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1
Cai, Yihui. „Mechanosynthesis of 3D, 2D and quasi-2D hybrid perovskites and MAPbI3@graphite composites : mechanisms and potential applications“. Electronic Thesis or Diss., Strasbourg, 2024. https://publication-theses.unistra.fr/public/theses_doctorat/2024/Cai_Yihui_2024_ED222.pdf.
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Les pérovskites hybrides (PH) sont prometteuses pour des applications optoélectroniques au-delà de la photovoltaïque, avec d'autres applications explorées ici. Un défi majeur est d'obtenir une synthèse reproductible, pure et évolutive. La mécanosynthèse (MS), une méthode verte sans solvant, a permis de synthétiser des composites 3D PH MAPbI3 et graphite en 30 minutes, avec des propriétés similaires à celles des MAPbI3 à base de solvant. Le broyage prolongé a introduit des défauts, améliorant l'absorption des ondes électromagnétiques. Des PHs 2D purs n=1 et leurs composites ont été synthétisés avec succès avec trois ammoniums différents. Les PHs de faible dimension (n>2) ont montré une plus grande hétérogénéité de composition. La compaction des poudres de PHs 3D, 2D et quasi 2D a induit une préservation de la taille des grains, l’apparition d’une orientation préférentielle et une diminution de la réabsorption améliorant ainsi leur photoluminescence. Au niveau photodétection, le graphite a amélioré leur performance et les PHs (n>2) à la base phényléthylammonium ont montré des performances très prometteusesHybrid perovskites (HPs) are promising for optoelectronic applications beyond photovoltaics, with other application explored here. A main challenge is achieving reproducible, pure, and scalable synthesis. Mechanosynthesis (MS), a green and solvent-free method, was used to synthesize 3D HP MAPbI3 and graphite composites in 30 minutes, yielding properties similar to solvent-based MAPbI3. Extended grinding introduced defects, enhancing electromagnetic wave absorption. MS was also applied to low-dimensional HPs (n=1–3) with different ammoniums. Pure n=1 2D HPs and composites were synthesized successfully, while n>2 showed compositional heterogeneity. The compaction of 3D, 2D and quasi-2D PHs powders resulted in the preservation of grain size, the appearance of a preferential orientation and a reduction in reabsorption, thereby improving their photoluminescence. Graphite improved photodetection performance and phenylethylammonium-based PHs (n>2) showed very promising results
2
Rogier, Clémence. „Vers le développement d’un pseudocondensateur asymétrique avec des électrodes composites à base d’oxydes métalliques (MnO2, MoO3) et de carbones nanostructurés“. Thesis, CY Cergy Paris Université, 2020. http://www.theses.fr/2020CYUN1098.
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Les supercondensateurs sont des systèmes de stockage de l’énergie destinés à des applications de nécessitant de fortes densité de puissance. Leur densité d’énergie peut être augmentée en développant de nouveaux matériaux d’électrode à forte capacitance. Dans cet objectif ces travaux décrivent le développement de matériaux composites à base de carbones nanostructurés (architectures avec des nanotubes de carbones et/ou de graphène oxydé réduit) et d’oxydes métalliques pseudocapacitifs (MnO2 et MoO3 pour les électrodes positive et négative respectivement). Les oxydes métalliques permettent de générer de fortes capacitances grâce à des réactions redox réversibles sur une large gamme de potentiels. La matrice carbonée nanostructurée induit une porosité et une conductivité des électrodes optimisées et assure le transport des ions et des électrons au sein des matériaux.L’électrode positive MnO2-rGO-CNTs est développée par pulvérisation des nanomatériaux carbonés directement sur le collecteur de courant avec un spray dynamique robotisé puis par croissance électrochimique de l’oxyde. Sa capacitance maximale est de 265 F/g. Dans une approche similaire, l’électrode négative MoO3-CNTs est développée, avec une capacitance maximale de 274 F/g. Les matériaux d’électrodes sont caractérisés par différentes techniques physicochimiques (microscopies, analyses de porosité, DRX, spectroscopies).Ces électrodes sont ensuite associées au sein d’un pseudocondensateur hybride asymétrique utilisant un électrolyte organique (LiTFSI/GBL) avec une tension de fonctionnement de 2V. Les performances de ce système en termes de densités d’énergie et de puissance ainsi que de stabilité électrochimique sont étudiées sur plusieurs milliers de cycles. La densité d’énergie maximale est calculée à 25 Wh/kg pour une densité de puissance de 0,1 kW/kgSupercapacitors are energy storage devices for applications requiring high power densities. By developing new electrode materials with high capacitance energy densities can be enhanced. In that regard this work presents the development of composites materials associating nanostructured carbons (architectures with carbon nanotubes and/or reduced graphene oxide) and pseudocapacitive metal oxides (MnO2 and MoO3 for positive and negative electrodes respectively). Metal oxides generate high capacitances thanks to reversible redox reactions in a wide range of potentials. The nanostructured carbon matrix optimizes porosity and conductivity of the electrodes to ensure good ionic and electronic transport within the materials.First MnO2-rGO-CNTs is developed as a positive electrode using spray gun deposition of carbon nanomaterials before electrochemical growth of the oxide. The interest of these elaboration techniques lies in their easy large-scale implementation. Its maximum capacitance is measured at 265 F/g. In a similar approach MoO3-CNTs is developed as a negative electrode with a maximum capacitance of 274 F/g. The materials are characterized using different physicochemical methods (microscopy, spectroscopy, porosity analysis, XRD).These electrodes are then combined in an asymmetric hybrid pseudocapacitor in an organic electrolyte (LiTFSI/GBL) with an operating voltage window of 2V. The performances of this system in terms of energy and power densities as well as electrochemical stability were studied over several thousand cycles. The maximum energy density was found to be of 25 Wh/kg for a power density of 0.1 kW/kg
3
Repasi, Ivett. „Expanded graphite filled polymer composites“. Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557649.
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The aim of this project was to produce expanded graphite (EO) and modified EO-filled electrically conductive polymer composites and to investigate the effects of different additive modifications and preparation conditions on the microstructure and electrical properties of these composites. Modifications included the use of dry blending and ultrasound to reduce their size, use of various suspension media and surfactants to stabilize particle suspensions. To compare the effectiveness of different filler modification processes on electrical conductivity, unmodified and treated EO were incorporated into polypropylene (PP) by melt mixing and EO based dispersions were used to make polyvinyl alcohol (PV A) composites by solution casting. The PP composites were made using various processing methods and conditions at filler concentrations up to 12 wt%, while the polyvinyl alcohol samples contained graphite concentrations up to 8 wt%. To analyse the crystalline morphology of sample and the dispersion of the filler in the composites samples were analysed by light and electron microscopy, DSC and X-ray diffraction. TOA was also used to investigate the thermal stability of the composites. It was found that the presence of graphite, significantly changed the crystal morphology of PP. Solution mixed PVA samples showed improved dispersion and the particle size was effectively reduced.
4
Savage, Gary. „Mechanical properties of carbon/graphite composites“. Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38153.
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5
Leesirisan, Siriwan. „Polyethersulphone/graphite conductive composites for coatings“. Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/13597.
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In this research, the electrical conductivity and thermal properties of polyethersulphone (PES) insulating polymer were improved, at its optimum micromechanical properties, by filling with electrically and thermally conductive graphite, for use in coatings for electrostatic dissipation applications. The graphite employed was a micro-/nano-graphite with aspect ratios in the range 100-600. Two types of the graphite, untreated and treated, were used for PES composites and LiCI-doped PES composite fabrication via a solution method. The treated graphite was surface functionalised by concentrated nitric acid treatment. FT-IR indicated the effectiveness of concentrated nitric acid treatment in introducing additional -COOH groups on the surfaces of the graphite. XRD, SEM and TEM revealed the dispersion of the graphite throughout the PES matrix in both an immiscIble and disordered manner, and the existence of aggregates of graphite. Nanoindentation testing showed insignificant decreases in the nanohardness and elastic modulus of the PES/treated graphite composites when the treated graphite content was not more than 5 wt%; whereas, increasing the content of the treated graphite increased the nanoscratch resistance of the composites. Due to the high aspect ratio of the graphite, the electrical conductivities of the PES/untreated and PES/treated graphite composites were enhanced at low loadings. An initial conducting pathway was formed at lower than 3 wt% of the filler. The enhancement by 2 orders of magnitude of the electrical conductivity of a PES/treated graphite composite could be accomplished by doping with 0.06 wt% of LiC!. MDSC showed improvements in the thermal conductivity of the PES matrix by 165 and 91% with the addition of 5 wt% of the untreated and treated graphite, respectively. DSC curves illustrated higher glass transition temperatures of the PES/graphite composites and doped PES/graphite composites, compared to the pure PES. Decreases in relaxation enthalpy WIth time, due to physical ageing of PES, were smaller when the PES was filled with the graphite or LiCI-doped graphite. The decrease in relaxation enthalpy of the materials was accompanied by increases in glass transition temperature and characteristIc length. Physical ageing also led to a decrease in the electrical conductivities of the PES/graphite composites and doped PES/graphite composites.
6
Chen, Rong-Sheng. „Hygrothermal response of graphite/epoxy composites /“. The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487326511715323.
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7
Crews, Lauren K. (Lauren Kucner) 1971. „High temperature degradation of graphite/epoxy composites“. Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/42815.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1998.Includes bibliographical references (p. 266-270).
The problem of determining the response of a laminated composite plate exposed to a high temperature environment while mechanically loaded is approached by identifying the underlying mechanisms and addressing them separately. The approach is general, but the work focuses on the response of AS4/3501-6 graphite/epoxy composites. The mechanisms studied and modeled in this work are thermal response, degradation chemistry, and changes in mechanical material properties. The thermal response of an orthotropic plate exposed to convective heating is modeled using generalized heat transfer theory. The key parameters identified as controlling the thermal response include well-known parameters from heat transfer literature and a new parameter called the geometry-orthotropy parameter. From these parameters, the accuracy with which a multi-dimensional temperature distribution may be approximated using a onedimensional thermal model is quantified. The degradation chemistry of 3501-6 epoxy is studied through thermogravimetric analysis (TGA) experiments conducted in an inert atmosphere. A model of degradation based on a single Arrhenius rate equation is developed. Reaction constants for the degradation model are determined empirically and the validity of the model is verified through separate TGA experiments. A novel method for assessing the degradation state of a sample with an unknown thermal history is proposed. Analyses employing the method achieve estimates of the degradation state within 0.3 to 28% of the actual values. Changes in mechanical material properties are quantified by measuring the modulus and tensile strength of unidirectional [0]4 and [90]12 coupons exposed to temperatures as high as 400°C in a furnace. Some coupons are loaded to failure while exposed to the test temperature, others are first cooled to room temperature, allowing at-temperature and residual properties to be directly compared. Transverse properties are very sensitive to temperature around the glass transition temperature, but may recover when the coupon cools. Transverse properties are also very sensitive to small values (-0.03) of degradation state. Longitudinal properties are less sensitive to these variables. Temperature and degradation state are identified as appropriate metrics for quantifying changes in material properties. Models of the measured properties as functions of these variables are developed. A methodology for integrating models of the various mechanisms underlying structural response is presented. The thermal response model, degradation chemistry model, and material property models developed in this work are integrated with a thermomechanical response model based on classical laminated plate theory and implemented in a one-dimensional predictive code. This work establishes a foundation upon which a complete mechanism-based integrated model of the response of mechanically-loaded composites exposed to high temperatures may be developed. Specific recommendations for further work are provided.
by Lauren K. Crews.
Ph.D.
8
Lubaba, Nicholas C. H. „Microstructure and strength of magnesia-graphite refractory composites“. Thesis, University of Sheffield, 1986. http://etheses.whiterose.ac.uk/10254/.
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The relationships between fabrication variables, microstructure and selected properties of carbon bonded magnesia-graphite refractory composite materials have been investigated. A novel optical microscope method of characterizing the morphology of flake graphites was developed and used to determine distributions of length and thickness and average aspect ratios for the four graphite samples used in the study. The compaction behaviour of magnesia alone and in combination with the flake graphites has been studied in some detail and the microstructures of the products elucidated. It is shown that the amount of magnesia of small particle size plays a significant role in determining the graphite-graphite contact area in the structure. An irreversible volume expansion is observed on firing composites, the magnitude of which can be related to the microstructure and the graphite content. A phenolic resin binder restricts this expansion. It is shown that the carbon binder does not bond to the graphite phase and only weakly, if at all, to the magnesia. Consequently the strengths and moduli are low and show only a small variation with graphite type. The effect of adding graphite to carbon-bonded magnesia is to lower the strength slightly, but increasing the graphite content from 20-30% causes a small increase in strength. Increasing the amount of carbon bond from pitch has little effect on strength at levels of 5-15% whereas over the range 5-13% the resin binder has a more pronounced effect. The most significant factor affecting the strength and modulus of fired composites is the amount of silicon or aluminium, added as oxidation inhibitors, which react to form carbide and nitride phases. Finally, a brief study of slag penetration shows that this can be reduced by decreasing the amount of oxide fines in the composite because of the changes in microstructure that, result.
9
Engelbert, Carl Robert. „Statistical characterization of graphite fiber for prediction of composite structure reliability“. Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA238020.
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Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Wu, Edward M. "June 1990." Description based on signature page as viewed on October 21, 2009. DTIC Identifier(s): Graphite fiber strength testing, graphite fiber statistical evaluation. Author(s) subject terms: Graphite fiber strength testing, graphite fiber statistical evaluation, composite reliability predictions. Includes bibliographical references (p. 78-79). Also available in print.
10
Elmore, Jennifer Susan. „Dynamic mechanical analysis of graphite/epoxy composites with varied interphases“. Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-10312009-020414/.
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11
Bin, Junid Ramli. „Multiscale carbon fibre composites with epoxy-graphite nanoplatelet matrices“. Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/multiscale-carbon-fibre-composites-with-epoxygraphite-nanoplatelet-matrices(332f171a-d7a8-4346-90c1-fa08e42b058b).html.
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This thesis reports the effects of incorporating graphite nanoplatelets (GNPs) to epoxy-carbon fibre (CF) laminates to produce multiscale composites. A grade of epoxy resin typical for the application in aerospace engineering, triglycidyl-p-aminophenol (TGPAP), was used in this work cured with 4,4'-diaminodiphenyl sulfone (DDS). To improve the processability of TGPAP, a diluent, the diglycidyl ether of bisphenol F (DGEBF), was added to formulations. Compositions of TGPAP/DGEBF/DDS were optimised using response surface methodology (RSM) with the target response being to obtain high glass transition temperature (Tg) and low resin viscosity. From RSM, the optimum values were obtained at 55.6 wt. % of DGEBF and a stoichiometric ratio of 0.60. Before addition into epoxy, GNPs were treated either covalently using 3-aminopropyltriethoxysilane (APTS) or non-covalently using a commercial surfactant, Triton X-100 (abbreviated as A-GNPs and T-GNPs, respectively). After treatment, XPS analysis showed a new peak at 100 eV for A-GNPs indicating silicon and the C/O ratio increased from 11.0 to 26.2 for T-GNPs relative to unmodified GNPs (U-GNPs), suggesting attachment of the modifier molecules had occurred. Nanocomposites (NCs) were prepared by incorporate GNPs into epoxy using mechanical mixing. Rheological percolation threshold of GNP-epoxy suspensions were determined using oscillatory-shear rheometry as 3.9 wt. % for AR-GNPs, 3.6 wt. % for U-GNPs, 3.2 wt. % for A-GNPs and 3.5 wt. % for T-GNPs, suggesting surface treatment improved dispersion. At 4 wt. % of GNPs, flexural strain of NCs was decreased relative to neat epoxy by 46% for AR-GNPs, 48.6% for U-GNPs, 4.6% for A-GNPs and 30.8% for T-GNPs but flexural moduli showed small increases of 6.1-7.4%. Fracture toughness (K1C) also improved. For example, the K1C increased from 0.80 ± 0.04 MPa.m1/2 for neat epoxy to 1.32 ± 0.01 MPa.m1/2 for NCs containing 6 wt. % of U-GNPs possibly due to the branching of cracks resulting from the embedded GNPs. Due to their mechanical performance, A-GNPs were used to fabricate epoxy/CF/A-GNPs multiscale composites. Multiscale composites showed inferior properties relative to a comparable conventional composite in flexural testing, interlaminar shear strength (ILSS) and interlaminar fracture toughness mode II (G11C) due to weaker bonding at the matrix-CF interface. However, multiscale composites showed ~40% higher capability than conventional composite to absorb energy during impact due to greater interfaces formed by the inclusion of A-GNPs into the system.
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Morris, Justin Howard. „The tribological and wear properties of carbon-graphite composites“. Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/10799.
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A range of carbon-graphites with differing properties has been evaluated for wear resistance. These include carbons with a high degree of graphitic order (natural and synthetic graphite), those with little or no such order (pitch bonded cokes, glassy carbons) and impregnated grades. Testing has been carried out using abrasive wear, dry sliding wear, particle erosion, slurry erosion, cavitation erosion and the corresponding wear rates have been related to the bulk properties of the different materials. In all tests; hardness, elastic modulus, porosity and the presence of fillers were found to influence the wear rates of the various grades. Maximum wear rates were consistently observed with the softer, more porous unfilled carbons.
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Desai, Shanta Anand. „Fabrication and analysis of highly conducting graphite flake composites“. Thesis, University of Leeds, 2006. http://etheses.whiterose.ac.uk/4046/.
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Graphite has high in-plane thermal conductivity and is a potential candidate to combat the thermal management problems in high density electronic devices. However, the properties of graphite are not fully exploited and this study was carried out with the aim of fabricating and analysing high thermally conducting graphite based composites. Model composites were prepared with three different average flake sizes: 180 μm, 300 μm and 600 μm. The constituents( flakes and binders) were characterised in terms of density, carbon yield and crystallographic perfection using combination of techniques. The electrical resistivity of a single flake was found to be 0.6 μS2 m. A fabrication route was developed using 75% starting volume fraction (67% - 72%) estimated volume fraction in the composite) of small flake graphite. A high volume fraction was used so as to obtain composites with properties dominated by the flakes. The selection of the optimum route of fabrication was based on achieving the lowest electrical resistivity of the composite after carbonisation (1000 °C). An extensive study was carried out on composites prepared using 75% (starting volume fraction) flakes. The mis-alignment of the 002 plane was found to decrease with an increase in the flake size. The optical texture of small flake composites showed that the binder was inhomogeneously distributed and was observed to shrink away from the flakes whereas in the case of composites with large flakes, the binder was found to wet the flakes. The layers of the binder were also found to align along the basal planes of the flakes in the vicinity of the flakes. The composites with small flakes were found to be `brittle' whereas the large flake composites showed a more `ductile' behaviour. The Young's modulus and work-of-fracture were estimated from load versus extension curves. Raman studies showed an increase in the a-direction coherence length in the binder with an increase in heat-treatment temperature and the electrical resistivity of the composites was found to decrease with increase in flake size and heat-treatment temperature. The thermal conductivities were determined and samples were imaged in a thermal microscope. Comparison between quantitative thermal conductivity and that predicted using Lavin's relationship showed that Lavin's relationship is not applicable to these composites. A thermal conductivity of 655 W/m K (160% of that of copper) was achieved in graphitised large flake composites. The volume fraction of graphite was varied (estimated volume fraction 45%-75% in the composite) and graphitised large flake composites were studied. The density of the composites increased with an increase in the volume fraction whereas the mis-alignment of the 002 plane was found to decrease with an increase in the estimated volume fraction of graphite up to -70%. When the estimated volume fraction of graphite was further increased (-75%), the mis-alignment was found to increase. This was attributed to the microstructure which showed high packing density giving rise to twisting and distortion of flakes in the composite. Existing composite-type models failed to correctly predict the transport properties and hence, a first approach to developing a model specifically for these composites was attempted. However, due to their complex nature and insufficient information to define the modelling parameters its validity is uncertain. A thermal conductivity of 750 W/m K (190% that of copper) and density -1.8 g/cm3 (nearly one fourth of that of copper) and all this at relatively lower cost was achieved in graphitised large flake composites with -75% estimated volume fraction of graphite. This material is particularly attractive to combat thermal management problems.
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Ramanujam, B. T. S. „Structure, properties and applications of conducting graphite thermoplastic composites“. Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2010. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/3719.
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15
Geng, Yan. „Preparation and characterization of graphite nanoplatelet, graphene and graphene-polymer nanocomposites /“. View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20GENG.
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16
Patil, Amit k. „ADVANCED PROCESSING OF NICKEL-TITANIUM-GRAPHITE BASED METAL MATRIX COMPOSITES“. Cleveland State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=csu1560298763233401.
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Li, Wei. „Composite polymer/graphite/oxide electrode systems for supercapacitors“. University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439309266.
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18
Brender, Patrice. „Etude de l'influence de la température sur les réactions tribochimiques des matériaux carbonés : Application au freinage aéronautique de composites Carbone/Carbone“. Thesis, Mulhouse, 2012. http://www.theses.fr/2012MULH5872.
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L’objectif de ce travail est d’étudier quantitativement l’évolution des propriétés de surface des matériaux carbonés et leur réactivité dans les conditions proches de celles rencontrées lors du taxiage des avions. Les essais de freinage ont été réalisés à l’aide d’un Banc d’Essai Tribométrique à Simulation Inertielle. Les composites C/C frottés et les débris d’usure sont caractérisés par des techniques non-conventionnelles multi-échelles. Les composites frottés (dans leur totalité) et les débris d’usure sont caractérisés par thermo-désorption programmée et chimisorption d’oxygène. Ces analyses permettent de déterminer la nature et la quantité de groupes fonctionnels et la teneur en sites actifs, caractéristique de la réactivité intrinsèque du carbone et responsable de l’interaction avec les espèces gazeuses de l’environnement. Ces caractérisations sont complétées par des analyses morphologiques, structurales et texturales par microscopies, diffractions des rayons X, adsorption de gaz. L’analyse des caractéristiques physico-chimiques des débris d’usure et des disques frottés permet de remonter aux réactions tribochimiques ayant eu lieu dans le contact : des réactions chimiques entre l’oxygène ou l’eau et les liaisons C-C rompues ont été mises en évidence. Un modèle permettant de justifier les différences de propriétés tribologiques lors des essais de taxiage a été proposé. Ce modèle, basé sur la réactivité du système et sur les propriétés de l’interface de frottement, permet d’élucider les problématiques liées à la température dans ce type de systèmeThe objective of this work is to study quantitatively the evolution of carbon materials surface properties and reactivity under breaking conditions similar to those encountered during taxiing. The breaking tests were carried out using a Tribometric Test Bench. The rubbed C/C composites and the wear debris collected are then characterized by mutiscale unconventional techniques. The whole rubbed composites and the wear debris are characterized by Temperature-Programmed Desorption and by oxygen chemisorption. These analyzes are used to determine the nature and amount of functional groups and the content of active sites that is characteristic of the reactivity of the carbon material and also responsible of its interaction with the surrounding environment. The characterizations are completed by morphological, structural and textural analysis, such as Electron Microscopy, X-Ray Diffraction and gas adsorption. The analysis of the physic-chemical characteristics of wear debris and of the rubbed discs enables to evidence the tribochemical reactions occurring in the mechanical contact: chemical reactions between oxygen or water and the broken C-C bonds have been evidenced. A model is finally proposed, justifying the differences in the tribological properties during taxiing tests. The later is based on the carbon reactivity and on the interface properties and justify the temperature dependence of this system
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Hansen, Robert C. „Thermal and mechanical fatigue of 6061 Al - P100 Gr metal matrix composite“. Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA238795.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, September 1990.Thesis Advisor(s): Dutta, Indranath ; Mitra, Shantanu. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Fatigue (mechanics), thermal fatigue, metal matrix composites, laminates, bending, ultimate strength, fiber reinforced composites, theses. Author(s) subject terms: Aluminum-graphite composite, bend fatigue, thermal fatigue. Includes bibliographical references (p. 64-65). Also available in print.
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Cerezo, Frances Therese, und francestherese_cerezo@hotmail com. „Thermal stability and mechanical property of polymer layered graphite oxide composites“. RMIT University. Applied Sciences, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080627.161157.
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Polymer composites formed from layered fillers with high surface volume ratio show enhanced reinforcement. Graphite oxide is a high modulus material that can be separated into thin layers with high surface area. The aim of this study is to prepare polymer layered graphite oxide composites using functionalised polyolefin to enhance compatibility with various forms of layered graphite oxide in varying concentration. Functionalised polyolefins reinforced with layered graphite oxides and expanded graphite oxides were prepared using solution blending and melt blending methods. Three different mixing methods with varying shear intensity were employed to prepare polymer layered graphite oxide composites. The crystalline structure, thermal and mechanical properties of the prepared polymer layered graphite oxide composites was studied. Oxidised graphite prepared from the Staudenmaier method and its exfoliated form were dispersed in poly(ethylene-co-methyl acrylate-co-acrylic acid) (EMAA) via solution blending to prepare EMAA layered composites. The thermal stability was determined using thermogravimetric analysis. The EMAA layered composites showed higher thermal stability in comparison with pure EMAA. The mechanical properties of these EMAA layered composites were determined through dynamic mechanical analysis. Shear modulus, yield stress and storage modulus of EMAA in the presence of graphite oxide fillers decreased. A solution blending method was used to prepare poly(propylene-grafted-maleic anhydride) layered expanded graphite oxide composites (PPMA-EGO). Two types of PPMA-EGO were prepared using different mixing methods - low and high shear were employed. The effects of preparative mixing methods on the PPMA-EGO properties were investigated. The mechanical properties of PPMA-EGO obtained from dynamic mechanical analysis indicated that EGO had a reinforcing effect on the elastic behaviour of PPMA-EGO. This is due to strong interfacial adhesion between PPMA and EGO as a result of hydrogen bonding. The elastic behaviour of PPMA-EGO was affected by the surface area of graphite flakes. Low sheared PPMA-EGO elastic behaviour was found to be higher compared with that of high sheared PPMA-EGO. A melt blending method was used to prepare PPMA-EGO with varying EGO concentration. The interconnected network structure of EGO in the PPMA-EGO was not observed as shown by its scanning electron microscopy images. Thermogravimetric analysis of PPMA-EGO indicates increased decomposition temperature of the PPMA matrix. Dynamic mechanical analysis showed enhanced storage modulus of PPMA-EGO. The maximum elastic modulus of PPMA-EGO was observed at 3 %wt of EGO. The electrical conductivity of PPMA-EGO was measured only for EGO concentrations above 2 %wt. The EGO concentration was found to be the most critical factor in the enhancement of the electrical conductivity of PPMA-EGO. Wide angle X-ray diffraction analysis of all polymer layered graphite oxide composites revealed no change in interlayer spacing of graphite layers, indicating the absence of EMAA intercalation in the graphite layers. The crystallisation temperature and crystallinity of all polymer layered graphite oxide composites were determined using differential scanning calorimetry. The results indicated that graphite oxide and expanded graphite oxides acted as nucleating agents in inducing the crystallisation of functionalised polyolefin in the layered composites. However, the degree of crystallinity of functionalised polyolefin decreased in the layered composites.
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Vandenbossche, Benoit. „Measurement of ultrasonic wave mode transition in unidirectional graphite/epoxy composites“. Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10242009-020340/.
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Wang, Jianjian Ph D. Massachusetts Institute of Technology. „Transport properties of graphite-loaded composites in liquid and solid states“. Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103476.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 117-133).
Composites, either in solid state or liquid state, are widely used to improve the transport properties of the matrix phase in the composites. For instance, high thermal conductivity particles are frequently added into heat transfer liquids, forming colloidal suspensions sometimes also called nanofluids, to increase the liquids thermal conductivity. High electrical and/or thermal conductivity particles are also commonly added into polymers to increase their electrical and thermal conductivities. The properties of composites depend strongly on the microstructures formed. This thesis investigates thermal, rheological, and electrical properties of graphite loaded composites in liquid and solid states. First, we use combined optical microscope and AC impedance spectroscopy technique to study the composite microstructure transformation with respect to the volume fraction to understand the peculiar thermal conductivity behavior in the graphite suspensions we observed: the thermal conductivity increases more rapidly below the percolation threshold than above it, with a sharp kink at the percolation. Our study suggests that the below the percolation, the aggregation of graphite flakes is tighter and interfacial resistance is smaller, while above the percolation threshold, the aggregation of graphite flakes becomes looser and interfacial resistance is larger. Next, we study rheological properties of graphite-loaded liquids. We observed complicate temperature-dependent rheological properties of graphite suspension at different shear rates and temperature. We rationalize the experimental data using ideas from Stokesian dynamics simulations and combined with understandings of the internal structures of suspensions. Our studies show although Brownian motion is not important for thermal transport, it is important for rheological properties of the graphite-loaded suspensions. Chapter 4 studies thermal and electrical properties of graphite flakes loaded into a material going through liquid-to-solid phase transition in the percolated regime and shows that the transport properties can be switched via the phase transition reversibly, especially achieving high contrast in the electrical conductivity. We found that the stress generated during the freezing regulates the contacts among graphite flakes if a crystal-forming liquid is use, thus leading to a dramatically increase in the electrical conductivity in the solid state. In Chapter 5, we study thermal and electrical conductivities of composites with graphite flakes loaded into ultra-high molecular weigh polyethylene that are stretched at different ratios. The mechanical stretching of the composites affect the morphology and transport properties of both the polymer and the fillers, leading to some interesting thermal conductivity behavior. The graphite-loaded composites in liquid and solid states studies in this thesis may have applications in convective heat transfer, resettable fuse, seasonal regulation of building temperature, thermal interface materials, directional heat spreader, etc. The understanding of structure-property relation could also help uS better design composite materials with superior performance..
by Jianjian Wang.
Ph. D.
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Haddouch, Kamal. „Comportement des composites époxy-fibres de graphite sous rayonnement micro-onde“. Toulouse 3, 1990. http://www.theses.fr/1990TOU30124.
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Le memoire porte sur l'activation par les micro-ondes (2,45 ghz) de la reticulation de materiaux composites a fibres courtes de grahite et a matrice thermodurcissable epoxyde. Il comporte quatre parties principales: la premiere fait le point sur les travaux publies sur l'activation des reactions de polymerisation et de reticulation des materiaux composites a matrice polymere; la seconde decrit les appareillages et les produits chimiques utilises; la troisieme presente les resultats des travaux sur l'activation de la reticulation des composites par les micro-ondes fonctionnant en modes continu et pulse, sur le comportement sous rayonnement micro-onde de materiaux composites a concentration en fibres variable prealablement reticules, et la reticulation des composites en ondes pulsees; la quatrieme partie, intitulee conclusion, dresse le bilan des recherches effectuees. Enfin, dans une annexe, sont donnees des generalites sur la relaxation dielectrique des polymeres, le chauffage dielectrique des materiaux et la percolation electrique dans les composites a matrice polymere et a renfort divise
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Lussien, Jérôme. „Etude des mécanismes d'ablation de matériaux composites graphite-carbure métallique réfractaire“. Paris 6, 2001. http://www.theses.fr/2001PA066330.
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Kiesling, Thomas C. „Impact failure modes of graphite epoxy composites with embedded superelastic nitinol“. Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-09162005-115046/.
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Mohamed, Ibrahim Abdi-Salam. „Études expérimentales de l'interaction de l'oxygène et de l'eau avec des surfaces carbonées d’intérêt astrophysique“. Thesis, CY Cergy Paris Université, 2020. http://www.theses.fr/2020CYUN1052.
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Le milieu interstellaire (MIS), situé entre les étoiles, est le lieu d'une chimie complexe qui résulte de l'interaction entre le gaz et les particules solides : les grains de poussière (IDG). Les observations spectroscopiques indiquent que les grains de poussière sont principalement composés de matériaux carbonés et silicatés d’une taille variant de 1 nm à 15 μm (Desert, 1990) même si la composition exacte reste incertaine. Les observations ont également permis d'obtenir des informations sur la composition et la nature physique des manteaux de glace. La matière carbonée interstellaire a de nombreuses formes différentes, notamment: diamant, graphite, hydrocarbures aromatiques polycycliques (PAH) et carbones amorphes. Les PAH constituent un réservoir de carbone représentant environ 10% du bilan de carbone galactique (Tielens, 2013) et représentent la plus grande surface géométrique de la distribution des IDG (Weingartner and Draine, 2001). Dans les nuages moléculaires denses qui sont extrêmement froids (T < 50 K), la plupart des PAH devraient être efficacement condensés sur les IDG, soit sous forme d' agrégats de PAH (ou bien des très petits grains) ou sous forme de " molécules invitées" dans des manteaux de grains glacés, comme c'est le cas de la plupart des autres molécules interstellaires (Sandford and Allamandola,1993). Ce travail de thèse de doctorat est une étude expérimentale de l’interaction de l'oxygène et de l’eau avec différents types de surfaces simulant les IDG présents dans le MIS (le graphite et le coronène, un PAH modèle). Dans ce but, différentes expériences ont été réalisées en utilisant le dispositif FORMOLISM qui réunit les techniques d’ultra-vide, de cryogénie, de jets atomiques ou moléculaires et de spectrométrie de masse. Nous avons d'abord étudié la cinétique de l'adsorption et de la désorption de l'oxygène sur un film de coronène et sur le graphite à 15K, en utilisant la technique de TPD (Themally Programmed Desorption). Nous avons observé que la désorption O2 se produit à plus base température sur le coronène que sur le graphite. Nous avons mesuré que l'énergie de liaison de l'oxygène adsorbé sur le graphite est de 12,5 kJ/mol, plus élevée que l'énergie de liaison sur coronène qui vaut 10,6 kJ/mol. Ces résultats sont en accord avec les calculs DFT réalisés pour cette étude. Nous avons étudié l’interaction l'oxygène atomique avec le graphite à 15K. Nous avons utilisé les TPD d’O2 comme un outil diagnostique de l’état de surface du graphite. L’exposition de O sur le graphite conduit à une modification de la surface et à la création de défauts sur le graphite. Ces défauts fournissent des sites d'adsorption d'énergie plus élevée, et une distribution d'énergies d'adsorption continue. Nous avons ensuite étudié, expérimentalement et par simulations Monté-Carlo, la diffusion d’O2 sur le graphite. Nous avons montré que ces molécules diffusent sur la surface durant le TPD pour trouver les sites d'adsorption les plus favorables. Grâce aux défauts que nous avons introduits à la surface du graphite et à la dépendance de la température de dépôt sur le peuplement de ces sites, nous avons essayé de contraindre la diffusion par rapport à la désorption. Nous avons étudié expérimentalement, en collaboration avec un groupe théorique, l'oxydation à basse température (50K) du coronène par les atomes O, ainsi que l'oxydation des coronènes hydrogénés. Il apparaît que la réactivité est plus élevée que prévu et que la fragmentation du coronène est un canal important de l'oxydation. Enfin, nous avons présenté les résultats des études préliminaires d'adsorption et de désorption de l'eau sur graphite et coronène. Nous observons que la molécule de coronène empêche la cristallisation de l'eau. Nous avons également montré que l'adsorption de l'eau sur le coronène est plus rapide et plus efficace que sur le graphiteThe interstellar medium (ISM), located between the stars, is the place of a complex chemistry that results from the interaction between the gas and solid particles such as dust particles. Spectroscopic observations indicate that dust grains are mainly composed of carbonaceous and silicate materials ranging in size from 1 nm to 15 μm (Desert,1990), although the exact composition remains a matter of debate. Progress in interstellar spectroscopy has also provided detailed information on the composition and physical nature of frozen ices on dust grains. Interstellar carbonaceous material has many different forms, including: diamond, graphite, polycyclic aromatic hydrocarbons (PAH) and amorphous carbons. Diamond and graphite are the two cristalline forms of carbon. Graphite is composed of infinite aromatic planes parallel to each other. PAH are a family of molecules composed of at least two aromatic rings to which hydrogen atoms are attached. They constitute a carbon reservoir representing about 10% of the galactic carbon budget (Tielens, 2013) and represent the largest geometric surface of the grain distribution (weingartner and Draine, 2001). In dense molecular clouds that are extremely cold (T < 50 K), most PAH should be efficiently condensed on dust grains, either as PAH aggregates (or very small grains VSGs) or as "invited molecules" in ice grain mantles, as is the case with most other interstellar molecules (sandford and Allamandola,1993). This doctoral thesis work is an experimental study of the interaction of oxygen and water with different types of surfaces simulating the dust grains present in the ISM (graphite and coronene, a PAH model). To this end, several experiments were carried out using the FORMOLISM device, which combines ultra-high vacuum, cryogenics, atomic or molecular beams and mass spectrometry techniques. We first studied the kinetics of oxygen adsorption and desorption on a coronene film and on graphite held at 15 K, using the Themally Programmed Desorption (TPD) technique. We observed that the desorption of O2 takes place at a lower temperature on the coronene than on graphite. From the energy point of view we have demonstrated that O2 is less bound to coronene film than to graphite. We measured that the binding energy of oxygen adsorbed on graphite is 12.5 kJ/mol, higher than the binding energy on coronene which is 10.6 kJ/mol. We studied the interaction of atomic oxygen with graphite at 15K. We used our knowledge of O2 desorption as a diagnostic tool for graphite surface status. Exposure of atomic oxygen to graphite leads to a modification of the graphite network and the creation of defects on the surface. These defects provide higher energy adsorption sites, but also a more continuous distribution of adsorption energies. We then studied, experimentally and by Monte-Carlo simulation, the diffusion of O2 on graphite. We have shown that O2 molecules diffuse on the graphite surface during TPD to find the most favourable adsorption sites. Thanks to the defects that we introduced to the graphite surface and the dependence of the deposition temperature on the settlement of these defect sites, we tried to constrain the diffusion in respect to the desorption process. We studied experimentally, in collaboration with a theoretical group, the oxidation at low temperature (50 K) of the coronene by oxygen atoms, as well as the oxidation of hydrogenated coronenes. It appears that reactivity is higher than expected and that coronene fragmentation is an important channel for oxidation. Finally, we presented the results of the preliminary studies of water adsorption and desorption on graphite and coronene. We observe that the coronene molecule prevents the crystallization of water. We have also shown that the adsorption of water on the coronene is faster and more efficient than on graphite
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Fourt, Erwan. „Étude de joints radiaux en carbone graphite avec application aéronautique“. Electronic Thesis or Diss., Poitiers, 2021. http://www.theses.fr/2021POIT2292.
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Cette thèse a pour but d’étudier expérimentalement plusieurs technologies de joints radiaux segmentés. L’introduction permet de situer le contexte du travail tout en évoquant plusieurs technologies d’étanchéités couramment employées dans les moteurs aéronautiques. Au cours de ce chapitre, les contraintes auxquelles les joints radiaux segmentés doivent faire face sont également détaillées. La première étude menée a pour but d’étudier trois technologies différentes de joints radiaux segmentés : sans poche, avec poche sur les patins et enfin une technologie de joint sans poche en vis-à-vis de rainures inclinées sur le rotor. Dans un premier temps, les performances de chaque étanchéité sont évaluées et comparées.Ensuite, une étude métrologique a été menée sur la technologie de joint sans poche afin d’investiguer l’usure subie par ce dernier au cours des essais. Au cours de ce travail, la fragilité de ce type d’étanchéité a été mis en avant. C’est pourquoi, des joints similaires présentant une défaillance ont été étudiés. Comme précédemment, les performances de ces joints ainsi que l’usure subie ont été évaluées. Il a été montré que malgré la défaillance, ces joints n’ont montré aucun signe de détérioration supplémentaire.Enfin, l’influence de la rugosité de surface a été étudié afin de mettre en avant les phénomènes liés au soulèvement des segments. Pour cela, une méthode numérique multi-échelles a été développée. Il a été montré que cette dernière permettait de résoudre un tel problème avec un effort de calcul faible en comparaison des méthodes standardThe main goal of this thesis is the experimental study of several technologies of radial segmented seals. First of all, an introduction presents the context of the study by detailing the most commonly used seals technologies in aero engines.Firstly, three different technologies of radial segmented seals have been studied: without pocket, with pocket and without pocket and inclined grooves on the rotor. The performance of each technologies has been investigated and compared. In complement, the wear of the pocket-free technology has been study. The work highlights the fragility of this kind of seals. It is why the performance and the wear of faulty seals have been investigated.This second study shows that despite the failure, the seals do not show more serious complications.Then, the impact of roughness on a gas flow was investigate to highlight the lift effect of the segments. For this, a multiscale method was developed. It was shown that this method works well to study such a problem with a very low computational effort in comparison with two other existent methods
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BHARGAVA, SUMEET. „TEMPERATURE AND GAS SENSING CHARACTERISTICS OF GRAPHITE/POLYMER (PEO) BASED COMPOSITE STRUCTURES“. University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1152821559.
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Magampa, Philemon Podile. „Properties of graphitic composites“. Thesis, University of Pretoria, 2013. http://hdl.handle.net/2263/40244.
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The Pebble Bed Modular Reactor (PBMR) is a high temperature graphite-moderated nuclear reactor that uses helium as a coolant. The triple coated (TRISO) particles contain enriched uranium oxide fuel which is coated with layers of various forms of pyrolytic carbon and silicon carbide. The TRISO particles are further embedded in the matrix of spherical graphite pebbles. The graphite matrix is a composite moulded from a compound containing natural flake graphite (64 wt.%), synthetic graphite (16 wt.%) and a phenolic resin binder (20 wt.%) heated to 1800 °C in inert atmosphere. The graphitic composite provides structural integrity, encasement and act as a moderator material. In this work, low density model graphite composites similar to those used in nuclear applications as encasement material in fuel pebbles were made by uniaxial cold compression moulding. The graphitic composites contained various ratios of natural flake graphite and synthetic graphite at fixed phenolic novolac resin binder content of 20 wt.% (green state). The fabrication process employed entails mixing the graphite powders, followed by addition of methanol phenolic resin solution to the graphite powder mix, drying, grinding, milling and sieving; and finally compression moulding in a stainless steel die at 13 MPa using a hydraulic press. The green moulded disc specimens were then carbonized at 900 °C in nitrogen atmosphere to remove volatiles followed by annealing at 1800 °C in helium atmosphere. The annealing step diminishes structural defects and result in densification of the composites.
The microstructure of fabricated graphitic composites was characterized using various techniques. Particle Size Distributions determined using Laser diffraction showed that the inclusion of the binder leads to agglomeration. The composite powders had larger mean particle sizes than the raw graphite powders showing the binding effect of the novolac phenolic resin. X-ray diffraction studies showed that the graphitic composites had a hexagonal crystal structure after annealing. Raman spectroscopy revealed the presence of the structurally disordered phase derived from the resin carbon (indicated by the pronounced D-band in the Raman spectra). XRD and Raman observations were consistent with literature and gave results supporting existing knowledge base. Optical microscopy revealed a flake-like microstructure for composites containing natural graphite and needle-coke like particles for composites containing mainly synthetic graphite. Optical microscopy confirmed that the effect of the manufacturing route employed here was to align the particles in the direction perpendicular to the compression moulding direction. As a result, the graphitic composites exhibited anisotropic property behavior.
The bulk density of the composites increased with the increase in the natural graphite content due to compactability of natural flakes in the manufacturing route. Thermogravimetric analysis studies on the composites showed that they were stable in air to 650 °C. Composites containing mainly synthetic graphite were thermally more stable in air compared to their natural graphite counterparts. The linear coefficients of thermal expansion of the composites were measured using thermomechanical analysis (20-600 °C). In the moulding direction, the average CTE (αP) values were in the range (5-9) × 10-6 K-1 and increased with increment in the natural graphite content in the composite. In the direction perpendicular to moulding direction, the average CTE (αN) values were in the range (1.7-2.1) × 10-6 K-1 showing that the expansion was similar or constant in this direction. Therefore an anisotropic expansion ratio, i.e. αP:αN, of about 3 was observed in the composites. This anisotropy is attributable to the alignment of the filler particles in the manufacturing route. The thermal conductivity of the annealed composites were measured in the pressing direction from 100 to 1000 °C and the values ranged from 19 to 30 W m-1 K-1. Anisotropy was also observed as far as strength was concerned. A composite containing 64:16:20 wt.% ratio had the best mechanical properties, high thermal conductivity and slightly high expansion coefficient. This work demonstrates the complimentary properties of the graphite fillers in the composites. It also reports for the first time, data on the effect of variation of the filler graphites on microstructure and properties of model low density compression moulded graphitic composites.Thesis (PhD)--University of Pretoria, 2013.
gm2014
Chemistry
unrestricted
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Ajrhourh, Hamid. „Adhérence et réactivité des multimatériaux à base de graphite“. Ecully, Ecole centrale de Lyon, 1992. http://www.theses.fr/1992ECDL0004.
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Le graphite a toujours été largement utilise dans l'industrie: parmi ses usages les plus classiques, son application privilégiée dans le domaine des hautes températures et ceci malgré sa grande réactivité avec l'oxygène et sa grande perméabilité. Pour élargir ses domaines d'applications, il faut augmenter ses performances en l'associant à des métaux ou à des céramiques. Ceci permettra de repousser les limites d'utilisation des matériaux classiques et d'élaborer de nouveaux matériaux aux propriétés exceptionnelles, dits matériaux composites et multimatériaux. Le cas du graphite intervenant dans un multimatériau est particulièrement complexe, car à ce problème d'adhérence s'ajoute celui de la grande réactivité de ce matériau vis-à-vis du milieu ambiant (nécessité d'une protection parfaite sans le moindre défaut (porosite, fissure)) par les autres couches. Il est donc intéressant de trouver ou de mettre au point des revêtements écrans destinés à isoler le graphite du milieu extérieur. Dans tous les cas, la réussite sera liée à la maîtrise de l'adhérence du revêtement au carbone par accommodation des contraintes mécaniques et augmentation des énergies d'adhésion. Les multimatériaux choisis, élaborés et caractérisés sont les systèmes suivants: métal (cr, mo, al, si)/graphite; aluminium (a5)/carbure (cr#3c#2, sic)/graphite; oxyde (al#2o#3, zro#2)/graphite; oxyde (al#2o#3, zro#2)/carbure (cr#3c#2 et sic)/graphite. Pour élaborer ces matériaux, nous avons mis en œuvre trois techniques: la thermocompression, le slurry-coating et la projection plasma. Elles nous ont permis de bien analyser les problèmes rencontrés dans la réalisation des liaisons, qu'ils soient d'ordre réactionnel, mécanique, physico-chimique ou même simplement technologique. Dans chacun des cas, nous avons d'une part optimise les conditions d'élaboration et d'autre part précise la nature et la morphologie des interfaces obtenues.
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Kalaitzidou, Kyriaki. „Exfoliated graphite nanoplatelets as reinforcement for multifunctional polypropylene nanocomposites“. Diss., Connect to online resource - MSU authorized users, 2006.
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Thesis (Ph. D.)--Michigan State University. Dept. of Chemical Engineering and Materials Science, 2006.Title from PDF t.p. (viewed on June 19, 2009) Includes bibliographical references. Also issued in print.
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Grandin, Martina. „Tribology of Metal-Graphite Composites : A Study of Sliding Electrical Contact Surfaces“. Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-329860.
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An environmentally sustainable production of electrical power is important for preserving the earth’s natural resources. In order to utilize this power as efficiently as possible, it is of great importance to minimize the losses, for example in sliding electrical contacts. A sliding electrical contact is where current is transferred from one rotating to one stationary component and power is lost due to friction and contact resistance. Also in some signal applications, high performance sliding contacts are crucial to ensure stable signal transfer with low noise. Although sliding electrical contacts are primarily designed for good electrical performance, the system will benefit also from optimization of the tribological properties. The aim of this thesis is to increase the fundamental knowledge of the tribological and electrical performance of metal-graphite composite materials for sliding electrical contacts. The influence of mechanical and electrical load was investigated. Different stationary materials, from pure copper to nanocomposite coatings, were tested against copper- and silver-graphites. Two complementary test setups were used, one with reciprocating and one with unidirectional sliding. Surface analysis was essential to gain deepened understanding of the influence of the interaction on the surfaces. Especially my novel imaging of cross-sections has advanced the level on knowledge in this research field. On the stationary material surface, a tribofilm forms with constituents from the metal-graphite and the surrounding atmosphere. Cross-sectioning reveals a material flow that indicates turbulence. Furthermore, the presence of oxides in the tribofilm is not necessarily detrimental for the contact resistance as long as there is also pure metal available. The presence of graphite is vital for low friction and wear. It is shown that the tribological and electrical behaviour of this system is only marginally influenced by the material selection of the stationary contact. Increasing the metal content in the composite, on the other hand, greatly reduces the contact resistance while there is no significant impact on friction and wear. The mechanical load has to be optimized to compromise between low wear (achieved with low load) and low contact resistance (achieved with high load). Pure mechanical tests show a lower friction and higher wear rate in comparison to tests with a five ampere current.
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DeVincent, Sandra Marie. „Interfacial effects on the thermal and mechanical properties of graphite/copper composites“. Case Western Reserve University School of Graduate Studies / OhioLINK, 1994. http://rave.ohiolink.edu/etdc/view?acc_num=case1061300766.
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Carbonell, Laure-Arminia. „Conductivité électrique et résistance de contact de matériaux composites Cu-Ni-graphite“. Grenoble INPG, 1990. http://www.theses.fr/1990INPG0017.
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L'etude porte sur des materiaux susceptibles d'etre utilises comme contact electrique, constitues de particules de graphite dans une solution solide cu, ni. Ces materiaux anisotropes contiennent 3 a 20 vol % de graphite, un peu de porosite residuelle et presentent trois types de microstructures caracterisees par analyse d'images. La conductivite electrique est mesuree sur des materiaux de texture soit parallele soit perpendiculaire a la direction du courant. Les resultats experimentaux font ressortir le role isolant du graphite, et une decroissance de la conductivite produite par l'augmentation de fraction de phase isolante, beaucoup plus rapide pour les textures perpendiculaires que paralleles. Le modele d'ondracek conduit a evaluer trois effets principaux dus a la fraction volumique, a l'anisotropie de forme de phase isolante et a l'anisotropie de texture. Est ensuite etudiee la resistance de contact, somme de la resistance de constriction specifique au materiau, et d'un terme pelliculaire fonction de la conductivite electrique et de la morphologie de la couche de surface. Les valeurs experimentales approchees de resistance de constriction sont confrontees au modele de holm: les fortes variations de conductivite electrique produisent sur la resistance de constriction des variations significatives mais faibles devant l'effet pelliculaire minimal. L'effet pelliculaire des materiaux soumis a l'arc electrique est analyse a partir de donnees experimentales d'erosion, de resistance de contact et de caracterisation des couches de surface. Ces resultats mettent en evidence le role important de la teneur en graphite des materiaux; on propose deux mecanismes prrincipaux pour l'interpreter
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Jagannathan, Vijay. „The influence of interphase structure on the kinetics of oxygen reduction on graphite used in aluminum-graphite metal matrix composites /“. The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487590702992934.
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Yoon, Tae-Ho. „Adhesion study of thermoplastic polymides with Ti-6Al-4V alloy and PEEK-graphite composites“. Diss., This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134525/.
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Burden, Adrian Paul. „Electron microscopy techniques to further the understanding of conductive polymer composites“. Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337609.
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Ellis, Roger L. „Ballistic Impact Resistance of Graphite Epoxy Composites With Shape Memory Alloy and Extended Chain Polyethylene Spectra Hybrid Components“. Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36564.
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Graphite epoxy composites lack effective mechanisms for
absorbing local impact energy often resulting in penetration
and a structural strength reduction. The effect of adding
small amounts of two types of high strain hybrid
components on the impact resis tance of graphite epoxy
composites subjected to projectiles traveling at ballistic
velocities (greater than 900 ft/sec) has been studied. The
hybrid components tested include superelastic shape
memory alloy (SMA), a material having an unusually high
stra in to failure (15 - 20%), and a high performance
extended chain polyethylene (ECPE) known as Spectraâ ¢,
a polymer fiber traditionally used in soft and hard body
armor applications. A 1.2% volume fraction superelastic
SMA fiber layer was embedded on the specimens front,
middle, and backface to determine the best location for a
hybrid component in the graphite composite. From visual
observation and energy absorption values, it was c
oncluded that the backface is the most suitable location for
a high strain hybrid component. Unlike the front and middle
locations, the hybrid component is not restricted from
straining by surrounding graphite material. However, no
significant increases in energy absorption were found when
two perpendicular SMA layers and an SMA-aramid
weave configuration were tested on the backface. In all
cases, the embedded SMA fibers were pulled through the
graphite without straining to their full potential. It is believed
that this is due to high strain rate effects coupled with a
strain mismatch between the tough SMA and the brittle
epoxy resin. However, a significant increase in energy
absorption was found by adding ECPE layers to the
backface of the composite . With only a 12% increase in
total composite mass, a 99% increase in energy absorption
was observed.Master of Science
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Mallow, Anne. „Stable paraffin composites for latent heat thermal storage systems“. Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54406.
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Phase change materials (PCMs) have the ability to store thermal energy as latent heat over a nearly isothermal temperature range. Compared to sensible heat storage, properly chosen PCMs can store an order of magnitude more energy when undergoing phase change. Organic PCMs present several advantages including their non-corrosive behavior and ability to melt congruently, which result in safe and reliable performance. Because of these qualities, organic PCMs have been proposed for use in latent heat thermal storage systems to increase the energy efficiency or performance of various systems such as cooling and heating in buildings, hot water heating, electronics cooling, and thermal comfort in vehicles. Current performance is hindered by the low thermal conductivity, which significantly limits the rate of charging and discharging. Solutions to this challenge include the insertion of high conductivity nanoparticles and foams to increase thermal transport. However, performance validation remains tied to thermal conductivity and latent heat measurements, instead of more practical metrics of thermal charging performance, stability of the composite, and energy storage cost.
This thesis focuses on the use of graphite nanoplatelets and graphite foams to increase the thermal charging performance of organic PCMs. Stability of graphite nanoplatelets in liquid PCM is realized for the first time through the use of dispersants and control of the viscosity, particle distribution, and oxidation. Thermal charging response of stable graphite nanoplatelet composites is compared to graphite foam composites. This study includes a correlation of thermal conductivity and latent heat to material concentration, geometry, and energy storage cost. Additionally, a hybrid PCM storage system of metal foam combined with graphite nanoplatelet PCM is proposed and evaluated under cyclic thermal conditions.
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Wang, Shu Jun. „Applications of graphene for transparent conductors and polymer nanocomposites /“. View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20WANGS.
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Etter, Thomas. „Material-physical description of interpenetrating graphite/aluminium composites produced by liquid metal infiltration /“. [S.l.] : [s.n.], 2005. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16096.
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Kinkenon, Douglas. „Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys“. Thesis, University of North Texas, 2013. https://digital.library.unt.edu/ark:/67531/metadc407776/.
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Monolithic composites are needed that combine low friction and wear, high mechanical hardness, and high fracture toughness. Thin films and coatings are often unable to meet this engineering challenge as they can delaminate and fracture during operation ceasing to provide beneficial properties during service life. Two material systems were synthesized by spark plasma sintering (SPS) and were studied for their ability to meet these criteria. A dual hybrid composite was fabricated and consisted of a nickel matrix for fracture toughness, TiC for hardness and graphite for solid/self‐lubrication. An in‐situ reaction during processing resulted in the formation of TiC from elemental Ti and C powders. The composition was varied to determine its effects on tribological behavior. Stellite 21, a cobalt‐chrome‐molybdenum alloy, was also produced by SPS. Stellite 21 has low stacking fault energy and a hexagonal phase which forms during sliding that both contribute to low interfacial shear and friction. Samples were investigated by x‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x‐ray spectroscopy (EDS), and electron back‐scattered diffraction (EBSD). Tribological properties were characterized by pin on disc tribometry and wear rates were determined by profilometry and abrasion testing. Solid/self‐lubrication in the TiC/C/Ni system was investigated by Raman and Auger mapping. A tribofilm, which undergoes a stress‐induced phase transformation from polycrystalline graphite to amorphous carbon, was formed during sliding in the TiC/C/Ni system that is responsible for low friction and wear. TiC additions help to further decrease wear. Stellite 21 was also found to exhibit acceptably low friction and wear properties arising from the presence of Cr23C6 in the matrix and work hardening of the cobalt and chromium during sliding.
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Bhat, Narendra Venugopal. „Delamination suppression in graphite/epoxy composites via efficient use of film adhesive layers“. Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/42979.
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Reddy, Mahesh. „Imbedded optical fiber sensor of differential strain and temperature in graphite/epoxy composites“. Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/101318.
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A novel optical fiber sensor for the measurement of strain and temperature in graphite-epoxy composite materials using differential interferometry is described. The sensor uses two single-mode optical fiber waveguides imbedded within the composite during prepreg ply lay-up. Strain and temperature changes arc obtained as a motion of an optical interference pattern. Values arc calculated for the strain and temperature dependence of the fringe motion. The results of measurement which attempt to duplicate modeled loading conditions are reported and compared with analytical results. Analytical and experimental extensions of the technique to the measurement of the differential temperature in graphite-epoxy composite specimens during cure cycle processing are also considered.M.S.
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Dash, Lawrence Christopher. „The mechanism of corrosion and corrosion control of aluminum/graphite metal matrix composites /“. The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487588249825594.
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Ellis, Marguerite. „Investigation of Multiwalled Carbon Nanofiber - Graphite Layer Composites and Analysis of Natural Chalks“. Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/205417.
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The first part of this dissertation focuses on self-assembled composites. Self-assembled composites composed of vertically aligned multiwalled carbon nanofibers (VA-MWCNF) combined with a graphitic layer (GL) arranged perpendicular to MWCNF axes‘ have been produced at low temperature (445 °C) using low pressure thermal chemical vapor deposition (LPCVD). Electron microscopy and Raman spectroscopy were used to analyze composite morphology, structure and quality. It is found that different composite morphologies and modification of the GL structure can be obtained by varying the nickel (Ni) catalyst underlayer materials, the catalyst pre-treatment method, the gas recipe, the gas flow rates and the pressure conditions of the LPCVD process. Pre-treatment of the catalyst with H2 plasma or NH₃ gas was also investigated. It is found that even a short, one minute H2 plasma pre-treatment of the catalyst results in a significant break-down of the VA-MWCNF/GL composite structure. On the other hand, a one or ten minute catalyst pre-treatment with NH₃ gas results in a structural modification of the GL but retains the VA-MWCNF/GL composite structure. An increase in time of NH₃ gas pre-treatment leads to reduced VA-MWCNF/GL composite height. A growth mechanism for VA-MWCNF/GL composites was proposed. The focus, of the second part of this dissertation, is on the analysis of natural chalks used in traditional old master drawings. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis were performed on bulk samples of natural black chalk, steatite and calcite natural white chalks and on samples of these chalks applied to paper using various techniques. Critical information was obtained about the morphology and sub-micron features of the chalk particles, the chalk/paper interaction of each application technique and elemental composition of the bulk chalk samples. It was found that the particle size and morphology of the natural white chalks reduced their ability to hold to the paper. This information provides insight as to why black chalk is more resistant to abrasion than the natural white chalks which is important for the conservation of extant chalk drawings.
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Bergemann, Thorsten. „Effets de l'arc électrique sur les caractéristiques structurales et les propriétés électriques de composites argent-carbone“. Orléans, 2002. http://www.theses.fr/2002ORLE2051.
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Depuis plus d'un siècle, le composite argent/graphite est le matériau le plus utilisé dans les disjoncteurs basse tension. Cette étude porte sur le comportement de composites argent/carbone à base de différents matériaux carbonés (graphite, noirs de carbone et fibres de carbone) lors de la coupure du courant. Aux températures existant au pied de l'arc électrique, l'oxydation des fibres de carbone entraîne leur désagrégation, ce qui se traduit par une accélération de la vitesse d'oxydation par rapport aux noirs de carbone et au graphite. Les études par adsorption physique d'azote, MET et diffraction des rayons X ont démontré que l'arc électrique sous air peut occasionner le recuit, la vaporisation, l'oxydation, ou encore la dissolution du carbone dans l'argent. La durée de l'arc détermine l'érosion lors de la coupure d'un courant continu de 85A. L'érosion suite aux coupures des courants alternatifs de 1700 à 4100A dépend principalement de la dispersion du carbone dans l'argent.
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Ogden, Andrea L. „The development and evaluation of an alternative powder prepregging technique for use with larc-tpi/graphite composites“. Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10222009-125042/.
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Badaud, Frédérique. „Étude de modèles composites au LEP avec ALEPH“. Clermont-Ferrand 2, 1992. http://www.theses.fr/1992CLF21405.
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Ce travail a porté sur des tests de modèles composites dans les interactions électron-positron au voisinage du pôle du Z avec le détecteur ALEPH. Les manifestations de la sous-structure envisagées dans cette thèse sont de deux sortes: rechercher des déviations des sections efficaces différentielles des états finals à 2 leptons ou à 2 photons par rapport aux prédictions du modèle standard et la recherche directe de neutrinos excités. Cette étude a utilisé les données expérimentales des années 1989, 90 et 91. Une nouvelle interaction, paramétrisée par un terme de contact à 4 leptons, eell, a tout d'abord été étudiée dans les réactions de production de paires de leptons, en envisageant plusieurs hypothèses sur la chiralité des courants. Un ajustement des prédictions théoriques à l'ensemble des données expérimentales a permis de mettre des limites sur l'échelle de sous-structure. Des déviations par rapport à l'état final à 2 photons peuvent être dues soit à un terme de contact comprenant 2 leptons et 2 bosons, soit à l'échange d'un électron excité. Nous nous sommes ensuite attachés à la recherche de la particule excitée qui pourrait être la plus légère: le neutrino excité, en étudiant la production simple et la production double, suivie de leur désintégration radiative
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Hidouci, Ahmed. „Elaboration et caractérisation de revetements sous faisceau laser : revêtements métalliques, intermétalliques et composites“. Lyon, INSA, 1999. http://www.theses.fr/1999ISAL0026.
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Cette étude consiste à caractériser dans un premier temps des revêtements métalliques simples (alliages base nickel, base cobalt et base fer), élaborés sur un substrat acier par projection de poudre sous faisceau laser. Nous avons par la suite étudié la faisabilité d'un dépôt de MoSi2 par la même technique. Nous avons d'abord réalisé des revêtements MoSi2 soit à partir d'un mélange de poudre Mo + Si soit directement à partir de poudre pré alliée MoSi2 sur substrat en acier ou en graphite. Nous avons tenté enfin d'améliorer les propriétés de ces revêtements (métalliques et intermétalliques) grâce à l'addition de particules actives, telles que la zircone, pour les dépôts à base de nickel et MoSi2 et de particules de carbure de tungstène pour les dépôts à base de nickel (Inconel 718). Les dépôts à base de nickel sont caractérisés par une structure austénitique, une dureté faible et une ductilité élevée. En revanche les bases cobalt sont durs et moins ductiles. Les dépôts à base de fer possèdent des structures austénitiques simples et des duretés modérées, néanmoins ils sont caractérisés par des forts durcissements lors d'une déformation plastique. Les dépôts de nickel renforcés par des particules de carbure de tungstène présentent quelques microfissures non débouchantes et un modules de Young de l'ordre de 375 GPa. Les dépôts MoSi2 ont une bonne adhérence avec le substrat acier, mais caractérisés par la présence d'un nombre important de fissures. Nous avons essayé de remédier à ce problème, par préchauffage du substrat acier à 450 °c pour réduire les gradients thermiques, par l'utilisation d'un substrat graphite en évitant la dilution du substrat et enfin par l'ajout de zircone non stabilisée pour former un matériau composite MoSi2 - Zr02 plus résistant à la fissuration. Mais toutes ces tentatives se sont montrées insuffisantes pour obtenir un matériau sain, exempt de fissure. L'emploi de la zircone montre cependant une réduction du phénomène de fissurationMicrostructure and mechanical properties of Ni -, Co- and Fe- base alloys coatings produced by laser cladding on steel substrate were investigated experimentally in the first time. After, the feasibility of depositing MoSi2 by the same technique has been studied. Coatings of MoSi2 were manufactured on steel or graphite substrate either using a Mo and Si powder mixture; or, in a second experiment using MoSi2 powder. Finally, the addition of Zr02 and WC particles to improve properties of these coatings has been performed. These include the use of Zr02 particle, for MoSi2 and Ni (Colmonoy) and WC for Ni (Inconel 718). The Ni- base alloys coating has an austenitic structure, a low hardness and a high ductility, while the Co- base alloys coating is hard and has less ductility. The Hadfield steel has an austenitic structure and is very ductile: relative deformation higher than 80 % are achieved without intermediate annealing and without deleterious damages. The Ni- base alloys coating reinforced with WC particles is dense, with good mechanical properties (Young modulus = 375 GPa), but contain many cracks. Coatings of MoSi2 have a good metallurgical bond with steel substrate, but characterised by high density of cracks. Various routes of processing have been used to remedy to this problem : by preheating the steel substrate to 450 °C, to reduce the thermal gradients, by using a graphite substrate to a void dilution of the substrate at high temperatures and finally, reinforcement by unstabilised zirconia to form a MoSi2 - Zr02 composite, more resistant to cracks. Unfortunately, these attempts appear insufficient to obtain a deposit of sound MoSi2, free of cracks. However, in the case of deposits manufactured with the addition of zirconia powder, the number of cracks is reduced compared with those manufactured with only MoSi2; the reduction is explained using a block schema, representing coating, heat affected zone and substrate