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In the frame of a potential contact of MOX fuels with the Na coolant in fast breeder reactors, the chemistry and charge distributions in α-Na2UO4, Na3NpO4, α-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 are investigated by XANES spectroscopy at the U-L3, Np-L3, and Pu-L3 edges.

The structures of the title compounds are determined by Rietveld refinement of powder XRD data.

The electronic structure and ground-state molecular properties of neutral Th and U tetracarbides were investigated by relativistic multireference calculations using complete active space self-consistent field/multiconfiguration second-order perturbation theory (CASSCF/CASPT2) with an all-electron basis set as well as by density functional theory (B3LYP) in conjunction with relativistic pseudopotentials. The former calculations were extended with complete active space state interaction (CASSI) calculations accounting for spin–orbit coupling. The four carbon atoms can be arranged in various forms around the actinide atom to result in ten structural isomers found altogether in our study. The electronic ground state in both molecules corresponds to a planar fan-type structure of C2v symmetry, in which the actinide atom is connected to a bent C4 moiety. Three structures arise from various arrangements of C2 moieties around the Th and U, whereas six isomers contain a C3 moiety and a lone C bonded to the actinide. The latter CAnC3-type structures are very high-energy structures (over 200 kJ mol–1 with respect to the ground state). The bonding characteristics in the most relevant structures were analysed on the basis of the valence molecular orbitals and the natural bond orbital method. We evaluated and interpreted the vibrational and electronic spectra. The present computed data for UC4 suggest a revision of the assignment of a previously observed IR absorption band to a different isomer.

BaTh(PO4)2 is synthesized from a gel obtained from aqueous solutions of Th(NO3)4, Ba(NO3)2, and NH4H2PO4 by annealing at 1250 °C (72 h).

The new title compound is prepared by solid state reaction of 237NpO2, Sr(NO3)2, and excess (NH4)2HPO4 (argon; 1.

The present paper reports the results of an investigation of the IR spectra of WCl 6 in the gas phase, as well as in CCl 4 solution. These data enable us to calculate the thermodynamic functions of WCl 6 (g) with higher precision

The IR and Raman spectra of gaseous and liquid tetraethoxysilane, Si(OC2H5)4, have been recorded and a complete assignment has been made. A structure for gaseous tetraethoxysilane has been proposed based upon S4 symmetry as in tetramethoxysilane and tetramethoxymethane. Thermodynamic functions of gaseous tetraethoxysilane have been calculated from the moment of inertia, derived from this structure, and the assigned vibrational frequencies.

The vibrational spectrum of the vapor above NbF5(s) in the 300 to 350 K temperature range has been studied by infrared spectroscopy. The number of frequencies in the Nb-F stretching region indicates that a polymeric species predominates in the temperature range of the experiments, but it is not possible to differentiate between di- and trimeric species. A thermodynamic analysis of available vapor pressure measurements strongly supports the presence of dimeric (NbF5)2 under the conditions of the experiments. From this analysis recommended data for the thermodynamic properties of gaseous (NbF5)2 and NbF5 are derived.

The enthalpy increment of solid and liquid PbI2 have been measured by drop calorimetry from 528 to 763 K and the X-ray diffraction pattern has been recorded from 300 to 633 K. The calorimetric data show evidence for a reversible transition at ∼ 580 K, the enthalpy difference between the two phases being small, 339 J mol−1. The X-ray diffraction results show a transition of the 2H to the 4H polytype at ∼ 440 K, for which the reverse reaction is not observed. The melting point of PbI2 has been found at (679 ± 1) K by DSC, the enthalpy of fusion was obtained as ΔfusH° = 23471 J mol−1 from the enthalpy increments of the solid and liquid phase.

The molecular structure of SbI3 and BiI3 have been studied by gas-phase electron diffraction and infrared spectroscopy, BiI3 has been studied by electron diffraction, and SbI3 has been studied by infrared spectroscopy for the first time. Both molecules are pyramidal (C3v symmetry), and their geometries are characterized by the following bond lengths (rg) and bond angles (∠α): Sb−I 2.721 ± 0.005 A, I−Sb−I 99.0 ± 0.3°, Bi−I 2.807 ± 0.006 A, and I−Bi−I 99.5 ± 0.3°. Three of the four normal modes of vibration were observed for both molecules: SbI3, ν2 = 74.4 cm-1, ν3 = 193.6 cm-1, and ν4 = 54.6 cm-1; BiI3, ν2 = 59.7 cm-1, ν3 = 163.5 cm-1, and ν4 = 47.0 cm-1. A joint electron diffraction/vibrational spectroscopic analysis was also carried out, from which the harmonic equilibrium geometries were estimated. Force field parameters from a normal coordinate analysis are reported for both molecules.

Physico-chemical experiments are reviewed and the thermodynamic properties of solid and gaseous zirconium halides of the general formula ZrX n (X = F, Cl, Br, I; n = 1–4) are evaluated and, where necessary, estimated by analogy with other metal halide systems. Thermodynamic key values at 298.15 K and heat capacity equations are tabulated up to 1500 K for the solid phase and 3000 K for the gas phase.

This work is a critical review of the chemical–physical properties of the fluoride salts of interest in the Molten Salt Reactor project. In total five salt compositions are discussed. Two of them are choices for coolant applications (based on LiF–BeF 2 and NaF–NaBF 4 systems) one is considered as a heat transfer salt (LiF–NaF–KF system) whereas the other two are the main candidates for the fuels in non-moderated breeder and thermal breeder reactors, respectively (LiF–ThF 4 and LiF–BeF 2 –ThF 4 systems). For all the systems the phase diagrams are presented with the emphasis on the melting behaviour and the vapour pressure. Heat capacity, density, viscosity and thermal conductivity, as well as the solubility for actinides in case of the fuels are presented also.

The chemistry of phosphates of barium and tetravalent cations [BaM IV (PO4)2] is reviewed. Such phosphates crystallise in the C2/m space group for M IV ¼ Ti, Zr, Hf, Ge, Sn, and Mo, and in the P21/n space group for BaTh(PO4)2. The existence of BaM IV (PO4)2 in which M IV ¼ Pb, Ce, and U is further evaluated. Several aspects, such as phase transitions in the compounds with yavapaiite structure, solid solutions of BaM IV (PO4)2 compounds and practical applications are briefly discussed.

In this work the three binary phase diagrams LiF–ZrF 4 , BeF 2 –ZrF 4 and UF 4 –ZrF 4 were thermodynamically assessed. The three ternary phase diagrams LiF–BeF 2 –ZrF 4 , BeF 2 –ZrF 4 –UF 4 and LiF–ZrF 4 –UF 4 were approximated on the basis of binary data. A pseudo-ternary LiF–BeF 2 –ZrF 4 system with constant amount of UF 4 set to 0.83 mol% was calculated as well, typical for molten salt reactor fuel. Based on this diagram a suggestion for the composition of the fuel in this system was made.

We have studied the structural evolution of monoclinic BaZr(PO4)2 during heating up to 835 K by Raman spectroscopy. In agreement with previous studies we found a first-order phase transition at about 730 K during heating while upon cooling the reverse transition occurs at 705 K. However, some disagreement about the crystal structure of the high-temperature polymorph occurs in the literature. While the space group has not yet been determined, the X-ray diffraction pattern of the high-temperature phase has been indexed on either an orthorhombic or a hexagonal unit cell. We found that the number of Raman active internal PO4 vibrational modes decrease from nine to six during the transition. A group theoretical survey through all orthorhombic, trigonal, and hexagonal factor groups revealed that the observed number of vibrations would only be consistent with the Ba and Zr atoms located at a D 3 d ( 3 ¯ m ) site, the P and two O atoms at a C3v(3m), and six O atoms at a Cs(m) site in the D3d factor group. Based on our Raman data, the space group of the high-temperature polymorph is thus either D 3 d 1 ( P 3 ¯ 1 m ) , D 3 d 3 ( P 3 ¯ m 1 ) , or D 3 d 5 ( R 3 ¯ m ) .

High-temperature heat capacity and thermal diffusivity of neodymium zirconate (Nd 2 Zr 2 O 7 ) were measured by differential scanning calorimetry and laser flash, respectively. Measurements were made on pellets with the pyrochlore structure ( a =1.07 nm) that were fabricated from milled beads obtained by gel supported precipitation. The thermal conductivity, calculated from the measured heat capacity and thermal diffusivity, was lower than that for ZrO 2 stabilised in its cubic structure. These results show that the pyrochlore-type zirconate can be used as an inert matrix for minor actinides transmutation, but only in a composite form.