
- Gantar, Darja,Frlec, Boris
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- Separation and recovery study of uranium from spent NaF (fillers)
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The molten salt technique is considered to be a feasible technique applicable for the removal of uranium from the spent NaF (fillers). Simple spent NaF or NaF with NaCl, i.e. mixed salt, was used as an electrolyte and the uranium concentrations in the bath, pre-treatment condition, electrolytic temperature, current density, etc. were given as parameters in this experiment. Results from the fundamental experiments showed the potential applicability of the molten salt technique for the removal of uranium from spent NaF.
- Amamoto, Ippei,Terai, Takayuki,Oobayashi, Hiroshi,Fujita, Reiko
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- Some Reactions of Uranium Chloride Pentafluoride
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The molecule UF5Cl has been isolated, together with an excess of UF6, in a solid matrix of Ar, N2, or CO and characterised by its i.r. spectrum.Under these conditions it dissociates under the action of radiation having wavelengths close to 500 nm to give UF5; OCCl radical and OCClF are also formed on photolysis in a solid CO matrix, whereas a species believed to be U2F11 is formed on photolysis in a solid N2 matrix.CCl3F solutions of fluoride-rich mixtures of uranium(VI) chloride fluorides have been shown to function as chlorinating, fluorinating, or chlorofluorinating reagents in their reactions with various unsaturated molecules at temperatures low enough to preclude thermal decomposition of the mixed halides ( -60 deg C).
- Downs, Anthony J.,Gardner, Christopher J.
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- Direct conversion of uranium dioxide UO2 to uranium tetrafluoride UF4 using the fluorinated ionic liquid [Bmim][PF6]
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The industrial fluorination of UO2 to UF4 is based on a complex process involving the manipulation of a large amount of HF, a very toxic and corrosive gas. We present here a safer way to accomplish this reaction utilizing ionic liqui
- Joly, Florian,Simon, Pardis,Trivelli, Xavier,Arab, Mehdi,Morel, Bertrand,Solari, Pier Lorenzo,Paul, Jean-Francois,Moisy, Philippe,Volkringer, Christophe
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- REACTION BETWEEN URANIUM HEXAFLUORIDE AND TRIMETHYLSILYLHALIDES.
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Reaction involving 1. 1:1 molar ratios of uranium hexafluoride to either trimethylsilylchloride or trimethylsilylbromide in halocarbon solutions yield beta -UF//5 at room temperature. With 2 mol equivalents of trimethylsilylchloride the product is UF//4.
- Brown,Berry,Holloway,Staunton
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- The reactions of uranium hexafluoride with hydrogen sulfide and with carbon disulfide
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Uranium hexafluoride reacts with hydrogen sulfide at 25° to produce uranium tetrafluoride, sulfur tetrafluoride, and hydrogen fluoride. Uranium hexafluoride reacts with carbon disulfide vapor at 25° to produce uranium tetrafluoride, sulfur tetrafluoride, bistrifluoromethyl disulfide [(CF3)2S2], and bistrifluoromethyl trisulfide [(CF3)2S3], and at elevated temperatures the reaction also produces sulfur hexafluoride and tetrafluoromethane, CF4. When uranium hexafluoride vapor reacts with carbon disulfide vapor at 25° in the presence of helium as a diluent, the favored perfluoroalkyl product is bistrifluoromethyl trisulfide. Uranium hexafluoride is compared with other metal fluorides with respect to their reactions with carbon disulfide.
- Trevorrow,Fischer, Jack,Gunther
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- Synthesis of UF4 and ThF4 by HF gas fluorination and re-determination of the UF4 melting point
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Basic thermodynamic and electrochemical data of pure actinide fluorides and their mixtures are required for the design and safety assessment of any presently studied molten salt reactor concept based on molten fluoride salt fuel. Since the actinide fluorides are usually not produced commercially, they have to be prepared from the available input materials, typically oxides. In this work, a specially designed facility for synthesis of pure actinide fluorides using pure HF gas is described, as well as a complete procedure of synthesis and characterisation of pure UF4 and ThF4. The fluorination installation consists of a glove box kept under a purified argon atmosphere, a high temperature horizontal fluorination reactor and a HF supply gas line connected to the glove box. The fluorides were synthesised from high specific surface oxides prepared from the respective oxalates by low temperature calcination. The fluorination was partly stationary and partly in a HF gas flow, based on a heterogeneous powder-gas reaction at high temperatures. The products were characterised by X-ray diffraction and differential scanning calorimetry, which confirmed high purity products obtained by this method. Moreover, the melting point of UF4 was revised using a pure sample and a new value is suggested.
- Sou?ek, Pavel,Bene?, Ond?ej,Claux, Benoit,Capelli, Elisa,Ougier, Michel,Tyrpekl, Václav,Vigier, Jean-Francois,Konings, Rudy J.M.
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- The 5f2→5f16d1 absorption spectrum of Cs2GeF6:U4+ crystals: A quantum chemical and experimental study
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Single crystals of U4+-doped Cs2GeF6 with 1% U4+ concentration have been obtained by the modified Bridgman-Stockbarger method in spite of the large difference in ionic radii between Ge4+ and U4+ in octahedral coordination. Their UV absorption spectrum has been recorded at 7 K, between 190 and 350 nm; it consists of a first broad and intense band peaking at about 38 000 cm -1 followed by a number of broad bands of lower intensity from 39 000 to 45 000 cm-1. None of the bands observed shows appreciable fine vibronic structure, so that the energies of experimental electronic origins cannot be deduced and the assignment of the experimental spectrum using empirical methods based on crystal field theory cannot be attempted. Alternatively, the profile of the absorption spectrum has been obtained theoretically using the U-F bond lengths and totally symmetric vibrational frequencies of the ground 5f2 - 1A1g and 5f 16d(t2g)1 - iT1u excited states, their energy differences, and their corresponding electric dipole transition moments calculated using the relativistic ab initio model potential embedded cluster method. The calculations suggest that the observed bands are associated with the lowest five 5f2 - 1A1g → 5f 16d(t2g)1 - iT1u (i = 1 - 5) dipole allowed electronic origins and their vibrational progressions. In particular, the first broad and intense band peaking at about 38 000 cm-1 can be safely assigned to the 0-0 and 0-1 members of the a1g progression of the 5f2 - 1A1g → 5f16d(t 2g)1 -1T1u-1T1u electronic origin. The electronic structure of all the states with main configurational character 5f2 - 1A1g → 5f16d(t2g) 1 has been calculated as well. The results show that the lowest crystal level of this manifold is 5f2 - 1A1g → 5f16d(t2g)1 -1Eu and lies about 6200 cm-1 above the 5f2 level closest in energy, which amounts to some 11 vibrational quanta. This large energy gap could result in low nonradiative decay and efficient UV emission, which suggest the interest of investigating further this new material as a potential UV solid state laser.
- Ordejon, Belen,Karbowiak, Miroslaw,Seijo, Luis,Barandiaran, Zoila
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- Two- and three-dimensional open-framework uranium arsenates: Synthesis, structure, and characterization
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Hydrothermal reactions between uranium salts and arsenic pentoxlde in the presence of two different amines yielded six new uranium arsenate phases exhibiting open-framework structures, ethylenedlamine (en): [C2N 2H9][(UO2)(AsO4)], I; [C 2N2H10][(UO2)F(HAsO 4)]2-4H2O, II; [C2N 2H9][U2F5(HAsO4)J, III; [C2N2H9][UF2(AsO4)], IV; diethylenetriamine (DETA), [C4N3H16][U 2F3(AsO4)2(HAsO4)], V; and [C4N3H16][U2F 6(AsO4)(HAsO4)], Vl. The structures were determined using single crystal studies, which revealed two- (I, II, V) and three-dimensional (III, IV, Vl) structures for the uranium arsenates. The uranium atom, in these compounds, exhibits considerable variations In the coordination (6 to 9) that appears to have some correlation with the synthetic conditions. The water molecules in [C2N2H 10][(UO2)F(HAsO4)]2-4H2O, II, could be reverslbly removed, and the dehydrated phase, [C2N 2H10][(UO2)F(HAsO4)]2, IIa, was also characterized using single crystal studies. The observation of many mlneralogical structures In the present compounds suggests that the hydrothermal method could successfully replicate the geothermal conditions. As part of this study, we have observed autunite, Ca[(UO2)(PO 4)]2(H2O)11; metavauxite, [Fe(H 2O)6][Al(OH)(H2O)(PO4)] 2, linarite, PbCu(SO4)(OH)2, and tancoite, LiNa2H[Al(PO4)2(OH)], structures. The repeated observation of the secondary building unit, SBU-4, In many of the uranium arsenate structures suggests that these are viable building units. Optical studies on the uranium arsenate compound, [C4N3H 16][U2F6(AsO4)(HAsO4)], Vl, containing uranium In the +4 oxidation state Indicates a blue emission through an upconverslon process. The compound also exhibits antlferromagnetic behavior.
- Rao, V. Koteswara,Bharathi,Prabhu, Ramanath,Chandra, Manabendra,Natarajan, Srinivasan
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- Spectroscopic properties of K5Li2UF10
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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.
- Karbowiak,Gajek,Drozdzyński
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- UF4 and the High-Pressure Polymorph HP-UF4
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A laboratory-scale synthesis of UF4 is presented that utilizes the reduction of UF6 with sulfur in anhydrous hydrogen fluoride. An excess of sulfur can be removed by vacuum sublimation, yielding pure UF4, as shown by powde
- Scheibe, Benjamin,Bruns, J?rn,Heymann, Gunter,Sachs, Malte,Karttunen, Antti J.,Pietzonka, Clemens,Ivlev, Sergei I.,Huppertz, Hubert,Kraus, Florian
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- Actinide-silicon multiradical bonding: Infrared spectra and electronic structures of the Si(μ-X)AnF3 (An = Th, U; X = H, F) molecules
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We report a series of Si(μ-X)AnF3 (An = Th, U; X = H, F) complexes with silicon-actinide(IV) single bonds and unexpected multiradical features that form rare triplet silylenes. These bridged molecules have been prepared in microscopic scale through reactions of laser-ablated uranium and thorium atoms with silicon fluorides and identified from infrared spectra in argon and neon matrixes and relativistic quantum chemical calculations. Similar neon matrix experiments for the reactions of uranium with CF4 and CHF3 were carried out for comparison. Our density functional theory calculations show that the Si-U single-bonded species Si(μ-X)UF3 (X = H, F) with U(IV) oxidation state and the quasi-agostic bridge ligand of H or F are most stable among all the isomers, whereas the naively anticipated triple-bonded species XSii - UF3 with U(VI) oxidation state and the double-bonded species XSi?=?UF3 with U(V) oxidation state lie markedly higher in energy. Similar thorium products from reactions with XSiF3 are also found to prefer the Si(μ-X)ThF3 structures with Si-Th single bonds and bridged H or F ligands. High level ab initio wave function theory calculations with the CCSD(T) and CASPT2 methods confirm that the ground states are quintet for Si(μ-X)UF3 and triplet for Si(μ-X)ThF3 with two unpaired electrons on the silylene group. These silicon-bearing molecules as the lowest-energy isomer of XSiAnF3 represent the first silicon-actinide systems with unusual triplet silylenes and Si-An single bonds with multiradical character. They are in dramatic contrast to the uranium-carbon analogs, XCi - UF3, which form triple-bonded singlet ground states with C3v symmetry. The calculated vibrational frequencies of the Si(μ-X)AnF3 complexes agree well with experimental observations. These results accentuate the critical difference of chemical bonding of 3p- and 2p-row main-group elements with actinides. The Lewis electron-pair model and the octet rule break down for these silicon compounds.
- Hu, Han-Shi,Wei, Fan,Wang, Xuefeng,Andrews, Lester,Li, Jun
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- Preparation and properties of several ammonium uranium(IV) and ammonium plutonium(IV) fluorides
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A series of anhydrous fluoride complexes is formed between NH4F and actinide tetrafluorides. Compounds with NH4F : MF4 (M = U or Pu) mole ratios of 4:1, 2:1, 7:6, 1: 1, and 1:3 were prepared by reaction of stoichionictric quantities in sealed tubes or by gravimetric arrests during NH4F distillation. X-Ray powder diffraction data are presented. Corresponding U(IV) and Pu(IV) compounds are isostructural. The 7NH4F·6MF4 compounds are rhombohedral, a0 = 9.55 and 9.42 A?., α = 107.4° and 107.4° for M = U and Pu, respectively. A method of chemical analysis for NH4, U, and F on a single sample was developed using pyrohydrolysis, ion exchange, and volumetric techniques.
- Benz,Douglass,Kruse,Penneman
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- Solubility of UF4, ThF4, and CeF3 in a LiF-NaF-KF melt
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The solubility of UF4, ThF4, and CeF3 in fluoride melt of the composition 45 mol % LiF-12 mol % NaF-43 mol % KF in the temperature interval 773-973 K was determined. The solubility of the fluorides increases with an increase in the melt temperature. The CeF3 solubility in the LiF-NaF-KF system is high: 19.9 mol % at 923 K and 23.3 mol % at 973 K. Experimental data on the solubility of CeF3 (PuF 3 imitator) were compared to the calculated data on the PuF 3 solubility in the LiF-NaF-KF melt. The results showed that CeF3 can be considered as PuF3 imitator in FLINAK melt.
- Seregin,Parshin,Kuznetsov,Ponomarev,Mel'Nikov,Mikhalichenko,Rzheutskii,Manuilov
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- Standard enthalpies of formation of uranium compounds VII. UF3 and UF4 (by solution calorimetry)
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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.
- Cordfunke, E. H. P.,Ouweltjes, W.
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- Vaporization behaviour of uranium tetrafluoride
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The vapour pressure of solid and liquid UF4 has been measured in the temperature range 1169 to 1307 K and 1312 to 1427 K respectively, by both transpiration and evaporation-temperature methods.The vapour pressures obtained by the two methods agree well an
- Nagarajan, K.,Bhupathy, M.,Prasad, Rajendra,Singh, Ziley,Venugopal, V.,Sood, D. D.
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- Isotope effect in photoreduction of 18O-enriched UO 2F2 in an isopropanol solution
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The behavior of the [16O-U-16O]2+, [ 16O-U-18O]2+, and [18O-U- 18O]2+ isotopic species in uranyl fluoride complexes was studied in isopropanol under pulsed
- Gorshkov,Izosimov,Kolychev,Smirnov,Firsin
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- Preparation and Characterization of U2O2F7
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Reaction of UO2F2 with UF5 at 400 deg C under UF6-pressure of 3 atm followed by evaporation of excess UF5 has yielded a greenish white residue.Its X-ray diffraction pattern and infrared spectrum are sufficiently unique to establish that this material is a true compound.Its chemical formula has been shown to be U2O2F7, on the grounds of chemical analysis and thermal decomposition.The oxygen content was determined directly by means of 18O isotopic dilution method based on the combustion of the samples with BrF5.
- Asada, Kameo,Ema, Keiko,Iwai, Takashi
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- Facile Syntheses of pure Uranium(III) Halides: UF3, UCl3, UBr3, and UI3
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Herein we describe a convenient lab scale synthesis for pure and solvent-free binary uranium(III) halides UCl3, UBr3, and UI3. This is achieved by the reduction of the respective uranium(IV) halides with elemental silicon in borosilicate ampoules at moderate temperature. The silicon tetrahalides SiX4 formed as a side product are utilized for the removal of excess starting material via a chemical vapor transport reaction. The syntheses introduced herein avoid the need for pure metallic uranium and are based on uranium(IV) halides synthesized from UO2 and the respective aluminum halides and purified by chemical vapor transport. These uranium(III) halides are obtained in single crystalline form. A similar reaction yields UF3 as a microcrystalline powder. However, no beneficial transport reaction occurs with this halide. Also, a higher temperature has to be applied and steel ampoules have to be used. The identities and purity of the products were checked by powder X-ray diffraction as well as IR spectroscopy. The synthesis of UI3 enabled its crystal structure determination on single crystals for the first time. UI3 crystallizes in the PuBr3 structure type with space group type Cmcm and a = 4.3208(9), b = 13.923(3), c = 9.923(2) ?, V = 596.9(2) ?3, and Z = 4 at T = 100 K.
- Rudel, Stefan S.,Deubner, H. Lars,Scheibe, Benjamin,Conrad, Matthias,Kraus, Florian
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p. 323 - 329
(2018/04/05)
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- Formation and characterization of HUF and DUF in solid argon
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Reactions of laser-ablated U atoms with HF and DF in condensing and solid rare gas produce HUF and DUF as the major new products based on close agreement between observed and calculated vibrational frequencies and deuterium shifts for U-H and U-F stretchi
- Vent-Schmidt, Thomas,Hunt, Rodney Dale,Andrews, Lester,Riedel, Sebastian
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p. 3863 - 3865
(2013/07/25)
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- As≡UF3 molecule with a weak triple bond to uranium
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After reactions of uranium atoms with NF3 and PF3 to form the N≡UF3 and P≡UF3 molecules, the analogous reaction with AsF3 produced the novel terminal arsenide As≡UF3. This first molecule wi
- Andrews, Lester,Wang, Xuefeng,Roos, Bjoern O.
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p. 6594 - 6598
(2009/10/30)
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- Enthalpies of Formation of Manganese Di- and Trifluorides
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Temperature dependence of saturation vapor pressures of MnF2 and MnF3 and equilibrium constants for the reaction MnF2(k) + UF6(g) = MnF3(k) + UF5(g) are determined by the effusion method combined with mass spectrometry analysis of the gas phase. Enthalpies of sublimation of MnF2 and MnF3and the enthalpy of the reaction are calculated by the third law to be 295.5+-0.3, 266.8+-0.4, and 33.9+-0.4 kJ/mol, respectively, at 0 K. Base d on the results obtained and data in the literature, the enthalpies of formation of gaseous MnF2 and MnF3, and crystalline MnF3 at 0 K are taken to be -558.7+-5.0, -784.5+-6.0, and -1048.8+-6.0 kJ/mol, respectively.
- Nikitin, M. I.,Rakov, E. G.,Tsirel'nikov, V. I.,Khaustov, S. V.
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p. 1039 - 1042
(2008/10/08)
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- Matrix IR spectra of the products from F2, ClF, and Cl2 reactions with pulsed-laser evaporated uranium atoms
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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.
- Hunt, Rodney D.,Thompson, Craig,Hassanzadeh, Parviz,Andrews, Lester
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p. 388 - 391
(2008/10/08)
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- Kinetics of the Uranium Hexafluoride Reaction with Hydrogen Chloride in the Gas Phase
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A decrease in the concentration of gaseous uranium hexafluoride with time in the reaction with hydrogen chloride at near-room temperatures was studied by IR spectroscopy.The process is a first-order reaction in both UF6 and HCl and has an activation energy of 7.6+/-0.7 kcal/mol.A characteristic feature of the kinetics is an inversely proportional dependence of the effective rate constant on the initial UF6 pressure.
- Ezubchenko, A. N.,Ilyukhin, A. I.,Merzlyakov, A. V.
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p. 1942 - 1944
(2007/10/02)
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- Reactions of aluminum with uranium fluorides and oxyfluorides
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Every 30 to 40 million, or so, operating hours a destructive reaction is observed in one of the approximately 4000 large compressors that move UF6 through the gaseous diffusion plants. Despite its infrequency, the reaction can be costly in terms of equipment and time. Laboratory experiments reveal that the presence of moderate pressures of UF6 actually cools heated aluminum, although thermodynamic calculations indicate the potential for a 3000-4000°C temperature rise. Within a narrow and rather low (6 or UO2F2. 1. An initiating source of heat must be provided. 2. The film protecting the aluminum must be breached. 3. Reaction products must not be allowed to build up and smother the reaction.
- Leitnaker,Nichols,Lankford
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p. 271 - 291
(2008/10/08)
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- Thermochemical quantities for gas-phase iron, uranium, and molybdenum fluorides, and their negative ions
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Ion-to-molecule equilibria among gaseous iron, uranium, and molybdenum fluorides, and their negative ions, have been studied by Knudsen-cell mass spectrometry with the help of a combined ion source.On the basis of thermochemical quantities, derived by third-law analysis and from the literature for enthalpies of formation of gaseous species, electron affinities have been calculated for a number of molecules: FeF3, (349 +/- 13) kJ*mol-1; UF5, (361 +/- 21) kJ*mol-1; UF6, (488 +/- 19) kJ*mol-1; MoF5, (335 +/- 17) kJ*mol-1; MoF6, (369 +/- 18) kJ*mol-1; Mo2F9, (350 +/- 40) kJ*mol-1; and Mo2F10, (363 +/- 25) kJ*mol-1.
- Borshchevskii, A. Ya.,Boltalina, O. V.,Sorokin, I. D.,Sidorov, L. N.
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p. 523 - 538
(2007/10/02)
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- Synthesis and characterization of a new uranium(V) compound: H3O+UF6-
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The reaction of equimolar amounts of UF5 and H2O in hydrogen fluoride results in the partial dissolution of UF5, yielding a blue-green solution from which the new salt oxonium hexafluorouranate(V) (H3O+UF6-) could be isolated as a green crystalline solid. Calorimetric measurements showed H3O+UF6- to decompose at about 68°C and its heat of formation to be equal to -628 ± 2 kcal mol-1. Its ionic nature in the solid state and in HF solutions was demonstrated from vibrational and electronic spectra. The electronic spectrum is closely similar to those of LiUF6, NaUF6, and CsUF6 and differs from those of RbUF6 and KUF6. This adduct shows a strong ESR signal, with g = -0.78 ± 0.10, characteristic of UF6- salts. Based on its x-ray powder diffraction pattern, H3O+UF6- is cubic with a = 5.2229 ± 0.0005 A?.
- Masson,Desmoulin,Charpin,Bougon
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p. 2529 - 2531
(2008/10/08)
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- Interaction of uranium and its alloys with alkali metal fluorides
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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
- NOVOSELOV GP,KASHCHEEV IN,DOGAEV YUD
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- Hydrazinium heptafluorouranate(V). Preparation, properties, and thermal decomposition
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The new compound, hydrazinium heptafluorouranate(V), was prepared at 0° by the reaction of hydrazinium difluoride and uranium hexafluoride both in anhydrous hydrogen fluoride and in carbon tetrachloride. The magnetic moment of the yellowish compound at 0° is 1.66 BM. X-Ray powder diffraction data are given. The thermal decomposition of the compound in an inert atmosphere proceeds as follows: (Chemical Equation Presented) A detailed discussion of this thermal decomposition is given.
- Frlec,Br?i?,Slivnik
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p. 542 - 546
(2008/10/08)
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- Reactivity of transition metal fluorides. II. Uranium hexafluoride
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Reactions have been studied between uranium hexafluoride and a series of lower fluorides of other elements. The study has also included reaction with a wide range of covalent chlorides. The reactivity of uranium hexafluoride is compared with that of the higher fluorides of d-transition elements, chromium, molybdenum, and tungsten, and considered in the light of uranium as an f-transition element.
- O'Donnell,Stewart,Wilson
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p. 1438 - 1441
(2008/10/08)
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