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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
191

Magnétisme, structure et morphologie des films minces de cobalt déposés sur des surfaces vicinales de cuivre Cu(1 1 11) et Cu(1 1 5)

Chaumin Midoir, Anne 04 November 2002 (has links) (PDF)
Les nanostructures magnétiques peuvent avoir des propriétés très différentes de celles des matériaux massifs. Une des méthodes pour élaborer de petits objets est l'évaporation sur un substrat nanostructuré tel qu'une surface vicinale présentant des marches à l'échelle atomique. La compréhension des propriétés magnétiques de ces systèmes nécessite une caractérisation précise de leur structure et de leur morphologie afin d'évaluer les effets dus aux contraintes épitaxiales et aux dimensions réduites. Nous avons étudié les films de cobalt déposés sur des surfaces de Cu(1 1 11) et Cu(115) par trois techniques. Leur magnétisme a été sondé par effet Kerr magnéto-optique tandis que leur morphologie et leur structure cristallographique ont fait l'objet de mesures respectivement par microscopie à effet tunnel et EXAFS de surface. Les mesures par effet Kerr montrent une anisotropie uniaxiale magnétique avec un axe de facile aimantation parallèle aux bords de marches. L'anisotropie mesurée sur Cu(115), le substrat ayant les terrasses les moins larges, est plus importante. Les expériences de STM montrent la forte mobilité du cuivre dès les faibles taux de couverture ainsi qu'une grande évolution de la morphologie en fonction de la quantité de cobalt déposée. Grâce à l'EXAFS, nous avons montré que dès 3 monocouches (MC) de cobalt sur Cu(1 1 11) et 5 MC sur Cu(115), la structure est quasiment identique à celle observée sur Cu (001) i.e. tétragonale à faces centrées et que la présence de terrasses étroites n'engendrent pas d'anisotropie dans le plan (001). Des simulations de l'anisotropie magnétique prenant en compte les liaisons manquantes à la surface et en bord de marche (modèle de Néel) ainsi que les effets magnétoélastiques induits par la tétragonalisation de la maille montrent que l'anisotropie uniaxiale est très majoritairement due à la morphologie des films et que la distorsion de la maille de cobalt y contribue très peu.
192

Étude des mécanismes de formation de phases dans des films minces du système ternaire Al-Cu-Fe

Haidara, Fanta 21 July 2011 (has links) (PDF)
Les mécanismes de formation de phases dans des films minces du système ternaire Al-Cu-Fe et des systèmes binaires Al-Cu, Al-Fe et Cu-Fe ont été étudiés. Dans chacun des systèmes, plusieurs échantillons avec des compositions distinctes ont été préparés par pulvérisation cathodique. Des couches d'aluminium, de cuivre et de fer ont été déposées séquentiellement sur des substrats de silicium oxydé et ont été traités thermiquement par différentes méthodes puis caractérisés. Des mesures de diffraction de rayons X et de résistivité in-situ ont été effectuées pour suivre la formation des phases. Des recuits thermiques suivis de trempe ont été réalisés et les échantillons ont été caractérisés par diffraction des rayons X. L'analyse enthalpique différentielle a également été utilisée ainsi que des mesures simultanées in-situ de résistivité et de diffraction des rayons X. L'ensemble des résultats obtenus nous a permis de proposer des mécanismes de formation de phases pour chacun des échantillons étudiés et en utilisant des modèles théoriques de croissance de phases nous avons pu déterminer des données cinétiques sur la formation de phases dans ces films.
193

Atomic Simulations on Phase Transformation and Cyclic Deformation Mechanisms in Various Binary Metallic Glasses

Lo, Yu-chieh 04 August 2009 (has links)
The bulk metallic glasses (BMGs) are potential metallic materials due to their interesting properties, such as the high strength, high elastic strain limit, and high wear/corrosion resistance. Over the past four decades, a variety of studies have been done on the characteristics of the mechanical, thermodynamic properties of such category of metallic materials, but there still remain many questions about basic deformation mechanisms and their microstructures so far. Molecular dynamics (MD) simulation can provide significant insight into material properties under the atomic level and see a detailed picture of the model under available investigation in explaining the connection of macroscopic properties to atomic scale. MD simulation is applied to study the material properties and the deformation mechanisms in various binary metallic glasses and intended to examine the feasibility of MD simulation to compare the experimental results obtained in our laboratory over the past few years. The gradual vitrification evolution of atom mixing and local atomic pairing structure of the binary Zr-Ni, Zr-Ti alloys and pure Zr element during severe deformation at room temperature is traced numerically by molecular dynamic simulation. It is found that the icosahedra clusters will gradually develop with the increasing of disorder environment of alloys in the Zr-Ni, Zr-Ti systems, forming amorphous atomic packing. Other compound-like transition structures were also observed in transient in the Zr-Ni couple during the solid-state amorphization process under severe plastic deformation. The crystalline pure Zr can be vitrified in the simulation provided that the rolling speed is high enough and the rolling temperature is maintained at around 300 K. On the other hand, the effective medium theory (EMT) inter-atomic potential is employed in the molecular dynamics (MD) simulation to challenge the study of the diffusion properties in the Mg-Cu thin films. The transition of local structures of Mg-Cu thin films is traced at annealing temperatures of 300, 413, and 500 K. Furthermore, the simulation results are compared with the experimental results obtained from the transmission electron microscopy and X-ray diffraction. The gradual evolution of the local atomic pairing and cluster structure is discussed in light of the Mg and Cu atomic characteristics. Lately, the progress of the cyclic-fatigue damage in a binary Zr-Cu metallic glass in small size scale is investigated using classical molecular-dynamics (MD) simulations. The three-dimensional Zr-Cu fully amorphous structure is produced by quenching at a cooling rate 5 K/ps (ps = 10-12 s-1) from a high liquid temperature. The Nose-Hoover chain method is used to control the temperature and pressure to maintain a reasonable thermodynamic state during the MD-simulation process, as well as to bring the imposed cyclic stress on the subsequent simulation process. Both the stress- and strain-control cyclic loadings are applied to investigate the structural response and free-volume evolution. The overall structure would consistently maintain the amorphous state during cyclic loading. The plastic deformation in simulated samples proceeds via the network-like development of individual shear transition zones (STZs) by the reversible and irreversible structure-relaxations during cyclic loading, dislike the contribution of shear band in large-scale specimens. Dynamic recovery and reversible/irreversible structure rearrangements occur in the current model, along with annihilation of excessive free volumes. This behavior might be able to retard the damage growth of metallic glass and enhance their fatigue life.
194

Nanostruktur ionenbestrahlter Fe/Al- und Co/Cu-Grenzschichten

Noetzel, Joachim 16 August 2000 (has links) (PDF)
In dieser Arbeit wird die nanoskalige Struktur von Grenzschichten in binären metallischen Multischichten untersucht. Ausgangspunkt sind laserdeponierte Multischichten des mischbaren Systems Fe/Al und des nichtmischbaren Systems Co/Cu. Die Struktur der durch die hochenergetischen Teilchen bei der Deposition entstandenen Grenzschichten wird mit Hilfe von zahlreichen Analyseverfahren (RBS, CEMS, EXAFS, Röntgenverfahren, TEM, AES und magnetische Messungen), sowie Simulationsrechnungen auf Basis des ballistischen Mischens (TRIDYN) untersucht. Anschließend wird mit Hilfe von Ionenstrahlmischen und thermischem Anlassen die Grenzschichtstruktur weiter modifiziert.
195

Scanning Tunnelling Microscopy of Co-impurified Noble Metal Surfaces: Kondo-Effect, Electronic Surface States and Diffusive Atom Transport / Rastertunnelmikroskopie an verdünnt Co-legierten Edelmetalloberflächen: Kondo-Effekt, Oberflächenzustände und diffusiver Atomtransport

Quaas, Norbert 10 December 2003 (has links)
No description available.
196

Atmospheric corrosion of zinc-aluminum and copper-based alloys in chloride-rich environments : Microstructure, corrosion initiation, patina evolution and metal release

Zhang, Xian January 2014 (has links)
Fundamental understanding of atmospheric corrosion mechanisms requires an in-depth understanding on the dynamic interaction between corrosive constituents and metal/alloy surfaces. This doctoral study comprises field and laboratory investigations that assess atmospheric corrosion and metal release processes for two different groups of alloys exposed in chloride-rich environments. These groups comprise two commercial Zn-Al alloy coatings on steel, Galfan™ (Zn5Al) and Galvalume™ (Zn55Al), and four copper-based alloys (Cu4Sn, Cu15Zn, Cu40Zn and Cu5Zn5Al). In-depth laboratory investigations were conducted to assess the role of chloride deposition and alloy microstructure on the initial corrosion mechanisms and subsequent corrosion product formation. Comparisons were made with long-term field exposures at unsheltered marine conditions in Brest, France. A multitude of surface sensitive and non-destructive analytical methods were adopted for detailed in-situ and ex-situ analysis to assess corrosion product evolution scenarios for the Zn-Al and the Cu-based alloys. Scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS) were employed for morphological investigations and scanning Kelvin probe force microscopy (SKPFM) for nobility distribution measurements and to gain microstructural information. SEM/EDS, infrared reflection-absorption spectroscopy (IRAS), confocal Raman micro-spectroscopy (CRM) and grazing incidence x-ray diffraction (GIXRD) were utilized to gain information on corrosion product formation and possibly their lateral distribution upon field and laboratory exposures. The multi-analytical approach enabled the exploration of the interplay between the microstructure and corrosion initiation and corrosion product evolution. A clear influence of the microstructure on the initial corrosion product formation was preferentially observed in the zinc-rich phase for both the Zn-Al and the Cu-Zn alloys, processes being triggered by microgalvanic effects. Similar corrosion products were identified upon laboratory exposures with chlorides for both the Zn-Al and the Cu-based alloys as observed after short and long term marine exposures at field conditions. For the Zn-Al alloys the sequence includes the initial formation of ZnO, ZnAl2O4 and/or Al2O3 and subsequent formation of Zn6Al2(OH)16CO3·4H2O, and Zn2Al(OH)6Cl·2H2O and/or Zn5(OH)8Cl2·H2O. The patina of Cu sheet consists of two main layers with Cu2O predominating in the inner layer and Cu2(OH)3Cl in the outer layer, and with a discontinuous presence of CuCl in-between. Additional patina constituents of the Cu-based alloys include SnO2, Zn5(OH)6(CO3)2, Zn6Al2(OH)16CO3·4H2O and Al2O3. General scenarios for the evolution of corrosion products are proposed as well as a corrosion product flaking mechanism for some of the Cu-based alloys upon exposure in chloride-rich atmospheres. The tendency for corrosion product flaking was considerably more pronounced on Cu sheet and Cu4Sn compared with Cu15Zn and Cu5Al5Zn. This difference is explained by the initial formation of zinc- and zinc-aluminum hydroxycarbonates Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3·4H2O on Cu15Zn and Cu5Al5Zn, corrosion products that delay the formation of CuCl, a precursor of Cu2(OH)3Cl. As a result, the observed volume expansion during transformation of CuCl to Cu2(OH)3Cl, and the concomitant flaking process of corrosion products, was less severe on Cu15Zn and Cu5Al5Zn compared with Cu and Cu4Sn in chloride-rich environments. The results confirm the barrier effect of poorly soluble zinc and zinc-aluminum hydroxycarbonates Zn5(OH)6(CO3)2 and Zn6Al2(OH)16CO3·4H2O, which results in a reduced interaction between chlorides and surfaces of Cu-based alloys, and thereby reduced formation rates of easily flaked off corrosion products. From this process also follows reduced metal release rates from the Zn-Al alloys. / Bättre molekylär förståelse för metallers atmosfäriska korrosion kräver en fördjupad kunskap i det dynamiska samspelet mellan atmosfärens korrosiva beståndsdelar och metallytan. Denna doktorsavhandling omfattar laboratorie- och fältundersökningar av korrosions- och metallfrigöringsprocesser av två grupper av legeringar som exponerats i kloridrika atmosfärsmiljöer: två kommersiella Zn-Al beläggningar på stål, Galfan™ (Zn med 5% Al, förkortat Zn5Al) och Galvalume™ (Zn55Al), samt fyra kopparbaserade legeringar (Cu4Sn, Cu15Zn, Cu40Zn och Cu5Zn5Al). Undersökningar har genomförts i renodlade laboratorie-miljöer med för-deponerade NaCl-partiklar i en atmosfär av varierande relativ fuktighet. Syftet har varit att utvärdera betydelsen av kloriders deposition och legeringarnas mikrostruktur på korrosionsmekanismen samt bildandet av korrosionsprodukter. Jämförelser av korrosionsmekanismer har även gjorts efter flerårsexponeringar av samma legeringar i en marin fältmiljö i Brest, Frankrike. Undersökningarna har baserats på ett brett spektrum av analysmetoder för detaljerade studier dels under pågående atmosfärisk korrosion (in-situ), och dels efter avslutad korrosion (ex-situ). Legeringarnas mikrostruktur och tillhörande variation i ädelhet hos olika faser har undersökts med svepelektronmikroskopi och energidispersiv röntgenmikroanalys (SEM/EDS) samt med en variant av atomkraftsmikroskopi (engelska: scanning Kelvin probe force microscopy, SKPFM). Korrosionsprodukternas tillväxt har analyserats in-situ med infraröd reflektions-absorptionsspektroskopi (IRAS), samt morfologi och sammansättning av bildade korrosionsprodukter ex-situ med SEM/EDS, konfokal Raman mikro-spektroskopi (CRM) samt röntgendiffraktion vid strykande ifall (GIXRD). Det multi-analytiska tillvägagångssättet har medfört att det komplexa samspelet mellan de skilda legeringarnas mikrostruktur, korrosionsinitiering och bildandet av korrosionsprodukter kunnat studeras i detalj. En tydlig påverkan av mikrostruktur på det initiala korrosionsförloppet har kunnat påvisas. Korrosionsinitieringen sker företrädesvis i mer zinkrika faser för såväl Zn-Al- som Cu-Zn-legeringar och orsakas av mikro-galvaniska effekter mellan de mer zinkrika, mindre ädla, faserna och omgivande faser. Deponerade NaCl-partiklar påskyndar den lokala korrosionen oberoende av mikrostruktur. Snarlika sekvenser av korrosionsprodukter har kunnat påvisas såväl efter laboratorie- som fältexponeringar. För Zn-Al-legeringar bildas först ZnO, ZnAl2O4 och/eller Al2O3, därefter Zn6Al2(OH)16CO3·4H2O och Zn2Al(OH)6Cl·2H2O och/eller Zn5(OH)8Cl2·H2O. På ren koppar bildas ett inre skikt dominerat av Cu2O, ett mellanskikt av CuCl och ett yttre skikt med i huvudsak Cu2(OH)3Cl. Beroende på legeringstillsats har även SnO2 och Zn5(OH)6(CO3)2 kunnat identifieras. En mekanism för flagning av korrosionsprodukter på kopparbaserade legeringar i kloridrika atmosfärer har utvecklats. Tendensen för flagning har visat sig vara mycket mer uttalad på ren Cu och Cu4Sn än på Cu15Zn och Cu5Al5Zn. Skillnaden kan förklaras med hjälp av det tidiga bildandet av Zn5(OH)6(CO3)2 och Zn6Al2(OH)16CO3·4H2O på Cu15Zn och Cu5Al5Zn som fördröjer bildandet av CuCl, en föregångare till Cu2(OH)3Cl. Därigenom hämmas även den observerade volymexpansionen som sker när CuCl omvandlas till Cu2(OH)3Cl, en process som visar sig vara den egentliga orsaken till att korrosionsprodukterna flagar. Resultaten bekräftar barriäreffekten hos de mer svårlösliga faserna Zn5(OH)6(CO3)2 och Zn6Al2(OH)16CO3·4H2O, vilken dels resulterar i en minskad växelverkan mellan klorider och de legeringsytor där dessa faser kan bildas, och dels i en reducerad metallfrigöringshastighet. / <p>QC 20140915</p> / Autocorr, RFSR-CT-2009-00015 Corrosion of heterogeneous metal-metal assemblies in the automotive industry / Atmospheric corrosion and environmental metal dispersion from outdoor construction materials
197

Mechanical milling of Al-Cu-Fe quasicrystals and their Reinforcement in Aluminum matrix composites

Ali, Fahad 11 April 2012 (has links) (PDF)
In this thesis, the effect of mechanical deformation on structure, thermal stability and hardness of a single-phase spray-deposited quasicrystalline alloy with composition Al62.5Cu25Fe12.5 has been investigated in detail. The purpose of the investigation was to study the effect of mechanical milling at different milling speeds (which approximately scale with the milling intensity) on mechanically-induced phase transformations during milling and on the phase evolution during subsequent heating. The results of the milling experiments indicate that, irrespective of the milling speeds used, mechanical milling of Al62.5Cu25Fe12.5 quasicrystals leads to the formation of a disordered CsCl-type ß phase with grain size of about 10 – 20 nm. The analysis of the kinetics of the QC–to–ß phase transformation reveals that the milling intensity has a considerable effect on the characteristics of the transformation. The increase of the milling speed considerably shortens the incubation time needed to start the QC–to–ß phase transformation. Also, the overall transformation is much faster for milling at high speeds. The QC–to–ß phase transformation starts when the grain size of the quasicrystals is reduced to about 10 nm irrespective of the milling speed used and clearly indicates that a critical grain size of the quasicrystals for initiating the transformation exists. On the other hand, no critical value of lattice strain was found for the QC–to–ß transformation. This indicates that the phase transformation is controlled by the local length scale (i.e. the grain size) and by the corresponding grain boundaries rather than by the energy stored in the lattice. Energetic considerations obtained through a simple model based on the mass and velocity of the milling balls reveal that the energy needed for the QC–to–ß transformation increases with increasing the milling speed, that is, the energetic efficiency of the process decreases with increasing the milling intensity. This indicates that part the extra energy supplied during milling at high intensities is not used to induce the phase transformation but it is dissipated by heat. During heating, the milled powder displays a multi-step thermal behavior characterized by the grain growth of the disordered ß phase at low temperatures, followed, at higher temperatures, by its transformation into the original icosahedral quasicrystalline phase. The transformation is gradual and the quasicrystals and the disordered ß phase coexist over a temperature interval of more than 250 K. The phase transformations occurring during milling and subsequent annealing have a remarkable effect on the hardness, which can be tuned within a wide range of values (7–9.6 GPa) as a function of the volume fraction of the different phases. This suggests that a composite material with optimized mechanical properties can be produced by an appropriate thermo-mechanical treatment. The quasicrystals milled at a very low speed show a transition between Hall-Petch to inverse Hall-Petch behavior at a grain size of about 40 nm, which represents the critical value for grain size softening of the present Al62.5Cu25Fe12.5 quasicrystals. This behavior may be attributed to the complexity of the quasicrystalline structure and to its peculiar deformation mechanism at room temperature (i.e. shear banding), where meta-dislocation-assisted deformation is almost absent. In order to analyze the effectiveness of the Al62.5Cu25Fe12.5 quasicrystals as reinforcing agent in metal matrix composites, Al-based composites were synthesized by hot extrusion of elemental Al blended with different amounts of Al62.5Cu25Fe12.5 quasicrystalline particles. The work was focused on two specific aspects: evaluation of the mechanical properties through room temperature compression tests and modeling of the resulting properties. The addition of the quasicrystalline reinforcement is very effective for improving the room temperature mechanical properties of pure Al. The compressive strength increases from 155 MPa for pure Al to 330 and 407 MPa for the composites with 20 and 40 vol.% of reinforcement, respectively, reaching an ultimate strain of 55 % and 20 % before fracture occurs. These results indicate that the addition of the QC reinforcement leads to composite materials with compressive strengths exceeding that of pure Al by a factor of 2 – 2.5, while retaining appreciable plastic deformation. The mechanical properties of the composites have been modeled by taking into account the combined effect of load bearing, dislocation strengthening and matrix ligament size effects. The calculations are in very good agreement with the experimental results and reveal that the reduction of the matrix ligament size, which results in a similar strengthening effect as that observed for grain refinement, is the main strengthening mechanism in the current composites. Finally, the interfacial reaction between the Al matrix and the QC reinforcement has been used to further enhance the strength of the composites through the formation of a new microstructure consisting of the Al matrix reinforced with Al7Cu2Fe w-phase particles. The optimization of the structure-property relationship was done through the systematic variation of the processing temperature during consolidation. The mechanical behavior of these transformation-strengthened composites is remarkably improved compared to the parent material. The yield strength of the composites significantly increases as the Al + QC -> ω transformation progresses from 195 MPa for the sample reinforced only with QC particles to 400 MPa for the material where the Al + QC -> ω reaction is complete. These results clearly demonstrate that powder metallurgy, i.e. powder synthesis by ball milling followed by consolidation into bulk specimens, is an attractive processing route for the production of novel and innovative lightweight composites characterized by high strength combined with considerable plastic deformation. In addition, these findings indicate that the mechanical behavior of Al-based composites reinforced with Al62.5Cu25Fe12.5 quasicrystalline particles can be tuned within a wide range of strength and plasticity depending on the volume fraction of the reinforcement as well as on the extent of the interfacial reaction between Al matrix and QC reinforcing particles.
198

Σχεδιασμός, σύνθεση και κρυσταλλική μηχανική συμπλόκων ενώσεων του Cu(II) με 2-φαινυλοϊμιδαζόλιο ως υποκαταστάτη

Κίτος, Αλέξανδρος 19 July 2012 (has links)
Βασικός στόχος της παρούσης Διπλωματικής Εργασίας ήταν η μελέτη της κρυσταλλικής μηχανικής συμπλόκων ενώσεων του CuII με το 2-φαινυλοϊμιδαζόλιο ως υποκαταστάτη. Η κρυσταλλική μηχανική μπορεί να θεωρηθεί ως ο κλάδος της υπερμοριακής χημείας στη στερεά κατάσταση. Η υπερμοριακή χημεία (supramolecular chemistry) είναι μια από τις πλέον δημοφιλείς και γρήγορα αναπτυσσόμενες περιοχές της πειραματικής χημείας. Χαρακτηρίζεται ως η χημεία των ασθενών διαμοριακών δυνάμεων και εστιάζει στη δομή και λειτουργία χημικών συστημάτων με υψηλή πολυπλοκότητα (υπερμόρια) που προκύπτουν από το συνδυασμό δύο ή περισσοτέρων διακριτών χημικών ειδών (μορίων, ιόντων) και συγκρατούνται με ασθενείς (και αντιστρεπτές) διαμοριακές δυνάμεις (π.χ. αλληλεπιδράσεις π-π, δεσμούς υδρογόνου, υδρόφοβες αλληλεπιδράσεις, δυνάμεις van der Waals, αλληλεπιδράσεις διπόλου-διπόλου, δεσμούς ένταξης μετάλλου-υποκαταστάτη κλπ). Ένα σημαντικό πεδίο της υπερμοριακής χημείας είναι αυτό της κρυσταλλικής μηχανικής (crystal engineering) που αναφέρεται στη στρατηγική σχεδιασμού ενός κρυσταλλικού υλικού με επιθυμητές ιδιότητες και βασίζεται στην κατανόηση και τον έλεγχο των διαμοριακών αλληλεπιδράσεων των μορίων στην κρυσταλλική κατάσταση. Καταρχήν, πραγματοποιήθηκε η σύνθεση συμπλόκων ενώσεων με γενικό τύπο ΜΙΙ/Χ-/L, όπου ΜΙΙ = CuII, X- = Cl-, NO3-, ClO4-, SiF62-, SO42- και L = 2-φαινυλοϊμιδαζόλιο. Από τις συνθετικές παραμέτρους που μεταβάλλαμε -γραμμομοριακή αναλογία μετάλλου:υποκαταστάτη, πολικότητα του διαλύτη (MeOH, EtOH, MeCN, DMF, CH2Cl2), συνθήκες θερμοκρασίας και μέθοδο κρυστάλλωσης– απομονώσαμε και χαρακτηρίσαμε τα σύμπλοκα: (LH)+(NO3)- (1), [CuCl2L2] (2), [Cu2(OMe)2(L)4(NO3)2]∙2MeOH (3∙2MeOH), [Cu(L)4](NO3)2 (4), [Cu2(OMe)2(L)4](ClO4)2 (5), [Cu(L)4](ClO4)2 (6), [Cu2(OMe)2(L)4]SiF6 (7) και [Cu2(SO4)2(L)4] (8). Με τη βοήθεια της κρυσταλλογραφικής ανάλυσης με ακτίνες Χ των ανωτέρων συμπλόκων, διαπιστώθηκε ότι οι διαμοριακές αλληλεπιδράσεις που είναι υπεύθυνες για την υπερμοριακή οργάνωση των δομών τους είναι ισχυροί και ασθενείς δεσμοί υδρογόνου και αλληλεπιδράσεις τύπου π-π. Αναλυτικότερα: • Σταθερά μοτίβα διαμοριακών αλληλεπιδράσεων (συνθόνια) σχηματίζονται μεταξύ των τεκτονίων N-H των ιμιδαζολικών δακτυλίων και των ανόργανων ανιόντων X- (Cl-, NO3-, ClO4-, SiF62-, SO42-) ή/και πλεγματικών μορίων διαλύτη, οδηγώντας σε 1D, 2D και 3D υπερμοριακές δομές. • Οι δομές σταθεροποιούνται περαιτέρω μέσω ενδομοριακών (σύμπλοκα 4, 5 και 6) και διαμοριακών (σύμπλοκο 2) αλληλεπιδράσεων τύπου π-π. • Το μέγεθος και το φορτίο των ανιόντων δεν επηρεάζουν τους δομικούς πυρήνες των μορίων, σε αντίθεση με την υπερμοριακή οργάνωση που επηρεάζεται καθοριστικά και οδηγεί σε 2D και 3D αρχιτεκτονικές. / The main target of this diploma thesis was the crystal engineering studies of coordination compounds of CuII using 2-phenylimidazole as ligand. Crystal engineering may be regarded as the solid-state branch of supramolecular chemistry. Supramolecular chemistry is one of the most popular and rapidly developing areas of experimental chemistry. It may be defined as the chemistry of weak intermolecular forces and focuses on the structure and function of chemical systems of high complexity (supermolecules), resulting from the association of two or more discrete chemical species (molecules, ions) held together by weak (and reversible) intermolecular forces (e.g. π-π interactions, hydrogen bonds, hydrophobic interactions, van der Waals forces, dipole-dipole interactions, metal-ligand coordination bonds etc). Crystal engineering is an important field of supramolecular chemistry that refers to the design and synthesis of a crystalline material with desired properties, based on the understanding and exploitation of intermolecular interactions in the crystalline state. Initially the synthesis of coordination complexes with general formula ΜΙΙ/Χ-/L [ΜΙΙ = CuII, X- = Cl-, NO3-, ClO4-, SiF62-, SO42- and L =2-phenylimidazole] took place. By altering the parameters of synthesis –metal:ligand molar ratio, solvent polarity (MeOH, EtOH, MeCN, DMF, CH2Cl2), temperature, as well as crystallization method– we were able to isolate and study the following complexes: (LH)+(NO3)- (1), [CuCl2L2] (2), [Cu2(OMe)2(L)4(NO3)2]∙2MeOH (3∙2MeOH), [Cu(L)4](NO3)2 (4), [Cu2(OMe)2(L)4](ClO4)2 (5), [Cu(L)4](ClO4)2 (6), [Cu2(OMe)2(L)4]SiF6 (7) και [Cu2(SO4)2(L)4] (8). Based on the X-ray crystal structure determination of the above complexes, it was established that the intermolecular interactions responsible for the supramolecular organization of the structures are strong and weak hydrogen bonds, as well as π-π interactions. Specifically: • Supramolecular synthons between the N-H tectons of imidazole rings and the inorganic anions X- (Cl-, NO3-, ClO4-, SiF62-, SO42-) or/and lattice solvent molecules are formed, leading to 1D, 2D and 3D supramolecular structures. • The structures are further stabilized by intramolecular (complexes 4, 5 and 6) and intermolecular (complex 2) π-π interactions. • The size and charge of the anions X- used does not affect the structural core of the complexes, in contrast to their supramolecular organization which is decisively affected, leading to 2- and 3D architectures.
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Estudo da s?ntese e sinteriza??o de p?s comp?sitos do sistema Ta-Cu

Silva J?nior, Jos? Ferreira da 17 March 2008 (has links)
Made available in DSpace on 2014-12-17T14:06:47Z (GMT). No. of bitstreams: 1 JoseFSJ_DISSERT_2008.pdf: 20908474 bytes, checksum: 6066ac5af7bd753501dc151675ed9175 (MD5) Previous issue date: 2008-03-17 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Ta-Cu bulk composites combine high mechanical resistance of the Ta with high electrical and thermal conductivity of the Cu. These are important characteristics to electrical contacts, microwave absorber and heat skinks. However, the low wettability of Ta under Cu liquid and insolubility mutual these elements come hard sintering this composite. High-energy milling (HEM) produces composite powders with high homogeneity and refines the grain size. This work focus to study Ta-20wt%Cu composite powders prepared by mechanical mixture and HEM with two different conditions of milling in a planetary ball mill and then their sintering using hydrogen plasma furnace and a resistive vacuum furnace. After milling, the powders were pressed in a steel dye at a pressure of 200 MPa. The cylindrical samples pressed were sintered by resistive vacuum furnace at 10-4torr with a sintering temperature at 1100?C / 60 minutes and with heat rate at 10?C/min and were sintered by plasma furnace with sintering temperatures at 550, 660 and 800?C without isotherm under hydrogen atmosphere with heat rate at 80?C/min. The characterizations of the powders produced were analyzed by scanning electron microscopy (SEM), x-ray diffraction (XRD) and laser granulometry. After the sintering the samples were analyzed by SEM, XRD and density and mass loss tests. The results had shown that to high intense milling condition produced composite particles with shorter milling time and amorphization of both phases after 50 hours of milling. The composite particles can produce denser structure than mixed powders, if heated above the Cu melting point. After the Cu to arrive in the melting point, liquid copper leaves the composite particles and fills the pores / O comp?sito Ta-Cu alia a alta resist?ncia mec?nica do Ta com a alta condutividade t?rmica e el?trica do Cu. Estas s?o caracter?sticas importantes para contatos el?tricos, absorvedores de microondas ou dissipadores de calor. Todavia, a baixa molhabilidade do Cu l?quido no Ta s?lido e a m?tua insolubilidade desses elementos tornam dif?cil a densifica??o deste material. A moagem de alta energia (MAE) produz p?s comp?sitos com alta homogeneidade e refina o tamanho de gr?o. Este trabalho faz um estudo sobre p?s comp?sitos Ta-20%Cu preparados por mistura mec?nica e moagem de alta energia com duas condi??es distintas de moagem em um moinho do tipo planet?rio e sua posterior sinteriza??o em um forno a plasma de hidrog?nio e em um forno resistivo sob v?cuo. Amostras cil?ndricas foram obtidas usando uma press?o de 200 MPa. Elas foram sinterizadas em forno resistivo a 1100?C por 60 minutos sob um v?cuo de 10-4torr com uma taxa de aquecimento de 10?C/min e em um forno a plasma de H2 a 550, 660 e 800?C sem tempo de isoterma de sinteriza??o com uma taxa de aquecimento de 80?C/min. Para caracteriza??o dos p?s produzidos foram realizadas microscopia eletr?nica de varredura (MEV), difra??es de raios x (DRX) e granulometria a laser. Ap?s a sinteriza??o as amostras foram analisadas atrav?s de MEV, DRX, densidade e perda m?ssica. Os resultados mostram que para condi??o de moagem mais intensa part?culas comp?sitas s?o produzidas com poucas horas de moagem e h? uma amorfiza??o do t?ntalo e do cobre ap?s 50 horas de moagem. A MAE produz part?culas comp?sitas com uma densidade estrutural maior do que os p?s misturados, se as amostras forem aquecidas acima do ponto de fus?o do cobre. Ap?s o cobre atingir o ponto de fus?o, o cobre l?quido deixa as part?culas comp?sitas e preenche os poros
200

Caracteriza??o de comp?sitos Nb-20%cu obtidos por moagem de alta energia e sinterizados por fase l?quida

Melchiors, Gilberto 31 January 2011 (has links)
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

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