Academic literature on the topic 'Medium métallique'
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Dissertations / Theses on the topic "Medium métallique":
Lecoq, Marie. "Étude du colmatage de filtres métalliques par un aérosol liquide." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0006.
Industrial installations often contain hazardous materials in aerosol form. High efficiency filters (HEPA) are usually the last barrier that ensure the containment of these airborne particles. In the nuclear industry, a large amount of radioactivity is handled in liquid form, that may release, in few scenarios, liquid aerosols. These particles may affect the performance of HEPA filters with a huge increase of the pressure drop, which lead in return to a significant reduction of the ventilation flowrate. In such scenarios the pressure drop increase may exceed the filter mechanical strength and induce degradations of the media and leading to a deterioration of its capacity to retain aerosol pollutants. To overcome this problem, and to protect HEPA filter, one of the solutions is to use pre-filter (more mechanically resistant but less efficient) made up with metallic fibers. To validate this approach, it is necessary to study the behavior of these prefilters, composed of a stack of different monolayers of media. In my work, I first focused on the clogging of industrial prefilters with liquid aerosol particles. Then, for a more analytical study, I study the clogging each layer separately, in order, to model, on the future, the behavior of the assembly. The microphysical of each media (thickness, packing density, and fiber size distribution) are determined. The evolution of both filter collection efficiency and pressure drop are studied along the clogging by a submicron liquid aerosol DEHS, for different filtration velocity (0,9 à 18 cm/s). For monolayer filters, I measure pressure drops in line with the previous results found in the literature. These experiments first highlight a quasi-linear increase of the pressure drop, associate with a collection of the droplets by the fibers. Then an exponential growth is measures, that corresponds to the clogging of the pores. And finally, an abrupt stabilization is observed corresponding a liquid film formation and its continuous drainage by the airflow. However, I show a more gradual stabilization for multilayer filters. A clogging scenario is proposed, and a simplistic model is established to forecast the pressure drop as a function of the mass of liquid accumulated. To this aim, I develop a new method to freeze the liquid accumulation using resin, that where further analyze using X-ray tomography
Habiyaremye, Frederic. "Mechanisms of plastic deformation near grain boundaries in CrCoNi medium entropy alloy." Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0012.
The interactions of dislocations and grain boundaries significantly influence the strength of metallic materials, as proven by the well-known Hall-Petch relationship. The latter is particularly effective in the CrCoNi medium entropy alloy because the alloy exhibit a higher Hall-Petch slope than most conventional alloys. However, the relation assumes that all grain boundaries are of the same types and respond equally to incoming dislocations, which is not true in polycrystalline materials. Therefore, the understanding of the interactions of dislocations different grain boundaries in CrCoNi medium entropy alloys is very crucial for the design of optimized grain boundaries, but also for improving the performance of other engineering alloys. This thesis employed accurate electron channeling contrast imaging to examine evolution of microstructure before and after nanoindentation of single and polycrystalline samples of CrCoNi medium entropy alloys. Moreover, numerical elasticity calculations and atomistic simulations were used to access cases unavailable from the experiments. The results revealed mechanisms responsible for the incipient plasticity are homogeneous and heterogeneous nucleation of dislocations, which are controlled by distance from the indentation axis to the nearest dislocation and different configurations of dislocations. The nucleated dislocations pile up along specific face-centered slip planes until they meet grain boundaries. Low angle grain accommodates plasticity by blocking and absorbing incoming lattice dislocations as well as collective motion of its constitutive dislocations. Similarly, the twin boundary accommodates plasticity by blocking and absorption of dislocations. Moreover, the slip was transferred from one grain to the other adjacent to the twin boundary. The results of this thesis bring new insights into intragranular plasticity and interactions of lattice dislocations with low angle and twin boundaries as well as their respective micromechanical responses in metallic materials, specifically, medium- and high-entropy alloys
Mader, Dorathea Felicitas. "Relation structure - propriétés de commutation dans les matériaux à transition de spin : effet de nanostructuration et de dilution du cation métallique." Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10124/document.
In the last years, intensive research activity has been dedicated to iron(II)-based spin transition compounds, for a better understanding of the fundamental phenomena as within the scope of practical application. These molecular materials possess two electronic configurations, which are interchangeable by the application of an external perturbation (thermal and optic bistability). Strong electron-lattice coupling may lead to cooperative behaviour, consequently abrupt spin transitions and hysteretic behaviour at the origin of a memory effect. Understanding and controlling this property is of primary interest in fundamental and applied research. The influence of metal dilution on the photo-induced transitions in FexZn1-x(btr)2(NCS)2.H2O is investigated by X-Ray diffraction on single crystals. We suggest a microscopic model interpreting the dynamics of the phase transition (nucleation and growth mechanisms of spin-like domains) through a structural analysis of the diffraction data. The effects of nanostructuration on the physicochemical properties have been studied on the one-dimensional coordination polymer [Fe(Htrz)2trz](BF4). Different surfactant-based organized molecular systems with various structural organizations are chosen for the synthesis in confined environments: reverse micellar solutions as well as lamellar (Lalpha) and reverse hexagonal (HII) liquid crystal phases. A relationship between size and shape, microstructure and physicochemical properties is established with a specific attention to reaction dynamics in the liquid crystal phase
Deng, Xiaodong. "Nondestructive evaluation of thermal sprayed coating by acoustic microscopy and Eddy current testing." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0030/document.
In the current work, we investigate the nondestructive evaluation of a thermal sprayed coating (Hastelloy C22 Ni-based alloy) on substrate (type 304 austenitic stainless steel) using acoustic microscopy and ECT method. Two models were built for the evaluation of this kind of material: one is for acoustic V(z) measurement and the other is for swept eddy current measurement. The implementation of these two models is used for the evaluation and properties measurement of the thermal sprayed coatings, such as elastic properties, electromagnetic properties. In particular, the main achievements and results are as follows: 1. Acoustic wave propagation in an anisotropic multilayered medium was investigated. The formula for calculating the reflection and transmission coefficients of the multilayered medium on or without a substrate were derived, which is necessary for the modeling of acoustic V(z) measurement of the thermal sprayed coating on substrate. 2. A model was built for the acoustic V(z) measurement of the thermal sprayed coatings on substrate, which can deal with anisotropic multilayered media. Specifically, we used a model of multilayered coatings with graded properties on substrate to calculate the acoustic reflection coefficient of our sample. Treating the thermal sprayed coating, deposited on a 304 steel substrate, as FGMs, we evaluated the coating thickness and the Young’s modulus evolution along the depth of the coating. 3. A model was built for the swept eddy current measurement of the thermal sprayed coatings. Since before the spraying process, the surface of the substrate is usually shot-peened (SP), the coated material is considered as a three-layer medium. The coating thickness and electromagnetic properties of each of the 3 layers were determined by an effective reverse process. 4. The thermal sprayed coated material after exposure in different conditions, i.e., as-received, heat-treated in air and heat-treated in SO2 environment, and after different exposure time was evaluated by the integrity of acoustic microscopy and ECT method. The coating thickness and the electromagnetic properties of the coated material under different conditions were measured
Geindreau, Christian. "Modélisation du comportement viscoplastique des poudres métalliques : simulation à l'aide d'un matériau analogique." Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10169.
Mansour, Yehia. "Études théorique et expérimentale de la formation des nanoparticules métalliques par ablation laser en milieu liquide. Modélisations des propriétés optiques et thermiques de l'interaction Laser-Nanoparticules." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0283.
Noble metal nanoparticles (NPs) are the site of a surface plasmon resonance phenomenon resulting from the collective oscillation of their conduction electrons under the effect of an electromagnetic wave. In the case of gold and silver NPs, the resonant frequency is in the visible range, which gives these plasmonic NPs unique optical properties. In particular, the position and intensity of the plasmon resonance depend on their size, shape (aspect ratio) and the index of the host medium. The possible applications require pure samples and mono-dispersed distribution. The chemical synthesis of NPs allows the shape and size of NPs to be controlled. However, it requires the use of stabilizing agents, which lead to surface contamination by synthetic residues. To limit this disadvantage, the physical technique of laser ablation in a liquid medium is a promising alternative, which, however, suffers from a lack of control over the shape and size of the NPs produced. The shape and size of NPs produced by liquid laser ablation (ALML) are closely related to the three essential steps of the process: Target / laser interaction; Mass transport; Laser / NPs interaction suspended in the liquid. In order to understand the mechanisms governing each of these stages, it is necessary to study them separately. In this work, we focused on the mechanisms of interaction between the laser beam and the NPs suspended in the liquid. Depending on the energy density absorbed by the suspended NPs, they undergo fragmentation or remodeling. We then studied the mechanisms behind the phenomenon of fragmentation. The evolution of the shape distribution of NPs during NP fragmentation was studied by developing an original and quantitative technique of in-situ optical spectroscopy. And, the evolution of the volume fraction of NPs during their preparation by ALML by in-situ optical spectroscopy is obtained and analyzed. In parallel with the experimental work, we have developed theoretical models for understanding the mechanisms of formation of metallic nanoparticles by laser ablation in a liquid medium. A modest study on the modeling of optical and thermal properties of the Laser-Nanoparticle interaction is discussed in this thesis. A modified Takami thermal model named MTM was also presented. Its important utility has been demonstrated for mechanisms for the interpretation of the mechanisms of laser-NPs interaction
Colin, Dominique. "Obtention, corrosion et analyse de surface d'alliages amorphes inoxydables." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0111.