Formation-decomposition equilibrium of the NpO<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>·UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> complex in chloride melts

The absorption spectra of the NpO ₂ ⁺ (5f ²) ion were examined in the region of the 3H ₅ ← ³ H ₄ magnetic dipole transition (1530–1760 nm) for series of melts with the UO ₂ ²⁺ concentration varied in the opposite directions: (1) NaCl-2CsCl eutectic melt with growing additions of the Cs₂UO₂Cl₄ complex salt and (2) Cs₂UO₂Cl₄ melt with growing additions of the NaCl-2CsCl mixture. Measurements of the integrated intensities of the bands belonging to the NpO ₂ ⁺ ·UO ₂ ²⁺ complex and unbound NpO ₂ ⁺ throughout the UO ₂ ²⁺ concentration range examined (up to 4.4 M in neat Cs₂UO₂Cl₄ melt) and processing of the data obtained in terms of the mass action law showed that the formation-decomposition reaction of the cation-cation complex can be described adequately only using the equation of reaction in the form NpO₂Cl ₄ ^3? + UO₂Cl ₄ ^2? ? {Cl₄ONpO?UO₂Cl₃}^4? = Cl^? (with the equilibrium constant of 1.3±0.1). Thus, the formation of the cationcation complex should be treated as replacement of chloride ion in the equatorial plane of uranyl(VI) by neptunyl(V), rather than as simple addition of UO ₂ ²⁺ to NpO ₂ ⁺ . The reverse reaction, decomposition of the cation-cation complex, consists essentially in replacement of neptunyl(V) by chloride ion.     

NpO 2 + -UO 2 2+ cation-cation interaction in NaCl-KCl-CsCl and LiCl-KCl-CsCl eutectic melts

Absorption spectra of the NpO ₂ ⁺ ion in UO ₂ ²⁺ -containing NaCl-KCl-CsCl (0.300:0.245:0.455) and LiCl-KCl-CsCl (0.575:0.165:0.260) eutectic melts in the region of the 5f-5f transitions, 700–2000 nm, were studied at 650 and 500°C, respectively. Processing of the spectra allowed the previously discovered phenomenon, cation-cation interaction of actinides in melts, to be interpreted for the first time in terms of the mass action law. It was shown that, at the concentrations of the interacting components studied (C _Np = 0.2 M and C _U = 0.1–2 M), a 1: 1 NpO ₂ ⁺ ·UO ₂ ²⁺ cation-cation complex is formed. Its concentration stability constant was estimated at 0.06(6) and 0.11 1 mol^?1 for the NaCl-KCl-CsCl and LiCl-KCl-CsCl systems, respectively.     

Synthesis and Crystal Structure of Cs4[UO2(CO3)3]

Light green transparent crystals of Cs₄[UO₂(CO₃)₃] were prepared by evaporation from aqueous solutions. The crystal structure was refined to R ₁ = 0.039 (wR ₂ = 0.081) for 2311 reflections with |Fhkl| 4|Fhkl|. Monoclinic system, space group C2/c, a = 11.5131(9), b = 9.6037(8), c = 12.9177(10) Å, = 93.767(2)°, V = 1425.2(2) ų. The structure of Cs4[UO2(CO3)3] consists of isolated complex ions [UO₂(CO₃)₃]^{4 -} formed by uranyl cation UO₂ ^{2 +} and three CO₃ ^{2 -} groups. The equatorial planes of the [UO₂(CO₃)₃]^{4 -} ions are approximately parallel to the (201) plane. The nine-coordinate Cs⁺ cations are located between the complex anions. The compound is isostructural with M4[UO2(CO3)3] with M = K, NH₄, and Tl, but not isostructural with Na₄[UO₂(CO₃)₃].     

Standard enthalpies of formation of gaseous thorium,uranium, and plutonium oxides

Recently available spectroscopic data have been used to derive new values for the enthalpies of formation at 298.15 K of gaseous ThO, ThO₂, UO, UO₂, UO₃, and PuO, and PuO₂. These new values of H _f ⁰ (298.15 K) are in good agreement with previously recommended values for UO, UO₂, and PuO, but not for the other molecules. Inconsistencies among evaluated thermodynamic data have been resolved for ThO (g) and UO₃ (g). Recommended values are derived for PuO₂ (g) and ThO₂ (g); however, additional experimental work on these molecules is needed.     

Relationship between thermal conductivity,speed of sound,and isobaric heat capacity of liquids

Using two liquids-water and toluene — as an example, the author determines the dependence of the coefficient of thermal conductivity on the speed of sound and isobaric molar heat capacity for high state parameters.Notation coefficient of thermal conductivity - u speed of sound - _S same for a saturated liquid - c isobaric molar heat capacity - density - p_s same, for a saturated liquid - p pressure - p_s same, for a saturated liquid - R gas constant - T absolute temperature - x coefficient of thermal activity - x _s same, for a saturated liquid - L, constants in Eqs. (1) and (2) Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 2, pp. 311–314, August, 1980.     

Crystal Structure of U(VI) Peroxo Complex with Triphenylphosphine Oxide {(UO2)2O2[OP(C6H5)3]6}(ClO4)2

The peroxo complex {(UO₂)₂O₂[OP(C₆H₅)₃]₆}(ClO₄)₂ was synthesized, and its crystal structure was determined [triclinic unit cell: a = 10.523(2), b = 16.242(3), c = 16.978(3) Å, = 65.79(3)°, = 85.06(3)°, = 77.14(3)°, space group P-1, Z = 1, V = 2580.1(9) ų, d _{c a l c} = 2.789 g cm^{- 3}; CAD4, MoK , graphite monochromator, direct method, R ₁ = 0.0368 for 3115 observed reflections, wR ₂ = 0.1107 for 4403 unique reflections, 622 refined parameters]. {(UO₂)₂O₂[OP(C₆H₅)₃]₆}(ClO₄)₂ has monomeric structure and consists of the complex cations {(UO₂)₂O₂[OP(C₆H₅)₃]₆}^{2 +} and ClO₄ ^- anions. The uranium atom has a pentagonal-bipyramidal oxygen surrounding (CN 7). Uranyl groups UO₂ ^{2 +} are linear and symmetrical, the U = O bond lengths are 1.780(8) and 1.787(8) Å, the O(1) = U = O(2) bond angles are 178.7(4) Å. The equatorial planes of bipyramids are formed by oxygen atoms of three TPPO molecules [U-O_{T P P O} 2.352(8)-2.368(7) Å, average 2.362 Å] and peroxo group O₂ ^{2 -} [U-O_{p e r} 2.285(8) and 2.323(8) Å, average 2.305 Å]. Two pentagonal bipyramids sharing the common edge O(3)-O(3)^(a) form the centrosymmetrical peroxo-bridged diuranyl complex {(UO₂)₂O₂[OP(C₆H₅)₃]₆}^{2 +} with the [UO₂O₂UO₂]^{2 +} core. The length of the O(3)-O(3)^{( 9a )} edge is 1.426(15) Å.     

Synthesis and crystal structure of double Np(V) cesium oxalate CsNpO2C2O4 · nH2O

An X-ray diffraction study of CsNpO₂C₂O₄ · nH₂O was carried out. The structure consists of NpO ₂ ⁺ and Cs⁺ cations, oxalate anions, and water molecules. Dioxo cations are combined by cation-cation interaction into cyclic trimer in which each NpO ₂ ⁺ cation act as monodentate ligand. The coordination polyhedron of the Np(V) atom is a pentagonal bipyramid. The similarity of the structures of MNpO₂C₂O₄ · nH₂O (M = NH₄, Cs) based on cyclic trimers combined by oxalate ions into a three-dimensional framework was confirmed. Original Russian Text I.A. Charushnikova, N.N. Krot, I.N. Polyakova, 2006, published in Radiokhimiya, 2006, Vol. 48, No. 3, pp. 202–204.     

High-Pressure Phase Transitions of M2O5(M = V, Nb, Ta) and Thermal Stability of New Polymorphs

The stability regions of various M₂O₅(M = V, Nb, Ta) polymorphs were studied by quenching samples from 600–1300°C at pressures in the range 5.0–8.0 GPa. Above 7.0 GPa, Nb₂O₅and Ta₂O₅were found to have a new polymorph (Zphase) in which the metal atoms are in sevenfold coordination. In addition, the samples contained the high-pressure polymorph B-M₂O₅ with the rutile-related structure. Differential thermal analysis at atmospheric pressure showed a weak, broad exotherm, indicating that the transformation of Z-M₂O₅into other phases begins at 100–150°C and reaches completion at 400°C in Nb₂O₅and 550°C in Ta₂O₅. At p 8.0 GPa and t> 750°C, a new high-pressure phase B-V₂O₅, isostructural with B-Nb₂O₅, was identified (a= 11.9640(6) Å, b= 4.6986(3) Å, c= 5.3249(3) Å, = 104.338(4)°, V= 290.01 ų, Z= 4, sp. gr. C2/c). At atmospheric pressure, B-V₂O₅transforms into -V₂O₅, with two strong exothermic peaks at 230 and 270°C. Experiments in the pressure range 5.0–8.0 GPa confirmed that the high-pressure phase -V₂O₅has a broad stability region.     

Liquid phosphors POCl3-ZrCl4-235UO 2 2+ -Nd3+

Liquid phosphors POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ and POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ with concentrations of Nd³⁺ and UO ₂ ²⁺ of up to 0.75 and 0.12 M were prepared; the lifetime of the Nd³⁺ luminescence was up to 300 μs. The lifetime of the Nd³⁺ luminescence in POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions decreases with increasing neodymium concentration, and this decrease is more pronounced than that in POCl₃-ZrCl₄-Nd³⁺ solutions. At molar ratio [ZrCl₄]/[Nd³⁺] < 1.5, the luminescence lifetime sharply decreases with decreasing ZrCl₄ concentration. The intensity of the absorption bands of the OH groups observed in the near-IR range of the absorption spectra of POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions increases with increasing neodymium concentration. Upon storage of POCl₃-ZrCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions for 2 years without contact with the environment, the intensity of the IR absorption bends of the OH groups gradually increases, whereas the lifetime of the Nd³⁺ luminescence decreases to 60-80 μs.     

Influence of Temperature on the Lifetime of Electronically Excited Uranyl Ion: III. Effect of Solvent Deuteration

The shape of the temperature dependences of the lifetime () of electronically excited uranyl ion (UO₂ ^{2 +})*, measured on warming from 77 K of UO2SO4 solutions in H2SO4 + H2O, differs from that measured in D2SO4 + D2O. The lifetime in glassy D2SO4 is shorter than in the polycrystalline sample, whereas in frozen H2SO4 solutions the pattern is opposite. The isotope effect is due both to different course of phase transitions in H2SO4 and D2SO4 solutions and to the fact that the probability of nonradiating deactivation of (UO₂ ^{2 +})* adsorbed on the surface of D₂SO₄·4H₂O crystal hydrate is appreciably lower than that of (UO₂ ^{2 +})* adsorbed on the surface of H₂SO₄·4H₂O and H₂SO₄·6.5H₂O crystal hydrates. We suggest that the increase in due to adsorption appreciably exceeds the concentration quenching of excited uranyl ions in the course of crystallization of deuterated sulfuric acid.     

Fluid Luminophores POCl3-TiCl4-235UO22+-Nd3+: 1. Synthesis and Absorption Spectra

Samples of fluid luminophores POCl₃-TiCl₄-²³⁵UO₂ ²⁺-Nd³⁺ were prepared for the first time. The absorption spectra of POCl₃-TiCl₄ containing Nd³⁺ and UO₂ ²⁺ ions were studied. The IR spectra exhibited absorption bands that were previously unknown for solutions of phosphorus oxychloride. These bands were identified as overtones 1 and 2 of the stretching vibrations of the OH group. The absorption band grows in intensity with increasing both the synthesis time and the titanium tetrachloride concentration in solution. Changes in the uranyl concentration affect the intensity and position of the Nd3+ absorption band maximum, corresponding to the ⁴ I9/2⁴ F3/2 transition.     

Influence of cations on the vibrational spectra and structure of [WO<Subscript>4</Subscript>] complexes in molten tungstates

The vibrational spectra and structure of isolated [WO₄]^2– anions in molten alkali, alkaline-earth, rare-earth, Pb, Bi, Zn, Sc, and Cd tungstates are studied by high-temperature Raman spectroscopy. The degenerate modes of the [WO₄]^2– anion in K-Gd tungstate melts are found to be split, which is interpreted in terms of the symmetry of the cation environment of the [WO₄]^2– anion in the melts. The frequency of the fully symmetric stretching mode (₁) of the [WO₄]^2– group in molten tungstates is examined in relation to the polarizing power P and electronegativity of the cation. The origin of the nonmonotonic variation of ₁ with P and for the tungstate melts studied is discussed.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 4, 2005, pp. 493–502.Original Russian Text Copyright © 2005 by Voronko, Sobol.     

The Density of UO2–ZrO2 Alloys

The density of a UO₂–ZrO₂ melt (atomic ratio U/Zr = 1.528) is experimentally measured by a pycnometric method in the temperature range of 2973–3373 K. The found temperature dependence of density has the form (T) = (7.0 ± 0.01) – (4.5 ± 0.4) × 10^–4 × (T – 2973 K), g/cm³. The temperature dependence measured enables one to calculate the values of the density of UO₂–ZrO₂ melts depending on the temperature and composition for any atomic ratio U/Zr.     

Electron paramagnetic resonance of Cu2+ and VO2+ ions in phosphate glasses

Electron spin resonance (ESR) spectra ofx(CuO · V₂O₅ (1 –x) (Na₂O · P₂O₅) andx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) glasses for 0 x 40 have been studied at the X-band and at 300 K. It is found that forx 5, both Cu²⁺ and VO²⁺ are present, mostly as isolated species. Forx 10, broad resonance lines atg = 2.1524 forx(CuO · V₂O₅) (1 –x) (Na₂O · P₂O₅) and atg = 2.1448 forx(CuO · 2V₂O₅) (1 –x) (Na₂O · P₂O₅) are observed which may be mainly due to dipole-dipole type interaction between transition metal (TM) ions. Spin Hamiltonian parameters of TM ions have been calculated. Optical spectra of the sodium phosphate glasses doped with single TM ions have also been studied. The theoretical optical basicity, A_th, of these doped glasses has been calculated. It is found that for VO²⁺ ionsg ,g and increase whileA ,P and g _|/g decrease with increase in A_th. However, no significant change is observed in the spin Hamiltonian parameters of Cu²⁺ with the change in A_th.     

The growth of non-stoichiometric apatites using the constant composition method

The kinetics of the crystal growth of calcium-deficient hydroxyapatites with different stoichiometry (Ca₅-(HPO₄)(PO₄)₃-(OH)₁-) have been investigated at 37°C using the constant composition method. The growth was performed in solutions supersaturated only with respect to Ca₅(PO₄)₃(OH) (HAp) by inoculating with well-characterized seed crystals. The stoichiometry of the grown apatites was consistent with values of 00.185. The deviation from HAp stoichiometry of the growing apatite increased with increasing supersaturation degree (S). The constant composition method also provides relevant information about the solubility behaviour of the growing phase with a definite composition. From the decrease of the normalized growth rate j with decreasing S, an estimate could be made of the composition of the solution for which the growth ceases. The determined solubility product of the grown apatite (4.28×10^-54 M⁹) was higher than the value obtained by the equilibration of the seed material. The results were interpreted on the basis of differences in crystal lattice perfection.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Preparation and photovoltaic properties of anodically grown Ag2O films

The semiconducting and photovoltaic properties of p-type Ag₂O films grown anodically on silver electrodes were studied, in view of possible applications in solar energy conversion. Films were grown in different alkaline solutions; the best results were obtained for 0.02M Ag₂SO₄ + 0.17M NH₄OH + 5.7 × 10^–3M Ba(OH)₂ saturated with Ag₂O powder, stirred mechanically at room temperature. Film thicknesses of up to 10m were thus obtained for the first time in anodically grown Ag₂O. Photovoltaic spectra taken at 300 K give a bandgap ofEg = 1.42 ± 0.04 eV. Evaporated gold on Ag₂O appears to be ohmic while aluminium and platinum are rectifying. The barrier height of Ag/Ag₂O is 0.90 ± 0.02 eV, that of Al/Ag₂O is 0.93 ± 0.02 eV, and that of platinum 0.94 ± 0.02 eV. The best cells give an open-circuit voltage,V _oc, of over 150 mV, and a short circuit current,I _sc = 100A cm^–2 under 50 mW cm^–2 illumination.     

Crystal Structure of K[UO2(NO3)3] and Some Features of Compounds M[UO2(NO3)3] (M = K,Rb, and Cs)

Greenish-yellow transparent crystals of K[UO₂(NO₃)₃] were prepared from aqueous solutions as by-product in synthesis of potassium chromatouranylates. The crystal structure was solved by the direct methods and refined to R ₁ = 0.037 (wR ₂ = 0.070) for 1452 reflections with |F _hkl| 4|F _hkl|. Mono- clinic system, space group C2/c, a = 13.4877(10), b = 9.5843(7), c = 7.9564(6) Å, = 116.124(2)°, V = 923.45(12) ų. The structure of K[UO₂(NO₃)₃] contains isolated complex ions [UO₂(NO₃)₃]^- whose uranyl groups are aligned parallel to the [-101] plane. The K⁺ cations, coordinated by twelve oxygen atoms, are located between the complex anions. Comparison of the structure with known data on M[UO₂(NO₃)₃] compounds (M = K, Rb, Cs) suggests the possibility of phase transitions due to relatively small displacements of [UO₂(NO₃)₃]^- anions and K⁺ cations, retaining the general structural motif.     

Liquid luminophores POCl3-SiCl4-235UO 2 2+ -Nd3+

Samples of liquid luminophores POCl₃-SiCl₄-Nd³⁺, POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ , and POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ Nd³⁺ were prepared for the first time. The physicochemical properties and absorption spectra of the samples were compared. The solubility of Nd and U(VI) compounds in the POCl₃ SiCl₄ binary solvent was examined. The Nd³⁺ concentration attains a maximum of 0.3 mM when Nd and U(VI) trifluoroacetates are jointly dissolved at the [POCl₃]/[SiCl₄] molar ratio of 6 8. The shapes of the absorption band of the Nd ions at 860–900 nm, corresponding to the ⁴ I _9/2 → ⁴ F _3/2 electronic transition, differ significantly in POCl₃-SiCl₄-Nd³⁺ and POCl₃-SnCl₄-Nd³⁺ solutions, and in POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions the band shape also depends on the type of the Nd and U(VI) compounds introduced. The near-IR region of the absorption spectra of POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ and POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions contains absorption bands of the OH groups. The band intensity is analyzed in relation to the characteristics of the solutions. The Nd³⁺ luminescence lifetime τ in the luminophores synthesized was estimated at 70–20 μs.     

Reduction of U(VI) in laser liquids POCl3-SnCl4-235UO 2 2+ -Nd3+

U(IV) is irreversibly accumulated during synthesis of laser liquids POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ prepared from various initial Nd(III) and U(VI) compounds, irrespective of the way of their introduction. The rate of U(IV) accumulation in POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions increases with increasing UO ₂ ²⁺ and Nd³⁺ concentrations; for laser liquids with the Nd³⁺ luminescence lifetime τ > 150 μs the observed rate constant of U(IV) accumulation by the second-order reaction k ₂[U⁴⁺] is equal to (3 ± 1) × 10^?5 1 mol^?1 s^?1 at T = 380 K. U(IV) is accumulated during storage of POCl₃-SnCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions in hermetically sealed glass cells at room temperature and upon irradiation of solutions by xenon lamp light in the spectral region of UO ₂ ²⁺ absorption. The U(VI) reduction proceeds by chemical and photochemical activation of uranyl with formation of stable U⁴⁺ complexes with dichlorophosphate ions and also with Nd³⁺. Deactivation of the uranyl ion excitation with proton-and chlorine-containing impurities prevents U(VI) reduction.