Improvement of microfluidic tools for kinetic data measurement
The development and modeling chemical processes require the acquisition of many thermodynamic and kinetic data . Conventional methods for measuring these data generally involve significant amounts of reagents. In particular for the reactive crystallisation, where the stochastic nature of nucleation requires the realization of a large number of experiments . The subject is to continue the work already done on the development of a dedicated chip to measure rapid nucleation kinetics . Firstly , the validity of kinetic measurements obtained by microfluidics technique will be evaluated and optimized based on well known and non- radioactive chemical systems . The microfluidic tool will then be used to study the sensitivity of these reactions to various operating parameters ( supersaturation , impurities , additives, etc. . ), before considering its transposition to nuclear processes such as decontamination of radioactive effluents. Finally, a new chip design could be proposed for the measurement of kinetics of liquid-liquid extraction , in connection with the development of new hydrometallurgical processes.
Multiscale Modelling of Radiation Induced Segregation
Irradiation produces in materials excess vacancies and self-interstials that eliminate by mutual recombination or by annihilation at sinks (surfaces, grain boudaries, dislocations).
It sustains permanent fluxes of point defects towards those sinks. In case of preferential transport of one componant of an alloy, the chemical composition is modified in the vicinity of the sinks: a Radiation Induced Segregation (RIS). Its modelling requires a good description of the alloy properties: its driving forces (derived from the thermodynamics) and its kinetic coefficients (the Onsager matrix). The objectif on this project is to combine (i) atomic models (Kinetic Monte Carlo simulations and Self-Consistent Mean Field), fitted on ab initio calculations, that provide the Onsager coeffcients and the driving forces and (ii) a Phase-Field modelling that will give a description of the evolution of the alloy under irradiation at much larger time- and space-scales. The approach will be applied to Fe-Cr and Fe-Cu alloys, already modelled at the atomic scale. RIS will be first modelled near grain boundaries, then near dislocation loops. Special attention will be paid to the effect of elastic stresses on the RIS.
Development of methods for U quantification in cells after exposure to uranium
This project fits into the transverse Toxicology Program, led by CEA, whose purpose is to address by multidisciplinary approaches, the potential effects on living organisms of elements of strategic interest to the CEA. The objective is to provide some understanding on the mechanisms of uranium toxicity and behavior, in connection with its speciation in cells. Indeed, the radionuclides speciation governs their bioavailability, accumulation, biodistribution, toxicity, detoxification mechanisms and their interaction at the molecular level.
The post-doctoral project (12 months) consists in:
- Developing methods to quantify U accumulated in the cells as well as endogenous content of trace elements after exposure of cells to uranium.
- Developing methods to determine the precise isotopic composition of U in the cells after their exposure.
The candidate will be in charge of developing chemical purification and measurement methods for precise elemental and isotopic analyses. The analyses will be performed using inductively coupled plasma quadrupole mass spectrometer (ICP- MS Q) or inductively coupled plasma multi- collection mass spectrometer of the latest generation (ICP- MS MC), to achieve the lowest level of uncertainties.
Electric field and ab initio simulations, application to RRAM
Since several years, LETI/DCOS is engaged in a simulation effort of microscopic phenomena at the heart of oxide-based RRAM operation (made of HfO2, Ta2O5, Al2O3). The correct description of an external electric field applied to a MIM device (Metal-Insulator-Metal) is now possible thanks to two methods one by an orbital separation approach [1] the other by using the non equilibrium green function formalism [2]. In this work, we propose to develop and to handle these methods by combining already existing simulation approaches. The main goal is to study the degradation mechanisms of an oxide by following the oxygen atoms movements coupled directly to the applied external electric field. These mechanisms are not known and this study will support the optimization and characterization efforts already engaged at LETI on RRAM functional prototypes. The targeted simulations tools are SIESTA for the DFT part, and TB_SIM for the electronic transport part.
[1] S. Kasamatsu et al., « First principle calculation of charged capacitors under open-circuit using the orbital separation approach, PRB 92, 115124 (2015)
[2] M. Brandbyge et al., « Density functional method for nonequilibrium electron transport », PRB 65, 165401 (2002)
Thermodynamic modelling of protective coating for solid oxide electrolysis cells
In the pursuit of a sustainable energy future, solid oxide electrolysis cells (SOECs) are a highly promising technology for producing clean hydrogen by electrolysis of water at high temperature (between 500 and 850°C). Although high operating temperature offers many benefits (high efficiency and low power consumption), it can lead to degradation of the interconnectors. Coatings are proposed to improve the long-term performance of interconnectors and reduce corrosion problems. The aim is to find the best coating candidates with high thermodynamic stability, high electrical conductivity and low cation diffusivity. In this context, you will join the LM2T team within the DIADEM Project (https://www.diadem.cnrs.fr/2023/03/29/atherm_coat/) for innovative materials.
Your role will be to:
1)Perform thermodynamic simulations using CALPHAD method and Thermo-Calc Software to predict the stability range of a set of coating candidates (e.g. spinel oxides and perovskites) and the possible decomposition reactions in different atmosphere conditions (temperature and oxygen partial pressure). In this step, the candidate will also perform a critical review of the thermodynamic data available in the literature.
2)To couple information obtained from CALPHAD calculations and the thermodynamic database to estimate the thermal expansion and electrical conductivity of the most promising compositions.
The candidate will work closely with the experimental team (ISAS/LECNA and UMR-IPV) producing the coatings to guide future trials and adapt the method to better meet large-scale production needs.
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.
Carbon nanotubes grafting for positive electrodes of lithium/sulfur cells
In a view to develop electric vehicles, researches on lithium batteries are now focusing on sulfur active material. Indeed, this new system should allow to produce cheap and high energy batteries of about 600 Wh/kg. While being developed for more than 40 years, the limitations of such a system are still quite problematic: elemental sulfur is an electronic insulator, sulfur and intermediate lithium polysulfides are soluble in the electrolyte and final discharge product Li2S is non-soluble and insulating too.
This post-doctoral position will thus aim at improving the performances of the sulfur positive electrode, by combining :
- Carbon nanotubes that will allow to improve the electronic conductivity of the positive electrode, as well as to provide a substrate for sulfur grafting
- Disulfide functions that will be grafted on the nanotubes. Thanks to this chemical grafting of active material, the electrochemical reaction would occur without leading to sulfur and polysulfides dissolution, thus leading to higher capacity and cyclability along with lower self-discharge.
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.
New electrode materials for Na-ion batteries
Na-ion battery is a challenging technology to replace Li-ion battery as it is cost competitve and may allow better cycle life. Sodium has also similar property to Lithium (light and electronegative element).
The eletrochemistry of the sodium is somewhat different of lithium with much less studies reported in the litterature.
The work will consist in the elaboration and characterization of promising electrode materials for Na-ion batteries.