Synthesis of inorganic monoliths functionalized with nanoparticles
Since 2008, the "Institut de Chimie Separative de Marcoule" (ICSM) and specifically the "Laboratoire des Nanomateriaux pour l’Energie et le Recyclage" (LNER) has developped specific skills in synthesis routes and studies of porous materials (BET, TEM, SEM, SAXS).
This post-doctoral position is devoted to the synthesis of inorganic monoliths using high internal phase emulsion (HIPE) as soft template, and particularly to the functionalization of these materials with nanoparticles (NP).
The use of an emulsion in the procedure allows to consider innovative ways of functionalizing the material. For example, the oil-water interface in the emulsion may be the site of adsorption of nanoparticles of interest for a given application. In our case the goal is to prepare an emulsion with high internal phase (> 50% vol) stabilized by both surfactants (required for mesoporosity) and NP of interest to functionalize the macroporosity. NPs are chosen to cover liquid effluent decontamination (zeolite, nonatitanate, clathrate)
Evolution of the surface layers resulting from the physico-chemical interactions between low pH concrete and clays: experiments and modeling
The design of an industrial facility for storage of radioactive wastes in geological environment is an important issue taken into account in the French nuclear energy sector. In this context the cementitious materials are an important (packages, structures).
The main objective of the proposed study is to characterize alterations of the materials in the concrete-clay interfaces, caused by chemical exchanges. At the current stage, a comprehensive approach was initiated taking into account simultaneously the chemistry of the storage site and concrete considered for this application, based on commercial cements or innovative binders (low pH) formulated specifically. On these low pH materials in particular, questions remain as to their mineralogical and microstructural evolution. An experimental program (dedicated testing, microscopic characterization), supplemented by digital simulations, will increase the essential knowledge for use of these materials.
This project will involve both of the specialists of cementitious materials of the CEA, and researchers at the laboratory Hydrasa of the University of Poitiers.
Crystalline materials for the selective extraction of monovalent metal cations: understanding the link between the crystalline structure and the selectivity
The selective extraction of monovalent metal cations from aqueous solutions have complex compositions is a key step in many energy-related fields. In this work, specific adsorbents for Cs, to decontaminate effluents produced by the nuclear industry, and for Li, to extract this strategic metal for the development of batteries, will be studied. Due to their modularity in terms of porosity and structure, crystalline oxides (as zeolites) are promising for the selective extraction of such cations. With a view to understand the role of their microstructure on their sorption/desorption performances and mechanisms, identify the selective sorption sites within these crystal structures is crucial.
For that purpose, the objective of this research work is, on the one hand, to synthesize crystal structures allowing the selective sorption of Cs or Li. Then, by using fine characterization techniques at the atomic scale as well as structures reconstruction effort, we will identify the location of selective sorption sites within these materials and, in this way, better understand their sorption mechanisms and properties.
For this post-doctoral position, we are looking for a PhD in material science with strong skills in synthesis and characterization of crystalline materials by X-ray diffraction. Experience in the study of crystalline oxides, such as zeolites, would be an advantage.
Micro-energy sources for biomedical applications
There is a growing interest towards wireless implantable systems for in vivo biomedical applications. However, such implantable systems have a limited lifetime determined by the battery capacity. CEA LITEN is working on innovative miniaturized systems integrating an energy harvesting component with a rechargeable battery. This type of micro-systems will be used for powering sensors or other implantable medical devices. The post-doctoral researcher will work on the design, the fabrication and the characterization of demonstrators consisting of the energy harvesting component, the battery and a power management circuit. Numerical simulations could also be performed, with the help of specialized engineers. The characterization of the demonstrators and the numerical simulation results will allow the post-doctoral researcher to propose innovative solutions for optimizing the system. The post-doctoral researcher will work in a multi-disciplinary team, which requires strong abilities for team working and communication.
Nonlinear dynamic analysis of a reinforced concrete structure subjected to seismic loadings: Deterministic and probabilistic study of response spectra
The proposed work is based on the experimental campaign of the ENISTAT project and is composed of three parts:
1. Calibration and enhancement of the numerical model (5 months)
Based on the nonlinear numerical model that has been realized in CEA, the applicant will have to compare the results to those provided by the experimental campaign. The potential gaps will be interpreted and the model should be calibrated (and/or enhanced) to ensure a satisfactory accordance with the experimental results and observations.
2. Deterministic and probabilistic analysis of response spectra (5 months)
Based of the numerical model that will have been calibrated, the response spectra will be computed in given points. They will be compared the demand spectra prescribed by the design rules such as the EC8. Based on probabilistic methods that are developed in CEA for seismic applications, the uncertainties not only of the input parameters but also of the seismic signals will be taken into account. The induced variability of the response spectra will be quantified and discussed. One can notice that the knowledge of these data is particularly interesting since design rules in seismic engineering are based on them.
3. Study of the effect of the thermic brick elements
Thanks to the experimental results, not only experimental but also numerical, a discussion on the effect of the thermic brick elements will be realized with the aim to draw first conclusions on their effect on the overall structural behavior under seismic loading.
Development of a Metal Supported Cell for Hydrogen production by High Temperature Steam Electrolysis
The development of Metal Supported Cells (MSC) for High Temperature Steam Electrolysis (HTSE) constitutes an interesting innovation able to reduce the degradation of this component under operation. An increase in the cell life time would be a valuable contribution to cost reduction and is able at positioning HTSE as an alternative process to other hydrogen production technologies. However, some progresses in the elaboration of MSCs are still required. Within the current process, functional ceramic layers of the MSC are joined to the metallic substrate at elevated temperature (> 1000 °C). Mismatch of the mechanical properties of the materials as well as the reducing conditions fixed by the metal substrate during sintering lead to MSCs having insufficient electrochemical performances. The post-doctorate aims, on the one hand, at obtaining a better understanding of the mechanisms that occur in the multilayer structure during sintering and, on the other hand, at proposing and testing technological solutions able to improve to reliability of MSC elaboration.
Modelling of actinide electrorefining
Modelling of an actinide electrorefining process
In the frame of the SACSESS European project CEA, ITU and CNRS are studying jointly a pyrochemical process for the reprocessing of spent nuclear fuels by electrolysis in molten chloride salts.
The main objective of the proposed post-doctoral work concerns the modelling of electrorefining runs onto aluminium cathodes using U-Pu-Zr-Am-Gd-Nd-Ce-Y metallic alloy. The modelling aims to evaluate the efficiency of this electrolytic process in terms of separation factors and to optimize the process flow sheets for a safe nuclear materials management.
Model reduction in dynamics : application to earthquake engineering problems
The complexity and refinement of the numerical models used to predict the behavior of structures under seismic loading often impose computation times of several days for solving the partial differential equations of the reference problem.
Furthermore, in the context of optimization , model identification, or parametric and stochastic analyses, the aim is not to predict the response of a unique model but of a family of models.
To reduce the computation time, model reduction techniques (Proper Orthogonal/Generalized Decomposition) may be considered. This post-doctoral study proposes to define and implement (especially in the FE code CAST3M) a technique suitable for the reduction of reinforced concrete type models subjected to seismic loading.
Droplets motion through modulation of surface energy gradient
Droplet motion through electro-wetting is nowadays largely studied and used in several systems and applications. In order to be useful, this technique needs an electrical field to monitor the droplet. For this post-doctoral fellowship, the main objective is to define an alternative method to the using of the electro-wetting technique in order to generate a droplet motion. The elaboration of surfaces with energy gradients conceived by thin film deposition or by laser ablation will be realized inside this study. The main difficulty is related to the patterns realization in order to obtain the appropriate hydrophilic/hydrophobic resolution. Apart from these “classical” techniques, an innovative method will be studied here by using switchable molecules. These molecules could modify the contact angle between a surface and a droplet, when acting on the potential of hydrogen (pH) or the wall temperature. For all the defined surfaces, the post-doctoral fellow will also analyze the coupling effect between the surface energy gradient and a thermal energy gradient on the droplet motion dynamics.
Study of aerosol transport through degraded materials
Radioactive Waste (RW) are produced during nuclear activities and are categorized as a function of their activities and their half-life in order to manage their conditioning, transport, storage… Mortar can be used in order to immobilize and/or create a safe barrier forming a Radioactive Waste Package (RWP) in order to protect the environment. It is important to study the efficiency of this mortar barrier for long term and safety assessment have to investigate the case of crack mortar formation as radioactive particles could then migrate in the cracks.
The LECD laboratory investigated this problematic by measuring the migration of CeO2 particle in mortar cracks using X-Ray microtomography. The cracks were synthesized by dissolving plastic molds (designed by 3D printing). This study showed the influence of particle interactions with tortuosity and roughness of the crack, but was limited to 40 µm particle diameter.
The aim of the postdoctoral work is to develop an experimental approach similar to the method developed to study the efficiency of HEPA filters, with particles of 0.05 - 5 µm diameter. Quantitative measurements will be performed on the particle flows on both sides of the cracked mortar sample. LECD has acquired an aerosol generator, a light-scattering aerosol spectrometer system for particle size analysis and concentration determination and an Universal Scanning Mobility Particle Sizers. The researcher will also develop modelling work using numerical tools as STARCCM+.
This project will be carried out under the format of an 12-month fixed-term contract at the Atomic Energy and Alternative Energies Commission (CEA), at the Cadarache site (Saint-Paul-lez-Durance, 13) at the Expertise and Destructive Characterization Laboratory (LECD) of the Expertise and Characterization CHICADE Service (SECC).
Contacts: ingmar.pointeau@cea.fr (R&D engineer) – Olivier.vigneau@cea.fr (Head of the Laboratory)