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1. In situ synchrotron study of sintering of gas-atomized Ti-6Al-4 V powders using concomitant micro-tomography and X-ray diffraction: Effect of particle size and interstitials on densification and phase transformation kinetics

Author

M. Pontoreau, M. Coffigniez, V. Trillaud, C. Le Bourlot, J. Lachambre, L. Gremillard, M. Perez, E. Maire, J. Adrien, P. Steyer, T. Douillard, A. King, and X. Boulnat

Subjects
Polymers and Plastics, Metals and Alloys, Ceramics and Composites, Electronic, Optical and Magnetic Materials
Published
2023

3. A multiscale in situ high temperature high resolution transmission electron microscopy study of ThO2 sintering

Author

V. Trillaud, G.I. Nkou Bouala, Christian Ricolleau, Renaud Podor, Nicolas Clavier, Nicolas Dacheux, Etude de la Matière en Mode Environnemental (L2ME), Institut de Chimie Séparative de Marcoule (ICSM - UMR 5257), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Interfaces de Matériaux en Evolution (LIME), Laboratoire Matériaux et Phénomènes Quantiques (MPQ (UMR_7162)), Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), and Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité)

Subjects
Materials science, Diffusion, Analytical chemistry, Stacking, Sintering, 02 engineering and technology, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, 0104 chemical sciences, [CHIM]Chemical Sciences, General Materials Science, Grain boundary, Crystallite, Dislocation, 0210 nano-technology, High-resolution transmission electron microscopy, Single crystal
Abstract

Two-grain model systems formed by ThO2 nanospheres have been used to experimentally study for the first time the initial stage of sintering from room temperature to 1050 °C using high temperature high resolution transmission electron microscopy. In each grain, oriented attachment drove the reorganization and growth of the crystallites up to 300 °C to form a pseudo single crystal. Crystallite size kept growing up to 950 °C. At this temperature, a fast transformation probably corresponding to the elimination of stacking faults or dislocation walls led to the formation of single-crystals. The contact formed at room temperature between the two grains was stabilized during heat treatment by a slight reorientation of the crystallographic planes (T ≈ 400 °C), leading the neck to be formed by numerous boundaries between the crystallites. At higher temperatures, the neck evolved and stabilized in the form of a plane of crystallographic orientation mismatch between the grains, which corresponds to the usual definition of the grain boundary. The growth of the neck by the addition of atomic columns was further observed in real time and quantified. At T = 950 °C, the evolution of the microscopic sintering parameter λ was obtained from HT-HRTEM images and indicated that the neck formation mostly proceeded through volume diffusion.

Published
2021

4. Early stages of UO2+x Sintering by in situ High-Temperature Environmental Scanning Electron Microscopy

Author

V. Trillaud, S. Gossé, Renaud Podor, Nicolas Dacheux, Adel Mesbah, Nicolas Clavier, Interfaces de Matériaux en Evolution (LIME), Institut de Chimie Séparative de Marcoule (ICSM - UMR 5257), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), Etude de la Matière en Mode Environnemental (L2ME), Laboratoire de Modélisation, Thermodynamique et Thermochimie (LM2T), Service de la Corrosion et du Comportement des Matériaux dans leur Environnement (SCCME), Département de Physico-Chimie (DPC), CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-CEA-Direction des Energies (ex-Direction de l'Energie Nucléaire) (CEA-DES (ex-DEN)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Département de Physico-Chimie (DPC), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010302 applied physics, Diffraction, Materials science, Diffusion, Analytical chemistry, Oxide, Sintering, 02 engineering and technology, Activation energy, [CHIM.MATE]Chemical Sciences/Material chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, chemistry.chemical_compound, chemistry, Volume (thermodynamics), 0103 physical sciences, Materials Chemistry, Ceramics and Composites, 0210 nano-technology, Environmental scanning electron microscope, [CHIM.RADIO]Chemical Sciences/Radiochemistry, Stoichiometry, ComputingMilieux_MISCELLANEOUS
Abstract

Early stages of various uranium oxides sintering were monitored in situ through High Temperature Environmental Scanning Electron Microscopy. Systems composed of two UO2+x microspheres were heated up to 900−1200 °C under PO2 ranging from 10−10 to 25 Pa. The oxide phases stabilized were assessed through thermodynamic calculations and powder X-ray diffraction. In all the conditions tested, the formation and the development of a neck was evidenced and image processing led to quantitative data describing the morphological changes. The evolution of the sintering degree was fitted using an exponential law and allowed the evaluation of the activation energy. When PO2 led to stabilize hyper-stoichiometric UO2+x oxides, the values obtained increased with x, typically in the 200−400 kJ mol−1 range. Under air atmosphere, the stabilization of U3O8 led to EA = 260 ± 40 kJ mol−1. Finally, the main diffusion mechanism driving neck formation was found to be volume diffusion, independently from the oxide stoichiometry.

Published
2020

5. Microstructural evolution of UO2 pellets containing metallic particles of Ru, Rh and Pd during dissolution in nitric acid solution: 3D-ESEM monitoring

Author

Laurent Claparede, T. Cordara, V. Trillaud, Renaud Podor, Nicolas Dacheux, C. Lavalette, Adel Mesbah, X. Le Goff, Stéphanie Szenknect, Interfaces de Matériaux en Evolution (LIME), Institut de Chimie Séparative de Marcoule (ICSM - UMR 5257), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Etude de la Matière en Mode Environnemental (L2ME), AREVA NC, Institut de Physique Nucléaire d'Orsay (IPNO), Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA), and Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11)

Subjects
Precipitation (chemistry), Uranium dioxide, 0211 other engineering and technologies, Metals and Alloys, Analytical chemistry, chemistry.chemical_element, 02 engineering and technology, [CHIM.MATE]Chemical Sciences/Material chemistry, Uranium, [CHIM.INOR]Chemical Sciences/Inorganic chemistry, Microstructure, Industrial and Manufacturing Engineering, chemistry.chemical_compound, 020401 chemical engineering, chemistry, Nitric acid, Materials Chemistry, Grain boundary, 0204 chemical engineering, Environmental scanning electron microscope, Dissolution, 021102 mining & metallurgy
Abstract

International audience; Uranium dioxide containing 3 mol.% platinum group metals (PGMs) (Ru, Rh, Pd) was synthesized by hydroxide precipitation. The powders were converted to oxides, pelletized and sintered to prepare dense pellets of UO 2 incorporating PGMs particles. The characterization techniques performed revealed a microstructure similar to that of spent nuclear fuel (SNF). Dissolution tests in nitric acid demonstrated that in the presence of PGMs, the uranium dissolution rate was increased and the induction period was shortened. We used a new method based on the acquisition of Environmental Scanning Electron Microscopy (ESEM) micrographs recorded at three tilt angles and at different dissolution times. This method allowed the reconstruction of the topography of the solid/liquid interface. By monitoring the evolution of the solid/liquid interface during dissolution by means of 3D reconstructions, we were able to observe preferential dissolution zones in the vicinity of the PGMs particles and to determine microscopic dissolution rates for several regions of interest. PGMs particles were found mainly at the grain boundaries. In 0.1 M HNO 3 solution at 60˚C, the normalized dissolution rate for uranium at the grain boundaries reached R L (U) = (7 ± 1)×10-2 g.m-2 .d-1 , a value similar to the normalized dissolution rate determined for the whole image over the first 30 days of the experiment. This result showed that the dissolution occurred mainly at the UO 2 grain boundaries in the vicinity of PGMs particles. Furthermore, the 3D reconstructions of the solid/liquid interface were used to determine the evolution of the surface area of the pellet. By combining the weight losses determined at the macroscopic scale using the uranium concentrations in solution with the reactive surface area values, it was possible to estimate an effective normalized dissolution rate for the whole pellet.

Published
2019

6. Synthesis of size-controlled UO2 microspheres from the hydrothermal conversion of U(IV) aspartate

Author

Jérémie Manaud, Renaud Podor, Jérôme Maynadié, V. Trillaud, J. Hidalgo, Daniel Meyer, Nicolas Dacheux, Nicolas Clavier, Interfaces de Matériaux en Evolution (LIME), Institut de Chimie Séparative de Marcoule (ICSM - UMR 5257), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Systèmes HYbrides pour la Séparation (LHyS), Etude de la Matière en Mode Environnemental (L2ME), and Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Montpellier (UM)-Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)

Subjects
hydrothermal, Morphology (linguistics), Materials science, Dispersity, nuclear safeguards, chemistry.chemical_element, 02 engineering and technology, [CHIM.INOR]Chemical Sciences/Inorganic chemistry, 010402 general chemistry, 01 natural sciences, Hydrothermal circulation, Microsphere, General Materials Science, conversion, General Chemistry, [CHIM.MATE]Chemical Sciences/Material chemistry, Uranium, 021001 nanoscience & nanotechnology, Condensed Matter Physics, Uranium oxide, 0104 chemical sciences, chemistry, Chemical engineering, Particle diameter, microsphere, 0210 nano-technology, Dispersion (chemistry), [CHIM.RADIO]Chemical Sciences/Radiochemistry, Wet chemistry
Abstract

International audience; A simple wet chemistry route towards micrometric spherical UO2 particles was designed through the conversion of uranium(IV) aspartate under mild hydrothermal conditions (T = 160 °C). A multiparametric study examining the effects of hydrothermal treatment duration, the initial uranium/aspartic acid molar ratio and magnetic stirring allowed us to point out the role of organic species in the shaping of the particles and to specify the operating conditions leading to monodisperse and size-controlled particles. In a turbulent flow regime (i.e. Rea > 104), particles with a diameter ranging from 400 nm to 2500 nm were obtained with a typical dispersion of less than ±10%. Moreover, the protocol was found to be robust and reproducible, with only limited size variation from one batch to another (typically less than ±5% on the particle diameter). The effect of an additional heat treatment step was also investigated which showed that residual traces of water and organics can be removed after firing at 600 °C without altering the initial morphology. This wet chemistry route appears to be very promising for the production of spherical UO2 particles and can be simply implemented in any nuclear chemistry lab, which paves the way to applications of such materials in various scientific areas.

Published
2018

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