Lors d’un freinage aéronautique, les disques en composite C/C constituant les freins sont susceptibles d'être pollués par différentes substances émanant d'éléments de structure de l’avion ou de produits déverglaçants. Ces impuretés, introduites en faible proportion, ont un impact sur les propriétés tribologiques et thermiques des carbones et peuvent être à l’origine d’une usure précoce du frein. Dans cette étude, le nickel, le calcium et le zirconium ont été retenus pour simuler ces contaminants. L’objectif de la thèse fut de déterminer l’influence de la réactivité et de la chimie de surface du substrat sur l’activité de ces additifs. Un graphite Slx50 (Timcal®) a été broyé sous atmosphère contrôlée afin de contrôler sa réactivité. Après l’étape d’imprégnation par différentes solutions salines, les clichés de microscopie électronique en transmission (MET) montrent que la répartition de ces éléments est tributaire de la réactivité du support carboné. La désorption programmée en température couplée à un spectromètre de masse (TPD-MS) a mis en évidence des réactions entre le carbone et ces éléments. La spectrométrie de photoélectrons X (XPS) a permis de compléter l’étude et de proposer un mécanisme réactionnel pour chacun des additifs. / At the moment of aircraft braking, discs in composite C/C constituting the brakes may be polluted by various substances from structural elements of the aircraft or by icing agent products. These impurities introduced in small proportion, have an impact on the tribological and thermal properties of carbon and can be the cause of premature aging of the brake. In this study, nickel, zirconium and calcium were selected to simulate these contaminants. The aim of the thesis was to determine the influence of the reactivity and the surface chemistry of the substrate on the activity of these additives. A graphite Slx50 (Timcal®) was milled under controlled atmosphere in order to control its reactivity. After the impregnation step by various salt solutions, Transmission electron microscopy (TEM) shows that the distribution of these elements is dependent on the reactivity of the carbon support. Temperature Programmed Desorption coupled to Mass Spectrometer (TPD-MS) showed reactions between carbon and these elements. The X-ray Photoelectron Spectroscopy (XPS) allowed to complete the study and to propose a reaction mechanism for each additive.

Les batteries à ions lithium alimentent la plupart des petits appareils électriques, portables. Elles font usage du graphite comme électrode négative. Pour optimiser celle-ci, il faut réduire la perte spécifique de charge du premier cycle d’intercalation du lithium. Cette perte est principalement due à la formation d’une couche passive par décomposition de l’électrolyte. Les propriétés du graphite qui l’influencent sont partiellement connues. En particulier, une meilleure compréhension de l’exfoliation du graphite, responsable d’une grande perte spécifique de charge, est souhaitée. Ce phénomène est provoqué par la co-intercalation de solvant à travers les plans de bord des particules. Des paramètres comme la cristallinité, la chimie de surface et la réactivité du graphite semblent jouer un rôle. Une étude systématique a été entreprise afin de déterminer leur influence sur le premier cycle dans un électrolyte standard à base de carbonate d’éthylène et de diméthyle. Il apparaît que les complexes de surface oxygénés ne jouent pas de rôle particulier tandis que les complexes hydrogénés favorisent la co-intercalation de solvant. De plus, les graphites ayant une faible teneur en sites actifs constituant l’Active Surface Area (ASA), mesurée par chimisorption d’oxygène, sont plus enclins à exfolier. Comme les atomes de bord à deux voisins sont les plus réactifs en raison de la présence d’un électron célibataire, la plus grande sensibilité à la co-intercalation de solvant des graphites de faible ASA peut s’expliquer par la formation d’une couche passive inappropriée sur des plans de bord peu réactifs laissant passer le solvant. / In the field of small portable electrical devices, lithium-ion batteries are common. Graphite is used as the negative electrode. To improve its electrochemical performances, the first cycle specific charge loss must be decreased. It is predominantly attributed to the electrolyte reduction into a passivation layer. The graphite properties which influence this charge loss are not clearly identified. In particular, the graphite exfoliation which is responsible for a huge specific charge loss must be better understood. This dramatic phenomenon is due to solvent co-intercalation through the particle edge planes. Many graphite parameters such as crystallinity, surface chemistry and reactivity are thought to play a role. A systematic study was carried out in which the influence of each parameter on the first cycle was assessed in a standard ethylene and dimethyl carbonate based electrolyte. It appears that the presence of oxygen surface complexes does not have any influence whereas C6H bonds cause slight exfoliation. In addition, graphite samples containing low amount of active sites : the so-called Active Surface Area (ASA), quantified by oxygen chemisorption, are more likely to exfoliate. Since graphite active sites are mainly the edge atoms because of unpaired electron presence, low ASA graphite exfoliation can be explained by the formation of inappropriate passivation layer on the edge planes letting solvent molecules co-intercalate.

L’objectif de ce travail est d’étudier quantitativement l’évolution des propriétés de surface des matériaux carbonés et leur réactivité dans les conditions proches de celles rencontrées lors du taxiage des avions. Les essais de freinage ont été réalisés à l’aide d’un Banc d’Essai Tribométrique à Simulation Inertielle. Les composites C/C frottés et les débris d’usure sont caractérisés par des techniques non-conventionnelles multi-échelles. Les composites frottés (dans leur totalité) et les débris d’usure sont caractérisés par thermo-désorption programmée et chimisorption d’oxygène. Ces analyses permettent de déterminer la nature et la quantité de groupes fonctionnels et la teneur en sites actifs, caractéristique de la réactivité intrinsèque du carbone et responsable de l’interaction avec les espèces gazeuses de l’environnement. Ces caractérisations sont complétées par des analyses morphologiques, structurales et texturales par microscopies, diffractions des rayons X, adsorption de gaz. L’analyse des caractéristiques physico-chimiques des débris d’usure et des disques frottés permet de remonter aux réactions tribochimiques ayant eu lieu dans le contact : des réactions chimiques entre l’oxygène ou l’eau et les liaisons C-C rompues ont été mises en évidence. Un modèle permettant de justifier les différences de propriétés tribologiques lors des essais de taxiage a été proposé. Ce modèle, basé sur la réactivité du système et sur les propriétés de l’interface de frottement, permet d’élucider les problématiques liées à la température dans ce type de système. / The objective of this work is to study quantitatively the evolution of carbon materials surface properties and reactivity under breaking conditions similar to those encountered during taxiing. The breaking tests were carried out using a Tribometric Test Bench. The rubbed C/C composites and the wear debris collected are then characterized by mutiscale unconventional techniques. The whole rubbed composites and the wear debris are characterized by Temperature-Programmed Desorption and by oxygen chemisorption. These analyzes are used to determine the nature and amount of functional groups and the content of active sites that is characteristic of the reactivity of the carbon material and also responsible of its interaction with the surrounding environment. The characterizations are completed by morphological, structural and textural analysis, such as Electron Microscopy, X-Ray Diffraction and gas adsorption. The analysis of the physic-chemical characteristics of wear debris and of the rubbed discs enables to evidence the tribochemical reactions occurring in the mechanical contact: chemical reactions between oxygen or water and the broken C-C bonds have been evidenced. A model is finally proposed, justifying the differences in the tribological properties during taxiing tests. The later is based on the carbon reactivity and on the interface properties and justify the temperature dependence of this system.

京都大学 / 新制・課程博士 / 博士(エネルギー科学) / 甲第24853号 / エネ博第462号 / 新制||エネ||87(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 野平, 俊之, 教授 萩原, 理加, 教授 佐川, 尚 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

No description available.

Graphite materials are vital industrial products. The rapid development of the battery and electronic computer industries has incentivized a great demand for graphite materials. However, today, graphite materials are commercially produced via thermal treating fossil oil or coal derived coke at a temperature higher than 2500℃. Both of the fossil-based feedstock and the energy-intensive production process are contrary to the concept of sustainable development. This thesis proposes a sustainable low-temperature catalytic graphitization process to produce graphite materials with highly ordered crystallinity by using commercial biomass pyrolysis biochar as the feedstock. Iron nitrate was selected as the graphitization catalyst. The effect of the graphitization temperature and the iron loading amount on the properties of the produced carbon products was studied. Produced graphite materials were characterized by performing X-ray diffraction, Nitrogen adsorption-desorption, and elemental analysis. Results show that the average graphitic crystalline size and the degree of graphitization of the product increased with the increase of the graphitization temperature and the iron loading amount. However, the increase of the iron loading amount reduced the catalyst removal efficiency of the acid washing process. When the graphitization temperature is higher than 1100℃ and the iron loading amount is higher than 11.2 wt.%, the crystallinity of the produced graphite material is better than that of the commercial graphite. The graphite material with the best crystallinity, which was produced at a temperature of 1300℃ and an iron loading of 33.6 wt.%, has crystallinity very close tothe pure graphite. / Grafitmaterial är viktiga industriprodukter. Den snabba utvecklingen av batteri- och elektronikdatorindustrin har stimulerat en stor efterfrågan på grafitmaterial. Idag framställs emellertid grafitmaterial kommersiellt via termisk behandling av fossil olja eller kol härledd koks vid en temperatur högre än 2500℃. Både det fossilbaserade råvaran och den energikrävande produktionsprocessen strider mot begreppet hållbar utveckling. Denna avhandling föreslår en hållbar katalytisk grafitiseringsprocess vid låg temperatur för att producera grafitmaterial med högt ordnad kristallinitet genom att använda kommersiell biomassapyrolysbiokol som råmaterial. Järnnitrat valdes som grafitiseringskatalysator. Effekten av grafitiseringstemperaturen och järnbelastningsmängden på egenskaperna hos de producerade kolprodukterna studerades. Framställda grafitmaterial kännetecknades av utförande av röntgendiffraktion, kväve-adsorptionsdesorption och elementaranalys. Resultaten visar att den genomsnittliga grafitiska kristallina storleken och graden av grafitisering av produkten ökade med ökningen av grafitiseringstemperaturen och järnbelastningsmängden. Ökningen av järnbelastningsmängden minskade emellertid katalysatorns avlägsnande effektivitet för syratvättprocessen. När grafitiseringstemperaturen är högre än 1100℃ och järnbelastningsmängden är högre än 11,2 viktprocent, är kristalliniteten hos det producerade grafitmaterialet bättre än den för den kommersiella grafiten. Grafitmaterialet med den bästa kristalliniteten, som producerades vid en temperatur av 1300℃ och en järnbelastning på 33,6 viktprocent, har kristallinitet mycket nära den rena grafiten.

O Distrito Grafitífero Aracoiába-Baturité apresenta depósitos do tipo gnaisse grafitoso (minério disseminado) e veio (minério maciço) com diferentes origens genéticas e com características físicas e ambientes geológicos de formação próprios. O minério tipo gnaisse grafitoso é de origem sedimentar, singenético, com teores de 1,5 a 8% de C, que se distribuem ao longo de duas extensas faixas paralelas, hospedadas na Subunidade Baturité, que constitui um importante metalotecto regional. A associação de grafita metamórfica disseminada em metassedimentos da Sequência Acarápe constitui um geoindicador de antiga bacia sedimentar neoproterozóica e, também, pode ser considerado como zona de geosutura resultante do subsequente fechamento de um oceano primitivo. As rochas desta subunidade correspondem na paleogeografia da Sequência Acarápe aos fácies de sopé de talude e de planície abissal. O minério tipo veio (fluido depositado) é epigenético e, com teores entre 20% e 70% de C, forma corpos tabulares e bolsões, controlados em escala local por estruturas de alívio (falhas, fraturas, zonas de contato, eixos de dobras etc.) que permitiram a percolação de soluções penumatolíticas relacionadas ao corpo plutônico de Pedra Aguda. As variações dos valores das relações entre isótopos estáveis de carbono (δ13C) na grafita do minério disseminado são de -26,72 a -23,52 e do minério maciço de -27,03 a -20,83, revelando sinal de atividades biológicas (bioassinaturas) e permitem afirmar que a grafita das amostras acima são derivadas de matéria orgânica. Foram apresentados os principais guias de prospecção para grafita e testados os seguintes métodos geofísicos: Eletro-Resistividade; GPR - Ground Penetrating Radar; Magnetometria; VLF (Very Low Frequency); e Polarização Induzida Espectral (IPS) / Resistividade (ER). A conjugação dos métodos de Polarização Induzida Espectral (IPS) e Eletro Resistividade (ER) foi o que demonstrou a melhor eficiência. Com relação à determinação do teor de carbono por termogravimetria (ATG), que é o método mais utilizado para este elemento. Verificou-se, que as faixas de queima atribuídas ao carbono no minério do Distrito de Aracoiába-Baturité (340 a 570C e de 570 a 1050C) eram diferentes das faixas do minério de Minas Gerais (350C a 650C e 650C a 1.050C). Esta constatação indica a necessidade de se determinar previamente as faixas de temperatura para cada região pesquisada. / The Aracoiába-Baturité Graphite-bearing District has graphitic gneiss deposits (disseminated ore) and vein (solid ore) with different genetic origins and their own physical characteristics and geological environments. The graphite gneiss ore is of sedimentary, syngenetic origin, with 1.5% to 8% C content, which is distributed along two long parallel belts, hosted in the Baturité Sub-unit, which consists of a major regional metallotect. The association of metamorphic graphite disseminated in metasediments of the Acarápe Sequence consists of a geoindicator of an old Neo-Proterozoic sedimentary basin and also can be considered a geosuture zone, the result of the subsequent closing of a primitive ocean. The rocks of this subunit correspond in the paleogeography of the Acarápe Sequence to the facies of the bottom of a slope and of an abyssal plain. The vein ore (deposited fluid) is epigenetic and, with C contents of between 20% and 70%, forms tabular bodies and pockets, controlled on a local scale by relief structures (faults, fractures, contact zones, fold axes, etc.), which allowed seepage of pneumatolithic solutions relating to the plutonic body of Pedra Aguda. The variations in the values of the ratios between stable carbon isotopes (δ13C) in the graphite of the disseminated ore are -26.72 to -23.52 and of the solid ore -27.03 to -20.83, showing a sign of biological activities (biosignatures), and it can be said that the graphite of the above samples is derived from organic matter. The main prospecting guides for graphite were presented and the following geophysical methods tested: Electro-resistivity (ER); Ground Penetrating Radar (GPR); Magnetometry; Very Low Frequency (VLF); and Spectral Induced Polarization (SIP) / Electro-resistivity (ER). It was found that the combination of the Spectral Induced Polarization (SIP) and Electro-resistivity (ER) methods proved the most efficient. In relation to determining the carbon content using thermogravimetry (TG), which is the most commonly used method for this element, it was found that the bands of burning attributed to the carbon in the ore in the Aracoiába-Baturité District (340 to 570C and from 570oC to 1050C) were different from the bands of the ore in Minas Gerais (350C to 650C and 650C to 1050C). This finding suggests the need to determine beforehand the temperature ranges for each region studied.

Les propriétés tribologiques intrinsèques des composés lamellaires sont généralement attribuées à la présence de gap de van der Waals dans leur structure. La possibilité de faire varier de manière contrôlée la structure cristalline et la structure électronique du graphite par processus d'intercalation de différentes espèces chimiques (électrophile, nucléophile ...) sont utilisées pour étudier de façon plus approfondie les processus de réduction du frottement par les composés de basse dimensionnalité. Trois familles d'intercalants sont étudiées et les propriétés tribologiques sont corrélées aux évolutions structurales et chimiques.

O Distrito Grafitífero Aracoiába-Baturité apresenta depósitos do tipo gnaisse grafitoso (minério disseminado) e veio (minério maciço) com diferentes origens genéticas e com características físicas e ambientes geológicos de formação próprios. O minério tipo gnaisse grafitoso é de origem sedimentar, singenético, com teores de 1,5 a 8% de C, que se distribuem ao longo de duas extensas faixas paralelas, hospedadas na Subunidade Baturité, que constitui um importante metalotecto regional. A associação de grafita metamórfica disseminada em metassedimentos da Sequência Acarápe constitui um geoindicador de antiga bacia sedimentar neoproterozóica e, também, pode ser considerado como zona de geosutura resultante do subsequente fechamento de um oceano primitivo. As rochas desta subunidade correspondem na paleogeografia da Sequência Acarápe aos fácies de sopé de talude e de planície abissal. O minério tipo veio (fluido depositado) é epigenético e, com teores entre 20% e 70% de C, forma corpos tabulares e bolsões, controlados em escala local por estruturas de alívio (falhas, fraturas, zonas de contato, eixos de dobras etc.) que permitiram a percolação de soluções penumatolíticas relacionadas ao corpo plutônico de Pedra Aguda. As variações dos valores das relações entre isótopos estáveis de carbono (δ13C) na grafita do minério disseminado são de -26,72 a -23,52 e do minério maciço de -27,03 a -20,83, revelando sinal de atividades biológicas (bioassinaturas) e permitem afirmar que a grafita das amostras acima são derivadas de matéria orgânica. Foram apresentados os principais guias de prospecção para grafita e testados os seguintes métodos geofísicos: Eletro-Resistividade; GPR - Ground Penetrating Radar; Magnetometria; VLF (Very Low Frequency); e Polarização Induzida Espectral (IPS) / Resistividade (ER). A conjugação dos métodos de Polarização Induzida Espectral (IPS) e Eletro Resistividade (ER) foi o que demonstrou a melhor eficiência. Com relação à determinação do teor de carbono por termogravimetria (ATG), que é o método mais utilizado para este elemento. Verificou-se, que as faixas de queima atribuídas ao carbono no minério do Distrito de Aracoiába-Baturité (340 a 570C e de 570 a 1050C) eram diferentes das faixas do minério de Minas Gerais (350C a 650C e 650C a 1.050C). Esta constatação indica a necessidade de se determinar previamente as faixas de temperatura para cada região pesquisada. / The Aracoiába-Baturité Graphite-bearing District has graphitic gneiss deposits (disseminated ore) and vein (solid ore) with different genetic origins and their own physical characteristics and geological environments. The graphite gneiss ore is of sedimentary, syngenetic origin, with 1.5% to 8% C content, which is distributed along two long parallel belts, hosted in the Baturité Sub-unit, which consists of a major regional metallotect. The association of metamorphic graphite disseminated in metasediments of the Acarápe Sequence consists of a geoindicator of an old Neo-Proterozoic sedimentary basin and also can be considered a geosuture zone, the result of the subsequent closing of a primitive ocean. The rocks of this subunit correspond in the paleogeography of the Acarápe Sequence to the facies of the bottom of a slope and of an abyssal plain. The vein ore (deposited fluid) is epigenetic and, with C contents of between 20% and 70%, forms tabular bodies and pockets, controlled on a local scale by relief structures (faults, fractures, contact zones, fold axes, etc.), which allowed seepage of pneumatolithic solutions relating to the plutonic body of Pedra Aguda. The variations in the values of the ratios between stable carbon isotopes (δ13C) in the graphite of the disseminated ore are -26.72 to -23.52 and of the solid ore -27.03 to -20.83, showing a sign of biological activities (biosignatures), and it can be said that the graphite of the above samples is derived from organic matter. The main prospecting guides for graphite were presented and the following geophysical methods tested: Electro-resistivity (ER); Ground Penetrating Radar (GPR); Magnetometry; Very Low Frequency (VLF); and Spectral Induced Polarization (SIP) / Electro-resistivity (ER). It was found that the combination of the Spectral Induced Polarization (SIP) and Electro-resistivity (ER) methods proved the most efficient. In relation to determining the carbon content using thermogravimetry (TG), which is the most commonly used method for this element, it was found that the bands of burning attributed to the carbon in the ore in the Aracoiába-Baturité District (340 to 570C and from 570oC to 1050C) were different from the bands of the ore in Minas Gerais (350C to 650C and 650C to 1050C). This finding suggests the need to determine beforehand the temperature ranges for each region studied.

Vita. / Digitized by Kansas Correctional Industries