Design and fabrication of magnetic cores having permeability gradient using additive manufacturing

As a major technological research institute, the CEA-Liten plays a decisive role in the development of future technologies for the energy transition and the limitation of greenhouse gas emissions. The laboratory develops magnetic components working at high frequency (> 100 kHz) for an integration in compact power electronics converters. Today, the discrete magnetic components are among the most bulky parts in the power converters (~30-40%) and they are responsible of almost 40-50% of the heat losses. The advent of wide band gap semiconductors (SiC or GaN) increases the switching frequency to values above 100 kHz. This strategy helps to reduce, theoretically, the dimensions of the passives but the thermal constraints (due to the losses produced at a higher frequency) and the electromagnetic compatibility (EMC; due to the noise emerging from faster switching commutations) may constitute an issue (in a system approach). In this sense, the developments of new architectures (based on advanced core geometries or clever magnetic materials arrangements) may constitute a breakthrough. The diversity of present cores and fabrication technologies permit small incremental gains on these magnetic components integrations. Additive manufacturing is a very emerging fabrication process that allow not only developing new core geometry but also, the adjustment of core composition (by allowing the deposition of layers containing different ferrite powder composition). The post-doctoral fellow will work on the design of a core having a permeability gradient and on its electrical and thermal characterizations. The post-doctoral fellowship is of 2 years duration located in the city of Grenoble (France) with a minimum wage of 40 k€ per year. If you want to have more detail please use the following link: https://liten.cea.fr/cea-tech/liten/Documents/Postdoc-Carnot-EF/AMbassador.pdf

Batteries recycling :Development and understanding of a new deactivation concept of lithium ion domestic batteries

Domestic lithium ion batteries gather all batteries used in electronic devices, mobile phone, and tooling applications. By 2030, the domestic lithium-ion battery market will increase up to 30%. With the new European recycling regulation and the emergency to find greener and safer recycling process, it is today necessary to develop new deactivation process of domestic lithium ion batteries.

The process has to address several lithium ion chemistries, be continuous, safe, controllable and low cost.
To develop this new concept, the first step will be to define the most appropriate chemical systems. Then these chemical systems will be tested in a dedicated experimental laboratory setup using chemistry and electrochemistry, allowing the simulation of real conditions of domestic batteries deactivation.
The third step will be to characterize, understand and validate the electrochemical and physico chemical mechanisms. The last step will be to participate to the validation of the deactivation concept on a real object (a lap top battery) in representative conditions (on the abuse tests plateform of CEA).

High entropy alloys determination (predictive thermodynamics and Machine learning) and their fast elaboration by Spark Plasma Sintering

The proposed work aims to create an integrated system combining a computational thermodynamic algorithm (CALPHAD-type (calculation of phase diagrams)) with a multi-objective algorithm (genetic, Gaussian or other) together with data mining techniques in order to select and optimize compositions of High entropy alloys in a 6-element system: Fe-Ni-Co-Cr-Al-Mo.
Associated with computational methods, fast fabrication and characterization methods of samples (hardness, density, grain size) will support the selection process. Optimization and validation of the alloy’s composition will be oriented towards two industrial use cases: structural alloys (replacement of Ni-based alloys) and corrosion protection against melted salts (nuclear application)

Lean-Rare Earth Magnetic materials

The energy transition will lead to a very strong growth in the demand for rare earths (RE) over the next decade, especially for the elements (Nd, Pr) and (Dy, Tb). These RE, classified as critical materials, are used almost exclusively to produce NdFeB permanent magnets, and constitute 30% of their mass.
Several recent international studies, aiming to identify new alloys with low RE content and comparable performances to the dense magnetic phase Nd2Fe14B, put hard magnetic compounds of RE-Fe12 type as advantageous substitution solutions, allowing to reduce more that 35% of the amount of RE, while keeping the intrinsic magnetic properties close to those of the Nd2Fe14B composition.
The industrial developments of the RE-Fe12 alloys cannot yet be considered due to the important technological and scientific challenge that remain to be lifted in order to be able to produce dense magnets with resistance to demagnetization sufficient for current applications (coercivity Hc > 800 kA/m).
The aim of the post-doctoral work is to develop Nd-Fe12 based alloys with optimized intrinsic magnetic properties and to master the sintering of the powders in order to obtain dense magnets with coercivity beyond 800 kA/m, to fulfil the requirements of the applications in electric mobility. Two technological and scientific challenges are identified:
- understanding of the role of secondary phases on the coercivity. This will open the way to the implementation of techniques called "grain boundary engineering", well known for the NdFeB magnets to have remarkably improved the resistance to demagnetization.
- mastering the sintering step of these powders at low temperature (< 600°C) in order to avoid the decomposotion of the magnetic phase by grain boundary engineering

Wood modifications by supercritical CO2

In order to replace current high environmental impact construction materials, CEA leads research work on chemical functionalization of wood (from French local forests) to improve its properties and make them a viable substitute of these construction materials or imported construction wood.
In this frame, chemistry under supercritical CO2 appears to be an efficient way to carry innovative chemistries while liùmiting the environmental impact & VOCs emissions of such processes.
Thus, you will be in charge of the development of new processes of chemical modification of local wood species under supercritical CO2. You will lead the research project by perfroming the state of the art, making technical propositions (around the adapted functionalization chemistries), carrying out the eperiments & the characterizations and will be in charge of respecting the deadlines & redacting the associated deliverables.

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.

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.

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.

Predictive design of heat management structures

Heat management is a paramount challenge in many cutting edge technologies, including new GaN electronic technology, turbine thermal coatings, resistive memories, or thermoelectrics. Further progress requires the help of accurate modeling tools that can predict the performance of new complex materials integrated in these increasingly demanding novel devices. However, there is currently no general predictive approach to tackle the complex multiscale modeling of heat flow through such nano and micro-structured systems. The state of the art, our predictive approach “ShengBTE.org”, currently covers the electronic and atomistic scales, going directly from them to predict the macroscopic thermal conductivity of homogeneous bulk materials, but it does not tackle a mesoscopic structure. This project will extend this predictive approach into the mesoscale, enabling it to fully describe thermal transport from the electronic ab initio level, through the atomistic one, all the way into the mesoscopic structure level, within a single model. The project is a 6 partner effort with complementary fields of expertise, 3 academic and 3 from industry. The widened approach will be validated against an extensive range of test case scenarios, including carefully designed experimental measurements taken during the project. The project will deliver a professional multiscale software permitting, for the first time, the prediction of heat flux through complex structured materials
of industrial interest. The performance of the modeling tool will be then demonstrated in an industrial setting, to design a new generation of substrates for power electronics based on innovating layered materials. This project is expected to have large impacts in a wide range of industrial applications, particularly in the rapidly evolving field of GaN based power electronics, and in all new technologies where thermal transport is a key issue.

Nanoparticle synthesis for photovoltaic appliation

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