Etude et réalisation de couches minces à caractère magnétique par pulvérisation cathodique magnétron (Application pour des capteurs de type GMI)

Cette étude vise à établir des corrélations entre les propriétés structurales et les propriétés magnétiques des revêtements Fe-Si élaborés par pulvérisation cathodique magnétron. L'alliage Fe-Si (coté riche en Fe) a été choisi en raison de son caractère ferromagnétique doux et de son fort potentiel applicatif dans différents systèmes magnétiques. Dans cet esprit, nous avons réalisé une série d'alliages avec différentes teneurs en Si. Les résultats obtenus nous ont permis de mettre en évidence les propriétés magnétiques extrêmement douces de l'alliage Fe-Si à 25 at.% de Si. L'étude des domaines magnétiques de cet alliage par effet Kerr a révélé une configuration en domaines parfaitement parallèle sur une surface importante de l'échantillon. Ce type de configuration est particulièrement recherché dans les couches minces magnétiques utilisées dans les capteurs à magnéto-impédance géante. C'est pourquoi nous avons étendu notre étude des propriétés de cet alliage par la réalisation de capteurs à magnéto-impédance en structure sandwich. La caractérisation de ces capteurs a clairement montré l'influence de l'orientation des domaines magnétiques ainsi que l'épaisseur totale des capteurs sur la variation d'impédance de ces derniers.This study aims to correlate the structural and magnetic properties of Fe-Si coatings prepared by magnetron sputtering. The Fe-Si alloy (Fe-rich side) was chosen due to its soft ferromagnetic character and potential application in various magnetic systems. In thispurpose, we carried out a series of alloys with various Si contents. The obtained results allowed to highlight the extremely soft magnetic properties of Fe-Si alloy at 25 at.% Si. The magnetic domains study using Kerr effect revealed a perfectly parallel configuration of wall domains over a significant area of the sample. This type of configuration is particularly required in the magnetic thin layers used in the giant magneto-impedance sensors. Why we extended our study of the alloy properties by the realization of magneto-impedance sensors using sandwich structure. Characterization of these sensors has clearly shown the influence of the magnetic domains orientation and the total thickness of the sensors on the impedance variation.BELFORT-UTBM-SEVENANS (900942101) / SudocSudocFranceF

Ab initio study of La10_xSrx(Si,Ge)6O27_0.5x apatite for SOFC electrolyte

International audienceApatite structure materials have outstanding performances as electrolytes for SOFC. Among them,La10_xSrx(Si,Ge)6O27_0.5x (LSO) series have attracted more attention for a higher ionic conductivity. Twodoping positions have been investigated, Sr dopant at La position and Ge dopant at Si position. DopedLSO conductivity was studied using first principle density functional theory (DFT) calculations. Withthe increase of Sr-doped ratio, the DOS (density of states) peaks above Fermi level shift to a higher energylevel. Furthermore, the electron energy gap broadening reduces the electron migration, while ion migrationwas limited. However, few changes of DOS with Ge substitution can be observed. The activationenergies of these two dopants are simulated by the energy barriers of the migration channel. We haveobserved that the two dopant positions affect the apatite ionic conductivities with different mechanisms.Indeed, La doped position change the electron energy level and activation energy. However, the Siposition can affect the density of electrons since it is surrounded by the oxygen and away from themigration channel. The calculation results of ionic conductivity are also consistent with those obtainedby experiments

Electrochemical properties of Ti2Ni hydrogen storage alloy

International audienceIn this paper, the long cycling behavior, the kinetic and thermodynamic properties of Ti2Nialloy used as negative electrode in nickel-metal hydride batteries have been studied bydifferent electrochemical techniques. Several methods, such as, galvanostatic charge anddischarge, the constant potential discharge and the potentiodynamic polarization areapplied to characterize electrochemically the studied alloy. The studied electrodes areobserved before and after electrochemical tests at different temperatures by scanningelectron microscopy.The amorphous Ti2Ni is activated after five cycles and the achieved maximumdischarge capacity is about 67 mAh g_1 at ambient temperature. Despite the low values ofthe maximum discharge capacity and the cycling stability (17%) and the steep decrease ofthe discharge capacity after activation, this alloy conserves a good stability lifetime duringa long cycling. A good correlation is observed between the evolution of the discharge capacityand those of the redox parameters during a long cycling.The enthalpy change, the entropy change and the activation energy of the formationreaction of the Ti2Ni metal hydride are evaluated electrochemically. The found values ofthe enthalpy change, the entropy change and the activation energy are about_43.3 kJ mol_1, 51.7 J K_1 mol_1 and 34.9 kJ mol_1, respectively

Additive Manufacturing of Soft Ferromagnetic Fe 6.5%Si Annular Cores: Process Parameters, Microstructure, and Magnetic Properties

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Multi-Material BESO Topology Optimization for SynRM based on printed FeSi6.5%

International audienceThis paper presents a design methodology for electric machines (EM). It is based on discrete multi-material topology optimization (TO) and printed material characteristics. Our methodology uses the Bi-directional Evolutionary Structural Optimization (BESO) heuristic for optimization, and to maximize EM torque, we propose a reformulated problem to accelerate simulation time. It permits considering both ferromagnetic materials and permanent magnets with discrete variables. Printed material characteristics are taken into account, considering several process parameters. A comparison of the final designs for different BH curves is presented

Energetic modeling, simulation and experimental of hydrogen desorption in a hydride tank

International audienceThis paper presents a zero-dimensional (0D) model of hydride tank. The model aims to study the dynamic heat and mass transfers during desorption process in order to investigate the thermal-fluidic behaviors of this hydride tank. This proposed model has been validated experimentally thanks to a tailor-made developed test bench. This test bench allows the hydride characterization at tank scale and also the energetic characterization. The simulation results of the heat exchanges and mass transfer in and between the coupled reaction bed, show good agreement with the experimental ones. It is shown that the heat produced by a Proton Exchange Membrane Fuel Cell (PEMFC) (estimated starting from an electrical model) is enough to heat the metal alloy (FeTi) and therefore release the hydrogen with a sufficient mass flow rate to supply the PEMFC. Furthermore, the obtained results highlight the importance of the developed model for energy management of the coupling of fuel cell and hydride tank system

Influence of the key parameters on the dynamic behavior of the hydrogen absorption by LaNi5

International audienceThe optimal design of hydride tanks is a major technological issue for the rapid developmentof this technology. In this paper, a two-dimensional model of a closed metalehydrogenreactor is presented. The temperature and the pressure temporal evolutions withinthe reactor as a function of time are reported. In order to determine the parameters tooptimize a fast kinetic and optimal heat exchange, the impact of the supply pressure, theporosity and the dynamic viscosity have been studied. The results show that the effect ofthese parameters are key-factors for an optimized tank design

Synthesis of apatite type La10−xSrxSi6O27−0.5x powders for IT-SOFC using sol–gel process

International audienceApatite-type lanthanum silicates draw researchers' attention due to their good performance as electrolyte materials for IT-SOFC (intermediate temperature solid oxide fuel cells). In this paper we present the synthesis of Sr-doped La10Si6O27 obtained by optimizing a water-based sol–gel process. The relevant synthesis parameters have been investigated to get pure, highly crystalline powders. The mechanisms occurring in the sol–gel reactions are discussed to improve the process of the sol formation. Using this optimized sol–gel process, pure apatite powders have been obtained by calcination from a temperature as low as 800 °C for 2 h and characterized using scanning electron microscopy and X-ray diffraction. The sintering treatment was performed at the temperature of 1500 °C leading to well-crystallized electrolytes likely to be used in fuel cell applications. Ionic conductivities have been measured in order to investigate the effect of the Sr-doping. The results show that the ionic conductivity is thermally activated and its value lies between 3 × 10−2 and 1 × 10−6 S cm−1 at 873 K as function of the composition and powder preparation conditions

Structure, Microstructure, Hyperfine, Mechanical and Magnetic Behavior of Selective Laser Melted Fe_92.4Si_3.1B_4.5 Alloy

A disordered ε-FeSi crystalline structure was produced by selective laser melting in Fe92.4Si3.1B4.5 powder alloys fabricated with different laser powers at a laser scanning speed of 0.4 m/s. The phase formation, microstructure, roughness, microhardness, and hyperfine and magnetic properties were studied using X-ray diffraction, scanning electron microscopy, atomic force microscopy, a profilometer, a microdurometer, transmission 57Fe Mössbauer spectrometry and vibrating sample magnetometry. The aim of this work was therefore to study the effect of laser power on the phase formation, microstructure, morphology, and mechanical, hyperfine and magnetic properties. The XRD patterns revealed the coexistence of a bcc α-Fe0.95Si0.05, a tetragonal Fe2B boride phase and a disordered ε-FeSi type structure. The existence of the disorder was confirmed by the presence of different FeSi environments observed in the Mössbauer spectra. The Fe2B boride contained about 51–54% of Fe atoms. The porosity and roughness decreased whereas laser power increased. The sample produced with a laser power of 90 W had a smooth and dense surface, high microhardness (~1843 Hv) and soft magnetic properties (saturation magnetization Ms = 200 emu/g and coercivity Hc = 79 Oe)

Multi-Material BESO Topology Optimization for SynRM based on printed FeSi6.5%

This paper presents a design methodology for electric machines (EM). It is based on discrete multi-material topology optimization (TO) and printed material characteristics. Our methodology uses the Bi-directional Evolutionary Structural Optimization (BESO) heuristic for optimization, and to maximize EM torque, we propose a reformulated problem to accelerate simulation time. It permits considering both ferromagnetic materials and permanent magnets with discrete variables. Printed material characteristics are taken into account, considering several process parameters. A comparison of the final designs for different BH curves is presented