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International audience; The uranium and plutonium co-conversion process constitutes a continuous subject of interest for MOx fuel fabrication. Among the various routes considered, chemical coprecipitation by the salt effect has been widely investigated regarding its simplicity of integration between the partitioning and purification steps of the PUREX process, and the straightforward recovery of precursors that are easily converted into oxide phases by thermal decomposition. The present study focuses on the coprecipitation behavior of U–Th and U–Pu actinide peroxide mixed systems by examining the precipitation yields and settling properties for nitric acidity in the range of 1 to 3 M and hydrogen peroxide concentration in the range of 4.5 to 7 M. The precipitated solids have been characterized by powder XRD, IR and Raman spectroscopy, laser granulometry and SEM-EDS analyses revealing the synthesis of studtite and actinide(IV) peroxo-nitrates as aggregated particles. The actinide solid phases are uniformly distributed within the filtered cakes. The precursor thermal decomposition results in the formation of oxide phases at low temperature according to a sequential release of water molecules, peroxide ligands and nitrate ions. The calcination step has a limited effect on the morphology of the powders which remain highly divided. The high precipitation rate of actinides makes this chemical route potentially interesting as a co-precipitation process.

International audience; For the understanding of severe accidents in sodium cooled fast reactors (SFR), it is necessary to understand two prototypic accident scenarios such as ULOF (Unprotected Loss of Flow Accident) and UTOP (Unprotected Transient OverPower). As the base knowledge, it is also important to understand high temperature chemical interaction among major core materials such as MOx fuel (MOx: mixed oxide of uranium and plutonium), steel cladding and B4C neutron absorber have to be investigated. This study aims at providing experimental data on phase formation and phase-stability at various temperature and pressure conditions. A first series of samples containing a mixture of B4C and steel were prepared to obtain a homogenous metallic solid. In a second step, these metallic samples were mixed and melted with small UO2 pieces by arc melting. Then these samples underwent a heat treatment at 1900 °C for 1 hour. EDS, EBSD and EPMA analyses were performed to identify the phases formed during the solidification. In addition, thermodynamic calculations were performed for the interpretation of the results, revealing that a carbo-reduction reaction occurs: UO2 + 2 C = 2 CO + U. A significant amount of uranium from the fuel is dissolved in the metallic liquid phase, leading to the formation of mixed borides (UM3B2, UMB4, UM4B, M=Fe,Cr,Ni). In comparison with the UO2/steel interaction, the present results show that the presence of B and C in the melt improves the wetting behaviour of the metallic liquid towards UO2.

International audience; The UMo/Al dispersion fuel in plate form is considered for the conversion of high-performance research reactors in Europe. In the framework of the UMo fuel qualification program, the adequate margin of safety performance by considering several technological solutions associated with the fabrication parameters, such as heat-treatment of the UMo particles, coating with a diffusion barrier material and powder size distribution as some examples. All these parameters, along with the effect of the hot-rolling process were evaluated by means of image processing and detailed microstructural characterizations for fresh samples i.e. prior to irradiation tests. Principle macroscopic features of powder batches include the size and shape distributions and coating surface examinations. Microscale investigations explored both the coating and kernel microstructures as well as the interface layer between them. Finally, nanoscale analyses examined the UMo–coating interface. The extensive stresses associated with the hot-rolling process have a significant impact on the deformation of the UMo kernels and the degradation of the coated film. The UMo kernels mostly lost their spherical shape for faceted and elongated shapes whereas three types of film degradations were identified including cracks, chippings and delamination.

The European Mini-Plate Irradiation Experiment (EMPIrE) aims to test the in-pile behavior of various ZrN coated UMo powder batches, produced using different technological processes. UMo(ZrN) particles are typical core-shell systems taking advantages of a dense fissile material, UMo, with a coated ZrN layer acting as a diffusion barrier. The U-7Mo kernels were produced by centrifugal or rotating electrode atomization processes and the ZrN coating was performed by physical vapor deposition or atomic layer deposition processes. A total of ten batches of UMo(ZrN) powders were examined in the as-obtained state, i.e prior to fuel-plate fabrication and before in-pile irradiation. The present investigation gives a characterization of each powder batch mainly in terms of morphological and microstructural features carried out by means of SEM-EDS, LOM, EPMA, AFM and TEM analyses. Digital image processing using ImageJ software was employed to determine several particle size (major axis, minor axis, Feret’s diameters, and equivalent diameter) and shape (aspect ratio, circularity, convexity and concavity) parameters as well as the ZrN deposited layer thickness. The quality of the ZrN layer was examined in terms of surface roughness, grain structure and aggregated habits. Our characterization results draw a detailed portrait of the UMo(ZrN) powders selected for the EMPIrE experiment and allow a classification of the powder batches which is presented as radar chart (Kiviat diagram).

International audience; Nine new ternary uranium transition metal germanides U3TGe5 with T = V, Cr, Mn, Zr, Nb, Mo, Hf, Ta and W have been discovered, in addition to the previously reported compound for T = Ti. These ten intermetallics adopt the anti-CuHf5Sn3-type of structure (hexagonal, P63/mcm, Z = 2). Scanning electron microscopy images, energy dispersive spectroscopy, differential thermal analyses and X-ray data refinements were employed for chemical, thermal and structural characterizations. For the purest samples, obtained for T = Ti, V and Cr, the investigation of the magnetic and transport properties were analyzed revealing the subsequent influence of the 3d metals on the ground-state properties. Ab initio calculations of the band structure of these three U3TGe5 compounds were performed, showing nested Fermi surface which may be associated to the presence of Dirac cones for the magnetically ordered compounds, i.e. for T = Ti and V.

A novel ternary compound, namely U3Pt12Si4, which is best described by the crystallographic formula U3Pt12+x-ySi4-x-z (x = 0.15, y = 0.23, z = 0.16), has been discovered in the U-Pt-Si phase diagram. It crystallizes in a hexagonal unit cell (P63/mmc space group) with a = 8.7267(1) Å and c = 9.3385(2) Å. Its structure is an ordered variant of the EuMg5.2 type with partial occupancies of the Si 4e and Pt 2b positions and mixed Si/Pt occupancy of the 6g site. Magnetic properties measurements revealed that the compound is a Curie-Weiss paramagnet with an effective magnetic moment μeff = 3.18 μB. Its low temperature specific heat is moderately enhanced (its Sommerfeld coefficient γ is equal to 79(1) mJ molU-1 K-2) and the electrical resistivity exhibits some characteristic features of dense Kondo lattices.

International audience; The phase relations in the binary U-Ga and ternary U-Al-Ga systems were established as an isopleth section and two isothermal sections at 900 K and 1150 K for the whole concentration range, respectively. They were experimentally determined by means of powder and single crystal XRD, SEM-EDS analyses on both as-cast and heat-treated samples and DTA measurements. Both systems were thermodynamically assessed using the Calphad method based on the available data, i.e. phase relations and thermodynamic properties. The new description of the U-Ga phase diagram improves the composition-temperature description for most of invariant reactions. The U-Al-Ga system is characterized by large ternary extensions of the binary phases and the absence of ternary intermediate phase at both 900 K and 1150 K. These experimental results are nicely reproduced by the Calphad assessment, allowing to extract the thermodynamic parameters further used to calculate the liquidus projection and the invariant reactions along with their temperature.

International audience; A novel erbium rich ternary intermetallic compound, Er10Co1+xAl3−x (x = 0.30) has been discovered in the Er–Co–Al ternary system. It crystallizes in a hexagonal ordered variant of the Co2Al5-type in presence of substitutions on two adjacent crystallographic positions. The magnetic behaviour is mainly dominated by an antiferromagnetic ordering observed at TN = 12.7(7) K

U(Mo) particles are obtained by centrifugal atomisation or by mechanical grinding fabrication processes and display microstructures which strongly influence the gas retention efficiency and consequently the behaviour of the fuel. Moreover, during fuel plate fabrication, a partial decomposition of the γ-U(Mo) phase toward the α-U and U2Mo phases can occur and is supposed to influence also the irradiation behaviour of the fuel. In situ X-ray and neutron diffraction experiments have been performed in order to study the γ-U(Mo) phase decomposition for two types of powders produced by the atomisation and the grinding routes. The present study allows assessing differences between these powders, in terms of γ-U(Mo) phase decomposition kinetics and mechanisms.

A novel gadolinium and cobalt based aluminide, namely Gd3Co4+xAl12−x (x = 0.50(3)) is shown to crystallize in the hexagonal Gd3Ru4Al12 structure-type (space-group P63/mmc, a = 8.6830(1) A, c = 9.3164(2) A at room temperature). The investigation of its magnetic properties revealed a reversible ferromagnetic ordering at TC ≈ 40 K but expanding in a wide temperature range, potentially due to the geometrical magnetic frustrations expected in this structure-type. The magnetocaloric properties of this intermetallic, determined from both magnetization and specific heat data, are dominated by a maximum entropy variation of −3.28 J kg−1 K−1 at 39(1) K and an adiabatic temperature change of about 1.5 K extending from 20 to 40 K, highlighting some interest for low temperature applications.

International audience; The phase relations in the ternary U–Ti–Al system were established for the whole concentration range for two temperatures, 923 K and 1123 K. They were derived from quenched samples annealed at 1123 K for about 500 h and at 923 K for about 720 h using X-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopic analysis. Only one ternary phase, the Al-rich compound, UTi2Al20, was found. It forms by a peritectic reaction at 1365(5) K, and remains stable at least down to 923 K. Based on single-crystal structure refinements, it was confirmed that it adopts the CeCr2Al20 structure type (cubic, View the MathML sourceFm3¯d, n°227) with lattice parameter at room temperature, a = 14.634(1) Å. Unlike most of the isotypic aluminides, UTi2Al20 should be regarded as a line compound. At 1123 K, the isothermal section is characterized by the extended homogeneity ranges due to mutual exchange between U and Ti and between Ti and Al in the unary phases, whereas at 923 K, the mutual solubility between U and Ti was found null. Regarding the binary phases, only in the Laves phase, UAl2 (cubic-C15, MgCu2-type) such solubilities were observed with limits of about 2 at% of U by Ti and 5.5 at% of Al by Ti, at 1123 K. For the other binary compounds, the solubility of the third component was found negligible at both temperatures.

International audience; Magnetic susceptibility, magnetization, specific heat, electrical resistivity and thermoelectric power of polycrystalline Ce5CoGe2, CeCoGe and CeCo2Ge2 were studied at temperatures down to 2 K and in magnetic fields up to 5 T. The novel phase Ce5CoGe2 was found to be a ferromagnet with the Curie temperature of about 11 K, which exhibits in the paramagnetic region some features of a dense Kondo system with strong crystal field effect. The re-investigated CeCoGe was found to order antiferromagnetically below 4.6 K, while CeCo2Ge2 is an intermediate-valence system, in agreement with previous reports. The thermoelectric power of the latter compound is large (up to 40 μV/K) and positive in the whole temperature range studied, while in the magnetically ordered systems Ce5CoGe2 and CeCoGe it is mostly negative and distinctly smaller (down to −1.5 and −11 μV/K, respectively).

International audience; In the framework of the development of a low 235U enriched nuclear fuel for material testing reactors, γ-U(Mo)/Al based materials are considered as the most interesting prospect. In the process to optimize their composition, addition to both γ-U(Mo) and Al have been proposed. In this paper, the crystallographic composition of Interaction Layers (ILs) in γ-U(Mo,X)/Al and γ-U(Mo,X)/AlSi7 diffusion couples, with X = Cr, Ti, Zr, heat-treated at 600 °C for 2 h, were studied by micro-X-ray diffraction (μ-XRD). When compared to the U(Mo)/Al and U(Mo)/Al(Si) reference systems, all investigated systems involving either Al or Al(Si) as counterparts show interaction products composed of similar phases and related sequences of phase formation. Only relative thicknesses of sub-layers and relative fractions of intermediate phases are correlated with the nature of the X element in the γ-U(Mo,X) alloy. More generally this work shows that γ-U(Mo)/Al and γ-U(Mo)/Al(Si) ILs are now robustly described down to the micrometer scale.

The necessity for Material Testing Reactors (MTRs) to use a low-enriched uranium (LEU) fuel has leaded to the development of a dense fissile material based on γ-U(Mo) alloys. The designed fuel is a composite material, made of dispersed γ-U(Mo) particles embedded in an Al based matrix. Depending on the nature of the particles obtained with various fabrication processes (centrifugal atomisation or mechanical grinding), noticeable differences about gas retention capabilities and behaviour under irradiation of the fuel are observed [1, 2 ]. Up to now, no precise links between the microstructure of the fuel and its behaviour under irradiation have been established. Several methods of characterisation have then been developed, more particularly, to characterise various types of defects and the γ-U(Mo) phase stability, which are both supposed to influence the gas retention capacities of the fuel [1, [2] , [3] ]. Our method is based on a multi-scale approach, high temperature X-Ray diffraction experiments have first been carried out followed by observations using transmission electron microscopy (TEM). X-Ray diffraction has revealed being a pertinent tool in order to study the kinetic of decomposition of the γ-U(Mo) phase as a function of temperatures and times, for different kind of powders. TEM is also among one of these techniques and allows a microstructure characterisation at a grain size scale. It has required the development of an original protocol set up for producing thin sections from large particles introducing a minimum quantity of defects within the material. This protocol has provided first encouraging results with the observation of dislocations within different kind of U-(Mo) powder particles. Obtained results, in both cases, are also discussed together with the fabrication processes of the studied powders.

The new ternary compound U 3 Fe 4 Ge 4 was prepared by melting the pure metals in the stoichiometric ratio. An ingot of large scale domain was obtained by decreasing the temperature from the liquid state down to 1000 °C over 4 h. Single crystal X-ray diffraction revealed that U 3 Fe 4 Ge 4 crystallizes with the Gd 3 Cu 4 Ge 4 -type of structure, in the orthorhombic space group Immm (no. 71), Z = 2, with unit-cell parameters at room temperature of, a = 4.090(1) A, b = 6.639(1) A and c = 13.702(1) A. The crystal structure is characterized by two U, one Fe and two Ge independent crystallographic positions and can be described as resulting from the condensation by face-sharing and edge-sharing of U(1)Ge6 octahedrons, U(2)Ge6 trigonal prisms and Fe(1)Ge4 tetrahedrons. The electronic properties of this new compound were investigated by means of electrical resistivity, thermopower, ac and dc magnetic susceptibility and 57 Fe Mossbauer spectroscopy. U 3 Fe 4 Ge 4 undergoes a ferromagnetic transition below T C = 17(1) K. The low temperature (4 K) 57 Fe Mossbauer spectra can be well fitted using a model with Fe atoms in a paramagnetic state, suggesting that the magnetic ordering originates from the U sublattice alone.

U(Mo)/Al(Si) diffusion couples are studied to provide a better understanding of the interaction processes between the U(Mo) fuel and the Al(Si) matrix and, more specifically, to determine the molybdenum behaviour in the interaction product, close to the U(Mo) alloy. Micro-computed tomography and micro-X-ray diffraction measurements in transmission mode, coupled with scanning transmission electron microscopy and energy dispersive X-ray spectroscopy analysis show that molybdenum is present in the interaction layer, close to the U(Mo) interface, in an U 4 Mo(Mo x Si 1− x )Si 2 ternary intermediate phase, mixed with the U 3 Si 5 phase. The formation of this Mo-containing phase is accompanied by a Mo depletion process, in the underlying U(Mo) alloy, this depletion leading to a γ-U(Mo) phase local destabilisation. A strong correlation between the Si and the Mo behaviours, in the U(Mo)/Al(Si) system, is thus evidenced.

The existence of the binary compounds Th 3 Pt 4 and U 3 Pt 4 has been established in the course of the reinvestigation of the U-Pt and Th-Pt systems. Their structural and physical properties have been studied for the first time. Both compounds solidify from the melt of the elemental components with the stoichiometric ratio. Rietveld refinements reveal that they both adopt the trigonal Pu 3 Pd 4 structure type ( R 3 ¯ space group) with lattice parameters at room temperature of a = 13.6870(3) A, c = 5.7991(2) A for Th 3 Pt 4 and a = 13.2380(2) A, c = 5.6808(2) A for U 3 Pt 4 . Magnetic and specific heat measurements show that Th 3 Pt 4 behaves as a typical metal; it was further used as phonon analogue of the U-counterpart. U 3 Pt 4 undergoes a ferromagnetic ordering below T C = 6.5(5) K. Its low temperature specific heat is dominated by an enhanced Sommerfeld coefficient (246(2) mJ mol U −1 K −2 ) classifying this phase into the heavy fermion family.

The phase relations in the ternary U-Nb-Al system were established for the whole concentration range for 900 K and 1200 K. They were derived from quenched samples annealed at 900 K for three months and at 1200 K for two months by using x-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopic analyses. The formation of the two ternary phases, UNb 2 Al 20 and U 6 Nb 4 Al 43 was confirmed. Both phases form by peritectic reaction, at 1200(5) K and at 1262(5) K for UNb 2 Al 20 and U 6 Nb 4 Al 43 respectively. Single-crystal structure refinements confirmed that UNb 2 Al 20 adopts the CeCr 2 Al 20 type (cubic, F d 3 ¯ m ) and that U 6 Nb 4 Al 43 crystallizes with the Ho 6 Mo 4 Al 43 type (hexagonal, P 6 3 / mcm ). The isothermal sections are characterized by (i) the extended homogeneity ranges due to mutual exchange between U and Nb and between Nb and Al in the bcc -phases (γU and Nb), at 1200 K, and (ii) a substantial ternary extension with limits of about 6(1) to 10(1) at.% U at 900 K and 1200 K respectively, of the σ-phase (Nb 2 Al, tetragonal, P 4 2 / mnm ). The modeling of these isothermal sections was carried out by the Calphad method. The liquidus projection and the invariant reactions along with their corresponding temperatures were calculated using our optimized database. The electronic properties of both intermediate compounds were measured by means of dc -susceptibility, specific heat and resistivity measurements in the temperature range 2–300 K, revealing for UNb 2 Al 20 enhanced Pauli paramagnetism and complex magnetic features for U 6 Nb 4 Al 43 at low temperature. For the latter compound a composite behavior involving long-and short-range orderings, resulting from intra and inter U dimeric chains along the c -axis is suspected below 12 K.

International audience; The novel intermetallics R3Co4+xAl12-x (R = Tb → Er) crystallize in the hexagonal Gd3Ru4Al12 structure-type where the rare earth atoms form a heavily distorted kagome network. Single crystal X-ray diffraction reveals an unusual 2b substitution site of Co for Al probably driven by steric effects. The four phases order ferromagnetically below 24.0, 17.4, 11.5 and 5.0 K for R = Tb, Dy, Ho and Er, respectively, linearly decreasing with the de Gennes factor of the rare earth. The magnetocaloric properties have been estimated for R = Ho and Er by measuring the magnetization isotherms at various temperatures. The magnetic entropy changes reach maximum values of −12 and −10 J kg−1 K−1 for a magnetic field change from 5 to 0 T. © 2017 Elsevier Ltd

Among the 10 phases reported to exist at 973 K in the Ce-Co-Ge ternary system, a strong dependence of the magnetic and transport properties on the constituent concentration has been evidenced. Close to the Ce-Ge binary axis, the ternary phases exhibit ferromagnetic-like ordering with low TC, while increasing the cobalt concentration leads first to a paramagnetic area, then to an antiferromagnetic one and finally to ferromagnetism with high TC for cobalt and Co-rich binaries. Similarly, electrical resistivity and thermopower measurements evidence a rather metallic behavior for cerium poor phases while an increase in the Ce-content results in an increase of the Kondo-like interactions.

A systematic study on the ternary uranium-iron-antimony was made at 700 and 750°C through powder X-ray diffraction and Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry. The assessed sections confirmed the existence and crystal structure of the binary intermetallic compounds as well as the ternary phase UFeSb2. Moreover it was found that UFeSb2 is part of a solid solution, UFe1-xSb2, stable for 193Fe3-xSb4, crystallizing in the cubic type Y3Au3Sb4 and stable for 22

The isothermal sections of the U-Mo-C ternary system have been established at 1000°C and 1400°C, using powder X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray analysis for the quantification of U and Mo and differential thermal analysis. The main differences between the two sections are the appearance of liquid phase at about 1230°C, due to the peritectic decomposition of γ-UMo, and the peritectoid decompositions of MoC and β’’ Mo2C. No other transformation was detected in this temperature range, especially one involving the two only ternary phases found, UMoC2and U2Mo2C3.

International audience; In the context of radioactive ion beams, fission targets, often based on uranium compounds, have been used for more than 50 years at isotope separator on line facilities. The development of several projects of second generation facilities aiming at intensities two or three orders of magnitude higher than today puts an emphasis on the properties of the uranium fission targets. A study, driven by Institut de Physique Nucléaire d'Orsay (IPNO), has been started within the SPIRAL2 project to try and fully understand the behavior of these targets. In this paper, we have focused on five uranium carbide based targets. We present an off-line method to characterize their fission product release and the results are examined in conjunction with physical characteristics of each material such as the microstructure, the porosity and the chemical composition.

International audience; In this work, an experimental study of the radiance of liquid and solid uranium and plutonium carbides at wavelengths 550 nm ⩽ Î" ⩽ 920 nm is reported. A fast multi-channel spectro-pyrometer has been employed for the radiance measurements of samples heated up to and beyond their melting point by laser irradiation. The melting temperature of uranium monocarbide, soundly established at 2780 K, has been taken as a radiance reference. Based on it, a wavelength-dependence has been obtained for the high-temperature spectral emissivity of some uranium carbides (1 ⩽ C/U ⩽ 2). Similarly, the peritectic temperature of plutonium monocarbide (1900 K) has been used as a reference for plutonium monocarbide and sesquicarbide. The present spectral emissivities of solid uranium and plutonium carbides are close to 0.5 at 650 nm, in agreement with previous literature values. However, their high temperature behaviour, values in the liquid, and carbon-content and wavelength dependencies in the visible-near infrared range have been determined here for the first time. Liquid uranium carbide seems to interact with electromagnetic radiation in a more metallic way than does the solid, whereas a similar effect has not been observed for plutonium carbides. The current emissivity values have also been used to convert the measured radiance spectra into real temperature, and thus perform a thermal analysis of the laser heated samples. Some high-temperature phase boundaries in the systems Uâ€"C and Puâ€"C are shortly discussed on the basis of the current results.

The new compound UCo3-xGex with x = 0.4 was prepared by direct solidification of the corresponding liquid phase, followed by annealing at 973 K. Single crystal X-ray diffraction carried out at room temperature showed that it crystallizes with the hexagonal space group P63/mmc (n°194) and the unit-cell parameters a = 4.890(5) Å and c = 16.405(5) Å. The substitution of Co atoms by germanium atoms in UCo3 (PuNi3 structure type) yields stabilization of the CeNi3 structure. The homogeneity range, evaluated by energy dispersive spectroscopy analysis, extends from x = 0.2(1) to 0.4(1). The electronic properties were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The phase is a Pauli paramagnet and exhibits electrical conductivity characteristic of strongly disordered metals.

The new compounds U{sub 3}Co{sub 12-x}X{sub 4} with X=Si, Ge were prepared by direct solidification of the corresponding liquid phase, followed by subsequent annealing at 1173 K. Single crystal X-ray diffraction carried out at room temperature showed that they crystallize with the hexagonal space group P6{sub 3}/mmc (no.194) and the unit-cell parameters a=8.130(5), c=8.537(5) A and a=8.256(1), c=8.608(1) A for the silicide and germanide, respectively. Their crystal structure derives from the EuMg{sub 5.2} structure type, and is closely related to the Sc{sub 3}Ni{sub 11}Si{sub 4} and Gd{sub 3}Ru{sub 4-x}Al{sub 12+x} types. For the present compounds, no substitution mechanisms have been observed, the partial occupancy of one Co site results from the presence of vacancies, only. The homogeneity ranges, evaluated by energy dispersive spectroscopy analysis, extend from x=0.0(2) to 0.3(2) and from x=0.0(2) to 1.0(2) for U{sub 3}Co{sub 12-x}Si{sub 4} and U{sub 3}Co{sub 12-x}Ge{sub 4}, respectively. The electronic properties of both compounds were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The U{sub 3}Co{sub 12-x}X{sub 4} compounds are both Pauli paramagnets with their electrical resistivity best described as poor metallic or dirty metallic behavior. - Graphical abstract: The crystal structure of the new compounds U{sub 3}Co{sub 12-x}X{submore » 4}, X=Si, Ge is a ternary ordered variant of the EuMg{sub 5.2}-type with a site preference for the 4e position.« less

The solid state phase equilibria in the Ce–Co–Ge ternary system at 700 °C were investigated by means of X-ray diffraction and scanning electron microscope–energy dispersive X-ray spectroscopy. A total number of nine intermediate phases were characterized and the homogeneity ranges of the various ternary solid solutions of the binary boundary systems (Ce–Co, Ce–Ge and Co–Ge) were studied. The new ternary phase, CeCo 13− x Ge x (4 ≤ x ≤ 4.5) has been discovered. It crystallizes in the tetragonal space group I 4 /mcm (no. 140), with the cell parameters a = 7.974(5) A and c = 11.856(5) A for x = 4. CeCo 9 Ge 4 derives from the CeNi 8.5 Si 4.5 -type, but, with a perfect ordering of the atoms on the crystallographic sites. The phase diagram comprises seven extensions of binaries into the ternary system, eight stoichiometric ternary phases, CeCoGe, CeCo 2 Ge 2 , CeCoGe 3 , Ce 2 Co 3 Ge 5 , Ce 2 CoGe 3 , Ce 3 CoGe 2 , Ce 5 CoGe 2 and Ce 5 Co 4 Ge 13 and two intermediate solid solutions, CeCo 1− x Ge 2 (0 ≤ x ≤ 0.24) and CeCo 13− x Ge x (4 ≤ x ≤ 4.5).

The phase relations in the U-Mo-Al system of quenched samples annealed at 800°C for 2 weeks and at 400 °C for 2 months have been established using X-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopic analysis performed at room temperature. Two ternary Al-rich phases, UMo 2-x Al 20+x and U 6 Mo 4+x Al 43-x are found stable at 800 °C and 400 °C. They show significant homogeneity ranges resulting from Mo/Al substitution mechanism on various mixed crystallographic sites, as evidenced by single-crystal structure refinements. Substitution of up to 25 at.% of Al by Mo atoms is also observed for UAl 2 (cubic MgCu 2 -type) giving a quite large extension (UAk 2-x Mo x , 0 < x < 0.5) into the ternary system. Larger substitution (0.6 < x < 0.7 at T = 800°C) stabilizes another ternary Laves phase, UAl 2-x Mo x with the hexagonal MgZn 2 -type. There is no detectable solubility of Mo in UAl 4 , and it is of the order of 1 at.% in UAl 3 . The interaction layers between the γU―Mo alloys and the Al matrix in nuclear fuel plates can be successively estimated as composed of the two- and three-phase fields equilibrium indicated on the assessment of the phase relations drawn for samples heat-treated at 400 °C.

The U3Fe4+xAl12−x (0 < x < 0.5) intermetallic was prepared by arc melting, followed by annealing at 850 °C. This compound crystallizes in the hexagonal Gd3Ru4Al12-type structure (e.g. P63/mmc), with room temperature parameters a = 8.7516(3) A and c = 9.2653(4) A for x = 0. The structure is characterized by planar layers of M3Al4 (M = Gd, U), containing M atoms in a triangular arrangement and forming a distorted Kagome net. Magnetic measurements revealed a spin-glass-type behaviour with a freezing temperature, Tf = 7.9 K. The magnitude of the frequency shift of the freezing temperature is ≈0.03 and a Vogel–Fulcher law is followed with values typical for a spin-glass. 57Fe Mossbauer data show that there is no freezing of the iron magnetic moments directions below Tf, indicating that the origin of the spin-glass-like behaviour is related to topological frustration of the uranium moments.

A new ternary uranium intermetallic compound, U2Fe3Ge, was synthesized and investigated. This compound crystallizes in the MgZn2-type structure ( a = 5.1870 ( 3 ) A and c = 7.8501 ( 5 ) A , space group P 6 3 / m m c ), with uranium–uranium distances well below the Hill limit. Magnetization measurements indicate a ferromagnetic-type transition at 55(1) K. Mossbauer studies show that the magnetic ordering is due only to the uranium sub-lattice, pointing to U2Fe3Ge as a new exception to Hill’s rule.

A systematic study of the U–Fe–Si ternary system was carried out in the whole concentration range, by means of scanning electron microscope observations, associated with energy dispersive X-ray spectroscopy analyses and X-ray powder diffraction measurements performed on as-cast and annealed samples. At 900 °C, the phase diagram is characterized by the existence of nine ternary compounds: U2FeSi3 with the AlB2-type, UFe2Si2 with the ThCr2Si2-type, U3Fe2Si7 with the La3Co2Sn7-type, U2Fe3Si with the MgZn2-type, UFeSi with the TiNiSi-type, U1.2Fe4Si9.7 with the Er1.2Fe4Si9.7-type, U2Fe3Si5 with the Lu2Co3Si5-type, U6Fe16Si7 of the Mg6Cu16Si7-type and UFe5Si3 with its own type of structure. Two intermediate solid solutions, U2Fe17−xSix (3.2

International audience; In the framework of a R&D program aiming to develop uranium carbide (UCx) targets for radioactive nuclear beams, the Institut de Physique Nucléaire d’Orsay (IPNO) has developed an experimental setup to characterize the release of various fission fragments from UCx samples at high temperature. The results obtained in a previous study have demonstrated the feasibility of the method and started to correlate the structural properties of the samples and their behavior in terms of nuclear reaction product release. In the present study, seven UCx samples have been systematically characterized in order to better understand the correlation between their physicochemical characteristics and release properties. Two very different samples, the first one composed of dense UC and the second one of highly porous UCx made of multi-wall carbon nanotubes, were provided by the ActILab (ENSAR) collaboration. The others were synthesized at IPNO. The systems for irradiation and heating necessary for the release studies have been improved with respect to those used in previous studies. The results show that the open porosity is hardly the limiting factor for the fission product release. The homogeneity of the microstructure and the pore size distribution contributes significantly to the increase of the release. The use of carbon nanotubes in place of traditional micrometric graphite particles appears to be promising, even if the homogeneity of the microstructure can still be enhanced

International audience; The phase relations within the U-Al-Ge ternary system were studied for two isothermal sections, at 673 K for the whole Gibbs triangle and at 1173 K for the concentration range 25-100 at% U. The identification of the phases, their composition ranges and stability were determined by x-ray powder diffraction, scanning electron microscopy coupled to energy dispersive spectroscopy and differential thermal analysis. The tie-lines and the solubility domains were determined for the U-Ge and U-Al binaries, the UAl3-UGe3 solid-solution and for the unique ternary intermediate phase U3Al2-xGe3+x. The experimental isopleth section of the pseudo-binary UAl3-UGe3 reveals an isomorphous solid solution based on the Cu3Au-type below the solidus. The U3Al2-xGe3+x solid solution extends for -0.1

The new compounds U6Fe16Si7 and U6Fe16Si7C were prepared by arc-melting and subsequent annealing at 1500 °C. Single-crystal X-ray diffraction showed that they crystallize in the cubic space group Fm 3 ¯ m (No. 225), with unit-cell parameters at room temperature a=11.7206(5) A for U6Fe16Si7 and a=11.7814(2) A for U6Fe16Si7C. Their crystal structures correspond to ordered variants of the Th6Mn23 type. U6Fe16Si7 adopts the Mg6Cu16Si7 structure type, whereas U6Fe16Si7C crystallizes with a novel “filled” quaternary variant. The inserted carbon is located in octahedral cages formed by six U atoms, with U–U interatomic distances of 3.509(1) A. Insertion of carbon in the structure of U6Fe16Si7 has a direct influence on the U–Fe and Fe–Fe interatomic distances. The electronic properties of both compounds were investigated by means of DC susceptibility, electrical resistivity and thermopower. U6Fe16Si7 is a Pauli paramagnet. Its electrical resistivity and thermopower point out that it cannot be classified as a simple metal. The magnetic susceptibility of U6Fe16Si7C is best described over the temperature range 100–300 K by using a modified Curie–Weiss law with an effective magnetic moment of 2.3(2) μB/U, a paramagnetic Weiss temperature, θp=57(2) K and a temperature-independent term χ0=0.057(1) emu/mol. Both the electrical resistivity and thermopower reveal metallic behavior.

The phase equilibria in the ternary Ce-Fe-Si system at 900°C was investigated by means of X-ray diffraction and Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDS). A total number of six ternary compounds were characterized and the homogeneity ranges of the various ternary solid solutions of the binary boundary systems (Ce-Fe, Ce-Si and Fe-Si) were studied. A new ternary phase, Cefe 13-y Si y (3.5

A new ternary compound with stoichiometry U2Co3Al9 has been synthesized. It adopts the orthorhombic Y2Co3Ga9-type structure (space group Cmcm, Z = 4, a = 12.824(2) A, b = 7.515(1) A, c = 9.249(2) A). Measurements of dc- and ac-magnetic susceptibility, electrical resistivity, and magnetoresistivity on polycrystalline samples have been performed. The Curie–Weiss law is strictly followed, with θCW = −48 K and μeff = 3.2 μB. A small kink observed in the temperature dependence of the resistivity is attributed to a phase transition at Tt = 8 K. The magnetoresistivity was found to be negative at all temperatures examined below 45 K, with a sharp minimum at Tt = 8 K.

The new compound UFe5Si3 was prepared by rapid solidification of the melt using a splat cooling technique, followed by annealing at 1173 K for 10 days. Its crystal structure was determined ab initio from powder X-ray diffraction data. It crystallizes in the tetragonal space group P4/mmm, with lattice parameters at room temperature of a = 3.9298(3) A and c = 7.7133(6) A. The structure of UFe5Si3, which is new among intermetallic compounds, can be viewed as built up from an infinite three-dimensional framework of Fe and Si atoms defining along the a direction, tunnels of hexagonal sections, where the U atoms lie. Alternating and direct current magnetic measurements reveal that UFe5Si3 behaves as a hard ferromagnet with a Curie temperature of about 310 K. Measurements on magnetically oriented powder suggest that UFe5Si3 has a uniaxial anisotropy with c as the easy axis. The electrical resistivity decreases monotonously with decreasing temperature suggesting no other magnetic transition below 300 K. In line w...

Er10Co1.3Al2.7 is prepared by arc melting of the elements followed by annealing (alumina crucible in evacuated silica ampoule, 1123 K, 1 week).

The isothermal section at 900 °C of the U–Fe–Ge ternary system was assessed using experimental results from X-ray diffraction and observations by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy chemical analysis. The phase diagram at this temperature is characterized by the formation of fourteen stable phases: four homogeneity ranges and ten intermetallic compounds. Among these, there is an extension of the binary compound UFe2 into the ternary system (UFe2−xGex, x

The isothermal section at 900 °C of the phase diagram of the U—Fe—Ge ternary system is investigated by melting and annealing the elements for 4 weeks prior to quenching in H2O.

Isothermal sections at 673 K and 1073 K of the ternary U–Zr–Al system were established in the whole concentration range, by means of powder X-ray diffraction, scanning electron microscopy–energy dispersive X-ray spectroscopy and differential thermal analysis. All measured compositions and unit-cell refinements were performed at room temperature from quenched samples annealed at 1073 K and 673 K for four and eight weeks respectively. For both temperatures, the Al-rich corner of the phase diagram is characterized by extended homogeneity ranges due to mutual exchange between U and Zr in UAl3 (cubic, AuCu3-type) and in the Laves phase UAl2 (cubic, MgCu2-type). Minute U solubility in ZrAl2 (hexagonal, MgZn2-type) and in Zr2Al (hexagonal, Ni2In-type) was evaluated to be of the order of 1 at.% U. For the other binary compounds, the solubility of the third component was found negligible. At 1073 K, the solid solution based on γU (cubic, W-type) which covers the U–Zr binary axis up to 95.5 at.% Zr, allows also some limited solubility of Al [maximum of 5 at.%]. For Al-content below 66 at.%, most of the phase relations comprise equilibria between the Zr–Al binaries and the γ(U,Zr,Al) solid solution. At 673 K, the U–Zr axis is found in agreement with the literature data and no Al solubility could be detected in αU, αZr and UZr2 (δ phase). The phase relations are mainly established between Zr–Al binaries and αU. For monolithic UMo fuel with a Zr diffusion barrier foil cladded with Al, the main interaction product is expected to involve the U-based alloy with the Zr–Al binary compounds and the pseudo-binary U1−xZrxAl2 and U1−xZrxAl3 phases.

The Ce–Co–Al ternary phase diagram has been reinvestigated at 973 K by means of powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and differential thermal analyses. It contains 5 ternary phases (CeCo 2 Al 8 , Ce 2 Co 6 Al 19 , CeCoAl 4 , Ce 3 Co 3 Al 4 and CeCoAl) as well as 7 extensions in the ternary field of pseudo-binaries (CeAl 2 − x Co x with 0 ⩽ x ⩽ 0.18; CeCo 2 − x Al x with 0 ⩽ x ⩽ 0.21; CeCo 3 − y Al y with 0 ⩽ y ⩽ 0.20; Ce 2 Co 7 − x Al x with 0 ⩽ x ⩽ 0.73; Ce 5 Co 19 − y Al y with 0 ⩽ y ⩽ 0.20; CeCo 5 − x Al x with 0 ⩽ x ⩽ 0.71 and Ce 2 Co 17 − y Al y with 0 ⩽ y ⩽ 2.2). Two liquid areas are present at the Al and Ce-rich corners of this isothermal section.

Three new compounds have been found in the U–Pt–Si ternary system, U 3 Pt 23 Si 11 , U 3 Pt 5 Si and U 6 Pt 30 Si 19 . They were prepared by reaction of the elemental components in an arc-melting furnace followed by heat-treatment at 900 °C for several days. Their chemical composition was checked by scanning electron microscopy and by energy dispersive spectroscopy. Their crystal structure was determined by single crystal X-ray diffraction techniques. The compound U 3 Pt 23 Si 11 , formerly reported as U 2 Pt 15 Si 7 , crystallizes in the cubic space group F m 3 ¯ m , with a unit-cell parameter at room temperature, a = 16.8341(3) A. The most striking feature of the structure is the occurrence of octahedral clusters of uranium with short U–U bonds of 3.004(2) A. U 3 Pt 5 Si crystallizes in the orthorhombic space group Imma , in a cell of dimension at room temperature a = 7.1733(3) A, b = 12.9671(6) A and c = 7.3578(3) A. Its crystal structure is closely related to that of Ce 3 Pd 5 Si, from which it only differs by a partial disorder of one Pt-atom site. The dc-magnetic measurement revealed that U 3 Pt 5 Si orders antiferromagnetically at T N = 11(1) K. U 6 Pt 30 Si 19 crystallizes in the hexagonal space group P 6 3 / m , in a cell of dimension at room temperature a = 15.9377(2) A and c = 3.9874(1) A. It belongs to a large family of ternary alloys obeying the general formula, R n ( n + 1 ) T 6 ( n 2 + 1 ) M 4 n 2 + 3 , where R stands for f-metal, T for d-transition metal and M for the main-group element.

The praseodymium cobalt aluminides, PrCo 2 Al 8 and Pr 2 Co 6 Al 19 , were prepared by reaction of the elemental components in an arc-melting furnace, followed by heat treatment at 900 °C for several days. Their chemical composition was checked by scanning electron microscopy and energy dispersive spectroscopy, and their crystal structure was refined from single crystal X-ray diffraction data. PrCo 2 Al 8 adopts the CaCo 2 Al 8 type of structure, crystallizing with the orthorhombic space group Pbam , with four formula units in a cell of dimensions at room temperature: a = 12.4623 ( 3 ) A , b = 14.3700 ( 4 ) A , c = 4.0117 ( 1 ) A . Pr 2 Co 6 Al 19 crystallizes in the monoclinic space group C2/m , with four formula units in a cell of dimensions at room temperature: a = 17.6031 ( 4 ) A , b = 12.1052 ( 4 ) A , c = 8.2399 ( 2 ) A and β = 103.903 ( 1 ) ° . Its structure belongs to the U 2 Co 6 Al 19 type. The crystal structures of both compounds studied can be viewed as three-dimensional structures resulting from the packing of Al polyhedra centred by the transition elements. Along the c -axis, the coordination polyhedra around the Pr atoms pack by face sharing to form strands, which are separated one from another by an extended Co–Al network. Magnetic measurements have revealed that PrCo 2 Al 8 orders antiferromagnetically at T N = 5 K , with a clear metamagnetic transition occurring at a critical field H c =0.9(1) T. The temperature dependence of the susceptibility of Pr 2 Co 6 Al 19 does not provide any evidence for long-range magnetic ordering in the temperature domain 1.7–300 K. At low temperatures ( T μ B and 3.41(2) μ B for PrCo 2 Al 8 and Pr 2 Co 6 Al 19 , respectively. These values are close to the theoretical value of 3.58 μ B expected for a free Pr 3+ ion and exclude any contribution due to the Co atoms. Both compounds exhibit in the temperature range 5–300 K metallic-like electrical conductivity, and their Seebeck coefficient is of the order of several μV/K.

Phase relations in the Uranium–Cobalt–Aluminum ternary system have been investigated by X-ray diffraction and scanning electron microscopy. A total number of six ternary phases were found to form in the isothermal section at 900 °C among which three have been discovered in the present study namely; U2Co6Al19 (Monoclinic, C2/m, a = 17.4617 ( 3 ) A , b = 12.0474 ( 2 ) A , c = 8.2003 ( 1 ) A , β = 103.915 ( 1 ) ), U2Co3Al9 (Orthorhombic, Cmcm, a = 12.789 ( 1 ) , b = 7.477 ( 1 ) , c = 9.258 ( 1 ) ), U3Co4+xAl12−x (Hexagonal, P63/mmc, a = 8.6518 ( 2 ) A , c = 9.2620 ( 2 ) A ). Another new ternary compound: UCoAl4 (Hexagonal, P-62m, a = 9.161 ( 1 ) A , c = 4.114 ( 1 ) A was found to form only in as-cast samples.

The new compound U 3 Co 4+ x Al 12− x , where x =0.55(2), was prepared by arc-melting of the elemental components, followed by a prolonged annealing at elevated temperature. Scanning electron microscopy-energy-dispersive spectroscopy and powder X-ray diffraction were used to determine the deviation from the ideal stoichiometry. A small homogeneity range, that extends around the composition U 3 Co 4+ x Al 12− x with 0.4(1) ⩽ x ⩽0.7(1), could be detected. Single-crystal diffraction experiments revealed that U 3 Co 4.55 Al 11.45 crystallizes with the Gd 3 Ru 4 Al 12 type-structure, (space group P 6 3 / mmc , Z =2) in a cell of dimensions at room temperature, a =8.6518(2) A, c =9.2620(2) A. The crystal structure can be viewed as an intergrowth of two distinct layers of Co and Al atoms, and U, Al and mixed Al/Co atoms that pile up along the hexagonal axis. The results of the DC magnetization suggest the occurrence of a spin glass state at low temperature ( T f =8 K). The origin of freezing of the magnetic moments may arise from a topological frustration due to the location of the U atoms on the apexes of a distorted Kagome lattice.

Experimental results on AC susceptibility, DC magnetization, electrical resistivity and magnetoresistivity up to 8 T have been obtained for a well annealed polycrystalline sample of the novel ternary aluminide U2Co6Al19. As a reference, similar experiments on the Th counterpart were also done. The U-containing aluminide exhibits two phase transitions at 8 and 12.5 K, probably of ferromagnetic and antiferromagnetic type, respectively. Moreover, U2Co6Al19 is a Kondo system showing the coherence effect below about 40 K. On the other hand, the Th counterpart showed unexpectedly a spin fluctuation behaviour, which was inferred from the broad maximum seen in its χ(T) dependence near 600 K. However, the low temperature variation of ρ(T) leads rather to an AT5/2 power dependence instead of to the AT2 one characteristic for a spin fluctuation behaviour.