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1
Qiu, Xiaoyu. "Procédé d'exfoliation du graphite en phase liquide dans des laboratoires sur puce". Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI056/document.
Testo completoAbstract (sommario):
L’exfoliation en phase liquide du graphite est un procédé simple susceptible de produire du graphène à faible coût. Ces dernières années, de nombreuses équipes ont exploité la cavitation acoustique et la cavitation hydrodynamique comme moyen d’exfoliation. La cavitation acoustique ne peut traiter qu’une quantité limitée de fluide et génère des défauts sur la structure du graphène,tandis que la cavitation hydrodynamique dans une solution en écoulement n’agit que localement pendant une durée très brève. Les équipes de recherche utilisant ce dernier procédé compensent cette brièveté en imposant à la solution chargée en graphite des différences de pression très fortes, et utilisent alors des infrastructures macroscopiques lourdes pour lesquelles il est difficile de distinguer le rôle du cisaillement de celui de la cavitation. Nous avons cherché à développer un nouveau procédé d’exfoliation basé sur l’utilisation de microsystèmes fluidiques capables de générer un écoulementcavitant avec un débit supérieur à 10 L/h pour une différence de pression modérée n’excédant pas 10 bar. Une nouvelle génération de laboratoires ‘sur puce’ a ainsi été imaginée et réalisée, permettant de traiter des solutions surfactées chargées en microparticules de graphite. Il est apparu que laconcentration solide et la durée de traitement sont des paramètres cruciaux pour l’efficacité du procédé. Par rapport à un écoulement monophasique laminaire microfluidique, l’écoulement cavitant produit plus de produits exfoliés et de graphène, avec un rendement de l’ordre de 6%. Ceci indique que l’implosion des bulles et la turbulence favorisent également les interactions entre particules. Ce procédé d’exfoliation microfluidique, qui ne nécessite une puissance que de quelques Watts, permet d’envisager à terme une production économe et écologique de graphène en suspensionLiquid phase exfoliation of graphite is a simple and low-cost process, that is likely to produce graphene. The last few years, many researchers have used acoustic or hydrodynamic cavitation as an exfoliating tool. Acoustic cavitation is limited to low volumes and defects are present on the graphenesheets ; hydrodynamic cavitation inside a flowing solution acts briefly. So, people are using big reactors running with high pressure drops, and it is difficult from a fundamental point of view to know the physical role of shear rate versus cavitation, in the exfoliation process. We have tried to develop a new process funded on hydrodynamic cavitation ’on a chip’, with flow rates above 10 L/h and pressure drop below 10 bar. A new generation of ’labs on a chip’ has been designed and performed, processing with aqueous surfactant graphite solutions. The solid concentration and the duration of the process have proved to be key parameters. Cavitating microflows have exhibited a better efficiency (up to ~6%) than laminar liquid microflows, for the production of graphene flakes. Collapsing bubbles and turbulence are also likely to enhance particles interactions. Such a microfluidic process, which requires an hydraulic power of a few Watt, makes possible a further low-cost and green production of graphene sheets
2
Ballestar, Ana. "Superconductivity at Graphite Interfaces". Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-141196.
Testo completoAbstract (sommario):
The existence of superconductivity in graphite has been under discussion since the 1960s when it was found in intercalated graphitic compounds, such as C8K, C8Rb and C8Cs. However, it was only about 40 years ago when the existence of superconductivity in pure graphite came up. In this work we directly investigate the interfaces highly oriented pyrolytic graphite (HOPG) has in its inner structure, since they play a major role in the electronic properties. The results obtained after studying the electrical transport provide clear evidence on granular superconductivity localized at the interfaces of graphite samples. Zero resistance states, strong current dependence and magnetic field effect on the superconducting phase support this statement. Additionally, an abrupt reduction in the measured voltage at temperatures from 3 to 175 K has been observed. However, the upper value of this transition temperature seems to not have been reached yet. A possible method to enhance it is to increase the carrier density of graphite samples. In order to preserve to quasi-two-dimensional structure of highly oriented pyrolytic graphite, chemical doping has been dismissed in the frame of this work. We used an external electric field to move the Fermi level and, hence, try to trigger superconductivity in multi layer graphene samples. A drop on the resistance at around 17 K has been measured for a large enough electric field applied perpendicular to the graphene planes. This transition is strongly affected by magnetic field and only appeared at low temperatures. As a result of the studies included in this work, it appears clear that graphite has a superconducting phase located at certain interfaces with a very high transition temperature.
3
Yu, Wenlong. "Infrared magneto-spectroscopy of graphite and graphene nanoribbons". Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/54244.
Testo completoAbstract (sommario):
The graphitic systems have attracted intensive attention recently due to the discovery of graphene, a single layer of graphite. The low-energy band structure
of graphene exhibits an unusual linear dispersion relation which hosts massless Dirac fermions and leads to intriguing electronic and optical properties. In particular, due to the high mobility and tunability, graphene and graphitic materials have been recognized as promising candidates for future nanoelectronics and optoelectronics. Electron-phonon coupling (EPC) plays a significant role in electronic and optoelectronic devices. Therefore, it is crucial to understand EPC in graphitic materials and then manipulate it to achieve better device performance. In the first part of this thesis, we explore EPC between Dirac-like fermions and infrared active phonons in graphite via infrared magneto-spectroscopy. We demonstrate that the EPC can be tuned by varying the magnetic field. The second part of this thesis deals with magnetoplasmons in quasineutral graphene nanoribbons. Multilayer epitaxial graphene grown on the carbon terminated silicon carbide surface behaves like single layer graphene. Plasmons are excited in the nanoribbons of undoped multilayer epitaxial graphene. In a magnetic field, the cyclotron resonance can couple with the plasmon resonance forming the so-called upperhybrid mode. This mode exhibits a distinct dispersion relation, radically different from that expected for conventional two dimensional systems.
4
Solane, Pierre-Yves. "Spectroscopie optique du graphite-graphène sous champs mégagauss". Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1874/.
Testo completoAbstract (sommario):
La découverte expérimentale du graphène (monocouche de graphite) en 2004 a provoqué un grand engouement dans la communauté scientifique. Cela a également renouvelé l'intérêt pour l'étude du graphite. Les propriétés de ces deux matériaux ont largement été étudiées par le biais de différentes techniques expérimentales (transport, optique. . . ). Dans cette thèse nous démontrons que les mesures de transmission effectuées sous champ magnétiques très intenses (> 1 millions de fois le champ magnétique terrestre) sont un outil très puissant pour étudier la structure électronique du graphène et du graphite. Dans un premier temps, nous montrerons que l'asymétrie électron-trou dans le graphite est causée par le terme souvent négligé de l'énergie cinétique d'un électron libre. Ce terme, également présent dans l'Hamiltonien décrivant les propriétés électroniques du graphène, explique élégamment l'asymétrie électron trou qui y est observée. Deuxièmement, l'utilisation de nombreuses sources dans l'infrarouge et dans le visible (200meV à 2eV) nous a permis d'observer de grandes séries de transitions interbandes dans le graphite entre les quatre bandes (E3+, E3-, E1 et E2) jusqu'à 150 T et à température ambiante. La résonance au point K peut être parfaitement décrite avec le modèle du bicouche effectif et la résonance au point H correspond à celle d'une monocouche de graphène. Enfin, nous démontrerons que ces résonances peuvent être réduites à une simple mesure de la relation de dispersion décrite par la formule relativiste E2=m02v4 + p2v2, avec v la vitesse de Fermi et, où l'énergie d'une particule au repos m0v² est égale à 385 meV au point K et est nulle au point HSince its experimental discovery in 2004, graphene (a single layer of graphite) has attracted a lot of attention. It also leads to a renewed interest in graphite. Subsequently, both these materials have extensively been studied using different experimental techniques. In this thesis we demonstrate that transmission measurements performed in extremely high magnetic field (> 1 million times the earth's magnetic field) are a very useful tool to investigate the electronic structure of graphene and graphite. In particular, we will demonstrate that electron-hole asymmetry in graphite is caused by the often neglected free-electron kinetic energy term. This term is also present in the Hamiltonian describing electronic properties of graphene, hence it will lead to an asymmetry in graphene. Additionally, using near-infrared and visible sources from 200meV to 2eV we observe strong series of interband transitions in graphite between the four interlayer split bands (E3+, E3-, E1 and E2) up to 150 T at room temperature. The K-point electron resonances can be described well using an effective bilayer graphene model and the H-point transitions correspond to monolayer graphene. It is demonstrated that this can be reduced to a single measurement of the dispersion relation which is described by the relativistic formula where E2=m02v4 + p2v2 with v the Fermi velocity and a single particle rest energy m0v² of 385 meV for the K-point electrons and zero as expected for the H-point
5
Geng, Yan. "Preparation and characterization of graphite nanoplatelet, graphene and graphene-polymer nanocomposites /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MECH%202009%20GENG.
Testo completo
6
Risley, Mason J. "Surfactant-assisted exfoliation and processing of graphite and graphene". Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48980.
Testo completoAbstract (sommario):
Surfactant assisted solution exfoliation of expanded graphite by means of sonication was carried out in an attempt to produce non-covalent charge functionality on the surface of graphene for the directed self assembly of graphene films on patterned substrates via electrostatic interactions. This thesis includes the results of experimental research associated with: 1) quantifying the effectiveness of various di-functionalized dithienothiophene surfactant small molecules, 2) further understanding the surface affinity and interaction mechanism between these surfactant molecules and the surface of expanded graphite and graphene and 3) experimentally testing the feasibility of the directed self-assembly of graphene films by means of charge functionalization of graphene by the surfactant molecules adsorbed onto the surface of exfoliated graphene.
7
Abro, Mehwish. "Modelling the exfoliation of graphite for production of graphene". Thesis, Uppsala universitet, Fasta tillståndets elektronik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-272339.
Testo completoAbstract (sommario):
The aim of my thesis is to make a theoretical model of data obtained from liquid-phase exfoliation of graphene. The production of graphene in the liquid phase exfoliation is a cost efficient method One part of this work is devotedto learn the method of production of graphene by the shear mixing technique from the graphite and to estimate some important parameters which are crucial for the process. Other part of my work is based on studying the liquid-phase exfoliation mechanism of graphene through ultrasonication technique. This method is time consuming as compared to shearmixing.
8
Alofi, Ayman Salman Shadid. "Theory of phonon thermal transport in graphene and graphite". Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/15687.
Testo completoAbstract (sommario):
Thermal properties of graphene and graphite have been investigated by employing the analytical expressions for the phonon dispersion relations and the vibrational density of states derived by Nihira and Iwata, which are based on the semicontinuum model proposed by Komatsu and Nagamiya. The thermal conductivities of graphene and graphite are computed within the framework of Callaway’s effective relaxation time theory. The Normal-drift contribution (the correction term in Callaway’s theory) produces a significant addition to the result obtained from the single-mode relaxation time theory, clearly suggesting that the single-mode relaxation time approach alone is inadequate for describing the phonon conductivity of graphene. Its contribution to the thermal conductivity arises from the consideration of the momentum conserving nature of three-phonon Normal processes and is found to be very important for explaining the magnitude as well as the temperature dependence of the experimentally measured results for graphene and graphite. This model has not been implemented before for studying the thermal conductivity of graphene. Also the model has been applied to compute the thermal conductivity of graphene, graphite basal planes, and graphite c-axis. This has further been used to investigate the evolution of thermal properties from graphene to graphite as a function of layer thickness and temperature. The effects of isotopes and tensile strain on the graphene thermal properties have been examined within this model and compared with other available studies.
9
Shokri, Roozbeh [Verfasser], e Günter [Akademischer Betreuer] Reiter. "Self-Assembly of supra-molecular systems on graphene or graphite = Selbstorganisation von Supramolekularen Systemen auf Graphen oder Graphit". Freiburg : Universität, 2013. http://d-nb.info/1123475415/34.
Testo completo
10
Csapo-Hounkponou, Elisabeth. "Etude du comportement tribologique de couples graphite/cuivre et graphite/graphite dans un contact électrique glissant". Vandoeuvre-les-Nancy, INPL, 1993. http://www.theses.fr/1993INPL152N.
Testo completo
11
Solane, P. Y. "Spectroscopie Optique du Graphite et du Graphène sous Champ Mégagauss". Phd thesis, Université Paul Sabatier - Toulouse III, 2012. http://tel.archives-ouvertes.fr/tel-00777855.
Testo completoAbstract (sommario):
La découverte expérimentale du graphène (monocouche de graphite) en 2004 a provoqué un grand engouement dans la communauté scientifique. Cela a également renouvelé l'intérêt pour l'étude du graphite. Les propriétés de ces deux matériaux ont largement été étudiées par le biais de différentes techniques expérimentales (transport, optique...). Dans cette thèse nous démontrons que les mesures de transmission effectuées sous champ magnétiques très intenses (> 1 millions de fois le champ magnétique terrestre) sont un outil très puissant pour étudier la structure électronique du graphène et du graphite. Dans un premier temps, nous montrerons que l'asymétrie électron-trou dans le graphite est causée par le terme souvent négligé de l'énergie cinétique d'un électron libre. Ce terme, également présent dans l'Hamiltonien décrivant les propriétés électroniques du graphène, explique élégamment l'asymétrie électron trou qui y est observée. Deuxièmement, l'utilisation de nombreuses sources dans l'infrarouge et dans le visible (200meV à 2eV) nous a permis d'observer de grandes séries de transitions interbandes dans le graphite entre les quatre bandes (E3+, E3-, E1 et E2) jusqu'à 150 T et à température ambiante. La résonance au point K peut être parfaitement décrite avec le modèle du bicouche effectif et la résonance au point H correspond à celle d'une monocouche de graphène. Enfin, nous démontrerons que ces résonances peuvent être réduites à une simple mesure de la relation de dispersion décrite par la formule relativiste E2=m02v4 + p2v2, avec v la vitesse de Fermi et, où l'énergie d'une particule au repos m0v² est égale à 385 meV au point K et est nulle au point H.
12
Sokolov, Denis A. "Investigation of Graphene Formation from Graphite Oxide and Silicon Carbide". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/53642.
Testo completoAbstract (sommario):
Graphene is a novel two dimensional material that is revolutionizing many areas of science and it is no surprise that a significant amount of effort is dedicated to its investigation. One of the major areas of graphene research is the development of procedures for large scale production. Among many recently developed methodologies, graphene oxide reduction stands out as a straightforward and scalable procedure for producing final material with properties similar to those of graphene. Laser reduction of graphite oxide is one of the novel approaches for producing multilayer graphene, and this work describes a viable approach in detail. It is determined that a material which is comprised of a combination of laser reduced graphite oxide-coupled to an unreduced graphite oxide layers beneath it, produces a broadband photosensitive material. The efficiency of light conversion into electrical current is greatly dependent upon the oxygen content of the underlying graphite oxide. Developing novel ways for reducing graphite oxide is an ongoing effort. This work also presents a new method for achieving complete reduction of graphite oxide for producing predominantly sp2 hybridized material. This approach is based on the irradiation of graphite oxide with a high flux 3 keV Ar ion beam in vacuum. It is determined that the angle of irradiation greatly influences the final surface morphology of reduced graphite oxide. Also, multilayer epitaxial graphene growth on silicon carbide in ultra-high vacuum was investigated with quadrupole mass spectrometry (QMS). Subliming molecular and atomic species were monitored as a function of temperature and heating time. The grown films were characterized with X-ray photoelectron spectroscopy coupled with Ar ion depth profiling.
13
Cuharuc, Anatolii S. "Electron transfer on graphene and graphite : theoretical and experimental study". Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/78764/.
Testo completoAbstract (sommario):
The redox behaviour of several couples on highly oriented pyrolytic graphite (HOPG) and graphene has been studied using both micro- and macroscopic measurements supported by detailed analysis. The ET kinetics of Ru(NH3)6 3+/2+ , (ferrocenylmethyl)trimethylammonium (FcTMA2+/+ ), and ferrocenylcarboxylic acid (FcCOO-/0 ) was found fast, on the time-scale of voltammetric measurements, on a freshly cleaved HOPG surface, but on “aged” one, Ru(NH3)6 3+/2+ exhibited sluggish ET, showing quite unusual macroscopic cyclic voltammograms. The other two couples retained their fast response on an “aged” surface. The surface of “aged” HOPG is proposed to consist of graphene layers of different thicknesses, which, from graphite to monolayer graphene, have progressively diminishing capacity to support fast ET specifically for Ru(NH3)6 3+/2+ . Such a redox-selectivity correlates with the position of formal potentials of the three redox couples relative to the band structure of graphene, with Ru(NH3)6 3+/2+ being most close to the minimum in density of states (DOS) of undoped monolayer graphene. Based on macroscopic voltammetry, low grade HOPG, whose surface is abundant with step edges, was found not to be redox-selective in the sense described above, meaning that its “aged” surface was as good as fresh one. It is highly likely that step edges being a type of crystal lattice defects, retain their capacity for fast ET, which correlates with their elevated DOS, and, thus, secure fast voltammetric response of low grade HOPG in macroscopic experiments on these complex “aged” surfaces. IrCl6 2-/3- , Fe(CN)6 3-/4- and the three couples discussed above were all found to have fast electrochemistry on freshly cleaved surfaces of high grade HOPG. Estimated heterogeneous rate constants were > 0.1 cm s- 1 for Ru(NH3)6 3+/2+ and > 1.7 cm s- 1 for IrCl6 2-/3-and Fe(CN)6 3-/4 . This suggests that basal planes of graphite have, though low, but sufficient DOS to perform ET at a rate comparable with that on some metals. Furthermore, these results unarguably defy those opinions, that have been long circulating in the published literature, stating that basal plane of HOPG (and also sidewalls of carbon nanotubes) are nearly inert towards ET and that the defects were solely responsible for the observed electrochemical activity of this material. The study of adsorption of three ferrocene derivatives on HOPG revealed FcTMA+ and FcCOO- adsorb weakly and approximately equally whereas zero-charged FcCH2OH adsorbs notably more strongly. The adsorption was studied with cyclic voltammetry and quantitative information was extracted from the experimental data basing on a simple dedicated theory developed in this thesis. The “aged” surface of high grade HOPG exhibited enhanced adsorption as compared to fresh one, but low grade HOPG did not show the difference. It is suggested that the highly flat surface of high grade HOPG (large terraces widths) facilitates formation of airborne contaminating film made of hydrocarbons on, which serves as a “trap” for ferrocene derivatives owing to their largely non-polar ferrocene moieties.
14
Arbuzov, A. A., V. E. Muradyan e B. P. Tarasov. "Synthesis of Few-layer Graphene Sheets via Chemical and Thermal Reduction of Graphite Oxide". Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35063.
Testo completoAbstract (sommario):
Few-layer graphene sheets were produced from graphite oxide (GO) chemical and thermal reduction.
For the chemical reduction of GO as reducing agents were used hydrazine hydrate, hydroxylammonium
chloride, sodium borohydride and sodium sulfite. The reduced material was characterized by elemental
analysis, thermo-gravimetric analysis, scanning electron microscopy, X-ray diffraction, Fourier transform
infrared and Raman spectroscopy. A comparison of the deoxygenation efficiency of graphene oxide suspension by different method or reductants has been made, revealing that the highest degree of reduction was
achieved by thermal reduction and using hydrazine hydrate and hydroxylammonium chloride as a reducing agents.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35063
15
Salamanca-Riba, Lourdes G. "Structural studies of graphite intercalation compounds and ion implanted graphite". Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/97287.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Includes bibliographical references.
by Lourdes G. Salamanca-Riba.
Ph.D.
16
Herraiz, Michael. "Graphène et fluorographène par exfoliation de graphite fluoré : applications électrochimiques et propriétés de surface". Thesis, Université Clermont Auvergne (2017-2020), 2018. http://www.theses.fr/2018CLFAC094/document.
Testo completoAbstract (sommario):
Sa conductivité électronique ou encore sa transparence optique sont autant de propriétés physico-chimiques singulières du graphène qui expliquent le nombre accru de méthodes d’exfoliation de précurseurs graphitiques développées pour l’obtention de ce matériau. Pour palier à l’utilisation d’un oxyde de graphite/graphène caractérisé par une chimie de surface mal maitrisée, des graphites fluorés, de cristallinité mais aussi de concentration en fluor variables, ont été préparés par fluoration de graphite sous fluor moléculaire pur après optimisation des paramètres. Les précurseurs, que ce soit par fluoration dynamique ou statique, ainsi obtenus ont été caractérisés finement : diffraction des rayons X, spectroscopies IR et Raman et leur texture sondée par Microscopie Electronique à Balayage et à Transmission. Suite à cela, trois méthodes d’exfoliation ont été mises en place, basées sur des mécanismes différents : i) une exfoliation par choc thermique, déjà connue mais dont les mécanismes de décomposition ont été affinés dans cette étude, ii) une exfoliation en voie liquide, avec l’utilisation pour la première fois d’un graphite fluoré pour la synthèse de graphène fluoré multi feuillets par voie électrochimique pulsée, et enfin iii) une méthode originale, peu conventionnelle, basée sur l’interaction laser femtoseconde/graphite hautement fluoré pour induire des mécanismes de réduction contrôlée, et surtout d’exfoliation de la matrice. Ces méthodes ont permis de mettre en évidence l’intérêt de la présence de fluor dans la course actuelle pour la synthèse de graphène, et ont montré l’obtention de matériaux graphéniques,possédant une fonction résiduelle fluorée intéressante pour certaines applicationsIts electronic conductivity or its optical transparency are unequaled physicochemicalproperties of graphene which explain the increased number of exfoliation methods based ongraphitic precursors to obtain this material. To overcome the use of a graphite/graphene oxidecharacterized by a poorly controlled surface chemistry, graphite fluorides, with variablecrystallinity and also fluorine concentration, were prepared by fluorination of graphite under puremolecular fluorine atmosphere after optimization of the process parameters. The obtainedprecursors, whether by dynamic or static fluorination, were characterized : X-Ray diffraction, FTIRand Raman spectroscopies for the structure, and their texture probed by Scanning andTransmission Electron Microscopy. After that, three methods of exfoliation were developed, basedon different mechanisms: i) a thermal shock, already known but decomposition mechanisms wererefined in this study, ii) an exfoliation within liquid medium by pulsed electrochemical treatment,using for the first time a fluorinated graphite for the synthesis of few-layered fluorinated grapheneand finally iii) an unconventional method, based on the interaction between femtosecond laser andhighly fluorinated graphite to induce mechanisms like controlled reduction, and especially for thisstudy exfoliation of the matrix. These methods have permit to highlight the interest of fluorine inthe current race for the synthesis of graphene, and have shown the production of graphenematerials, having an interesting fluorinated residual functionalization for some applications
17
Zhang, Guohui. "Electrochemistry and applications of sp2 carbon materials : from graphite to graphene". Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/89303/.
Testo completoAbstract (sommario):
This thesis can be divided into three themes: (i) the electrochemistry of sp2 carbon materials, with a focus on graphite and graphene, where electron transfer (ET) kinetics and surface functionalisation were considered; (ii) methodology development for graphene transfer, to facilitate the fabrication of versatile tools for microscopy research and allow the properties of supported and suspended graphene to be readily assessed and compared; (iii) the electrowetting of graphite, providing a new mechanism for droplet actuation on a conducting surface with an applied electric field. There is a large body of literature that the basal plane of highly oriented pyrolytic graphite (HOPG) is inert or has little electroactivity for outer-sphere redox couples and adsorbed species. Here, the model is revisited with the macroscopic ET kinetics studies of three classical (outer-sphere) redox couples on different grades of HOPG using a droplet-cell setup. It is shown that the ET kinetics for all of the redox species studied is fast on all grades of HOPG (comparable to metal electrodes), despite the low density of electronic states (DOS) on graphite. This is in line with the results where the ‘special’ redox couple, Fe3+/2+, associated with a slow kinetics, is tested. Moreover, localised surface mapping measurements of HOPG using scanning electrochemical cell microscopy (SECCM), reveal a relatively uniform activity on basal plane and step edges of HOPG towards Fe3+/2+, highlighting that the basal plane is electroactive and the major site for the ET kinetics of Fe3+/2+. The next goal is to elucidate whether adsorbed electroactive anthraquinone-2,6-disulfonate (AQDS) can be used as a marker of step edges, previously regarded as the main electroactive sites of graphite. Step edges are shown to have little effect on the extent of adsorbed electroactive AQDS in macroscopic studies. The amount of adsorbed electroactive AQDS and the ET kinetics are independent of the step edge coverage, as determined by fast scan cyclic voltammetry-SECCM. Further, SECCM reactive patterning shows essentially uniform and high activity across the basal surface of HOPG, indicative of the dominance of basal plane in HOPG electroactivity. Regarding the close relation between graphene and graphite, effort is put to introduce a polymer-free method for transferring chemical vapour deposition (CVD)-grown graphene, to arbitrary substrates, using an organic/aqueous biphasic configuration. Avoiding any polymeric contamination, graphene is coated on arbitrary substrates, such as atomic force microscopy (AFM) tips and transmission electron microscopy (TEM) grids, generating tools for conductive AFM and high resolution TEM imaging. Furthermore, electrochemical and wetting measurements at either a freestanding graphene film or a copper-supported graphene area, are readily made and compared. As an example of the myriad potential applications of graphite, electrowetting is demonstrated at HOPG, using cyclic voltammetry, with significant changes in contact angle and relative contact diameter seen. These are comparable to the widely studied electrowetting-on-dielectric (EWOD) system, but over a much lower voltage range. Electrowetting is found to be due to the intercalation/de-intercalation of anions between the graphene layers of graphite, driven by the applied potential, providing a new mechanism for electrowetting and diversifying the means by which electrowetting can be controlled and applied.
18
Xia, Jun. "Syntheses and studies of some graphite and graphite flouride intercalation compounds". Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/29823.
Testo completoAbstract (sommario):
The oxidative intercalation of S₂O₆F₂ into graphite ( SP-1 powder) in the gas phase has been studied. X-ray powder diffraction spectra shows that stage-1, stage-2 and stage-3 graphite fluorosulfates have been obtained. The compositions of these three compounds are C₇.₈SO₃F, C₁₅.₅SO₃F and C₂₄S0₃F according to gravimetry with the repeat space distances of 7.8lÅ, 11.08Å and 14.33Å respectively.
X-ray photoelectron spectroscopy (XPS) has been extensively used to study some graphite acceptor intercalation compounds. Two effects have been observed, charge transfer leads to higher binding energy and Fermi Level shift to the lower binding energy relative to that of graphite.
Graphite fluoride intercalation compounds of S₂O₆F₂, HSO₃F and HSO₃CF₃ have been synthesized by direct reactions. X-ray powder diffraction, XPS, IR, Raman and microanalysis have been employed to study these compounds.
The results show that:
A. There are some graphite islands in graphite fluorides, CF[formula omitted], when xChemistry, Department of
Graduate
19
Henni, Younes. "Etudes magnéto-Raman de systèmes - graphène multicouches et hétérostructures de graphène-nitrure de bore". Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY060/document.
Testo completoAbstract (sommario):
Comme le quatrième élément le plus abondant dans l’univers, le carbone joue un rôle important dans l’émergence de la vie sur la terre comme nous la connaissons aujourd’hui. L’ère industrielle a vu cet élément au cœur des applications technologiques en raison des différentes façons dont les atomes forment les liaisons chimiques, ce qui donne lieu à une série d’allotropies chacun ayant des propriétés physiques extraordinaires. Par exemple, l’allotrope le plus thermodynamiquement stable du carbone, le cristal de graphite, est connu pour être un très bon conducteur électrique, tandis que le diamant, très apprécié pour sa dureté et sa conductivité thermique, est néanmoins considéré comme un isolant électrique en raison de sa structure cristallographique différente par rapport au graphite. Les progrès de la recherche scientifique ont montré que les considérations cristallographiques ne sont pas le seul facteur déterminant pour une telle variété dans les propriétés physiques des structures à base de carbone. Ces dernières années ont vu l’émergence de nouvelles formes allotropiques de structures de carbone qui sont stables dans les conditions ambiantes, mais avec dimensionnalité réduite, ce qui entraîne des propriétés largement différentes par rapport aux structures en trois dimensions. Parmi ces nouvelles classes d’allotropes il y a le graphene, qui est le premier matériau à deux dimensions. L’isolation réussi de monocouches de graphène a contesté une croyance établie depuis longtemps en physique : le fait que les matériaux purement 2D ne peuvent pas exister dans les conditions ambiantes parce qu'ils sont instables en raison de l’augmentation des fluctuations thermiques lorsqu’ils se prolongent dans les 2D. Afin de minimiser son énergie, un matériau se brisera en îlots coagulées. Le graphène arrive cependant à surmonter cette barrière en formant des ondulations continues sur la surface du substrat et est stable même à température ambiante et pression atmosphérique. Une grande intention dans la communauté scientifique a été donnée au graphène, après les premiers résultats publiés sur les propriétés électroniques de ce matériau. Les propriétés fondamentales et mécaniques du graphène sont fascinants. Grace aux atomes de carbone qui sont emballés dans un mode sp2 hybridé, formant ainsi une structure de réseau hexagonal, le graphène possède le plus grand module de Young et la plus grande capacité d’étirement, en même temps des centaines de fois plus dur que l’acier. Il conduit la chaleur et l’électricité de manière très efficace. L’aspect le plus fascinant à propos du graphène est surement la nature de ses porteurs de charge à basse énergie. En effet, le graphène présente des bandes d’énergie linéaires au point de neutralité de charge, donnant aux porteurs de charge une nature relativiste. De nombreux phénomènes observés dans ce matériau sont des conséquences de la nature relativiste de ses porteurs. Transport balistique, conductivité optique universelle, absence de rétrodiffusion, et une nouvelle classe d’effet Hall quantique sont de bons exemples de phénomènes nouvellement découverts dans ce matériau. Il est cependant encore trop tôt pour affirmer que toutes les propriétés physiques du graphene sont bien comprises. Dans cette thèse, nous avons mené des expériences de spectroscopie magnéto-Raman pour répondre à certaines des questions ouvertes dans la physique du graphène, notamment l’effet de couplage de Coulomb sur le spectre d’énergie du graphène, et le changement dans les propriétés physiques du graphène multicouche en fonction de sa cristallographie. Nos echantillions ont été soumis à de forts champs magnétiques, appliqués perpendiculairement aux plans atomiques. Le spectre d’excitation sous champ magnétique montre un couplage entre ces excitations et les modes de vibratoires. Cette approche expérimentale permet de remonter à la structure de bande du graphene en champs nul, ainsi que de nombreuses autres propriétés du matériauAs the fourth most abundant element in the universe, Carbon plays an important rolein the emerging of life in earth as we know it today. The industrial era has seen this element at the heart of technological applications due to the different ways in which carbon forms chemical bonds, giving rise to a series of allotropes each with extraordinary physical properties. For instance, the most thermodynamically stable allotrope of carbon, graphite crystal, is known to be a very good electrical conductor, while diamond very appreciated for its hardness and thermal conductivity is nevertheless considered as an electrical insulator due to different crystallographic structure compared to graphite. The advances in scientific research have shown that crystallographic considerations are not the only determining factor for such a variety in the physical properties of carbon based structures. Recent years have seen the emergence of new allotropes of carbon structures that are stable at ambient conditions but with reduced dimensionality, resulting in largely different properties compared to the three dimensional structures. Among these new classes of carbon allotropes is the first two-dimensional material: graphene.The successful isolation of monolayers of graphene challenged a long established belief in the scientific community: the fact that purely 2D materials cannot exist at ambient conditions. The Landau-Peierls instability theorem states that purely 2D materials are very unstable due to increasing thermal fluctuations when the material in question extends in both dimensions. To minimize its energy, the material will break into coagulated islands, an effect known as island growth. Graphene happens to overcome such barrier by forming continuous ripples on the surface of its substrate and thus is stable even at room temperature and atmospheric pressure.A great intention from the scientific community has been given to graphene, since 2004. Both fundamental and mechanical properties of graphene are fascinating. Thanks to its carbon atoms that are packed in a sp2 hybridized fashion, thus forming a hexagonal lattice structure, graphene has the largest young modulus and stretching power, yet it is hundreds of times stronger than steel. It conducts heat and electricity very efficiently, achieving an electron mobility as high as 107 cm−2V−1 s−1 when suspended over the substrate. The most fascinating aspect about graphene is the nature of its low energy charge carriers. Indeed, graphene has a linear energy dispersion at the charge neutrality, giving the charge carriers in graphene a relativistic nature. Many phenomena observed in this material are consequences of this relativistic nature of its carriers. Ballistic transport, universal optical conductivity, absence of back-scattering, and a new class of room temperaturequantum Hall effect are good examples of newly discovered phenomena in thismaterial. Graphene has become an active research area in condensed matter physics since 2004. It is however still early to state that all the physical properties of this material are well understood. In this thesis we conducted magneto-Raman spectroscopy experiments to address some of the open questions in the physics of graphene, such as the effect of electron-electron coupling on the energy spectrum of monolayer graphene, and the change in the physical properties of multilayer graphene as a function of the crystallographic stacking order. In all our experiments, the graphene-based systems have been subject to strong continuous magnetic fields, applied normal to the graphene layers. We study the evolution of its energy excitation spectra in the presence of the magnetic field, and also the coupling between these excitations and specific vibrational modes that are already in the system. This experimental approach allows us to deduce the band structure of the studied system at zero field, as well as many other lowenergy properties
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Song, Zhimin. "Fabrication and Characterization of Nanopatterned Epitaxial Graphene Films for Carbon Based Electronics". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/13943.
Testo completoAbstract (sommario):
In this thesis, we show that planar graphene ribbons have properties similar to those of nanotubes. Both exhibit semiconducting or metallic properties depending on crystal orientation. The band gap varies approximately as the inverse of the ribbon width. Both can be doped and gated. Due to these similarities, the patterned graphene also has nanotube like transport properties, which include coherent transport, ballistic transport, and high current capabilities. In essential contrast to nanotubes, graphene ribbons can be rationally patterned using standard electron beam lithography methods; functional graphene devices could be fabricated eliminating the need for metal interconnects on the wafer. This would remove many obstacles faced by carbon nanotubes, while retaining the benefits of high carrier mobility and quasi-1D transport.
We have produced ultrathin epitaxial graphite films on single-crystal silicon carbide by vacuum graphitization, which show remarkable 2D electron gas (2DEG) behavior. The most highly ordered samples exhibit Shubnikov-de Haas oscillations that correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nanopatterned epitaxial graphene (NPEG) with the potential for large-scale integration. The research created a foundation for graphene science and technology and established a path toward graphene-based nanoelectronics.
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Smith, Richard Alan Paul. "Photoemission and tunnelling microscopy studies of graphite and argon ion irradiated graphite". Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269571.
Testo completo
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Rida, Hania. "Nouvelles données sur les systèmes graphite-lithium-europium et graphite-lithium-calcium". Thesis, Nancy 1, 2011. http://www.theses.fr/2011NAN10019/document.
Testo completoAbstract (sommario):
La méthode solide-liquide en milieu alliage fondu à base de lithium a permis ces dernières années la synthèse de plusieurs composés d'intercalation du graphite (CIG) insérés à coeur au sein des systèmes graphite-lithium-alcalino-terreux. Dans le cadre de cette thèse, cette méthode de synthèse a été étendue aux systèmes graphite-lithium-lanthanoïde, avec une difficulté supplémentaire qui est la méconnaissance des diagrammes de phases binaires lithium-lanthanoïde dont les données sont capitales pour déterminer les domaines de température et de composition chimique des alliages susceptibles de conduire à des CIG. L'immersion de plaquettes de pyrographite dans certains alliages lithium-europium judicieusement choisis a mené à un composé binaire EuC6 ainsi qu'à un composé ternaire graphite-lithium-europium de premier stade.La cinétique de formation de EuC6 a été suivie par diffraction des rayons X ex situ afin de comprendre les différentes étapes de la réaction et d'identifier les phases intermédiaires menant au composé final thermodynamiquement stable. Ce mécanisme révèle un processus réactionnel plus « coopératif » que celui menant au composé CaC6 et a été décrit par une succession d'étapes contribuant à l'insertion à coeur de l'europium.La composition élémentaire du composé ternaire a été déterminée grâce à une analyse par faisceau d'ions qui a permis de doser simultanément les trois éléments lithium, carbone et europium. Le résultat de cette analyse a conduit à la formule chimique Li0,25Eu1,95C6. EuC6 a également été étudié par microsonde nucléaire, le rapport atomique C/Eu de 6 a ainsi notamment pu être confirmé.Des études structurales ont été menées pour les composés binaires et ternaires. D'une part, il a été possible d'effectuer la résolution structurale complète du binaire EuC6, qui cristallise dans une maille hexagonale de groupe d'espace P63/mmc. D'autre part pour le ternaire Li0,25Eu1,95C6, la séquence d'empilement poly-couche selon l'axe c du feuillet inséré a été modélisée, par combinaison des données structurales avec les informations issues de l'analyse par faisceau d'ions.Les composés d'intercalation du graphite sont des solides de basse dimensionnalité qui se prêtent idéalement à l'étude des relations structure-propriétés. Ainsi dans le système graphite-lithium-calcium, le caractère supraconducteur des composés CaC6 et Li3Ca2C6 a été étudié par spectroscopie de spin de muon ([mu]SR). Pour le système graphite-lithium-europium, des mesures magnétiques réalisées préalablement à ce travail ont été poursuivies et complétées par des analyses [mu]SR (pour Li0,25Eu1,95C6 et EuC6) ainsi que par spectrométrie Mössbauer de 151Eu (pour Li0,25Eu1,95C6) à basse températureThe molten alloy solid-liquid method containing lithium has recently enabled the synthesis of several bulk graphite intercalation compounds (GICs) in graphite-lithium-alkaline earth metal systems. As part of this thesis, this synthesis method was extended to graphite-lithium-lanthanide systems, with an additional difficulty which is the lack of knowledge of lithium-lanthanide binary phase diagrams whose data are crucial for determining the temperature range and chemical composition of alloys that may lead to GICs.The immersion of pyrographite platelets in some europium-lithium alloys wisely chosen led to a binary EuC6 compound as well as a graphite-lithium-europium first stage ternary compound.Kinetics study of EuC6 compound was followed by ex situ X-ray diffraction in order to understand the different reaction steps and identify intermediate phases leading to the thermodynamically stable final compound. This mechanism revealed a reaction process more "cooperative" than that leading to CaC6 binary compound and was described by a succession of steps that contribute to the bulk insertion of europium.The elementary composition of the ternary compound was determined by ions beam analysis allowing the simultaneous quantification of the three elements lithium, carbon and europium. The refinement of these analyses led to the chemical formula Li0,25Eu1,95C6 for the ternary compound. EuC6 has also been studied by nuclear microprobe analysis, and especially the C/Eu atomic ratio equal to 6 has been confirmed.Structural studies have been undertaken for binary and ternary compounds. On one hand, it was possible to fully resolve the three-dimensional structure of the binary EuC6, which crystallizes in a hexagonal unit cell with P63/mmc space group. On the other hand, the c axis stacking sequence of the poly-layered intercalated sheet of the ternary compound was modeled by combining structural data with information from the ions beam analysis. The graphite intercalation compounds are low-dimensional solids that are ideal for the study of structure-properties relations. Thus in graphite-lithium-calcium system, superconducting character has been studied for CaC6 and Li3Ca2C6 compounds by muons spin spectroscopy ([mu]SR). For the graphite-lithium-europium system, previous magnetic measurements have been continued and supplemented by [mu]SR analysis (for Li0,25Eu1,95C6 and EuC6) and by low temperature 151Eu Mössbauer spectroscopy (for Li0,25Eu1,95C6)
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Dandan, Satia Mohd Saidina. "Fabrication et caractérisation d’encres à base de graphène pour l’électronique souple". Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0091/document.
Testo completoAbstract (sommario):
L'objectif principal de la présente étude est de développer des encres à base de graphène présentant d'excellentes propriétés de stabilité, électriques et physiques pour l'électronique d'impression en utilisant des techniques de revêtement par pulvérisation et d'impression par jet d'encre. Premièrement, la comparaison des différents types de matériaux similaires au graphène a montré que la mousse de graphène (GF) présentait la plus grande surface spécifique avec une valeur de 2136 m2g-1. Par ailleurs, les nanoplaquettes de graphite (GNPs) et le graphite synthétique (SG) présentaient des structures hautement cristallines avec la présence d'un pic aigu et étroit (002) et de particules de haute qualité avec un rapport ID/IG inférieur. Deuxièmement, les résultats ont montré que la viscosité et l'angle de contact des encres conductrices augmentaient significativement avec l'augmentation des charges de GF, GNPs et SG dans un liant de vernis polyester (PV). L'incorporation de 10 % en volume de PNB a amélioré la conductivité électrique du PV de 186 %, et seulement 40 % pour la SG et 10 % pour le GF avec la même charge de remplissage. Ensuite, il a été constaté que les PNB dispersés dans l'éthylène glycol (EG) présentaient une meilleure stabilité avec une diminution de 85% de la concentration initiale après un mois, une viscosité et une mouillabilité supérieures à celles du propylène glycol (PG) et du 2-propanol (IPA). D'autre part, le GF dispersé dans un solvant mélangé IPA:EG avec un rapport de 1:1 n'a montré qu'une diminution de 50 % par rapport à la concentration initiale après un mois comparant à ceux des encres GNP dans le même rapport de mélange. Dans la dernière partie, l'encre hybride GF/poly(3,4-éthylènedioxythiophène) poly(styrène-sulfonate) (PEDOT:PSS) a montré une meilleure stabilité que l'encre hybride GF et l'encre hybride GF/nanoparticules d’argent (AgNPs) où l'encre a montré 30 % de réduction de concentration après un mois, 100 % d'amélioration en termes de conductivité superficielle à 50 couches imprimées et un facteur de gauge de 4.3. En conclusion, l'encre hybride imprimée GF/PEDOT:PSS a le potentiel d'être utilisée pour les applications de capteurs de contrainteThe main aim of the present study is to develop graphene-based ink with excellent stability, electrical and physical properties for printing electronics by utilizing spray coating and inkjet printing techniques. Firstly, comparison on the different types of graphene-like materials showed that graphene foam (GF) exhibited the highest surface area with the value of 2136 m2g-1. Meanwhile, graphite nanoplatelets (GNPs) and synthetic graphite (SG) displayed highly crystalline structures with the presence of sharp and narrow (002) peak, and high-quality particles with lower ID/IG ratio. Secondly, results showed that viscosity and contact angle of the conductive inks increased significantly with increasing GF, GNPs and SG filler loadings in a polyester varnish (PV) binder. The incorporation of 10 vol.% GNPs improved the electrical conductivity of PV by 186 %, and only 40 % for SG and 10 % for GF at the same filler loading. Next, it is found that GNPs dispersed in ethylene glycol (EG) exhibited better stability with 85 % decrement of the initial concentration after a month, viscosity and wettability than those of propylene glycol (PG) and 2-propanol (IPA). On the other hand, GF dispersed in IPA:EG mixed solvent at ratio of 1:1 showed only 50 % decrement from the initial concentration after a month compared to those of GNPs inks at the same mixed ratio. In the last part, GF/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) hybrid ink exhibited better stability than GF ink and GF/silver nanoparticles (AgNPs) hybrid ink where the ink showed 30 % decrement from the concentration after a month, 100 % improvement in surface conductivity at 50 printed layers and gauge factor of 4.3. As a conclusion, printed GF/PEDOT:PSS hybrid ink has the potential to be used for strain sensor applications
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Gaskell, Peter. "Optical measurements of graphene and thin graphite films on low index substrates". Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66999.
Testo completoAbstract (sommario):
The optical and electrical properties of the recently isolated two dimensional crystal graphene are explored in detail, both theoretically and experimentally. The physical theory for the behavior of electrons in graphene is introduced. Electromagnetic theory is applied to the understanding of optical measurements on graphene samples. Original work on the measurement of layers on bulk transparent substrates is presented. A design for a free space optical instrument intended to make optical measurements on graphene is shown in detail, and measurements made with the system are presented. Finally, suggestions are made for future experiments that could be performed with the designed instrument.Les propriétés optiques et électriques du crystal bi-dimensionel graphene qui a été récemment isolésont explorées en détail de façon théorique et expérimentale. La théorie physique pour le comportement des électrons est également présentée. La théorie électromagnétique est révisée de façon générale et utilisée comme cadre afin de comprendre les mesures optiques prises sur des échantillons de graphene. Une mesure du nombre de couches sur des substrats transparents est présentée de façon originale. Un plan pour un instrument de mesure optique pouvant prendre des mesures dans l'espace libre est présenté en détail. De plus, des mesures prises avec le système sont également présentées. Finalement, des expériences futures à faire sur l'instrument présenté sont suggérées.
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Espeland, Erlend. "Gold Nanostructures on Graphite". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22433.
Testo completoAbstract (sommario):
Gold nanoparticles supported on a graphite substrate are prepared by thermal evaporation, and subsequently studied by X-ray photoelectron spectroscopy (XPS), temperature programmed desorption (TPD) of carbon monoxide and scanning electron microscopy (SEM).Increasing the amount of gold deposited leads to a shift of the desorption peak to higher temperatures, and the gold particles become larger.Depositing approximately the same amount of gold at different evaporation ratios does not seem to affect the desorption.Triangularly shaped gold particles appeared at higher evaporation rates.This is thought to be caused by diffusion effects dominating the formation of the particles.
26
Theodosiou, Alex. "Simulation of irradiated graphite". Thesis, Cardiff University, 2010. http://orca.cf.ac.uk/55507/.
Testo completo
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Schneider, Johannes. "Propriétés électroniques du graphite". Grenoble, 2010. http://www.theses.fr/2010GRENY047.
Testo completoAbstract (sommario):
Dans cette thèse le magnétotransport à basse température (T = 10 mK) et l'effet de Haas-van Alphen sont examinés pour le graphite naturel et le graphite HOPG. Dans la première partie, le magnétotransport au champ magnétique jusqu'à B = 11 T est présenté. Une analyse de Fourier du signal après soustraction du fond de magnétorésistance montre que le transport électrique dans le graphite est dominé par deux types de porteurs avec des fréquences et phases en accord avec le modèle SWM. Nous confirmons la validité du modèle SWM par des calculs détaillés de la structure de bande en champ magnétique. Le mouvement de l'énergie de Fermi pour B > 2 T est calculé d'une manière auto-cohérente en supposant que la somme des concentrations des électrons et des trous est constante. Des mesures sous champs magnétiques intenses (0 < B < 28 T) sont employées pour étudier l'effet Zeeman et la phase de l'onde de densité de charge. En ce qui concerne l'effet Zeeman, les calculs SWM incluant le mouvement de l'énergie de Fermi nécessitent un facteur de Lande g = 2. 5 pour reproduire la séparation de spin des motifs dans les données. Les mesures de l'onde de charge de densité confirment que le champ magnétique auquel l'onde de charge de densité apparait est lie a la température par une formule de type Bardeen-Cooper-Schrieffer (BCS). Des mesures de l'effet de Haas-van Alphen confirment les résultats obtenus par de magnétotransport à bas champIn this thesis, low-temperature magnetotransport (T = 10 mK) and the de Haas-van Alphen effect of both natural graphite and highly oriented pyrolytic graphite (HOPG) are examined. In the first part, low field magnetotransport up to B = 11 T is discussed. A Fourier analysis of the background removed signal shows that the electric transport in graphite is governed by two types of charge carriers, electrons and holes. Their phase and frequency values agree with the predictions of the SWM-model. The SWM-model is then confirmed by detailed band structure calculations using the magnetic field Hamiltonian of graphite. The movement of the Fermi at B > 2 T is calculated self-consistently assuming that the sum of the electron and hole concentration is constant. The second part of the thesis deals with high field magnetotransport of natural graphite in the magnetic field range 0 < B < 28 T. Both spin splitting of magnetotransport features in tilted field configuration and the onset of the charge density wave (CDW) phase for different temperatures with the magnetic field applied normal to the sample plane are discussed. Concerning the Zeeman effect, the SWM calculations including the Fermi energy movement require a g-factor of g = 2. 5 to reproduce the spin spilt features. The measurements of the charge density wave confirm that the onset magnetic field of the charge density wave state can be described by a Bardeen-Cooper-Schrieffer (BCS)-type formula. The measurements of the de Haas-van Alphen effect agree with the results of the magnetotransport measurements at low field
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Janot, Raphaël. "Mécanosynthèse en milieu liquide de composés graphite-lithium superdenses, de graphite très anisométrique et de maghémite supportée ou non sur graphite". Nancy 1, 2001. http://www.theses.fr/2001NAN10173.
Testo completoAbstract (sommario):
De nouveaux matériaux anodiques pour les batteries lithium-ion ont été préparés par mécanosynthèse. Dans le cas de la synthèse de composés graphite-lithium, un composé d'intercalation de stoechiométrie LiC3 est obtenu par broyage en milieu liquide. La mécanosynthèse est la première technique qui permet de préparer un composé aussi riche en lithium stable dans les conditions ambiantes. Le broyage de graphite seul en milieu liquide a également été étudié. En utilisant un broyeur planétaire, il est possible de préparer du graphite très anisométrique (facteur de forme voisin de 100) à partir d'un simple graphite naturel. Ce graphite est intéressant du point de vue électrochimique, puisqu'il présente une faible perte irréversible lors de la première charge. Enfin, par simple broyage de fer en milieu aqueux, des nanoparticules de maghémite ont été synthétisées. Ces dernières ont été dispersées sur du graphite anisotrope et les propriétés électrochimiques des composites ont été examinéesNew anodic materials for lithium-ion batteries are prepared by ball-milling. In the case of the graphite-lithium compounds synthesis, an intercalation compound with a LiC3 stoechiometry is obtained by grinding in liquid media. The ball-milling is the first technique, which allows to prepare a compound richer in lithium than the classical LiC6 and stable under ambient conditions. Ball-milling of natural graphite in liquid media was also studied. The use of a planetary ball-mill allows to prepare very anisometric graphite particles (geometrical anisotropy around 100). This graphite is interesting from the electrochemical point of view, since the corresponding irreversible capacity during the first charge is low. Finally, maghemite (γ Fe2O3) nanoparticles are synthesized by milling of iron powder within water. These grains are dispersed on anisometric graphite and the electrochemical properties of such composites are investigated
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Engelbert, Carl Robert. "Statistical characterization of graphite fiber for prediction of composite structure reliability". Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA238020.
Testo completoAbstract (sommario):
Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Wu, Edward M. "June 1990." Description based on signature page as viewed on October 21, 2009. DTIC Identifier(s): Graphite fiber strength testing, graphite fiber statistical evaluation. Author(s) subject terms: Graphite fiber strength testing, graphite fiber statistical evaluation, composite reliability predictions. Includes bibliographical references (p. 78-79). Also available in print.
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Precker, Christian E., Pablo D. Esquinazi, Ana Champi, José Barzola-Quiquia, Mahsa Zoraghi, Santiago Muinos-Landin, Annette Setzer et al. "Identification of a possible superconducting transition above room temperature in natural graphite crystals". Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-216014.
Testo completoAbstract (sommario):
Measuring with high precision the electrical resistance of highly ordered natural graphite samples from a Brazil mine, we have identified a transition at ∼350 K with ∼40 K transition width. The steplike change in temperature of the resistance, its magnetic irreversibility and time dependence after a field change, consistent with trapped flux and flux creep, and the partial magnetic flux expulsion obtained by magnetization measurements, suggest the existence of granular superconductivity below 350 K. The zero-field virgin state can only be reached again after zero field cooling the sample from above the transition. Paradoxically, the extraordinarily high transition temperature we found for this and several other graphite samples is the reason why this transition remained undetected so far. The existence of well ordered rhombohedral graphite phase in all measured samples has been proved by x-rays diffraction measurements, suggesting its interfaces with the Bernal phase as a possible origin for the high-temperature superconductivity, as theoretical studies predicted. The localization of the granular superconductivity at these two dimensional interfaces prevents the observation of a zero resistance state or of a full Meissner state.
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Letoffé, Adrien. "Élaboration et caractérisation d’une matrice polypropylène chimiquement modifiée et chargée GNP/graphène fonctionnalisés". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0076.
Testo completoAbstract (sommario):
Au cours de la dernière décennie, la prise de conscience écologique a impacté les domaines de la recherche. Pour diminuer la production de gaz à effet de serre de nombreux changements sont à apporter aux modes de consommations. Dans le domaine des transports, plusieurs pistes de recherche sont possibles comme l’allégement des structures. L’une des pistes pour permettre cet allégement est l’élaboration de nouveaux matériaux composites métal/polymère. Le polymère de ce composite doit présenter une bonne adhésion aux surfaces métalliques, de bonnes propriétés mécaniques, et de conductivité thermoélectrique. L’objectif de ce travail de thèse est l’élaboration d’une telle matrice par l’emploi de procédé facilement transposable à l’échelle industrielle. Afin d’assurer l’adhésion aux surfaces métalliques, la matrice sélectionnée est le polypropylène greffé anhydride maléique. Cette matrice grâce à ses greffons MAH présente des propriétés chimiques intéressantes au détriment de ses propriétés mécaniques. Pour contourner ce problème, une méthode de réticulation du PP-g-MAH par polyéther amine a été développée. Plusieurs configurations de réticulation ont été réalisées par extrusion réactive. L’évolution de la réticulation suivant le type d’élaboration et son impact sur les matrices ont été déterminés. Le principal changement est le passage d’un comportement mécanique fragile à ductile. Ce changement a été analysé de manière post mortem et in situ à un essai de traction uniaxial, ce qui a permis de mettre en évidence l’impact de la réticulation sur les micro-mécanismes de déformation des matrices. Les propriétés de conductivité thermoélectrique souhaitées sont assurée l’ajout d’une nano-charge de graphite lors de l’extrusion. Afin d’améliorer la dispersion du carbone et d’assurer une percolation mécanique et électrique à faible concentration, une nouvelle méthode d’exfoliation/fonctionnalisation du graphite par décharges plasma a été mise au point. Cette méthode de fonctionnalisation a permis la diminution de l’épaisseur des nanocharges ainsi que l’oxydation de leurs surfaces sans impliquer la création de défaut de structure. Deux gammes de nanocomposites ont été réalisées à l’aide de la nanocharge initiale et traitée. Bien que de hautes teneurs en carbone aient pu être atteintes, il n’a pas été possible d’atteindre la percolation électrique. Malgré cela, une meilleure dispersion de la charge traitée a été observéeIn the last decade, the environmental awareness of the need to reduce human impact on the environment affects the research sector. Reducing the fuel consumption and the human gas emissions became a priority, the humanity needs to switch to more eco-efficient patterns of consumption. In the transport field, numerous new lines of research are possible, like lighter structure. Composite materials, like multi-layered steel/polymer, appeared to be the perfect candidates to reach that objective. The polymer part of such material needs to present good shock absorption and thermo-electrical properties, and good compatibility with a metallic surface. The objective of this thesis is the elaboration and characterization of a polymer material with such properties that can be produced at industrial scale. To obtain good compatibility with the metal surfaces, the isotactic polypropylene-grafted-Maleic anhydride was selected as the initial material. This matrix presents good chemical property, its major drawback is its brittleness. A crosslinking reaction based on the reaction between MAH and amine groups was used to modify the mechanical properties of the matrix. The PP-g-MAH were crosslinked by twin-screw reactive extrusion with different configurations. The reaction affects the microstructure and the mechanical behavior of the materials, with a switch from brittle to ductile. The switch is explained by the variation of micro-mechanism of deformation implied by the crosslinked network. The solution used to modify the thermo-electrical properties of the material is the dispersion of different carbon nano-fillers such as graphite. To raise the dispersion quality of the fillers, and the compatibility between the carbon filler and the polymer matrix, a new method of functionalization of the graphite, by plasma discharge was developed. This new method implied a diminution of the filler thickness and an oxidation of the graphene surface, without any significative degradation of the fillers quality. Two types of nanocomposites were produced, one with an unmodified graphite filler and another one with a graphite modified by plasma treatment. Even with high filler concentration no electrical percolation was obtained, a high fillers exfoliation process need to be obtained. The functionalization of the graphite implied a carbon dispersion improvement, thus a better compatibility between the filler and the matrix
32
van, den Berg Jacobus Petrus. "Graphite: origin, deposits and economics: an exploration study of the Orom Graphite project". Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/63786.
Testo completoAbstract (sommario):
Developing exploration projects successfully requires that the Reasonable Prospects for Eventual Economic Extraction (RPEEE) be confirmed and based on the global market perception and trend. The exploration methods applied in the attempt to establish this RPEEE must be based on a key management framework that assures the results, and eventually the conclusion, are obtained with best practical and technical approaches whilst managing the risks and capitalizing on each result. The Orom Graphite project is located within the East African Orogenic belt, a suture zone between the Congo craton and the SLAMIN shield, formed during the formation of Gondwana during the late Proterozoic to early-Phanerozoic era. The closing of the Mozambique ocean, and the eventual collision between the craton and shield, occurred along the paleo-earths equator and migrated towards lower latitudes. This, along with the period’s biodiversity boom, provided the perfect deposition environment for carbonaceous sediments which were later metamorphosed to amphibolite and granulites grade metamorphism, resulting in the carbonization and the eventual graphitization of these carbonaceous sediments. The project is located within a poorly developed part of Uganda with the closest port situated some 1 500 km to the east in Kenya. The poorly developed infrastructure along with probable high logistical cost assigns a low competitivity index if compared to the economic costs of peer projects. However, the potential resources of the Orom Graphite project suggest that the Life of Mine (LOM) can rival the largest resource currently reported within the market. The current market conditions suggest that a possible oversupply of graphite concentrate will dominate the market within the next 4 to 10 years. This suggests that new graphite projects such as the Orom Graphite project are likely to develop into the production phase once the global supply and demand stabilize. This requires the Orom Graphite project to develop from its current scoping study level to a project development study level associated with a definitive feasibility study. To date, the project developed through mapping, reconnaissance drilling, geophysical survey and trenching programs increasing the Net Present Value (NPV) considerably based upon a Cost-Based Valuation approach using Prospectivity Enhancement Multiplier (PEM). The metallurgical studies could however not produce a graphite concentrate product within industrial grade standards. The risk associated with developing the project further into the Mineral Resource Estimation (MRE) phase was quantified and risk was evaluated by implementing a point decision tree and calculating the Expected Monetary Value (EMV). Due to the unfavourable metallurgical results obtained to date, the risk associated with undertaking an additional metallurgical test is considerable with a slight chance of producing a negative project value estimated at 65%. JP van den Berg Rhodes University Overall, the Orom Graphite project contains favourable geological formations with a potential large resource. Market trends indicate that a considerable resource is currently being developed and can supply the global market for the next 4 to 10 years. The project’s location within a landlocked country decreases its economic competitiveness with peer project and the unfavourable, but not conclusive, metallurgical results obtained during the scoping phase do not instil confidence that the project will develop into a productive mine soon. Managing the project development with future graphite demand in mind is the key to determining whether the project still has future value.
33
Outti, Brahim. "Nouvelles études sur les systèmes ternaires graphite-alcalin-mercure et graphite-alcalin-thallium". Nancy 1, 1993. http://www.theses.fr/1993NAN10210.
Testo completoAbstract (sommario):
Les études réalisées sur l'insertion dans le graphite des alliages alcalin lourd-mercure et alcalin lourd-thallium, présentaient aujourd'hui un certain nombre de points obscurs et même des lacunes (structure des thallographitures). Une étude approfondie de l'action sur le graphite de ces alliages nous a permis de déterminer ou de confirmer les conditions thermodynamiques de formation des divers composes ternaires, ainsi que de mettre en évidence les mécanismes réactionnels. L'examen structural de ces composés a fourni un très grand nombre de renseignements concernant l'organisation cristalline des feuillets métalliques insérés. On a pu montrer que les thallographitures étaient réellement ordonnés, et ce, aussi bien dans la direction de l'axe c que dans le plan perpendiculaire. Des mesures de résistivité électrique ont été réalisées sur ces ternaires dans les directions parallèle et perpendiculaire aux feuillets carbonés. Dans la première direction, la conductivité s'avère être de type métallique, tandis que dans la seconde, les phénomènes observés font intervenir des processus de conduction encore mal connus à l'heure actuelle
34
Nyangiwe, Nangamso Nathaniel. "Graphene based nano-coatings: synthesis and physical-chemical investigations". Thesis, UWC, 2012. http://hdl.handle.net/11394/3237.
Testo completoAbstract (sommario):
Magister Scientiae - MScIt is well known that a lead pencil is made of graphite, a naturally form of carbon, this is important but not very exciting. The exciting part is that graphite contains stacked layers of graphene and each and every layer is one atom thick. Scientists believed that these graphene layers could not be isolated from graphite because they were thought to be thermodynamically unstable on their own and taking them out from the parent graphite crystal will lead them to collapse and not forming a layer. The question arose, how thin one could make graphite. Two scientists from University of Manchester answered this question by peeling layers from a graphite crystal by using sticky tape and then rubbing them onto a silicon dioxide surface. They managed to isolate just one atom thick layer from graphite for the first time using a method called micromechanical cleavage or scotch tape. In this thesis chemical method also known as Hummers method has been used to fabricate graphene oxide (GO) and reduced graphene oxide. GO was synthesized through the oxidation of graphite to graphene oxide in the presence of concentrated sulphuric acid, hydrochloric acid and potassium permanganate. A strong reducing agent known as hydrazine hydrate has also been used to reduce GO to rGO by removing oxygen functional groups, but unfortunately not all oxygen functional groups have been removed, that is why the final product is named rGO. GO and rGO solutions were then deposited on silicon substrates separately. Several characterization techniques in this work have been used to investigate the optical properties, the morphology, crystallography and vibrational properties of GO and rGO.
35
Konschuh, Sergej [Verfasser], e Jaroslav [Akademischer Betreuer] Fabian. "Spin-orbit coupling effects: from graphene to graphite / Sergej Konschuh. Betreuer: Jaroslav Fabian". Regensburg : Universitätsbibliothek Regensburg, 2011. http://d-nb.info/1023276178/34.
Testo completo
36
Sole, C. G. "Application of few layer graphene and exfoliated graphite materials in lithium ion batteries". Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3019844/.
Testo completo
37
Torche, Abderrezak. "Simulations ab-initio des spectres Raman résonants dans le graphène, les multicouches de graphène et le graphite". Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066522/document.
Testo completoAbstract (sommario):
Les multicouches de graphène en empilement rhomboédrique sont considérés comme une phase prometteuse du carbone. Cela est due à la particularité de cette phase de pouvoir exhiber des états à forte corrélation électronique comme le magnétisme ou la supraconductivité à haute température critique. Ce qui est due, a son tour, à l’occurrence d’un état de surface avec une dispersion d’énergie électroniques quasi-nulle à proximité du niveau de Fermi. Malgré que le graphite Bernal soit la forme la plus stable du graphite, des échantillons a trois et quatre couches de graphène en empilement rhomboédrique ont pu être synthétisés. Plus récemment, des flocons d’épaisseur dépassant les 17 couches ont été isolés et provisoirement attribués à des séquences d’empilement rhomboédrique. Cette attribution à été faite via des expériences de spectroscopie Raman sous champ magnétique, bien que l’empreinte Raman des multicouche de graphène en empilement rhomboédrique est actuellement inconnue. Même le cas simple du spectre Raman résonnant à deux phonons (le pic 2D) du graphite Bernal n’est pas totalement compris. Dans ce travail de thèse, nous fournissons une description ab-initio complète du pic Raman 2D dans les systèmes de graphène à trois et quatre couches pour tous les empilements possibles, ainsi que pour le graphite Bernal, rhomboédrique et une alternance de graphite Bernal et rhomboédriqueMulti-layer graphene with rhombohedral ABC stacking is considered as a promising carbon phase possibly displaying correlated states like magnetism or high-T c superconductivity due to the occurrence of an ultraflat electronic surface band at the Fermi level. Despite Bernal graphite being the most stable form of graphite, three and four layers graphene samples with rhombohedral stacking can be synthesized. Recently, flakes of thickness up to 17 layers were tentatively attributed ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D two-phonon resonant Raman spectrum of Bernal graphite not completely theoretically understood. Here we provide a complete first principles description of the 2D Raman peak in three and four layer graphene for all possible stackings, as well as for bulk Bernal, rhombohedral and an alternation of Bernal and rhombohedral graphite, that can be seen as a periodic sequence of ABA and ABC trilayers. Calculations for several laser energies are performed and we give practical prescriptions are proposed to identify long range sequences of ABC multi-layer graphene flakes
38
Torche, Abderrezak. "Simulations ab-initio des spectres Raman résonants dans le graphène, les multicouches de graphène et le graphite". Electronic Thesis or Diss., Paris 6, 2017. http://www.theses.fr/2017PA066522.
Testo completoAbstract (sommario):
Les multicouches de graphène en empilement rhomboédrique sont considérés comme une phase prometteuse du carbone. Cela est due à la particularité de cette phase de pouvoir exhiber des états à forte corrélation électronique comme le magnétisme ou la supraconductivité à haute température critique. Ce qui est due, a son tour, à l’occurrence d’un état de surface avec une dispersion d’énergie électroniques quasi-nulle à proximité du niveau de Fermi. Malgré que le graphite Bernal soit la forme la plus stable du graphite, des échantillons a trois et quatre couches de graphène en empilement rhomboédrique ont pu être synthétisés. Plus récemment, des flocons d’épaisseur dépassant les 17 couches ont été isolés et provisoirement attribués à des séquences d’empilement rhomboédrique. Cette attribution à été faite via des expériences de spectroscopie Raman sous champ magnétique, bien que l’empreinte Raman des multicouche de graphène en empilement rhomboédrique est actuellement inconnue. Même le cas simple du spectre Raman résonnant à deux phonons (le pic 2D) du graphite Bernal n’est pas totalement compris. Dans ce travail de thèse, nous fournissons une description ab-initio complète du pic Raman 2D dans les systèmes de graphène à trois et quatre couches pour tous les empilements possibles, ainsi que pour le graphite Bernal, rhomboédrique et une alternance de graphite Bernal et rhomboédriqueMulti-layer graphene with rhombohedral ABC stacking is considered as a promising carbon phase possibly displaying correlated states like magnetism or high-T c superconductivity due to the occurrence of an ultraflat electronic surface band at the Fermi level. Despite Bernal graphite being the most stable form of graphite, three and four layers graphene samples with rhombohedral stacking can be synthesized. Recently, flakes of thickness up to 17 layers were tentatively attributed ABC sequences although the Raman fingerprint of rhombohedral multilayer graphene is currently unknown and the 2D two-phonon resonant Raman spectrum of Bernal graphite not completely theoretically understood. Here we provide a complete first principles description of the 2D Raman peak in three and four layer graphene for all possible stackings, as well as for bulk Bernal, rhombohedral and an alternation of Bernal and rhombohedral graphite, that can be seen as a periodic sequence of ABA and ABC trilayers. Calculations for several laser energies are performed and we give practical prescriptions are proposed to identify long range sequences of ABC multi-layer graphene flakes
39
Law, A. R. "A photoemission study of graphite". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355882.
Testo completo
40
Hodgkins, Andrew D. "Crack propagation in nuclear graphite". Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488486.
Testo completo
41
Repasi, Ivett. "Expanded graphite filled polymer composites". Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.557649.
Testo completoAbstract (sommario):
The aim of this project was to produce expanded graphite (EO) and modified EO-filled electrically conductive polymer composites and to investigate the effects of different additive modifications and preparation conditions on the microstructure and electrical properties of these composites. Modifications included the use of dry blending and ultrasound to reduce their size, use of various suspension media and surfactants to stabilize particle suspensions. To compare the effectiveness of different filler modification processes on electrical conductivity, unmodified and treated EO were incorporated into polypropylene (PP) by melt mixing and EO based dispersions were used to make polyvinyl alcohol (PV A) composites by solution casting. The PP composites were made using various processing methods and conditions at filler concentrations up to 12 wt%, while the polyvinyl alcohol samples contained graphite concentrations up to 8 wt%. To analyse the crystalline morphology of sample and the dispersion of the filler in the composites samples were analysed by light and electron microscopy, DSC and X-ray diffraction. TOA was also used to investigate the thermal stability of the composites. It was found that the presence of graphite, significantly changed the crystal morphology of PP. Solution mixed PVA samples showed improved dispersion and the particle size was effectively reduced.
42
Patterson, Adele. "Retention properties of porous graphite". Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342124.
Testo completo
43
Andriotis, Andreas. "Fracture instability in nuclear graphite". Thesis, University of Bristol, 2018. http://hdl.handle.net/1983/8f4c72b9-6a8a-4c69-8ded-5425f847a148.
Testo completoAbstract (sommario):
This dissertation considers the fracture instability of nuclear graphite, specifically of isotropic Gilsocarbon, grade IM1-24, which acts as a structural component and neutron moderator within reactors. The presence of cracks within this graphite informs its behaviour and necessitates a study of fracture properties and instability. Amongst the factors studied, a major finding was that the size effect was the most prevalent. Two aspects of instability were also examined: the crack driving force or energy release rate and the fracture resistance or the incremental work of fracture. The conditions between the extremes of load control and displacement control affecting the energy release rate were studied, based on the compliance of the surrounding components or additional elastic material, generally known as elastic follow-up. The effects of elastic follow-up and specimen geometry on fracture instability was investigated in an idealised model. Two sets of experiments were presented to quantify the effect and to validate the idealised benchmark study. No measurable differences were exhibited at the equivalent degrees of elastic follow-up achieved in the experimental work. Additionally, the effects of load multiaxiality on the fracture of graphite were investigated. Despite the influence of load multiaxiality on fracture stress of graphite, there was little effect in post-peak fracture behaviour indicating the lack of influence on fracture stability. Moreover, to evaluate fracture resistance, this work investigated the crack growth resistance curves, KR and R. To produce these curves, a considerable number of experiments of cyclic load and unload, with crack propagation, is presented. Different sized compact tension specimens were tested, to investigate the size effect typically exhibited in quasi-brittle materials which describes the fracture behaviour of IM1-24. The rising KR and R-curve behaviour observed in all sizes, especially in the more distinct initial fracture stages of KR, can be attributed to the formation of a bridging zone in the wake of the propagating crack. A mismatch between the scaling of the fracture process zone and the specimens was also exhibited, evident from the considerable differences in apparent toughness KQ as well as the linear elastic contributions to the work of fracture. The results indicated that the fracture stability of IM1-24 graphite is only marginally affected by elastic follow-up, whilst size effect is a more prominent contributor.
44
Crump, Timothy. "Modelling dynamic cracking of graphite". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/modelling-dynamic-cracking-of-graphite(71e81d6f-e712-458c-aa48-0a256749258a).html.
Testo completoAbstract (sommario):
Advances in dynamic fracture modelling have become more frequent due to increases in computer speed, meaning that its application to industrial problems has become viable. From this, the author has reviewed current literature in terms of graphite material properties, structural dynamics, fracture mechanics and modelling methodologies to be able to address operational issues related to the ageing of Advanced Gas-cooled Reactor (AGR) cores. In particular, the experimentally observed Prompt Secondary Cracking (PSC) of graphite moderator bricks which has yet to be observed within operational reactors, with the objective of supporting their plant life extension. A method known as eXtended Finite Element Method with Cohesive Zones (XCZM) was developed within Code_Aster open-source FEM software. This enabled the incorporation of velocity toughening, irradiation-induced material degradation effects and multiple 3D dynamic crack initiations, propagations and arrests into a single model, which covers the major known attributes of the PSC mechanism. Whilst developing XCZM, several publications were produced. This started with first demonstrating XCZM's ability to model the PSC mechanism in 2D and consequently that methane holes have a noticeable effect on crack propagation speeds. Following on from this, XCZM was benchmarked in 2D against literature experiments and available model data which consequently highlighted that velocity toughening was an integral feature in producing energetically correct fracture speeds. Leading on from this, XCZM was taken into 3D and demonstrated that it produced experimentally observed bifurcation angle from a literature example. This meant that when a 3D graphite brick was modelled that the crack profile was equivalent to an accepted quasi-static profile. As a consequence of this validation, the XCZM approach was able to model PSC and give insight into features that could not be investigated previously including: finer-scale heterogeneous effects on a dynamic crack profile, comparison between Primary and Secondary crack profiles and also, 3D crack interaction with a methane hole, including insight into possible crack arrest. XCZM was shown to improve upon previous 2D models of experiments that showed the plausibility of PSC; this was achieved by eliminating the need for user intervention and also incorporation of irradiation damage effects through User-defined Material properties (UMAT). Finally, while applying XCZM to a full-scale 3D graphite brick including reactor effects, it was shown that PSC is likely to occur under LEFM assumptions and that the Secondary crack initiates before the Primary crack arrests axially meaning that modal analysis would not be able to fully model PSC.
45
Ashaboglu, Ahmet F. (Ahmet Fadil). "Cryotribology of graphite and diamond". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38115.
Testo completo
46
Lasithiotakis, Michail Georgioy. "Irradiated graphite waste - stored energy". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/irradiated-graphite-waste--stored-energy(c93c7581-5273-4d30-a05b-2153b4c7cfaf).html.
Testo completoAbstract (sommario):
The cores of early UK graphite moderated research and production nuclear fission reactors operated at temperatures below 150°C. Due to this low temperature their core graphite contains significant amounts of stored (Wigner) energy that may be released by heating the graphite above the irradiation temperature. This exothermic behavior has lead to a number of decommissioning issues which are related to long term "safe-storage", reactor core dismantling, graphite waste packaging and the final disposal of this irradiated graphite waste. The release of stored energy can be modeled using kinetic models. These models rely on empirical data obtained either from graphite samples irradiated in Material Test Reactors (MTR) or data obtained from small samples obtained from the reactors themselves. Data from these experiments is used to derive activation energies and characteristic functions used in kinetic models. This present research involved the development of an understanding of the different grades of graphite, relating the accumulation of stored energy to reactor irradiation history and an investigation of historic stored energy data. The release of stored energy under various conditions applicable to decommissioning has been conducted using thermal analysis techniques such as Differential Scanning Calorimetry (DSC). Kinetic models were developed, validated and applied, suitable for the study of stored energy release in irradiated graphite components. A potentially valid method was developed, for determining the stored energy content of graphite components and the kinetics of energy release. Another parameter investigated in this study was dedicated in the simulation of irradiation damage using ion irradiation. Ion bombardment of small graphite samples is a convenient method of simulating fast neutron irradiation damage. In order to gain confidence that irradiation damage due to ion irradiation is a good model for neutron irradiation damage the properties and microstructure of various grades of ion irradiated nuclear graphite were also investigated. Raman Spectroscopy was employed to compare the effects of ion bombardment with the reported effects of neutron irradiation on the content of the defects. The changes of the of defect content with thermal annealing of the ion irradiated graphite have been compared with the annealing of neutron irradiated nuclear graphite.
47
Hartley, Mark. "The friability of nuclear graphite". Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362196.
Testo completo
48
Lacaze, Emmanuelle. "Etude par microscopie a effet tunnel de polymeres conjugues : adsorbats sur graphite, films electropolymerises sur or et sur graphite, defauts de surface du graphite". Paris 7, 1991. http://www.theses.fr/1991PA077051.
Testo completoAbstract (sommario):
Durant les dix dernieres annees, les polymeres conjugues ont ete intensivement etudies notamment a cause des possibilites de dopage qui leur permettent de devenir conducteurs. La stm (scanning tunneling microscopy ou microscopie a effet tunnel) semble une technique parfaitement adaptee a leur etude. Mais c'est une technique tres jeune, en particulier sur les materiaux organiques. C'est pourquoi une partie de cette these concerne la comprehension des informations apportees par des images stm de macromolecules. Une autre partie de la these est l'etude de macromolecules de polythiophene adsorbees sur graphite, ce qui constitue un systeme modele pour la comprehension des phenomenes d'adhesion. Nous avons pu deduire des structures creees sur graphite par la presence des adsorbats, des informations sur leur interaction (transfert de charge) avec le graphite. Nous avons egalement observe des conformations nouvelles des polythiophenes (par rapport a la situation en solution), des helices par exemple. La derniere partie de la these est l'etude de films minces de polymeres greffes electrochimiquement sur graphite et sur or (polydimethyl phenylene oxyde et polynaphtol). Nous avons observe de grandes differences entre les greffages sur les deux substrats: sur graphite, le greffage demarre essentiellement en bord de marche et de defauts, alors que sur or, des les premieres etapes, il semble parfaitement homogene sur les terrasses d'or
49
N'Guessan, Gilbert Kouakou. "Réduction électrochimique du composé d'insertion graphite-chlorure de cobalt : étude du composé réduit graphite-cobalt". Grenoble INPG, 1989. http://www.theses.fr/1989INPG0082.
Testo completoAbstract (sommario):
Le compose d'insertion du graphite c#5cocl#2#,#1#0 est utilise en cathode d'une pile au lithium. La decharge d'une telle pile conduit a la reduction en deux etapes du chlorure de cobalt insere. Le compose ainsi reduit de formule chimique moyenne c#1#1co#0#,#6##0#,#8(co cl#2)#0#,#4##0#,#2(licl)#0#,#5 contient une phase dans laquelle le cobalt est insere en 1#e#r stade
50
Leve, Zandile Dennis. "Determination of paracetamol at the electrochemically reduced graphene oxide-metal nanocomposite modified pencil graphite (ERGO-MC-PGE) electrode using adsorptive stripping differential pulse voltammetry". University of Western Cape, 2020. http://hdl.handle.net/11394/7350.
Testo completoAbstract (sommario):
>Magister Scientiae - MScThis project focuses on the development of simple, highly sensitive, accurate, and low cost electrochemical sensors based on the modification of pencil graphite electrodes by the electrochemical reduction of graphene oxide-metal salts as nanocomposites (ERGO-MC-PGE; MC = Sb or Au nanocomposite). The electrochemical sensors ERGO-Sb-PGE and ERGO-Au-PGE were used in the determination of paracetamol (PC) in pharmaceutical formulations using adsorptive stripping differential pulse voltammetry. The GO was prepared from graphite via a modified Hummers’ method and characterized by FTIR and Raman spectroscopy to confirm the presence of oxygen functional groups in the conjugated carbon-based structure whilst, changes in crystalline structure was observed after XRD analysis of graphite and GO.
2023-10-07