A5051986448- Radioactive element chemistry and processing
- Nuclear materials and radiation effects
- Nuclear Materials and Properties
- Chemical Synthesis and Characterization
- Nuclear reactor physics and engineering
- Luminescence Properties of Advanced Materials
- Geochemistry and Geologic Mapping
- Groundwater flow and contamination studies
- Zeolite Catalysis and Synthesis
- Crystal Structures and Properties
- Geological and Geochemical Analysis
- Thermal and Kinetic Analysis
- Advanced Condensed Matter Physics
- Radioactive contamination and transfer
- Crystallization and Solubility Studies
- Metal Extraction and Bioleaching
- Catalytic Processes in Materials Science
- Nuclear and radioactivity studies
- Glass properties and applications
- Extraction and Separation Processes
- X-ray Diffraction in Crystallography
- Catalysis and Oxidation Reactions
- Atmospheric and Environmental Gas Dynamics
- Graphite, nuclear technology, radiation studies
- Electron and X-Ray Spectroscopy Techniques
Université de Montpellier
2016-2025
Institut de Chimie Séparative de Marcoule
2016-2025
École Nationale Supérieure de Chimie de Montpellier
2016-2025
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2016-2025
Centre National de la Recherche Scientifique
2016-2025
CEA Marcoule
2016-2025
Aix-Marseille Université
2020
Direction des énergies
2017-2020
Unité Matériaux et Transformations
2006-2018
CEA LITEN
2005-2013
Several CeO(2)-based mixed oxides with general composition Ce(1-x)Ln(x)O(2-x/2) (for 0 ≤ x 1 and Ln = La, Nd, Sm, Eu, Gd, Dy, Er, or Yb) were prepared using an initial oxalic precipitation leading to a homogeneous distribution of cations in the oxides. After characterization Ce/Nd oxalate precursors then thermal conversion at T 1000 °C, investigation crystalline structure these was carried out by XRD μ-Raman spectroscopy. Typical fluorite Fm ̅3m obtained for relatively low Ln(III) contents,...
Coffinite, USiO4, is an important U(IV) mineral, but its thermodynamic properties are not well-constrained. In this work, two different coffinite samples were synthesized under hydrothermal conditions and purified from a mixture of products. The enthalpy formation was obtained by high-temperature oxide melt solution calorimetry. Coffinite energetically metastable with respect to UO2 (uraninite) SiO2 (quartz) 25.6 ± 3.9 kJ/mol. Its standard the elements at 25 °C -1,970.0 4.2 Decomposition...
Hydrated rhabdophane with a general formula REEPO4·nH2O (REE: La → Dy) has been always considered to crystallize in the hexagonal system. A recent re-examination of this system by use synchrotron powder data SmPO4·0.667 H2O compound led structure crystallizing monoclinic C2 space group = 28.0903(1) Å, b 6.9466(1) c 12.0304(1) β 115.23(1)°, and V 2123.4 (1) Å3 24 units per unit cell. The consists infinite channels oriented along [101] direction formed connection Sm-polyhedra P-tetrahedra...
The dissolution of Th1–xCexO2 solid solutions samples prepared by thermal conversion oxalate precursors was studied varying independently several parameters (such as chemical composition, leachate acidity, leaching temperature, firing and crystallization state). relative effects these on the normalized rate were examined. Either obtained partial order related to proton activity (n = 0.50 ± 0.01) or activation energy (EA 57 6 kJ.mol–1) suggested that mainly driven surface reactions occurring...
Evolution of sintered Ce<sub>1−x</sub>Ln<sub>x</sub>O<sub>2−x/2</sub>samples during dissolution tests in acidic media was followed the same zone by environmental scanning microscopy.
A systematic study of the solubility rhabdophanes LnPO 4 · 0.667H 2 O (Ln = La–Dy) was performed through oversaturation and undersaturation experiments at different temperatures (298–363 K) to demonstrate reversibility equilibria. The structure neoformed phase controlled carefully over entire temperature range enable unambiguous attribution products derived thermodynamic data rhabdophane phases. log K ° s,0 (298 values for ranged from –25.6 ± 0.8 (Pr) –24.9 1.7 (Eu), minimum were Pr Sm,...
The dissolution of Ce1–xLnxO2–x/2 solid solutions was undertaken in various acid media order to evaluate the effects several physicochemical parameters such as chemical composition, temperature, and acidity on reaction kinetics. normalized rates (RL,0) were found be strongly modified by trivalent lanthanide incorporation rate, due presence oxygen vacancies decreasing samples cohesion. Conversely, nature cation considered only weakly impacted RL,0 values. dependence temperature then appeared...
Rare earth phosphates comprise a large family of compounds proposed as possible nuclear waste disposal forms. We report structural and thermodynamic properties series rare rhabdophanes monazites. The water content the rhabdophanes, including both adsorbed water, decreases linearly with increase in ionic radius earth. energetics transformation rhabdophane to monazite plus enthalpy formation from constituent oxides was determined by high temperature drop solution calorimetry. former varies...
The formation of U(VI) intrinsic colloids has a non-negligible impact on the dissemination actinides in environment. It is therefore essential to better identify their nature, conditions, and stability domains. These specific points are especially important since behavior these elements environment generally estimated by geochemical transport modeling. This modeling relies accurate prediction speciation various situations based thermodynamic databases that have be continuously updated. In...
Abstract Synthetic thorite and huttonite, two polymorphs of ThSiO4, were investigated by a combination in situ high-pressure synchrotron X-ray powder diffraction high pressure Raman spectroscopy. The average onset the thorite-to-huttonite transition was determined to be 6.6 ± 0.2 GPa, using both techniques. bulk moduli huttonite 139(9) 246(11) respectively, fitting their unit-cell volume data second order Birch-Murnaghan equation state (EOS). Based on its modulus, is most compressible...
Coffinite, USiO4, is the second most abundant U(4+) mineral on Earth, and its formation by alteration of UO2 in spent nuclear fuel a geologic repository may control release radionuclides to environment. Despite abundance nature, synthesis characterization coffinite have eluded researchers for decades. On basis recent we can now define experimental conditions under which efficiently formed. Optimal are defined four parameters: pH, T, heating time, U/Si molar ratio. The adjustment pH between...
High-temperature oxide melt solution calorimetric measurements were completed to determine the enthalpies of formation uranothorite, (USiO4)x–(ThSiO4)1–x, solid solution. Phase-pure samples with x values 0, 0.11, 0.21, 0.35, 0.71, and 0.84 prepared, purified, characterized by powder X-ray diffraction, electron probe microanalysis, thermogravimetric analysis differential scanning calorimetry coupled in situ mass spectrometry, high-temperature calorimetry. This work confirms energetic...
Experiments on the solubility of intermediate members Th1–xUxSiO4 solid solution were carried out to determine impact Th–U substitutions thermodynamic properties and then allow extrapolation coffinite end member. The ion activity products in solutions equilibrated with (0 ≤ x 0.5) determined by dissolution experiments conducted 0.1 mol·L–1 HCl under Ar atmosphere at several temperatures ranging from 298 346 K. For all experiments, was congruent, a constant composition aqueous reached after...
Lanthanide disilicates and oxyapatites have potential roles in high-temperature applications as thermal (TBC) environmental barrier coatings (EBC) or possible alteration phases geological nuclear waste repositories. However, those Ce3+-bearing silicates only been limitedly studied. In this work, we performed detailed structural thermodynamic investigations on A-Ce2Si2O7 (tetragonal, P41) Ce4.67(SiO4)3O (hexagonal, P63/m). The behaviors coefficients of expansion were determined by situ...
Orthosilicates adopt the zircon structure types (I41/amd), consisting of isolated SiO4 tetrahedra joined by A-site metal cations, such as Ce and U. They are significant interest in fields geochemistry, mineralogy, nuclear waste form development, material science. Stetindite (CeSiO4) coffinite (USiO4) can be formed under hydrothermal conditions despite both being thermodynamically metastable. Water has been hypothesized to play a role stabilizing forming these orthosilicate phases, though...
The preparation of Th(1-x)U(x)SiO(4) uranothorite solid solutions was successfully undertaken under hydrothermal conditions (T = 250 °C). From XRD and EDS characterization, the formation a complete solution between x 0 (thorite) 0.8 evidenced. Nevertheless, additional (Th,U)O(2) dioxide amorphous silica were systematically observed for highest uranium mole loadings. influence kinetics parameters then studied to avoid such side products. variation synthesis duration allowed us point out...