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Li, Ying. "The oxidation of NdFeB alloys." Thesis, University of Birmingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395924.
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Al-Khafaji, Mohammed Ali. "Magnetic force microscopy of NdFeB hard magnetic alloys." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284776.
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Brooks, Oliver Peter. "The hydrogen ductilisation process (HyDP) for NdFeB alloys." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8433/.
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The work in this thesis aims to investigate the ductility of s-HD (solid hydrogenation disproportionation) processed book mould cast NdFeB material in order to develop a novel processing route for producing fully dense magnetic material with a high energy product. A major drawback of NdFeB–based alloys is that they are extremely brittle. Therefore, to produce a fully dense magnet these alloys must be broken down into a powder and hot pressed or sintered followed by cutting and grinding to the desired shape and precise dimensions. This process is time consuming, energy intensive and produces a significant amount of waste which is not readily recyclable. This thesis reports a potentially new application of hydrogen as a promising high temperature processing tool in which the normally brittle Nd\(_2\)Fe\(_1\)\(_4\)B based intermetallic absorbs and reacts with hydrogen, converting it into a ductile, disproportionated condition, which can be subsequently compressed at room temperature. It can then be restored to its original state by removal of the hydrogen under partial vacuum at elevated temperatures. By maintaining a solid form throughout, almost zero waste material is produced and the deformed material exhibits a high coercivity and a useful degree of anisotropy.
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Lorenz, Amanda Leigh. "Improvement of NdFeB permanent magnets via diffusion annealing." Master's thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/10142.
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Mestrado em Ciência e Engenharia de MateriaisOs magnetos sinterizados de Nd-Fe-B, têm o maior produto de energia de todos os magnetos e têm vindo a substituir progressivamente os magnetos ferróicos em aplicações onde é necessária uma maior densidade de energia. São áreas como carros híbridos, acionamento de turbinas eólicas, bobines de motores, e também na miniaturização de dispositivos eletrónicos. Um parâmetro importante é a sua coercividade, e respetiva dependência na temperatura, que determina o intervalo de temperatura de aplicação. A fim de melhorar as temperaturas de funcionamento, elementos diversos, especialmente terras raras pesadas (HRE), tais como disprósio ou térbio, têm sido adicionadas como um meio de aumentar a coercividade, levando, no entanto, a uma diminuição da remanência. Embora as HREs sejam tradicionalmente incorporadas durante o processo de sinterização, foi demonstrado que a aplicação de uma camada superficial de Dy, seguida de recozimento pode exigir menos Dy, a fim de obter uma determinada coercividade. Este processo utiliza a difusão por fronteiras de grão (Grain Boundary Diffusion, GBD). O objetivo deste trabalho foi reduzir a quantidade de Dy necessário para atingir um desejado aumento da coercividade em pequenos magnetos de Nd-Fe-B utilizando processos GBD e experimentação com adições de Cu. Os magnetos foram revestidos usando deposição física de vapor (PVD), sujeitos a tratamento térmico e, em seguida caracterizados utilizando técnicas de medição magnética, bem como microscopia electrónica de varrimento SEM. As medições magnéticas foram também usadas para avaliar o processo de difusão de Cu e Dy durante o recozimento. A coercividade aumentou com o tempo de recozimento, em que Dy é difundido no sistema, alcançando melhorias de cerca de 50% na coercividade. No entanto, a distância de difusão foi limitada a cerca de 100 μm a partir da superfície da amostra. Os aumentos relativos na coercitividade por unidade de Dy adicionado ao sistema usando GBD foram maiores do que com Dy incorporado durante a sinterização. A Inclusão de Cu não foi considerada benéfica para o sistema.
Sintered Nd-Fe-B rare earth (RE) magnets have the highest energy product of any magnets and have been progressively replacing ferrous magnets in applications where a high energy density is needed. This pertains to areas such as hybrid cars, direct-drive wind turbines, voice coil motors, as well as the miniaturization of electronic devices. An important parameter of these magnets is their coercivity, respectively the temperature dependence thereof, which determines the temperature range accessible to the magnets. In order to improve the working temperatures, various elements, most notably heavy rare earth (HRE) elements such as dysprosium or terbium, have been alloyed in order to increase the coercivity; however, a remanence decrease results. Although HREs are traditionally included during the sintering process, it has been shown that applying the Dy as a coating after sintering followed by annealing may require less Dy in order to reach a given coercivity. This process is called Grain Boundary Diffusion (GBD). The aim of this work was to reduce the amount of Dy needed to attain a desired increase in coercivity in small Nd-Fe-B magnets by employing GBD processes and experimentation with Cu additions. Magnets were coated using physical vapor deposition (PVD) techniques, heat treated, and then assessed using magnetic measurement techniques as well as scanning electron microscopy (SEM). Magnetic measurements were also used to assess the diffusion process of Dy and Cu into the magnets during annealing. The coercivity increased as annealing time progressed and Dy interdiffused throughout the system, reaching improvements in coercivity of about 50%. However, the diffusion distance was limited to about 100 μm from the sample surface. For small Dy additions, the relative gains in coercivity per unit Dy added to the system using GBD were greater than magnets with Dy incorporated during sintering. Inclusions of Cu were not found to be beneficial to the system.
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Silva, Bruno Ferreira Antunes da. "Preparação de ímãs híbridos aglomerados com mistura de pós a base de TR-Fe-B e ferrite." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-29052013-075721/.
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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.
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Ciuta, Georgeta. "Une étude expérimentale de la coercivité des aimants NdFeB." Phd thesis, Université de Grenoble, 2013. http://tel.archives-ouvertes.fr/tel-00952842.
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Les processus d'aimantation dans des aimants de type NdFeB ont été étudiés dans le cadre de cette thèse, sur la base de mesures d'aimantation macroscopiques et de caractérisations locales (MFM). Deux types d'échantillons ont été analysés : des aimants massifs dont les propriétés excellentes résultent d'un processus d'infiltration de NdCu le long des joints de grain (échantillons fournis par Toyota Motor Corporation) et des échantillons sous forme de couches épaisses, dont les microstructures, et, de ce fait les propriétés magnétiques, diffèrent. La variation thermique du champ coercitif et celle du volume d'activation ont été analysées dans le cadre de deux modèles, respectivement dénommé micromagnétique et global. Les valeurs déduites des deux paramètres principaux caractérisant la coercitivité (N représentant les effets du champ démagnétisant et α reliant le champ coercitif aux propriétés magnétiques intrinsèques de la phase dure) indiquent que dans les aimants massifs les différences de coercitivité entre échantillons sont dues pour l'essentiel à la variation de N alors que dans les films, c'est la variation du paramètre α qui joue le rôle principal. Le volume d'activation à une température donnée, dérivé de mesures de trainage magnétique, a des valeurs proches pour tous les échantillons massifs. Au contraire, il varie d'un échantillon à l'autre dans le cas des films : plus le champ coercitif est fort, plus petit est le volume d'activation. Une conclusion générale de cette étude est que les propriétés magnétiques au sein du volume d'activation sont proches de celles de la phase dure Nd2Fe14B. Le lien entre microstructure et coercivité a été examiné dans les films épais par microscopie de force magnétique (MFM). Des observations de films dans différents états rémanents le long du cycle d'hystérésis ont été réalisées. Des " domaines d'interactions " ont été révélés dans les films de faible coercitivté. Dans de tels films, comme dans ceux de coercitivité moyenne, le renversement d'aimantation est dominé par la propagation de domaines, alors que dans les films de plus forte coercitivité, la nucléation suivie de la propagation de domaines d'orientation inverse à celle de l'aimantation principale dominent.
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Adrwish, Salahadin Muhammed Ali. "The processing and characterisation of recycled NdFeB based magnets." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4122/.
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The scrap magnets were turned into a powder using the HD process. The powder was milled for specific times and sintered for 1-3hrs at 1090 °C. The magnet samples were measured using a permeameter to determine their magnetic properties. Cross sections of these samples were then mounted in bakelite and subject to metallographic studies using SEM analysis by means of Joel6060 and 7000. Some of the recycled magnets did achieve magnetic properties close to the starting magnets. It was shown that the nature of the starting magnets determines the appropriate sintering conditions during recycling. Sintering for 3hrs was good for magnets with high oxygen content but too long for fresh material and magnets with lower oxygen content, as indicated by the dilatometer measurements. Some magnets were studied further due to a lean rare content. These were treated with various heat treatments and other techniques (e.g. grain boundary diffusion) and the addition of various additives such as Dy, Co, Nd, Nband Tb. A study of how reactive recycled magnets in 3% salt-bath (Sodium Chloride NaCI) compared with starting magnets. The corrosion study was conducted over 30 weeks where results had indicated that recycled magnets have better corrosion resistance than the original material. This was due mainly to the shape of the magnets and the magnets being anisotropic, where there is a concentration of corrosion sites on the poles. The corrosion initiated at the Nd rich phase where it propagates further as time goes on. Furthermore, the magnetic properties decrease over the period, as expected. An investigation was made into the use of scrap magnetic powder in bonded magnets using tin as binder was also undertaken.
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Herraiz, Lalana Enrique. "Production of sintered NdFeB magnets from scrap alloy powders." Thesis, University of Birmingham, 2017. http://etheses.bham.ac.uk//id/eprint/7609/.
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Rare earth metals are at highest supply risk of all metals for clean technologies due to supply restrictions. Rare earth elements are essential for the highest energy permanent magnets which are used in high-tech green applications such as wind turbines and electric motors. This rare earth 'crisis' has been addressed by many authors by reducing or substituting the rare earths for less critical elements. The focus of this thesis, however, is on recycling of rare earth magnetic materials. Previous work has been focused on recycling NdFeB by re-sintering and blending alloying elements to improve the final magnetic properties. However, none of these studies have addressed the systematic addition of alloying elements or the particle size effect on the final magnetic performance of the recycled magnet. The work in this thesis is aimed at maximising the magnetic performance of recycled NdFeB magnets by investigating the effect of the manufacturing route and the influence of adding alloying elements. Uncoated end-of-life sintered NdFeB were exposed to hydrogen at room temperature to break them down into a friable powder; which was then milled, sieved, aligned, pressed and sintered into recycled magnets. The resulting magnets were tested on a permeameter at room temperature, 75 and 150oc to measure the magnetic properties. Scanning electron microscopy was used to assess the microstructures. Mechanical properties such as Vickers hardness and fracture toughness were also studied.
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Sheridan, Richard Stuart. "Optimisation of HDDR processing parameters of sintered NDFEB magnets." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/4929/.
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In recent years rare earth metals have hit the headlines due to supply restrictions of neodymium and dysprosium from the main supplier China. The work in this thesis investigates the possibility of recycling sintered NdFeB-type magnets using a combination of hydrogen decrepitation (HD) and the HDDR process (Hydrogenation Disproportionation Desorption and Recombination). In this work the development of microstructure during the HDDR process has been identified and the route taken by hydrogen during absorption and desorption. The microstructure and magnetic properties have been shown to be affected by the process temperature, disproportionation pressure and recombination pressure and time. Sample batches up to 100g exhibit little variation in magnetic properties however 400g batches result in large variations partially due to incomplete recombination. By increasing the disproportionation pressure it was possible to simultaneously process mixed scrap feeds with different Dy and Co levels, however a large variation in magnetic properties was also observed. Optimal processing of sintered Nd\(_{13.4}\)Dy\(_{0.7}\)Fe\(_{78.6}\)Al\(_{0.7}\)Nb\(_{0.4}\)B\(_{6.3}\) was performed by in-situ HD followed by HDDR at 880\(^o\)C with a disproportionation pressure of 1500mbar and recombination under vacuum. The resultant powder exhibited a remanence of 1.08 T, coercivity of 840 kAm\(^{-1}\) and maximum energy product of 178 kJm\(^{-3}\).
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Elwert, Tobias [Verfasser]. "Entwicklung eines hydrometallurgischen Recyclingverfahrens für NdFeB-Magnete / Tobias Elwert." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2015. http://d-nb.info/1070920673/34.
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Hugonnet, Brice. "Frittage et évolution de la microstructure au cours des traitements thermiques d'aimants NdFeB : influence sur les propriétés magnétiques." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI079/document.
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Les aimants NdFeB sont les aimants les plus puissants que l’on peut trouver actuellement sur le marché. Leurs propriétés exceptionnelles proviennent des propriétés intrinsèques de la phase Nd2Fe14B mais également de la microstructure imposée par le mode d’élaboration. Ces aimants sont généralement réalisés par frittage avec phase liquide à partir d’une poudre monocristalline préalablement orientée sous champ magnétique. Cette voie permet d’obtenir une microstructure à grains fin découplés magnétiquement les uns des autres par une fine couche de phase riche en néodyme, dont la distribution est optimisée après un recuit à une température donnée. Pour une utilisation dans des moteurs et générateur électriques, il est courant d’ajouter du dysprosium pour conserver une coercitivité suffisante à la température de fonctionnement. Mais ce gain de coercitivité se fait au détriment de l’induction rémanente et du coût de l’aimant de par la rareté du dysprosium. Il est donc nécessaire de pouvoir s’affranchir de son utilisation par une meilleure compréhension des liens entre le procédé d’élaboration et la microstructure du matériau, afin d’optimiser les propriétés magnétiques finales.Cette thèse s’intéresse tout d’abord au frittage d’aimants NdFeB pour une nuance du commerce et donc fortement alliée. La forte anisotropie de retrait lors de la densification n’est pas clairement expliquée dans la littérature et son interprétation peut apporter un éclairage sur les propriétés magnétiques. Le frittage a ainsi été étudié à l’aide d’essais de dilatométrie dans la direction d’orientation de la poudre ainsi que dans la direction transverse. Le frittage a également été interrompu à différents moments et la microstructure analysée. Des analyses d’images ont permis de comprendre, à l’aide d’un modèle analytique du frittage, qu’une partie de l’anisotropie de retrait s’expliquait par une distribution anisotrope des surfaces de contact entre les grains de poudre, issue de l’étape d’orientation sous champ. Cette analyse a été confirmée par des simulations par éléments discrets.Le deuxième volet de la thèse s’intéresse au rôle des éléments d’alliage les plus couramment rencontrés dans les aimants hors dysprosium. Le rôle de l’aluminium, du cobalt et du cuivre sur les propriétés magnétiques a été examiné en étudiant une vingtaine de compositions simplifiées avec des quantités d’éléments d’alliage voisines des valeurs que l’on retrouve dans les aimants du commerce. Les différents échantillons ont été recuits à des températures déduites d’essais DSC. Les résultats montrent que ces trois éléments d’alliage agissent de manière croisée sur la coercitivité. Au-delà de la mesure de coercitivité, l’évolution de la forme de la courbe de désaimantation en fonction de la composition et de la température de recuit apporte des informations importantes sur l’action des éléments d’alliage sur la microstructureNdFeB hard magnets are the most powerful magnets commercially available. Their outstanding properties originate from Nd2Fe14B intrinsic properties and from the microstructure imposed by the manufacturing process. These magnets are generally obtained by liquid phase sintering of an oriented monocrystalline powder which enables a microstructure made of grain magnetically decoupled by a thin neodymium-rich layer which is optimally distributed in the magnet after a low temperature annealing. For them to be used in electrical engines and generators, dysprosium is usually added so that the coercivity is high enough at the working temperature. But dysprosium is rare and expensive and lowers the remnant induction. It is therefore important to get free of its usage by a better understanding of the links between the manufacturing process and the microstructure, so that the final magnetic properties can be optimized.First, this thesis deals with NdFeB sintering on an alloyed commercial grade. The high shrinkage anisotropy during densification is not clearly explained and its interpretation could bring information on the magnetic properties. Dilatometric studies have been performed along orientation direction as well as along the transverse direction. Sintering has been interrupted at different times and the microstructure was observed. Image analysis has enabled to understand, thanks to an analytical model, that a part of the anisotropy could be explained by an anisotropic contact orientation distribution, originating from the magnetic orientation step. Discrete element modelling has confirmed this approach.The second part of the thesis deals with the role of the most commonly used alloying elements on the magnetic properties: aluminum, cobalt and copper. Around twenty different model grades were examined with composition close to the ones of commercial magnets. After having been sintered, the samples were annealed at temperatures deduced from DSC measurements. Results show that the three elements have cross effects on coercivity. Beyond coercivity, demagnetizing curve shape is sensitive to the composition and annealing temperature and gives important information on the role of the alloying elements on the microstructure
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Neto, Teofilo Mendes. "Estudo microestrutural e propriedades magnéticas em ímãs permanentes sinterizados a base de PrFeCoBNb com adições de elementos de ligas." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-28092011-094845/.
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Neste estudo, as propriedades magnéticas dos ímãs sinterizados, produzidos a partir de uma mistura de ligas Pr16Fe76B8 e Pr14FebalCo16B6Nb0,1Mx, onde M= Al, Cu, P, Si, Gd, Ga, Dy, Tb e x= 0,1, 0,3, 0,5 % at. em iguais proporções, foram correlacionadas com as características microestruturais através de microscopia eletrônica de varredura (MEV) e de transmissão (MET). Utilizou-se microscopia eletrônica de varredura (MEV) e processamento computacional das micrografias, na investigação das características associadas ao tamanho e formato dos grãos magnéticos (Φ). A correlação utilizada indicou que fatores de quadratura superiores estão associados a grãos mais arredondados e com distribuição de tamanho mais estreita. Considerando que a variação no tamanho de grão e os valores de coercividade não se mostraram conclusivas com MEV, utilizou-se o recurso da microscopia eletrônica de transmissão (MET), microanálise com EDS e padrão de difração eletrônica. A associação da coercividade com a microestrutura foi feita com base nas investigações das fases não magnéticas, ricas em praseodímio dos pontos triplos e nos contornos de grãos. Com o microscópio de transmissão de alta resolução (HRTEM), foi possível observar a presença de uma camada contínua e regular entre os grãos da fase magnética para o ímã com adição de Ga 0,25% at. A modificação da microestrutura no contorno de grão do ímã com adição de Ga pode ser indicada como responsável pelo aumento de 10% na coercividade (1100 mT) comparado com o ímã Pr15FebalCo8B7Nb0,05.In this study the magnetic properties of sintered magnets, prepared with a mixture of Pr16Fe76B8 and Pr14FebalCo16B6Nb0.1Mx alloys, where M = Al, Cu, P, Si, Gd, Ga, Dy, Tb and x = 0.1, 0.3, 0.5 at.% in the same proportions, were correlated with the microstructural features by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and computer processing of the micrographs were used in order to provide the characteristics associated with the size and shape of the magnetic grains (Φ phase). The correlation used shows that superior squareness factors are associated with rounder and narrower size distribution grains. Considering that the variation in the grain size and coercivity values were not conclusive with SEM, it has been used TEM, micro analysis by EDS and electron diffraction pattern. The coercivity relation with the microstructure was based on investigations of non-magnetic phases, in triple points, and in the grain boundary. With a high resolution transmission microscope (HRTEM), it was possible to observe a regular and continuous layer between the grains of the magnetic phase for the magnet with 0.25 at.% of Ga. The presence of such boundary can be indicated as responsible for higher coercivity values of this magnet. Microstructure was modified in the grain boundary by Ga addition and can be indicated as responsible for coercivity value (1100 mT) 10% higher than Pr15FebalCo8B7Nb0.05 magnet.
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Périgo, Elio Alberto. "Estudo das correlações entre microestrutura, propriedades magnéticas e fator de quadratura em ímãs sinterizados de PrFeB e NdFeB processados com Hidrogênio." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-30092009-153608/.
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Neste trabalho, avaliou-se inicialmente a preparação de ímãs sinterizados de Pr16Fe76B8 (% at.) por meio de moagem de alta energia em moinho tipo planetário, averiguando-se os efeitos do tempo de moagem bem como da velocidade rotacional do moinho. Encontraram-se as melhores propriedades magnéticas para um magneto preparado com a matéria-prima cominuída durante 75 minutos e velocidade rotacional de 200rpm [JR = (1,02 ± 0,02) T, 0JHc = (1,42 ± 0,03) T e (BH)max = (200 ± 4) kJm-3]. De forma a melhorar a remanência, reduziu-se o tempo de exposição da liga ao hidrogênio, de 60 minutos para 2 minutos, obtendo-se um ímã com JR = (1,14 ± 0,02) T, 0JHc = (1,44 ± 0,03) T e (BH)max = (250 ± 5) kJm-3, constatando-se que a causa para a reduzida remanência no primeiro caso decorria do baixo grau de orientação cristalográfica. Durante esta investigação, desenvolveu-se e validou-se uma nova metodologia para quantificação do parâmetro . Posteriormente, propôs-se uma correlação quantitativa inédita entre a microestrutura e o fator de quadratura em magnetos anisotrópicos de TR16Fe76B8 (TR = Nd ou Pr) sinterizados. A expressão apresentada utiliza o tamanho, a elongação e a circularidade médios dos grãos e seus respectivos desvios padrões. Melhora-se o fator de quadratura quando a microestrutura apresenta grãos arredondados e com estreita distribuição de tamanho. A homogeneidade de tamanho dos grãos apresenta uma influência maior sobre o fator de quadratura quando comparada à homogeneidade de forma dos grãos. Ademais, verificou-se que o tratamento térmico após a sinterização melhora a ix homogeneidade de forma ao passo que a moagem melhora a homogeneidade de tamanho dos grãos. Avaliou-se, adicionalmente, o efeito da temperatura sobre o fator de quadratura em magnetos sinterizados anisotrópicos, verificando-se que o mesmo é controlado principalmente por sua microestrutura e confirmando a expressão previamente proposta. Além disso, propôs-se uma correlação quantitativa entre o produto de energia máximo e o fator de quadratura. Compararam-se valores experimentais e calculados, utilizando a expressão apresentada, e a discrepância encontrada foi de 5%. Por fim, avaliou-se qual seria o valor mínimo do fator de quadratura em ímãs sinterizados, constatando-se que magnetos isotrópicos devem apresentar o menor valor para tal parâmetro em virtude do reduzido grau de alinhamento cristalográfico. Ademais, verificou-se que para este tipo de amostra, em geral, 0,20 FQ 0,30.In this work, it has firstly been evaluated the preparation of Pr16Fe76B8 sintered permanent magnets (% at.) by means of high-energy milling using a planetary ball mill. The influence of both milling speed and time has been verified. The best magnetic properties [JR = (1.02 ± 0.02) T, 0JHc = (1.42 ± 0.03) T and (BH)max = (200 ± 4) kJm-3] have been found for a permanent magnet prepared with the magnetic alloy milled during 75 minutes using a rotational milling speed of 200 rpm. In order to improve the remanence, the hydrogen decrepitation process time has been reduced from 60 minutes to 2 minutes. In this case, it has been obtained a sintered magnet with JR = (1.14 ± 0.02) T, 0JHc = (1.44 ± 0.03) T and (BH)max = (250 ± 5) kJm-3 due to the improvement of crystallographic alignment of the hard magnetic phase. During such investigation, a new methodology to quantify the parameter has been developed. Subsequently, for the first time, a quantitative correlation between the microstructure and the squareness factor in anisotropic sintered RE16Fe76B8 (RE = Nd or Pr) magnets has been proposed. The presented expression utilizes the mean size, the mean elongation and the mean roundness of the hard magnetic grains as well as their respective standard deviations. The squareness factor can be improved with a microstructure with rounder grains and with a sharp grain size distribution. The grain size homogeneity is more important to enhance the squareness factor compared to grain shape homogeneity. Furthermore, it has also been verified that the annealing after sintering improves the grain shape homogeneity and the milling enhances the xi grain size homogeneity. Moreover, the effect of the temperature on the squareness factor of anisotropic sintered magnets has also been evaluated. Such parameter is mainly controlled by the samples microstructure, in agreement with the proposed expression. Furthermore, a quantitative correlation between the maximum energy product and the squareness factor has been proposed. Experimental and calculated values have been compared and the discrepancy found has been, in general, inferior to 5%. At last, the minimum squareness factor value of sintered permanent magnets has also been evaluated. Isotropic samples should show the smallest squareness factor due to the reduced degree of crystallographic alignment. In general, for this kind of sample, 0.20 SF 0.30
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Pollard, Robert James. "The microstructure and magnetic properties of NdFeB based permanent magnets." Thesis, University of Salford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328260.
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Wang, Zhiran. "The demagnetising factors for bonded neodymium iron boron (NdFeB) magnets." Thesis, University of Sheffield, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340145.
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Degri, Malik John Jamaji. "The processing and characterisation of recycled NdFeB-type sintered magnets." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5516/.
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A study of the processing and characterisation of sintered NdFeB magnets made from recycled feed stock was undertaken. Initially the hydrogen decrepitated (HD) powder was investigated using two different milling techniques. The powders were analysed with optical microscopy, with the aid of a magnetic field. It was found that with light milling the HD powder breaks up to a similar particle size to that of the grain size of the starting material. A data logging system was built to investigate the desorption behaviour of green compacts during sintering. Desorption traces showed desorption from the matrix phase and the intergranular Nd-rich phase. The start of desorption was seen to shift to lower temperatures as the mean particle size of the green compact was reduced. For the processing route used in this work intergranular additions of neodymium hydride were required to increase the density and magnetic properties. To investigate the oxidation behaviour of lightly milled HD powder, powder was exposed to air for varying times. The exposed powder was aligned pressed and sintered. The Nd-rich desorption peak reduced with exposure time, the density and magnetic properties also reduced. Post exposure additions of Intergranular neodymium hydride to the powder recovered density and magnetic properties.
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Kuo, Chun-Hsin. "The effect of Zr and ZrB2 additions to NdFeB alloys." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/1018/.
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Alloy compositions near to stoichiometric Nd2Fe14B produced under normal casting conditions, with subsequent isothermal heat treatments and with sintering have been characterised. The possible mechanisms for removing the soft magnetic phase, free α-Fe, via additions of 0.6 at% of Zr or 1.0 at% of ZrB2 have been investigated by EPMA (Electron Probe Microanalysis) and TEM (Transmission Electron Microscopy). 1.0 at% of ZrB2 has been found to be very effective in suppressing the formation of free α-Fe dendrites during solidification, but the excessive ZrB2-type needles formed in the NdFeB alloy may have a deleterious effect on the magnetic properties. However, the coercivity of the NdFeB sintered magnets can be improved to some extent by addition of Zr or ZrB2 to the composition Nd12.68Fe77.91-80.91B6.41-8.41Zr0-1 (at%) due to the smaller and more uniform grains of the Nd2Fe14B phase (~6.5 μm) in the sintered magnets. Both SEM (equipped with WDX) and TEM (equipped with EDX) have been employed to investigate ZrB2 needles in Nd12.68Fe77.91-80.91B6.41-8.41Zr0-1 (at%) alloys. It is found that suppression of free α-Fe dendrites in both Zr-containing NdFeB alloys resulted from different solidification routes. Since the sequences of formation of the ZrB2-type needles in Zr-containing alloys are different, the Nd2Fe14B grain growth is inhibited via different mechanisms. Meanwhile, evidence for the high temperature solubility of Fe in ZrB2 needles is found for both Zr-containing NdFeB alloys. Chemical analysis shows that the ZrB2-type needles in the NdFeB alloys are composed mainly of B (~70 at%) and Zr (~20 at%) with a small but significant amount of Fe (~7 at%), a formula which can be expressed as (Zr1-x, Fex)B2 (x~0.3).
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Samin, Adib J. Jr. "An analysis of neutron radiation effects on NdFeB permanent magnets." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1405899609.
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Mapley, Martin C. "Additive Manufacturing of Bonded NdFeB Magnets by Selective Laser Sintering." Thesis, Griffith University, 2020. http://hdl.handle.net/10072/395100.
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Permanent magnets are used in many everyday devices to assist in the conversion of electronic energy into mechanical energy. Traditional manufacturing pathways are well established, however, they inherently suffer from long lead times and high costs for low volume production runs. A technique known as additive manufacturing (colloquially 3D printing) has been applied to many industries using a multitude of materials with success in reducing both product development times and cost for prototypes and low volume production runs. Due to this reported success, several additive manufacturing techniques have been investigated in order to rapidly produce magnets of custom geometries using isotropic magnetic material (specifically neodymium-iron-boron). Although some of these techniques have shown promise, many require pre-processing of the raw powders into a filament or fluid suspension, thus increasing the number of steps in the process. As permanent magnet raw material is commercially available in powdered form, it was hypothesised that a powder-based additive manufacturing technique known as selective laser sintering could be used to produce permanent magnets by mechanical alloying of magnetic powder with a powdered polymer binder. It was further hypothesised that by combining the use of high energy anisotropic magnetic powder with an in-situ alignment fixture, as used in the industrial manufacturing process, permanent magnets with higher performance than those produced using additive manufacturing from isotropic powders. Accordingly, there were three key aims in this research project: ii Additive Manufacturing of Bonded NdFeB Magnets by Selective Laser Sintering Develop a selective laser sintering machine from off-the-shelf components and compare the geometrical and mechanical properties of the produced polyamide-12 parts with that of a commercial machine. Using two commercially available isotropic magnetic powders with flake and sphere particle morphologies mixed with polyamide-12 powder, determine the processing parameters and mixing ratios which lead to magnets with the most accurate geometrical and strongest mechanical and magnetic properties. Develop and test an in-situ particle alignment fixture and examine its effect on the geometrical and magnetic properties of magnets produced from anisotropic magnetic powder mixed with polyamide-12. The first experimental chapter (Chapter 3) covers designing, building and validating the tool required to conduct the research which is a selective laser sintering machine produced solely from off-the-shelf parts. Over the next two chapters (Chapters 4 and 5), the influence of machine processing parameters (laser power = 0.5 – 1.17 W, scan spacing = 0.11, 0.22, 0.31 mm) and powder loading fraction (0 – 90%/vol) on the properties of magnets produced from two commercially available neodymium-iron-boron powders was examined. By examining the geometrical, mechanical and magnetic properties, preferred processing parameters and mixing ratios could be identified based on their deviation from model data and highest mechanical and magnetic strength. Next (Chapter 6), an in-situ alignment fixture based upon a Helmholtz coil was proposed and a prototype developed. The ability of the coil to impart torque to anisotropic particles while minimising translational forces was examined using images captured with an optical microscope then evaluated using image processing techniques to characterise the percentage of loose particles it could align. Finally (Chapter 7), the Helmholtz coil-based alignment fixture was added to the selective laser sintering machine where it was used to provide an alignment field to each layer of anisotropic powder prior to consolidation by the laser. The geometry, density and magnetic properties of the permanent magnets were examined in the presence and absence of the alignment field. The constructed selective laser sintering machine was demonstrated to produce parts from polyamide-12 reaching densities of 918 ± 9 kg/m3 and achieving an elastic Additive Manufacturing of Bonded NdFeB Magnets by Selective Laser Sintering iii modulus of 358.36 ± 3.04 MPa and elongation at break of 11.13 ± 0.02%. Permanent magnets produced from the mechanically alloyed commercial powders demonstrated the best properties with a supplied energy density of 0.255 J/mm2 possessing comparable magnetic characteristics to those produced with other AM methods (311 ± 9 and 363 ± 6 mT for the flake and spherical powders respectively). It was also demonstrated that magnetic powder loading fractions above 30%/vol for the spheres and 50%/vol for the flakes showed no significant increases in magnetic performance while the mechanical performance deteriorated significantly. An in-situ alignment fixture, based upon a Helmholtz coil, demonstrated 30% alignment of a selection of particles according to optical image analysis of randomly orientated flake particles. When used during the processing of magnets, the magnetic performance, when using anisotropic powder, was shown to increase by 28%. However, the low loose packing density of the starting powder (2880 kg/m3) compared to the isotropic powders (3023 kg/m3 for the flakes and 4017 kg/m3 for the spheres) limited the maximum density of the magnets and thus suffered from poorer than expected magnetic performance. The content of this thesis demonstrates the development of an open source-based selective laser sintering machine which was then used to explore the production of permanent magnets from commercially available isotropic and anisotropic powders with the addition of an in-situ alignment fixture.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Fliegans, Jérôme. "Coercivity of NdFeB-based sintered permanent magnets : experimental and numerical approaches." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY071.
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Les aimants permanents Nd-Fe-B sont actuellement les plus puissants du marché. Ils sont indispensables pour des applications telles que les moteurs des véhicules électriques ou les générateurs des éoliennes. Leurs propriétés exceptionnelles viennent des propriétés magnétiques intrinsèques de la phase Nd2Fe14B et de leur microstructure. Cependant, les machines électriques fonctionnent entre 120 et 180°C et les propriétés magnétiques extrinsèques telles que la coercitivité et la rémanence diminuent avec la température. Un moyen d’améliorer la coercitivité des aimants frittés Nd-Fe-B est la substitution du Nd par des terres rares lourdes comme le Dy, afin d’augmenter l’anisotropie magnétocristalline. Néanmoins, le Dy est un matériau critique et un objectif majeur de la recherche est actuellement de développer des aimants possédant d’excellentes propriétés magnétiques extrinsèques et contenant peu de Dy. Cela nécessite une meilleure compréhension du lien entre microstructure et coercitivité. Dans les aimants frittés Nd-Fe-B, un des points-clés est le contrôle de la taille de grain et de la répartition des phases secondaires aux joints de grains de façon à limiter la nucléation du retournement de l’aimantation et à garantir un bon découplage magnétique des grains. La première partie de la thèse est une étude comparative des caractérisations magnétiques en circuit ouvert et fermé réalisées sur des aimants frittés Nd-Fe-B. Les différences de coercitivité observées sont expliquées par les phénomènes de viscosité magnétique et d’effets de champ démagnétisant. La deuxième partie traite du procédé de diffusion aux joints de grains appliqué aux aimants frittés Nd-Fe-B et utilisant des alliages Dy-Co. Des caractérisations microstructurales ont été réalisées en complément de mesures magnétiques afin de déterminer les profils de diffusion et de coercitivité, et ainsi d’établir le lien entre les variations locales de composition chimique et le champ coercitif. De plus, des simulations micromagnétiques ont permis de décrire le retournement de l’aimantation à l’échelle nanométrique dans un modèle simplifié cœur-coquille. Enfin, la dernière partie de la thèse constitue une discussion sur la coercitivité des aimants diffusés au Dy-Co (à gradient de champ coercitif) à l’aide d’un modèle de diffusion et de simulations sur un modèle polycristallinNd-Fe-B permanent magnets are the most powerful among all commercially available magnets. They play a significant role in energy applications, such as motors of electric vehicles and generators of windmills. Their outstanding properties come from the excellent intrinsic magnetic properties of the Nd2Fe14B phase and from their microstructure. However, electrical machines operate at about 120-180°C and extrinsic magnetic properties such as coercivity and remanence decrease rapidly with temperature. One way of improving coercivity of Nd-Fe-B sintered magnets is to substitute Nd with a heavy rare earth such as Dy, so as to increase the magnetocrystalline anisotropy. However, Dy is a strategic element and a major objective of the research community is therefore to develop Nd-Fe-B magnets that possess excellent extrinsic magnetic properties with a reduced content of Dy. This requires a better understanding of the link between microstructure and coercivity. The key point is the control of the grain size and the distribution of secondary phases at grain boundaries to prevent magnetization reversal and magnetic coupling. The first part of this thesis concerns a comparison of open-circuit and closed-circuit magnetization measurements carried out on Nd-Fe-B sintered magnets. The observed differences in coercivity values are discussed in terms of magnetic viscosity and demagnetizing field effects. The second part deals with the grain boundary diffusion process performed on Nd-Fe-B sintered magnets using Dy-Co alloys. Microstructural observations and magnetic measurements have been carried out to characterize the diffusion and coercivity profiles and to establish the link between local variations in composition and coercivity. Moreover, micromagnetic simulations have been performed to describe magnetization reversal at the nanoscale in a simple core-shell model. The last part constitutes a discussion about coercivity in graded magnets via a diffusion model and further simulations on a polycrystalline model
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Biswas, Kaushik. "Effect of melt convection on microstructure evolution of peritectic Nd-Fe-B and Ti-Al alloys." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1222335463187-47437.
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In dieser Arbeit wurde der Einfluss der Schmelzkonvektion auf das erstarrende Gefüge von peritektischen Nd-Fe-B – und TiAl-Legierungen mit Hilfe neuartiger Methoden untersucht. Da die magnetischen und mechanischen Eigenschaften dieser technisch relevanten Legierungen stark vom Gefüge und insbesondere vom Volumenanteil der properitektischen Phase abhängen, sind diese Untersuchungen von großem Interesse. Auf der Basis der numerischen Simulationen der Schmelzkonvektionsmoden und des elektromagnetischen Problems in einer induktiv beheizten Schmelze, die am Forschungszentrum Dresden-Rossendorf durchgeführt wurden, wurden am IFW Dresden neuartige Versuchsaufbauten entwickelt, die die Modifizierung der Konvektion in einer Metallschmelze ermöglichen. Dies sind ein Aufbau zur erzwungenen Schmelzrotation in einem Tiegel und eine modifizierte Floating-Zone-Anlage. Die erzwungene Schmelzrotation, bei der der Schmelztiegel mit einer definierten Frequenz rotiert, führt in Übereinstimmung mit der Simulation zu einer starken Reduzierung der Konvektion in Abhängigkeit von der Frequenz. Diese Methode wurde auf Nd-Fe-B-Legierungen angewendet mit dem Ziel, die Bildung der unerwünschten weichmagnetischen Eisenphase zu unterdrücken bzw. deren Volumenanteil zu reduzieren. Im Ergebnis konnte der Volumenanteil der properitektischen Phase mit diesem Verfahren um 38.5 % reduziert werden. Das dendritische Gefüge wurde einer ausführlichen statistischen Analyse unterzogen, bei der die Abstände der sekundären Dendritenarme (SDAS) gemessen wurden. Es konnte gezeigt werden, dass die SDAS sich mit steigender Frequenz der Tiegelrotation, was einer reduzierten Schmelzkonvektion entspricht, verringern. Die Verringerung des Volumenanteils der properitektischen Eisenphase und der SDAS wird mit dem reduzierten konvektiven Massentransport unter reduzierter Schmelzkonvektion erklärt. Starke interdendritische Strömung reduziert die Dicke der Diffusionsgrenzschicht um die properitektische Phase. Dadurch wird der Stofftransport durch die Grenzschicht erleichtert. Kleinere Dendritenarme werden in die Schmelze zurückgeschmolzen, wodurch sich der Abstand zwischen den verbleibenden Dendritenarmen vergrößert. Eine Floating-Zone-Anlage, die das tiegelfreie Prozessieren von Metallschmelzen erlaubt wurde so modifiziert, dass mit Hilfe eines Doppelspulensystems eine zusätzliche wohl definierte elektromagnetische Kraft eingebracht wird, über die eine sehr intensive (Zweiphasenrührer in Parallelschaltung) bzw. stark verringerte Strömung (Doppelspule in Reihenschaltung) in der Schmelze eingestellt werden kann. Die experimentellen Ergebnisse der Untersuchungen am Nd-Fe-B-System mit der Doppelspule in Reihenschaltung zeigten, dass sich bei einem optimalen Spulenabstand von 5,1 mm die geringste Schmelzkonvektion ergab, wobei der Anteil des a-Eisen-Volumenanteils weiter verringert werden konnte. Im Gegensatz dazu wurde mit dem Zweiphasenrührer in Parallelschaltung eine sehr starke Schmelzkonvektion mit einem maximalen Volumenanteil der a-Eisen-Phase eingestellt, wobei durch die starke Rührung ein Wechsel der Morphologie von dendritisch zu globular zu beobachten war. Die Untersuchungen zum Einfluss der starken Schmelzkonvektion wurden auf ein weiteres peritektisch erstarrendes System ausgedehnt, um eine generalisierte Aussage zum Einfluss der Konvektion auf Gefüge und Eigenschaften peritektisch erstarrender Legierungen zu erhalten. Die ausgewählte Ti45Al55 - Legierung erstarrte unter starker Schmelzkonvektion ebenfalls globulitisch, wobei Reste dendritisch erstarrter properitektischer Phase gefunden wurden. Der Volumenanteil der properitektischen Phase steigt dabei mit zunehmender Rührwirkung an. Der Wechsel der Morphologie von dendritisch zu globular/dendritisch kann mit sphärischem Wachstum oder Fragmentierung der Dendritenarme erklärt werden. Die mechanischen Eigenschaften unter unterschiedlicher Schmelzkonvektion erstarrter Ti45Al55 – Legierung wurden bei Druckversuchen untersucht. Es wurde eine signifikant höhere plastische Verformbarkeit an der unter starker Schmelzkonvektion erstarrten Ti45Al55 – Legierung gefunden. Dies wird der isotropen spherischen Morphologie der lamellaren a2/g-Phase zugeordnet, während die anisotrope Orientierung der dendritisch- lamellaren Phase unerwünschte plastische Eigenschaften zeigt. Die Untersuchungen des Einflusses der Schmelzkonvektion auf das Gefüge peritektisch erstarrender Legierungen zeigten, dass ein maßgeschneidertes Gefüge durch optimale Wahl der Schmelzkonvektion möglich ist und damit magnetische bzw. mechanische Eigenschaften verbessert werden können. Die Kontrolle der Schmelzkonvektion ist daher ein geeignetes Mittel gewünschte Gefüge und Eigenschaften in Abhängigkeit von den Prozessabläufen einzustellenIn this work, the effect of melt convection on the microstructure evolution of peritectic Nd-Fe-B and Ti-Al alloy systems was studied using novel techniques. The microstructural formation including the change in volume fraction and morphology of the properitectic phase influences the magnetic and mechanical properties for the Nd-Fe-B and Ti-Al alloy systems, respectively. On the basis of numerical simulations by the research group of Dr. Gunter Gerbeth from Department of Magnetohydrodynamics, Forschungszentrum Dresden-Rossendorf, two types of specially designed facilities were developed where melt convection can be altered by changing a number of parameters. These are: forced rotation facility and modified floating zone facility. According to the numerical simulation, an additional crucible rotation suppresses the internal melt motion significantly during forced rotation experiments, where the molten alloy is rotated at a well-defined frequency. This method was applied during the solidification of Nd-Fe-B alloys with the aim to suppress the volume fraction of undesired soft magnetic a-Fe phase. As a result, the volume fraction of properitectic phase with this method can be reduced up to 38 %. A detailed statistical analysis of secondary dendritic arm spacing (SDAS) measurements of a-Fe showed that the SDAS decreases as the rotational frequency increases and melt convection decreases. The reduction in the phase fraction and SDAS of properitectic phase is attributed to the reduced convective mass transfer under reduced melt motion. At high fluid velocity and low rotational frequency, the stronger interdendritic flow reduces the solute boundary layer and increases the transfer of solute through the interface. The smaller dendrite arms dissolve into the melt and thus the SDAS becomes higher than that of the samples solidified at higher rotational frequencies with reduced melt convection. Floating zone facility, which allows contactless heating without any contamination for highly reactive melts, was modified with a double coil system so that an additional electromagnetic force is introduced inside the melt. This induces either very intensive (two-phase stirrer in parallel connection coil system) or very reduced flow (series connection coil system) inside the melt The experimental results of series connection coil system showed that a reduced melt convection state is achieved near 5.1 mm coil distance where a-Fe volume fraction becomes minimum. On the contrary, the parallel coil system experiments showed that a-Fe volume fraction becomes maximum when the phase shift between the coils is close to 90°. The morphology of the a-Fe becomes globular due to spherical growth under strong convection. The study on the effect of strong stirring was extended to another alloy to get a generalized idea about the influence of melt convection on the microstructure development and resulting properties of peritectic alloys. Peritectic Ti45Al55 alloys were investigated by the two-phase stirrer using the coils connected in parallel to study the effect of enhanced melt convection. The increase in the properitectic phase fraction together with a strong change in the morphology from dendritic to spherical were observed in the stirred samples. The increase in the properitectic phase fraction occurs due to the enhanced effective mass transfer under strong melt convection. The change in morphology of the properitectic phase is attributed to spherical growth or fragmentation of dendrite arms under strong convection. The mechanical properties of Ti45Al55 alloys, which are solidified at different convection states, were studied. There was a significantly higher plastic deformability of stirred samples compared to unstirred samples. The coarse anisotropic orientation of the dendritic lamellar phase is detrimental for the plastic deformability, which is absent in the stirred samples due to the spherical and discrete morphology of the properitectic phase. This study indicates that tailored microstructure can be obtained either by decreasing (e.g. for Nd-Fe-B alloy) or increasing (e.g. for Ti-Al alloy) the convection state using effective techniques inside the melt to improve the magnetic and mechanical properties, respectively. Thus, controlling convection is a useful way to get favorable microstructure according to the process need
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Jönsson, Christian Tobias. "The use of hydrogen to extract NdFeB magnets and REES from assemblies." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8717/.
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Recycling of end-of-life NdFeB magnet could provide a sustainable supply of the critical elements Nd and Dy. These are found in waste streams of electronic and electric equipment (WEEE) and drive motors of electric vehicles. Hard disk drives have been identified as an ideal recycling candidate, and a promising process has been developed at the University of Birmingham, called HPMS, which uses hydrogen to extract NdFeB in the form of a demagnetized hydrogenated powder. This thesis has identified loudspeakers from laptops and flat screens to have a good recycling potential. They are all coated with Zn meaning that HPMS should be fully applicable. The HPMS process was then successfully applied to large automotive rotors, extracting more than 95% of the NdFeB. However, it was shown that rotor magnets react slower due to the higher Dy content and lower REE content, meaning that higher pressures might be needed. The hydrogenated powder was disproportionated at high temperature in hydrogen to create large spheres of NdH2 in the Fe matrix, opening up for physical separation of NdH2 from NdFeB. The oxidation of various hydrogen-processed powders was also studied, showing that hydrogenation is beneficial for roasting which is used in the pyrometallurgical recycling flowsheet.
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SALIBA, SILVA ADONIS M. "Desenvolvimento de um processo de fosfatacao para protecao anticorrosiva em imas NdFeb." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10975.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Ahmad, Ishtiaq. "Magnetic properties and structures of high coercivity melt spun NdFeB hard magnetic alloys." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387495.
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Farr, Matthew. "Production of anisotropic injection moulded NdFeB magnets from end-of-life sintered magnets." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8116/.
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In this work, the hydrogenation-disproportionation-desorption-recombination (HDDR) processing conditions were optimised for scrap sintered NdFeB magnets from hard disk drives (HDDs). The HDDR process was then performed on scrap sintered NdFeB magnets, which were separated from HDD assemblies using hydrogen, on a large scale in order to produce anisotropic NdFeB alloy powder. The HDDR powder was then used to produce injection moulded magnets on pilot scale equipment (5 kg load) at Kolektor Magnet Technology GmbH, Germany. Sintered NdFeB magnets were separated from cropped hard disk drive corners as a hydrogenated powder, before being purified to remove any contaminants. The material was then HDDR processed using parameters optimised for this material (900 °C and 1200 mbar). The powder was compounded with polyamide 12 at a 90/10 ratio of HDDR powder to binder before injection moulding in a 500 mT field to form bonded magnets. The best bonded magnets produced had a remanence of 0.64 T, a coercivity of 623 kA/m and a BHmax of 61.7kJ/m\(^3\). Despite the mixed composition input feed, there was very little variation in the magnetic properties between 5 randomly selected magnets where a standard deviation for BHmax of 0.34 kJ/m\(^3\) was observed.
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Biswas, Kaushik. "Effect of melt convection on microstructure evolution of peritectic Nd-Fe-B and Ti-Al alloys." Doctoral thesis, Technische Universität Dresden, 2007. https://tud.qucosa.de/id/qucosa%3A23731.
Full textAbstract:
In dieser Arbeit wurde der Einfluss der Schmelzkonvektion auf das erstarrende Gefüge von peritektischen Nd-Fe-B – und TiAl-Legierungen mit Hilfe neuartiger Methoden untersucht. Da die magnetischen und mechanischen Eigenschaften dieser technisch relevanten Legierungen stark vom Gefüge und insbesondere vom Volumenanteil der properitektischen Phase abhängen, sind diese Untersuchungen von großem Interesse. Auf der Basis der numerischen Simulationen der Schmelzkonvektionsmoden und des elektromagnetischen Problems in einer induktiv beheizten Schmelze, die am Forschungszentrum Dresden-Rossendorf durchgeführt wurden, wurden am IFW Dresden neuartige Versuchsaufbauten entwickelt, die die Modifizierung der Konvektion in einer Metallschmelze ermöglichen. Dies sind ein Aufbau zur erzwungenen Schmelzrotation in einem Tiegel und eine modifizierte Floating-Zone-Anlage. Die erzwungene Schmelzrotation, bei der der Schmelztiegel mit einer definierten Frequenz rotiert, führt in Übereinstimmung mit der Simulation zu einer starken Reduzierung der Konvektion in Abhängigkeit von der Frequenz. Diese Methode wurde auf Nd-Fe-B-Legierungen angewendet mit dem Ziel, die Bildung der unerwünschten weichmagnetischen Eisenphase zu unterdrücken bzw. deren Volumenanteil zu reduzieren. Im Ergebnis konnte der Volumenanteil der properitektischen Phase mit diesem Verfahren um 38.5 % reduziert werden. Das dendritische Gefüge wurde einer ausführlichen statistischen Analyse unterzogen, bei der die Abstände der sekundären Dendritenarme (SDAS) gemessen wurden. Es konnte gezeigt werden, dass die SDAS sich mit steigender Frequenz der Tiegelrotation, was einer reduzierten Schmelzkonvektion entspricht, verringern. Die Verringerung des Volumenanteils der properitektischen Eisenphase und der SDAS wird mit dem reduzierten konvektiven Massentransport unter reduzierter Schmelzkonvektion erklärt. Starke interdendritische Strömung reduziert die Dicke der Diffusionsgrenzschicht um die properitektische Phase. Dadurch wird der Stofftransport durch die Grenzschicht erleichtert. Kleinere Dendritenarme werden in die Schmelze zurückgeschmolzen, wodurch sich der Abstand zwischen den verbleibenden Dendritenarmen vergrößert. Eine Floating-Zone-Anlage, die das tiegelfreie Prozessieren von Metallschmelzen erlaubt wurde so modifiziert, dass mit Hilfe eines Doppelspulensystems eine zusätzliche wohl definierte elektromagnetische Kraft eingebracht wird, über die eine sehr intensive (Zweiphasenrührer in Parallelschaltung) bzw. stark verringerte Strömung (Doppelspule in Reihenschaltung) in der Schmelze eingestellt werden kann. Die experimentellen Ergebnisse der Untersuchungen am Nd-Fe-B-System mit der Doppelspule in Reihenschaltung zeigten, dass sich bei einem optimalen Spulenabstand von 5,1 mm die geringste Schmelzkonvektion ergab, wobei der Anteil des a-Eisen-Volumenanteils weiter verringert werden konnte. Im Gegensatz dazu wurde mit dem Zweiphasenrührer in Parallelschaltung eine sehr starke Schmelzkonvektion mit einem maximalen Volumenanteil der a-Eisen-Phase eingestellt, wobei durch die starke Rührung ein Wechsel der Morphologie von dendritisch zu globular zu beobachten war. Die Untersuchungen zum Einfluss der starken Schmelzkonvektion wurden auf ein weiteres peritektisch erstarrendes System ausgedehnt, um eine generalisierte Aussage zum Einfluss der Konvektion auf Gefüge und Eigenschaften peritektisch erstarrender Legierungen zu erhalten. Die ausgewählte Ti45Al55 - Legierung erstarrte unter starker Schmelzkonvektion ebenfalls globulitisch, wobei Reste dendritisch erstarrter properitektischer Phase gefunden wurden. Der Volumenanteil der properitektischen Phase steigt dabei mit zunehmender Rührwirkung an. Der Wechsel der Morphologie von dendritisch zu globular/dendritisch kann mit sphärischem Wachstum oder Fragmentierung der Dendritenarme erklärt werden. Die mechanischen Eigenschaften unter unterschiedlicher Schmelzkonvektion erstarrter Ti45Al55 – Legierung wurden bei Druckversuchen untersucht. Es wurde eine signifikant höhere plastische Verformbarkeit an der unter starker Schmelzkonvektion erstarrten Ti45Al55 – Legierung gefunden. Dies wird der isotropen spherischen Morphologie der lamellaren a2/g-Phase zugeordnet, während die anisotrope Orientierung der dendritisch- lamellaren Phase unerwünschte plastische Eigenschaften zeigt. Die Untersuchungen des Einflusses der Schmelzkonvektion auf das Gefüge peritektisch erstarrender Legierungen zeigten, dass ein maßgeschneidertes Gefüge durch optimale Wahl der Schmelzkonvektion möglich ist und damit magnetische bzw. mechanische Eigenschaften verbessert werden können. Die Kontrolle der Schmelzkonvektion ist daher ein geeignetes Mittel gewünschte Gefüge und Eigenschaften in Abhängigkeit von den Prozessabläufen einzustellen.In this work, the effect of melt convection on the microstructure evolution of peritectic Nd-Fe-B and Ti-Al alloy systems was studied using novel techniques. The microstructural formation including the change in volume fraction and morphology of the properitectic phase influences the magnetic and mechanical properties for the Nd-Fe-B and Ti-Al alloy systems, respectively. On the basis of numerical simulations by the research group of Dr. Gunter Gerbeth from Department of Magnetohydrodynamics, Forschungszentrum Dresden-Rossendorf, two types of specially designed facilities were developed where melt convection can be altered by changing a number of parameters. These are: forced rotation facility and modified floating zone facility. According to the numerical simulation, an additional crucible rotation suppresses the internal melt motion significantly during forced rotation experiments, where the molten alloy is rotated at a well-defined frequency. This method was applied during the solidification of Nd-Fe-B alloys with the aim to suppress the volume fraction of undesired soft magnetic a-Fe phase. As a result, the volume fraction of properitectic phase with this method can be reduced up to 38 %. A detailed statistical analysis of secondary dendritic arm spacing (SDAS) measurements of a-Fe showed that the SDAS decreases as the rotational frequency increases and melt convection decreases. The reduction in the phase fraction and SDAS of properitectic phase is attributed to the reduced convective mass transfer under reduced melt motion. At high fluid velocity and low rotational frequency, the stronger interdendritic flow reduces the solute boundary layer and increases the transfer of solute through the interface. The smaller dendrite arms dissolve into the melt and thus the SDAS becomes higher than that of the samples solidified at higher rotational frequencies with reduced melt convection. Floating zone facility, which allows contactless heating without any contamination for highly reactive melts, was modified with a double coil system so that an additional electromagnetic force is introduced inside the melt. This induces either very intensive (two-phase stirrer in parallel connection coil system) or very reduced flow (series connection coil system) inside the melt The experimental results of series connection coil system showed that a reduced melt convection state is achieved near 5.1 mm coil distance where a-Fe volume fraction becomes minimum. On the contrary, the parallel coil system experiments showed that a-Fe volume fraction becomes maximum when the phase shift between the coils is close to 90°. The morphology of the a-Fe becomes globular due to spherical growth under strong convection. The study on the effect of strong stirring was extended to another alloy to get a generalized idea about the influence of melt convection on the microstructure development and resulting properties of peritectic alloys. Peritectic Ti45Al55 alloys were investigated by the two-phase stirrer using the coils connected in parallel to study the effect of enhanced melt convection. The increase in the properitectic phase fraction together with a strong change in the morphology from dendritic to spherical were observed in the stirred samples. The increase in the properitectic phase fraction occurs due to the enhanced effective mass transfer under strong melt convection. The change in morphology of the properitectic phase is attributed to spherical growth or fragmentation of dendrite arms under strong convection. The mechanical properties of Ti45Al55 alloys, which are solidified at different convection states, were studied. There was a significantly higher plastic deformability of stirred samples compared to unstirred samples. The coarse anisotropic orientation of the dendritic lamellar phase is detrimental for the plastic deformability, which is absent in the stirred samples due to the spherical and discrete morphology of the properitectic phase. This study indicates that tailored microstructure can be obtained either by decreasing (e.g. for Nd-Fe-B alloy) or increasing (e.g. for Ti-Al alloy) the convection state using effective techniques inside the melt to improve the magnetic and mechanical properties, respectively. Thus, controlling convection is a useful way to get favorable microstructure according to the process need.
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Vallereau, Robin. "Fabrication additive d'aimants liés anisotropes par dépôt de fil fondu." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALI012.
Full textAbstract:
Les aimants permanents anisotropes à base de terres rares possèdent d’excellentes propriétés magnétiques et sont de ce fait utilisés dans de nombreux dispositifs électromécaniques tels que les moteurs, actionneurs, générateurs, et même aux petites dimensions dans les microsystèmes électromécaniques. On les retrouve sous forme frittée ou liée. Bien que les aimants liés soient moins aimantés que les frittés puisque dilués dans une matrice polymère, ils ont l’avantage de pouvoir être fabriqués en très grande série par moulage par injection et peuvent être de forme complexe. Cependant la production de petites séries, ou d’aimants à la texture magnétique complexe n’est pas actuellement envisageable. La technique de fabrication additive par dépôt de fil fondu répond à certaines de ces problématiques : contrairement au moulage, l’impression 3D est adaptée aux petites séries, permet des formes plus complexes et ne consomme que le volume de matière nécessaire. Quant à la texture, cette thèse décrit une tête d’impression basée sur une extrudeuse à piston et équipée d’un aligneur magnétique, qui a permis d’obtenir des aimants liés à base de terres rares sensiblement anisotropes. Les composites ont été formulés dans du nylon PA12 avec des poudres NdFeB de qualité industrielle, et issues du recyclage d’aimants frittés ; nous avons également employé du SmFeN déjà formulé sous forme de granulés.L’extrudeuse à piston est alimentée par des granulés qui, contrairement aux filaments bobinés, peuvent être hautement chargés de poudre magnétique. L’aligneur magnétique est une couronne d’aimants SmCo assemblés autour de la buse ; il oriente les particules magnétiques lors de l’extrusion pour induire une anisotropie axiale du cordon et améliorer son aimantation rémanente. Il a été dimensionné à la suite d’une étude visant à déterminer la température et le champ à appliquer pour obtenir un alignement optimal dans les conditions d’extrusion. Ce dispositif produit une induction axiale de 545 mT dans la zone d’intérêt. Contrairement aux têtes d’impressions classiques, dans notre extrudeuse le composite fondu est extrudé par un piston, ce qui permet de vaincre les forces de friction qui confinent les particules magnétiques dans la buse sous l’effet des forces radiales liées au gradient de champ magnétique.La fabrication d’aimants liés denses et de bonne qualité requiert d’optimiser les paramètres d’impression. Cependant il persiste toujours une part de porosité générée par le procédé lui-même, qui participe à diminuer l’aimantation rémanente. Quant à l’anisotropie, elle est obtenue en suivant une stratégie de construction de l’aimant lié qui consiste à déposer tous les cordons dans la même direction et dans le même sens. Lors de l’impression d’aimants anisotropes, le frottement de la buse sur la couche fraichement déposée conduit à en désaligner mécaniquement les particules en surface, contribuant ici aussi à dégrader les propriétés maximales. Le composite chargé à 63 %vol de NdFeB (MF-P15) dans du nylon PA12 est particulièrement affecté et présente un degré d’alignement quasiment nul (µ0Mr = 0,3 T et Hc = 995 kA/m) ; tandis que le SmFeN/PA12 (60 %vol) présente un degré d’alignement de 0,3 (µ0Mr = 0,5 T, Hc = 875 kA/m). Les particules de SmFeN sont très fines (d0,5 = 3 µm) par rapport à celle de NdFeB (d0,5 ~75-100 µm) et de forme sphéroïdale : une couche imprimée de 200 µm d’épaisseur contient donc beaucoup plus particules de SmFeN que de NdFeB, et les particules en surface, mécaniquement désalignées lorsque la buse les touche, représentent ainsi une moindre fraction volumique.L’objectif à long terme du projet 6DMag est d’exploiter cette stratégie de dépôt anisotrope par alignement, pour imprimer des aimants liés composés de régions possédant différentes directions d’aimantation. Le prochain défi sera d’aimanter les différentes régions d’un aimant multipolaire sans impacter les régions voisinesRare earth-based anisotropic permanent magnets have excellent magnetic properties and are therefore used in many electromechanical devices such as motors, actuators, generators, and even at small dimensions in micro-electromechanical systems. They can be found in sintered or bonded form. Although bonded magnets are less magnetised than sintered ones because they are diluted in a polymer matrix, they have the advantage of being able to be manufactured in very large series by injection moulding and can be complex in shape. However, the production of small series, or of magnets with a complex magnetic texture, is not currently feasible. The technique of additive manufacturing using molten wire deposition provides a solution to some of these problems: unlike moulding, 3D printing is suitable for small production runs, allows more complex shapes and consumes only the necessary volume of material. As for the texture, this thesis describes a print head based on a piston extruder and equipped with a magnetic aligner, which made it possible to obtain substantially anisotropic rare-earth-based bonded magnets. The composites were formulated in PA12 nylon with industrial-grade NdFeB powders, derived from the recycling of sintered magnets; we also used SmFeN already formulated in granulated form.The piston extruder is fed with pellets which, unlike wound filaments, can be highly charged with magnetic powder. The magnetic aligner is a ring of SmCo magnets assembled around the nozzle; it orients the magnetic particles during extrusion to induce axial anisotropy in the strand and improve its remanent magnetisation. It was designed following a study to determine the temperature and field to be applied to obtain optimum alignment under extrusion conditions. This device produces an axial induction of 545 mT in the zone of interest. Unlike conventional printheads, in our extruder the molten composite is extruded by a plunger, overcoming the frictional forces that confine the magnetic particles in the nozzle under the radial forces of the magnetic field gradient.The manufacture of dense, good quality bonded magnets requires optimisation of the printing parameters. However, there is always some porosity generated by the process itself, which helps to reduce remanent magnetisation. As for anisotropy, this is obtained by following a construction strategy for the bonded magnet that consists of depositing all the strands in the same direction and in the same sense. When printing anisotropic magnets, the friction of the nozzle on the freshly deposited layer mechanically misaligns the particles on the surface, again contributing to a degradation of the maximum properties. The composite filled with 63 %vol NdFeB (MF-P15) in PA12 nylon is particularly affected and has a degree of alignment of almost zero (µ0Mr = 0.3 T and Hc = 995 kA/m), while SmFeN/PA12 (60 %vol) has a degree of alignment of 0.3 (µ0Mr = 0.5 T, Hc = 875 kA/m). The SmFeN particles are very fine (d0.5 = 3 µm) compared with those of NdFeB (d0.5 ~75-100 µm) and spheroidal in shape: a printed layer 200 µm thick therefore contains many more SmFeN particles than NdFeB, and the particles on the surface, mechanically misaligned when the nozzle touches them, thus represent a smaller volume fraction.The long-term objective of the 6DMag project is to exploit this strategy of anisotropic deposition by alignment, to print bonded magnets composed of regions with different directions of magnetisation. The next challenge will be to magnetise the different regions of a multipolar magnet without impacting neighbouring regions
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McCain, Stephen. "Characterisation of the aqueous corrosion process in NdFeB melt spun ribbon and MQI bonded magnets." Thesis, University of Birmingham, 2012. http://etheses.bham.ac.uk//id/eprint/3680/.
Full textAbstract:
A major factor limiting the use and longevity of rare earth based magnetic materials is their susceptibility to aqueous corrosion and associated detrimental effects upon the magnetic properties of the material. This process was investigated through a combination of exposure to simulated environmental conditions and hydrogen absorption/desorption studies (HADS) in conjunction with magnetic characterisation. This study utilises NdFeB MQP-B melt-spun ribbon manufactured by Magnequench, in the form of MQI bonded magnets and also in its unbonded state as MQ powder. Specifically, it was concerned with how effective a variety of bonding media (epoxy resin,PTFE, zinc) and surface coatings (PTFE, Qsil, zinc LPPS, Dex-Cool) were at limiting the impact of aqueous corrosion in MQI bonded magnets. To characterise the effect of hydrogen absorption upon the magnetic properties of the MQP-B, hydrogen uptake was induced followed by a series of outgassing heat treatments with subsequent magnetic characterisation accompanied by HADS techniques performed after each outgas. This allowed comparisons to be made between the effects of aqueous corrosion process and hydrogen absorption upon the magnetic properties of the alloy. This study has clearly demonstrated the link between the abundance of environmental moisture and rate of Hci losses in MQI bonded magnets. In addition to this the key mechanism responsible for the degradation of magnetic properties has been identified. These losses have been attributed to the absorption of hydrogen generated by the dissociation of water in the presence of NdFeB during the aqueous corrosion process. It has been shown that the use of a bonding media that is impermeable to water can limit the effects of aqueous corrosion by limiting water access to the Magnequench particles (MQP) and also the positive effects of the use of suitable surface coatings has been shown to be effective for the same reason.
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Khlopkov, Kirill. "Mikrotextur und magnetische Mikrostruktur in Hartmagneten aus (Nd,Pr)2Fe14B-Verbindungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1170169439987-14458.
Full textAbstract:
In der vorliegenden Arbeit werden die Zusammenhänge zwischen der magnetischen Mikrostruktur und der Ausrichtung der Kristallite, sowohl in Sintermagneten als auch in feinkristallinen, warmumgeformten Magneten auf Nd2Fe14B- und Pr2Fe14B-Basis, untersucht. Die EBSD-Technik (electron backscatter diffraction) wurde für Sintermagnete und für feinkristalline, warmumgeformte Magnete auf Nd2Fe14B-Basis erstmals erfolgreich eingesetzt, um eine quantitative Texturanalyse durchzuführen. Die Polfiguren des hoch texturierten Sintermagneten bzw. warmumgeformten Magneten zeigen eine stark ausgeprägte [001] Fasertextur. Aus dem Vergleich von REM-, EBSD- und Kerr-Untersuchungen an ein- und derselben Probenoberfläche der Sintermagnete konnte quantitativ gezeigt werden, wie die Domänenstruktur von der individuellen Orientierung der Nd2Fe14B-Körner abhängt. Die Domänenstruktur der hoch texturierten Sintermagnete weist auf eine starke magnetostatische Wechselwirkung zwischen den Kristalliten hin. In den Heißpresslingen und in den warmumgeformten Magneten auf Nd2Fe14B-Basis und Pr2Fe14B-Basis wurden Wechselwirkungsdomänen mittels Magnetkraftmikroskopie nachgewiesen. Die Wechselwirkungsdomänen, deren Größe stark vom Umformgrad abhängt, sind immer größer als die einzelnen Kristallite. Die Bildung der Wechselwirkungsdomänen wurde auf magnetostatische Wechselwirkung zwischen den Kristalliten zurückgeführt, was mit Hilfe der Wohlfarth-Analyse der Remanenzverhältnisse bestätigt werden konnte. Die magnetische Mikrostruktur der warmumgeformten Magnete wurde mit einem Modell, das auf der Bildung von Ketten magnetischer Momente (parallel zur Kettenachse) beruht, beschrieben. Unterhalb der Temperatur des Spinumorientierungsüberganges der Nd2Fe14B-Phase weisen die Sintermagnete rechteckige Domänenmuster auf. Diese magnetische Mikrostruktur wird durch eine spezifische Verteilung der Domänenwände in Bezug auf Änderungen der magnetischen Anisotropie ausgebildet. Im Gegensatz dazu ändern sich die Wechselwirkungsdomänen in dem warmumgeformten Magneten nicht, was auf die starke magnetostatische Wechselwirkung zwischen den Kristalliten zurückgeführt wurdeIn this work, the correlation between magnetic domain structure and grain alignment in sintered and die-upset magnets, based on Nd2Fe14B and Pr2Fe14B compounds, is investigated. For the first time, EBSD (electron backscatter diffraction) has been successfully applied to conduct a quantitative analysis of the texture of sintered and die-upset Nd2Fe14B magnets. Pole figures of the highly textured sintered and die-upset magnets show a strong [001] fiber texture. By a comparison of SEM, EBSD and Kerr images of the same surface of sintered magnets it was possible to correlate the domain structure of individual grains to their orientation. The domain structure of the highly textured sintered magnet indicates to the presence of a strong magnetostatic interaction between individual grains. Interaction domains have been studied in hot-pressed und die-upset magnets based on Nd2Fe14B and Pr2Fe14B compounds by MFM. The lateral expansion of interaction domains is always larger than grain size and depends from the degree of deformation. The formation of interaction domains is attributed to magnetostatic interaction between individual grains, which has been confirmed by a Wohlfarth’s analysis of the remanence ratio. The magnetic domain structure of die-upset magnets can be described by a model, based on the formation of chains of magnetic moments parallel to the chain direction. Below the spinreorientation temperature of the Nd2Fe14B phase, sintered magnets show a rectangular domain structure. This domain structure is formed by a specific domain wall distribution corresponding to changes of the magnetocrystalline anisotropy. In contrast to this, the interaction domains in the die-upset magnets show no changes below the spinreorientation temperature, what can be also ascribed to the magnetostatic interaction between individual grains
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Silva, Melissa Rohrig Martins da. "Influência de elementos de liga na microestrutura e propriedades magnéticas de ímãs à base de PrFeCoB." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-06092017-110307/.
Full textAbstract:
Os ímãs permanentes de terras-raras tem um papel relevante na indústria de dispositivos eletromagnéticos, principalmente no que se refere à produção de motores para veículos híbridos e elétricos e geradores para turbinas eólicas. Com a recente restrição chinesa a exportação de terras-raras, os altos preços e a necessidade de substituição do Dy nesses ímãs, há um interesse mundial por alternativas a essas questões. A adição de elementos de liga em ímãs permanentes de terras raras tem como objetivo a melhora das propriedades magnéticas. O presente trabalho avalia a influência do Ti, V, Cr, Ni, Zr, Nb e Mo na microestrutura e nas propriedades magnéticas de ímãs sinterizados. Os ímãs foram preparados via metalurgia do pó, a partir de pós obtidos pelo processo de decrepitação por hidrogênio (HD). Na produção do ímã Pr16Fe66,9Co10,7B5,7Cu0,7, sem adição de elementos de liga, foi utilizada a mistura das ligas Pr20Fe73B5Cu2 (33% em peso) e Pr14Fe64Co16B6 (67% em peso). Para avaliar a influência das adições foi utilizada a liga Pr14Fe64Co16B6M0,1, onde M = Ti, V, Cr, Ni, Zr, Nb e Mo (67% em peso). As ligas utilizadas e os ímãs produzidos foram caracterizados por Microscopia Eletrônica de Varredura (MEV) e Difração de Raios-X (DRX), e as propriedades magnéticas foram obtidas por meio de Permeâmetro. O ímã com adição de Cr (iHc = 836 KA.m-1) apresentou coercividade intrínseca 11,8% superior ao ímã sem adição de elemento de liga (iHc = 748 KA.m-1). A maior remanência foi observada para o ímã com adição de Nb (Br = 1,04 T). Os ímãs com as adições de Ti, V e Zr apresentaram os maiores valores de produto de energia (BHmáx = 145, 145 e 144 KJ.m-3, respectivamente). Já o ímã com adição de Mo apresentou o maior fator de quadratura (FQ = 0,73) entre todas as amostras, 28% superior ao ímã sem adição de elementos de liga.Rare earth permanent magnets perform an important role in the electromagnetic devices industry, particularly in the production of hybrid and electric vehicle engines and generators for wind turbines. With the recent Chinese restriction on the export of rare-earth elements, the increasing prices and the need to replace the Dy in the permanent magnets, there is a worldwide interest in alternatives to these issues. The addition of alloying elements on rare-earth permanent magnets is one of the methods used to improve the magnetic properties. This present work evaluates the influence of Ti, V, Cr, Ni, Zr, Nb and Mo as alloying elements on the microstructure and magnetic properties of sintered Pr-Fe-Co-B based permanent magnets. The permanent magnets were produced by the conventional powder metallurgy route using powder obtained by hydrogen-decrepitation (HD) method. In order to produce the magnet Pr16Fe66,9Co10,7B5,7Cu0,7 without alloying elements the mixture of alloys method was employed, mixing two compositions: Pr20Fe73B5Cu2 (33% w.t) and Pr14Fe64Co16B6 (67% w.t). With the purpose of evaluating the influence of the alloying elements, the Pr14Fe64Co16B6M0,1 (where M= Ti, V, Cr, Ni Zr, Nb or Mo) (67% w.t) alloy was employed. The characterization of the alloys and the magnets was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD) and the magnetic properties were measured using a permeameter. The magnet with Cr addition (iHc = 836 KA.m-1) presented intrinsic coercivity 11,8% higher in comparsion with the magnet without any addition (iHc = 748 KA.m-1). The highest remanence was observed for the magnet with Nb addition (Br = 1.04 T). The magnets with additions of Ti, V and Zr produced the highest energy products (BHmáx = 145, 145 and 144 KJ.m3 respectively). The magnet with Mo addition showed the highest squareness factor (SF = 0.73) among of all samples, 28% higher than the magnet without addition.
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Süptitz, Ralph. "Einfluss homogener und inhomogener Magnetfelder auf die Korrosion ferromagnetischer Elektroden." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-84255.
Full textAbstract:
Im Rahmen der vorliegenden Arbeit konnten Einflüsse magnetischer Felder, insbesondere mit hohen Gradienten der magnetischen Flussdichte, auf Korrosionsprozesse am Beispiel Eisen quantifiziert und deren Wirkungsmechanismus erklärt werden. Als ein besonders in technisch relevanten gering konzentrierten sauren wässrigen Lösungen bedeutsamer Effekt wurde eine sekundäre Wirkung der Feldgradientenkraft über den Mechanismus der Wahrung der Ladungsneutralität auf den pH-Wert an der Elektrodenoberfläche identifiziert. Somit konnte ein signifikanter Magnetfeldeinfluss auf die formal ladungstransferkontrollierte Korrosionsreaktion nachgewiesen werden.
Um die komplexen Korrosionsvorgänge an mehrphasigen NdFeB-Magneten mit paramagnetischer intergranularer Nd-reicher Phase aufklären zu können, war zunächst eine vertiefte Analyse der freien und anodischen Korrosionsreaktionen des Neodyms notwendig. Die dabei gewonnenen Erkenntnisse erlauben den Magnetfeldeinfluss bei der Korrosion aufmagnetisierter NdFeB-Magnete zu verstehen.
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Khlopkov, Kirill. "Mikrotextur und magnetische Mikrostruktur in Hartmagneten aus (Nd,Pr)2Fe14B-Verbindungen." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A24995.
Full textAbstract:
In der vorliegenden Arbeit werden die Zusammenhänge zwischen der magnetischen Mikrostruktur und der Ausrichtung der Kristallite, sowohl in Sintermagneten als auch in feinkristallinen, warmumgeformten Magneten auf Nd2Fe14B- und Pr2Fe14B-Basis, untersucht. Die EBSD-Technik (electron backscatter diffraction) wurde für Sintermagnete und für feinkristalline, warmumgeformte Magnete auf Nd2Fe14B-Basis erstmals erfolgreich eingesetzt, um eine quantitative Texturanalyse durchzuführen. Die Polfiguren des hoch texturierten Sintermagneten bzw. warmumgeformten Magneten zeigen eine stark ausgeprägte [001] Fasertextur. Aus dem Vergleich von REM-, EBSD- und Kerr-Untersuchungen an ein- und derselben Probenoberfläche der Sintermagnete konnte quantitativ gezeigt werden, wie die Domänenstruktur von der individuellen Orientierung der Nd2Fe14B-Körner abhängt. Die Domänenstruktur der hoch texturierten Sintermagnete weist auf eine starke magnetostatische Wechselwirkung zwischen den Kristalliten hin. In den Heißpresslingen und in den warmumgeformten Magneten auf Nd2Fe14B-Basis und Pr2Fe14B-Basis wurden Wechselwirkungsdomänen mittels Magnetkraftmikroskopie nachgewiesen. Die Wechselwirkungsdomänen, deren Größe stark vom Umformgrad abhängt, sind immer größer als die einzelnen Kristallite. Die Bildung der Wechselwirkungsdomänen wurde auf magnetostatische Wechselwirkung zwischen den Kristalliten zurückgeführt, was mit Hilfe der Wohlfarth-Analyse der Remanenzverhältnisse bestätigt werden konnte. Die magnetische Mikrostruktur der warmumgeformten Magnete wurde mit einem Modell, das auf der Bildung von Ketten magnetischer Momente (parallel zur Kettenachse) beruht, beschrieben. Unterhalb der Temperatur des Spinumorientierungsüberganges der Nd2Fe14B-Phase weisen die Sintermagnete rechteckige Domänenmuster auf. Diese magnetische Mikrostruktur wird durch eine spezifische Verteilung der Domänenwände in Bezug auf Änderungen der magnetischen Anisotropie ausgebildet. Im Gegensatz dazu ändern sich die Wechselwirkungsdomänen in dem warmumgeformten Magneten nicht, was auf die starke magnetostatische Wechselwirkung zwischen den Kristalliten zurückgeführt wurde.In this work, the correlation between magnetic domain structure and grain alignment in sintered and die-upset magnets, based on Nd2Fe14B and Pr2Fe14B compounds, is investigated. For the first time, EBSD (electron backscatter diffraction) has been successfully applied to conduct a quantitative analysis of the texture of sintered and die-upset Nd2Fe14B magnets. Pole figures of the highly textured sintered and die-upset magnets show a strong [001] fiber texture. By a comparison of SEM, EBSD and Kerr images of the same surface of sintered magnets it was possible to correlate the domain structure of individual grains to their orientation. The domain structure of the highly textured sintered magnet indicates to the presence of a strong magnetostatic interaction between individual grains. Interaction domains have been studied in hot-pressed und die-upset magnets based on Nd2Fe14B and Pr2Fe14B compounds by MFM. The lateral expansion of interaction domains is always larger than grain size and depends from the degree of deformation. The formation of interaction domains is attributed to magnetostatic interaction between individual grains, which has been confirmed by a Wohlfarth’s analysis of the remanence ratio. The magnetic domain structure of die-upset magnets can be described by a model, based on the formation of chains of magnetic moments parallel to the chain direction. Below the spinreorientation temperature of the Nd2Fe14B phase, sintered magnets show a rectangular domain structure. This domain structure is formed by a specific domain wall distribution corresponding to changes of the magnetocrystalline anisotropy. In contrast to this, the interaction domains in the die-upset magnets show no changes below the spinreorientation temperature, what can be also ascribed to the magnetostatic interaction between individual grains.
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Winkler, Robert. "Developement of an "all-in-one" approach for the synthesis of silica-based hybrid materials." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS075.
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Ce travail de thèse porte sur la synthèse de nouveaux précurseurs d'organosilane et leur utilisation dans des matériaux hybrides à base de silice par une approche tout-en-un pour l'extraction de terres rares.Pour atteindre cet objectif, cinq précurseurs d'organosilane ont été synthétisés avec un bon rendement. Premièrement, ces nouveaux précurseurs ont été utilisés pour élaborer des matériaux hybrides à base de silice dense (SHM). La caractérisation de la structure locale par FTIR et de la mésostructure par SAXS du SHM final a permis de mettre en évidence le lien entre les interactions chimiques et physiques entre les groupes fonctionnels des précurseurs et les autres espèces présentes dans le mélange réactionnel qui déterminent la connectivité locale du réseau siloxane et la mésostructure des matériaux obtenus (phases lamellaire et hexagonale 2D). Deuxièmement, afin d'améliorer les propriétés du matériau, une approche innovante en deux étapes a été proposée. La première étape est basée sur la structuration de mélanges binaires alcool/eau afin d’influencer le comportement à l’agrégation des nanoparticules de silice préparé à partir de tétraéthyl orthosilicate. Ainsi, une surface spécifique remarquable de 2000 m² g-1 a pu être obtenue. Dans une seconde étape, les conditions de réaction conduisant aux matériaux ayant la plus grande surface spécifique ont été utilisées avec l’addition d’un précurseur d’organosilane synthétisé ne présentant pas de groupe fonctionnel générant de forte interaction physico-chimique. Les résultats montrent le potentiel de cette approche pour adapter les propriétés des matériaux obtenus. Enfin, les SHM synthétisés à partir de précurseurs d'organosilane purs ont été testés avec succès pour l'extraction sélective et efficace d'éléments tel que des terres rares présents dans un lixiviat modèle d’aimant NdFeB.Ces travaux offrent des perspectives prometteuses pour la synthèse « tout-en-un » de SHM à applications directesIn this work, we investigated the synthesis of new organosilane precursors and their polymerization to silica hybrid materials with REE extracting properties via an all-in-one approach.To reach this goal, five organosilane precursors were synthetized in good yield. First, these new precursors were used to elaborate dense silica hybrid materials (SHM). The characterization of the local structure by FTIR and of the mesostructure by SAXS of the SHMs highlighted the link between the chemical and physical interactions between the headgroups of the precursors and the others species existing in the reaction mixture. These interactions drive the local connectivity of the siloxane network and the mesostructure of the obtained materials (lamellar and 2D hexagonal phases). Second, in order to improve the material properties, an innovative approach in two steps was proposed. The first step was based on the structuring of binary alcohol/water mixtures to influence the aggregation behavior of silica nanoparticles prepared from tetraethyl orthosilicate (TEOS). Here, a remarkable specific surface area of 2000 m2 g-1 was achieved. In a second step, the reaction conditions that lead to materials with the highest specific surface area were used in combination with the synthesized organosilane precursors. The results show the potential of this approach to tailor the properties of the obtained materials. Finally, the SHMs synthesized from the pure organosilane precursors were successfully tested for the selective and efficient extraction of rare earth elements present in a simulated leachate of NdFeB magnets.This work offers promising prospects for the "all-in-one" synthesis of SHMs with direct applications
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Zhou, Wei. "High resolution microscopy of NdFeB magnets produced from flash spark plasma sintering (FSPS) and the hydrogen ductilisation process (HyDP)." Thesis, University of Birmingham, 2019. http://etheses.bham.ac.uk//id/eprint/8710/.
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In recent years, the increasing demand for rare earth magnets for use in motors and machines has led to the need for more efficient use of NdFeB materials. Novel processing techniques have been developed to produce NdFeB materials with excellent magnetic properties without the need for heavy rare earth elements. Two specific novel processes including the Flash Spark Plasma Sintering (FSPS) process and the Hydrogen Ductilisation Process (HyDP) were studied in this project with the focus on the use of microstructural analysis and magnetic measurements to fully understand the mechanisms, hence develop and optimise the processing conditions for production of fully dense anisotropic magnets. The most optimal FSPS sample demonstrates a uniform, fine-grained structure with a high degree of crystallographic alignment, leading to a high coercivity (1438 kA m\(^−\)\(^1\)) and remanence (1.16 T) giving a BH\(_m\)\(_a\)\(_x\) of 230 kJ m\(^−\)\(^3\). While with appropriate s-HDDR and compression conditions, the HyDPed sample exhibits a typical s-HDDR microstructure with a submicron grain size. It is shown in the work that the disproportionated sample shows an enhanced ductility and thus can be shaped at room temperature, and a useful degree of anisotropy is produced within the HyDPed sample during the compression.
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Walther, Arnaud. "Développement de couches magnétiques dures pour MEMS : application à un microswitch magnétique bistable." Phd thesis, Grenoble 1, 2007. http://www.theses.fr/2007GRE10110.
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Le but de ce travail de thèse est de réaliser un microswitch magnétique bistable à base d'aimants permanents. De nouveaux designs de tels microswitch ont été dessinés afin d'obtenir à la fois des forces de contact plus élevés et des courants de commutation plus faibles que les systèmes semblables existants déjà. Des logiciels de simulations magnétiques ont été utilisés afin d'évaluer le comportement statique et dynamique de c~s micro relais. Des couches épaisses (> 1 /lm) de matériaux magnétiques durs hautes performances (NdFeB, SmCo) ont été déposées par pulvérisation cathodique triode. Cette technique de pulvérisation permet d'avoir des vitesses de dépôt élevées sur de grandes surfaces. Les conditions de dépôt et de traitements thermiques de ces couches ont été étudiés afin d'obtenir de grandes coercivités, de grandes rémanences et des textures particulières. Enfin, des briques de base technologiques ont été développées afin d'intégrer ces films magnétiques dans un process de microtechnologie et de réaliser fmalement de nouveaux microsystèmes magnétiques. Ce travail est inclus dans le projet ANR Nanomag2 dont le but final est de fabriquer des micro-relais RF pour des applications spatialesThe aim of this PhD thesis is to realize a bistable microswitch using integrated magnets. New designs of such microswitches have been drawn in order to obtain both higher contact forces and lower commutation currents compared to such existing systems. Magnetic simulation softwares have been used to assess static and dynamic behaviour of the micro-switches. Then thick films (> 1 /lm) of high performance hard magnetic materials (NdFeB, SmCo) have been deposited with triode sputtering, which enables high deposition rates on large areas. Conditions of sputtering and heat treatments were studied to get high coercivities, high remanences and special textures. Basic technological steps have been developed to integrate these magnetic films into a micro-technological process in order to finally realize new magnetic micro-systems. This work was part of the project Nanomag2 whose final goal is to fabricate a RF-microswitch for spatial applications
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Walther, Arnaud. "Développement de couches magnétiques dures pour MEMS : application à un microswitch magnétique bistable." Phd thesis, Université Joseph Fourier (Grenoble), 2007. http://tel.archives-ouvertes.fr/tel-00348109.
Full textAbstract:
Le but de ce travail de thèse est de réaliser un microswitch magnétique bistable à base d'aimants permanents. De nouveaux designs de tels microswitch ont été dessinés afin d'obtenir à la fois des forces de contact plus élevés et des courants de commutation plus faibles que les systèmes semblables existants déjà. Des logiciels de simulations magnétiques ont été utilisés afin d'évaluer le comportement statique et dynamique de ces micro relais. Des couches épaisses (>1 µm) de matériaux magnétiques durs hautes performances (NdFeB, SmCo) ont été déposées par pulvérisation cathodique triode. Cette technique de pulvérisation permet d'avoir des vitesses de dépôt élevées sur de grandes surfaces. Les conditions de dépôt et de traitements thermiques de ces couches ont été étudiés afin d'obtenir de grandes coercivités, de grandes rémanences et des textures particulières. Enfin, des briques de base technologiques ont été développées afin d'intégrer ces films magnétiques dans un process de microtechnologie et de réaliser finalement de nouveaux microsystèmes magnétiques. Ce travail est inclus dans le projet ANR Nanomag2 dont le but final est de fabriquer des micro-relais RF pour des applications spatiales.
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PERIGO, ELIO A. "Estudo das correlacoes entre microestrutura propriedades magneticas e fator de quadratura em imas sinterizadas de PrFeB e NdFeB processados com hidrogenio." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9423.
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
FAPESP:05/04711-2
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Xu, Hanou. "Characterization and Simulation of Magnetorheological Elastomer Filled with Carbonyl Iron and NdFeB Particles under Uniaxial Tension, Compression, and Pure Shear modes." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20731.
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In recent decades, magnetorheological elastomer (MRE) has been widely used in engineering applications as vibration absorbers or isolators due to its field-dependent property. Thus, researches on the correlations of the variables and MRE behaviors are increasingly needed. This study aims to characterize and simulate magnetorheological behavior of elastomer filled with carbonyl iron and NdFeB particles under uniaxial tension, compression, and pure shear modes. First, tensile tests were performed for both isotropic and anisotropic magnetorheological elastomer (MRE) with carbonyl iron particle (CI), under the magnetic field of a pair of permanent magnets, to observe the feasibility of a portable, lightweight setup without the need of power supply. It turned out that the MR effect was apparent but not significant enough for real application. Also, there was a negative MR effect for anisotropic MRE when the magnetic flux is vertical to the particle chains. The compression test showed that Neodymium magnet powder (NdFeB) filled specimen always had higher compressive strength than the CI specimen. The outcome helped to the complementation of hard particle MRE characterization. A systematic shear test was conducted on isotropic CI and NdFeB MRE specimens. The shear test was divided into two parts. The first part observed the large-strain behavior of each specimen under a steady magnetic flux; 0, 200, 400, and 600 mT magnetic flux was applied during this part. NdFeB MRE specimens showed very little change in shear strength under different flux, while CI MRE was influenced substantially. The second part is conducted under dynamic flux ranging from -600 mT to 600 mT with small oscillation displacement. It turned out the hard MRE specimens had far more significant storage modulus than its counterpart. The result of the shear test proved that hard MRE has lower magnetization saturation and high storage modulus, and it is now further characterized. COMSOL simulation for tensile testing showed fair agreement with the experimental outcomes. Further improvements were proposed to make the model practical for future MRE studies.
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Ismail, Abir. "Etude de la diffusion du Dy dans les aimants polycristallins frittés Nd2Fe14B par microscopie électronique." Electronic Thesis or Diss., Université Grenoble Alpes, 2023. http://www.theses.fr/2023GRALY093.
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Les aimants permanents frittés type NdFeB contenant du dysprosium (Dy) sont des éléments clés pour la transition vers des transports décarbonés et le déploiement massif des véhicules électriques. Or, le Dy est identifié comme un élément critique par l’Union Européenne à cause du monopole chinois entrainant un risque d’approvisionnement. Pour faire face à cette vulnérabilité d’approvisionnement, une technique de diffusion aux joints de grains connue sous le terme anglais Grain Boundary Diffusion Process (GBDP) a été développée. Cette méthode cherche à minimiser la quantité du Dy utilisé dans ces aimants en favorisant sa diffusion uniquement dans les joints de grains et leurs périphéries. Cela amène à une microstructure de type cœur-coquille c.-à-d. un grain dont le cœur est pauvre en Dy et la périphérie est riche en Dy. Cette distribution hétérogène du Dy est intéressante car elle permet de maximiser le gain en performances magnétiques apportée par la terre rare lourde toute en limitant l’utilisation de cette matière critique.L’objectif de cette thèse est de caractériser à différentes échelles la microstructure des aimants pour mieux comprendre le mécanisme à l’origine de la formation de cette microstructure et ainsi pouvoir proposer des leviers permettant une optimisation du procédé de diffusion aux joints de grains.Dans le cadre de cette thèse, des aimants NdFeB ont été fabriqués par métallurgie des poudres sur la ligne pilote du laboratoire LMCM au CEA/LITEN. Une partie de ces échantillons a été revêtue par un alliage binaire Dy-Co puis soumise à des recuits visant à permettre la diffusion du Dy dans l’aimant (GBDP). Plusieurs techniques de microscopie électronique ont été utilisées (MEB, EDX, EBSD et TEM) pour mener une étude fine de la microstructure de ces aimants avant et après ce traitement de diffusion. Plus particulièrement, des mesures quantitatives par EDS/WDS ont été mises en œuvre pour déterminer la composition et l’épaisseur des coquilles riches en Dy au sein des grains en fonction de la distance à la surface.Les performances magnétiques des aimants (rémanence et coercivité) sont également déterminées avant et après GBDP à partir des courbes expérimentales de désaimantation. Les différents mécanismes proposés dans la littérature pour expliquer la formation de la microstructure cœur-coquille impliquent la formation d’une phase liquide aux joints de grains à partir de laquelle les coquilles peuvent se développer soit par diffusion en volume, soit par solidification ou soit encore par migration de films liquides. Les données d’entrée sur lesquelles se basent ces mécanismes sont passées en revue en les confrontant à l’ensemble de nos résultats. Nous montrons que ces hypothèses ne sont pas complétement satisfaisantes pour rendre compte de nos observations. Nous proposons des améliorations du modèle de diffusion par des simulations par Eléments Finis. Nous concluons ce travail en proposant de nouveaux éléments à prendre en compte qui permettent de mieux comprendre les mécanismes à l’origine de la formation de la microstructure cœur-coquilleDy-containing sintered NdFeB permanent magnets are key elements in the transition to low-carbon transport and the mass deployment of electric vehicles. However, Dy has been identified as a critical element by the European Union, due to the Chinese monopoly, which poses a supply risk. To address this supply vulnerability, a Grain Boundary Diffusion Process (GBDP) has been developed. This method seeks to minimize the amount of Dy used in these magnets by limiting its presence to the grain boundaries and their peripheries. This results in a core-shell microstructure, i.e., a grain whose core is low in Dy and whose periphery is high in Dy. This heterogeneous distribution of Dy is interesting because it maximizes the gain in magnetic performance provided by the heavy rare earth, while limiting the use of this critical material.The aim of this thesis is to characterize the microstructure of magnets at different scales, in order to better understand the mechanism behind the formation of this microstructure, and thus be able to propose levers for optimizing the grain boundary diffusion process.As part of this thesis, NdFeB magnets were manufactured by powder metallurgy on the LMCM laboratory pilot line at CEA/LITEN. Some of these samples were coated with a binary Dy-Co alloy and then annealed to allow Dy diffusion into the magnet (GBDP). Several electron microscopy techniques (SEM, EDX, EBSD and TEM) were used to carry out a detailed study of the microstructure of these magnets before and after this diffusion treatment. In particular, quantitative EDS/WDS measurements were used to determine the composition and thickness of Dy-rich shells within the grains as a function of distance from the surface. The magnetic performances of the magnets (remanence and coercivity) are also determined before and after GBDP from experimental demagnetization curves. The various mechanisms proposed in the literature to explain the formation of the core-shell microstructure involve the formation of a liquid phase at the grain boundaries, from which the shells can develop either by volume diffusion, solidification, or liquid film migration. We review the input data on which these mechanisms are based, comparing them with our results. We show that these hypotheses are not completely satisfactory for our observations. We propose improvements to the diffusion model using finite element simulations. We conclude this work by proposing new elements to be considered in order to better understand the mechanisms behind the formation of the core-shell microstructure
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Siyambalapitiya, Chamila Shyamalee. "Model and Validation of Static and Dynamic Behavior of Passive Diamagnetic Levitation for Energy Harvesting." Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4406.
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This dissertation reports the investigation conducted on the static and dynamic behavior of the passive diamagnetic levitation systems.
Attachment of a device to a substrate hinders the optimum performance ability of vibrating devices by altering the dynamic behavior of the moving part whilst introducing higher overall stiffness. The significance of this effect is prominent especially in vibration based energy harvesters as higher stiffness elevates the resonance frequency of the system, making it difficult to tune into ambient low frequencies. Other advantages of the proposed method are given by the removal of mechanical bending elements, which are often the source of energy dissipation through thermo-elastic damping and affects device reliability and durability. In this research, diamagnetically levitated resonators that can be utilized in energy harvesting were proposed and investigated as a possible solution to overcome these problems. Permanent magnets in an opposite neighboring poles (ONP) configuration were used to provide the magnetic field required for levitation. Pyrolytic graphite (PG), which is the known highest diamagnetic material, serves as the levitating proof mass.
Experimental results show that the static levitation height has a linear dependence on the thickness and a nonlinear dependence on the area of the levitating proof mass that can be approximated to a third order polynomial equation. Also, the study proved that a thinner proof mass provides a higher air gap while length of the proof mass beyond a certain value (l >10 mm for the experimental system considered in this dissertation) has no significant effect on increasing the air gap. It was also observed that levitation can slightly increase by attaching magnets to a sheet of steel (ferromagnetic material).
To the best of my knowledge, this dissertation is the first to address the parameterized studies in the dynamics of diamagnetic levitated objects by permanent magnets. Measurements performed on a diamagnetic levitating prototype system show that the resonance frequencies are lowered by approximately 3- 4 orders of magnitude in levitated systems compared to the attached systems demonstrating the feasibility of using levitating techniques for micro to meso scale energy harvester applications. Also, there is a significant dissimilarity observed in this study compared to the mechanically attached systems: The resonance frequency has a dependence on magnetic field strength, and is shifting towards lower values when increasing the strength of the magnetic field. This indicates that the virtual spring of a levitated proof mass is not a constant and therefore, the resonance frequency of the diamagnetic levitated systems is able to be fine-tuned by varying the magnetic field.
Finite Element Method (FEM) models were developed using COMSOL software that can simulate 3D magnetic flux formation of an array of permanent magnets and the diamagnetic levitation. The appropriate magnetic force equation from the two force equations that exist in the literature was established for the static levitation with the help of experimental and simulation results. Moreover, these models are able to provide the magnetic force exerted on diamagnetic objects at different heights, stable levitation height and position and also an indication of the maximum stably levitated size of the diamagnetic material.
Future endeavor of this study is to realize the diamagnetic levitation in energy harvesters. The results obtained from this research will not be limited to harvester applications but will also be beneficial to other diamagnetic levitation related systems, as these parameters are fundamental and necessary for the foundation of the research in the field of interest.
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Itabaiana, Sobrinho Sisenando. "Obtenção de nanocompósitos na forma de filmes finos a partir do processo sol-gel, para proteção anticorrosiva de magnetos de NdFeB empregados em ortodontia." reponame:Repositório Institucional da UFOP, 2014. http://www.repositorio.ufop.br/handle/123456789/3532.
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Programa de Pós-Graduação em Engenharia de Materiais. Rede Temática em Engenharia de Materiais, Pró-Reitoria de Pesquisa e Pós-Graduação, Universidade Federal de Ouro Preto.Submitted by Maurílio Figueiredo (maurilioafigueiredo@yahoo.com.br) on 2014-07-17T19:48:25Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) TESE_ObtençãoNanocompósitosForma.pdf: 7430806 bytes, checksum: 070da0f0ebdd2a474ee2b066590fb71b (MD5)
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A despeito do êxito clínico dos magnetos na movimentação ortodôntica é relevante inibir através de um revestimento seguro o processo corrosivo decorrente das interações do meio bucal com os materiais magnéticos. Buscou-se neste estudo a obtenção de filmes finos obtidos pelo processo sol-gel a partir de soluções alcoólicas contendo isopropóxido de titânio (IV) como precursor do TiO2 e AgNO3 como precursor da prata metálica além do ácido metacrílico (AMA). Almejou-se com os filmes finos, uma melhor perfomance anticorrosiva dos magnetos NdFeB em ambiente ácido simulando o meio bucal. No sol formado foi empregada uma luz ultravioleta (UV-C) para promover a redução dos íons (Ag+ - Ago) com a finalidade antibacteriana do filme Ag/TiO2. Os filmes foram confeccionados pelo método dip-coating variando de 1 a 4 camadas e em seguida tratados termicamente a diferentes temperaturas. Para selecionar a solução mais apropriada a ser depositada na superfície dos substratos magnéticos, testou-se previamente os nanocompósitos híbridos Ag/TiO2, Ag/TiO2/AMA e TiO2/AMA depositados sobre lâminas de aço austenítico da série 316L e também sobre os magnetos NdFeB. Os filmes finos obtidos foram analisados com o auxílio de técnicas de microscopia de alta resolução que forneceram informações composicionais (EDS), morfológicas, topográficas e espessura do filme fino (MEV e microscopia de força atômica) e sobre a cristalinidade dos mesmos (difração de raios X). Foram realizados testes de resistência mecânica do filme TiO2/AMA por meio de nanoindentação. A eficácia anticorrosiva dos filmes finos TiO2/AMA depositados sobre os magnetos NdFeB foi testada analisando o comportamento do campo magnético das amostras e a microestrutura após a imersão dos mesmos em solução de ácido lático 1% por um período amostral de 70 dias. Empregou-se um teste estatístico ANOVA para avaliar a variação das médias dos mesmos. Os resultados mostraram que os magnetos revestidos em TiO2/AMA praticamente não sofreram corrosão, quando comparados com o controle, podendo os mesmos serem empregados na clínica ortodôntica para a movimentação dentária. No caso clínico ortodôntico relatado, os magnetos revestidos em TiO2/AMA, mostraram-se eficientes na geração de forças ortodônticas, bem como uma eficiência anticorrosiva corroborando as análises in vitro. __________________________________________________________________________________________
ABSTRACT: Despite the clinical success of the magnets in orthodontic movement is relevant inhibit via a secure coating the corrosion process resulting from interactions of the oral environment with magnetic materials. In this study we attempted to obtain thin films obtained by the sol-gel process from alcoholic solutions containing titanium isopropoxide (IV) as the precursor of TiO2 and AgNO3 as silver metal precursor addition of methacrylic acid (AMA). Craved with thin films, better corrosion performance of NdFeB magnets in acidic environment simulating the oral environment. In the formed sol was used an ultraviolet light (UV-C) to promote the reduction of ions (Ag + - Aug) for the purpose of antibacterial film Ag/TiO2. The films were prepared by the dip-coating method ranging from 1 to 4 layers and then heat treated at different temperatures. To select the most appropriate solution to be deposited on the surface of the magnetic substrates, we tested previously Ag/TiO2 hybrid nanocomposites, Ag/TiO2/AMA TiO2/AMA and deposited on 316L austenitic steel series and also on the NdFeB magnets. The thin films were analyzed with the aid of microscopy techniques that provide high resolution information compositional (EDS), morphology, topography and thickness of thin film (SEM and atomic force microscopy) and the crystallinity of the same (ray diffraction X). Tests of mechanical strength of the film TiO2/AMA by nanoindentation. Later the thin film Ag/TiO2 was tested for its antibacterial and anticorrosive simultaneously. The effectiveness of corrosion TiO2/AMA thin films deposited on the NdFeB magnet was tested by analyzing the behavior of the magnetic field of the samples after soaking in solution of the same lactic acid 1% for a sample period of 70 days. Employed is an ANOVA to assess the variation of the averages of them. The results showed that the magnets coated TiO2/AMA hardly undergo corrosion when compared with the control, the same may be employed in orthodontic treatment for tooth movement. In orthodontic clinical case reported, the magnets coated in TiO2/AMA, were effective in generating orthodontic forces, as well as an anticorrosive efficiency corroborating the in vitro assays.
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Welzel, Lisa. "End-Of-Life Wind Turbines in the EU : An Estimation of the NdFeB-Magnets and Containing Rare Earth Elements in the Anthropogenic Stock of Germany and Denmark." Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-394910.
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Securing rare earth elements (REE) for a stable supply require sustainable management strategies in Europe due to a missing local primary production and a dependence on China as the main producer of REE. These elements, like neodymium (Nd) and dysprosium (Dy), are contained in permanent magnets (PM) (mostly NdFeB-magnets) in wind turbines. Addressing the question whether PM-material, Nd- and Dy-contents from wind turbines could help to meet future demands of REE in Europe while reducing simultaneously the import dependence, the purpose of the present work was to analyze the urban mining opportunities, recovery - and recycling potentials for REE from end-of-life (EoL) wind turbines. This thesis aimed to identify current and upcoming stocks as well as material flows of the PM and their containing REE in the wind energy sector. Two European countries, Germany and Denmark, were chosen as case studies to be compared based on created future scenarios and the modeling of the theoretical recycling potential of Nd and Dy in both countries. It could have been identified that the German anthropogenic stock contains greater amounts of NdFeB-magnets and REE compared to the Danish stock. Overall it could be concluded that the countries’ demand could partly be met by using secondary Nd and Dy from the EoL-wind turbines. Although future scenarios were used, the results realistically illustrate the German and Danish anthropogenic stock until 2035 by relying on data of already installed turbines up to 2018, which makes an evaluation of capacities and EoL-turbines, which need to be decommissioned by 2035, achievable. The provided information is valuable for further investigations regarding recovery strategies, feasibility analysis, and future decision-making processes.För att säkra tillgången på jordartsmetaller (REE) i Europa krävs hållbara beslutsstrategier. Detta på grund av avsaknaden av en inhemsk primärproduktion samt ett beroende av Kina som en huvudprodu-cent av REE. Jordartsmetaller som neodymium (Nd) och dysprosium (Dy), finns kvar i permanenta magneter (PM) (mestadels NdFeB-magneter) i vindturbiner. För att ta itu med frågan om huruvida Nd- och Dy-innehållet i PM-material, från vindturbiner skulle kunna bidra till att uppfylla framtida efter-frågan på REE i Europa samtidigt som importberoendet skulle minskas, var syftet med detta arbete att analysera möjligheterna till urban utvininng, återvinning och materialutnyttjande av REE från vindtur-biner i uttjänt tillstånd (EoL).Syftet med denna uppsats var att identifiera nuvarande och kommande tillgångar samt materialflöden av PM och därav följande REE inom vindkraftsektorn. Två europeiska länder, Tyskland och Danmark, valdes ut som fallstudier och jämfördes i framtida scenarier och mo-dellering av Nd -och Dy teoretiska återvinningspotential i båda länderna. Det kunde konstaterats att det tyska antropogena beståndet innehåller större mängder NdFeB-magneter och REE än det danska beståndet. Sammanfattningsvis kan man dra slutsatsen att ländernas efterfrågan delvis kunde tillgodo-ses genom att man använde sekundär Nd och Dy från EoL-vindturbiner. Även om framtida scenarier användes illustreras resultatet på ett realistiskt sätt det det antropogena lagret i Tyskland och Danmark fram till 2035 genom att man förlitar sig på uppgifter om redan installerade turbiner fram till 2018, vilket gör det möjligt att göra en utvärdering av kapaciteten och antal EoL-turbiner, som måste av-vecklas senast 2035. Informationen är värdefull för ytterligare utredningar om återvinningsstrategier, genomförbarhetsanalys och framtida beslutsprocesser.
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Thielsch, Juliane. "Wechselwirkungsdomänen in permanentmagnetischen Seltenerd-Übergangsmetall-Verbindungen." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-163196.
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Im Rahmen der Dissertation wurde das Phänomen der Wechselwirkungsdomänen sowohl experimentell als auch unter Zuhilfenahme mikromagnetischer Simulationen untersucht. Gegenstand der Untersuchungen waren einphasige NdFeB-Magnete, die durch Heißpressen und anschließender Warmumformung hergestellt wurden. Zusätzlich wurden über den gleichen Herstellungsweg Kompositproben aus NdFeB und Fe mit unterschiedlichen Partikelausgangsgrößen erhalten und studiert.
Korrelationsuntersuchungen verschiedener Messmethoden haben gezeigt, dass im thermisch entmagnetisierten Zustand die Grenzen der Wechselwirkungsdomänen an der Oberfläche größtenteils entlang von Korngrenzen verlaufen. Mittels in-situ MFM wurden erstmalig Untersuchungen von Wechselwirkungsdomänen an massiven NdFeB-Magneten im Magnetfeld durchgeführt. Die Ummagnetisierung erfolgt dabei über die Bewegung der Domänengrenze durch schrittweises Wandern von einer Korngrenze zur benachbarten. Die Beweglichkeit der Domänengrenzen ist durch das Haften an den Korngrenzen gehemmt, was sich in der geringeren Suszeptibilität der warmumgeformten Magnete im Vergleich zu Sintermagneten bemerkbar macht.
Aufgrund der eingestellten Mikrostruktur in den warmumgeformten Magneten kann folglich gesagt werden, dass die Ummagnetisierungsprozesse sowohl Merkmale von klassischen Nukleations-, als auch von klassischen Pinningmagneten aufweisen. Mit Hilfe von mikromagnetischen Simulationen konnte eine Eindomänenteilchengröße prismatischer Partikel mit quadratischer Grundfläche ermittelt werden. Außerdem konnte gezeigt werden, dass der Winkel des Streufeldvektors eine entscheidende Rolle bei Ummagnetisiserungsprozessen in solchen Partikeln spielt. Die Superposition des Streufeldvektors mit dem Vektor des angelegten Feldes führt zu einem Gesamtfeldvektor, dessen Winkelabhängigkeit ein Stoner-Wohlfarth ähnliches Verhalten zeigt.
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Maenz, Torsten. "Spritzgießtechnische Herstellung duroplastgebundener Dauermagnete." Universitätsverlag der Technischen Universität Chemnitz, 2017. https://monarch.qucosa.de/id/qucosa%3A23550.
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Kunststoffgebundene Dauermagnete kommen bereits seit einem dreiviertel Jahrhundert in diversen Anwendungen zum Einsatz. Dabei werden die gängigen Kunststoffverarbeitungsverfahren wie beispielsweise Spritzgießen, Extrudieren, Pressen und Kalandrieren angewandt. Ähnlich zu der Aufteilung in der Verarbeitung von herkömmlichen Kunststoffen, werden auch für die kunststoffgebundenen Dauermagnete nur selten duroplastische Matrixmaterialien im Spritzgießverfahren eingesetzt. Dabei bringt gerade diese Werkstoffklasse hervorragende Eigenschaften mit sich, die eine Verbesserung der Eigenschaften von kunststoffgebundenen Dauermagneten zur Folge haben können. Neben der Medien- und Temperaturbeständigkeit dieser Werkstoffklasse spielt dabei auch deren Viskosität eine bedeutende Rolle für diese Anwendung. Im Rahmen der vorliegenden Arbeit soll geprüft werden, ob der Einsatz duroplastischer Matrixmaterialien zu einer Verbesserung der Eigenschaften kunststoffgebundener Dauermagnete führen kann. Hierfür werden
anisotrope Magnetpartikel in den Kunststoff eincompoundiert und während der Verarbeitung im Spritzgießverfahren orientiert. Dies geschieht durch ein integriertes Magnetfeld im Spritzgießwerkzeug. Insbesondere sollen der Einfluss des Matrixmaterials, der Partikelgeometrie, der Fließrichtung sowie des Richtfeldes auf die Partikelorientierung untersucht werden. Zusammen mit grundlegenden analytischen Untersuchungen der Ausgangsmaterialien sollen abschließend Richtlinien für eine Bauteilauslegung definiert und erste Ansätze
für eine Simulation der magnetischen Bauteileigenschaften erarbeitet werden.Polymer bonded magnets are used for different applications for over 70 years yet. These materials are produced within known polymer processing procedures as injection molding, extruding, compression molding and calendaring. However, as for standard plastics thermoset materials are seldom used in injection molding even though they show great potential regarding temperature and media resistance as well as in terms of a low viscosity. These properties could be of use in case of polymer bonded magnets. Within this work the use of thermoset matrix materials for polymer bonded magnets should be evaluated and thus their properties shall be improved. Therefore anistotropic magnetic particles will be incorporated in the thermoset matrix and they will be oriented during the injection molding process which requires a magnetic field in the cavity during processing. Especially the influences of the matrix material, the particle geometry, the flow direction and the aligning field on the particle orientation should be investigated and together with fundamental analytical procedures guidelines for engineering of parts should be generated as well as first approaches for a simulation of the part properties shall be given.
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Kurfűrst, Jiří. "Optimalizace stroje s permanentními magnety na rotoru pomocí umělé inteligence." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-233585.
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The dissertation thesis deal with the design and the optimization of the permanent magnet synchronous machine (SMPM) based on the artificial intelligence. The main target is to apply potential optimization methods on the design procedure of the machine and evaluate the effectiveness of optimization and the optimization usefulness. In general, the optimization of the material properties (NdFeB or SmCo), the efficiency maximization with given nominal input parameters, the cogging torque elimination are proposed. Moreover, the magnet shape optimization, shape of the air gap and the shape of slots were also performed. The well known Genetic algorithm and Self-Organizing migrating algorithm produced in Czech were presented and applied on the particular optimization issues. The basic principles (iterations) and definitions (penalty function and cost function) of proposed algorithms are demonstrated on the examples. The results of the vibration generator optimization (VG) with given power 7mW (0.1g acceleration) and the results of the SMPM 1,1kW (6 krpm) optimization are practically evaluated in the collaboration with industry. Proposed methods are useful for the optimization of PM machines and they are further theoretically applied on the low speed machine (10 krpm) optimization and high speed machine (120 krpm) optimization.
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Nevřivý, Tomáš. "Kompaktní měnič pro BLDC motor." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2013. http://www.nusl.cz/ntk/nusl-219927.
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The work describes the design and implementation of compact inverter for brushless DC motor, which have mechanical power 600 W and rated torque 1.6 Nm. Motor is designed for DC link voltage with value 300 V. The focus is placed on the cost and simplicity. On this basis, the inverter is designed for uses single purpose power and control circuit. The power part is solved using a circuit FSBB15CH60C. The circuit is placed on a separate board of power electronics. Cooling of the power circuit is performed by the surface structure of BLDC motor. Control of the inverter ensures circuits LB11696V and NE566. The both circuits are placed on separate board of control electronics. Circuit LB11696V contains a control algorithm, as well as protections, which are necessary for safe operation of the inverter. Power supply of electronics is performed using step-down converter from MYRRA company.
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Nejedlý, Vladislav. "Analýza a inovace elektrických motorků pro automobily." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218796.
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In this thesis analysis and inovation of electric machines for cars is discused. There are described principles of basics DC and AC electric machines. In detail this thesis deals with small electric machines used in cars. At least, electro motor for wiper is investigated and possibilities of its inovation in different ways are also mantioned.
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Partzsch, Sven. "Magnetoelectric Coupling Mechanisms in YMn2-xFexO5 and NdFe3(BO3)4 Revealed by Resonant X-ray Diffraction." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138793.
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Multiferroic materials with a coupled ordering of electric and magnetic moments could be used to build energy-efficient, magnetic computer memory that is written with an electrical field. To understand the interaction between the magnetic and electric ordering in such materials, two examples, namely yttrium manganate YMn2O5 and neodymium iron borate NdFe3(BO3)4, are studied by means of resonant x-ray diffraction. The important role of a pure electronic contribution to the ferroelectric polarization is shown in YMn2O5. Furthermore, substitution of Fe can change the magnetic order of YMn2O5 from antiferromagnetic into ferrimagnetic, allowing the storage of easily readable magnetic information. Therefore the change of the magnetic structure upon small Fe substitution is studied. Although most of the magnetic structure of the parent compound is kept, the Fe moments have larger components along the c-direction. In NdFe3(BO3)4 the microscopic origin of the magnetoelectric coupling is addressed as the consequence of the frustration of the Fe and Nd magnetic sublattices. The application of an electrical field shifts the balance from the helical to the collinear magnetic domains, revealing again the strong magnetoelectric couplingMultiferroische Materialien mit einer starken magnetoelektrischen Kopplung können als energieeffizienter, magnetischer Speicher benutzt werden, welcher mit einem elektrischen Feld geschrieben wird. Um die Wechselwirkung der elektrischen mit der magnetischen Ordnung in solchen Materialien zu verstehen, werden hier zwei Beispiele, nämlich Yttriummanganat YMn2O5 und Neodymeisenborat NdFe3(BO3)4, mit resonanter Röntgenbeugung untersucht. In YMn2O5 wird die wichtige Rolle eines rein elektronischen Beitrags zur ferroelektrischen Polarisation gezeigt. Um die magnetische Struktur von YMn2O5 von antiferromagnetisch zu ferrimagnetisch zu verändern, kann Fe substituiert werden. Dies ermöglicht es, leicht zu lesende, magnetische Informationen zu speichern. Daher wurde die Änderung der magnetischen Struktur bei leichter Fe Substituierung untersucht. Auch wenn die magnetische Struktur von Fe im wesentlichen der magnetischen Struktur von Mn folgt, haben die Fe Momente größere Komponenten entlang der c-Richtung. In NdFe3(BO3)4 wird der Ursprung der starken magnetischen Kopplung als Folge der Frustration des Nd und Fe Untergitters erklärt. Das Anlegen eines elektrischen Feldes führt zur Verschiebung des Gleichgewichts von den helikalen zu den kollinearen magnetischen Domänen, welches wieder die starke magnetoelektrische Kopplung veranschaulicht
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Popa, Ioana. "Procédés d'optimisation des caractéristiques structurales et magnétiques des matériaux NdFe(12-x)Vx à vocation d'aimants permanents." Université Joseph Fourier (Grenoble), 2003. http://www.theses.fr/2003GRE10170.
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Janoschek, Marc. "Investigation of the chiral magnets NdFe 3 ( 11 BO 3 ) 4 and MnSi by means of neutron scattering." kostenfrei, 2008. http://mediatum2.ub.tum.de/node?id=667524.
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