Matériaux composites Argent/Carbone à propriétés thermiques adaptatives PDF Download

Author: Benjamin Thomas
Publisher:
ISBN:
Category :
Languages : fr
Pages : 0

View

Book Description
Du fait leur conductivité thermique élevée, les matériaux composites à matrice métallique et renfort carbone possèdent un fort potentiel d'application pour la gestion thermique en électronique. Ces travaux présentent le développement d'un nouveau procédé pour la synthèse de matériaux composites Ag/rGO (argent / « reduced Graphene Oxide ») et Ag/GF (argent / « Graphite Flakes ») par métallurgie des poudres. Ce procédé, inspiré des méthodes de « molecular level mixing », permet d'obtenir des poudres composites Ag/rGO dans lesquelles les nano-renforts sont individualisés jusqu'à une concentration volumique de 1 %. Lorsqu'il est appliqué à la synthèse de matériaux composites Ag/GF, ce dernier permet l'élaboration de matériaux composites denses avec une concentration volumique en graphite jusqu'à 70 % et une conductivité thermique jusqu'à 675 W.m-1.K-1 (426 W.m-1.K-1 pour l'argent pur). En outre, il a été montré que le procédé d'élaboration des poudres composites Ag/GF a une forte influence sur l'anisotropie structurale des matériaux massifs ainsi que sur la résistance thermique d'interface extrinsèque Ag-graphite. Le procédé d'élaboration développé dans ces travaux permet ainsi d'obtenir des matériaux ayant une conductivité thermique jusqu'à 19 % supérieure à celle des matériaux obtenus par un procédé de mélange conventionnel. Néanmoins, comme la plupart des matériaux composites métal/GF (à matrice Cu, Al, Mg et Fe), la dilatation thermique des matériaux composites Ag/GF présente des « anomalies ». En effet, l'anisotropie de leur coefficient d'expansion thermique (CTE) est opposée à leur anisotropie structurale, leur CTE a une dépendance anormalement élevée vis-à-vis de la température et ces matériaux présentent une instabilité dimensionnelle en cyclage thermique. S'il est communément admis dans la littérature que ces anomalies sont la conséquence des contraintes internes générées lors de l'élaboration des matériaux (du fait de la différence de CTE entre matrice et renfort), ce phénomène reste mal compris et difficile à maitriser. Une part importante de ces travaux est consacrée à l'étude de ces « anomalies » et en particulier à l'étude de l'influence des propriétés mécaniques de la matrice d'argent sur la dilation thermique des matériaux composites. Grâce à la combinaison des caractérisations d'EBSD, de DRX, de microdureté instrumentée et de microscopie, des phénomènes clés responsables des propriétés thermomécaniques des matériaux composites Ag/GF ont pu être identifiés. En particulier, il a été montré qu'une part importante des contraintes internes est relaxée via la déformation plastique de la matrice d'argent et la déformation pseudo plastique du graphite lors du refroidissement post-densification des matériaux composites. Ainsi, le contrôle des propriétés mécaniques de la matrice métallique (en particulier de sa limite d'élasticité) permet d'atténuer les anomalies en CTE et confère une meilleure stabilité dimensionnelle aux matériaux composites Ag/GF lors d'un cycle thermique. L'addition de rGO dans la matrice d'argent des matériaux composites Ag/GF a également permis de réduire l'instabilité dimensionnel des matériaux jusqu'à 50 % grâce aux propriétés d'amortissement du rGO.

Author: Nabil Chamroune
Publisher:
ISBN:
Category :
Languages : fr
Pages : 0

View

Book Description
Les matériaux composites à matrice métallique (CMM) sont actuellement étudiés pour être utilisés dans de nombreux domaines d'application. L'une des applications potentielles concerne leur utilisation en tant que drain thermique pour les modules de puissance. Pour cette application, deux conditions sont requises : une conductivité thermique (CT) élevée pour évacuer la chaleur générée par la puce électronique et un coefficient d'expansion thermique (CTE) proche du substrat céramique (2-8×10-6 /K) utilisé dans le module de puissance.Ainsi des matériaux composites à matrice aluminium (Al : CT de 217 W/m.K et CTE de 24×10-6 /K) et à renfort plaquette de graphite (GF : CT de 1000 W/m.K et CTE de -1×10-6 /K dans le plan de la plaquette) ont été élaborés. Ces matériaux composites ont été fabriqués par Métallurgie des Poudres (MP) conventionnelle mais aussi par un procédé original nommé Flake Powder Metallurgy (FPM). Ce procédé, qui consiste à utiliser une poudre métallique à morphologie plaquette, a permis d'optimiser l'orientation des renforts plaquette dans un plan perpendiculaire à la direction de densification sous l'action d'une pression uniaxiale. De plus, ce procédé a permis d'obtenir une meilleure adhésion entre la matrice et le renfort comparé aux matériaux composites élaborés par MP conventionnelle. Cela a abouti à une amélioration de la CT qui est passée de 400 W/m.K à 450 W/m.K pour un taux de renfort de 50%vol. Néanmoins, concernant la dilatation thermique, des CTE de 21,8×10-6 /K et 21,7×10-6 /K ont été obtenus par MP et FPM respectivement, ce qui est incompatible avec l'application visée.Pour surmonter cette problématique, des matériaux composites à renfort multiple ont été élaborés par frittage en phase liquide. Ainsi des fibres de carbone (FC) ont été rajoutées à l'aluminium et aux plaquettes de graphite. L'ajout de ce second renfort au graphite a permis de diminuer de manière importante le CTE des composites Al/(GF+FC) avec une faible proportion en FC tout en maintenant une haute CT. De plus les matériaux composites Al/(GF+FC) présentent des CTE nettement inférieurs aux composites Al/FC avec un %vol. de FC équivalent. Ainsi des matériaux composites Al/(GF+FC) ont été élaborés par frittage en phase liquide permettant d'obtenir une CT de 400 W/m.K (comparable à la CT du cuivre) et un CTE de 8×10-6 /K (comparable au CTE de l'alumine). De plus la légèreté de l'aluminium confère aux matériaux composites Al/C une faible densité (d=2,4). Par conséquent, les matériaux développés dans cette étude sont prometteur en tant que drain thermique léger, notamment dans le domaine de l'électronique embarquée.

Author: OECD
Publisher: OECD Publishing
ISBN: 9264545190
Category :
Languages : en
Pages : 152

View

Book Description
The artificial intelligence (AI) landscape has evolved significantly from 1950 when Alan Turing first posed the question of whether machines can think. Today, AI is transforming societies and economies. It promises to generate productivity gains, improve well-being and help address global challenges, such as climate change, resource scarcity and health crises.

Author: Wade H. Shafer
Publisher: Springer
ISBN:
Category : Education
Languages : en
Pages : 328

View

Book Description
Masters Theses in the Pure and Applied Sciences was first conceived, published, and disseminated by the Center for Information and Numerical Data Analysis and Synthesis (CINDAS) * at Purdue University in 1 957, starting its coverage of theses with the academic year 1955. Beginning with Volume 13, the printing and dissemination phases of the activity were transferred to University Microfilms/Xerox of Ann Arbor, Michigan, with the thought that such an arrangement would be more beneficial to the academic and general scientific and technical community. After five years of this joint undertaking we had concluded that it was in the interest of all con cerned if the printing and distribution of the volumes were handled by an interna tional publishing house to assure improved service and broader dissemination. Hence, starting with Volume 18, Masters Theses in the Pure and Applied Sciences has been disseminated on a worldwide basis by Plenum Publishing Cor poration of New York, and in the same year the coverage was broadened to include Canadian universities. All back issues can also be ordered from Plenum. We have reported in Volume 28 (thesis year 1 983) a total of 10,661 theses titles from 26 Canadian and 197 United States universities. We are sure that this broader base for these titles reported will greatly enhance the value of this important annual reference work. While Volume 28 reports theses submitted in-1983, on occasion, certain univer sities do report theses submitted in previous years but not reported at the time.

Author: Andy Nieto
Publisher: CRC Press
ISBN: 1000377504
Category : Technology & Engineering
Languages : en
Pages : 376

View

Book Description
This discovery of carbon nanotubes (CNT) three decades ago ushered in the technological era of nanotechnology. Among the most widely studied areas of CNT research is their use as structural reinforcements in composites. This book describes the development of CNT reinforced metal matrix composites (CNT-MMCs) over the last two decades. The field of CNT-MMCs is abundant in fundamental science, rich in engineering challenges and innovations and ripe for technological maturation and commercialization. The authors have sought to present the current state of the-art in CNT-MMC technology from their synthesis to their myriad potential end-use applications. Specifically, topics explored include: • Advantages, limitations, and evolution of processing techniques used to synthesize and fabricate CNT-MMCs • Emphasizes dispersion techniques of CNTs in metallic systems, a key challenge to the successful and widespread implementation of CNT-MMCs. Methods for quantification and improved control of CNT distributions are presented • Methods for quantification and improved control of CNT distributions are presented • Characterization techniques uniquely suited for charactering these nanoscale materials and their many chemical and physical interactions with the metal matrix, including real-time in-situ characterization of deformation mechanisms • Electron microscope images from premier studies enrich discussions on micro-mechanical modeling, interfacial design, mechanical behavior, and functional properties • A chapter is dedicated to the emergence of dual reinforcement composites that seek to enhance the efficacy of CNTs and lead to material properties by design This book highlights seminal findings in CNT-MMC research and includes several tables listing processing methods, associated CNT states, and resulting properties in order to aid the next generation of researchers in advancing the science and engineering of CNT-MMCs. In addition, a survey of the patent literature is presented in order to shed light on what the first wave of CNT-MMC commercialization may look like and the challenges that will have to be overcome, both technologically and commercially.

Author: S. Roussos
Publisher: Springer Science & Business Media
ISBN: 9401706611
Category : Technology & Engineering
Languages : en
Pages : 641

View

Book Description
G.HAINNAUX Departement Milieu et Activites Agricoles, Centre ORSTOM, 911 Avenue d' Agropolis, B.P. 5045, 34032 Montpellier Cedex , France. Solid state fermentation, popularly abbreviated as SSF, is currently investigated by many groups throughout the world. The study of this technique was largely neglected in the past in European and Western countries and there is now a high demand for SSF, meaning in food, environment, agricultural, phannaceutical and many other biotechnological applications. It gives me satisfaction to note that the importance of this technique was realised at my department way back in 1975 since then, our team has put concentrated efforts on developing this technique. xvii Foreword Advances in Solid State Fermentation Foreword M. PUYGRENIER Agropolis Valorisation, Avenue d' Agropolis, 34394 Montpellier Cedex 5, France. On the name of the Scientific Community, I would like to express the wish that this International Symposium on SSF should be successful. Solid State Fermentation is part of biotechnology research. It consists on seeding solid culture medium with bacteria or fungi (filamentous or higher) and on producing, in this medium (solid components and exudates) metabolites and high value products. In fact, this process is very old. In older industries such the food and agricultural, this technique has been extensively used. An example of this is the production of pork sausages and Roquefort cheese. Pharmaceutical industry could make extensive use of SSF in the production of secondary metabolites of many kinds and development in this direction is soon expected.

Author: OECD
Publisher: OECD Publishing
ISBN: 9264305912
Category :
Languages : en
Pages : 132

View

Book Description
Government at a Glance Southeast Asia 2019 is the first edition in the Government at a Glance series for the region. It provides the latest available data on public administrations in the 10 ASEAN member countries: Brunei Darussalam, Cambodia, Indonesia, Lao People’s Democratic Republic, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Viet Nam.

Author: Ajay Kumar Mishra
Publisher: Nova Science Publishers
ISBN: 9781620819142
Category : Carbon
Languages : en
Pages : 0

View

Book Description
Carbon nanotubes possess unusual fascinating properties which have attracted the scientific world. This book covers a very wide domain of research and development where the synthesis and properties of carbon nanotubes are discussed. This book describes the carbon nanotube general introduction, various synthesis procedures and properties. This book is going to be beneficial to the researchers who are working for their postgraduate degree in nanomaterials and nanotechnology. This book also provides a platform for all the academics and researchers as it covers a vast background for the recent literature, abbreviations, and summaries. This book will be worth reading for the researchers who are more interested in the general overview of carbon nanotubes, fundamentals concepts and various synthetic procedures in the multidisciplinary areas. This book contains the fundamental knowledge with the recent advancements for the research and development in the field of nanomaterials and nanotechnology.

Author: ASM International
Publisher:
ISBN: 9780871707086
Category :
Languages : en
Pages :

View

Book Description

Author: Randall M. German
Publisher: Wiley-Interscience
ISBN: 9780471057864
Category : Technology & Engineering
Languages : en
Pages : 0

View

Book Description
Although sintering is an essential process in the manufacture ofceramics and certain metals, as well as several other industrialoperations, until now, no single book has treated both thebackground theory and the practical application of this complex andoften delicate procedure. In Sintering Theory and Practice, leadingresearcher and materials engineer Randall M. German presents acomprehensive treatment of this subject that will be of great useto manufacturers and scientists alike. This practical guide to sintering considers the fact that while thebonding process improves strength and other engineering propertiesof the compacted material, inappropriate methods of control maylead to cracking, distortion, and other defects. It provides aworking knowledge of sintering, and shows how to avoid problemswhile accounting for variables such as particle size, maximumtemperature, time at that temperature, and other problems that maycause changes in processing. The book describes the fundamental atomic events that govern thetransformation from particles to solid, covers all forms of thesintering process, and provides a summary of many actual productioncycles. Building from the ground up, it begins with definitions andprogresses to measurement techniques, easing the transition,especially for students, into advanced topics such as single-phasesolid-state sintering, microstructure changes, the complications ofmixed particles, and pressure-assisted sintering. German draws onsome six thousand references to provide a coherent and lucidtreatment of the subject, making scientific principles andpractical applications accessible to both students andprofessionals. In the process, he also points out and avoids thepitfalls found in various competing theories, concepts, andmathematical disputes within the field. A unique opportunity to discover what sintering is all about--bothin theory and in practice What is sintering? We see the end product of this thermal processall around us--in manufactured objects from metals, ceramics,polymers, and many compounds. From a vast professional literature,Sintering Theory and Practice emerges as the only comprehensive,systematic, and self-contained volume on the subject. Covering all aspects of sintering as a processing topic, includingmaterials, processes, theories, and the overall state of the art,the book * Offers numerous examples, illustrations, and tables that detailactual processing cycles, and that stress existing knowledge in thefield * Uses the specifics of various consolidation cycles to illustratethe basics * Leads the reader from the fundamentals to advanced topics,without getting bogged down in various mathematical disputes overtreatments and measurements * Supports the discussion with critically selected references fromthousands of sources * Examines the sintering behavior of a wide variety of engineeredmaterials--metals, alloys, oxide ceramics, composites, carbides,intermetallics, glasses, and polymers * Guides the reader through the sintering processes for severalimportant industrial materials and demonstrates how to controlthese processes effectively and improve present techniques * Provides a helpful reference for specific information onmaterials, processing problems, and concepts For practitioners and researchers in ceramics, powder metallurgy,and other areas, and for students and faculty in materials scienceand engineering, this book provides the know-how and understandingcrucial to many industrial operations, offers many ideas forfurther research, and suggests future applications of thisimportant technology. This book offers an unprecedented opportunity to explore sinteringin both practical and theoretical terms, whether at the lab or inreal-world applications, and to acquire a broad, yet thorough,understanding of this important technology.