Tesis: "Composite materials Cu"

1

Guazzone, Federico. "Engineering of substrate surface for the synthesis of ultra-thin composite Pd and Pd-Cu membranes for H₂ separation". Link to electronic thesis, 2005. http://www.wpi.edu/Pubs/ETD/Available/etd-011006-123013/.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

2

Kaforey, Monica L. "Solid state thermal gradient processing of Y₁Ba₂Cu₃O₇âx/Ag superconducting composite ribbons". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28038.

Texto completo

Resumen

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994.
Vita. Title as it appears in the Feb. 1994 MIT Graduate List: Solid state temperature gradient processing of Y₁Ba₂Cu₃O₇âx/Ag superconducting composite ribbons.
Includes bibliographical references (leaves 197-202).
by Monical L. Kaforey.
Ph.D.

Los estilos APA, Harvard, Vancouver, ISO, etc.

3

Kraiem, Nada. "Impression 3D de matériaux composites à base de diamant pour des applications de gestion thermique". Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0129.

Texto completo

Resumen

Avec la tendance à la miniaturisation croissante des équipements électriques et à l'augmentation constante de la densité de puissance dans les dispositifs à base de semiconducteurs, la gestion efficace de la chaleur est devenue un enjeu majeur pour les chercheurs. En effet, cette évolution technologique impose des contraintes de plus en plus strictes en termes de dissipation thermique, nécessitant des solutions innovantes pour garantir une meilleure durabilité et fiabilité des composants. Dans ce contexte, l'utilisation de matériaux composites offrant une conductivité thermique élevée et un coefficient de dilatation thermique faible par rapport aux métaux purs est devenue essentielle pour résoudre les problèmes de surchauffe des composants électroniques. L'intégration de matériaux avancés tels que le diamant (D), avec ses propriétés exceptionnelles de conductivité thermique et de dureté, constitue une option privilégiée pour renforcer les matrices métalliques. Toutefois, son incorporation dans les matériaux composites nécessite la création d'une interface D-métal bien définie, à la fois pour éviter la formation de porosité et assurer un transfert efficace des propriétés thermiques. La fabrication additive de matériaux 3D par fusion laser émerge comme une solution prometteuse, non seulement pour la facilité de mise en œuvre de ces composites, mais aussi pour la création de structures complexes dédiées à la dissipation de chaleur. Ces structures jouent un rôle crucial dans l'optimisation de la surface d'échange thermique par convection avec l'air environnant, permettant ainsi une dissipation efficace de la chaleur générée par les dispositifs électroniques modernes.Dans cette étude, l`impression 3D du cuivre (Cu) a été réalisée grâce à l`ajout d`une quantité optimale d’aluminium. Cette approche a permis d'améliorer considérablement la densification de matériaux à base de cuivre, malgré les défis posés par sa forte réflectivité. Par la suite, l'investigation approfondie et l'optimisation de l`impression 3D laser de l'alliage AlSi10Mg, avant et après l'incorporation de D, ont été réalisées. Enfin, une étape cruciale de post-traitement a été optimisée consistant à polir des matériaux composites Al/D par ablation laser.Ce travail a été réalisé dans le cadre d'une collaboration internationale entre l'Université du Nebraska, Lincoln aux États-Unis d'Amérique, et l'Université de Bordeaux en France
With the trend towards miniaturization of electrical equipment and the constant increase in power density in semiconductor devices, efficient heat management has become a major concern for researchers. Indeed, this technological evolution imposes increasingly strict constraints in terms of thermal dissipation, necessitating innovative solutions to ensure better durability and reliability of components. In this context, the use of composite materials offering high thermal conductivity and low coefficient of thermal expansion compared to pure metals has become essential to address overheating issues in electronic components. The utilization of advanced materials such as diamond (D), with exceptional thermal conductivity and hardness properties, stands out as a preferred choice for reinforcing metal matrices. However, its incorporation into composite materials requires the creation of a well-defined D-metal interface, both to avoid porosity formation and to ensure efficient transfer of thermal properties. Additive manufacturing of 3D materials by laser fusion is emerging as a promising solution, not only for the ease of implementation of these composites, but also for the creation of complex structures dedicated to heat dissipation. These structures play a crucial role in optimizing the heat exchange surface by convection with the surrounding air, thus allowing efficient dissipation of heat generated by modern electronic devices.In this study, 3D printing of copper (Cu) was achieved through the addition of an optimal amount of aluminum. This approach significantly improved the densification of copper-based materials, despite the challenges posed by its high reflectivity. Subsequently, in-depth investigation and optimization of laser 3D printing of the AlSi10Mg alloy, before and after the incorporation of D, were carried out. Finally, a crucial post-processing step was optimized, consisting of polishing Al/D composite materials using laser ablation.This work was carried out as part of an international collaboration between the University of Nebraska, Lincoln in the United States of America, and the University of Bordeaux in France

Los estilos APA, Harvard, Vancouver, ISO, etc.

4

Tilliander, Ulrika. "Synthesis of nano sized Cu and Cu-W alloy by hydrogen reduction". Licentiate thesis, KTH, Materials Science and Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-353.

Texto completo

Resumen

The major part of the present work, deals with the reduction kinetics of Cu₂O powder and a Cu₂O-WO₃ powder mixture by hydrogen gas, studied by ThermoGravimetric Analysis (TGA). The reduction experiments were carried out both isothermally and non-isothermally on thin powder beds over different temperature intervals. During the experiments, the reductant gas flow rate was kept just above the starvation rate for the reaction to ensure that chemical reaction was the rate-controlling step. The activation energy for the reactions was evaluated from isothermal as well as non-isothermal reduction experiments.

In the case of the reduction of Cu₂O, the impact of the stability of the copper oxide on the activation energy for hydrogen reduction under identical experimental conditions is discussed. A closer investigation of additions of Ni or NiO to Cu₂O did not have a perceptible effect on the kinetics of reduction.

In the case of the reduction of the Cu₂O-WO₃mixture, the reaction mechanism was found to be affected in the temperature range 923-973 K, which is attributed to the reaction/transformation in the starting oxide mixture. At lower temperatures, Cu₂O was found to be preferentially reduced in the early stages, followed by the reduction of the tungsten oxide. At higher temperatures, the reduction kinetics was strongly affected by the formation of a complex oxide from the starting materials. It was found that the Cu₂O-WO₃mixture underwent a reaction/transformation which could explain the observed kinetic behavior.

The composition and microstructures of both the starting material and the reaction products were analyzed by X-ray diffraction (XRD) as well as by microprobe analysis. vi Kinetic studies of reduction indicated that, the mechanism changes significantly at 923 K and the product formed had unusual properties. The structural studies performed by XRD indicated that, at 923 K, Cu dissolved in W forming a metastable solid solution, in amorphous/nanocrystalline state. The samples produced at higher as well as lower temperatures, on the other hand, showed the presence two phases, pure W and pure Cu. The SEM results were in conformity with the XRD analysis and confirmed the formation of W/Cu alloy. TEM analysis results confirmed the above observations and showed that the particle sizes was about 20 nm.

The structure of the W/Cu alloy produced in the present work was compared with those for pure copper produced from Cu2O produced by hydrogen reduction under similar conditions. It indicated that the presence of W hinders the coalescence of Cu particles and the alloy retains its nano-grain structure. The present results open up an interesting process route towards the production of intermetallic phases and composite materials under optimized conditions.

Los estilos APA, Harvard, Vancouver, ISO, etc.

5

Guazzone, Federico. "Engineering of Substrate Surface for the synthesis of Ultra-Thin Composite Pd and Pd-Cu Membranes for H2 Separation". Digital WPI, 2006. https://digitalcommons.wpi.edu/etd-dissertations/442.

Texto completo

Resumen

This work describes a novel technique to prepare ultra-thin composite Pd-porous metal membranes for H2 separation. This novel technique consists of the gradual smoothing of the Porous Metal (PM) support's surface with several layers of pre-activated alumina particles of different sizes. The deposition of coarse, fine and ultra-fine alumina particles resulted in the narrowing of the PM' surface pore size distribution. The excellent surface smoothness achieved after the grading of the PM 's surface support allowed for the preparation of gas tight Pd layers as thin as 5.6?m. The Pd layers were extremely uniform due to the presence of the grade layer and strongly attached to the support. Composite Pd membranes prepared on graded supports showed H2 permeance as high as 50 m3/(m2 h bar0.5) at 500ºC and ideal selectivities (H2/He) as high as 27000. Moreover, the H2 permeance and ideal selectivity were stable over 1100 hours at 500ºC in H2 atmosphere. Composite Pd-Cu membranes showed H2 permeance as high as 30 m3/(m2 h bar0.5) at 450ºC and ideal selectivities (H2/He) as high as 900. The H2 permeance and ideal selectivity of Pd-Cu membranes were stable over 500 hours at 450ºC in H2 atmosphere. The outstanding long-term H2 permeance and ideal selectivity stability of all composite Pd and Pd-Cu membranes represented a breakthrough in composite Pd membrane synthesis. The thermal stresses arising from the mismatch in the coefficient of thermal expansion between the Pd film and the support were determined by means of x-ray diffraction. The results indicated that the release of stresses began to occur at temperatures close to 400ºC. Also, the release of stresses took place with a visible sintering of Pd clusters within the thin Pd film. The stresses due to the absorption of H2 were also studied and modeled. It was estimated that the maximum compressive stress under which these composite Pd membranes were characterized was equal to 260 MPa.

Los estilos APA, Harvard, Vancouver, ISO, etc.

6

Quelennec, Xavier. "Nanostructuration d'un composite Cu-Fe par déformation intense : vers un mélange forcé à l'échelle atomique". Phd thesis, Université de Rouen, 2008. http://tel.archives-ouvertes.fr/tel-00648688.

Texto completo

Resumen

Les techniques d'élaboration par déformation plastique intense permettent d'obtenir des matériaux nanostructurés à l'état massif. La grande quantité de défauts (dislocations, lacunes,...) peut donner lieur à des transformations de phases hors équilibre. L'objectif de ce travail à été de produire par HPT (high pressure torsion) une solution solide hors équilibre à partir du système modèle Cu-Fe et de comprendre les mécanismes physiques à l'origine de sa formation. Le matériau initial est un nanocomposite filamentaire Cu-cfc/Fe-α. Des tranches de ce composite ont été déformées par HPT pour une large gamme de taux de déformation. Le matériau obtenu a été caractérisé par DRX, spectroscopie Mössbauer, MET et sonde atomique tomographique. Les filaments de ferrite sont dans une premier temps amincis jusqu'à environ 5nm. Le mélange forcé commence alors par diffusion de Fe dans Cu-cfc pour enfin aboutir à une solution solide homogène de Fe dans Cu-cfc. A la vue des données, les dislocations et le cisaillement répété des interfaces ne peuvent pas expliquer la formation du mélange forcé. Celle-ci est attribuée à la diffusion accélérée par les lacunes en excès.

Los estilos APA, Harvard, Vancouver, ISO, etc.

7

Shi, Hailong. "Recrystallization of 2D dimensioned Copper (Cu) foils and graphene nanosheets (GNSs) reinforced Cu matrix laminated composites". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0096.

Texto completo

Resumen

La recristallisation est le processus des métaux déformés à froid qui se produit lors du traitement thermique. La texture de recristallisation contribue à l'anisotropie des propriétés mécaniques et physiques. Motivés par la minimisation des produits, les matériaux 2D et les composites stratifiés sont de plus en plus demandés pour des applications. Ainsi, à des fins scientifiques et techniques, des recherches sur la recristallisation de tels matériaux sont nécessaires pour comprendre les mécanismes sous-jacents. Dans ce travail, des feuilles de Cu et des composites stratifiés à matrice de Cu renforcé de nanofeuilles de graphène (GNS) avec des épaisseurs de Cu de 10 μm et 30 μm ont été fabriqués. La recristallisation a été étudiée de l'échelle microscopique à l'échelle macroscopique par SEM-EBSD pour l'observation de microstructure, rayonnement neutronique et synchrotron pour l'analyse de texture et rayonnement synchrotron in situ pour l'évaluation de la déformation du réseau. Les données obtenues ont été analysées dans le cadre de la cristallographie combinée à l'élasticité et à l'énergie de surface. Les résultats ont montré que le comportement de recristallisation de Cu était grandement affecté par l'épaisseur de la feuille de Cu et l'ajout des GNSs. Pour les feuilles de Cu de 10 μm sans GNSs, elles ont subi une transition de la texture de laminage à froid à une texture de recristallisation dominée par des composants Cube tourné RD et Copper tourné φ2. La transition a été contrôlée par des facteurs intrinsèques microstructuraux et extrinsèques géométriques d'échantillons. Les orientations des germes sont héritées des orientations de déformation. Ceux avec des facteurs de Taylor faibles (Cube, Goss et Brass) ont montré une préférence de taille. La croissance post-nucléation a été affectée par la contrainte d'élasticité thermique biaxiale et l'énergie de surface. En raison de leurs effets opposés, les orientations ayant des modules biaxiaux et une densité d'énergie de surface modérés (S, Copper, Brass et composants de recristallisation) ont survécu, résultant en une texture mixte à la fin de la recristallisation. Les joints Σ3 cohérents entre les nouvelles composantes ont stabilisé leur croissance en consommant les autres séparés par des joints aléatoires à grand angle. Une fois le Cu fritté en masse, sa texture était dominée par les orientations des grains à croissance anormale. Les effets des GNSs sur la recristallisation des feuilles de Cu dépendaient également de l'épaisseur de la feuille de Cu. Pour les feuilles de 10 μm d'épaisseur, l'effet des GNSs se manifeste après le frittage des échantillons à des températures élevées (> 700 ℃). Au lieu de créer beaucoup de contraintes à l'expansion des feuilles de Cu adjacentes, les GNSs ont fonctionné comme une barrière empêchant la pénétration des grains de Cu développés, entraînant la stabilisation de la texture de recristallisation représentée par les deux composantes tournées. Pour le composite Cu/GNS avec une épaisseur de Cu de 30 μm, les résultats ont montré qu'une forte orientation Cube était produite dans le composite Cu/GNS au lieu des orientations individuelles non Cube dans l'empilement de Cu pur sans GNSs. Une analyse détaillée de l'état de déformation de Cu dans le composite Cu/GNS a révélé que le comportement d'expansion anisotrope du GNS qui est incompatible avec celui de Cu imposait de multiples contraintes élastiques aux feuilles, entraînant un état isocontrainte biaxiale dans la couche en surface et un état de déformation en compression uniaxiale dans la couche centrale. L'anisotropie élastique du Cu favorise la croissance des grains orientés Cube pour minimiser l'énergie totale de déformation. Les résultats du présent travail fournissent des informations quantitatives détaillées sur la recristallisation de feuilles de Cu et de composites stratifiés, ce qui contribue à approfondir la compréhension du comportement de recristallisation des matériaux 2D
Recrystallization is the intrinsic process of cold-deformed metallic materials that occurs inevitably during the thermal treatment. The produced recrystallization texture contributes to the anisotropy of the mechanical and physical properties. Motivated by the minimization of modern products, 2D materials and laminated composites are increasingly demanded by many applications. Thus, for both scientific and engineering purposes, investigations on the recrystallization of such materials are needed to understand the underlying mechanisms. In this work, Cu foils and graphene nanosheets (GNSs) reinforced Cu matrix laminated composites with Cu foil thicknesses of 10 μm and 30 μm were fabricated, and the recrystallization features were thoroughly investigated from microscale to macroscale by means of SEM-EBSD for microstructure observation, neutron and synchrotron radiation for texture analysis and in-situ synchrotron radiation for lattice strain evaluation. The obtained data were analyzed in the frame of crystallography combined with crystal elasticity and surface energy. The results showed that the recrystallization behavior of the Cu foils were greatly affected by the Cu foil thickness and the addition of the GNSs. For the 10 μm thick Cu foils without GNS, they underwent a transition from the cold-rolling texture to a recrystallization texture dominated by RD-rotated Cube and φ_2-rotated Copper components. The transition was screened by both intrinsic microstructural and extrinsic sample geometrical factors. The orientations of the nuclei were mainly inherited from the deformation orientations. Those with low Taylor factors (Cube, Goss and Brass) demonstrated size preference. The post-nucleation growth was affected by the biaxial thermal elastic constraint and surface energy. Due to their opposite effects, the orientations having moderate biaxial moduli and surface energy density (S, Copper, Brass and recrystallization components) survived, resulting in a mixed texture at the completion of recrystallization. The coherent Σ3 boundaries between the new components stabilized their growth through consuming the other oriented crystals separated by random high-angle boundaries. When sintered into bulk, the texture of the Cu was dominated by the orientations of the abnormally grown grains. The effects of GNSs on the recrystallization of Cu foils were also Cu foil thickness dependent. For the 10 μm thick foils, the effect of the GNSs manifested after the samples were sintered to high temperatures (> 700 ℃). Instead of creating much constraint to the expansion of the adjacent Cu foils, the GNSs worked as a barrier preventing the penetration of the grown Cu grains, resulting in the stabilization of the recrystallization texture represented by the two rotated components. For the Cu/GNS composite with Cu foil thickness of 30 μm, the results evidenced that a strong Cube orientation was produced in the Cu/GNS composite instead of the individual non-Cube orientations in the pure Cu stack without GNSs. Detailed strain-state analysis of the Cu foils in the Cu/GNS composite revealed that the anisotropic expansion behavior of the GNS that is incompatible with that of the Cu foils imposed multiple elastic constraints to the foils, resulting in a biaxial isostrain state in the surface layers and a uniaxial compressive strain state in the central layer. The elastic anisotropy of Cu favors the growth of the Cube oriented grains to minimize the total strain energy. The results of the present work provide quantitative and detailed information on recrystallization of thin Cu foils and laminated composite, which contributes to deepening the understanding of recrystallization behaviour of 2D materials. The mechanisms revealed are useful for analysing abnormal grain growth in elastically strained materials and can also be applied to fabrication process for texturization or even monocrystallization

Los estilos APA, Harvard, Vancouver, ISO, etc.

8

H, Lavrenyuk O. Mykhalichko V. Olijnyk B. Mykhalichko. "Stereochemical aspect of influence of [Cu(diethylenetriamine)(H2O)] SO4 H2O chelate compound onto combustibility decrease of epoxy-amine composite materials". Thesis, Book of abstr. Third EuCheMS Inorganic Chemistry Conference “Chemistry over the horizon” , Wroclaw, 2015. http://hdl.handle.net/123456789/1645.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

9

COSTA, FRANCINE A. da. "Sintese e sinterizacao de pos compositos do sistema W-Cu". reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11176.

Texto completo

Resumen

Made available in DSpace on 2014-10-09T12:49:13Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T13:57:43Z (GMT). No. of bitstreams: 1 09808.pdf: 15249724 bytes, checksum: 28b6b5cf9f351da89e42817bc182390d (MD5)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
FAPESP:00/00255-9

Los estilos APA, Harvard, Vancouver, ISO, etc.

10

Tang, Fei. "The Microstructure-Processing-Property Relationships in an Al Matrix Composite System Reinforced by Al-Cu-Fe Alloy Particles". Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2004. http://www.osti.gov/servlets/purl/835313-syGDu9/webviewable/.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

11

Vallet, Guy-Marie. "Elaboration de matériaux composites à matrice métallique (Cu-NTC) ayant des propriétés électriques améliorées pour application filaire". Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0350/document.

Texto completo

Resumen

Le remplacement des systèmes de distribution d’énergie actuels dans les avions (pneumatiques, hydrauliques, mécaniques et électriques) par des systèmes 100% électriques est un enjeu majeur dans le cadre du projet de l’avion « plus électrique ». Le processus d’électrification de l’avion conduit à une augmentation de la puissance embarquée à bord des aéronefs, et par conséquent à une augmentation de la masse du réseau filaire. Afin de pallier à cette augmentation, un nouveau matériau composite possédant des propriétés électriques supérieures à celle du cuivre a été développé dans le but d’augmenter la capacité de courant admissible dans le conducteur à section constante. Ce travail de thèse présente le procédé d’élaboration du matériau composite cuivre-nanotubes de carbone développé ainsi que les techniques de caractérisation utilisées et les résultats associés. Différents paramètres tels que la qualité de la dispersion des renforts dans la matrice, le type de nanotubes de carbone utilisés (multi-parois vs mono-paroi), la nature de l’interface créée entre le cuivre et les renforts (mécanique vs chimique) ainsi que les techniques de mise en forme du matériau (pressage uni-axial à chaud, extrusion à chaud) et de post-traitements (recuit, laminage à chaud) ont été étudiés afin d’obtenir des propriétés physiques optimales. Il en résulte une augmentation des propriétés thermiques (+6,8% pour la conductivité thermique), mécaniques (+32% pour la dureté Vickers) et également électriques - pour la première fois observée- (+3,4 % pour la conductivité électrique) et ce en comparaison avec à une matrice de cuivre pur
The substitution of the current energy chains in aircrafts (pneumatic, hydraulic, mechanical and electrical) by a 100% electrical chain is a major issue in the field of the “more electric” aircraft. The electrification process leads to an increase of the inboard power of aircrafts, and therefore to an increase of the wired network weight. To counterbalance this increase of mass, a new composite material with higher electrical properties that copper should be considered, in order to increase the current density in the conductor at constant cross section. Several parameters have been studied such as the quality of the carbon nanotubes dispersion, the type of CNTs used (single-walled vs. multi walled), the interface between the matrix and the reinforcements (mechanical vs. chemical), the shaping of material (uni-axial hot pressing, hot extrusion process) and the post treatments processes (heat treatment, hot lamination process). An enhancement of the thermal properties (+ 6.8% of thermal conductivity), the mechanical properties (+32% of Vickers hardness) and for the first time an increase of the electrical properties (+3.4 % for the electrical conductivity) have been observed in comparison with pure copper

Los estilos APA, Harvard, Vancouver, ISO, etc.

12

Han, Jixiong. "Processing Microstructure Evolution and Properties of Nanoscale Aluminum Alloys". University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1121701078.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

13

Chesser, Ian (Ian W. ). "Atomistic simulation of deformation induced rotation in Cu-Nb composites". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104150.

Texto completo

Resumen

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 44-46).
Accumulative roll bonding (ARB) of three copper-niobium (Cu-Nb) nano-composite models is simulated using molecular statics techniques to assess the rotational stability of Cu-Nb interfaces at high strains up to 90% thickness reduction. Crystals strain and rotate under compression, and certain Cu-Nb composites have been shown to reach a steady state of rotation at large rolling reductions. These steady-state rotations correspond to the formation of a preferred interface character between layers. Cumulative rotation of Cu and Nb layers was tracked as a function of strain using a rotation algorithm. A Cu-Nb bicrystal and poly-crystalline model with a {111}<110> Cu// {110}<111> Nb interface character were found to rotate significantly from their initial crystallographic orientation under compression. A Cu-Nb bi-crystal model with a {112}<111>Cu // {112}<110>Nb interface character was found to rotate less when rolled in the transverse direction compared to the typical <111>Cu//<110>Nb rolling direction. Results show that experimentally observed plastic stability of rolled Cu-Nb composites comes from a factor not accounted for in the simulation, like thermally activated dislocation mechanisms. The study refines the current knowledge of plastic stability in Cu-Nb composites.
by Ian Chesser.
S.B.

Los estilos APA, Harvard, Vancouver, ISO, etc.

14

Gill, Puneet K. Singh. "Synthesis and investigation of highly conductive Cu-Cr-MWCNT composites". FIU Digital Commons, 2008. https://digitalcommons.fiu.edu/etd/3938.

Texto completo

Resumen

There is great demand for contact materials with superior electrical and thermal conductivities and mechanical strength, for use in Vacuum Circuit Breakers (VCB). Copper (Cu) and chromium (Cr) alloy, developed in the 1970’s [1] has been the most common contact material in VCBs. Although Cu-Cr alloys possess good conductivity and mechanical properties, 50% of Cr (a strategic metal) in the alloy is resource prohibitive. A reduction in Cr usage without compromising desired properties is desirable. Previous researchers focused on developing Cu-Cr alloys with fine and uniform microstructure to enhance their physical properties. This investigation focused on the development of a Cu-Cr-MWCNT (Multi walled Carbon Nanotubes) composite with enhanced properties as compared with currently used materials. The electrical conductivity of the composite increased up to 18 times that of Cu and there was also an increase in the Vicker’s hardness.

Los estilos APA, Harvard, Vancouver, ISO, etc.

15

Puga, Joel Bento. "WC-(Cu, Fe, Cr, Ni) composites attained by mechanosynthesis". Master's thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/12263.

Texto completo

Resumen

Mestrado em Engenharia de Materiais
This work aims to study the feasibility of replacing cobalt by copper and stainless steel in tungsten carbide composite. The composites were prepared with a binder content of 12 wt% using the powder metallurgy method in which the conventional milling was replaced by high energy ball milling. To obtain a composite with high density, good microstructure uniformity and controlled phase composition, suitable for a good mechanical performance, the processing conditions of the high energy ball milling (HEBM) and sintering methods were enhanced. Within the studied parameters, the prime milling conditions were found at the rotation speed of 350 rpm and ball-to-powder weight ratio of 20:1, varying the milling times between 8-10 hours for the studied compositions. The HEBM process was able to reduce the particle size of the composite powders down to the nanoscale and a good binder homogenization was reached. After compacting, the powders were submitted to vacuum sintering, in a temperature range of 1300 – 1500ºC followed by HIP (hot isotactic pressing). This procedure allowed attaining dense compacts and introduce efficiently copper in the stainless steel binder up to 30%, without substantial decrease of the sintered relative density. The WC-SS composite powders show a significant amount of M6C phase formed during sintering, endorsed by the high reactivity of the small powder particles and the appearing of the M6C phase. Adding copper to the WC-SS composite allowed the decrease of the M6C phase formation. The WC-Cu sintered samples revealed two distinct major phases, W2C and Cu0.4W0.6 and their appearance depends on the applied sintering technique, in the case of being conventional or two stages sintering, respectively. The mechanical characterization revealed that the hardness of the WC-SS compacts is equivalent to the reported values in the literature for WC-Co. On the other hand, the fracture toughness remains below the reference values. Nevertheless, it was possible to attain a good balance between hardness and fracture toughness in the WC-(SSCu) composites, which make them promising candidates for substituting the traditional WC-Co composite.
Este trabalho tem como objetivo estudar a viabilidade da substituição do ligante cobalto por cobre e aço inoxidável em compósitos de carboneto de tungsténio. Estes compósitos foram preparados com um teor de ligante de 12% pp, utilizando o método de pulverometalurgia no qual a moagem convencional foi substituída pela moagem de alta energia (MAE). Por forma a obter compósitos de elevada densidade, boa uniformidade microestrutural, e composição de fases adequada a um bom desempenho mecânico, foram otimizadas as condições de processamento das etapas de moagem de alta energia e da sinterização. As melhores condições de moagem foram verificadas com uma velocidade de rotação de 350 rpm, um rácio de peso bolas:material de 20:1 e, dependendo da composição estudada, um tempo de moagem variável entre 8 – 10 horas. Utilizando o processo de MAE foi possível reduzir o tamanho de partícula dos pós compósitos até à nanoescala e ainda obter uma boa uniformidade da distribuição da fase ligante. Após compactação, os pós foram submetidos a uma etapa de sinterização em vácuo num intervalo de temperaturas entre 1300 - 1500 °C, seguindo-se uma etapa de prensagem isostática a quente. Este método permitiu obter compactos de densidade elevada e introduzir de forma eficiente até 30% de cobre na fase ligante de aço inoxidável sem se verificarem reduções substanciais da densidade dos compactos sinterizados. Os compósitos de WC-SS apresentam uma composição de fases com uma quantidade elevada de fase M6C, formada durante a sinterização e que é favorecida nestes materiais, devido à elevada reatividade dos pós nanométricos. Contudo, a adição de cobre ao compósito WC-SS permitiu a diminuição da formação de fase M6C. As amostras sinterizadas de WC-Cu apresentam maioritariamente duas fases distintas, W2C e Cu0.4W0.6 e o aparecimento desta última fase depende da técnica de sinterização utilizada, convencional e sinterização em duas etapas respetivamente. A caracterização mecânica revelou que a dureza dos compósitos de WC-SS é equivalente aos valores indicados na literatura para os compósitos de WC-Co, enquanto a tenacidade permanece abaixo dos valores de referência. No entanto, foi possível alcançar um bom equilíbrio entre a dureza e tenacidade nos compósitos de WC-(SSCu), o que poderá permitir a sua utilização em algumas aplicações dos tradicionais carbonetos cementados de WC-Co.

Los estilos APA, Harvard, Vancouver, ISO, etc.

16

Deshpande, Pranav Kishore. "Infrared Processed Copper-Tungsten Carbide Composites". University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1025107651.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

17

Watkins, Bobby Gene II. "Materials selection and evaluation of Cu-W particulate composites for extreme electrical contacts". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/39494.

Texto completo

Resumen

Materials for extreme electrical contacts need to have high electrical conductivity coupled with good structural properties. Potential applications include motor contacts, high power switches, and the components of electromagnetic launch (EML) systems. In particular, the lack of durability of these materials in rail components limits practical EML implementation. These rails experience significant amounts of Joule heating, due to extreme current densities, and subsequent thermally-assisted wear. New more durable materials solutions are needed for these components. A systematic materials selection study was executed to identify and compare candidate materials solutions. Several possible candidate non-dominated materials as well as hybrid materials that could potential fill the "white spaces" on the Ashby charts were identified. A couple potential candidate materials were obtained and evaluated. These included copper-tungsten W-Cu, "self-lubricating" graphite-impregnated Cu, and Gr-W-Cu composites with different volume fractions of the constituents. The structure-property relations were determined through mechanical and electrical resistivity testing. A unique test protocol for exposing mechanical test specimens to extreme current densities up to 1.2 GA/m2 was developed and used to evaluate these candidate materials. The systematic design of multi-functional materials for these extreme electrical contacts requires more than an empirical approach. Without a good understanding of both the tribological and structural performance, the optimization of the microstructure will not be quickly realized. By using micromechanics modeling and other materials design modeling tools coupled with systematic mechanical and tribological experiments, the design of materials for these applications can potentially be accelerated. In addition, using these tools, more complex functionally-graded materials tailored to the application can be systematically designed. In this study, physics- and micromechanics-based models were used to correlate properties to the volume fraction of the constituents of the evaluated candidate materials. Properties correlated included density, elastic modulus, hardness, strength, and electrical resistivity of the W-Cu materials.

Los estilos APA, Harvard, Vancouver, ISO, etc.

18

Carbonell, Laure-Arminia. "Conductivité électrique et résistance de contact de matériaux composites Cu-Ni-graphite". Grenoble INPG, 1990. http://www.theses.fr/1990INPG0017.

Texto completo

Resumen

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

Los estilos APA, Harvard, Vancouver, ISO, etc.

19

Papillon, Anthony. "Frittage de composites Cu-Cr pour l'élaboration de matériaux de contact d'ampoules à vide". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI099.

Texto completo

Resumen

Les composites Cu-Cr sont couramment utilisés comme matériaux de contact électrique pour ampoules à vide des disjoncteurs de moyenne tension. Pourtant très répandu, le frittage en phase solide de ces matériaux a été relativement peu étudié. L’optimisation du procédé passe par la compréhension des mécanismes de frittage. Cette étude est focalisée sur deux aspects importants du frittage : les processus d’oxydo-réduction liés aux oxydes de surfaces des poudres et la compétition entre mécanismes de densification et de gonflement au cours du frittage.L’oxydo-réduction a été étudiée par analyse thermogravimétrique couplée à différentes techniques de spectroscopie d’abord sur les matériaux purs puis sur les composites. Des analyses des interfaces par des coupes réalisées au FIB ont permis de préciser la localisation de l’oxyde dans les matériaux frittés. Un transfert d’oxygène a lieu entre les poudres de cuivre et de chrome. L’intensité de ce transfert dépend de la nature réductrice de l’atmosphère utilisée.La densification a été analysée par dilatométrie sur les matériaux purs et sur les composites. Ces analyses ont été appuyées par des observations microstructurales, notamment par tomographie des rayons X. L’effet des paramètres du procédé (atmosphère, vitesse de chauffage, poudres…) a été étudié. Les résultats montrent le lien entre la désoxydation des poudres de cuivre et le frittage. Un phénomène de gonflement du cuivre seul s’explique par le dégazage du cuivre à haute température lors de la fermeture des pores. Ce gonflement n’a pas lieu dans les composites Cu-Cr car le chrome retarde la fermeture des pores et piège les gaz émis par le cuivre en formant l’oxyde Cr2O3. L’atmosphère de frittage, la morphologie et la taille des poudres de chrome influent sur la densification. Le frittage sous vide permet de réduire la porosité. Une morphologie sphérique des particules de chrome limite l’effet inhibiteur de celui-ci sur la densification. Pour de faibles tailles de particules, le chrome participe à la densification, ce qui permet de mieux densifier le matériau. Ces résultats ouvrent des voies d’optimisation du procédé de frittage des matériaux.Les matériaux élaborés ont été testés dans leurs conditions d’utilisation, c'est-à-dire lors de coupures sur court-circuit en ampoule à vide. Ces essais ont montré l’intérêt de réduire la quantité d’oxyde de chrome et ont permis de déterminer l’effet des impuretés rencontrées usuellement sur les poudres de cuivre et de chrome
Cu-Cr composites are commonly used as contact materials for medium voltage circuit breakers vacuum bottles. Solid state sintering process of Cu-Cr composites is widespread but has been relatively little studied. Optimizing the process requires understanding the sintering mechanisms. This study was focused on two important aspects of sintering: the redox reactions associated to oxides on the powder surface and the competition between densification and swelling mechanisms during sintering.The redox reactions were studied by thermogravimetric analysis coupled to various spectroscopic techniques, first on isolated Cu and Cr, then on Cu-Cr composites. Interfaces analyses obtained by FIB clarified the location of the oxide inside the sintered materials. Oxygen transfer takes place between copper and chromium powders. This phenomenon strongly depends on the reducing character of the sintering atmosphere.Densification was analyzed by dilatometry on Cu, Cr and Cu-Cr composites. This analysis was supported by microstructural observations, including X-ray tomography .The effect of process parameters (atmosphere, heating rate, powders ...) was studied. The results show the relationship between sintering and copper oxide reduction. The swelling phenomenon of copper compacts is explained by high temperature degassing of copper during pore closure. This swelling does not occur in Cu-Cr composites as chromium delays pore closing and entraps the gases released by copper. Sintering atmosphere, chromium morphology and chromium particle size affect densification. Vacuum sintering reduces porosity. Chromium particles with spherical shape limit its inhibiting effect on densification. For small particle sizes, chromium participates to densification, leading to better densification of the material. These results open the route for optimizing the sintering of Cu-Cr composites.Cu-Cr composites were tested for short circuit performance in vacuum interrupters. The result of these tests showed the importance of reducing the chromium oxide amount. The effect of impurities commonly encountered on the powders copper and chromium powders was also determined

Los estilos APA, Harvard, Vancouver, ISO, etc.

20

Gu, Tang. "Modélisation multi-échelles du comportement électrique et élasto-plastique de fils composites Cu-Nb nanostructurés et architecturés". Thesis, Paris, ENSAM, 2017. http://www.theses.fr/2017ENAM0017/document.

Texto completo

Resumen

Les fils composites nanostructurés et architecturés cuivre-niobium sont de candidats excellents pour la génération de champs magnétiques intenses (>90T); en effet, ces fils allient une limite élastique élevée et une excellente conductivité électrique. Les fils Cu-Nb multi-échelles sont fabriqués par étirage et empaquetage cumulatif (une technique de déformation plastique sévère), conduisant à une microstructure multi-échelle, architecturée et nanostructurée présentant une texture cristallographique de fibres forte et des formes de grains allongées le long de l'axe du fil. Cette thèse présente une étude compréhensive du comportement électrique et élasto-plastique de ce matériau composite, elle est divisée en trois parties: modélisation multi-échelle électrique, élastique et élasto-plastique. Afin d'étudier le lien entre le comportement effective et la microstructure du fil, plusieurs méthodes d'homogénéisation sont appliquées, qui peuvent être séparées en deux types principaux: la méthode en champs moyens et en champs complets. Comme les spécimens présentent plusieurs échelles caractéristiques, plusieurs étapes de transition d'échelle sont effectuées itérativement de l'échelle de grain à la macro-échelle. L'accord général parmi les réponses de modèle permet de suggérer la meilleure stratégie pour estimer de manière fiable le comportement électrique et élasto-plastique des fils Cu-Nb et économiser le temps de calcul. Enfin, les modèles électriques prouvent bien prédire les données expérimentales anisotopique. De plus, les modèles mécaniques sont aussi validés par les données expérimentales ex-situ et in-situ de diffraction des rayons X/neutrons avec un bon accord
Nanostructured and architectured copper niobium composite wires are excellent candidates for the generation of intense pulsed magnetic fields (>90T) as they combine both high strength and high electrical conductivity. Multi-scaled Cu-Nb wires are fabricated by accumulative drawing and bundling (a severe plastic deformation technique), leading to a multiscale, architectured and nanostructured microstructure exhibiting a strong fiber crystallographic texture and elongated grain shapes along the wire axis. This thesis presents a comprehensive study of the effective electrical and elasto-plastic behavior of this composite material. It is divided into three parts: electrical, elastic and elasto-plastic multiscale modeling. In order to investigate the link between the effective material behavior and the wire microstructure, several homogenization methods are applied which can be separated into two main types: mean-field and full-field theories. As the specimens exhibit many characteristic scales, several scale transition steps are carried out iteratively from the grain scale to the macro-scale. The general agreement among the model responses allows suggesting the best strategy to estimate reliably the effective electrical and elasto-plastic behavior of Cu-Nb wires and save computational time. The electrical models are demonstrated to predict accurately the anisotropic experimental data. Moreover, the mechanical models are also validated by the available ex-situ and in-situ X-ray/neutron diffraction experimental data with a good agreement

Los estilos APA, Harvard, Vancouver, ISO, etc.

21

Melchiors, Gilberto. "Caracteriza??o de comp?sitos Nb-20%cu obtidos por moagem de alta energia e sinterizados por fase l?quida". Universidade Federal do Rio Grande do Norte, 2011. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12716.

Texto completo

Resumen

Made available in DSpace on 2014-12-17T14:06:58Z (GMT). No. of bitstreams: 1 GilbertoM_DISSERT_PARCIAL.pdf: 494543 bytes, checksum: da2d1ceb188b373977eacdb9f150846c (MD5) Previous issue date: 2011-01-31
In this work, was studied the formation of a composite of the refractory metal niobium with copper, through the process of high-energy milling and liquid phase sintering. The HEM can be used to synthesize composite powders with high homogeneity and fine size particle distribution. It may also produce the solid solubility in immiscible systems such as Nb-Cu, or extend the solubility of systems with limited solubility. Therefore, in the immiscible system Cu-Nb, the high-energy milling was successfully used to obtain the composite powder particles. Initially, the formation of composite particles during the HEM and the effect of preparation technique on the microstructure of the material was evaluated. Four loads of Nb and Cu powders containing 20%wt Cu were synthesized by MAE in a planetary type ball mill under different periods of grinding. The influence of grinding time on the metal particles is evaluated during the process by the withdrawal of samples at intermediate times of milling. After compaction under different forces, the samples were sintered in a vacuum furnace. The liquid phase sintering of these samples prepared by HEM produced a homogeneous and fine grained. The composite particles forming the sintered samples are the addition of a hard phase (Nb) with a high melting point, and a ductile phase (Cu) with low melting point and high thermal and electrical conductivities. Based on these properties, the Nb-Cu system is a potential material for many applications, such as electrical contacts, welding electrodes, coils for generating high magnetic fields, heat sinks and microwave absorbers, which are coupled to electronic devices. The characterization techniques used in this study, were laser granulometry, used to evaluate the homogeneity and particle size, and the X-ray diffraction, in the phase identification and to analyze the crystalline structure of the powders during milling. The morphology and dispersion of the phases in the composite powder particles, as well the microstructures of the sintered samples, were observed by scanning electron microscopy (SEM). Subsequently, the sintered samples are evaluated for density and densification. And finally, they were characterized by techniques of measuring the electrical conductivity and microhardness, whose properties are analyzed as a function of the parameters for obtaining the composite
Neste trabalho, foi estudada a forma??o de um comp?sito do metal refrat?rio ni?bio com o cobre, atrav?s do processo de moagem de alta energia e sinteriza??o por fase l?quida. A MAE pode ser usada para sintetizar p?s comp?sitos com alta homogeneidade e fina distribui??o de tamanho de part?culas. Ela tamb?m pode produzir a solubilidade s?lida em sistemas imisc?veis como o Nb-Cu, ou, estender a solubilidade de sistemas com limitada solubilidade. Portanto, no sistema imisc?vel Nb-Cu, a moagem de alta energia foi utilizada com sucesso para a obten??o das part?culas do p? comp?sito. Inicialmente a forma??o das part?culas comp?sitas durante a MAE e o efeito dessa t?cnica de prepara??o na microestrutura do material foi avaliada. Quatro cargas de p?s de Nb e Cu contendo 20% em massa de Cu foram sintetizados por MAE em um moinho de bolas tipo planet?rio, sob diferentes per?odos de moagem. A influ?ncia do tempo de moagem nas part?culas met?licas ? avaliada no decorrer do processo, atrav?s da retirada de amostras em tempos parciais da moagem. Ap?s a compacta??o sob diferentes for?as, as amostras foram sinterizadas em um forno ? v?cuo. A sinteriza??o por fase l?quida destas amostras preparadas por MAE produziu uma estrutura homog?nea e com granula??o refinada. As part?culas comp?sitas que formam as amostras sinterizadas, s?o a jun??o de uma fase dura (Nb) com alto ponto de fus?o, e uma fase d?ctil (Cu) de baixo ponto de fus?o e de elevadas condutividades t?rmica e el?trica. Com base nestas propriedades, o sistema Nb-Cu ? um material em potencial para in?meras aplica??es, como contatos el?tricos, eletrodos de solda, bobinas para gera??o de altos campos magn?ticos, dissipadores de calor e absorvedores de microondas, que s?o acoplados a dispositivos eletr?nicos. As t?cnicas de caracteriza??o utilizadas neste estudo, foram a granulometria ? laser para avaliar a homogeneidade e o tamanho das part?culas, e a difra??o de raios-X, na identifica??o das fases e an?lise da estrutura cristalina dos p?s durante a moagem. J? a morfologia e a dispers?o das fases nas part?culas do p? comp?sito, assim como as microestruturas das amostras sinterizadas, foram observadas atrav?s de microscopia eletr?nica de varredura (MEV). Posteriormente, as amostras sinterizadas foram avaliadas quanto ? densidade e densifica??o. E, finalmente, foram caracterizadas atrav?s de t?cnicas de medi??o da condutividade el?trica e microdureza Vickers, cujas propriedades s?o analisadas em fun??o dos par?metros de obten??o do comp?sito

Los estilos APA, Harvard, Vancouver, ISO, etc.

22

Carvalho, Werson Magno de. "Estudo da moagem de alta energia e sinteriza??o de p?s comp?sitos W-Cu". Universidade Federal do Rio Grande do Norte, 2008. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12665.

Texto completo

Resumen

Made available in DSpace on 2014-12-17T14:06:48Z (GMT). No. of bitstreams: 1 WersonMC.pdf: 1184207 bytes, checksum: f2f0598e463a68730749344c713c5bff (MD5) Previous issue date: 2008-02-22
The Tungsten/copper composites are commonly used for electrical and thermal objectives like heat sinks and lectrical conductors, propitiating an excellent thermal and electrical conductivity. These properties are dependents of the composition, crystallite size and production process. The high energy milling of the powder of W-Cu produces an dispersion high and homogenization levels with crystallite size of W very small in the ductile Cu phase. This work discusses the effect of the HEM in preparation of the W-25Cu composite powders. Three techniques of powder preparation were utilized: milling the dry with powder of thick Cu, milling the dry with powder of fine Cu and milling the wet with powder of thick Cu. The form, size and composition of the particles of the powders milled were observed by scanning electron microscopy (SEM). The X-ray diffraction (XRD) was used to analyse the phases, lattice parameters, size and microstrain of the crystallite. The analyse of the crystalline structure of the W-25Cu powders milled made by Rietveld Method suggests the partial solid solubility of the constituent elements of the Cu in lattice of the W. This analyse shows too that the HEM produces the reduction high on the crystallite size and the increase in the lattice strain of both phases, this is more intense in the phase W
Os comp?sitos de Tungst?nio/Cobre (W-Cu) s?o geralmente usadas para fins el?tricos e t?rmicos como dissipadores de calor e condutores el?tricos, devido as suas excelentes propriedades de condutividades t?rmica e el?trica. Essas propriedades s?o dependentes da composi??o, do tamanho de cristalito e principalmente do processo de fabrica??o. A moagem de alta energia de p?s W-Cu produz alto n?vel de homogeneiza??o e dispers?o com cristalitos de W muito fino na fase d?ctil Cu. Este trabalho discute o efeito da MAE na prepara??o dos p?s comp?sitos W-25Cu. Tr?s t?cnicas de prepara??o dos p?s foram utilizadas: moagem a seco com p? de Cu grosso, moagem a seco com p? de Cu fino e moagem a ?mido com p? de Cu grosso. A forma, tamanho e a composi??o das part?culas dos p?s mo?dos foram observadas por microsc?pio eletr?nico de varredura (MEV). A difra??o de raios-X(DRX) foi usada para observar as fases, par?metros de rede, tamanho e microtens?o dos cristalitos. A an?lise da estrutura cristalina dos p?s mo?dos de W-25Cu feita pelo m?todo de Rietveld sugere uma solubilidade s?lida parcial dos elementos constituintes do cobre (Cu) na rede do tungst?nio (W). Essa an?lise tamb?m mostra que a MAE produz uma alta redu??o no tamanho dos cristalitos e um aumento de tens?o na rede de ambas as fases, isto ocorre com maior intensidade na fase do W

Los estilos APA, Harvard, Vancouver, ISO, etc.

23

Bassaw, Benjamin. "Comportement en fatigue d'un alliage expérimental Cu-Al(2)O(3) : (base cuivre à dispersion d'alumine) élaboré par métallurgie des poudres". Poitiers, 1988. http://www.theses.fr/1988POIT2263.

Texto completo

Resumen

Des essais de traction-compression dans le domaine de fatigue plastique ont revele la grande stabilite cyclique du materiau. Analyse des conditions d'amorcage et de propagation des fissures. Mise en evidence du role des defauts de frittage ou des inclusions. Des essais de fissuration sont effectues dans le domaine des moyennes et basses vitesses en considerant l'effet du rapport de charge et de l'environnement. Description par la mecanique lineaire de rupture du comportement des microfissures

Los estilos APA, Harvard, Vancouver, ISO, etc.

24

Bordeaux, Frédéric. "Mélange atomique exothermique et amorphisation en phase solide dans des composites de multicouches fines métal-métal préparés par co-laminage". Grenoble INPG, 1989. http://www.theses.fr/1989INPG0108.

Texto completo

Resumen

Etude des reactions exothermiques de melange atomique et d'amorphisation par reaction en phase solide dans des composites de multicouches fines metal-metal fabriques par co-laminage de rubans de materiaux purs ou d'alliages amorphes ou cristallises. La simulation numerique des reactions exothermiques est comparee aux resultats experimentaux et les utilisations possibles de ces composites en tant que fusibles de coupe circuit et alliages de brasure sont detaillees

Los estilos APA, Harvard, Vancouver, ISO, etc.

25

NEUMANN, RICHARD. "Analyse cinétique de croissances cristallines hors-équilibres : mesure de l'avancée du front et détermination de la structure de croissance ; application aux croissances cristallines de chlorure de cuivre en présence d'impuretés". Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10016.

Texto completo

Resumen

La croissance cristalline de cucl 2, 2h 2o par evaporation en presence d'impuretes de type biologique donne naissance a une structure dendritique quasi-bidimensionnelle dont l'image est caracteristique des impuretes introduites. L'analyse de la cinetique de ces croissances cristallines, par analyse d'images, permet l'extraction d'une structure de croissance proche de la structure reelle a partir de laquelle des informations topologiques, geometriques et cinetiques sont accessibles. Apres avoir defini brievement les protocoles physique et chimique, ce memoire presente la methode d'acquisition des images de cristallisation. Puis, deux solutions au probleme de la segmentation d'images sont proposees, l'une basee sur une approche statique l'autre sur une approche dynamique. La determination de la structure de la cristallisation est ensuite proposee en utilisant le contour de l'objet segmente pour detecter, a chaque iteration, les sommets des dendrites. Un algorithme de correspondance de points permet alors de relier les sommets representant une meme dendrite a differents stades de croissance. Une structure de croissance issue de l'analyse dynamique est ainsi disponible. Un ensemble de parametres peuvent ensuite en etre extraits. Enfin, apres avoir decrit les facteurs influencant les croissances cristallines en general, et les cristallisations de cucl 2, 2h 2o en particulier, ce memoire se conclut sur une analyse des parametres extraits de la structure qui revele plusieurs comportements de croissance.

Los estilos APA, Harvard, Vancouver, ISO, etc.

26

Didier, Nicole. "Synthèse par dépôt chimique en phase vapeur, caractérisations structurales et électriques de super-réseaux YBa2Cu3O(7-delta)/PrBa2Cu3O(7-delta) de type supraconducteur/isolant". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0090.

Texto completo

Resumen

Pour la premiere fois, des multicouches epitaxiales supraconducteur / isolant yba#2cu#3o#7#-#y/prba#2cu#3o#7#-#y ont ete realisees par depot chimique en phase vapeur. Les depots sont realises a partir de precurseurs organometalliques -dicetonates sur srtio#3 (100). L'etude de la variation de la teneur en praseodyme de prba#2cu#3o#7#-#y a revele l'existence d'une solution solide pr#1#+#xba#2#-#xcu#3o#7#-#y pour - 0,1 x 0,52, deja observee dans des travaux effectues sur des ceramiques. L'evolution des proprietes electriques de ce materiau qui presente un comportement semi-conducteur a ete etudiee en fonction du rapport cationique pr/ba. Une augmentation de la resistivite de trois ordres de grandeur a 100 k a ete observee pour une variation de pr/ba comprise entre 0,2 et 1,85. Ces resultats ont ete utilises pour faire varier le couplage entre couches supraconductrices dans les empilements. Nous avons realise des super-reseaux du type (yba#2cu#3o#7#-#y)#n/(prba#2cu#3o#7#-#y)#m#1#0, ou n (m) est le nombre de mailles elementaires d'yba#2cu#3o#7#-#y (prba#2cu#3o#7#-#y) et 10, le nombre de periodes. L'ensemble des caracterisations structurales et microstructurales indique que les super-reseaux synthetises sont epitaxies avec une excellente qualite cristalline: en particulier, la planeite des interfaces et l'interdiffusion limitee des elements y / pr ont ete observees par spectrometrie de masse de particules neutres secondaires, diffraction x, microscopie electronique en transmission. Nous avons etudie les proprietes electriques des empilements avec l'epaisseur des couches. Nous sommes egalement parvenus a produire le decouplage des couches supraconductrices par variation de la resistivite en changeant la composition de la solution solide pr#1#+#xba#2#-#xcu#3o#7#-#y

Los estilos APA, Harvard, Vancouver, ISO, etc.

27

Omar, Abderrahim. "Contribution à l'étude des propriétés électromagnétitques des couches et multicouches supraconductrices à haute Tc : mesure d'impédance de surface par oscillateur à diode tunnel". Grenoble 1, 1993. http://www.theses.fr/1993GRE10168.

Texto completo

Resumen

Nous avons concu et realise un systeme de mesure d'impedance de surface z#s de films minces conducteurs ou supraconducteurs par couplage electromagnetique de ces films a un oscillateur a diode tunnel. La mesure de la resistance de films metalliques (or et aluminium) par cette technique inductive (sans contact) nous a permis, en comparant aux mesures directes (4 fils), de valider cette methode. Nous avons ensuite etudie la reponse electromagnetique de films supraconducteurs d'yba#2cu#3o#7 et de multicouches yba#2cu#3o#7/la#2##xsr#xcuo#4. Cette etude a mis en evidence le caractere granulaire de ces materiaux reflete par des valeurs trop elevees de la profondeur de penetration () et la presence d'une resistance residuelle dans la phase supraconductrice. Le comportement de en fonction de la temperature indique que le couplage intergranulaire serait de type sis dans le cas de films et sns dans le cas des multicouches etudiees. Cette difference devrait avoir son origine dans les procedes et conditions de fabrication de ces echantillons

Los estilos APA, Harvard, Vancouver, ISO, etc.

28

Chaud, Xavier. "Controle de la croissance sous champ magnétique de domaines texturés d'YBa2Cu3O(7-x) pour application à la lévitation". Université Joseph Fourier (Grenoble ; 1971-2015), 1996. http://www.theses.fr/1996GRE10029.

Texto completo

Resumen

La levitation magnetique stable et passive, irrealisable par des techniques conventionnelles, represente une application directe et prometteuse des pastilles de ceramique supraconductrice a haute temperature critique yba#2cu#3o#x. L'obtention de forces de levitation importantes necessite le developpement d'un materiau presentant de larges grains orientes. Un dispositif d'elaboration a haute temperature (1100c) et sous champ magnetique intense (8 t) a ete realise et permet de combiner l'orientation induite par une solidification sous champ magnetique intense avec un suivi en continu et in situ de la susceptibilite magnetique des echantillons mettant en evidence les transitions de phase dans les conditions memes de leur elaboration. Une fenetre de solidification etroite et l'existence d'une surfusion liee a l'histoire thermique et au taux d'oxygene des echantillons ont ete observees. Ces informations ont ete utilisees pour optimiser le traitement thermique de pastilles de composition fixe par rapport a la force de levitation. Le procede mis au point permet d'obtenir de maniere reproductible des pastilles jusqu'a 4 cm de diametre presentant des pressions magnetiques importantes (10 n/cm#2 par surface d'aimant) grace a une bonne orientation et une solidification controlee conduisant a de larges grains. Des forces de levitation jusqu'a 70 n ont ete mesurees. Ces pastilles ont pu etre fournies pour l'etude des interactions entre supraconducteur et aimant permanent et le developpement de paliers magnetiques supraconducteurs

Los estilos APA, Harvard, Vancouver, ISO, etc.

29

Schwerdtfeger, Michael. "Elaboration et caractérisation de multicouches supraconductrices YBaCuO/LaSrCuO". Grenoble 1, 1993. http://www.theses.fr/1993GRE10179.

Texto completo

Resumen

Ce travail est consacre a l'elaboration et a la caracterisation structurale et electrique de multicouches supraconductrices de type yba#2cu#3o#7#-#/la#2#-#xsr#xcuo#4 (ybco/lasrcuo). Deux dopages differents en strontium ont ete choisis afin de separer les couches d'ybco soit par des couches semi-isolantes de la#2cuo#4 (lco) pour x=0, soit par des couches metalliques de la#1#,#8#5sr#0#,#1#5cuo#4 (lsco) pour x=0,15. Le principal objectif de ce travail est donc d'etudier comment l'intercalation de couches de lasrcuo, de nature et d'epaisseur differentes, affecte la dimensionnalite et l'anisotropie de ces systemes. Les echantillons sont elabores par photo-ablation avec un laser excimere d'une longueur d'onde de 248 nm (krf). Une etude prealable, portant sur les proprietes structurales et electriques de couches minces d'ybco, de lco et de lsco, a permis de constituer une base de reference pour l'etude du comportement des multicouches. Les proprietes structurales et morphologiques ont ete analysees par diffraction de rayons x, par rbs et par microscopie electronique. En particulier les figures de poles x ont revele la rotation des axes a et b des couches de lco de 45 par rapport aux axes des substrats de srtio#3. L'etude de la magnetoresistance et des fluctuations de conductance des couches d'ybco a montre que ce compose est moderement anisotrope et qu'il ne presente pas un comportement purement bidimensionnel. La derniere partie de ce memoire est consacree a l'etude des proprietes des multicouches. Ainsi, la diffraction de rayons x a permis de constater la bonne qualite epitaxiale des echantillons, avec une rotation de 45 des axes a et b des couches de lco par rapport aux axes des substrats et des couches d'ybco. Cette etude a egalement revele la presence probable de contraintes aux interfaces entre les couches d'ybco et les couches de lasrcuo. A partir de l'analyse de la transition resistive, des fluctuations de conductance et de la magnetoresistance, il a ete montre que le decouplage des couches d'ybco par des couches de lasrcuo d'epaisseur croissante resulte en un abaissement de la temperature critique, la suppression du passage d'un regime bidimensionnel a un regime tridimensionnel et une anisotropie accrue

Los estilos APA, Harvard, Vancouver, ISO, etc.

30

Labrize, Florence. "Nouveaux précurseurs volatils de l'oxyde supraconducteur YBa2Cu3O(7-x) pour le procédé M. O. C. V. D : synthèse et caractérisation de fluoroalcoxydes, (beta)-dicétonates et (beta)-dicétonatoalcoxydes homo et hétérométalliques de l'yttrium, du baryum et du cuivre". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0015.

Texto completo

Resumen

La m. O. C. V. D. D'yba#2cu#3o#7#-#x necessite la synthese de precurseurs volatils et stables thermiquement, probleme crucial dans le cas du baryum, le tetramethylheptanedionate de baruym actuellement utilise presente une instabilite thermique entrainant des problemes de reproductibilite des depots. Afin d'ameliorer la volatilite des precurseurs du baryum, plusieurs voies ont ete explorees. La saturation de la sphere de coordination du ba(thd)#2 par l'action de bases de lewis bidentes a conduit a des adduits ba(thd)#2l#x#y, dont ba(thd)#2(hochmech#2nme#2)#2 et ba(thd)#2(tmeda)#2, caracterises par diffraction des rx sur monocristaux. Ils ont permis d'augmenter la stabilite thermique du ba(thd)#2 mais se dissocient en phase vapeur. La reactivite du thdh sur un aminoalcoxyde a egalement conduit a ba#5(oh)(ochmech#2nme#2)#4(thd)#5, premier beta-dicetonatoalcoxyde de baryum structuralement caracterise. La construction d'edifices heterometalliques y-ba et ba-cu volatifs a ensuite ete etudiee a partir de ligands or assembleurs entre les metaux et de ligands thd chelatants pour reduire la nuclearite et augmenter la volatilite. Plusieurs beta-dicetonatoalcoxydes heterometalliques ont ete isoles par reactions acide-base de lewis entre les alcoxydes de baryum et les tetramethylheptanedionates d'yttrium et de cuivre, notamment yba#3(o#tbu)#6(thd)#3(thf), volatil et ba#2cu(ochmech#2nme#2)#2(thd)#4(#iproh)#2, qui montre a l'etat solide la presence d'interactions metal-heteroatome. L'acces a des composes heterometalliques volatils a enfin ete realise grace a l'emploi de ligands fluoroalcoxydes susceptibles de reduire les forces de van der waals des complexes. Ba#5(oh)(hfip)#9(thf)#4(thf)#4(h#2o), (hfip=och(cf#3)#2) premier fluoroalcoxyde de baryum structuralement caracterise a ete obtenu. La reactivite de ce dernier a conduit a bacu#2(hfip)#4(thd)#2 et y#2ba(hfip)#4(thd)#4, volatils et stables thermiquement. Les particularites structurales de ba#5(oh)(hfip)#9(thf)#4(h#2o) et y#2ba(hfip)#4(thd)#4 sont la presence d'interactions ba-f. Ycu(hfip)#2(thd)#3 a egalement ete isole a partir de y(hfip)#3(thf)#3. Y#2ba(hfip)#4(thd)#4 bacu#2(hfip)#4(thd)#2 et ycu(hfip)#2(thd)#3 ont montre de meilleures proprietes de transport que ba(thd)#2

Los estilos APA, Harvard, Vancouver, ISO, etc.

31

Schmatz, Ulrich. "Synthèse par MOCVD de couches supraconductrices d'YBa2Cu3O(7-x) pour des applications en courants forts". Grenoble INPG, 1997. http://www.theses.fr/1997INPG0060.

Texto completo

Resumen

La realisation de couches supraconductrices a haute temperature critique pour des applications dans le domaine des courants forts (bobinages magnetiques, cables, limiteurs de courant) requiert un procede de synthese qui permet une croissance epitaxiale des couches sur des substrats adaptes (rubans), ainsi que des vitesses de croissance volumiques elevees. Pour repondre a ces objectifs et pour palier au probleme d'instabilite thermique de certains precurseurs organometalliques, de nouveaux procedes de cvd utilisant une seule source liquide ont ete developpes au lmgp. Au cours de cette these, nous avons etudie le depot de couches supraconductrices d'yba#2cu#3o#7#-#x en utilisant essentiellement la mocvd assistee par aerosol. Nous avons etudie le comportement de nouveaux precurseurs du baryum, ainsi que l'influence des parametres du depot (composition de la phase gazeuse, concentration de especes, pressions partielles, temperature et duree du depot) sur les proprietes structurales et supraconductrices des couches minces d'yba#2cu#3o#7#-#x sur differents types de substrats et synthetise des couches tampon de nature differente afin de determiner la comptabilite chimique et structural du depot avec son support. Des couches supraconductrices d'yba#2cu#3o#7#-#x de tres bonne qualite (tc90k, jc10#6a/cm#2) ont ete obtenues. Cette etude montre que plusieures solutions existent pour la synthese de couches supraconductrices d'yba#2cu#3o#7#-#x sur des substrats techniques. Sur al#2o#3, de bonnes couches d'yba#2cu#3o#7#-#x peuvent etre obtenues avec une couche tampon de ceo#2. Sur un substrat metallique, la couche tampon peut etre une couche de zircone (zro#2(y)) deposee par ibad ou une couche de ceo#2 sur un substrat a orientation biaxiale. Cette derniere solution permet de realiser des rubans supraconducteurs de bonne qualite, uniquement a l'aide de procedes cvd.

Los estilos APA, Harvard, Vancouver, ISO, etc.

32

Felten, Franck. "Synthèse et caractérisation de couches minces d'oxydes déposées par CVD à injection". Grenoble INPG, 1996. http://www.theses.fr/1996INPG0162.

Texto completo

Resumen

Le procede cvd a injection est une nouvelle technique d'introduction des vapeurs de precurseurs dans un reacteur de depot cvd. Son principe repose sur l'injection de micro-quantites de precurseurs (quelques 1), sous forme liquide, dans un evaporateur ou a lieu une evaporation flash. L'injection de la solution est assuree par une micro-electrovanne pilotee par ordinateur. Cette technique a ete developpee au lmgp afin de resoudre certains problemes de la cvd. L'objectif de cette these a ete de montrer la faisabilite et les potentialites de ce nouveau procede, en etudiant le depot de couches minces d'oxydes de complexite croissante: ta#2o#5, multicouches sio#2/ta#2o#5, zro#2(y), yba#2cu#3o#7#-#x. Des films de ta#2o#5 de bonne qualite ont ete obtenus (couches denses, faible rugosite de surface, indice de refraction eleve, bonnes caracteristiques electriques c(v) et g(v) des dispositifs mis w/ta#2o#5/sio#2/si). Nous avons egalement depose des multicouches ta#2o#5/sio#2 en utilisant plusieurs sources cvd a injection, avec un bon controle de l'epaisseur de chaque couche, sans lignes ni vannes chaudes qui auraient ete necessaires pour un depot par cvd classique. Dans une troisieme etape, nous avons depose des materiaux constitues de plusieurs elements chimiques, avec une seule source contenant un melange des differents precurseurs, ce qui est impossible a realiser par cvd classique (epitaxie de zro#2(y) sur al#2o#3 (01-12), couches supraconductrices ybco avec t#c > 90 k et j#c > 1 ma/cm#2). L'interet du procede cvd a injection est de permettre un controle souple et precis des tensions de vapeur, meme avec des precurseurs thermiquement instables (ex: ba(tmhd)#2). Cette etude montre que le procede cvd a injection est une technique tres performante pour le depot de couches minces. Sa compacite, sa souplesse d'utilisation, et les fortes vitesses de croissance obtenues constituent des atouts majeurs, en vue d'une utilisation a l'echelle industrielle

Los estilos APA, Harvard, Vancouver, ISO, etc.

33

Pisch, Alexander. "Étude thermodynamique et dépot chimique en phase vapeur de la phase supraconductrice : YBa2Cu3O(6+x)". Grenoble INPG, 1994. http://www.theses.fr/1994INPG0147.

Texto completo

Resumen

L'etude des composes supraconducteurs a haute temperature critique et de yba#2cu#3o#6#+#x en particulier presente un tres grand interet de part ses applications potentielles dans les domaines de l'electronique et de l'electrotechnique. L'analyse thermodynamique du systeme quaternaire y-ba-cu-o est un outil indispensable pour pouvoir comprendre et definir les chemins reactionnels qui permettent la synthese d'un compose de proprietes supraconductrices optimales. Dans le premier chapitre de ce memoire, apres un bref rappel sur les caracteristiques du compose yba#2cu#3o#6#+#x, les differentes methodes d'elaboration ont ete decrites. Parmi ces methodes, les principes du depot chimique en phase vapeur (cvd) a partir des precurseurs organometalliques, methode retenue dans ce travail, sont decrits plus en details. Le second chapitre est entierement consacre a l'analyse thermodynamique du systeme quaternaire y-ba-cu-o. Cette etude explore tous les sous-systemes (binaires, ternaires) pour donner un ensemble self-consistant de donnees thermodynamiques. Dans le diagramme quaternaire, la non-stchiometrie de la phase supraconductrice a ete modelisee. A partir des donnees relatives au systeme y-ba-cu-o-c-h-n-ar, une simulation de deux techniques de cvd differentes (cvd classique et cvd assiste par aerosol) est presentee dans le chapitre trois. Cette simulation a permis d'etablir les diagrammes de depot, directement utilisables par l'experimentateur, car ils indiquent la nature du depot en fonction des conditions operatoires. Le dernier chapitre est consacre a l'elaboration de couches minces par depot cvd assiste par aerosol. La comparaison entre previsions de calcul et resultats experimentaux illustre, en quelques exemples types, l'apport des simulations thermodynamiques pour l'optimisation des depots

Los estilos APA, Harvard, Vancouver, ISO, etc.

34

PANTINI, SARA. "Analysis and modelling of leachate and gas generation at landfill sites focused on mechanically-biologically treated waste". Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2013. http://hdl.handle.net/2108/203393.

Texto completo

Resumen

Despite significant efforts have been directed toward reducing waste generation and encouraging alternative waste management strategies, landfills still remain the main option for Municipal Solid Waste (MSW) disposal in many countries. Hence, landfills and related impacts on the surroundings are still current issues throughout the world. Actually, the major concerns are related to the potential emissions of leachate and landfill gas into the environment, that pose a threat to public health, surface and groundwater pollution, soil contamination and global warming effects. To ensure environmental protection and enhance landfill sustainability, modern sanitary landfills are equipped with several engineered systems with different functions. For instance, the installation of containment systems, such as bottom liner and multi-layers capping systems, is aimed at reducing leachate seepage and water infiltration into the landfill body as well as gas migration, while eventually mitigating methane emissions through the placement of active oxidation layers (biocovers). Leachate collection and removal systems are designed to minimize water head forming on the bottom section of the landfill and consequent seepages through the liner system. Finally, gas extraction and utilization systems, allow to recover energy from landfill gas while reducing explosion and fire risks associated with methane accumulation, even though much depends on gas collection efficiency achieved in the field (range: 60-90% Spokas et al., 2006; Huitric and Kong, 2006). Hence, impacts on the surrounding environment caused by the polluting substances released from the deposited waste through liquid and gas emissions can be potentially mitigated by a proper design of technical barriers and collection/extraction systems at the landfill site. Nevertheless, the long-term performance of containment systems to limit the landfill emissions is highly uncertain and is strongly dependent on site-specific conditions such as climate, vegetative covers, containment systems, leachate quality and applied stress. Furthermore, the design and operation of leachate collection and treatment systems, of landfill gas extraction and utilization projects, as well as the assessment of appropriate methane reduction strategies (biocovers), require reliable emission forecasts for the assessment of system feasibility and to ensure environmental compliance. To this end, landfill simulation models can represent an useful supporting tool for a better design of leachate/gas collection and treatment systems and can provide valuable information for the evaluation of best options for containment systems depending on their performances under the site-specific conditions. The capability in predicting future emissions levels at a landfill site can also be improved by combining simulation models with field observations at full-scale landfills and/or with experimental studies resembling landfill conditions. Indeed, this kind of data may allow to identify the main parameters and processes governing leachate and gas generation and can provide useful information for model refinement. In view of such need, the present research study was initially addressed to develop a new landfill screening model that, based on simplified mathematical and empirical equations, provides quantitative estimation of leachate and gas production over time, taking into account for site-specific conditions, waste properties and main landfill characteristics and processes. In order to evaluate the applicability of the developed model and the accuracy of emissions forecast, several simulations on four full-scale landfills, currently in operative management stage, were carried out. The results of these case studies showed a good correspondence of leachate estimations with monthly trend observed in the field and revealed that the reliability of model predictions is strongly influenced by the quality of input data. In particular, the initial waste moisture content and the waste compression index, which are usually data not available from a standard characterisation, were identified as the key unknown parameters affecting leachate production. Furthermore, the applicability of the model to closed landfills was evaluated by simulating different alternative capping systems and by comparing the results with those returned by the Hydrological Evaluation of Landfill Performance (HELP), which is the most worldwide used model for comparative analysis of composite liner systems. Despite the simplified approach of the developed model, simulated values of infiltration and leakage rates through the analysed cover systems were in line with those of HELP. However, it should be highlighted that the developed model provides an assessment of leachate and biogas production only from a quantitative point of view. The leachate and biogas composition was indeed not included in the forecast model, as strongly linked to the type of waste that makes the prediction in a screening phase poorly representative of what could be expected in the field. Hence, for a qualitative analysis of leachate and gas emissions over time, a laboratory methodology including different type of lab-scale tests was applied to a particular waste material. Specifically, the research was focused on mechanically biologically treated (MBT) wastes which, after the introduction of the European Landfill Directive 1999/31/EC (European Commission, 1999) that imposes member states to dispose of in landfills only wastes that have been preliminary subjected to treatment, are becoming the main flow waste landfilled in new Italian facilities. However, due to the relatively recent introduction of the MBT plants within the waste management system, very few data on leachate and gas emissions from MBT waste in landfills are available and, hence, the current knowledge mainly results from laboratory studies. Nevertheless, the assessment of the leaching characteristics of MBT materials and the evaluation of how the environmental conditions may affect the heavy metals mobility are still poorly investigated in literature. To gain deeper insight on the fundamental mechanisms governing the constituents release from MBT wastes, several leaching experiments were performed on MBT samples collected from an Italian MBT plant and the experimental results were modelled to obtain information on the long-term leachate emissions. Namely, a combination of experimental leaching tests were performed on fully-characterized MBT waste samples and the effect of different parameters, mainly pH and liquid to solid ratio (L/S,) on the compounds release was investigated by combining pH static-batch test, pH dependent tests and dynamic up-flow column percolation experiments. The obtained results showed that, even though MBT wastes were characterized by relatively high heavy metals content, only a limited amount was actually soluble and thus bioavailable. Furthermore, the information provided by the different tests highlighted the existence of a strong linear correlation between the release pattern of dissolved organic carbon (DOC) and several metals (Co, Cr, Cu, Ni, V, Zn), suggesting that complexation to DOC is the leaching controlling mechanism of these elements. Thus, combining the results of batch and up-flow column percolation tests, partition coefficients between DOC and metals concentration were derived. These data, coupled with a simplified screening model for DOC release, allowed to get a very good prediction of metal release during the experiments and may provide useful indications for the evaluation of long-term emissions from this type of waste in a landfill disposal scenario. In order to complete the study on the MBT waste environmental behaviour, gas emissions from MBT waste were examined by performing different anaerobic tests. The main purpose of this study was to evaluate the potential gas generation capacity of wastes and to assess possible implications on gas generation resulting from the different environmental conditions expected in the field. To this end, anaerobic batch tests were performed at a wide range of water contents (26-43 %w/w up to 75 %w/w on wet weight) and temperatures (from 20-25 °C up to 55 °C) in order to simulate different landfill management options (dry tomb or bioreactor landfills). In nearly all test conditions, a quite long lag-phase was observed (several months) due to the inhibition effects resulting from high concentrations of volatile fatty acids (VFAs) and ammonia that highlighted a poor stability degree of the analysed material. Furthermore, experimental results showed that the initial waste water content is the key factor limiting the anaerobic biological process. Indeed, when the waste moisture was lower than 32 %w/w the methanogenic microbial activity was completely inhibited. Overall, the obtained results indicated that the operative conditions drastically affect the gas generation from MBT waste, in terms of both gas yield and generation rate. This suggests that particular caution should be paid when using the results of lab-scale tests for the evaluation of long-term behaviour expected in the field, where the boundary conditions change continuously and vary significantly depending on the climate, the landfill operative management strategies in place (e.g. leachate recirculation, waste disposal methods), the hydraulic characteristics of buried waste, the presence and type of temporary and final cover systems.

Los estilos APA, Harvard, Vancouver, ISO, etc.

35

Jen-Hao, Wang. "Synthesis and Characterization of Si-Cu Composite Anode Materials for Lithium-ion Batteries". 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2806200619515100.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

36

Wang, Jen-Hao y 王仁壕. "Synthesis and Characterization of Si-Cu Composite Anode Materials for Lithium-ion Batteries". Thesis, 2006. http://ndltd.ncl.edu.tw/handle/04082376176473922573.

Texto completo

Resumen

碩士
國立臺灣大學
化學工程學研究所
94
The main purpose of this study is to explore new anode materials based on silicon for lithium-ion battery. Although silicon possesses a higher theoretical capacity (~3000 mAh/g) than graphite (372 mAh/g), the dramatic volumetric variation during cycling and intrinsic low conductivity, which resulted in structural instability and poor cyclability, obstruct its commercial application. Si-Cu composite materials are developed by two different methods to overcome the inherent problems of silicon. One is fluidized-bed type reduction (FB-reduction) with the precursor of CuCl powder, and the other is electroless plating in which formaldehyde was served as a reducing agent. Copper has been successfully reduced by both synthesized routes; however, the quality of coating was not satisfactory for FB-reduction and only a “Si + Cu” mixture was formed. Poor electrochemical performance hence has been observed for Si-Cu composites by FB-reduction due to inability to tolerate the volume expansion of silicon, in spite of the enhancement of electrode conductivity. Contrarily, scanning electron microscope (SEM) images show that more conformity and uniformity of coating can be achieved by using electroless plating and the cyclability, as compared with pure Si electrode, has been thereby improved. To enhance mechanical strength of the copper layer, fluidized-bed chemical vapor deposition (FB-CVD) technique has been carried out to coat a further carbon film on Si-Cu composites. Results show that the electrode made by electroless plating and heat treatment, comparing with Si electrode (<8 cycles), can be greatly improved to 60 cycles without fading at the discharge capacity of 1000 mAh/g. A new material copper silicide (Cu3Si) is found for Si-Cu composites after heat treatment in FB-CVD. In-situ X-ray diffraction shows that Cu3Si is a partially inactive material in the reaction of lithium. Moreover, electrochemical performance of single phase Cu3Si electrode has been studied.

Los estilos APA, Harvard, Vancouver, ISO, etc.

37

"Synthesis and characterization of nanocrystalline Cu(CuOx)/Al2O3 composite thin films". 2003. http://library.cuhk.edu.hk/record=b5891726.

Texto completo

Resumen

Xu Yan = 納米銅(銅的氧化物)與三氧化二鋁復合物薄膜的製備和特性研究 / 許燕.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.
Includes bibliographical references (leaves 50-51).
Text in English; abstracts in English and Chinese.
Xu Yan = Na mi tong (tong de yang hua wu) yu san yang hua er lv fu he wu bo mo de zhi bei he te xing yan jiu / Xu Yan.
Abstract --- p.i
摘要 --- p.ii
Acknowledgements --- p.iii
Table of Contents --- p.iv
List of Figures --- p.viii
List of Tables --- p.xi
Chapter CHAPTER 1 --- Introduction
Chapter 1.1 --- Nanostructured Materials --- p.1
Chapter 1.2 --- Objective of this Work --- p.1
Chapter CHAPTER 2 --- Background
Chapter 2.1 --- Correlation of AES-CuLMM spectrum and Cu nanocluster size --- p.3
Chapter 2.1.1 --- Typical AES-CuLMM spectra --- p.3
Chapter 2.1.2 --- A simplified model --- p.4
Chapter 2.1.3 --- correlation of AES-CuLMM spectra and the simplified model --- p.4
Chapter 2.2 --- Previous works --- p.5
Chapter CHAPTER 3 --- Instrumentation
Chapter 3.1 --- Sputtering --- p.6
Chapter 3.1.1 --- Principles of sputtering --- p.6
Chapter 3.1.1.1 --- Concepts of sputtering --- p.6
Chapter 3.1.1.2 --- Initiating the plasma --- p.8
Chapter 3.1.1.3 --- Depositing a film onto the substrate --- p.8
Chapter 3.1.2 --- Radio-frequency (RF) magnetron sputtering --- p.9
Chapter 3.1.2.1 --- RF sputtering --- p.9
Chapter 3.1.2.2 --- Magnetron Sputtering --- p.10
Chapter 3.2 --- Deposition system --- p.10
Chapter 3.2.1 --- Instrumentation --- p.11
Chapter 3.2.1.1 --- Vacuum system --- p.11
Chapter 3.2.1.2 --- Sputter target and power supplies --- p.12
Chapter 3.2.1.3 --- Substrate mounting --- p.13
Chapter 3.2.2 --- Experimental --- p.13
Chapter 3.3 --- X-ray Photoelectron Spectroscopy (XPS) --- p.14
Chapter 3.3.1 --- Basic Principles --- p.14
Chapter 3.3.2 --- Instrumentation --- p.17
Chapter 3.3.3 --- Qualitative and quantitative analysis --- p.17
Chapter 3.3.3.1 --- Spectra interpretations --- p.17
Chapter 3.3.3.2 --- X-ray emission line width --- p.18
Chapter 3.3.3.3 --- Qualification --- p.18
Chapter 3.3.3.3.1 --- Chemical composition --- p.18
Chapter 3.3.3.3.2 --- Sputter depth profiling --- p.18
Chapter 3.3.3.3.3 --- Auger parameter --- p.19
Chapter 3.4 --- Transmission Electron Microscopy (TEM) --- p.19
Chapter 3.4.1 --- An overview of TEM --- p.19
Chapter 3.4.2 --- Imaging mode and diffraction mode --- p.21
Chapter 3.4.3 --- Electron-Specimen interactions --- p.21
Chapter 3.4.3.1 --- Elastic scattering --- p.22
Chapter 3.4.3.2 --- Inelastic scattering --- p.22
Chapter 3.4.4 --- Imaging mechanisms for TEM --- p.23
Chapter 3.4.4.1 --- Mass-thickness contrast --- p.23
Chapter 3.4.4.2 --- Diffraction contrast --- p.23
Chapter 3.4.5 --- TEM sample preparation --- p.25
Chapter CHAPTER 4 --- Chemical and Structure Characterization of Cu(CuOx)/Al2O3 Composite Thin Films
Chapter 4.1 --- Overview --- p.26
Chapter 4.2 --- Results and discussions --- p.26
Chapter 4.2.1 --- Set I: Achieving the stoichiometry of A1203 matrix --- p.26
Chapter 4.2.2 --- Set II: keeping A1203 stoichiometry and studying on the correlation of CuLMM spectra and average Cu cluster size --- p.32
Chapter 4.2.2.1 --- Chemical information obtained by XPS --- p.32
Chapter 4.2.2.2 --- Nanostructure studied by TEM --- p.38
Chapter 4.2.2.3 --- Mechanical properties inspected by nano-indentation --- p.43
Chapter 4.2.2.4 --- Optical properties --- p.43
Chapter 4.2.3 --- Set III: Duration of deposition --- p.44
Chapter 4.2.4 --- Set VI: Pressure effect on the average size of Cu nanoclusters --- p.45
Chapter CHAPTER 5 --- Conclusions --- p.48
References --- p.50

Los estilos APA, Harvard, Vancouver, ISO, etc.

38

Chen, Jhih-Jheng y 陳枝政. "The study of Cu oxide and Cu-SiO2 composite materials as solar spectrally selective absorbers fabricated by plasma oxidation technology". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/30678932480168711839.

Texto completo

Resumen

碩士
國立臺灣科技大學
材料科技研究所
97
This thesis uses the magnetron sputter to deposit prime film, and combine with low-temperature plasma oxidation process, to produces solar energy selective absorbers, and then probe optical characteristic and crystal structure of absorbers. The first part of study included deposition a Cu film on stainless steel and quartz glass, plasma oxidation to form the CuO-Cu2O-Cu absorbers. The second part of study included deposition Cu-Si composite films on stainless steel and quartz glass, plasma oxidation to form the Cu-SiO2 composite absorbers, and examination of surface structure, and SPR characteristic. Furthermore a SiO2 anti-reflective(AR) layer was covered on Cu-SiO2 composite absorbers to improve properties of solar selective absorbers. XRD, SEM, UV-Vis-NIR, and FTIR were utilized to analysis solar spectrally selective absorbers. The results indicated that the part of oxidized Cu film does not exhibit to good optical characteristic as expected. The oxidized Cu films contained excess Cu2O oxide but few CuO. Cu2O has a band gap(Eg) of 2.2 eV, in order to form high solar absorptance(α), it must have enough thickness which yields a certain thermal emittance(ε). Optimum parameter of film thickness of Cu is 2 µm, and α is 0.71, ε is 0.08 for the solar absorber made by oxidizing Cu films. Solar absorber properties of Cu-Si composite film are best than those of Cu film. The Cu-Si composite with a film thickness of 100 nm, and without a SiO2 AR layer, has an α of 0.82, and an ε of 0.22, after oxidztion process. The oxidized Cu-Si film with a SiO2 AR layer, has an α of 0.89, and an ε of 0.35.

Los estilos APA, Harvard, Vancouver, ISO, etc.

39

Chen, Chin-Yuan y 陳致元. "Prepared Cu/ZnO/g-C3N4 composite materials for photoreduction of CO2 into CO, CH3OH and CH4". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/h37f69.

Texto completo

Resumen

碩士
靜宜大學
應用化學系
107
In this study, a hydrothermal method was used to prepare a Cu/ZnO/g-C3N4 honeycomb material for photoreduction by using graphite phase carbonitride nitrogen ( g-C3N4 ) as a photocatalyst material. The CO2 and H2O are then converted to CO, CH3OH and CH4. The prepare catalyst was characterized by instrument of XRD, SEM, TEM, XPS, BET, UV-Vis and PL instruments. In this study, the photocatalyst was added with the appropriate amount of precious metals for high photocatalytic yield. A high yield of CH4 ( 40.7 μmol g-1 h-1), CO ( 65.1 μmol g-1 h-1) and CH3OH ( 92.5 mol g-1 h-1) was obtained by the significantly improved of photocatalytic activity due to produce material in the base environment. The ZnO nanosheet material is more uniformly compounded with g-C3N4, further greatly reduce the agglomeration of ZnO nanosheets and pore size of honeycomb g-C3N4. The material is more efficient under light illumination. After the addition of Cu, it is more increase the absorption of 500 nm-800 nm. The PL spectrum also shows that the adhesion of nano metal materials helps to reduce the electron-hole recombination rate and contributes to the improvement of the halo activity. Finally, the quantum yield of CH4, CO and CH3OH were also calculated 1.09% 0.44% and 1.86%, and Cu/ZnO/g-C3N4 photoreduction reaction mechanism was also proposed. This study can be widely used in the conversion and storage of solar energy, bringing a cleaner and more convenient energy to the earth to achieve the goal of green chemistry and environmental sustainability.

Los estilos APA, Harvard, Vancouver, ISO, etc.

40

de, Falco Giacomo. "Adsorption of H2S and HCHO on new generation materials based on composite Zn-Cu sorbents and surface active carbon materials: effect of physico-chemical properties on the process performance". Tesi di dottorato, 2018. http://www.fedoa.unina.it/12706/1/PhD_thesis_de_Falco_Giacomo.pdf.

Texto completo

Resumen

This PhD Thesis in Chemical Sciences aims at a deep understanding of the intertwining among materials properties, experimental conditions and adsorption outcomes, with the focus on an experimental research activity dealing with the removal of two target pollutants that contribute to increase 1) outdoor pollution (hydrogen sulphide) and 2) indoor pollution (formaldehyde), by adsorption on materials of various nature.

Los estilos APA, Harvard, Vancouver, ISO, etc.

41

Kumar, Ajay. "In-Situ Polymer Derived Nano Particle Metal Matrix Composites Developed by Friction Stir Processing". Thesis, 2015. http://etd.iisc.ac.in/handle/2005/3937.

Texto completo

Resumen

Ceramic metal matrix composites (CMMCs) are materials generally created by mixing of hard ceramic particles in a metal matrix. They were expected to combine the ductility and toughness of the metal with the high strength and elastic modulus of the ceramic. MMCs have potential applications in automotive, aeronautical and aerospace industries. Hence, a simple and economical method for fabricating MMCs is an area of intense research. In MMCs, damage evolution starts preferentially at particle matrix interface or at particle clusters in the matrix. This is due to the different physical and mechanical properties of the particle and matrix. Higher local particle volume content leads to higher stress triaxiality making it a preferential site for damage nucleation. Problems with lowering of ductility, fatigue, fracture and impact resistance, agglomeration of ceramic phase and issues related to the predictability of properties of MMCs have been the major issues that have limited their use. In order to overcome some of these shortcomings, the use of nano particles has been attracting increasing attention. The reason is their capability in improving the mechanical and physical properties of traditional MMCs. The dispersion of a nanoscale ceramic phase is needed in order to overcome the problems related to fatigue, fracture toughness, and creep behaviour at high temperatures. However, manufacturing costs, preparation of nano composites and environmental concerns have to be addressed. Agglomeration of nano particles, when produced by the melt stir casting route, the primary route to produce MMCs, is a serious issue that limits the use of nano-particles to produce MMCs with good properties. To avoid agglomeration of the ceramic phase MMCs/nano MMCs have been produced through the powder metallurgy route. Agglomeration is avoided as this is a solid state process. Secondary processing, such as extrusion and rolling are often needed to fully consolidate materials produced in this manner. A high extrusion ratio is often required to get MMCs without porosity. A new method of making nano-ceramic MMC using a polymer derived ceramics (PDC) has been reported. A polymer derived ceramic is a material that converts itself into a ceramic when heated above a particular temperature. In the PDC method a polymer precursor is dispersed in the metal and then converted in-situ to a ceramic phase. A feature of this process is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal or air is not required to produce the ceramic phase. The polymer can be introduced through casting or powder metallurgy route. In the casting route, the polymer powder is directly added to molten metal and pyrolyzed in-situ to create castings of metal-matrix composites. These composites have shown better properties at elevated temperatures but the problem of agglomeration of particles due to Van der Waal's forces and porosity still remains. In the powder method, the organic precursor was milled with copper powder and then plasma sprayed to produce a metal matrix composite. It is reported that these composites retains its mechanical strength close to the melting point of the copper. However, getting a nano sized distribution is difficult through this route as the plasma spray route is a melting and solidification method. Solid state processing by powder metallurgy is possibly a better method to produce well dispersed nano-MMCs. However, powder metallurgy routes are much more expensive and only parts of limited sizes can be produced by this method. Another solid state process Friction Stir Processing (FSP) has successfully evolved as an alternative technique to fabricating metal matrix composites. FSP is based on the principles of Friction Stir Welding (FSW). In FSW, a rotating tool with a pin and a shoulder is inserted into the material to be joined, and traversed along the line of the joint. The friction between the tool and the work piece result in localized heating that softens and plasticizes the material. During production of MMCs using FSP method, the material undergoes intense plastic deformation resulting in mixing of ceramic particles and the metal. FSP also results in significant grain refinement of the metal and has also been used to homogenize the microstructure. FSP technology has also been used to fabricate surface/bulk composites of Al-SiC, friction stir surfacing of cast aluminum silicon alloy with boron carbide and molybdenum disulphide powders and to produce ultra-fine grained Cu-SiC composites. A major problem in the FSP of MMCs is severe tool wear that results from abrasion with hard ceramic particles. The progressive wear of the tool has been reported to increase the likelihood of void or defect development. This change in geometry has been reported in the friction stir welding of several MMCs. The problems concerning the tool life has become a serious issue in the application of FSP for producing MMCs. In the present work the advantages of the PDC method and FSP have been combined to produce polymer derived nano ceramic MMCs. This method mainly consists of three steps. In the first step, a polymer, which pyrolysis to form a PDC at temperatures lower than the melting point of the metal, is dispersed in the metal by FSP. This step is different from the melt route where the PDC forms at temperatures above the melting point of the metal. In the second step, external pyrolysis of the polymer dispersed material is carried out. Since this is a solid state process at stresses much higher than the shear or fracture of the polymer is expected to get evenly and finely distribution in the metal. This is done by heating the polymer dispersed material to a temperature above the pyrolysation temperature of the ceramic but lower than the melting point of the metal matrix. It should be mentioned that some pyrolysis of the polymer is possible during the FSP process itself. In the third step FSP is carried out on the pyrolised material for removing porosity that would form due to gas evolution during pyrolysis and to get a more uniform dispersion of polymer derived ceramic particles in the matrix. This method will produce nano-scale metal matrix composites with a relatively high volume fraction of the ceramic phase. This method can be extended to big sheets or a particular region in a sheet with no or low wear of tools. The material selected for the present study were pure Copper (99.9%) and Nickel Aluminum Bronze (NAB) copper alloy. The polymer precursor was poly (urea methyl vinyl) silazane, which is available commercially as CERASET. The polymer consists of silicon, carbon, nitrogen, oxygen and hydrogen atoms. The liquid precursor was thermally cross-linked into a rigid polymer, which was milled into a powder. This powder, having angular shaped particles of an average size of 10 µm, was used as the reinforcement. The polysilazanes convert into a highly refractory and amorphous ceramic upon pyrolysis and is known as polymer-derived silicon carbonitride which consists principally of silicon, carbon and nitrogen. The in-situ process is feasible because copper melts above the temperature at which the organic phase begins to pyrolise. The polysilazanes pyrolise in the temperature range of 973 to 1273 K, which lie below the melting temperature of copper, 1356K.The precursor has a density of approximately 1 gcm-3 in the organic phase and approximately 2 gcm-3 in the ceramic state. In the present work, we seek to introduce approximately 20 vol% of the ceramic phase into copper. The microstructure and mechanical properties of the developed copper-based in-situ polymer derived nano MMCs have been characterized in detail to understand the distribution of particles. The microstructure of the as received, processed as well as the FSP composite material was characterized using Optical Microscope (OM), Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and Transmission Electron Microscope (TEM). OM and SEM microstructural observations show that PDC particles are distributed uniformly with a bimodal (submicron+micron) distribution. In addition, TEM micrographs reveal the formation of very fine PDC particles of diameter 10-30 nm. X-ray diffraction and Thermo-gravimetric analysis confirms the presence of ceramic phase (Si3N4/SiC) in the matrix. Significant improvement in mechanical properties of the FSP PD-MMCs has been observed. This in-situ formed Cu/PDC composites show five times increase in micro-hardness (260Hv - 2.5GPa) compared to processed copper base metal and in-situ NAB/PDC composite shows two times increase in micro-hardness (325Hv- 3.2GPa) compared to NAB matrix. The Cu-PDC composites exhibited better tensile strength at room temperature. In-situ formed Cu-PDC composite’s yield strength increased from 110MPa to 235MPa as compared to processed base metal, where as ultimate tensile strength increases from 246MPa to 312MPa compared to processed base metal at room temperature. This strengthening could be attributed to the presence of in-situ formed hard phases and the concomitant changes in the microstructure of the matrix material such as reduction in grain size and contribution from Orowan strengthening. In the present work, we have observed tool wear by observing tool after each FSP pass and apart from producing a significantly harder material with higher elastic modulus, possibly for the first time, the issue of tool wear has been overcome. This is due to the fact that the composite is made by the polymer route and that the ceramic fractures easily till it reaches the nano-size. Wear studies of this composite was carried out in a pin-on-disc machine by sliding a pin made from the composite against an alumina disc. The wear rate of the FSP PD-MMC composites increased from 1.63×10-5 to 5.72×10-6 mm3/Nm. Improved wear resistance could be attributed to the presence of the in-situ formed hard nano-phase.

Los estilos APA, Harvard, Vancouver, ISO, etc.

42

Kumar, Ajay. "In-Situ Polymer Derived Nano Particle Metal Matrix Composites Developed by Friction Stir Processing". Thesis, 2015. http://etd.iisc.ernet.in/2005/3937.

Texto completo

Resumen

Ceramic metal matrix composites (CMMCs) are materials generally created by mixing of hard ceramic particles in a metal matrix. They were expected to combine the ductility and toughness of the metal with the high strength and elastic modulus of the ceramic. MMCs have potential applications in automotive, aeronautical and aerospace industries. Hence, a simple and economical method for fabricating MMCs is an area of intense research. In MMCs, damage evolution starts preferentially at particle matrix interface or at particle clusters in the matrix. This is due to the different physical and mechanical properties of the particle and matrix. Higher local particle volume content leads to higher stress triaxiality making it a preferential site for damage nucleation. Problems with lowering of ductility, fatigue, fracture and impact resistance, agglomeration of ceramic phase and issues related to the predictability of properties of MMCs have been the major issues that have limited their use. In order to overcome some of these shortcomings, the use of nano particles has been attracting increasing attention. The reason is their capability in improving the mechanical and physical properties of traditional MMCs. The dispersion of a nanoscale ceramic phase is needed in order to overcome the problems related to fatigue, fracture toughness, and creep behaviour at high temperatures. However, manufacturing costs, preparation of nano composites and environmental concerns have to be addressed. Agglomeration of nano particles, when produced by the melt stir casting route, the primary route to produce MMCs, is a serious issue that limits the use of nano-particles to produce MMCs with good properties. To avoid agglomeration of the ceramic phase MMCs/nano MMCs have been produced through the powder metallurgy route. Agglomeration is avoided as this is a solid state process. Secondary processing, such as extrusion and rolling are often needed to fully consolidate materials produced in this manner. A high extrusion ratio is often required to get MMCs without porosity. A new method of making nano-ceramic MMC using a polymer derived ceramics (PDC) has been reported. A polymer derived ceramic is a material that converts itself into a ceramic when heated above a particular temperature. In the PDC method a polymer precursor is dispersed in the metal and then converted in-situ to a ceramic phase. A feature of this process is that all the constituents of the ceramic phase are built into the organic molecules of the precursor (e.g., polysilazanes contain silicon, carbon, and nitrogen); therefore, a reaction between the polymer and the host metal or air is not required to produce the ceramic phase. The polymer can be introduced through casting or powder metallurgy route. In the casting route, the polymer powder is directly added to molten metal and pyrolyzed in-situ to create castings of metal-matrix composites. These composites have shown better properties at elevated temperatures but the problem of agglomeration of particles due to Van der Waal's forces and porosity still remains. In the powder method, the organic precursor was milled with copper powder and then plasma sprayed to produce a metal matrix composite. It is reported that these composites retains its mechanical strength close to the melting point of the copper. However, getting a nano sized distribution is difficult through this route as the plasma spray route is a melting and solidification method. Solid state processing by powder metallurgy is possibly a better method to produce well dispersed nano-MMCs. However, powder metallurgy routes are much more expensive and only parts of limited sizes can be produced by this method. Another solid state process Friction Stir Processing (FSP) has successfully evolved as an alternative technique to fabricating metal matrix composites. FSP is based on the principles of Friction Stir Welding (FSW). In FSW, a rotating tool with a pin and a shoulder is inserted into the material to be joined, and traversed along the line of the joint. The friction between the tool and the work piece result in localized heating that softens and plasticizes the material. During production of MMCs using FSP method, the material undergoes intense plastic deformation resulting in mixing of ceramic particles and the metal. FSP also results in significant grain refinement of the metal and has also been used to homogenize the microstructure. FSP technology has also been used to fabricate surface/bulk composites of Al-SiC, friction stir surfacing of cast aluminum silicon alloy with boron carbide and molybdenum disulphide powders and to produce ultra-fine grained Cu-SiC composites. A major problem in the FSP of MMCs is severe tool wear that results from abrasion with hard ceramic particles. The progressive wear of the tool has been reported to increase the likelihood of void or defect development. This change in geometry has been reported in the friction stir welding of several MMCs. The problems concerning the tool life has become a serious issue in the application of FSP for producing MMCs. In the present work the advantages of the PDC method and FSP have been combined to produce polymer derived nano ceramic MMCs. This method mainly consists of three steps. In the first step, a polymer, which pyrolysis to form a PDC at temperatures lower than the melting point of the metal, is dispersed in the metal by FSP. This step is different from the melt route where the PDC forms at temperatures above the melting point of the metal. In the second step, external pyrolysis of the polymer dispersed material is carried out. Since this is a solid state process at stresses much higher than the shear or fracture of the polymer is expected to get evenly and finely distribution in the metal. This is done by heating the polymer dispersed material to a temperature above the pyrolysation temperature of the ceramic but lower than the melting point of the metal matrix. It should be mentioned that some pyrolysis of the polymer is possible during the FSP process itself. In the third step FSP is carried out on the pyrolised material for removing porosity that would form due to gas evolution during pyrolysis and to get a more uniform dispersion of polymer derived ceramic particles in the matrix. This method will produce nano-scale metal matrix composites with a relatively high volume fraction of the ceramic phase. This method can be extended to big sheets or a particular region in a sheet with no or low wear of tools. The material selected for the present study were pure Copper (99.9%) and Nickel Aluminum Bronze (NAB) copper alloy. The polymer precursor was poly (urea methyl vinyl) silazane, which is available commercially as CERASET. The polymer consists of silicon, carbon, nitrogen, oxygen and hydrogen atoms. The liquid precursor was thermally cross-linked into a rigid polymer, which was milled into a powder. This powder, having angular shaped particles of an average size of 10 µm, was used as the reinforcement. The polysilazanes convert into a highly refractory and amorphous ceramic upon pyrolysis and is known as polymer-derived silicon carbonitride which consists principally of silicon, carbon and nitrogen. The in-situ process is feasible because copper melts above the temperature at which the organic phase begins to pyrolise. The polysilazanes pyrolise in the temperature range of 973 to 1273 K, which lie below the melting temperature of copper, 1356K.The precursor has a density of approximately 1 gcm-3 in the organic phase and approximately 2 gcm-3 in the ceramic state. In the present work, we seek to introduce approximately 20 vol% of the ceramic phase into copper. The microstructure and mechanical properties of the developed copper-based in-situ polymer derived nano MMCs have been characterized in detail to understand the distribution of particles. The microstructure of the as received, processed as well as the FSP composite material was characterized using Optical Microscope (OM), Scanning Electron Microscope (SEM), Electron Probe Micro Analyzer (EPMA) and Transmission Electron Microscope (TEM). OM and SEM microstructural observations show that PDC particles are distributed uniformly with a bimodal (submicron+micron) distribution. In addition, TEM micrographs reveal the formation of very fine PDC particles of diameter 10-30 nm. X-ray diffraction and Thermo-gravimetric analysis confirms the presence of ceramic phase (Si3N4/SiC) in the matrix. Significant improvement in mechanical properties of the FSP PD-MMCs has been observed. This in-situ formed Cu/PDC composites show five times increase in micro-hardness (260Hv - 2.5GPa) compared to processed copper base metal and in-situ NAB/PDC composite shows two times increase in micro-hardness (325Hv- 3.2GPa) compared to NAB matrix. The Cu-PDC composites exhibited better tensile strength at room temperature. In-situ formed Cu-PDC composite’s yield strength increased from 110MPa to 235MPa as compared to processed base metal, where as ultimate tensile strength increases from 246MPa to 312MPa compared to processed base metal at room temperature. This strengthening could be attributed to the presence of in-situ formed hard phases and the concomitant changes in the microstructure of the matrix material such as reduction in grain size and contribution from Orowan strengthening. In the present work, we have observed tool wear by observing tool after each FSP pass and apart from producing a significantly harder material with higher elastic modulus, possibly for the first time, the issue of tool wear has been overcome. This is due to the fact that the composite is made by the polymer route and that the ceramic fractures easily till it reaches the nano-size. Wear studies of this composite was carried out in a pin-on-disc machine by sliding a pin made from the composite against an alumina disc. The wear rate of the FSP PD-MMC composites increased from 1.63×10-5 to 5.72×10-6 mm3/Nm. Improved wear resistance could be attributed to the presence of the in-situ formed hard nano-phase.

Los estilos APA, Harvard, Vancouver, ISO, etc.

43

Chen, Ting-Yu y 陳廷宇. "Fabrication and Characterization of Cu/M composite Material". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/982a2f.

Texto completo

Resumen

碩士
國立屏東科技大學
材料工程研究所
105
With the industrial process automation and printing electronic technology to flourish, highlighting the high efficiency of mechanical and electrical integration and the importance of electronic materials. Therefore, this study to process integration and powder material preparation as the main axis, a series of studies. This study is divided into three parts: (1) to preparation of high purity by electrolytic copper powder machine, the particle size is less than 37 μm copper particles, and the structure of the machine to be improved and add design of new AC control system to increase the process of production efficiency, and study on the production efficiency of powder by using Taguchi L4 (23) orthogonal table (2) The copper particles were draped using chemical methods, and the scanning electron microscopy was carried out by using Scanning Electron Microscope and X-ray Diffraction on the microstructure and oxidation resistance of Cu / M composite microparticles. (3) Design and preparation of S powder by atomization. Then the surface morphology, particle size and production efficiency of the prepared powder were studied. The results show that the maximum electrolysis efficiency and the maximum effective yield can be obtained by designing the exchange machine and collecting system with T212 waveform, and Cu powder with average particle size less than 20 μm can be prepared. The Cu / M composite particles prepared by chemical method can effectively protect the oxidation resistance of copper powder for more than 90 days. In the process of atomizing tin powder, it was found that with the increase of working temperature, the proportion of spherical powder was also increased, which could effectively achieve the target of high spherical particle size.

Los estilos APA, Harvard, Vancouver, ISO, etc.

44

Chen, Jin-Zhong y 陳進忠. "Preparation of Cu-Al2O3 Composite Material by Mechanical Alloying". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/8bpf87.

Texto completo

Resumen

碩士
國立臺北科技大學
材料科學與工程研究所
97
Pure Cu powder and alumina powder are used for preparing Cu-3wt.%Al2O3 oxide dispersion strengthen（ODS）composite powders through mechanical alloying（MA）method. Fixed rotation speed of ball mill, BPR and temperature, milling time as the variety unit. The evolution of microstructure change and composite powder morphology are analyzed by XRD, SEM, EDS and Laser light scattering particle size analyzer. Cu oxides are formed during Cu powder preparation where open environment. The microstructure of powder changes the milling time with decreases. Uniformly mixed Cu-3wt.%Al2O3 oxide dispersion strengthened composite powder is obtained with BPR 80 at 30℃and rotating speed 600rpm for attrition milling 10hr, then undergoing reduced heat treatment can improve the oxidation and reducing the Cu oxide effectively. 10 hr milled composite powder is then hot pressed of uniaxial to form bulk, and observe how the parameters of hot pressing influence on material. The result shows that the hot pressing time influence on material is relatively small, but the hot pressing pressure and temperature are relatively high, as the hot pressing pressure and temperature increase, the density、hardness and electrical conductivity also increase, but the hardness will decrease when temperature is too high. The composite powder after proceeding hydrogen reduction is more advantageous for sintering and has much better mechanical properties than using unreduced powders and pure copper. The content of oxide also affects the electrical and mechanical properties of Cu base composite material.

Los estilos APA, Harvard, Vancouver, ISO, etc.

45

Behera, Akhya Kumar. "Electro-Formation of Cu-Graphene Composites and Its Property Evaluation". Thesis, 2020. http://ethesis.nitrkl.ac.in/10184/1/2020_PhD_AKBehera_514MM1012_Electro.pdf.

Texto completo

Resumen

In the current study, few-layer graphene particles (FLGPs) have been synthesized by electrochemical exfoliation method. Two different electrolytes of 1M H2SO4 and HNO3 were used. The electrolyte produces anions of 2 4 SO and 3 NOwhich interact with pyrolytic graphite sheets to intercalate and produce FLGPs. Further, the prepared FLGPs are reduced by ascorbic acid and hydrazine hydrate and are leveled as RFLGPs(Vc) and RFLGPs(Hy) respectively. The prepared graphene particles were then analyzed by various scientific analyses such as TGA, XRD, FTIR, XPS, UV and Raman spectroscopy. Thermal stability and yield of graphene particles are done by TGA analysis. XRD and Raman spectroscopy were used for structural properties, lattice spacing and crystal structure of graphene particles. The (001) and (002) lattice plane of graphene oxide and graphene has been observed at 13º and 26.2º from XRD analysis. The as-synthesized graphene were expected to be functionalized which was confirmed by FTIR analysis and the functional groups are hydroxy, carboxy, epoxides and alcohol. The prepared FLGPs were then analyzed by XPS to quantify carbon oxygen ratio. The electronic transitions of π-π* and n-π* have been analyzed by UV-visible spectra. The topographical and morphological analysis of graphene has been carried out by FESEM and TEM analysis. The FESEM microscopy shows the agglomeration and layer structure. The TEM analysis gives the number of layers of graphene particles. The in-house synthesized graphene was found to consist of few layers and was partially functionalized too. The prepared FLGPs and RFLGPs have been used as reinforcement with the copper matrix to synthesize Cu- FLGPs nanocomposite. Copper-graphene nano-composites were synthesized by the electrodeposition method. FLGPs and RFLGPs of different concentrations (0.1, 0.3 and 0.5 g/L) were added into the copper matrix. The Cu films are plated first onto the steel substrate at different temperatures (25, 20 and 15 °C) to decide the deposition temperature (based upon the film characteristics obtained). Synthesis of the composite films were then carried out and compared in both silent and ultrasonic stirring conditions in the aqueous electrolyte. Cu deposited at 15 °C was best and was chosen to carry out the composite film deposition. The synthesized specimens (Cu and composite films) were characterized by surface Profilometry, XRD, SEM, EDS and AFM analyses. Furthermore, the distribution of Xi graphene was found to be better in the presence of ultrasound as witnessed from the structural and micro-graphical analysis. Then after the micro and nano-mechanical as well as electrical resistivity properties of the composites were measured to evaluate the performance of the films. The composite films have 31% improved hardness as compared to the pure copper films. The electrical resistivity has been increased from 1.6×10-6 -cm to 3.6×10-6 -cm. The electrodeposited Cu-FLGPs composite shows improved mechanical and comparable electrical properties as well as compared to the pure copper thin film. The Cu-RFLGPs composite shows 38% higher hardness as compared to pure copper thin film. The Cu-RFLGPs composites did show an adhesive type of wear leading to delamination of Cu layers. Apart from mechanical properties, the electrical resistivity of the sono-electroplated films was found to be improved as well. The corrosion behaviors of Cu-FLGPs as well as Cu-RFLGPs composite films have been analyzed by threeelectrode cell setup. Tests were carried out in two solutions i.e. standard borate buffer and 3.5% NaCl to simulate the general and pitting corrosion behavior respectively. All the composite films show well developed passivation regions in borate buffer and the pitting was also evident from the potentio-dynamic polarization plots. The general corrosion tendency and rate was found to be less in composite films. Further pitting was also less in composite films. The mechanism of such observation was proposed by EIS study. Out of the two types, Cu-RFLGPs composites have superior mechanical, electrical and anticorrosive properties.

Los estilos APA, Harvard, Vancouver, ISO, etc.

46

Lai, Yi-An y 賴羿安. "Development of the Thermal Interface Materials for Joining Diamond/Cu Composites and Substrates". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/w5v8p6.

Texto completo

Los estilos APA, Harvard, Vancouver, ISO, etc.

47

Wang, Wei-Hsiang y 王韋翔. "The experimental studies of electrical and mechanical properties of the Cu/MWCNTs composite material". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/48838495155400444209.

Texto completo

Resumen

碩士
元智大學
機械工程學系
98
Multi-wall carbon nanotubes process outstanding mechanical properties, perfect tubular structure and self-lubricating effect, it often used to be as reinforcement material in composites. In research,electrolytic depositionwas employed to deposited carbon nanotubes and copperon to graphite substrate, aims to arrangecarbon nanotubes by applying different types of electrical current and dielectrophoretic effect. This research utilized scanning electron microscopy (SEM) to observing distribution of carbon nanotubes in copper, nanoindentation, multi-meter and wear &friction testing machine to observed the results of mechanical properties and electrical current of copper carbon nanotubes. The experiment results showedthe higher the current density, the higher mechanical properties ofcopper carbon nanotubes among in several different type of current. Adversely, the electro-resistance was increased as a consequence.

Los estilos APA, Harvard, Vancouver, ISO, etc.

48

Shu, Kuen Ming y 許坤明. "The Fabrication、Thermal Expansion and Electrical Discharge Machining/Grinding Characteristics of Cu/SiCp Composite Material". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/12703967743571539863.

Texto completo

Resumen

博士
國立交通大學
材料科學與工程系
91
On mold manufacturing industry, the electrical discharge machining (EDM) has been adopted for years; it is the most important machining tool for this industry. For progressing the EDM, three fields are always concerned; (1) to improved the machine set accuracy and update the control system, (2) to determine the optimum machining parameters for selected materials, (3) to composite EDM with others machining method to broaden the utility of EDM. This thesis aims at the third field, and tries to develop a new method, termed electrical discharge machining and grinding (EDMG), which increased material removal rate effectively. To fulfill the EDMG operation, a Cu/SiCp composite material electrode with high electrical conductivity and capable of operating at high temperature was fabricated and studied. Although there are various methods for fabricating metal matrix composite materials, the powder metallurgy method, feasible to enhance matrix/reinforcement bonding and mass production, is selected to fabricate the Cu/SiCp composite in this thesis. In order to obtain optimal bonding between SiCp and Cu particles, the electroless plating steps were introduced. The thesis is composed of six chapters and they cover all fundamental aspects of Cu/SiCp, from the fabrication and characterization of Cu/SiCp, to the application in EDM and EDMG. The first chapter provides the objective of this thesis. Chapter 2 provides definition information and the development of composite materials and metal matrix composite materials. The principles of EDM, EDG (electrical discharge grinding) and EDMG are also introduced in this chapter. Chapter 3 describes the fabrication and characterization of the Cu/SiCp composite and its application in EDM, The objective of this chapter is to investigate the mechanical properties of Cu/SiCp and the optimum composition of an electrode for EDM usage. Chapter 4 focuses on the microstructure and the thermal expansion property of Cu/SiCp. Thermal expansion property of as-formed product was measured in the temperature range from 50℃ to 550℃. The composites exhibited positive thermal hysteresis behavior when cooled down from the peak temperature to room temperature. The magnitude of this strain was a function of the SiCp volume fraction and the number of thermal cycles. The thermal expansion property of composites was compared with those predicted from various theoretical models. The feasibility of using a copper matrix composite electrode to perform the EDMG operation on mold steel is discussed in chapter 5. Cu/SiCp electrode with a rotating device was made and employed to study the EDMG technology. It was found that 3-7 times the normal EDM material removal rate could be achieved in EDMG under suitable conditions of electrode rotating speed, SiCp particle size and current. Thus a new revised machining methodology, termed electrical discharge machining and grinding, based on conventional EDM is formally proposed. Finally, discussion and general conclusions are in Chapter 6. Overhauling the present work, the following conclusions can be drawn. 1. The powder metallurgy method is a feasible fabricating process for SiC particulate reinforced copper composites. 2. Improved bonding can be achieved by activation of SiC powder surface through electroless-coating of Cu on to SiC powder. 3. The density of composites can be improved to a certain extent by coating a copper film on SiCp. The hot extrusion process can improve the density of the composites up to 95% of the theoretical density value. The promoted bonding between SiCp and Cu by the copper coating method lead to higher hardness. Both tensile strength and density of composite decrease with increasing amount of SiCp. The electrical resistivity increases with a higher SiCp content. 4. A larger SiCp content in the composite would induce more stress accumulation in the matrix, and more stress releasing would occur during the heating and cooling cycle, causing a larger CTE value. The CTE of metal matrix composite could be decreased effectively through good bonding between the reinforcement phase and metal matrix. 5. The CTE and thermal hysteresis strain generally increases with increasing SiCp particle size. The composites exhibited positive thermal hysteresis behavior when cooled down from higher temperature to room temperature. The magnitude of this strain was a function of the SiCp volume fraction and the number of thermal cycles. 6. In EDM, a higher material removal rate can be achieved at moderate SiCp content. However, tool wear ratio increases with increasing SiCp content. 7. The effectiveness of EDMG with a Cu/SiCp electrode is confirmed from the observed results, leading to a much higher material removal rate under suitable conditions of electrode rotating speed, SiCp particle size and current. 8. The morphology of EDMGed surfaces of mold steel differ greatly from that of EDMed surface and the surface roughness processed by EDMG is apparent improved.

Los estilos APA, Harvard, Vancouver, ISO, etc.

49

Dash, Khushbu. "Processing and characterization of Cu-Al2O3 and Al-Al2O3 composites: an evaluation for micro- and nano- particulate reinforcements". Thesis, 2014. http://ethesis.nitrkl.ac.in/6537/1/compiled_thesis.pdf.

Texto completo

Resumen

Composites are formed by the physical association of matrix and reinforcement and possess intermediate properties of the components’ it is constituted of. Metal matrix composites (MMCs) reinforced with ceramic particles furnishes ductility along with strength and has been into practice since decades. The applications cater the aerospace and automobile industries such as turbine rotatory machinery components, rocket turbine housing, cryostat, cryo-pump impeller and cryo-pump inducer. Powder metallurgy has been a conventional still inevitable technique to serve the automotive and aerospace industries with components of utmost importance. The powder metallurgy process consists of several steps which are crucial to the end products’ properties. This work aims at investigating some of the steps to assess the microstructure and properties of copper and aluminium based composites varying the reinforcement particle size and volume fraction. Structural integrity is a vital factor of a composite which accounts for the physical intimate bonding of matrix and reinforcement. This factor varies with the fabrication parameters and techniques which are also fundamental for effective stress transmissibility from matrix to reinforcement. Structural integrity of a composite material also fluctuates within the service life of the material, for eg. during harsh and hostile environment thermal exposures.

Los estilos APA, Harvard, Vancouver, ISO, etc.

Tesis sobre el tema "Composite materials Cu"

Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros