Characterization of uranium carbide target materials to produce neutron-rich radioactive beams

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

CALPHAD formalism for Portland clinker: thermodynamic models and databases

International audienceThe so-called CALPHAD method is widely used in metallurgy to predict phase diagrams of multi-component systems. The application of the method to oxide systems is much more recent, because of the difficulty of modelling the ionic liquid phase. Since the 1980s, several models have been proposed by various communities. Thermodynamic databases for oxides are available and still under development. The purpose of this article is to discuss the distinct approaches of the method for the calculation of multi-component systems for Portland cement elaboration. The article gives a state of the art of the most recent experimental data and the various calculations for the CaO-Al2O3-SiO2 phase diagram. A literature review of the three binary sub-systems leads to main conclusions: (i) discrepancies are found in the literature for the selected experimental data, (ii) the phase diagram data in the reference books are not complete and up to date and (iii) the two-sublattices model and the modified quasichemical model can be equally used for the modelling of the aluminates liquid. The predictive feature of the CALPHAD method is illustrated using the CaO-Al2O3-SiO2 system with the two-sublattices model: extrapolated (predicted) and fully-assessed phase diagrams are compared in the clinkering zone of interest. The recent application of the predictive method for the calculations of high-order systems (taking into account Fe2O3, SO3, CaF2, P2O5) shows that the databases developed with the two-sublattices model and the modified quasichemical model are no longer equivalent

Efficient Electrocatalysts for Alkaline Oxygen Evolution Reaction from Wolframite Derived Heteroatom Materials

International audienceNew materials for oxygen evolution reaction (OER) electro-Mn, Ni, Co) towards OER in basic conditions. Our results showed catalysts in alkaline conditions have been highly investigated in that Ni0.5Mn0.5WO4 is a promising electrocatalyst, exhibiting ease recent years for the advancement of water splitting. However, of preparation, stability over the course of our experiments, and questions such as the lack of stability and the use of noble OER activity comparable to the standard iridium oxide. This metals as electrocatalysts still need to be addressed. In this study highlights the potential of wolframite tungsten-based study, we report the synthesis and electrocatalytic properties of materials as a new class of electrocatalysts for OER in alkaline a series of wolframite tungsten-based materials (MWO4, M=Fe, conditions

Efficient Electrocatalysts for Alkaline Oxygen Evolution Reaction from Wolframite Derived Heteroatom Materials

International audienceNew materials for oxygen evolution reaction (OER) electrocatalysts in alkaline conditions have beenhighly investigated in recent years as an alternative to water splitting. However, questions such as the lackof stability and the use of noble metals as electrocatalysts still need to be addressed. We will describematerials based on natural wolframite (FexMn1−xWO4), exploring the impact of isotropic substitution of Niand Mn cations on the electrochemical catalytic performance in the oxygen evolution reaction (OER).Fe0.5Mn0.5WO4, Ni0.5Mn0.5WO4, Fe0.5Ni0.5WO4, Fe0.5Co0.5WO4, and Co0.5Mn0.5WO4 were successfullysynthesized through a hydrothermal reaction, characterized using X-ray diffraction analysis (XRD), andtested for their electrocatalytic properties towards OER in basic conditions (0.1 M KOH). Among thematerials prepared, Ni0.5Mn0.5WO4 has shown the most promising activity, exhibiting ease of preparation,stability over the course of our experiments, and OER activity comparable to the standard iridium oxide.Additionally, solid solutions of NixMn1-xWO4 (x = 1, 0.9, 0.75, 0.6, 0.5, 0.4, 0.25, 0) were synthesized,and morphologies investigated through scanning electron microscope (SEM) and transmission electronmicroscopy (TEM). The optimal Ni/Mo ratio for electrocatalytic activity was determined to be 50%. Thisstudy contributes to the development of a new class of transition-metal-based heterofunctional catalysts forelectrocatalytically splitting of water to produce O2

Thermal annealing effect on optical properties of electrodeposited ZnO thin films

7ppInternational audienceZnO thin films were electrodeposited in aqueous solution on gilded p-type Si wafer substrates. Thermal treatments were carried out on different films in Ar atmosphere at different temperatures, between 200 and 600 ◦C. Surface morphology studies using scanning electron microscopy and atomic force microscopy show a smooth surface for an annealing temperature of 400 ◦C with a roughness mean square value of about 15 nm and a precipitation of ZnO microcrystals on the deposit surface at 600 ◦C. X-ray diffraction experiments reveal a decrease in the c-parameter value from 5.223 to 5.206Å after treatment at 600 ◦C, due to the removal of hydrogen from the film. Raman spectroscopy analyses show an improvement in the crystal quality of the film and a decrease in the compressive stress inside the deposit. Photoluminescence observations reveal an important change in the UV emission band after annealing at 200 ◦C. A visible region emission band at 580 nm, ascribed to interstitial oxygen, is observed for the as-grown deposit and decreases as the annealing temperature increases. An emission band appears near 525 nm for samples annealed at 400 and 600 ◦C; this band is ascribed to oxygen vacancies created during annealing treatment. This result is in agreement with the energy dispersive x-ray spectroscopy experiments which revealed loss of oxygen

Structure and conductivity studies of electrodeposited delta-Bi2O3

International audienceBismuth oxide in its δ-phase (high-temperature fluorite structure) is a well-known solid electrolyte owing to its high oxygen ion conductivity. In this work, δ-Bi2O3 thin film was stabilized at room temperature by electrodeposition on different conductor substrates. Electrodeposited thin films have a good quality with an excellent adhesion to the substrate. The crystalline structure and the stability of the deposit were studied by Xray diffraction (XRD). Both XRD measurements and transmission electron microscopy (TEM) investigation revealed the nanocrystallinity of the films. XRD measurements showed a decrease of nanocrystallites size after thin film annealing. The resistivity measurements showed an excellent conductivity of electrodeposited δ-Bi2O3 thin films with an ionic conductive behaviour and an electrical conductivity value close to the theoretical value: the thin film deposited on a gilded silver substrate exhibit a conductivity of 0.39 S/cm at 440 °C

Photocatalytic active ZnO_1−xS_x@CNTs heteronanostructures

Herein, we report on the use of vertically aligned multiwall carbon nanotubes (CNTs) films as support for ZnO/ZnS photocatalytic active nanostructures. The CNTs were synthetized via a hot-filament chemical vapor deposition (HfCVD), using Fe catalyst on top of Al2O3 buffer layer. Controlled point defects in the CNTs outer walls were created by exposure to a low pressure nonthermal water vapors diffusive plasma and acted as seeds for subsequent pulsed-electrodeposition of Zn nanoparticles. This was to achieve a direct and improved contact between the nanoparticles and CNTs. To obtain ZnO, ZnS and mix phase of ZnO/ZnS spread on CNTs, the oxidation, sulfurization and 2 steps subsequent annealing in oxygen and sulfur rich atmospheres were applied. High resolution transmission electron microscopy (HRTEM) with energy dispersive X-rays spectroscopy (EDS) in scanning mode, provided the chemical mapping of the structures. X-ray diffraction (XRD) analyses proved the hexagonal phase of ZnO and ZnS, obtained after oxidation in H2O and S vapors, respectively. In the case of the samples obtained by the 2 steps subsequent annealing, XRD showed mainly the presence of ZnO and a small amount of ZnS. The benefit of the secondary annealing in S vapor was seen as absorption enhancement of the ZnO1-xSx@CNTs sample having the absorption edge at 417 nm, whereas the absorption edge of ZnO@CNTs was 408 nm and of ZnS@CNTs 360 nm. For all the samples, compared to the bare ZnO and ZnS, the absorption red shift was observed which is attributed to the CNTs involvement. Therefore, this study showed the double sides benefit to induce the absorption of ZnO of the visible light, one from S doping and second of CNTs involvement. The absorption enhancement had a positive impact on photocatalytic degradation of methyl blue dye, showing that ZnO1-xSx@CNTs heteronanostructure was the best photocatalyst among the studied samples

Influence of density and release properties of UCx_x targets on the fission product yields at ALTO

International audienceTo study the influence of the structural properties of UC$_x$ targets on their release properties, several types of targets using different precursors (carbon and uranium) were synthesized, characterized, irradiated and heated leading to the determination of the released fractions of eight elements. In this article, the production rates of these targets are estimated under the use conditions at ALTO, i.e. with targets bombarded by an electron beam (10 μA, 50 MeV). We have simulated the fission number produced using the FLUKA code. Then, we have determined the release efficiency as a function of the half-life of the isotopes using average diffusion coefficients deduced for the elements studied previously. Finally, we compare the production rates obtained from the various targets and conclude that the target must be adapted to the element studied. It is crucial to find in each case the best compromise between the target density and the release efficiency

Pulsed Electro Decoration of Carbon Nanotubes with FexZn1−xS

International audienceA wide ranging scientific interest in developing new and simple preparation methods for highly catalytic bimetallic sulfides provided our motivation to explore the possibility of using the pulsed electrodeposition technique for the decoration of a carbon nanotubes forest. The carbon nanotubes were obtained using the hot-filament chemical vapor deposition technique. A non-thermal plasma treatment enabled the controlled creation of defects on the carbon nanotubes’ surface. These defects served as anchoring sites for the subsequent deposition of Fe and Zn nanoparticles using the pulsed electrodeposition technique. Our findings showed that only in the case of Fe deposition prior to Zn provided the formation of FeZn bimetallic-based nanoparticles, with Zn present mainly on the outer surface of the Fe core. To induce sulfurization, a thermal treatment in sulfur vapor was conducted at 500 °C, and the obtained heterostructure consisted of Fe0.3Zn0.7S as the main phase, with the minor presence of ZnS and S residues, which was deduced from the XRD results. This study provides thorough imaging of the process, presenting for each preparation step SEM/HR-TEM findings, coupled with EDS chemical analyses. The samples were tested for photocatalytic degradation of methyl blue dye to demonstrate the photoactive behavior of the heterostructure

Synthesis and characterization of a Sb2Te3/Bi2Te3 p-n junction heterostructure via electrodeposition in nanoporous membranes

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