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Dissertations / Theses on the topic 'Neodymium magnet'
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DAMENTO, MICHAEL ANTHONY. "DETECTION OF MAGNETIZATION REVERSAL IN A NEODYMIUM-IRON-BORON MAGNET USING A HALL-EFFECT MICROPROBE." Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183945.
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Magnetization processes in a sintered Nd-Fe-B permanent magnet (NEOMAX-35) were examined on a small scale using a Hall-effect microprobe with an active area 75 μm on a side. Probes were made by evaporating bismuth through a stencil mask onto glass slides. Experiments were performed by placing a probe onto the polished pole face of a Nd-Fe-B magnet and inserting the probe-magnet assembly into an electromagnet. Barkhausen steps, indicating rapid domain wall motion, were observed (superimposed upon the blank probe signal) in the demagnetization of a fully magnetized magnet. Magnetization traces for a thermally demagnetized Nd-Fe-B magnet did not exhibit measurable Barkhausen steps until a field of approximately 1.2 T was applied. The following observations were made for two thermally demagnetized samples which were cycled through minor hysteresis loops (maximum applied field of approximately 2 T): (1) virgin magnetization traces did not contain measurable Barkhausen steps, however all other forward and reverse magnetization traces did; (2) the initial reverse magnetization trace exhibited more and larger Barkhausen steps than subsequent traces; and (3) some Barkhausen steps were repeatable, that is, occurring at approximately the same field on each subsequent forward or reverse trace. Hall voltage signals were on the order of millivolts for probe currents of 10 mA.
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Klešč, Tania. "Neodimio magnetų eksperimentinis tyrimas." Bachelor's thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130821_115730-10514.
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Bakalauro darbą „ Neodimio magnetų eksperimentinis tyrimas“ sudaro įvadas, keturi skyriai, išvados, priedai ir literatūros sąrašas. Šio darbo apimtis 30 puslapių. Darbe yra 26 paveikslėliai ir 1 lentelė.Įvade iškeliama darbo problema, tikslai ir uždaviniai. Pirmajame skyriuje pateikta literatūros analizė. Antrajame skyriuje aprašoma eksperimento metodika. Trečiajame skyriuje pateikti sistemų su neodimio magnetais tyrimo rezultatai. Ketvirtajame skyriuje pateikta eksperimento rezultatų analizė. Darbo pabaigoje pateiktos išvados apibendrinančios atliktą darbą ir pateikti pasiūlymai, kur būtų galima panaudoti neodimio magnetus.<br>The final bachelor‘s work “Experimental analysis of neodymium magnets” consist of introduction, four chapters, conclusions and references. The work consists of 30 pages. There are 26 images and 1 table.Problem of the research along with objectives and goals are provided in the introduction of this work. The first chapter provides analysis of literature. The second chapter is about methodology of experiment. The third chapter provides the results of systems of neodymium magnets. The fourth chapter provides analysis of the experiment results. At the end of the work there are conclusions and suggestions about neodymium magnets usage.
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Braconi, Dario. "Green two-wheeled mobility : Material Hygiene and life cycle analysis of anelectric scooter." Thesis, KTH, Maskinkonstruktion (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-157045.
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In the last years electric vehicles gained importance as a more sustainable alternative to traditional vehicles. The introduction of an electric powertrain leads to lower air-pollution emissions but it also involves the introduction of new materials in the product life cycle, e. g., the rare earths and lithium contained in the motor and in the batteries. Those materials have an environmental impact and they need to be disposed properly. The aim of this thesis is to have a quantitative knowledge of the environmental balance linked to the use of a different powertrain. Furthermore, this study explores how this balance can be modified improving the recycling and the end of life management. Specifically in this thesis, an average electric scooter has been chosen as a case study. The electric scooter is used as object of comparison with a traditional internal-combustion-engine scooter. The choice of a two-wheeled mean of transport is linked to the low level of facilities involved. This report first includes a definition of the case of study; this section also presents a description of the technologies taken into exam. It is also presented the result of interviews with dismantlers to depict the current process of EoL management of a scooter. The central part of thesis deals with different recycling scenarios. With the help of the Material Hygiene mind-set, a qualitative analysis and different recycling scenarios are proposed. The recycling scenarios involve the component of the electric powertrain that are peculiar of the electric vehicle. They mainly are the electric motor and the lithium battery pack. The last part of the analysis encompasses a Life Cycle Assessment of an average electric scooter to give a quantitative meaning to the life cycle comparison and to assess the environmental benefits of the proposed recycling scenarios. To perform the Life Cycle Assessment a software, SimaPro 7.3, is used. This software lets the user insert the bill of materials of the product and it associates to each material its environmental loads according to the database EcoInvent v.2.2. Keywords: electric scooter, lithium battery, permanent magnet, neodymium, Material Hygiene, Design for Disassembly, Life Cycle Assessment, LCA<br>Negli ultimi anni i veicoli elettrici sono emersi come un ’alternativa sostenibile ai veicoli tradizionali. L’introduzione di un gruppo propulsore elettrico permette emissioni inquinanti più basse ma comporta anche l’introduzione di nuovi materiali nel ciclo di vita del prodotto, e.g., le terre rare e il litio contenuti rispettivamente nel motore e nelle batterie. Questi materiali hanno un impatto ambientale e hanno bisogno di essere trattati correttamente. Lo scopo di questa tesi è di avere una comprensione quantitativa del bilancio dal punto di vista ambientale legato al l’adozione di sistema di propulsione elettrico. Inoltre, è indagato come questo bilanco possa essere influenzato migliorando il ricic laggio e la gestione dell’ultima fase di vita del prodotto. Nello specifico, in questa tesi, uno scooter elettrico è stato scelto come caso di studio. Lo scopo è di comparare questo scooter con uno tradizionale considerando il ciclo di vita del prodotto. Il mezzo di trasporto a due ruote è stato scelto perché considerato più semplice da modellare in quanto privo di componenti non inerenti al trasporto (es. aria condizionata, hi-fi, etc.). Questo report anzitutto include una definizione del caso di studio, questa sezione presenta anche una descrizione delle principali tecnologie coinvolte nel prodotto studiato. In questa parte del lavoro è anche riportato il risultato di interviste a rottamatori di scooter per illustrare l’attuale iter di rottamazione di uno scooter. La parte centrale della tesi tratta i differenti scenari di riciclaggio. Sfruttando la mentalità Material Hygiene vengono proposte un’analisi qualitativa e differenti scenari di rici claggio. Gli scenari di riciclaggio coinvologono il progettista a livelli differenti. Questi scenari riguardano i componenti del sistema di propulsione elettrico. Essi sono principalmente il motore elettrico e le batterie al litio. L’ultima parte dell’analisi riguarda il Life Cycle Assessment di uno scooter elettrico al fine di dare un significato quantitativo al confronto tra i cicli di vita delle due alternative. Inoltre, il life cycle assessment ha lo scopo di verificare e quantificare i benefici di impatto ambientale collegati all’adozione degli scenari di riciclaggio proposti. Per svolgere il Life Cycle Assessment è stato usato un sofware, SimaPro 7.3. Questo software permette all’utente di inserire l’elenco dei materiali di un prodotto e di associare a ciascun materiale il proprio impatto ambientale. Il software ha a disposizione per la modellazione i database di impatto ambientale EcoInvent 2.2. Parole chiave: scooter elettrico, batteria al litio, magnete permanente, neodimio, Material Hygiene, Design for Disassembly, Life Cycle Assessment, LCA
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Jubb, Gary Anthony. "Production and properties of neodymium-iron-boron permanent magnets." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236470.
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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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Attanasio, Steven A. 1967. "Corrosion and environmentally-assisted cracking of rapidly solidified neodymium-iron-boron permanent magnets." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39748.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1996.<br>Vita.<br>Includes bibliographical references (p. 383-388).<br>by Steven A. Attanasio.<br>Ph.D.
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MENDES, NETO TEOFILO. "Estudo microestrutural e propriedades magnéticas em imãs permanentes sinterizados à base de PrFeCoBNb com adições de elementos de liga." reponame:Repositório Institucional do IPEN, 2011. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9992.
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Meakin, Jonathan Philip. "Development of a pilot scale strip casting system to produce optimised alloys for neodymium-iron-boron magnets." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6791/.
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Strip casting is a rapid processing technique used in the production of alloys for both sintered and HDDR bonded NdFeB magnets. During strip casting, molten alloys are gravity fed onto a rotating copper wheel. The rapid cooling rate produces NdFeB microstructures which have many advantages over conventionally cast NdFeB book-mould alloys such as less alpha iron, near stoichiometric alloy compositions and a finer grain structure. The wheel texture of a pilot scale strip caster was altered in order to optimize the microstructure and improve the consistency of strip cast flakes for the production of NdFeB sintered magnets. This made it possible to reduce the flake thickness distribution and alpha iron content, improve the grain size consistency and increase lamellar alignment. In NdFeB alloys for HDDR (Hydrogenation Disproportionation Desorption and Recombination) powders, which are used in bonded magnets, a large grained material is preferable with little or no alpha iron. By implementing a combination of surface texture and reduced wheel speed, the grain width was increased from ~5 to ~40 μm, whilst maintaining a low alpha iron content. The magnetic performance has been shown to be comparable to conventional book-mould alloys that have been heat treated for 10 hours at 1140°C.
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OLIVEIRA, MARA C. L. de. "Estudo da influencia do campo magnetico na resistencia a corrosao em imas permanentes de Nd=Fe-B." reponame:Repositório Institucional do IPEN, 2004. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11214.
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SILVA, BRUNO F. A. da. "Preparação de ímãs híbridos aglomerados com mistura de pós a base de TR-Fe-B e ferrite." reponame:Repositório Institucional do IPEN, 2012. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10532.
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Wang, Huabin 1969. "The magnetic properties, crystal and magnetic structures of Nd5SixGe4-x /." Thesis, McGill University, 2007. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=101661.
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The magnetic properties, crystal and magnetic structures of Nd5 SixGe4-x were investigated by ac susceptibility and high resolution neutron powder diffraction. The magnetic and crystalline phase diagrams were derived. Four distinct structures exist in the Nd 5SixGe4-x system: Gd5Ge 4-type [O(II)], Gd5Si2Ge2-type (M), Gd5Si4-type [O(I)], and Zr5Si4-type (T). The refinements of the neutron powder diffraction patterns revealed that the Nd5SixGe4-x compounds exhibit mixed ferro-antiferromagnetic structures. The ac susceptibility measurements showed that the magnetic ordering temperature of Nd5SixGe 4-x increases slightly with increasing silicon content, except that it increases by a factor of 2 in the orthorhombic Gd5Si 4-type [O(I)] phase region. The abrupt change of the magnetic ordering temperature between x = 2.25 and x = 2.5, where the monoclinic Gd5Si 2Ge2-type (M) structure changes to the orthorhombic Gd 5Si4-type [O(I)] structure, suggested that a first order magnetostructural transition likely takes place in this narrow composition range (2.25 < x < 2.5). The investigation of Nd5Si2.335 Ge1.665 revealed that Nd5Si2.335Ge 1.665 adopts the Gd5Si2Ge2-type (M) structure and undergoes a first order magnetostructural transition from the paramagnetic-monoclinic Gd5Si2Ge2-type (M) structure to the orthorhombic Gd5Si4-type [O(I)] structure upon cooling. The T1-T1 bonds increases by ∼1 A when the the Gd 5Si4-type [O(I)] structure (10 K) transforms to the Gd 5Si2Ge2-type (M) structure (140 K). The giant magnetocaloric effect is not observed in Nd5Si2.335Ge 1.665 probably due to the co-existence of the M phase and the O(I) phase. The maximum magnetic entropy change in Nd5Si2.335Ge 1.665 is 7.3 J/kg K for magnetic field change from 0 to 7 Tesla, which is similar to that obtained in Nd5Si1.5Ge2.5, the neighboring phase O(I).
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MARTINS, EMERSON A. "Avaliacao do efeito de tratamentos superficiais na resistencia a corrosao de magnetos de Nd-Fe-B." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9404.
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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.<br>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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Le, Breton Jean-Marie. "Etude par spectrométrie Mössbauer de la corrosion d'alliages métalliques : aimants permanents Nd-Fe-B ; acier faiblement allié en eau de mer naturelle." Rouen, 1992. http://www.theses.fr/1992ROUES050.
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La spectrométrie Mössbauer du fer 57 a été utilisée en relation avec d'autres techniques (diffractions de rayons X, microscopie électronique à balayage, microsonde électronique) pour étudier la corrosion d'aimants permanents industriels Nd-Fe-B entre 90°C (avec humidité) et 400°C, et d'un acier faiblement allié (42CD4) en eau de mer naturelle en fonction de la pression hydrostatique. Dans les aimants Nd-Fe-B, l'évolution de la phase Nd2Fe1#4B a été plus particulièrement suivie. Cette phase semble disparaître sous l'effet de l'oxydation du Nd, en formant principalement du fer alpha. Un net ralentissement de ce processus a été mis en évidence dans les aimants avec Co et V préparés par décrépitation par l'hydrogène. La composition de la couche de rouille formée sur des plaques d'acier 42CD4 immergées en eau de mer naturelle pendant 15 jours ne varie pas pour des pressions supérieures à 3MPa. L'akaganéite n'est observée qu'aux pressions inferieures a 3MPa
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Knebl, Ladislav. "Návrh synchronního reluktančního motoru s permanentními magnety." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-318197.
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V dnešní době je kladen vysoký nárok na účinnost elektrických zařízení a to jak ze strany provozovatele, tak i legislativy. Nejlepší účinnosti dosahují synchronní motory s permanentními magnety umístěnými na povrchu rotoru (SMPM), se kterými lze i u malých motorů dosáhnout účinnosti nad 90%. Nicméně tyto motory jsou z důvodů použití magnetů ze vzácných zemin, např. NdFeB, drahé a jsou schopny provozu pouze s frekvenčním měničem. Z cenových důvodů jsou hledány levnější alternativy k SMPM motorům. Jedním z typů motorů, kterým lze SMPM nahradit je synchronní reluktanční motor s permanentními magnety (PMASR). Tento motor je cenově výhodnější, protože používá menší množství magnetů, při zachování podobných, mnohdy i lepších vlastností, nicméně neodpadá potřeba použití frekvenčního měniče. Navíc je zde možnost použití levnějších feritových magnetů a tím ještě výrazněji snížit cenu motoru. V této práci bude PMASR topologie popsána důkladněji včetně elektromagnetického návrhu metodou konečných prvků. Bude provedena i mechanická analýza zvoleného optimálního modelu. Výsledky dosažené metodou konečných prvků budou následně porovnány s analytickým modelem. Z navrženého modelu bude vyroben prototyp a naměřené výsledky budou porovnány s výpočty.
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Borges, Danilo da Silva. "UM ESTUDO SOBRE A INJEÃÃO DE FIOS MAGNÃTICOS EM CAVIDADES." Universidade Federal do CearÃ, 2016. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=17610.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico<br>No presente trabalho realizamos uma sÃrie de experimentos acerca do processo de injeÃÃo de um
fio magÃtico no interior de uma cavidade circular rı́gida com o objetivo de obter uma melhor
compreensÃo sobre as caracterı́sticas das morfologias geradas dependendo das condiÃÃes inici-
ais. Nossos resultados indicam a possibilidade de formaÃÃo de duas morfologias que apresentam
caracterı́sticas bastante distintas. Quando os dois fios injetados em posiÃÃes diametralmente
opostos na cavidade apresentam dipolos magnÃticos que apontam na mesma direÃÃo, porÃm em
sentidos opostos, observamos a formaÃÃo do padrÃo tipo Espiral. JÃ no caso dos dois fios apre-
sentarem dipolos que apontam na mesma direÃÃo e sentido, os padrÃes de empacotamentos sÃo
do tipo Loop. Em seguida, realizamos uma sÃrie de anÃlises estatı́sticas com bases nas imagens
das estruturas formadas durante a injeÃÃo do fio na cavidade. Como resultados destas anÃlises
observamos que a morfologia da estrutura no caso do empacotamento tipo Loop apresentava
uma distribuiÃÃo de tamanhos de laÃos que exibe um comportamento em lei de potÃncia quanto
a quantidade de laÃos formados em funÃÃo da fraÃÃo de ocupaÃÃo da cavidade φ do tipo N l ∝ φ α .
O expoente α que governa o comportamento em lei de potÃncia à bastante diferente dos expoen-
tes encontrados para o caso de empacotamento de fios. Acreditamos que esta diferenÃa se deve
a presenÃa de forÃas de longo alcance que estÃo presentes em sistemas magnÃticos.<br>In this work we created some experiments concerning about injection process of magnetic wire
into a rigid circular cavity in order to get a better understanding about characteristics of the
morphologies generate under certain initial conditions. Our results implies the possibility of
formation of two morphologies that have dierent characteristics. When the two wires injected
diametrically opposite, but have magnetic dipoles in opposite direction we achieve spiral
morphology. In the case of the two wires injected diametrically opposite, but have magnetic
dipoles in same direction we achieve loop morphology. So we make a series of statistical analysis
based on the image structures, form during the injection of the wire in the cavity. As a result
these analyzes we found that the loop morphology showed a size ties distribution like power law
in function of the packing fraction , behaving as Nl / . The exponent rules the behavior of
a power law is quite dierent from those found in other works about packing wires. We believe
the dierence comes from to the presence of long-range forces present in magnetic systems.
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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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Marashi, Seyed Pirooz Hoveida. "Transmission electron microscopy study of nanostructured Nd-Fe-B hard magnetic materials." Thesis, University of Sheffield, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366102.
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GUILHERME, ENEIDA da G. "Preparacao de materiais magneticamente duros a base de ligas de terra rara-ferro nitrogenadas." reponame:Repositório Institucional do IPEN, 1999. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10786.
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Ben, messaoud Yethreb. "Modélisation analytique du couplage multi-physique magnétique-thermique dans la phase de préconception d'un système mécatronique." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC079/document.
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Durant la phase de conception, les différentes équipes d’ingénierie procèdent à de multiples simulations par éléments finis traitant les comportements physiques variés afin d’assurer la vérification et la validation.Cependant, les résultats insatisfaisants engendrent des changements tardifs et par conséquent de longues itérations et des coûts croissants.Pour répondre à cette problématique, il est essentiel de prendre en considération les contraintes géométriques et multi-physiques dès la phase de préconception.En effet, un processus appelé SAMOS est développé visant à sélectionner l’architecture multi-physique 3D la plus adéquate tout en garantissant une collaboration efficace entre les équipes d’ingénieurs. D’ailleurs, il est basé sur deux extensions en SysML permettant l’enrichissement de l’architecture par des informations géométriques et multi-physiques.D’autre part, cette thèse se focalise sur l’étude des contraintes magnétiques et du couplage magnétique-thermique.Comme cette phase ne supporte pas les simulations par éléments finis, les modèles analytiques basés sur des géométries simplifiées sont suffisants pour fournir des résultats approximatifs satisfaisants.Dans ce contexte, différents modèles analytiques sont étudiés et validés à travers des simulations par éléments finis et des mesures pour plusieurs cas tels que les aimants permanents en Néodyme. En fait, l’augmentation de température ne fait pas seulement diminuer la densité du flux magnétique rémanente mais il est capable de causer des pertes irréversibles. En effet, lorsqu’on revient à la température initiale, les caractéristiques de l’aimant sont modifiées. Les différents facteurs affectant le processus de démagnétisation sont examinés.De plus, l’impact de la température sur les performances d’un moteur sans balais est étudié étant donné que ce dispositif représente un système mécatronique complexe<br>During the design phase, the different engineering teams make multiple FE simulations dealing with various physical behaviours in order to ensure both verification and validation.However, the unsatisfactory results lead to late changes and hence to long iterations and increasing costs.In order to tackle this problem, it is essential to take into account the geometrical and multi-physical constraints in the complex system architecture since the conceptual design phase.In fact, a process called SAMOS is developed aiming at selecting the most adequate 3D multi-physical architecture while ensuring an efficient collaboration between the engineering teams. Moreover, this framework is based on two SysML extensions which allow the enrichment of the architecture with geometrical and multi-physical data.Furthermore, this thesis focuses on magnetic constraints and magnetic-thermal coupling.Since this phase does not support long FE simulations, the analytical models based on simplified geometries are sufficient to provide satisfactory approximate results.In this context, different analytical models are studied and validated through FE simulations and measures for several cases such as NdFeB permanent magnets. Indeed, the temperature rise does not only decrease the remanent flux density but is able also to cause irreversible losses. In fact, once we go back to the initial temperature, the characteristics of the magnet are modified. The different factors impacting the demagnetization process are discussed.Besides, the temperature impact on brushless motors’ performances is studied since this device represents a complex mechatronic system
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Wehrenberg, Christopher. "Phase transformations in shock compacted magnetic materials." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43595.
Full textAbstract:
Shock compaction experiments were performed on soft magnetic phases Fe₄N and Fe₁₆N₂, and hard magnetic phases Nd₂Fe₁₄B and Sm₂Fe₁₇N₃ in order to determine their thermo-mechanical stability during shock loading and explore the possibility of fabricating a textured nanocomposite magnet. Gas gun experiments performed on powders pressed in a three capsule fixture showed phase transformations occurring in Fe₄N, Fe₁₆N₂, and Nd₂Fe₁₄B, while Sm₂Fe₁₇N₃ was observed to be relatively stable. Shock compaction of FCC Fe₄N resulted in a partial transformation to HCP Fe₃N, consistent with previous reports of the transition occurring at a static pressure of ~3 GPa. Shock compaction of Fe₁₆N₂ produced decomposition products alpha-Fe, Fe₄N, and FeN due to a combination of thermal effects associated with dynamic void collapse and plastic deformation. Decomposition of Nd-Fe-B, producing alpha-Fe and amorphous Nd-Fe-B, was observed in several shock consolidated samples and is attributed to deformation associated with shock compaction, similar to decomposition reported in ball milled Nd-Fe-B. No decomposition was observed in shock compacted samples of Sm-Fe-N, which is consistent with literature reports showing decomposition occurring only in samples compacted at a pressure above ~15 GPa. Nd-Fe-B and Sm-Fe-N were shown to accommodate deformation primarily by grain size reduction, especially in large grained materials. Hard/Soft composite magnetic materials were formed by mixing single crystal particles of Nd-Fe-B with iron nanoparticles, and the alignment-by-magnetic-field technique was able to introduce significant texture into green compacts of this mixture. While problems with decomposition of the Nd₂Fe₁₄B phase prevented fabricating bulk magnets from the aligned green compacts, retention of the nanoscale morphology of the alpha-Fe particles and the high alignment of the green compacts shows promise for future development of textured nanocomposite magnets through shock compaction.
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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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Bothamy, Nina. "Fractionnement anthropique et naturel des isotopes stables du néodyme (Nd) dans l'environnement." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0295.
Full textAbstract:
Avec une utilisation mondiale croissante pour des applications variées (nouvelles technologies, énergies vertes, etc.), les terres rares (REEs pour ‘rare earth elements’) sont devenues des polluants émergents. Ces pollutions peuvent/pourront être d’origine industrielle (ex. rejets dans l’environnement en sortie d’usine), minière, ou causées par le stockage inapproprié de produits industriels (ex. aimants à base de néodyme (Nd) fragiles à la corrosion). Dans ce contexte, ce projet de thèse a cherché à développer un nouvel outil : l’étude du fractionnement dépendant de la masse des isotopes du Nd (δNd en ‰). Les objectifs de ce projet ont été i) d’apporter un maximum d’éléments pour aider à tracer les pollutions anthropiques de Nd dans l’environnement et ii) d’aider à mieux comprendre comment fonctionne l’accumulation des REEs par les plantes, en particulier les fougères hyperaccumulatrices Dicranopteris linearis, dans le but d’appuyer les études de phytoremédiation des sites pollués. Le δNd de matériels anthropiques (solutions synthétiques de Nd pur et aimants industriels Nd2Fe14B) a été mesuré (gamme de variation de 1,45 ‰ en δ148Nd, littérature incluse) et comparé à la signature des roches terrestres de la littérature (gamme de 0,66 ‰). Les résultats montrent que l’utilisation combinée i) du rapport de l’isotope radiogénique 143Nd/144Nd (ε143Nd, traceur de sources), ii) de la composition des isotopes stables du Nd (δNd, traceur de sources et processus) et, iii) du type de fractionnement (cinétique ou à l’équilibre thermodynamique) des isotopes stables du Nd, peut permettre à l’avenir de distinguer le Nd naturel du Nd anthropique et de tracer ce Nd anthropique dans l’environnement. La mesure du δNd de 5 spécimens de fougères D. linearis, ainsi que de 3 standards biologiques (lichen, feuilles de pommes et lentilles d’eau) a permis de déterminer de façon évidente que la biologie peut fractionner les isotopes stables du Nd. Les valeurs extrêmes en δ148Nd, parmi les échantillons biologiques, sont -0,415 ± 0,060 ‰ et -0,011 ± 0,022 ‰ (2σmean), respectivement pour l’une des pétioles des fougères et pour les lentilles d’eau. Trois résultats principaux en découlent : i) le fractionnement des isotopes stables (δNd) est corrélé au fractionnement des REEs légères par rapport aux REEs lourdes pour tous les échantillons mesurés (fougères, lichen, feuilles de pomme, lentilles d’eau et tous les sols) ; ii) le transport et la distribution du Nd (et des REEs) dans les différentes parties des fougères sont corrélés à ceux du manganèse (Mn), suggérant un mécanisme de transport similaire des REEs et du Mn, pour les fougères mais aussi chez d’autres végétaux comme les pommiers ; iii) la dégradation de l’argile, sur laquelle les REEs sont massivement adsorbées dans les sols étudiés, peut induire le fractionnement des isotopes stables du Nd des sols, que ce soit une dégradation causée par des processus naturels (ex. biologie) ou anthropiques (extraction des REEs avec des acides miniers)<br>With the worldwide growing demand for various applications (new technologies, green energies, etc.), rare earth elements (REEs) are now considered as emerging pollutants. These pollutions are/will be of industrial origin (e.g. industrial wastes), of mining origin, or caused by the inappropriate storage of industrial products (e.g. neodymium (Nd) magnets fragile against corrosion). In this context, this PhD project aims to develop a new tool: the study of the mass-dependent isotopic fractionation of Nd (δNd in ‰). The goals of this work were to i) bring the maximum of information in order to help to identify and trace anthropogenic Nd in the environment, and ii) help the understanding of how plants accumulate REEs, especially the hyperaccumulator Dicranopteris linearis ferns, in order to support the studies about the phytoremediation of polluted areas. The δNd of anthropogenic materials (pure Nd synthetic solutions, Nd2Fe14B industrial magnets; δ148Nd range of 1.45 ‰, literature included) was compared to the signature of natural terrestrial rocks of the literature (δ148Nd range of 0.66 ‰). Our results show that the use together of i) the 143Nd radiogenic isotope (ε143Nd, tracer of sources), ii) the stable Nd isotopic composition of Nd (δNd, tracer of sources and processes) and, iii) the kind of stable Nd isotopic fractionation (kinetic or thermodynamic equilibrium), could allow the distinction of the natural from the anthropogenic Nd, and to trace the anthropogenic Nd in the environment. The measurement of the δNd of 5 D. linearis fern specimens, and of 3 biological standards (lichen, apple leaves and duck weed) allowed discovering that biology can fractionate the stable Nd isotopes. Extreme δ148Nd values are -0.415 ± 0.060 ‰ and -0.011 ± 0.022 ‰ (2σmean), respectively for one of the fern petiole and the duck weed. Three principal results were obtained: i) the δNd fractionation is correlated to the fractionation of the light REEs than the heavy REEs for all the studied samples (ferns, lichen, apple leaves, duck weed and all soil materials); ii) the distribution and transport of Nd (and REEs) in the different parts of ferns are correlated to those of manganese (Mn), suggesting similar transport mechanisms for REEs and Mn, for ferns but also for other plants as apple trees; iii) the degradation of clay minerals, on which REEs are mostly adsorbed in the studied soils, can induce the fractionation of stable Nd isotopes, from natural processes (e.g. biological) or anthropogenic processes (REEs mining acidic extraction)
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Courtois, Pierre. "Elaboration en creuset froid sous champ magnétique intense de quelques matériaux magnétiques en vue de leur texturation." Université Joseph Fourier (Grenoble), 1995. http://www.theses.fr/1995GRE10124.
Full textAbstract:
Un creuset froid inductif a ete mis en place sous champ magnetique intense. Ce dispositif permet d'appliquer au cours de la solidification de materiaux tres reactifs un champ magnetique homogene ou inhomogene dans l'espace. Il permet egalement de realiser la levitation stabilisee par courants de foucault d'alliages metalliques liquides paramagnetiques. De nombreuses applications sont ouvertes dans le domaine de l'elaboration de materiaux ultra-purs. Nd#2fe#1#4b est le compose le plus utilise a la fabrication d'aimants permanents performants. Les conditions de texturation de ce compose par solidification sous champ magnetique sont etudiees. Malgre la decroissance thermique de l'energie d'anisotropie, le champ oriente des cristallites de nd#2fe#1#4b dans l'etat paramagnetique en suspension dans un liquide eutectique ndcu. L'anisotropie de la susceptibilite magnetique de nd#2fe#1#4b existe jusqu'au point de fusion et elle est toujours dirigee suivant la direction cristallographique (001). Cependant, l'energie magnetocristalline n'est pas suffisante pour induire une orientation des germes de cristallisation de nd#2fe#1#4b. Par consequent, la solidification sous un champ de 8t d'alliages a base de nd#2fe#1#4b a partir du liquide faiblement surchauffe ne conduit pas a un materiau texture, au contraire de dy#2fe#1#4b qui s'oriente partiellement suivant une direction de facile aimantation. Des mesures de susceptibilite en fonction de la temperature et du temps ont permis d'observer les effets de la surchauffe sur la solidification d'un alliage a base de nd#2fe#1#4b. Une forte surchauffe a pour consequence de detruire les germes de nd#2fe#1#4b presents dans le liquide lorsque celui-ci est maintenu a une temperature proche de la fusion. La metastabilite des germes de cristallisation est mis en evidence par la formation d'une phase solide metastable apres forte surchauffe du liquide
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Ball, Andrew. "Commensurabilité magnétique à longue période et anisotropie dans la série hexagonale RGa2 (R=Pr, Nd, Gd)." Grenoble 1, 1993. http://www.theses.fr/1993GRE10075.
Full textAbstract:
Les composes hexagonaux simples rga(r=gd, pr et nd) sont d'excellents candidats pour l'etude de structures magnetiques frustrees complexes resultant des interactions d'echange a longue portee. Par l'utilisation de techniques experimentales variees, nous avons mis en evidence sur ces composes des proprietes magnetiques originales et hautement complexes. Dans le cas de gdga#2, un champ magnetique induit des changements subtils dans la configuration antiphase incommensurable de la phase en champ nul. Ces processus peuvent se resumer en trois diagrammes de phases champ-temperature d'une complexite etonnante vue l'absence d'anisotropie magnetocristalline. Un modele de champ moyen periodique montre que les structures sous champ sont de type x-y en eventail, mettant ainsi en evidence l'existence d'une faible anisotropie d'echange. Les composes prga#2 et ndga#2 presentent des structures magnetiques en champ nul de type ising, confinees dans le plan hexagonal. Pres de t#n, ces structures sont incommensurables et evoluent a basse temperature vers des structures commensurables a longue periode. Dans prga#2, le champ applique induit des transitions metamagnetiques de type spin-slip et spin-flip entre differentes configurations magnetiques commensurables a longue periode. Apres une etude approfondie du champ cristallin, le modele du champ moyen periodique nous a permis d'analyser quantitativement les proprietes magnetiques principales de ce compose: chaleur specifique, aimantation, susceptibilite. . .
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Guidetti, Giulia. "Cellulose photonics : designing functionality and optical appearance of natural materials." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277918.
Full textAbstract:
Cellulose is the most abundant biopolymer on Earth as it is found in every plant cell wall; therefore, it represents one of the most promising natural resources for the fabrication of sustainable materials. In plants, cellulose is mainly used for structural integrity, however, some species organise cellulose in helicoidal nano-architectures generating strong iridescent colours. Recent research has shown that cellulose nanocrystals, CNCs, isolated from natural fibres, can spontaneously self-assemble into architectures that resemble the one producing colouration in plants. Therefore, CNCs are an ideal candidate for the development of new photonic materials that can find use to substitute conventional pigments, which are often harmful to humans and to the environment. However, various obstacles still prevent a widespread use of cellulose-based photonic structures. For instance, while the CNC films can display a wide range of colours, a precise control of the optical appearance is still difficult to achieve. The intrinsic low thermal stability and brittleness of cellulose-based films strongly limit their use as photonic pigments at the industrial scale. Moreover, it is challenging to integrate them into composites to obtain further functionality while preserving their optical response. In this thesis, I present a series of research contributions that make progress towards addressing these challenges. First, I use an external magnetic field to tune the CNC films scattering response. Then, I demonstrate how it is possible to tailor the optical appearance and the mechanical properties of the films as well as to enhance their functionality, by combining CNCs with other polymers. Finally, I study the thermal properties of CNC films to improve the retention of the helicoidal arrangement at high temperatures and to explore the potential use of this material in industrial fabrication processes, such as hot-melt extrusion.
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Delamare, José. "Etude microstructurale d'alliages Nd-Fe et Nd-Fe-Al : corrélation aux phases secondaires des aimants Nd-Fe-B." Rouen, 1992. http://www.theses.fr/1992ROUES058.
Full textAbstract:
La microstructure d'un alliage eutectique Nd-Fe a été étudiée grâce à la microscopie électronique à transmission. Il apparaît que le composé métastable A1 est constitué de deux composés nanocristallins, dont les compositions sont proches de Nd20Fe80 et Nd40Fe60 (% at. ). L'origine de la formation de tels composés est interprétée dans un diagramme de phases binaire métastable, incluant la phase NdFe2. Les caractéristiques structurales des autres phases du système binaire sont également étudiées. L'addition d'aluminium aux alliages Nd-Fe dont la composition est riche en Nd modifie drastiquement les propriétés macroscopiques (coercitivité, dureté). Ces effets sont liés aux modifications microstructurales apportées par l'aluminium (disparition de la phase A1 au profit de la phase ternaire U). La microstructure de ces alliages est voisine de celle de la phase intergranulaire rencontrée dans les aimants (Fe, Al)-Nd-B. Une étude bibliographique a confirmé que la phase U s'y présentait sous la forme de lamelles. Son influence sur la coercitivité des aimants est discutée. La structure cristalline polytypique de la phase U a été mise en évidence par diffraction électronique. Les polytypes 12R, 4H, 8H ont été identifiés. Une méthode permettant de déterminer les positions atomiques au sein de la maille polytypique est brièvement expliquée
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Ravach, Gwennola. "Etude structurale, magnétique et thermique de rubans amorphes Fe-Tr-B (Tr, Nd, Ho, Dy) à anisotropie magnétique aléatoire." Rouen, 1997. http://www.theses.fr/1997ROUES056.
Full textAbstract:
Les alliages amorphes métal de transition-terre rare peuvent présenter de l'anisotropie magnétique aléatoire due au désordre structural et au couplage spin-orbite de la terre rare. Les propriétés structurales et magnétiques de rubans amorphes hypertrempés Fe80-xTrxB20 (Tr = Nd, Ho, Dy ; x 16 % at. ) Ont été étudiées par spectrométrie Mössbauer, spectroscopie d'absorption X, analyse thermique différentielle et diffraction X aux grands angles. On montre par Mössbauer que les propriétés structurales des alliages ne dépendent pas de la nature de la terre rare. Une discontinuité des variations des paramètres hyperfins a lieu dans le domaine de concentration X#T#R#C 8-9% at. . Elle a été attribuée à une modification structurale autour du fer. Au-dessous de X#T#R#C , les sites de fer apparaissent similaires à ceux de Fe#8#0B#2#0. Un autre type d'environnement, plus magnétique, est suggère au-delà de X#T#R#C. La discontinuité et son origine structurale sont confirmées par spectroscopie d'absorption X. La modification intervient déjà dans la première sphère de coordination du fer. Les caractéristiques des paires Fe-Fe, identiques pour X#T#R < X#T#R#C, sont analogues à celles de Fe#8#0B#2#0. Au voisinage de X#T#R#C, un atome de fer supplémentaire apparait dans la première sphère de coordination et la distance moyenne Fe-Fe augmente. Au-delà de X#T#R#C, la première sphère de coordination du fer se contracte progressivement. D'après l'étude de cristallisation de deux alliages situés de part et d'autre de X#T#R#C, les premiers composés formés sont en accord avec des environnements locaux différents dans les deux domaines. L'étude Mössbauer sous champ des alliages les plus concentrés en terre rare indique un rapport anisotropie/échange plus faible dans l'alliage à base de Ho que dans ceux à base de Nd et Dy. Un modèle décrivant l'évolution sous champ de la structure magnétique du fer en termes de déformation angulaire a été développé. Il explique quantitativement les résultats dans le cas de Ho et Dy.
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Li, Po-Liang, and 李柏樑. "Neodymium Magnet Modular Robot Having Configuration Recognition Capability." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/59372907356159676982.
Full textAbstract:
碩士<br>修平科技大學<br>電機工程碩士班<br>102<br>In this thesis, design and control of the modular robot are discussed. The Modular robot is made of a set of robotic modules with the ability to change the shape by having cooperation among the multiple robot modules. In these designed modular robots, they comprise several modules individually with actuators controlled by their own on-board processing units, and these individual modules have the basic motion capability and control functions. Based on the optical sensors mounted on the connected faces of the modular robot can provide the relative position information for self-recognition. Through the self-recognition program, the modular robot can judge their configuration and execute the different motion. The ZigBee wireless module is used to synchronous start the modular robot, and provided to select the different motion.
In the experimental results, using the neodymium magnet between connected faces of the robot modules, they can provide the connected force when the modular robot is motion. Based on the robotic module, the modular robot can be formed by a set of robotic modules with the ability to change the shape by letting the multiple robot modules cooperate. Furthermore, some experimental results are demonstrated to show the effectiveness of the Neodymium Magnet Modular Robot with satisfactory performances.
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Liu, Yi-Hsien, and 劉宜憲. "Recovery of Neodymium from Waste Permanent Magnet by Support Liquid Membrane System and Develop High Quality Photocatalyst." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/00500478746231323377.
Full textAbstract:
碩士<br>中原大學<br>環境工程學系<br>105<br>Neodymium (Nd) is a rare earth element (REE) that is also found in waste permanent magnets (WPMs). Permanent magnets (PMs) play an important role in manufacturing products as their demand is crucial in emerging countries such as Taiwan. Removing these waste products as well as enhancing the quality is very important for the recovery of these rare earth metals.The aim of the study is to recover and recycle Neodymium from waste permanent magnets (WPMs) by using a supported liquid membrane with strip dispersion (SLMSD) module with hollow fiber membrane. Thereafter, Neodymium would be used to enhance a high-quality photocatalyst.
Experimental results have shown that one gram of WPMs contained 450 mg of neodymium and 3M of H2SO4 can leach the maximum amount of neodymium ion in the powder and 3M of H2SO4 can leach the maximum amount of neodymium ion in the powder. The highest extraction efficiency of the pH feed phase (1.26 ~ 2.00), 0.6 mol/L of D2EHPA and as well as having the most effective solid-liquid ratio at 1:2. Nitric acid of 6M can strip all neodymium ions from the extractant with the O/A ratio 2:1. In addition, the operation of the hollow fiber SLMSD under this optimum condition showed a computable, the concentration of neodymium the strip solution was around 4120 mg/L while the initial concentration of neodymium in feed solution of 658 mg/L after a continuous extraction for 45min. Furthermore, the enhancement activity of a photocatalyst was obtained with a doping ratio at 0.5 wt% neodymium to remove 96% of RB5 under a fluorescent lamp. The best of calcination temperature was found to be 4000C for two hours. The fluorescent lamp has a relatively good catalytic efficiency and low power consumption.
Thus, the SLMSD used in this study could recover the Neodymium from waste neodymium magnets effectively. And Neodymium used in the doping of titanium dioxide could be synthesized successfully and improved the shortcomings of titanium dioxide. Finally, the Neodymium doped titanium dioxide could present high catalytic activity under the visible light irradiation.
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Narayan, Shashi Prakash. "The Effect Of Strain Rate And Temperature On The Development Of Magnetic Properties In Nano Crystalline Nd-Fe-B Alloy." Thesis, 1997. https://etd.iisc.ac.in/handle/2005/2137.
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Narayan, Shashi Prakash. "The Effect Of Strain Rate And Temperature On The Development Of Magnetic Properties In Nano Crystalline Nd-Fe-B Alloy." Thesis, 1997. http://etd.iisc.ernet.in/handle/2005/2137.
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(9852800), Athira N. Surendran. "Development of Fabrication Platform for Microfluidic Devices and Experimental Study of Magnetic Mixing and Separation." Thesis, 2020.
Find full textAbstract:
<div>
<div>
<div>
<p>Microfluidics is a new and emerging field that has applications in a myriad of microfluidic
industrial applications such as biochemical engineering, analytical processing, biomedical
engineering and separation of cells. Microfluidics operations are carried out in microfluidic chips,
and the traditional method of fabrication is carried out in a cleanroom. However, this fabrication
method is very costly and also requires professional trained personnel. In this thesis, a low-cost
fabrication platform was developed based on soft-lithography technique developed to fabricate the
microfluidic devices with resolution at microscale. This fabrication method is advantageous and
novel because it is able to achieve the microscale fabrication capability with simple steps and
lower-level laboratory configuration. In the developed fabrication platform, an array of ultraviolet
light was illuminated onto a photoresist film that has a negative photomask with a microfluidic
design on it. The photoresist film is then developed, and a silicon polymer of polydimethylsiloxane
(PDMS) is chosen to be the material for the device. In this work, the performance and resolution
of the fabrication system was evaluated using scanning electron microscopy (SEM), polymer
resolution test and light intensity analysis.
</p>
<p>Based on the success of the development of microfluidics fabrication platform, various
experiment of mixing and separation was conducted and studied because the utilization of the
microfluidic device for mixing and separation is very valuable in biomedical and chemical
engineering. Although there are a lot of applications reported, the precise separation and mixing
at microscale still meet some difficulties. Mixing in micromixers is extremely time-consuming and
requires very long microchannels due to laminar flow and low Reynolds number. Particle
separation is also hard to be achieved because the size of micron bioparticles is very small and
thus the force is not strong enough to manipulate their motion. The integration of magnetic field
is an active method to strengthen both mixing and separation that has been widely applied in the
biomedical industry overcome these difficulties because of its compatibility with organic particles.
However, most magnetic mixing and separation use bulky permanent magnets that leave a large
footprint or electromagnets that generate harmful Joule heat to organic and bio-particles. In this
work, microscale magnet made of a mixture of neodymium powder and polydimethylsiloxane was
developed and integrated into microfluidic system to achieve both rapid mixing of ferrofluids and
separation of microparticles. Systematic experiments were conducted to discuss the effect of various parameters on the performance of magnetic mixing and separation of microparticles. It
was found that channel geometry, flow filed, and magnetic properties will affect the transport
phenomena of ferrofluid and microparticles, and thus mixing and separation efficiency. These
findings are of great significance for the high throughput sorting of cancer cells and its mixing
between drug for therapy treatment.</p></div></div></div>
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Süptitz, Ralph. "Einfluss homogener und inhomogener Magnetfelder auf die Korrosion ferromagnetischer Elektroden." Doctoral thesis, 2011. https://tud.qucosa.de/id/qucosa%3A25929.
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.