L’objectif de ce travail a été d’apporter une meilleure compréhension des mécanismes réactionnels de l’hydratation de ciments appartenant à la famille de ciment BCSAF afin de développer des schémas réactionnels simplifiés permettant d’optimiser les ciments à base d’un clinker BCSAF et d’autres constituants pour des applications spécifiques. Les ciments étudiés ont été réalisés à partir d’un clinker contenant 52% de belite, 33% de ye’elimite and 14% de ferrite et diverses quantités d’anhydrite et de calcaire. A partir de l’étude détaillée de l’hydratation d’un ciment contenant 95% de clinker et 5% d’anhydrite, il a été démontré que le mécanisme de l’hydratation est constitué de deux périodes successives : le début de l’hydratation est contrôlé par l’hydratation de la ye’elimite réagissant avec l’anhydrite, tandis que la suite de l’hydratation est contrôlée par les hydratations de la belite et de la ferrite qui réagissent avec certains des hydrates formés lors de la première période. La vitesse de nucléation de la strätlingite contrôle le début de l’hydratation de la belite. Le principal paramètre qui contrôle cette dernière est la concentration en sulfate de la phase aqueuse qui doit être très faible. Ainsi C-S-H n’est pas formé au début de l’hydratation de la belite certainement à cause de l’inhibition de sa nucléation par de trop fortes quantités d’aluminate en solution. Par conséquence, c’est indirectement la concentration en sulfate de la solution qui contrôle le début de l’hydratation de la belite and ainsi les réactions conduisant à sa réduction à travers la précipitation de phase notamment lors de l’hydratation de la ye’elimite pour former de l’ettringite. Ainsi d’une façon générale, la strätlingite commence à nucléer quand la ye’elimite a complètement réagi. D’autre part, une synergie entre les hydratations de la belite et de la ferrite permet de former des hydrogrenats et des C-S-H à des temps longs au détriment de la strätlingite formée auparavant. Un mécanisme d’hydratation similaire a été trouvé pour les ciments contenant des quantités plus importantes d’anhydrite à l’exception de ceux qui contiennent une quantité d’anhydrite supérieure que la quantité théorique permettant de faire réagir toute la ye’elimite en ettringite. Toutefois pour le premier type de ciments, une augmentation de la quantité d’anhydrite allonge à la fois le temps d’apparition de la seconde période et la durée des différentes étapes de cette dernière. Donc l’hydratation est globalement plus lente. Pour le second type de ciment, contenant de fortes quantités d’anhydrite, le mécanisme d’hydratation est assez différent car l’hydratation de la belite commence dès le début de l’hydratation et conduit à la formation, soit d’ettringite contenant Si, soit de C-S-H. L’effet de 15% de calcaire a également été étudié pour le ciment contenant 95% de clinker et 5% d’anhydrite. Les résultats ont montré que le calcaire ne change pas la première période de l’hydratation mettant en jeu principalement la ye’elimite et l’anhydrite. Par contre la seconde période, durant laquelle la belite et la ferrite s’hydratent, est fortement retardée à son début. Ceci peut être dû à un retard de la nucléation de la strätlingite à cause de concentrations en sulfate de la solution restant plus longtemps élevées par le fait que l’ettringite est stabilisée en présence de carbonate par la formation de phases AFm carbonatées qui inhibent la formation de monosulfoaluminate de calcium hydraté. Pour finir, des perspectives sont données notamment afin de réduire la durée de la première période de l’hydratation et ainsi permettre un démarrage plus rapide de l’hydratation de la belite et de la ferrite. / The objective of this work was to better understand the hydration mechanisms of cements belonging to the family of BCSAF cement in order to develop simple mechanistic models which can help us to optimise mixtures of BCSAF clinker and other compounds for specific applications. The studied cements were made from a clinker containing 52% of belite, 33% of ye’elimite and 14% of a ferrite phase and various amounts of anhydrite and limestone. From the Detailed investigation of the hydration of cement containing 95% of clinker and 5% of anhydrite, it has been demonstrated that the mechanism of hydration has two main successive periods of hydration: the beginning of hydration is controlled by ye’elimite and anhydrite, while the remaining of hydration is governed by belite and the ferrite phase that react with some of the hydrates formed during the first period. It is C2ASH8 nucleation rate that governs the beginning of the hydration of belite. The main parameter that governs the nucleation rate of strätlingite is [SO4]2- that has to be low. C-S-H does not form as the initial hydrate for belite hydration due to the inhibition effect of high aluminate concentration on C-S-H nucleation. As a consequence, this is indirectly the sulphate concentration that controls the beginning of belite hydration and thus the reactions leading to its reduction, mainly the hydration of ye’elimite to form ettringite. Globally it is once ye’elimite has been completely reacted that strätlingite may nucleate. A synergy between the reactions of belite and ferrite is found to accelerate the formation of later hydrate, hydrogarnet and C-S-H at the expense of strätlingite.A similar mechanism of hydration has been found for cements having higher anhydrite contents at the exception of cements that have more anhydrite than the theoretical anhydrite content to consume all ye’elimite to form ettringite. For the former cements, more anhydrite can strongly delay the second period of the hydration where both belite and ferrite react. In the later cases, the mechanism of hydration is quite different as belite does start to react till the beginning of hydration certainly forming either a Si containing ettringite or C-S-H. The influence of 15% of limestone was investigated on the cement containing 95% of clinker and 5% of anhydrite. The results showed that limestone did not change the first period involving anhydrite and ye’elimite, but strongly delayed the beginning of the second period where both belite and ferrite hydrate. This may be due to a delayed nucleation of strätlingite induced by a longer period having higher [SO4]2- as ettringite is stabilised by the precipitation of carbonated AFm at the expense of calcium monosulfoaluminate hydrate, thanks to the carbonate ions brought by limestone. Finally some perspectives are given in order to reduce the duration of the first period and then to enable the hydration of both belite and ferrite more rapidly.

Différentes méthodes de synthèses ont été mises au point pour contrôler la forme et la composition des nanoparticules. L’effet de la nature et la concentration des surfactants, des solvants, la température et le temps de synthèse a également été étudié. Les poudres ont été caractérisées par diffraction des rayons X et microscopie électronique à transmission, couplée à la spectroscopie d'énergie dispersive. Des propriétés catalytiques et de détection ont été évaluées respectivement en présence de faibles concentrations de CO et de NO2 dans de l’air synthétique.Des nanooctaèdres de CoxFe3-xO4 ( x=1, 1,5 et x = 1,8 ) de 15-20 nm ont été produits par synthèse hydrothermale en utilisant différents surfactants (CTAB, SDS et PVP). Des nanocubes de tailles différentes de CoFe2O4 ont été produits par synthèse solvothermique en utilisant l'oléylamine comme surfactant. La poudre de CoxFe3-xO4 avec x = 1,5 a une activité plus élevée pour la conversion du CO que les nanooctaèdres x=1, et la conversion a lieu à plus basse température dans le cas des nanocubes. Les nanocubes présentent une sensibilité inférieure de détection au NO2 à celle des nanooctaèdres, ce qui indique que les faces {111} sont plus réactives que les faces {100} dans les nanoparticules de ferrites de cobalt. / Different synthesis methods such as hydrothermal, solvothermal and thermal decomposition were developed to control nanoparticles shape and composition. The influence of synthesis parameters such as the nature of surfactants, the solvents, temperature and time of synthesis were also investigated. The powders were characterized by X-ray Diffraction and Transmission Electron Microscopy coupled with Dispersive Energy Spectroscopy. The catalytic and detection properties were evaluated in presence of CO and NO2 in synthetic air. CoxFe3-xO4 (x = 1, 1.5 ) nanooctahedra with 15-20 nm were produced by hydrothermal synthesis using different surfactants (CTAB, SDS and PVP). Nanocubes of CoFe2O4 were successfully obtained by solvothermal synthesis using oleylamine as surfactant. Nanooctahedra of CoxFe3-xO4 with x = 1.5 have higher activity for the CO conversion than those with x=1, and the conversion starts at lower temperature for the nanocubes. The nanocubes show lower sensitivity for the detection of NO2 than the nanooctahedra which indicates that the {111} faces are more reactive than the {100} ones in cobalt ferrites nanoparticles.

Ce travail est consacré à l’élaboration et l’étude des propriétés catalytiques, électriques et magnétiques denanomatériaux à base de ferrite de cobalt. Les nanopoudres de ferrite de cobalt (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) ont étéélaborées par une nouvelle méthode chimique solvo-thermale. Les nanopoudres obtenues sont très bien cristallisées ontdes tailles de particules qui varient avec le taux de cobalt entre 4 et 7 nm et sont très homogènes en composition. Lesnanopoudres de ferrites de cobalt sont monophasées, de structure spinelle avec un paramètre de maille qui varie enfonction du taux de cobalt. Les nanopoudres de ferrites de cobalt ne s’oxydent pas sous air et en température .Lesnanopoudres de composition proches de x=1 sont stables jusqu’à 900°C, alors que pour de plus forts écarts à lastoechiométrie, des transformations de phase ont lieu au delà de 550°C.Les mesures catalytiques ont mis en évidence l’oxydation de CH4 en CO2 après passage sur le catalyseur pour tous leséchantillons. L’efficacité catalytique est maximale et l’énergie d’activation est la plus faible pour l’échantillon x=1.8 ;ceci est lié à la plus grande surface spécifique, et au plus fort taux de sites actifs pour cette composition.Les ferrites de cobalt élaborées présentent une conduction de type électronique avec un comportement semi conducteurjusqu’à 500-600°C et un comportement métallique au-delà. Les variations de conductivité d’une composition à l’autres’expliquent par les variations du nombre de paires [Co2+,Fe3+].Les nanoparticules ont un comportement superparamagnétique quelle que soit la composition. Ce comportement estdû principalement à un effet de taille et de forme, et à une distribution cationique différente entre les deux types desites tétraédriques et octaédriques de la structure spinelle. Ces ferrites présentent une aimantation à saturation prochede celle de l’état massif, du fait de la grande qualité cristalline attribuée à la méthode d’élaboration mise au point. / This work is devoted to the synthesis and the study of the physical properties of cobalt ferrite nanomaterials. Thecobalt ferrite nanopowders (CoxFe3-xO4 , x=0.6,1,1.2,1.8 ) were synthesized by a new solvo thermal chemical route.The nanopowders are highly crystallized, very homogeneous in size and chemical composition. The nanopowderssizes are ranged from 4 nm for high cobalt content to 7 nm for low cobalt content. They are single phased, with thespinel structure, and a cell parameter varying with the cobalt content. The cobalt ferrites do not oxidize, when heatedunder air. For compositions near x=1, the cobalt ferrites are stable when heated under air up to 900°C, as for the othercompositions, phase transformations occur above 550°C.The catalytic measurements have shown the oxidation of CH4 into CO2 in presence of the catalyst for all thecompositions. Cobalt ferrite with composition x=1.8, presents the lowest activation energy and the best catalyticefficiency; this can be related to the great specific surface and the high rate of active sites for this composition.Concerning the conduction properties, the cobalt ferrites exhibit a semiconductor character up to 500-600 ° C and ametallic one above. Changes in conductivity from a composition to another are explained by changes in the number ofpairs [Co2+, Fe3+].A superparamagnetic behaviour was evidenced whatever the composition. This is due for one part to a size and shapeeffect and for the other part to different cationic distribution between tetrahedral and octahedral sites. These ferriteshave a saturation magnetization close to that of the massive state, because of the high crystallinity of the nanopowders,attributed to the synthesis method developed in this work.

Ímãs híbridos aglomerados foram preparados por compactação uniaxial de pós magnéticos e curados ao ar e sob vácuo. Correlações entre tratamentos de cura, propriedades mecânicas e propriedades magnéticas foram estabelecidas com base em resultados obtidos por Histeresigrafia, Magnetometria de Amostra Vibrante, ensaios de Compressão e análises de Microscopia Óptica e Eletrônica de Varredura. Parâmetros como pressão de compactação, tempo e influência da temperatura e da atmosfera de cura nas propriedades mecânicas e magnéticas de ímãs aglomerados utilizados como padrão de referência, preparados com pós MQEP de NdFeB (partículas magnéticas impregnadas com resina epóxi), foram discutidos na primeira parte deste trabalho. A melhor condição de cura foi à temperatura de 200°C por cinco horas, sob vácuo. O produto de energia máximo (BHMáx) obtido para os ímãs padrão, curados ao ar e sob vácuo, foi de 76,2 KJ/m³ e 80,5 KJ/m³, respectivamente. Na segunda parte deste trabalho, ímãs híbridos foram produzidos a partir da mistura do pó MQEP aditivado com diferentes quantidades de pós de ferrite de estrôncio e NdFeB reprocessado por HDDR. O melhor resultado de BHMáx obtido para os ímãs híbridos de MQEP com ferrite de estrôncio e MQEP com pó reprocessado por HDDR, curados sob vácuo, foi de 73,2 KJ/m³ e 78,3 kJ/m³, respectivamente. Ímãs híbridos de MQEP com pó reprocessado por HDDR apresentaram melhor desempenho magnético que os ímãs híbridos de MQEP com pós de ferrite de estrôncio. / Bonded hybrid magnets were prepared by uniaxial pressing of magnetic powders cured in air and under vacuum. Correlations between cure treatments, mechanical properties and magnetic properties were established based on results obtained by Hysteresigraphy, Vibrating Sample Magnetometry, Compression tests, Optical Microscopy and Scanning Electron Microscopy. Parameters such as compaction pressure and the influence of time, temperature and atmosphere during the curing step in the mechanical and magnetic properties of the bonded magnets used as reference patterns, produced with NdFeB MQEP powder (epoxy encapsulated magnetic particles) were discussed in the first part of this work. The better cure condition was that performed at 200 oC for 5 hours under vacuum. The maximum energy product (BHMax) obtained for the patterns bonded magnets cured in air and under vacuum was 76.2 KJ/m³ and 80.5 KJ/m³, respectively. In the second part of this work, hybrid bonded magnets were produced by the mixture of MQEP powder with different amounts of strontium ferrite powder and NdFeB powder reprocessed by HDDR. The best results of BHMax obtained for the hybrid MQEP magnets with strontium ferrite powder and NdFeB reprocessed by HDDR, cured under vacuum were 73.2 KJ/m³ and 78.3 kJ/m³, respectively. Hybrid MQEP bonded magnets produced with the addition of HDDR reprocessed powder presented better magnetic performance than that obtained with strontium ferrite powders.

Ímãs híbridos aglomerados foram preparados por compactação uniaxial de pós magnéticos e curados ao ar e sob vácuo. Correlações entre tratamentos de cura, propriedades mecânicas e propriedades magnéticas foram estabelecidas com base em resultados obtidos por Histeresigrafia, Magnetometria de Amostra Vibrante, ensaios de Compressão e análises de Microscopia Óptica e Eletrônica de Varredura. Parâmetros como pressão de compactação, tempo e influência da temperatura e da atmosfera de cura nas propriedades mecânicas e magnéticas de ímãs aglomerados utilizados como padrão de referência, preparados com pós MQEP de NdFeB (partículas magnéticas impregnadas com resina epóxi), foram discutidos na primeira parte deste trabalho. A melhor condição de cura foi à temperatura de 200°C por cinco horas, sob vácuo. O produto de energia máximo (BHMáx) obtido para os ímãs padrão, curados ao ar e sob vácuo, foi de 76,2 KJ/m³ e 80,5 KJ/m³, respectivamente. Na segunda parte deste trabalho, ímãs híbridos foram produzidos a partir da mistura do pó MQEP aditivado com diferentes quantidades de pós de ferrite de estrôncio e NdFeB reprocessado por HDDR. O melhor resultado de BHMáx obtido para os ímãs híbridos de MQEP com ferrite de estrôncio e MQEP com pó reprocessado por HDDR, curados sob vácuo, foi de 73,2 KJ/m³ e 78,3 kJ/m³, respectivamente. Ímãs híbridos de MQEP com pó reprocessado por HDDR apresentaram melhor desempenho magnético que os ímãs híbridos de MQEP com pós de ferrite de estrôncio. / Bonded hybrid magnets were prepared by uniaxial pressing of magnetic powders cured in air and under vacuum. Correlations between cure treatments, mechanical properties and magnetic properties were established based on results obtained by Hysteresigraphy, Vibrating Sample Magnetometry, Compression tests, Optical Microscopy and Scanning Electron Microscopy. Parameters such as compaction pressure and the influence of time, temperature and atmosphere during the curing step in the mechanical and magnetic properties of the bonded magnets used as reference patterns, produced with NdFeB MQEP powder (epoxy encapsulated magnetic particles) were discussed in the first part of this work. The better cure condition was that performed at 200 oC for 5 hours under vacuum. The maximum energy product (BHMax) obtained for the patterns bonded magnets cured in air and under vacuum was 76.2 KJ/m³ and 80.5 KJ/m³, respectively. In the second part of this work, hybrid bonded magnets were produced by the mixture of MQEP powder with different amounts of strontium ferrite powder and NdFeB powder reprocessed by HDDR. The best results of BHMax obtained for the hybrid MQEP magnets with strontium ferrite powder and NdFeB reprocessed by HDDR, cured under vacuum were 73.2 KJ/m³ and 78.3 kJ/m³, respectively. Hybrid MQEP bonded magnets produced with the addition of HDDR reprocessed powder presented better magnetic performance than that obtained with strontium ferrite powders.

No description available.

No description available.

Twin induced plasticity (TWIP) steel is a new type of structural steel, which is characterized by both high strength and superior ductility. The key to twin formation lies in the control of the stacking fault energy (SFE) of the alloy. In this thesis, the effect of heat treatment on the tensile property and microstructure of a Fe-10Mn-3Al-0.6C alloy was studied. After annealing at 675¢J for different times, It was found that both austenite and ferrite phases existed. The volume fraction and composition of these two phases did not change significantly by the heat treatment conditions used. When annealed at 675¢J, increasing annealing time caused the carbides formed at grain boundaries gradually dissolved, and led to the higher ultimate tensile stress, 900MPa, and elongation, 40%. Deformation twins were formed in the austenite phase after tensile test in the annealed specimens, indicating that TWIP behavior occurred. The best tensile property of Fe-10Mn-3Al-0.6C alloy obtained by annealing at 675¢J is within the target property of the 3rd AHSS.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 57-58). Also available on the World Wide Web.

Made available in DSpace on 2018-08-01T21:58:48Z (GMT). No. of bitstreams: 1 tese_10763_Mayra Nicoli Moura - Dissertação corrigida.pdf: 3004599 bytes, checksum: 5d4e91152db73883ca3959418fd139f2 (MD5) Previous issue date: 2017-03-22 / Cobalto do cátodo das baterias de íon lítio (LIBs) exauridas de telefones celulares Samsumg® foi reciclado como ferrita dopada com cobalto. O zinco do ânodo das pilhas alcalinas (Zn-MnO2) Duracell® AA foi reciclado para a formação da ferrita dopada com zinco. As ferritas foram aplicadas como catalisadores em reações foto Fenton heterogêneo para a descoloração do corante azul de metileno. Pela análise de difração de Raios-X (DRX) identificou-se formação de ferritas não dopadas, dopada com cobalto e dopada com zinco do tipo espinélio. Com auxilio das técnicas: microscopia eletrônica de varredura (MEV) e microscopia eletrônica de transmissão (MET) verificou-se que as ferritas não dopadas, dopada com cobalto e dopada com zinco formam aglomerados de partículas nanométricas. Pelas análises de espectroscopia de emissão óptica com plasma indutivamente acoplado (ICP OES) e espectro de absorção atômica com chama (F AAS) foi possível determinar as concentrações dos metais presentes nas ferritas. As concentrações de cobalto foram 70,0 ± 4,0 mg.g-1 e 65,0 ± 2,0 mg.g-1 nas ferritas dopadas com cobalto a partir de reagente analítico e da bateria de íon lítio, respectivamente. As concentrações de zinco nas ferritas dopadas com zinco a partir de reagente analítico e da pilha alcalina, respectivamente foram iguais 26,0 ± 1,0 mg.g-1 e 89,0 ± 4,0 mg.g-1. A condição otimizada para a descoloração do corante foi avaliada por um planejamento fatorial. A melhor condição para reação catalítica usando como catalisador CoFe2O4 foi pH 3,0, 30 mg de catalisador e 8 mL de H2O2, obtendo a porcentagem de eficiência de degradação igual a 61,5%, 87,3% e 87,7% para ferrita não dopada, dopada com cobalto a partir de reagentes analíticos e dopada com cobalto a partir da solução lixiviada da bateria de íon-Li e CoFe2O4-LIBs, respectivamente, após 420 minutos. A dopagem melhorou a eficiência da descoloração da solução de azul de metileno. A melhor condição experimental otimizada para ZnFe2O4 foi 30 mg de catalisador, 8 mL de H2O2 em pH 6,0. A eficiência de descoloração obtida foi igual a 45,9%, 92,2% e 37,0% para ferrita não dopada, dopada com zinco a partir de reagente analítico e dopada com zinco a partir da lixiviação da pilha alcalina, após 240 minutos de reação.