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Dissertations / Theses on the topic 'Zinc ferrites'

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Published: 4 June 2021
Last updated: 11 February 2022

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1

Okatan, Mahmut Baris. "Microstructure Development In Nickel Zinc Ferrites." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12606924/index.pdf.

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Nickel zinc ferrites (NZF) have been considered as one of the basic components in high frequency electromagnetic applications especially in the field of telecommunications. In the present study, the aim was to produce high quality nickel zinc ferrite ceramics at low soaking temperatures. For this purpose, conventional ceramic manufacturing method based on mixed oxide precursors was followed using calcium fluoride, CaF2, as sintering additive. During the sintering studies, it was noticed that both the microstructure and the electromagnetic properties of the NZF ceramics were modified to a great extent by CaF2. Therefore, material characterization studies involving microstructural, dielectric and magnetic properties were conducted with respect to CaF2 content of ceramics and soak duration. The results showed that due to the presence of CaF2 in ceramics, significant improvements were achieved not only in kinetics of sintering but also in the parameters
DC electrical resistivity, dielectric constant and dielectric loss factor. For example, 1.0 wt% CaF2 added NZF ceramic produced in this study had a DC electrical resistivity of 1011 &
#61527
-cm which was 100,000 times bigger than the one attained in pure NZF ceramic. On the other hand, the dielectric constant exhibited a flat behavior up to 40 MHz with a value around 16. In addition, no resonance peak was observed in dielectric loss factor spectra, and the typical values of dielectric loss factor lied below 0.01. Besides the achievements mentioned, the magnetic properties such as relative magnetic loss factor and hysteresis parameters were also improved.
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2

Souza, NatÃlia Dantas Gomes de. "Obtaining magnetic nanobiocompÃsitos consisting of galactomannan, glycerol and nickel ferrite and zinc." Universidade Federal do CearÃ, 2014. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=11766.

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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
FundaÃÃo de Amparo à Pesquisa do Estado do CearÃ
Nos Ãltimos anos, um grande interesse na associaÃÃo de materiais magnÃticos e biolÃgicos tem sido relatado na literatura. A obtenÃÃo de novos compÃsitos constituÃdos de galactomanana (GM), nanopartÃculas magnÃticas (MNPs) de NiZn e glicerol (GL) foram produzidos em diferentes proporÃÃes com finalidade de potencializar as caracterÃsticas individuais de cada material para futuras aplicaÃÃes. Sendo assim, as propriedades estruturais, magnÃticas e dielÃtricas dos nanobiocompÃsitos foram investigadas por DifraÃÃo de Raios-X (DRX), Espectroscopia de AbsorÃÃo na RegiÃo de Infravermelho (FTIR), AnÃlise TÃrmica (TG), Calorimetria ExploratÃria Diferencial (DSC), Microscopia EletrÃnica de Varredura (MEV), Microscopia EletrÃnica de TransmissÃo (TEM), Medidas MagnÃticas e Medidas DielÃtricas. A estrutura de espinÃlio da ferrita de NiZn foi confirmada por DRX e TEM e a amostra GMGL apesar de ser um material amorfo apresentou em seus nanobiocompÃsitos picos caracteristicos da fase de NiZn. As bandas caracterÃsticas para as amostras foram confirmadas por FTIR. Estas por sua vez seguiram um perfil de degradaÃÃo de acordo com as quantidades de NiZn incorporados, confirmados nos termogramas de DSC. A caracterizaÃÃo por MEV foi importante para avaliaÃÃo da morfologia. Os resultados das medidas dielÃtricas apresentaram baixas perdas dielÃtricas e das medidas magnÃticas mostraram comportamento magnÃtico para todos os nanobiocompÃsitos. Portanto, os resultados da caracterizaÃÃo dos nanobiocompÃsitos foram satisfatÃrios para possÃveis aplicaÃÃes como biomaterias, dispositivos eletrÃnicos ou em Ãreas afins.
In recent years, a great interest in the association of magnetic and biological materials has been reported in the literature. New composite consisting of galactomannan (GM), magnetic nanoparticles (NPs) of NiZn and glycerol (GL) were produced in different proportions with the purpose of enhancing the individual characteristics of each material for future applications. Thus, the structural, magnetic and dielectric properties of nanobiocomposites were investigated by Absorption Spectroscopy in the Region of Infrared (FTIR), X-Ray Diffraction (XRD), Thermal Analysis (TG), Differential Scanning Calorimetry (DSC), Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Magnetic Measurements and Dielectric Measurements. The structure of spinel NiZn ferrite was confirmed by XRD and TEM. Sample GMGL despite being an amorphous material presented in their nanobiocomposites characteristic peaks of phase NiZn. The characteristic bands in the samples were confirmed by FTIR. These in turn followed a degradation profile in accordance with the amounts of NiZn incorporated, which was confirmed in the DSC thermograms. The characterization by SEM was important to assess the morphology. The results of dielectric measurements showed low dielectric loss and magnetic measurements showed magnetic behavior for all nanobiocomposites. Therefore, the results of the characterization of nanobiocomposites were satisfactory for potential applications as biomaterials, electronic devices or related areas.
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3

Verdier, Thomas. "Elaboration de poudres nanostructurées de ferrites de manganèse-zinc par mécanosynthèse : Influence des paramètres de broyage." Rouen, 2006. http://www.theses.fr/2006ROUES042.

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Les ferrites mixtes de Mn-Zn ont un grand intérêt commercial du fait de leurs propriétés magnétiques à haute fréquence. Cette thèse présente l’influence des modes de broyage sur la synthèse de ferrites Mn-Zn à partir d’oxydes simples. La ferrite obtenue par mécanosynthèse présente une réorganisation de la distribution cationique au sein de la structure spinelle, ce qui peut améliorer les propriétés du matériau massif après mise en forme. Des broyages réalisés dans un matériel en acier ont permis de mettre en évidence la présence de Fe2+ provenant de réactions d’oxydo-réduction entre le fer et les oxydes. Des broyages réalisés dans des jarres en WC ont conduit à l’obtention de phases pures de ferrites de zinc et de manganèse-zinc exemptes d’ions Fe2+. Des expériences de spectrométrie Mössbauer sous champ magnétique ont permis de préciser la distribution cationique des ferrites synthétisés
Spinel ferrites compounds are widely used for their technological applications, which are essentially their magnetic and catalytic properties. Nanocrystalline Mn-Zn ferrites have been synthesized by high-energy ball milling in different media (tempered steel and WC) starting from simple oxides (α-Fe2O3, ZnO and MnO). This technique leads to a change in the distribution of cations in both sites, resulting in an increase of magnetic properties. X-ray diffraction, Mössbauer spectrometry and VSM are used to characterize the powders. This work shows that a redox reaction is observed between Fe11 and metalling iron during milling in steel medium, leading to a spinel phase containing some Fe11. The mechanism for the appearance of this phase is studied : ZnO seems to have a non negligeable influence on the synthesis, by creating an intermediate wüstite-type phase solid solution with FeO. Millings in WC medium permit to avoid the Fe11 contamination
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4

Recouvreur, Michel. "Contribution à l'étude des liants organiques pour ferrites étude de l'alcool polyvinylique dans le ferrite manganèse-zinc /." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37600681v.

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5

Spiers, Hayley Ileana. "Time resolved x-ray diffraction and thermal imaging studies of magnesium zinc ferrites." Thesis, University College London (University of London), 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.415415.

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6

Adair, Antony. "Observed super-spin class behavior in Ni₀.₅Zn₀.₅Fe₂O₄ nanoparticles." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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7

Hochepied, Jean-François. "Nanocristaux de ferrites mixtes de cobalt et de zinc : évolution des propriétés magnétiques en fonction de l'occupation des sites." Paris 6, 1999. http://www.theses.fr/1999PA066245.

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8

Sousa, Marcelo Henrique. "Propriétés magnétiques et magnéto-optiques de fluides magnétiques à base de nanoparticules de ferrites de nickel, de cuivre et de zinc." Paris 6, 2003. http://www.theses.fr/2003PA066591.

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9

Abbali, Zineb. "Etude de la cristallisation de ferrites spinelles dans des verres borates." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb376110731.

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10

Bonholzer, Michael. "Magnetic Tunnel Junctions based on spinel ZnxFe3-xO4." Doctoral thesis, Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-212756.

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Die vorliegende Arbeit befasst sich mit magnetischen Tunnelkontakten (magnetic tunnel junctions, MTJs) auf Basis des Oxids Zinkferrit (ZnxFe3-xO4). Dabei soll das Potential dieses Materials durch die Demonstration des Tunnelmagnetowiderstandes (tunnel magnetoresistance, TMR) in zinkferritbasierten Tunnelkontakten gezeigt werden. Dazu wurde ein Probendesign für MTJs auf Basis der „pseudo spin valve“-Geometrie entwickelt. Die Basis für dieseStrukturen ist ein Dünnfilmstapel aus MgO (Substrat) / TiN / ZnxFe3-xO4 / MgO / Co. Dieser ist mittels gepulster Laserabscheidung (pulsed laser deposition, PLD) hergestellt. Im Rahmen dieser Arbeit wurden die strukturellen, elektrischen und magnetischen Eigenschaften der Dünnfilme untersucht. Des weiteren wurden die fertig prozessierten MTJ-Bauelemente an einem im Rahmen dieser Arbeit entwickeltem und aufgebautem TMR-Messplatz vermessen. Dabei ist es gelungen einen TMR-Effekt von 0.5% in ZnxFe3-xO4-basierten MTJs nachzuweisen. Das erste Kapitel der Arbeit gibt eine Einführung in die spintronischen Effekte Riesenmagnetowiderstand (giant magnetoresistance, GMR) und Tunnelmagnetowiderstand (TMR). Deren technologische Anwendungen sowie die grundlegenden physikalischen Effekte und Modelle werden diskutiert. Das zweite Kapitel gibt eine Übersicht über die Materialklasse der spinellartigen Ferrite. Der Fokus liegt auf den Materialien Magnetit (Fe3O4) sowie Zinkferrit (ZnxFe3-xO4). Die physikalischen Modelle zur Beschreibung der strukturellen, magnetischen und elektrischen Eigenschaften dieser Materialien werden dargelegt sowie ein Literaturüberblick über experimentelle und theoretische Arbeiten gegeben. Im dritten Kapitel werden die im Rahmen dieser Arbeit verwendeten Probenpräparations- und Charakterisierungsmethoden vorgestellt und technische Details sowie physikalische Grundlagen erläutert. Die Entwicklung eines neuen Probendesigns zum Nachweis des TMR-Effekts in ZnxFe3-xO4-basierten MTJs ist Gegenstand des vierten Kapitels. Die Entwicklung des Probenaufbaus sowie die daraus resultierende Probenprozessierung werden beschrieben. Die beiden letzten Kapitel befassen sich mit der strukturellen, elektrischen und magnetischen Charakterisierung der mittels PLD abgeschiedenen Dünnfilme sowie der Tunnelkontaktstrukturen.
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11

Marija, Milanović. "Sinteza i karakterizacija nanočestičnih prahova na bazi cink-ferita." Phd thesis, Univerzitet u Novom Sadu, Tehnološki fakultet Novi Sad, 2010. https://www.cris.uns.ac.rs/record.jsf?recordId=82019&source=NDLTD&language=en.

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U ovom radu prikazani su rezultati ispitivanja strukturnih i magnetnih osobina čistih cink- ferita, ZnFe2O4 i cink-ferita sa dodatkom indijuma Zn1-xInxFe2O4 i itrijuma, ZnYxFe2-xO4, gde je 0 ≤ x ≤ 0,6. Prahovi na bazi cink-ferita su sintetisani koristeći nisko temperaturnu metodu sinteze iz tečne faze – metodu koprecipitacije. Osnovni cilj ove doktorske disertacije je bio da se utvrdi veza između uslova sinteze, uticaja različitih katjona, strukture i osobina čistih cink-feritnih nanočestica, kao i cink-ferita sa dodatkom indijuma i itrijuma. Radi praćenja uticaja veličine čestica dobijenog praha na strukturu i osobine ovih materijala, sintetisani čist cink-ferit je kalcinisan na različitim temperaturama. Posebno je razmatran i uticaj dodatka različitih jona na distribuciju i preraspodelu katjona u spinelnoj strukturi. Pored toga ispitivan je uticaj tako pripremljenih prahova na njihove magnetne osobine. Rentgenostrukturna i TEM analize potvrdili su da ispitivani uzorci spadaju u klasu nanomaterijala spinelne strukture. Analiza Raman i Mössbauer spektara je ukazala na moguću raspodelu katjona između tetraedarskih i oktaedarskih mesta, te formiranje delimično inverznog spinela. Ispitivanja magnetnih osobina su pokazala da histerezisne petlje ne pokazuju saturaciju u prisustvu jakog magnetnog polja, što je potvrdilo superparamagnetnu i jednodomensku prirodu čestica. Pokazano je da pored uticaja veličine čestica, dodatak različitih katjona (u ovom slučaju itrijum i indijum) ima veliki uticaj na uređenje strukture, a posledično i na magnetno ponašanje ispitivanih nanočestičnih sistema.
This thesis presents the results of the investigation of the structural and magnetic properties of nanostructured zinc ferrites, ZnFe2O4 and zinc ferrites supstituted with different amount of indium and yttrium, Zn1-xInxFe2O4 and ZnYxFe2-xO4 (0 ≤ x ≤ 0,6). Powders based on zinc ferrites were synthesised by a low temperature wet-chemical method – coprecipitation. The main purpose of this thesis was to establish the relationship between the synthesis, dopants, structure and properties of zinc ferrite based materials. Nanoparticles of ZnFe2O4 were calcined at different temperatures in order to elucidate the influence of the particle size on the magnetic properties of the obtained nanoparticles. In addition, we have investigated the effect of dopant addition on cation distribution in spinel structure, in order to modify the magnetic properties and to obtain the magnetic ceramics with improved properties compared to the bulk-counterparts. The results of X-ray and TEM analyses confirmed the nanosized nature and spinel type structure of the investigated samples. Raman and Mössbauer spectroscopy studies implied on the possible cation distribution between the tetrahedral and octahedral sites and formation of the partially inversed spinel. The study of the magnetic properties showed that hysteresis loops do not saturate even in the presence of high magnetic fields, which confirmed the superparamagnetic and single domain nature of the samples. These observations imply that, besides the particle size, doping (e.g. yttrium and indium) causes significant structural rearrangements which in turn induce changes in magnetic behavior of the investigated nanoparticulate systems.
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12

Ngenda, Banka Richard. "Etude de valorisation des rejets des usines à zinc de Kolwezi, République démocratique du Congo." Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210144.

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Les rejets des Usines à Zinc de Kolwezi contiennent majoritairement du zinc sous forme réfractaire (ferrite) au traitement hydrométallurgique conventionnel. Ils contiennent d’autres métaux « lourds » qui les rendent dangereux vis-à-vis de l’environnement dans lequel ils sont actuellement entreposés. Ces métaux, dont la plupart peuvent être valorisés, font de ces rejets un véritable gisement secondaire. Il est donc impératif de mettre au point un procédé adéquat de valorisation ;d’où le thème de la présente thèse :« Etude de valorisation des rejets des Usines à Zinc de Kolwezi, RDC ».

A l’aide des techniques modernes de caractérisation (physico–chimique, minéralogique et morphologique), nous sommes arrivés à cibler, à adapter et à justifier l’utilisation d’une technique de valorisation des matières minérales existantes. Les minéraux utiles contenus dans les rejets UZK ont été sulfatés par digestion et sélectivement mis en solution après un grillage. La sulfatation s’est avérée l’étape déterminante du procédé et un intérêt particulier a été focalisé sur cette étape en réalisant une étude cinétique approfondie.

Les données et informations récoltées tout le long de cette recherche nous ont permis de réaliser une simulation du procédé par le logiciel ASPEN PLUS. Ce qui a permis de faire une ébauche d’un schéma de traitement industriel. Ce dernier s’est avéré souple vis-à-vis de l’utilisation d’autres matières comme les calcines des concentrés sulfurés cuivre-zinc.

Residues from the Kolwezi Zinc Plant (Usines à Zinc de Kolwezi UZK) essentially contain zinc in a refractory (ferrite) form, which is difficult to recover by conventional hydrometallurgical methods. « Heavy» metals are also present that make them hazardous towards the environment in which they are currently stored. Most of these metals are valuable; thus, the UZK residues are a real secondary deposit. It is therefore imperative to develop an appropriate method of treatment, hence the theme of the present thesis: « Recovery study of values metals from Kolwezi Zinc Plant residues, DRC ».

Using modern techniques of characterization (physical and chemical, mineralogical and morphological), we focused, adapted and justified the use of a technique for efficient recovery of the existing valuable minerals. The minerals contained in UZK residues have been sulphated by digestion and thereafter selectively dissolved after roasting. Sulphatation proved to be the decisive step of the process and a particular attention has been given to this step by performing a detailed kinetic study.

The data and information collected throughout this research allowed a simulation of the developed method by using the « Aspen Plus » software. This allowed us to propose a draft scheme of industrial processing. The latter proved flexible towards the use of other materials such as calcines of copper-zinc sulphide concentrates.


Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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13

Santos, Cochiran Pereira dos. "Síntese e caracterização de NiFe2O4 e efeitos da dopagem na magnetização de saturação." Universidade Federal de Sergipe, 2011. http://ri.ufs.br:8080/xmlui/handle/123456789/3515.

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The ferrites are a wide class of ferrimagnetic materials with great technological importance and are studied extensively for many decades. Their remarkable magnetic characteristics make it an element often used in induction transformers by his high magnetic permeability, high values of saturation magnetization and low coercivity, resulting in smaller losses in their hysteresis loops. In this work were characterized pure nickel ferrite (NiFe2O4), a soft magnetic material where the magnetic properties depend on the nature of the ions, their charges and their distribution among the tetrahedral and octahedral sites. Heat treatment and sintering time were emphasized. In order to improve one of the most important parameters for such an application, the saturation magnetization, new samples were doped with zinc at various concentrations (Ni1-xZnxFe2O4). Two new series were prepared starting from the higher value of the previous series (Ni0,6Zn0,4Fe2O4) with two new doping, indium and gadolinium. Finally, the values of saturation magnetization and initial permeability could be compared with samples of commercial cores, showing the potential of the compound to be used as the core of magnetic induction.
As ferritas formam uma ampla classe de materiais ferrimagnéticos com grande importância tecnológica e têm sido estudadas exaustivamente ao longo de décadas. Suas notáveis características magnéticas as tornam um elemento frequentemente utilizado em transformadores de indução por sua alta permeabilidade magnética, altos valores de magnetização de saturação e baixa coercividade, resultando em perdas menores observadas em seus ciclos de histerese. Neste trabalho foram caracterizadas ferritas de níquel pura (NiFe2O4), um material magnético mole onde as propriedades magnéticas dependem da natureza dos íons, suas cargas e sua distribuição entre os sítios tetraédricos e octaédricos. Nessa fase o tratamento térmico e o tempo de sinterização tiveram ênfase. A fim de melhorar um dos parâmetros mais importantes para tal aplicação, a magnetização de saturação, foram feitas novas amostras dopadas com zinco em várias concentrações (Ni1-xZnxFe2O4). Duas novas séries foram preparadas partindo-se do maior valor da série anterior (Ni0,6Zn0,4Fe2O4) com dois novos dopantes, o índio e o gadolínio. Finalmente, os valores de magnetização de saturação e permeabilidade inicial puderam ser comparados com amostras de núcleos comerciais, evidenciando a potencialidade do composto em ser utilizado como núcleo de indução magnética.
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14

Xia, Dan Kui. "Recovery of zinc from zinc ferrite and electric arc furnace dust." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq38338.pdf.

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15

Anchieta, Chayene Gonçalves. "SÍNTESE DE FERRITA DE ZINCO (ZnFe2O4) POR DIFERENTES ROTAS E SEU USO NA REAÇÃO HETEROGÊNEA DE FOTO-FENTON." Universidade Federal de Santa Maria, 2015. http://repositorio.ufsm.br/handle/1/7990.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
In this work, zinc ferrite oxide was performed (ZnFe2O4) was synthesized by the solvothermal conventional method and the microwave-assisted solvothermal route. The influence of different synthesis as well as their variables on the physical properties of the material were investigated. The powders were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption/desorption measurements by the Brunauer-Emmett-Teller method (BET), and atomic force microscopy (AFM). The produced ferrite was used as catalyst and its activity was investigated in the photo-Fenton reaction for the degradation of textile organic dye (Procion Red H-E7b) under visible light irradiation. In the experiments, different process variables such as dye and hydrogen peroxide concentrations, pH and reaction time were analyzed. The rate constants for the photo-Fenton reactions were determined for both materials prepared by different routes. The synthesis results demonstrated the formation of particles with different physical properties such as surface area, pore volume and size. The experiments of photo-Fenton reaction indicated that the materials prepared in this work present satisfactory activity for the degradation of organic pollutant, 97% de decolorization and 60% de mineralization, in aqueous solution. All studied variables of the reaction process significantly influenced on the catalytic process.
Neste trabalho, foi realizada a síntese do óxido ferrita de zinco (ZnFe2O4) pelo método solvotérmico convencional e pela rota solvotérmica assistida por microondas. A influência das diferentes rotas de síntese, bem como de suas variáveis de síntese sobre as propriedades físicas do material foi investigada. Os pós obtidos foram caracterizados por difração de raios-X (DRX), espectroscopia no infravermelho (FTIR), medições de adsorção-dessorção de nitrogênio pelo método Brunauer-Emmett-Teller (BET), e microscopia de força atômica (MFA). A ferrita produzida foi usada como catalisador e sua atividade foi investigada na reação de foto-Fenton para a degradação de um corante orgânico têxtil (Vermelho Procion H-E7B) sob irradiação de luz visível. Nos experimentos, foram analisadas diferentes variáveis de processo, tais como concentrações de corante e peróxido de hidrogênio, pH e tempo. As constantes de velocidade das reações de foto-Fenton foram determinadas para ambos os materiais preparados pelas diferentes rotas. Os resultados das sínteses demonstraram a obtenção de partículas com diferentes propriedades físicas, tais como área superficial, volume e tamanho de poros. Os testes da reação foto-Fenton indicaram que o material preparado neste trabalho apresenta satisfatória atividade para a degradação do poluente orgânico, até 97% de remoção de cor e 60% de mineralização, em solução aquosa. Todas as variáveis do processo reacional estudadas influenciaram significativamente no processo catalítico.
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16

Martins, Da Silva Fernando Henrique. "Etude structurale, distribution cationique et état d'oxydation dans des nanoparticules magnétiques de ferrite du type coeur-coquille." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066102/document.

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Nous explorons les propriétés structurales de nanoparticules cœur-coquille, avec un cœur de ferrite MFe2O4 (M = Mn et Co) ou de ferrite mixte Mn-Zn. Ces nanoparticules sont obtenues par co-précipitation hydrothermique et sont dispersées en milieu acide par un traitement de surface empirique au nitrate ferrique, protégeant les nanograins contre une dissociation chimique par une fine couche superficielle de maghémite. La fraction volumique du cœur, de la coquille et l’épaisseur de la couche superficielle sont déterminées par dosage chimique. Nous suivons les changements structurels des nanocristaux de MnFe2O4 et CoFe2O4, pendant la durée du traitement de surface, tandis que ceux des nanoparticules de ferrite mixte Mn-Zn sont étudiés en fonction de leur teneur en zinc. Diffraction de rayons-x et de neutrons sont utilisées pour déterminer les paramètres de structure, en particulier la diffusion de cations dans les interstices de la ferrite spinelle. Pour un haut degré de fiabilité, des raffinements de Rietveld sont réalisés. Les distances inter-atomiques, l’état d’oxydation moyen et le degré d’inversion sont déterminés par spectroscopie d’absorption des rayons-x. Morphologie, cristallinité et taille des nanoparticules de ferrite mixte Mn-Zn sont étudiées par TEM/HRTEM et par diffraction des électrons. Dans les nanoparticules MnFe2O4 et de ferrite mixte Mn-Zn, on constate la présence de cations Mn3+ en environnement octaédrique, responsables de déformations anisotropes (effet Jahn-Teller). Le degré d’inversion obtenu ici diffère de celui du bulk en raison de la réduction à l’échelle nanométrique et de l'augmentation du rapport surface/volume pendant le processus de synthèse
Structural properties of core-shell ferrite nanoparticles MFe2O4 (M = Mn and Co) and Mn-Zn ferrite nanoparticles are here investigated. The nanoparticles are synthesized by hydrothermal co-precipitation and are dispersed in acid medium thanks to an empirical surface treatment by ferric nitrate, which prevents the chemical dissociation by a thin maghemite layer incorporated at the surface of the nano-grains. Chemical titrations allow us to calculate volume fractions of core and shell, as well as the surface-layer thickness. Structural changes induced by the surface treatment are followed as a function of treatment duration in MnFe2O4 and CoFe2O4 nanocrystals. Whereas structural changes in Mn-Zn ferrite nanoparticles are investigated as a function of zinc content. X-ray and Neutron diffractions are used to determine the structural parameters, in particular cationic distribution in the spinel ferrite sites. Precise structural information with high degree of reliability is obtained by Rietveld refinements. To investigate the local structure of these materials, X-ray Absorption Spectroscopy measurements are performed, allowing determining interatomic distances, mean oxidation state and inversion degree. Morphology, crystallinity and size of mixed-ferrite nanoparticles are investigated by TEM/HRTEM and electron diffraction. In Mn-Zn ferrite nanoparticles, the presence of Mn3+ in octahedral environment is responsible for anisotropic distortions, known as Jahn-Teller effect. The inversion degree obtained in this work diverges from the bulk values due to the reduction to nanoscale and to the increase of the surface/volume ratio, associated to the synthesis process
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17

Castro, Kaíck Viana de Oliveira. "Antenas de microfita sobre substrato de ferrita de níquel dopadas com zinco." Universidade Federal Rural do Semi-Árido, 2018. http://bdtd.ufersa.edu.br:80/tede/handle/tede/832.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Microstrip antennas have a potential that was only initially studied in 1953, to receive more attention only in the 1970s. Since then, several techniques, methods of analysis, algorithms, and materials have been developed to study, understand and produce these antennas. Advantages such as low cost, small dimensions, low weight and volume, aerodynamically advantageous format, possibility to have flat or curved format made this antenna one of the most interesting for the military area, and now for commercial and industrial area. This work has as objective at the development of substrates for microfite antennas using Ni-Zn-type Ferrites using the Sol-Gel technique, a physicochemical process that allows the obtaining of nanometric particles, in view of the ease of execution of this technique. The experiments consisted in the production of three types of ferrites, NiFe2O4, ZnFe2O4 and Ni0,5Zn0,5Fe2O4 in which these pellets were used as substrates of the microfite antennas. Then, simulations were carried out using commercial HFSS software to verify the influence of the magnetic properties of the material on antenna parameters such as return loss, bandwidth, and Smith's chart. The simulated results were divided into groups called dielectric and standard, in which these groups differed in the presence or absence of the magnetic characteristics of the material. All the results were compared with the values measured and analyzed by verifying some effects such as the reduction of the resonance frequency of the antennas
As antenas de microfita têm um potencial que só foi inicialmente estudado em 1953, para receber mais atenção somente na década de 1970. Desde então foram desenvolvidas diversas técnicas, métodos de análises, algoritmos, e materiais com o intuito de estudar, compreender e produzir estas antenas. Vantagens como custo baixo, pequenas dimensões, baixo peso e volume, formato aerodinamicamente vantajoso, possibilidade de ter formato plano ou curvo fizeram desta antena uma das mais interessantes para a área militar, e agora para a área comercial e industrial. Este trabalho visou o desenvolvimento de substratos para as antenas de microfita utilizando Ferritas do tipo Ni-Zn através da técnica de Sol-Gel, um processo físico-químico que permite a obtenção de partículas nanométricas, tendo em vista a facilidade de execução dessa técnica. Os experimentos consistiram na produção de três tipos de pastilhas de Ferritas, NiFe2O4, ZnFe2O4 e Ni0,5Zn0,5Fe2O4 em que essas pastilhas foram utilizadas como substratos das antenas de microfita. Em seguida, foi realizado simulações, por meio do software comercial HFSS®, com o objetivo de verificar a influência das propriedades magnéticas do material em parâmetros das antenas como perda de retorno, largura de banda, carta de Smith. Os resultados simulados foram divididos em grupos chamados de dielétrico e padrão, no qual esses grupos se diferenciavam no tocante a presença ou não das características magnéticas do material. Todos os resultados foram comparados com os valores medidos e analisados verificando alguns efeitos como a redução da frequência de ressonância das antenas
2018-05-02
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18

Tauriainen, M. (Miia). "Decomposition of zinc ferrite from waste streams of steelmaking." Master's thesis, University of Oulu, 2015. http://urn.fi/URN:NBN:fi:oulu-201512022191.

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The goal of this study was to compare different methods to decompose the zinc ferrite from the waste streams of steel making. The samples were acquired from SSAB Raahe blast furnace and converter flue gas scrubbers and Outokumpu Tornio Works bag filters EAF1, EAF3, AOD and CRK. Sludges and dusts contain significant amounts of zinc in form of zinc oxide and zinc ferrite. Zinc ferrite is highly stable compound which makes recovery of the zinc difficult. The zinc could be recovered and recycled as a valuable material and the iron rich material could be fed back to process. New method was experimented to decompose the zinc ferrite. The pulsed corona discharge method creates highly oxidizing hydroxyl radicals and ozone which decompose impurities in water. The experiments with PCD equipment were not successful because the design of the equipment was not suitable for waters with particles. As another method, chemical leaching experiments were made with sulphuric acid and sodium hydroxide. The most promising method for the zinc was the chemical leaching with the 5 mol/L NaOH at starting temperature of 70 °C for 120 minutes in case of the blast furnace sludge and leaching with 2 mol/L H₂SO₄ at 50 °C for 360 minutes for converter sludge from SSAB Ruukki. For the Outokumpu dusts (EAF1, EAF2, AOD and CRK) the 5 mol/L NaOH at 70 °C for 180 to 300 minutes leaching produced good results. Further studies are needed to optimise the conditions for the chemical leaching
Työn tavoitteena oli verrata eri menetelmiä terästeollisuuden jätevirtojen sinkkiferriitin hajottamiseen SSAB Raahen masuunin ja konvertterin savukaasupesureiden lietteille sekä Outokumpu Oyj Tornio Worksin EAF1, EAF3, AOD ja CRK letkusuodatin pölyille. Lietteet ja pölyt sisältävät merkittäviä määriä sinkkiä sinkkioksidin ja sinkkiferriitin muodossa. Sinkkiferriitti on erittäin stabiili yhdiste, mikä tekee sinkin ja raudan erottamisen toisistaan vaikeaksi. Sinkki voidaan kerätä talteen ja kierrättää. Rautaa runsaasti sisältävä materiaali voitaisiin mahdollisesti kierrättää takaisin prosessiin, jos sinkki poistettaisiin lietteiden ja pölyjen seasta. Uutena menetelmänä sinkkiferriitin hajotukseen testattiin pulsed corona discharge -menetelmää, jossa vahvasti hapettavat hydroksyyliradikaalit ja otsoni hajottavat vedessä olevia epäpuhtauksia. Pulsed corona discharge -laitteisto ei sopinut kiintoaineita sisältävien jätevesien käsittelyyn, joten menetelmän toimivuudesta ei saatu tuloksia. Toisena menetelmänä testattiin kemiallista liuotusta rikkihapolla ja natriumhydroksidilla. Masuunilietteelle paras saanto saatiin 5 mol/L NaOH-liuotuksella lämpötilassa 70 °C 120 minuutin kontaktiajalla. Konvertterilietteelle paras saanto saatiin 2 mol/L H₂SO₄-liuotuksella lämpötilassa 50 °C 360 minuutin kontaktiajalla. Outokummun pölyille parhaat olosuhteet olivat 5 mol/L NaOH-liuotuksella lämpötilassa 70 °C 180–300 minuutin kontaktiajalla. Lisätutkimuksia optimaalisten olosuhteiden saavuttamiseksi tarvitaan vielä
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19

Bekka, Ahmed. "Etude cristallographique et magnétique de nouveaux ferrites de type [béta]" [A(y)B(n+)((1-y)/n)] (1+x) Zn (x) Fe(11-x) O17 (x [à peu près égal à] 0,9) avec A,B = Li, Na, K, Ag, Ca, Sr, Ba, Pb." Grenoble 1, 1986. http://www.theses.fr/1986GRE10138.

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Preparation sous forme de monocristaux et de polycristaux de na::(4,2) k::(1,8) fe::(30) me::(3) o::(51) (me = zn, mg, cu). Determination de la structure cristalline, et mesures de conductivite ionique, d'aimantation, determination des temperatures de curie et des constantes d'anisotropie magnetocristalline. Substitution partielle des cations na et k par li, na, k, ag, ca, sr, ba, pb. Caracterisation par diffraction rx, microscopie a balayage et a transmission
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20

Roberts, V. A. "The production of manganese zinc ferrite by the citrate gel route." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380216.

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21

Filippou, Dimitrios. "Reaction kinetics and reactor modelling of zinc-ferrite hot-acid leaching." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41588.

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The main objectives of this Thesis were the determination of the reaction kinetics of the dissolution of zinc-ferrite particles ((Zn$ sb{1-x}$, Fe$ sbsp{x}{2+}$)$ rm Fe sbsp{2}{3+}O sb4$, x $ le$ 0.4) in hot aqueous solutions of sulphuric acid, and the development of a mathematical model for the prediction of the performance of a series of continuous stirred-tank reactors where zinc ferrite is leached.
Well-characterised, porous zinc-ferrite particles of industrial origin were subjected to controlled leaching experiments at temperatures close to 373 K in sulphuric acid solutions of concentration higher than 0.25mol L$ sp{-1}$. The dissolution process was found to be described most adequately by the grain model with surface reaction being the rate-controlling step. After analysing the experimental results through this model, a unique rate equation for zinc-ferrite dissolution as a function of temperature and solution composition, was obtained.
Based on this rate equation, a mathematical framework was built for the analysis of the start-up and the steady-state of reactor cascades where zinc ferrite is continuously leached. This framework consisted of population-balance and mass-balance equations, which were solved analytically or numerically. Computer simulation results, which were obtained by this reactor model, showed very good agreement with actual industrial data.
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22

MARROQUIN, MERY CECILIA GOMES. "CONTRIBUTION TO THE STUDY OF THE FORMATION AND REDUCTION OF ZINC FERRITE." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=4943@1.

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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
No presente trabalho foi feita inicialmente uma revisão bibliográfica sobre a formação e redução da ferrita de zinco. Em seguida fez-se um estudo cinético e termodinâmico da sua formação a partir da mistura dos óxidos de ferro puro, Fe2O3 e de zinco puro, ZnO, em proporção mássica estequiométrica ã do composto Fe2O3/ZnO = 2/1, considerando que este composto tem sido considerado como o constituinte de maior porcentagem em peso nos pós de aciaria elétrica (fornos elétricos a arco).A ferrita de zinco, que geralmente se forma no aquecimento de diferentes proporções de misturas dos óxidos constituintes, incluindo a estequiométrica, foi caracterizada térmica (DTA-TGA) e estruturalmente (XRD). A temperatura onde começou a se formar a ferrita de zinco e os resultados quantitativos das conversões da sua síntese, foram calculadas pelo software Topas 2,1 Difracc Plus, usando o método Reitveld XRD. Os seguintes resultados da análise cinética da formação de ferrita de zinco, foram obtidos; a baixas temperaturas (650-730 graus Celsius) as conversões obtidas ajustaram-se ao modelo de reação de interface ou modelo topoquímico, sendo a reação química o mecanismo de controle obtendo-se uma Ea = 65,6 kcal / mol e um k = 2,32 x 10-3 K-1 ; nas altas temperaturas (750 - 1000 graus Celsius) o ajuste ao modelo de crescimento populacional modificado, foi o mais adequado, sendo o mecanismo de controle o difusional e obtendo-se uma Ea =16,1 kcal /mol e k = 570 K -1. Finalmente encontrou-se um estágio de transição entre os dois mecanismos numa temperatura aproximada de 745 graus Celsius (controle misto). Foram gerados vários diagramas operacionais de predominância de fases (DOPF)necessários para orientar os trabalhos perimentais. Estes diagramas consistiram de uma análise termodinâmica da redução de misturas de ZnO e Fe2O3 pelos gases redutores CO e H2, focando primordialmente à formação e a redução da ferrita de zinco. Foram utilizados os seguintes software: HSC versão 5,0 e Mathcad versão 6,0. Os resultados desta avaliação foram os DOPF dos seguintes sistemas: Zn-C-O, Zn-H-O, Zn-C-H-O, Fe-C-H-O e Zn-Fe-C-H- O com a variação das atividades de suas fases metálicas e de seus óxidos.
The present work includes initially a bibliographical revision on the formation and reduction of the zinc ferrite. Further a thermodynamic and kinetic study was made, focusing its formation from an equimolar mixture of pure iron oxide Fe2O3, and pure zinc oxide ZnO, due to the fact that this substance is often the major constituent in the electric arc furnace dust. The zinc ferrite that is formed during the operation of the electric arc furnaces doesn t necessarily results from an equimolar mixture; it could be produced from a wide range of constituents compositions. Initially the equimolar mixture was characterized thermally (DTA-TGA) and structurally (XRD). The temperature where this compound began its formation and the quantitative results regarding the zinc ferrite synthesis conversion were calculated by the software Topas 2,1 Difracc Plus, using the Reitveld XRD method. The following experimental results from the kinetic analysis of the zinc ferrite formation were obtained: at low temperatures (650-730 Celsius Degree) the phenomena fitted the interface reaction model, or topochemical model, being the chemical reaction the control mechanism. The obtained data in this case was: Ea = 65,6 kcal / mol and k = 2,32 x 10-3 K-1. On the other hand, at high temperatures (750-1000 Celsius Degree) the modified population growth formalism showed the best fit, being the diffusional mechanism the controlling process. Again the obtained data was: Ea = 16,1 kcal / mol and k = 570 K-1. Finally a transition between the two mechanisms was found to happen at approximate 744 Celsius Degree (mixed control). Several DOPF (phase predominance operational diagrams) were obtained based upon the thermodynamic analysis of the Fe2O3 - ZnO mixtures reduction driven by CO and H2 reducing gases, focusing the formation and reduction of zinc ferrite compound. For that purpose the softwares HSC 5,0 and MathCAD 6,0 were utilized. The DOPF for the systems: Zn-C-O, Zn-H-O, Zn-C-H- O, Fe-C-H-O and Zn-Fe-C-H-O, considering the activities of their metallic and their oxides phases, were generated and discussed.
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23

Brachwitz, Kerstin. "Defekt-induzierte Leitungsmechanismen und magnetische Eigenschaften spinellartiger Ferrite." Doctoral thesis, Universitätsbibliothek Leipzig, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-141251.

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Im Rahmen dieser Arbeit wurde der Einfluss von Defekten auf die Eigenschaften von Ferrit-Dünnfilmen untersucht. Die Dünnfilme wurden mit Hilfe von gepulster Laserabscheidung bei verschiedenen Züchtungsparametern hergestellt. Durch Variation der Substrattemperatur und des Sauerstoffpartialdrucks wurden Dünnfilme verschiedener kristalliner Qualität gezüchtet. Diese wurden hinsichtlich ihrer chemischen Komposition mit Hilfe von energie-dispersiver Röntgenspektroskopie und Röntgenphotoelektronenspektroskopie untersucht. Durch Korrelation der Ergebnisse mit Messungen zum zirkularen magnetischen Röntgendichroismus, konnte eine partielle Inversion der Spinellstruktur nachgewiesen werden. Der Grad der Inversion ist höher für geringe Abscheidetemperaturen. Für diese defektreichen Dünnfilme zeigen Röntgenbeugungsuntersuchungen eine geringere kristalline Ordnung der Dünnfilme. Die strukturellen Defekte haben einen maßgeblichen Einfluss auf die elektrischen und magnetischen Eigenschaften der Ferrit-Dünnfilme. So zeigen die Ferrit-Dünnfilme für geringe Züchtungstemperaturen eine erhöhte elektrische Leitfähigkeit, während Dünnfilme, die bei hohen Substrattemperaturen gezüchtet wurden, isolierend sind. Die Temperaturabhängigkeit der elektrischen Leitfähigkeit kann auf thermisch aktivierte Hopping-Leitung oder die Leitung zwischen Clustern, die in einer Matrix eingebettet sind, zurückgeführt werden. Die magnetischen Eigenschaften von Zinkferrit-Dünnfilmen werden maßgeblich durch Defekte in der Spinellstruktur bestimmt, da es nominell in der normalen Spinellstruktur kristallisiert und daher antiferromagnetisch ist. Die partielle Inversion der Eisen- und Zinkionen führt zu Ferrimagnetismus in den Zinkferrit-Dünnfilmen, der mit Hilfe von SQUID-Messungen in dieser Arbeit eingehend untersucht wurde. Durch Korrelation der Ergebnisse der verschiedenen Untersuchungsmethoden konnten Rückschlüsse auf die dominierenden Defekte in den Ferrit-Dünnfilmen geschlossen werden. So sind zum einen Defekte auf atomarer Skala, wie Antisite-Defekte und divalenten Fe-Ionen für die erhöhte elektrische Leitfähigkeit und die größere Magnetisierung der defektreichen Dünnfilme verantwortlich. Zum anderen können ausgedehnte Defekte, im Speziellen Cluster, die in einer amorphen Matrix eingebettet sind, nicht ausgeschlossen werden.
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24

Azevedo, Alexandre Marques. "Ressonância ferromagnética de filmes finos de ferrite de zinco." Master's thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/9227.

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Mestrado em Engenharia Física
Este projeto teve como objetivo o estudo de filmes finos de ZnFe2O4 (ZFO) crescidos por deposição por laser pulsado (PLD). As ferrites são muito sensíveis às condições de crescimento, e, por isso, é que apresentam uma variedade de propriedades em função do modo como são crescidas (microestrutura). Filmes finos de ferrites têm motivado vários estudos teóricos e experimentais devido a novas propriedades elétricas, óticas e magnéticas, bem como a aplicações destes materiais à microeletrónica, magneto-ótica e spintrónica. As amostras foram crescidas por (PLD) sob específicas condições (pressão parcial de oxigénio, aquecimento, temperatura dos substratos), em substratos de r-safira, de SrTiO3 (001),e de SrRuO3/SrTiO3(001). Medidas de ressonância ferromagnética (FMR) foram usadas para o estudo do comportamento magnético de várias séries de filmes finos de ZFO com diferentes orientações das amostras relativamente ao campo magnético externo. Dados da magnetização estática num SQUID, dados de difração de raios-X (DRX) e de energia de dispersão de raios-x (EDX) obtidos nas mesmas amostras foram analisadas em conjunto com os espectros de FMR com o intuito de atingir uma interpretação de confiança. As medidas de FMR foram realizadas no intervalo de temperaturas entre 5 K e 420K a uma frequência de aproximadamente 9.4 GHz (banda X de micro-ondas) em campos magnéticos até aos 1.5T, num espectrómetro ESP 300E da Bruker equipado com crióstatos de fluxo de azoto e hélio. Os espectros foram obtidos para rotações do campo magnético aplicado dentro do plano e fora do plano dos filmes. A análise das dependências angulares dos espectros de FMR foi efetuada no âmbito do formalismo de Smith-Beljers. Praticamente todos os filmes exibiram a razão quase estequiométrica Zn/Fe e a presença de ordem magnética, mesmo que a fase de ferrite de zinco com a estrutura de espinela não foi detetada nas amostras crescidas a temperaturas de substrato inferiores a Tsub = 1000K. Também foi constatado que a qualidade cristalina depende fortemente da pressão parcial de oxigénio durante a deposição dos filmes. Filmes de ZnxFe3−xO4 monofásicas e com textura pronunciada foram obtidos em substratos de SrTiO3 para PO2 = 210–3 mbar e Tsub = 1000 K. Medições de FMR revelaram a existência, nestes filmes, de anisotropia cúbica. Os valores de magnetização efetiva e parâmetro de anisotropia cúbica (4πMeff ≈ 3.0kOe e K1c = –1.5104 erg/cm3) foram obtidos através de uma análise detalhada dos espectros de FMR. Mesmo que nenhuma estrutura cristalina pudesse ser atribuída aos filmes crescidos a Tsub < 1000 K, ondas de spin bem resolvidas foram detetadas num destes a temperaturas criogénicas. O respetivo parâmetro de rigidez (~810–8 erg/cm) é cinco vezes menor do que o valor previamente relatado na literatura para filmes de ZFO. A largura de linha é em todos os casos bastante grande, indicando heterogeneidades internas. Na maioria das amostras, ressonâncias adicionais foram observadas que podem resultar de: modos superficiais, ondas de spin e ou da presença de fases magnéticas diferentes.
The object of this study have been ZnFe2O4 (ZFO) thin films grown by pulsed laser deposition (PLD). The ferrites are extremely sensible to the growth conditions, so that they represent a variety of properties as a function of the growth conditions (microstructure). Ferrite thin films have motivated a lot of theoretical and experimental studies owing to novel electric, optical and magnetic properties and possible applications in microelectronics, magnetooptics and spintronics. The samples were grown by pulsed laser deposition (PLD) under specific conditions (partial oxygen pressure, heating) on r-sapphire and (001) SrTiO3 substrates, with and without SrRuO3 buffer layers. For the study of the magnetic behavior of various series of ZFO thin films, ferromagnetic resonance (FMR) measurements as a function of the temperature and sample orientation with respect to the external magnetic field have been performed. Static magnetization data measured in a SQUID magnetometer, energy-dispersive X-ray spectrometry results and x-ray diffraction (XRD) curves obtained on the same samples have been analyzed together with the FMR spectra in order to obtain the most full and reliable interpretation of the results. FMR spectra were measured in the X-band (f ≈ 9.4 GHz) at temperatures from 5 to 420K on a Bruker ESP 300E EPR spectrometer equipped with a helium and a nitrogen continuous flow cryostats. Azimuthal (in-plane) and polar (out-of-plane) angular dependences of the FMR spectra for sample rotation in external magnetic field up to 1.5 T have been measured. The analysis of the angular dependences of the spectra have been performed in the framework of the Smith-Beljers formalism. A zinc ferrite spinel phase has been found only in the samples grown at Tsub = 1000K. Nevertheless, almost all samples exhibited a stoichiometric Zn/Fe ratio and magnetic (non-paramagnetic) ordering, even when the spinel phase was absent in film. The quality of the zinc ferrite films was found to be strongly dependent on the oxygen partial pressure during the deposition. Increasing of the oxygen pressure during the deposition efficiently removes second phases like iron and zinc oxides from the film. Monophase, highly textured zinc ferrite films have been grown on (001) SrTiO3 substrates at PO2 = 210–3 mbar and Tsub = 1000 K. FMR conducted on these films has revealed a fourfold cubic magnetic anisotropy with 4πMeff ≈ 3.0 kOe e K1c = –1.5104 erg/cm3. Though no crystalline structure could be found in the samples grown at Tsub < 1000 K, well-resolved spin wave spectra have been detected in one of them at cryogenic temperatures. The respective stiffness parameter (~810–8 erg/cm) is at least five times smaller than the value reported formerly in zinc-ferrite films. The FMR line width is in all cases pretty large, indicating internal heterogeneities in the films. In most of the samples, additional resonances were detected, possibly due to surface modes, spin waves and the presence of different magnetic phases.
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25

Neumann, James 1958. "THE INITIATION AND PROPAGATION OF HERTZIAN AND RADIAL CRACKS IN NICKEL-ZINC FERRITE." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/276523.

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This investigation was initiated by IBM to determine the types of cracks formed in hot-isostatic-pressed (HIP) Ni-Zn ferrite under impact and static loading conditions. A 1/8-inch tungsten carbide (WC) ball was used to apply the load in both cases. The impact loading condition was accomplished by dropping the WC ball from various heights between 40 and 200 cm. The static loading condition was accomplished by applying loads of 10 kg, 15 kg, and 30 kg on a Rockwell Hardness Tester. The response of HIP Ni-Zn ferrite to impact and static loading was elastic/plastic yielding permanent indentations. "Dimple" impressions, Hertzian-ring cracks, and radial cracks were formed upon applying increasing loads to the HIP Ni-Zn ferrite. As the grain size of the material was increased, both the Hertzian-ring and radial cracks were formed at lower loads compared to the as-received samples. The "dimple" impressions were not observed to follow this trend.
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26

Angermann, André. "Nasschemische Herstellung und Eigenschaften verlustarmer Mangan-Zink-Ferrite für Hochfrequenzanwendungen." Ilmenau Univ.-Verl, 2009. http://d-nb.info/996522050/04.

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27

Kvapilová, Vendula. "Vliv uvolňování zinku při slinování na permeabilitu/indukčnost feritové keramiky." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2021. http://www.nusl.cz/ntk/nusl-444216.

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The diploma thesis is focused on the investigation of the effect of zinc release during ferritic sintering on the permeability/inductance of ferrite ceramics. The theoretical part deals with the position of ferrites among other ceramic materials. It describes the basic characteristics of ferrites, their crystal structure and finally the problems that are directly related to their production and which fundamentally affect the magnetic properties of ferrites. In the second part of the work, the influence of the temperature and time of sintering and the position of the cores in the furnace during firing on the loss of zinc from the sample and subsequently on the electromagnetic properties of the prepared test specimens from industrial raw material mixtures was investigated. These are initial experiments, which will be followed by further research aimed at eliminating the problem of zinc loss in the production of Mn-Zn ferrites.
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28

MARROQUIN, MERY CECILIA GOMES. "CHARACTERIZATION AND ZINC FERRITE CONTAINED INTO STEELMAKING DUSTS REDUCTION, BY CO-CO2 GAS MIXTURES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2008. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=12488@1.

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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
O presente estudo foca o comportamento da redução da ferrita de zinco produzida em laboratório e a contida nos pós de aciaria elétrica (PAE) pelo CO puro e misturas COCO2, esta última tomada como exemplo de um caso real. Este trabalho se iniciou com a caracterização dos principais compostos presentes no PAE (óxido de ferro (III), óxido de zinco e ferrita de zinco) usando técnicas, metodologias e equipamentos para caracterizações térmica (ATD-ATG), estrutural (DRX), microscópica (MEV-MET analise de EDS), física (porosidade do briquete, massa especifica, tamanho médio e área superficial específica das partículas) e química. Constatou-se que as partículas dos materiais estudados são predominantemente de geometria esférica e, em particular o estudo via MET da ferrita de zinco, revelou aglomerados micrométricos e homogêneos tipo clusters, formados por partículas arredondadas e constituídas por alguns monocristais com tamanhos da ordem de 100 nm. Com a finalidade de estudar a cinética de redução da ferrita de zinco, foram realizados ensaios de redução por CO puro e misturas gasosas formadas por: 75%CO-25%CO2 e 50%CO-50%CO2 nas temperaturas de 1073, 1173, 1223, 1273 e 1373K. O tempo máximo de redução foi de 105 min. Os resultados obtidos permitiram propor uma seqüência cinética de redução, ao longo da qual os principais produtos de redução da ferrita de zinco foram caracterizados via MEV, visando estabelecer a fenomenologia/morfologia da redução. Conclui-se que a fenomenologia morfológica e cinética da redução da ferrita de zinco, embora complexa, é similar a da redução dos óxidos de ferro, dependendo das composições gasosas, temperatura e tempo de reação. O estudo morfológico permitiu constatar que a redução da ferrita de zinco evidencia sua decomposição nos óxidos constituintes (ZnO e Fe2O3), na faixa de 1073 a 1273K e a redução seqüencial do óxido de zinco e dos óxidos de ferro. Os típicos produtos sólidos da redução são: óxido de zinco (ZnO), wüstita (FeO), óxidos mistos do tipo (Zn, Fe)O e ferro metálico. O estudo cinético estabeleceu ainda que ocorre uma rápida redução do óxido de zinco, liberando zinco gasoso, evidenciando a seguinte seqüência de redução: primeiramente, o óxido de zinco se reduz, seguido dos óxidos de ferro. Isto ocorre significativamente nas temperaturas entre 1223 e 1373K. Estabeleceu-se um modelo geral de redução da ferrita de zinco usando a metodologia de superfície resposta (RSM), que envolveu o planejamento estatístico fatorial 3(4) para avaliar a influência dos fatores preestabelecidos sobre a % Redução (temperatura e tempo de reação, composição gasosa, e massa da amostra). Os modelos cinéticos que melhor ajustaram os mecanismos de redução foram: o modelo de reação química de interface-simetria esférica, seguido pelo modelo exponencial de reação contínua, representados por: [1 − raiz cúbica de (1 - alfa)] = kt e −ln(1 − alfa) = kt , respectivamente. O modelo de reação química de interface - simetria esférica, representado por: [1 − raiz cúbica de (1 - alfa)] = kt foi o que melhor adequou-se à redução da ferrita de zinco sintética. Os parâmetros cinéticos obtidos foram: (a) 100%CO: Ea de 55,60 kJ/mol e A= 8,833 mHz; (b) 75%CO-25%CO2: Ea = 88,21 kJ/mol e A= 127,74 mHz; (c) 50%CO-50%CO2: Ea = 95,21 kJ/mol e A = 193,37 mHz; De maneira similar, no caso da redução da ferrita de zinco presente no PAE, o modelo que melhor representou o processo, também foi o modelo de reação química de interface - simetria esférica, representado por: [1 − raiz cúbica de (1 - alfa)] = kt , sendo, Ea (energia de ativação aparente) e A (constante pré-exponencial de Arrhenius), os parâmetros cinéticos obtidos: (d) 100%CO: Ea = 52,34 kJ/mol, e A=4,98 mHz; (b) 75%CO-25%CO2: Ea = 66,70 kJ/mol e A= 76,06 mHz; (c) 50%CO-50%CO2: Ea = 86,28 kJ/
This work deals with the behavior of the synthetic zinc ferrite reduction as well as a case study for the same process using electric arc furnace dusts (EAFD). These processes were conducted under pure CO atmosphere and CO- CO2 gas mixtures. The research here reported onsets with the characterization of the compounds present in EAFD - Iron (III) oxide, zinc oxide and zinc ferrite - using techniques, methodologies and equipments for thermal characterization (DTA-TGA), structural (XRD), microscopic (SEM-TEM coupled to EDS), physical (briquette porosity, specific gravity, average size & particle specific surface) and chemical analysis. It was found that the studied materials particles showed predominantly spherical geometry and in particular, the TEM scans in the zinc ferrite, reveled cluster type micrometric and homogeneous agglomerates formed from single crystal round particles having the size of circa 100 nm. Aiming at the study of the kinetics of the zinc ferrite reduction experiments were conducted using synthetic and EAFD materials submitted to pure CO gas and mixtures of it with CO2 in the following proportions: 75%CO-25%CO2 e 50% CO-50%CO2. The runs were conducted at the temperatures 1073, 1173, 1223, 1273 e 1373K and the maximum reaction time was 105 min. The obtained results permitted the proposal of a kinetic reduction reaction chain. In the course of the study, also, the main zinc ferrite reduction products were characterized by the SEM analysis. This analysis also permitted the observation of phenomenological & morphological correlations during the process. It was concluded that the morphological and kinetic zinc ferrite reduction, in spite being a complex process, it is similar to iron oxides reduction, meaning, dependent on the gaseous compositions, temperature and reaction times. The morphological prism permitted to propose that the zinc ferrite reduction denounces its instantaneous decomposition in their constituent oxides (ZnO and Fe2O3) when submitted to temperatures in the range of 1073 to 1273K and also the sequential reduction of zinc and iron oxides. The typical reduction products were zinc oxide (ZnO), wüstite (FeO) and mix oxides type (Zn, Fe) O and metallic iron. Again, the kinetic study established that a rapid reduction of the zinc oxide occurs, as compared to the other present oxides, through the sequence: firstly the zinc oxide reduction takes place, and this is followed by the iron oxides reduction. The last processes occur significantly for temperatures in the range of circa 1223 to 1373K. A general model of the zinc ferrite reduction by the gaseous mixture of CO-CO2 was proposed using the response surface methodology (RSM) for the factorial analysis 3(4). This was done evaluating the effect of the following variables: temperature, reducing atmosphere composition, specimen mass and reaction time over the %Reduction. The kinetic models that presented the better adjustment for the reduction were the boundary chemical reaction model for spherical symmetry (BCRM`ss) with the equation [1 - cubic root (1 - alfa)] = kt and the model of simple exponential continuous reaction obeying the relation: − ln(1 - alfa) = kt . The kinetic parameters obtained (Ea, apparent activation energy, and A, Arrhenius preexponential frequency fator) were for the first model, that is synthetic zinc ferrite: (a) 100%CO gas: Ea=55,60 kJ/mol & A= 8,83 mHz; (b) 75%CO-25%CO2: Ea = 88,21 kJ/mol & A= 127,74 mHz; (c) 50%CO-50%CO2: Ea = 95,21 kJ/mol & A = 193,37 mHz. And for the second material, zinc ferrite contained in the EAF dusts: (a) 100%CO gas: Ea=52,34 kJ/mol & A= 4,98 mHz; (b) 75%CO-25%CO2: Ea = 66,70 kJ/mol & A= 76,06 mHz; (c) 50%CO-50%CO2: Ea = 86,28 kJ/mol & A = 289,59 mHz. The comparison between the apparent activation energy obtained from the best fitting kinetic models permitted to conclude that the zinc ferrite reduction as well as the electric arc furnace dusts reduction global
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29

Colán, Victoria Amelia Lázaro. "Perdas em ferritas de manganês zinco: o papel da sinterização e de parâmetros microestruturais." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-30112010-144937/.

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O uso das ferritas de manganês zinco em fontes de potência de carregadores de bateria vem crescendo nos últimos anos, devido a suas baixas perdas magnéticas em induções da ordem de 0,2 T. Estas ferritas pertencem à categoria de ferritas moles, são óxidos ferrimagnéticos, policristalinos com estrutura cúbica tipo espinélio. Pós desse material foram compactados em prensa uniaxial e em prensa automática de produção para anel e toróide, respectivamente. Foram realizados dois ciclos de queima variando o teor de oxigênio entre 5 e 15%, no patamar de sinterização, com o propósito de avaliar seu efeito na densidade, microestrutura, perdas magnéticas em altas induções (0,2 T) e permeabilidade. Amostras sinterizadas em posições mais quentes do forno resultaram em maior densidade e maior tamanho de grão, conforme esperado, mas resultaram em maiores perdas a 25 °C. O aumento do teor de oxigênio entre 5 e 15% não alterou sistematicamente a densidade, mas resultou num pequeno aumento do tamanho de grão. Já a correlação entre teor de oxigênio e perdas foi complexa. Foi observado que existe uma temperatura de mínimo nas perdas totais por volta de 60 °C. O mesmo comportamento foi observado na curva da perda histerética, compatível com a variação da constante de anisotropia magnetocristalina (K1). Foram realizados ensaios de curvas de histerese a partir de 25 até 100 °C, a 0,2 T com o objetivo de avaliar o efeito da temperatura nas duas parcelas da perda histerética. Amostras sinterizadas a 1290 °C com a menor pressão de oxigênio apresentaram menor temperatura de mínimo de perda. As técnicas de análise química do teor de Fe2+ não foram capazes de estabelecer, inequivocamente, a esperada relação entre essa variável e o teor de oxigênio da atmosfera de sinterização.
The use of manganese zinc ferrite in power sources of battery chargers is growing, due to its low magnetic power losses at inductions around 0.2 T. These ferrites belong to the soft magnetic materials group, they are polycrystalline ferromagnetic oxides with face centered cubic structure. Powders of this material were compacted in uniaxial press and in automatic press of production, by ring and toroidal form, respectively. Two firing cycles, varying the atmosphere oxygen content between 5 and 15%, were applied to evaluate its effect on microstructure, density, magnetic losses in high induction and permeability. Samples sintered in warmer positions inside the furnace resulted in higher density and larger grain size, as expected, but higher losses at 25 °C were achieved. Increasing the atmosphere oxygen content from 5 to 15% did not alter density significantly, but resulted in a slight increase in grain size. On the other hand, the correlation between oxygen content and losses was complex. There are lower losses, at 60 °C. Similar behavior was observed with hysteresis loss, which is compatible with the change in magnetocrystalline magnetic anisotropy (K1). Measurements were performed from 25 to 100 °C, at 0.2 T, aiming at the evaluation of the effect of temperature on the two parcels of hysteresis loss. Samples sintered at 1290 °C with low atmosphere oxygen content showing a minimum on the losses versus temperature curve. The available techniques to analyze Fe2+ content were not capable of establishing, unequivocally, the expected relation between this variable and the oxygen content of the sintering atmosphere.
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30

Mapukata, Sivuyisiwe. "Photocatalytic treatment of organic and inorganic water pollutants using zinc phthalocyanine-cobalt ferrite magnetic nanoparticle conjugates." Thesis, Rhodes University, 2019. http://hdl.handle.net/10962/67603.

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This work explores the synthesis and photophysicochemical properties of zinc phthalocyanines when conjugated to cobalt ferrite magnetic nanoparticles. Phthalocyanines with amine and carboxylic acid functional groups were synthesised so as to covalently link them via amide bonds to cobalt ferrite magnetic nanoparticles with carboxylic acid and amine groups, respectively. Spectroscopic and microscopic studies confirmed the formation and purity of the phthalocyanine-cobalt ferrite magnetic nanoparticle conjugates which exhibited enhanced triplet and singlet quantum yields compared to the phthalocyanines alone. The studies showed that the presence of cobalt ferrite nanoparticles significantly lowered fluorescence quantum yields and lifetimes. The conjugates not only showed much higher singlet oxygen quantum yields compared to the phthalocyanines alone but were also attractive because of their magnetic regeneration and hence reusability properties, making them appealing for photocatalytic applications. The photocatalytic ability of some of the phthalocyanines and their conjugates were then tested based on their photooxidation and photoreduction abilities on Methyl Orange and hexavalent chromium, respectively. For catalyst support, some of the zinc phthalocyanines, cobalt ferrite magnetic nanoparticles and their respective conjugates were successfully incorporated into electrospun polystyrene and polyamide-6 fibers. Spectral characteristics of the functionalized electrospun fibers confirmed the incorporation of the photocatalysts and indicated that the phthalocyanines and their respective conjuagates remained intact with their integrity maintained within the polymeric fiber matrices. The photochemical properties of the complexes were equally maintained within the electrospun fibers hence they were applied in the photooxidation of azo dyes using Orange G and Methyl Orange as model organic compounds.
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OLIVEIRA, R. C. S. "SÍNTESE DA FERRITA DE ZINCO E ÓXIDO DE ZINCO PELO MÉTODO SOL-GEL PROTEICO." Universidade Federal do Espírito Santo, 2017. http://repositorio.ufes.br/handle/10/8432.

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Neste trabalho, foi realizada a síntese da ferrita de zinco (ZnFe2O4) e óxido de zinco (ZnO) pelo método sol-gel proteico com a pectina do albedo da laranja pêra, que pode ser aproveitada de resíduos orgânicos. Os reagentes usados na síntese foram os sais de nitrato de ferro III nonahidratado (Fe(NO3)3·9H2O) e nitrato de zinco hexahidratado (Zn(NO3)2·6H2O). A mistura de nitratos com pectina foi submetida a um tratamento térmico de 4 h com as temperaturas de 1073 K, 1173 K, 1273 K, 1373 K, 1473 K e 1573 K. Estudou-se a influencia dos tratamentos térmicos sobre as propriedades do material usando as técnicas de espectroscopia no infravermelho, difração de Raio X e espectroscopia Mössbauer, essa ultima só para a ferrita de zinco. Na caracterização da ferrita de zinco observam-se a presença das fases ZnFe2O4, hematita (Fe2O3) e ZnO, a hematita é detectada nas três técnicas até a temperatura de 1173 K e deixa de existir em 1273 K, a fase da ferrita de zinco encontra-se presente em todas as técnicas como a fase principal. O ZnO é identificado nas técnicas de espectroscopia de infravermelho e difração de Raio X, sendo observado em todas as amostras, mas com redução de concentração em função do aumento da temperatura, chegando ao seu mínimo em 1573 K. Por apresentar propriedades magnéticas inesperadas a amostra da ferrita de zinco produzida a 1573 K foi submetida ao teste de carreamento de óleo obtendo um resultado de 3,6 vezes o carreamento da massa de óleo em relação a sua massa. Nas amostras de ZnO observam-se duas fases presentes no espectro de infravermelho, o ZnO e uma fase ainda desconhecida, enquanto o difratograma de Raio X apresenta todos os picos característicos referentes ao ZnO propriamente dito.
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32

Le, Guen Emmanuel. "Élaboration et réalisation de matériaux magnétodiélectriques pour la miniaturisation d'antennes en bande UHF." Thesis, Rennes 1, 2014. http://www.theses.fr/2014REN1S016.

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La miniaturisation des antennes s'accompagne d'une dégradation leurs performances (bande passante, gain, efficacité), surtout avec l'utilisation de substrats matériaux diélectriques. Pour relever le défi « intégration / performances », la conception de nouveaux matériaux tels que les ferrites magnétoélectriques constitue une alternative des plus prometteuses. Ce travail met en avant les principaux paramètres à l'élaboration de ferrite spinelle par coprécipitation. Un traitement thermique modéré a permis l'obtention de céramiques semi poreuses pour la montée en fréquence. En parallèle, l'anisotropie magnétocristalline, liée à la composition (rapport Nickel / Zinc, Cobalt, Fer 2+…) ; ainsi que l'anisotropie magnétoélastique lors de l'application d'une contrainte, étendent encore le domaine des faibles pertes des ferrites de Nickel-Zinc de 400 MHz à plus de 1 GHz. Ces matériaux ont ainsi pu équiper des antennes sur les fréquences du DVH-H (470 – 830 MHz) et répondent aux normes du DVB-H. De façon à profiter pleinement de la miniaturisation, nous avons proposé une antenne imprimée. Une bonne corrélation est trouvée entre les résultats de simulation et de mesure, ainsi que des relations adaptées aux antennes patch. Enfin dans le domaine émergent des communications On / Off bodies, nous avons développé des antennes flexibles sur un substrat de type PDMS. Pour assurer une bonne efficacité de l'antenne, celle-ci est encapsulée, ce qui évite une métallisation hasardeuse (fissures, manque d'adhérence)
Antenna miniaturization, especially with dielectric substrates, is accompanied by a radiation loss (bandwidth, gain, efficiency). To meet the challenge "integration / performance", the design of new materials such as magnetodielectrics ferrites is a promising alternative. To satisfy these requirements, this work highlights the main parameters of ferrite spinel development by coprecipitation. A moderate thermal treatment leads to semi porous ceramics. In parallel, the magnetocrystalline anisotropy, related to the composition (ratio Nickel / Zinc, Cobalt, Iron 2+ ...), and the magnetoelastic anisotropy with application of stress, extend the field of low-loss from 400 MHz to over 1 GHz, in the Nickel-Zinc ferrite. These materials were able to equip antennas on DVH-H frequencies (470-830 MHz). In order to take full advantage of miniaturization, we proposed a printed antenna. A good correlation between simulation results and measurement is obtained, together with relations adapted to patch antennas. Finally, in the emerging field of communications On / Off bodies, we have developed flexible antennas on PDMS substrate. To ensure good antenna efficiency, it is encapsulated, thereby avoiding a hazardous metallization (cracks, loss of adhesion)
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33

Andrade, Jefferson Maul de. "Ferritas de cobre e zinco do tipo espinélio sintetizadas pelos métodos: hidrotermal assistido por micro-ondas, precursores poliméricos, reação no estado sólido e decomposição térmica." Universidade Federal da Paraí­ba, 2012. http://tede.biblioteca.ufpb.br:8080/handle/tede/7067.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Ferrites are well studied materials due to their wide application as: gas detector, optical, electronic and magnetic devices, catalyst and pigments. In the synthesis of materials, the properties are extremely influenced by the synthesis method. In this work, four methods were used in the synthesis of spinel ferrites with composition Zn1-xCuxFe2O4 (x = 0,0; 0,25; 0,50; 0,75; 1,0). These were: microwave assisted hydrothermal method (HMO), polymeric precursor (PP), solid state reaction (ES) and thermal decomposition (CA). The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscopy, ultraviolet and visible spectroscopy (UV-Vis), surface area analysis by the BET method e field emission scanning electronic microscopy (FE-SEM). The synthesis realized with different methods presented very distinct results according to the characterization methods. The sample with composition Zn0,75Cu0,25Fe2O4 was selected as standard for comparison among the applied methods. Samples obtained by the hydrothermal method presented high surface area (128 m2.g-1) and using the particle size obtained by BET and crystallite size calculated from the XRD patterns, it was estimated that there is about 1 crystallite per particle. All samples had high short- and long-range disorder. The sample synthesized by de PP method presented the highest crystallinity, with high short and long range order, leading to a high photoconductivity, intermediary surface area due to the sintering among small particles. The CA method presented an intermediate characteristic between the PP and ES methods. Comparing to HMO method, the PP, ES and CA ones presented small surface areas (not exceeding 2 m2.g-1), and about 9 times more crystallites per particle. Generally, the formation of ZnFe2O4 spinel was achieved by all methods applied, with the synthesis of CuFe2O4 was not possible depending on the reaction media or at lower temperatures.
As ferritas são materiais bastante estudados devido às diversas aplicações como: detector de gases, dispositivos ópticos, eletrônicos e magnéticos, catalisadores e pigmentos. Na síntese de materiais, essas propriedades são influenciadas pelo método de síntese. Neste trabalho, quatro métodos foram empregados na síntese das ferritas do tipo espinélio com composição Zn1-xCuxFe2O4 (x = 0,0; 0,25; 0,50; 0,75; 1,0). Estes foram: o hidrotermal assistido por micro-ondas (HMO), o precursor polimérico (PP), reação no estado sólido (ES) e decomposição térmica (CA). As amostras foram caracterizadas por difração de raios-X (DRX), espectroscopia na região do infravermelho (IV), espectroscopia Raman, espectroscopia na região do ultravioleta e do visível (UV-Vis), análise de área superficial pelo método de BET e microscopia eletrônica de varredura com emissão de campo (MEV-EC). Nas sínteses realizadas pelas diferentes metodologias, resultados diferentes foram obtidos em todas as técnicas empregadas. A amostra de composição Zn0,75Cu0,25Fe2O4 foi utilizada como composição padrão como comparação entre os métodos. Amostras obtidas pelo método hidrotermal apresentaram elevada área superficial (128 m2.g-1) e utilizando o tamanho de partícula calculado pelo BET e o tamanho de cristalito calculado pela difração, pode ser estimado que praticamente há cerca de 1 cristalito por partícula. Todas as amostras apresentaram elevada desordem a curto e a longo alcance. A amostra sintetizada pelo método PP apresentou a maior cristalinidade, com elevada ordem a curto e longo alcance, gerando alta fotocondutividade, com área superficial intermediária, devido à sinterização entre partículas pequenas. O método CA, em geral, apresentou comportamento intermediário entre o método PP e ES. Os métodos PP, ES e CA, quando comparados ao método HMO, apresentaram pequena área superficial (não excedendo 2 m2.g-1) e cerca de 9 vezes mais cristalitos por partícula. De um modo geral, a formação do espinélio ZnFe2O4 foi alcançada por todos os métodos utilizados, enquanto a síntese do CuFe2O4 não foi possível em alguns meios reacionais ou em temperaturas mais baixas.
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Jesus, Camilo Bruno Ramos de. "Efeito da desordem catiônica nas propriedades magnéticas da ferrita de zinco." Pós-Graduação em Física, 2012. https://ri.ufs.br/handle/riufs/5320.

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In this work, we have investigated the structural and magnetic properties of ZnFe2O4 samples prepared via solid state reaction and co-precipitation obtained for using different annealing temperatures. Measurements of X-ray diffraction (XRD) were realized in order to verify both the single phase was obtained, as well as to determine the purity of the sample with respect to the amount of spurious phase existent. The magnetic characterization was carried out through magnetization measurements as function of applied magnetic field (65 < H < 65 kOe) and as function of temperature (2 < T < 400 K) using a magnetometer SQUID of the Quantum Design MPMS SQUID-EverCool. Besides, we analyze the dependence of the coercive field with the temperature in ZnFe2O4 nanoparticles. A theoretical model that considers the distribution of particles sizes was used to make the adjustment to our experimental data of coercivity as function of temperature
Neste trabalho nós investigamos as propriedades estruturais e magnéticas de amostras de ZnFe2O4 preparadas pelo método de reação do estado sólido e co-precipitação obtidas usando diferentes temperaturas de síntese. Medidas de difração de raios X (DRX) foram realizadas com o objetivo de verificar se a fase única foi obtida, assim como para determinar a pureza da amostra com relação à quantidade de fases espúrias existentes. A caracterização magnética foi feita através de medidas de magnetização em função do campo magnético aplicado (65 < H < 65 kOe) e em função da temperatura (2 < T < 400 K) usando um magentômetro SQUID da Quantum Design MPMS SQUID-EverCool. Além disso, nós analisamos a dependência do campo coercivo com a temperatura das nanopartículas de ZnFe2O4. Um modelo teórico que considera a distribuição de tamanhos de partículas foi utilizado para fazer o ajuste aos nossos dados experimentais de coercividade em função da temperatura
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35

Lebourgeois, Richard. "Elaboration et caractérisations de ferrite spinelle de nickel-zinc sous forme de céramique et de monocristaux pour applications aux hyperfréquences." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0097.

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Afin d'ameliorer les proprietes absorbantes des ferrites spinelles ni-zn, des plaquettes de composition chimique ni#0#,#4#5zn#0#,#5#5fe#2o#4 ont ete synthetisees selon deux methodes: la premiere est une reaction en sels fondus a partir de fe#2o#3 micace en poudre et permet d'obtenir des plaquettes de 10 a 30 microns, la seconde est une reaction d'echange a partir de kfe#1#1o#1#7 monocristallin et permet d'obtenir des plaquettes de 50 microns a plusieurs millimetres. Grace a une technique de mesure en ligne coaxiale, on a mesure la permeabilite complexe des plaquettes de ferrite spinelle en fonction de la frequence sur des ceramiques et des echantillons monocristallins
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36

Angermann, André [Verfasser]. "Nasschemische Herstellung und Eigenschaften verlustarmer Mangan-Zink-Ferrite für Hochfrequenzanwendungen / von André Angermann. [Technische Universität Ilmenau]." Ilmenau : Univ.-Verl, 2009. http://d-nb.info/999804472/34.

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37

Brito, Vera Lúcia Othéro de. "Seleção, elaboração e caracterização de ferritas Ni-Zn para aplicação em monitores de corrente pulsada." Instituto Tecnológico de Aeronáutica, 2007. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=422.

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As ferritas Ni-Zn são materiais que têm sido bastante estudados nas últimas décadas e que têm sido empregados em diversas aplicações na indústria eletro-eletrônica. Neste trabalho, estudou-se a microestrutura e a permeabilidade magnética complexa de algumas ferritas Ni-Zn com o objetivo de selecionar uma cerâmica deste tipo para aplicação como núcleo do transdutor de um monitor de corrente pulsada para a monitoração de pulsos com 1 s de duração. A utilização de uma ferrita para esta finalidade resulta em um monitor de fabricação simplificada e de baixo custo. Foram fabricadas amostras de ferritas do tipo Ni1-xZnxFe2O4 com x=0,9 (ferrita 1), x=0,7 (ferrita 2) e x0,5 (ferrita 3). Das três ferritas fabricadas, a ferrita 3 foi a que apresentou a permeabilidade magnética complexa mais adequada para a aplicação proposta. Foi elaborado um segundo lote de amostras com a composição da ferrita 3 inserindo-se algumas alterações no processo de fabricação cerâmico. As alterações inseridas foram: o uso de moagem de alta energia no pó pré-sinterizado, o emprego de desagregação com ultrassom desse pó moído e a adição de 200 ppm de Nb2O5 a esse mesmo pó. Verificou-se que a alternativa que gerou melhores resultados foi a que utilizou desagregação com ultrassom sem a adição do Nb2O5. Foi verificado que a indução magnética de saturação da ferrita fabricada por essa alternativa é de 0,074 T e que a sua permeabilidade magnética relativa complexa varia com a temperatura, entre -40 oC e +50 oC, da seguinte forma: r 203,2+1,1494T+0,0039T2 e 5 < r"< 10.
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38

Souza, Natália Dantas Gomes de. "Obtenção de nanobiocompósitos magnéticos constituídos de Galactomanana, Glicerol e Ferrita de Níquel e Zinco." reponame:Repositório Institucional da UFC, 2014. http://www.repositorio.ufc.br/handle/riufc/10735.

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SOUZA, N. D. G. Obtenção de nanobiocompósitos constituídos de Galactomanana, Glicerol e Ferrita de Níquel e Zinco. 2014. 73 f. Dissertação (Mestrado em Engenharia e Ciências de Materiais) - Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2014.
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In recent years, a great interest in the association of magnetic and biological materials has been reported in the literature. New composite consisting of galactomannan (GM), magnetic nanoparticles (NPs) of NiZn and glycerol (GL) were produced in different proportions with the purpose of enhancing the individual characteristics of each material for future applications. Thus, the structural, magnetic and dielectric properties of nanobiocomposites were investigated by Absorption Spectroscopy in the Region of Infrared (FTIR), X-Ray Diffraction (XRD), Thermal Analysis (TG), Differential Scanning Calorimetry (DSC), Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Magnetic Measurements and Dielectric Measurements. The structure of spinel NiZn ferrite was confirmed by XRD and TEM. Sample GMGL despite being an amorphous material presented in their nanobiocomposites characteristic peaks of phase NiZn. The characteristic bands in the samples were confirmed by FTIR. These in turn followed a degradation profile in accordance with the amounts of NiZn incorporated, which was confirmed in the DSC thermograms. The characterization by SEM was important to assess the morphology. The results of dielectric measurements showed low dielectric loss and magnetic measurements showed magnetic behavior for all nanobiocomposites. Therefore, the results of the characterization of nanobiocomposites were satisfactory for potential applications as biomaterials, electronic devices or related areas.
Nos últimos anos, um grande interesse na associação de materiais magnéticos e biológicos tem sido relatado na literatura. A obtenção de novos compósitos constituídos de galactomanana (GM), nanopartículas magnéticas (MNPs) de NiZn e glicerol (GL) foram produzidos em diferentes proporções com finalidade de potencializar as características individuais de cada material para futuras aplicações. Sendo assim, as propriedades estruturais, magnéticas e dielétricas dos nanobiocompósitos foram investigadas por Difração de Raios-X (DRX), Espectroscopia de Absorção na Região de Infravermelho (FTIR), Análise Térmica (TG), Calorimetria Exploratória Diferencial (DSC), Microscopia Eletrônica de Varredura (MEV), Microscopia Eletrônica de Transmissão (TEM), Medidas Magnéticas e Medidas Dielétricas. A estrutura de espinélio da ferrita de NiZn foi confirmada por DRX e TEM e a amostra GMGL apesar de ser um material amorfo apresentou em seus nanobiocompósitos picos caracteristicos da fase de NiZn. As bandas características para as amostras foram confirmadas por FTIR. Estas por sua vez seguiram um perfil de degradação de acordo com as quantidades de NiZn incorporados, confirmados nos termogramas de DSC. A caracterização por MEV foi importante para avaliação da morfologia. Os resultados das medidas dielétricas apresentaram baixas perdas dielétricas e das medidas magnéticas mostraram comportamento magnético para todos os nanobiocompósitos. Portanto, os resultados da caracterização dos nanobiocompósitos foram satisfatórios para possíveis aplicações como biomaterias, dispositivos eletrônicos ou em áreas afins.
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39

Bourrioux, Samantha. "Laser-pyrolysed ZnFe2O4 anode for lithium-ion batteries : understanding of the lithium storage mechanisms." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI014/document.

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Le graphite est le matériau d’électrode négative utilisé actuellement dans les batteries lithium-ion commerciales. Celui-ci souffre malheureusement d’une capacité spécifique relativement faible (372 mAh.g-1) ; son remplacement par un matériau de conversion comme l’oxyde ZnFe2O4, de capacité théorique plus élevée (1001 mAh.g-1) permettrait d’augmenter la capacité de stockage des batteries lithium-ion. Travailler avec des nanoparticules de ZnFe2O4 permettrait également de limiter l’expansion volumique à laquelle est soumis le matériau en cours de cyclage tout en améliorant la cinétique des ions lithium. Des nanopoudres ZnFe2O4 ont été synthétisées au Laboratoire Edifices Nanométriques (LEDNA) du CEA par la méthode de pyrolyse laser. Cette méthode de synthèse flexible a permis d’obtenir des nanopoudres d’oxydes zinc-fer de morphologies différentes grâce à l’ajustement de différents paramètres expérimentaux (précurseurs utilisés, choix et débit des gaz). Les performances électrochimiques de ces nanomatériaux ont été évaluées en demi-cellule face à une contre-électrode de lithium métallique. Des cyclages galvanostatiques à différentes vitesses ont été réalisés à l’Université Technologique de Nanyang (NTU) à Singapour. Les mécanismes fondamentaux régissant le stockage du lithium dans l’oxyde ZnFe2O4 mais aussi dans un mélange ZnO/Fe2O3 ont été étudiés par le biais de caractérisations operando (DRX, 57Fe Mössbauer), en collaboration avec l’Institut Charles Gerhardt de l’université de Montpellier (ICGM). Ces travaux de thèse ont permis de mettre en évidence les performances électrochimiques prometteuses d’une morphologie spécifique de ZnFe2O4 consistant en une population de taille bimodale de particules, ainsi que d’identifier les réactions de lithiation et de délithiation lors des cyclages
Graphite is currently used as negative electrode material in commercial lithium-ion batteries. Unfortunately, this material suffers from a relatively low specific capacity (372 mAh.g-1). Its substitution by a conversion material with a higher specific capacity as ZnFe2O4 (1001 mAh.g-1) would be interesting to increase the capacity of lithium-ion batteries.The use of nanomaterials can also limit the volumetric expansion of the electrode during cycling and enhance lithium ions kinetics.ZnFe2O4 nanopowders were synthesized in the Nanometric Structures Laboratory at the CEA (Atomic Energy and Alternative Energies Commission) by laser pyrolysis. This flexible synthesis method allowed the production of zinc iron oxides nanopowders with different morphologies, depending on the chosen experimental parameters (precursors, choice of gases and flow rates). Electrochemical performances were then evaluated vs. metallic lithium at the Energy Lab of Nanyang Technological University. Fundamental lithium storage mechanisms for ZnFe2O4 oxide were investigated by operando characterizations (XRD and 57Fe Mössbauer) and compared with those of a ZnO/Fe2O3 mixture. This study was realized in collaboration with the Charles Gerhardt Institute (University of Montpellier).This works highlighted the promising electrochemical performances of a specific morphology of ZnFe2O4 nanoparticles, consisting in a bimodal size population of particles, and allowed the deeper understanding of the lithiation and delithiation reactions
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40

Silva, Paulo Antonio Macedo. "S?ntese de ferritas de cobalto e n?quel dopadas com zinco e caracteriza??o de suas propriedades eletromagn?ticas." Universidade Federal do Rio Grande do Norte, 2015. http://repositorio.ufrn.br/handle/123456789/20671.

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No presente trabalho mostra que a s?ntese por combust?o, destaca-se como uma t?cnica alternativa para obten??o dos p?s-cer?micos de ?xidos superiores, nanoestrutrurados e de alta pureza, como as ferritas de f?rmulas Co(1-x)Zn(x)Fe2O4 e Ni(1-x)Zn(x)Fe2O4 com x variando de 0,2 mols, num intervalo de 0,2 ? x ? 1,0 mol, que apresentam propriedades, magn?ticas, em que ocorre ? coexist?ncia de estado ferroel?trico e ferrimagn?tico, as quais podem ser utilizadas em antenas de micro fitas e superf?cies seletivas de frequ?ncias em faixas de micro-ondas miniaturizadas, sem perda de desempenho. A obten??o ocorreu atrav?s do processo de combust?o e de processos f?sicos adequados a utiliza??o ao m?todo de sinteriza??o do substrato, resultando um material cer?mico, de elevado grau de pureza nanom?trico. An?lises no Magnet?metro de Amostra Vibrante (MAV) mostraram que estes materiais ferriticos apresentam par?metros como histereses de materiais que possuem comportamento pr?prio dos materiais magn?ticos de boa qualidade, em que os estados de magnetiza??o podem ser mudados bruscamente com uma varia??o relativamente pequena da intensidade do campo, tendo assim grandes aplica??es no campo de eletroeletr?nicos. A caracterizaram dos p?s-cer?micos sinterizados a 900?C, como suas propriedades estruturais, geom?tricas, tamanho do cristalito e dist?ncia Interplanar, foram feitas por Difra??o de Raios-X (DRX). Foram feitas outras an?lises, como a Microscopia Eletr?nica de Varredura (MEV), Fluoresc?ncia de Raios-X (FRX) , a permissividade el?trica e a tangente de perda, em altas frequ?ncias, atrav?s do aparelho ZVB - 14 Vector Network Analyzer 10 MHz-14 GHz, da ROHDE & SCHWART.
This work shows that the synthesis by combustion is a prominent alternative to obtain ceramic powders of higher oxides, nanostructured and of high purity, as the ferrites of formulas Co(1-x)Zn(x)Fe2O4 e Ni(1-x)Zn(x)Fe2O4 with x ranging from 0.2 mols, in a range from 0.2 ? x ? 1.0 mol, that presents magnetic properties in coexistence of ferroelectric and ferrimagnetic states, which can be used in antennas of micro tapes and selective surfaces of low frequency in a range of miniaturized microwaves, without performance loss. The obtainment occurred through the combustion process, followed by appropriate physical processes and ordered to the utilization of the substrate sinterization process, it gave us a ceramic material, of high purity degree in a nanometric scale. The Vibrating Sample Magnetometer (VSM) analysis showed that those ferritic materials presents parameters, as materials hysteresis, that have own behavior of magnetic materials of good quality, in which the magnetization states can be suddenly changed with a relatively small variation of the field intensity, having large applications on the electronics field. The X-ray Diffraction (XRD) analysis of the ceramic powders synthesized at 900 ?C, characterize its structural and geometrical properties, the crystallite size and the interplanar spacing. Other analysis were developed, as Scanning Electron Microscopy (SEM), X-ray Fluorescence (XRF), electric permittivity and the tangent loss, in high frequencies, through the equipment ZVB - 14 Vector Network Analyzer 10 MHz-14 GHz, of ROHDE & SCHWART.
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41

Martins, Murillo Longo. "Síntese e caracterização de ferritas de manganês e zinco visando aplicação como agente de contraste em diagnóstico médico (biosusceptometria de corrente alternada) /." Bauru : [s.n.], 2011. http://hdl.handle.net/11449/99701.

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Resumo: Para o aprimoramento de técnicas de diagnóstico e tratamentos de doenças o desenvolvimento de materiais magnéticos é de primordial importância. Neste trabalho as ferritas de manganês e zindo de fórmula geral Mn(1-x)ZNxFe204, onde x assume os valores entre 0,15 e 0,30, foram preparadas pelo método dos precursores poliméricos e caracterizadas por: análises térmicas (termogravimetria associada com análise térmica diferencial (TG/DTA), análise composicional semi-quantitativa por energia dispersiva de raios X (EDX), difratometria de raios X (DRX), refinamento estrutural (Método de Rietveld), adsorção de N2 a 77K (BET), microscopia eletrônica de varredura (MEV), microscopia óptica, espectroscopia de absorção atômica (testes de lixiviação) e medidas de susceptibilidade e permeabilidade magnética. As amostras de ferritas foram também revestidas com quitosana e analisadas com algumas dessas técnicas. Os materiais foram desenvolvidos com o objetivo de utilizá-los como rastreador em biosusceptometria de corrente alternada(BAC), um método de diagnóstico. O método de síntese empregado proporcionou materiais monofásicos em ferrita com baixa porosidade e área superficial. Os materiais apresentaram baixa lixiviação de metais em soluções que simulam os meios fisiológicos do trato gastrointestinal. O revestimento com quitosana foi eficiente suprimindo a dissolução de metais em meios com pHs 7,5 e 6,8. Em pH 1,2, o revestimento se mostrou menos eficiente, porém, ainda assim foi capaz de reduzir a dissolução das espécies que constituem a ferrita. Quanto ao comportamento magnético, as amostras apresentaram magnetizações satisfatórias em 10K e em temperatura ambiente. A amostra contendo zinco a x=0,15 apresentou a mais alta saturação magnética em temperatura ambiente e foi utilizada em um teste com a técnica de BAC apresentando resultados satisfatórios
Abstract: The development of magnetic materials is of primary importance for the improvement of diagnostic techniques and treatments of diseases. In this work, the manganese and zinc ferrites with general formula of Mn(1-x)ZNxFe204 and 0,15< x <0,30, was prepared by polymeric precursor method and characterized by the physical techniques as: thermal analysis [thermogravimetry and differential thermal analysis (TG/DTA)], ssemi-quantitative analysis of the composition by energy dispersive X ray (EDX), X ray diffractometry (XRD), structural refinement (Rietveld Method), N2 adsorption analysis at 77k (BET), scanning electron microscopy (SEM), optical microscopy, atomic absorption spectroscopy (lixiviation test) and magnetic susceptibility measurements. Chitosan coated samples were also prepared which were analyzed by some of those technique. The materials were developed to be used as a tracer in the alternating current biosusceptometry (ACB), a diagnostic method. The employed synthesis method provided monophasic samples of ferrites with low porosity and surface area. The materials showed low metal solubility in the media that simulate gastrointestinal tract solutions. The chitosan coating was efficient to suppress the metal dissolution in solutions with pHs 7.5 and 6.8. In pH=1.2 medium, the coating was not efficient, but still reduced the resolution of ferrite components. The magnetic measurements showed that the samples have satisfactory magnetizations at 10K and room temperature. The sample with x=0.15 exhibited the highest magnetic saturation at room temperature and it was applied in an ACB technique which showed satisfactory results
Orientador: Margarida Juri Saeki
Coorientador: Paulo Noronha Lisboa Filho
Banca: Luis Gallego Martinez
Banca: Andris Figueiroa Bakuzis
O programa de Pós-graduação em Ciência e Tecnologia de Materiais PosMat, tem caráter institucional e integra as atividades de pesquisa em materiais de diversos campi da UNESP
Mestre
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42

Martins, Murillo Longo [UNESP]. "Síntese e caracterização de ferritas de manganês e zinco visando aplicação como agente de contraste em diagnóstico médico (biosusceptometria de corrente alternada)." Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/99701.

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Para o aprimoramento de técnicas de diagnóstico e tratamentos de doenças o desenvolvimento de materiais magnéticos é de primordial importância. Neste trabalho as ferritas de manganês e zindo de fórmula geral Mn(1-x)ZNxFe204, onde x assume os valores entre 0,15 e 0,30, foram preparadas pelo método dos precursores poliméricos e caracterizadas por: análises térmicas (termogravimetria associada com análise térmica diferencial (TG/DTA), análise composicional semi-quantitativa por energia dispersiva de raios X (EDX), difratometria de raios X (DRX), refinamento estrutural (Método de Rietveld), adsorção de N2 a 77K (BET), microscopia eletrônica de varredura (MEV), microscopia óptica, espectroscopia de absorção atômica (testes de lixiviação) e medidas de susceptibilidade e permeabilidade magnética. As amostras de ferritas foram também revestidas com quitosana e analisadas com algumas dessas técnicas. Os materiais foram desenvolvidos com o objetivo de utilizá-los como rastreador em biosusceptometria de corrente alternada(BAC), um método de diagnóstico. O método de síntese empregado proporcionou materiais monofásicos em ferrita com baixa porosidade e área superficial. Os materiais apresentaram baixa lixiviação de metais em soluções que simulam os meios fisiológicos do trato gastrointestinal. O revestimento com quitosana foi eficiente suprimindo a dissolução de metais em meios com pHs 7,5 e 6,8. Em pH 1,2, o revestimento se mostrou menos eficiente, porém, ainda assim foi capaz de reduzir a dissolução das espécies que constituem a ferrita. Quanto ao comportamento magnético, as amostras apresentaram magnetizações satisfatórias em 10K e em temperatura ambiente. A amostra contendo zinco a x=0,15 apresentou a mais alta saturação magnética em temperatura ambiente e foi utilizada em um teste com a técnica de BAC apresentando resultados satisfatórios
The development of magnetic materials is of primary importance for the improvement of diagnostic techniques and treatments of diseases. In this work, the manganese and zinc ferrites with general formula of Mn(1-x)ZNxFe204 and 0,15< x <0,30, was prepared by polymeric precursor method and characterized by the physical techniques as: thermal analysis [thermogravimetry and differential thermal analysis (TG/DTA)], ssemi-quantitative analysis of the composition by energy dispersive X ray (EDX), X ray diffractometry (XRD), structural refinement (Rietveld Method), N2 adsorption analysis at 77k (BET), scanning electron microscopy (SEM), optical microscopy, atomic absorption spectroscopy (lixiviation test) and magnetic susceptibility measurements. Chitosan coated samples were also prepared which were analyzed by some of those technique. The materials were developed to be used as a tracer in the alternating current biosusceptometry (ACB), a diagnostic method. The employed synthesis method provided monophasic samples of ferrites with low porosity and surface area. The materials showed low metal solubility in the media that simulate gastrointestinal tract solutions. The chitosan coating was efficient to suppress the metal dissolution in solutions with pHs 7.5 and 6.8. In pH=1.2 medium, the coating was not efficient, but still reduced the resolution of ferrite components. The magnetic measurements showed that the samples have satisfactory magnetizations at 10K and room temperature. The sample with x=0.15 exhibited the highest magnetic saturation at room temperature and it was applied in an ACB technique which showed satisfactory results
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43

Junca, Eduardo. "Reciclagem de poeira de aciaria: estudo da redução da poeira de aciaria LD, elétrica e ferrita de zinco." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-29122014-180047/.

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Este trabalho teve como objetivo estudar a redução de poeira de aciaria LD, elétrica e ferrita de zinco utilizando duas composições diferentes de gases redutores. Inicialmente foram realizadas as caracterizações das matérias primas. Esta etapa foi executada através de análise química, difração de raios-X, microscopia eletrônica de varredura, análise granulométrica e densidade aparente. Foi feita também a caracterização térmica das poeiras de aciaria elétrica e LD. Na próxima etapa, pelotas foram confeccionadas a partir das matérias primas em estudo. Em seguida, foram realizadas as etapas de redução. Esta etapa foi desenvolvida com o uso de uma mistura redutora com 90% Argônio com 10% hidrogênio e outra simulando gás natural reformado (utilizando-se a primeira composição de gás redutor mais CO, na proporção de 75% de H2 e 25% de CO). Foram utilizadas vazões de 50, 100, 150 e 200mL/minuto de gás redutor para ambos os gases. Com os dados de perda de massas, partiu-se para a investigação cinética. Esta foi desenvolvida através de uma derivação do método conhecido por Stepwise Isothermal Analysis, onde ao invés da taxa de reação controlar o salto entre os patamares de temperatura, este é gerenciado pelo usuário. Os resultados de caracterização mostraram que a poeira de aciaria elétrica é composta por ferro e zinco e a poeira de aciaria LD é composta principalmente por ferro e cálcio. Na PAE, o ferro apresentou-se como magnetita e o zinco como zincita e franklinita. A poeira de aciaria LD apresentou como principais fases a base de ferro a wustita e a magnetita. Com relação à cinética de redução, foi notado que para as pelotas de poeira de aciaria LD, utilizando mistura gasosa, a etapa inicial de redução (550 a 650°C) foi controlada pela etapa de nucleação e a partir de 700°C, para ambos os gases, a reação passou a ser controlada pela difusão. No caso da redução da ferrita de zinco, foi notado que a etapa inicial de redução (entre 550 a 650°C) foi controlada por reação química. Após 700°C, foi concluído que a reação passou a ser controlada por difusão para ambos gases. Por fim, na redução das pelotas de poeira de aciaria elétrica foi observado que no estágio inicial, a redução foi controlada por nucleação. A partir de 700°C foi visto que a reação apresentou um controle misto entre nucleação e difusão.
The aim of this work was study of the reduction of basic oxygen furnace dust (BOFD), electric arc furnace dust (EAFD) and zinc ferrite. To do this, two different reducing gases were used. Initially, the raw materials were characterized by chemical analysis, X-ray, scanning electron microscope, size analysis and bulk density. Furthermore, thermal characterization was also performed in both BOFD and EAFD. The next step, pellets were made using the raw materials. The reduction tests were carried out on the pellets through two different reducing gases. The first gas used was a mixture between argon (90wt.%) and hydrogen (10wt.%). The last one was a gas simulating reformed natural gas. In this case, it was accomplished a mixture between the first gas with CO. Fluxes at 50, 100, 150 and 200mL/minute were used in this study in both reducing gas. The kinetic investigation was executed through loss mass curve obtained from reduction tests. The method used for kinetic analysis is a method derived from Stepwise Isothermal Analysis (SIA) where the isothermals are controlled by user. The results from characterization showed that EAFD is composed mainly of iron and zinc. The iron´s phase found was magnetite while zinc´s phases detected were zincite and franklinite. The BOFD is composed by iron and calcium. It was verified that the main iron´s phases encountered were wustite and magnetite. The kinetic analysis showed that pellets of BOFD reduced by gaseous mixture at 550 to 650°C was controlled by nucleation. After 700°C, in both reducing gases, the reactions were controlled by diffusion. To zinc ferrite, it was checked out that initially (550 to 650°C) the reaction was controlled by phase boundary reaction. After 700°C, it was concluded that reaction of reduction for zinc ferrite switched to diffusion in both reducing gases. Lastly, reduction of BOFDs pellet was noted (550 to 650°C) that the reduction was controlled by nucleation. Further 700°C, it was observed that the reaction showed a mix control between nucleation and diffusion.
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44

Silva, Daniela Terezinha Richter da. "Avaliação dos níveis séricos e de ingestão de micronutrientes em pacientes submetidos ao transplante de células tronco hematopoiéticas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/139799.

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Introdução: O transplante de células tronco hematopoiéticas é reconhecidamente uma opção terapêutica para doenças neoplásicas hematológicas, tumores sólidos, deficiências imunológicas e doenças metabólicas. É um procedimento associado a uma alta freqüência de complicações agudas e crônicas, causadas pela toxicidade do regime de condicionamento, dentre elas a mucosite, Doença do Enxerto versus Hospedeiro - DECH e infecções. Essas complicações podem causar grandes mudanças na composição corporal através de mudanças no metabolismo, piorando o estado nutricional. Um adequado consumo de alguns micronutrientes como zinco, vitamina D e ferro, tem sido investigado como forma de evitar ou minimizar essas complicações. Objetivo: Avaliar em pacientes submetidos a transplante de células tronco hematopoiéticas os níveis séricos de zinco, vitamina D e ferritina e o seu impacto nos desfechos do TCTH alogênico e os níveis de ingestão de zinco, vitamina D e ferro. Métodos: Foram avaliadas as dosagens séricas de zinco, vitamina D e ferritina, e os níveis de ingestão de zinco, vitamina D e ferro, os tipos de condicionamento, o grau de DECH e mucosite, a presença de infecções e o estado nutricional. Resultado: Foram incluídos na análise 32 pacientes. Não foi encontrado associação significativa entre a deficiência sérica de Zinco e mucosite e os níveis elevados de ferritina sérica com a ocorrência de infecções. Deficiência sérica de vitamina D aos 45 dias pós transplante foi associado com o desenvolvimento de DECH. Conclusão: Os nossos resultados reforçam a importância dos pacientes manterem os níveis adequados de micronutrientes e reforçam o papel da vitamina D na prevenção de DECH durante o TCTH.
Introduction: The transplantation of hematopoietic stem cells is recognized as a treatment option for hematological neoplastic diseases, solid tumors, immune deficiencies and metabolic diseases. It is a procedure associated with a high frequency of acute and chronic complications caused by the toxicity of the conditioning regimen, among them mucositis, Graft-versus-Host Disease - GVHD and infections. These complications can cause major changes in body composition through changes in metabolism, worsening the nutritional status. An adequate intake of some micronutrients such as zinc, vitamin D and iron, has been investigated as a way to avoid or minimize these complications. Objective: To evaluate in patients undergoing hematopoietic stem cell transplantation serum levels of zinc, vitamin D and ferritin and its impact on the outcomes of allogeneic HSCT and zinc intake levels of vitamin D and iron. Method: The following aspects were evaluated: serum levels of zinc, vitamin D and ferritin, and zinc intake levels of vitamin D and iron, the conditioning types, the degree of GVHD and mucositis, the presence of infections, the nutritional status. Result: The analysis included 32 patients. No significant association has been found between zinc serum deficiency and mucositis and elevated levels of serum ferritin with the occurrence of infections. The serum deficiency of vitamin D at 45 days post-transplantation has been associated with the development of GVHD. Conclusion: Our results reinforce that it is important for the patients to maintain adequate levels of micronutrients and reinforce the role of vitamin D in the prevention of GVHD during the HSCT. Keywords: hematopoietic stem cell transplantation, GVHD, mucositis, infections, Vitamin D, ferritin, zinc, nutritional status.
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45

Mukherjee, Devajyoti. "Growth and Characterization of Epitaxial Thin Films and Multiferroic Heterostructures of Ferromagnetic and Ferroelectric Materials." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3622.

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Multiferroic materials exhibit unique properties such as simultaneous existence of two or more of coupled ferroic order parameters (ferromagnetism, ferroelectricity, ferroelasticity or their anti-ferroic counterparts) in a single material. Recent years have seen a huge research interest in multiferroic materials for their potential application as high density non-volatile memory devices. However, the scarcity of these materials in single phase and the weak coupling of their ferroic components have directed the research towards multiferroic heterostructures. These systems operate by coupling the magnetic and electric properties of two materials, generally a ferromagnetic material and a ferroelectric material via strain. In this work, horizontal heterostructures of composite multiferroic materials were grown and characterized using pulsed laser ablation technique. Alternate magnetic and ferroelectric layers of cobalt ferrite and lead zirconium titanate, respectively, were fabricated and the coupling effect was studied by X-ray stress analysis. It was observed that the interfacial stress played an important role in the coupling effect between the phases. Doped zinc oxide (ZnO) heterostructures were also studied where the ferromagnetic phase was a layer of manganese doped ZnO and the ferroelectric phase was a layer of vanadium doped ZnO. For the first time, a clear evidence of possible room temperature magneto-elastic coupling was observed in these heterostructures. This work provides new insight into the stress mediated coupling mechanisms in composite multiferroics.
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46

Hochepied, Jean-François. "Précipitation d'hydroxydes et d'oxydes métalliques en solution aqueuse : vers le contrôle morphologique d'objets multi-échelles." Habilitation à diriger des recherches, Université Paris-Diderot - Paris VII, 2009. http://tel.archives-ouvertes.fr/tel-00574750.

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47

Jun-Rui, Huang, and 黃駿睿. "Preparation and Characterization of Manganese Doped Nickel-Zinc-Copper Ferrites." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/97988560900636137525.

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碩士
東海大學
化學工程與材料工程學系
102
In this study, we reported on the surface micro-structure, surface roughness, electrical impedance, and forward transmission of manganese doped nickel-zinc-copper ferrites (Ni0.2Zn0.6Cu0.2Fe2O3 + x MnCO3). Ferrites were prepared by solid state and sol-gel methods and mixed with acrylic resin for spin and direct coatings onto plastic sheets. The surface roughness increases with the doping ratio of manganese, and also increases with the number of coating layers. Forward transmission of ferrite prepared by direct coating is lower than that of ferrite prepared by spin coating. The influence of the manganese doping ratio on forward transmission is not obvious. Electrical impedance of ferrite prepared by direct coating is higher than that of ferrite prepared by spin coating. The electrical impedance shift resulted by the manganese doping ratio of 0.3 is most closed to that resulted by the reference sample. The electrical impedance shift resulted by the manganese doping ratio of 0.7 is most different to that resulted by the reference sample. Ferrites prepared by solid state and sol-gel methods have no difference on forward transmission and electrical impedance. However, the result of changing sample size, sample thickness, and the amount of ferrite shows that the influence of thickness is most obvious on forward transmission, but they are not obvious on electrical impedance.
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48

Chen, Chun-Hung, and 陳俊宏. "Gas Sensing Properies of Zinc Oxide Nanowires coated Bismuth Ferrites Thin Films." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/79296193479439706571.

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碩士
國立臺灣師範大學
機電工程學系
103
In this study, the ZnO nanowires are prepared on glass substrate by using hydrothermal method, and deposited BiFeO thin film on the ZnO nanowires by sputtering; later, comparing the sensitivity of the pure ZnO nanowires and the ZnO nanowires with BiFeO. Different thickness of ZnO seed layer can be obtained by changing the sputtering deposition power, so with the increase of the thickness of seed layer, the surface roughness is reduced, and its nanowires diameter and length will be reduced. Using a hydrothermal method prepares ZnO nanowires of three kind of thickness 27, 35 and, 45 nm, and conducts gas sensing experiment of acetone and ammonia at 100, 150 and 200 °C, respectively. The seed layer thickness of 35 nm grown ZnO nanowires have the best sensing sensitivity (S = 7.2 for acetone, S = 3.72 for ammonia). After that we adopt the surface modification process to deposit the bismuth ferrites thin film coated on ZnO nanowires to increase gas sensitivity, and we find that the BiFeO thin film on ZnO nanowires of sensing sensitivity has been improved (S = 7.41 for acetone, S = 4.61 for ammonia), and ammonia sensing sensitivity are increased when operating temperature increases. Finally, conduct gas sensing experiment of high-temperature (300 °C) and room temperature (25 °C) ammonia, and the response speed is proportional to the concentrations of ammonia, especially BiFeO thin film coated on ZnO nanowires, With the concentrations increase, the response is also increase, even at low concentrations (1 ppm) also have the same result.
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49

Msomi, Justice Zakhele. "Mossbauer spectroscopy and x-ray diffraction study of (Cd, Zn) substituted mixed ferrites." Thesis, 2002. http://hdl.handle.net/10413/4412.

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The study of magnetic properties and structures of Zn and Cd substituted mixed ferrites has been carried out using Mossbauer spectroscopy and X-ray diffraction on powdered samples at about 300 K. Two series of mixed ferrites, (Cd, Zn)xCol-xFe2-xAlxO4 and (Cd, Zn)xCo0.9Fe1.7-xTi0.4O 4 (where 0≤ x≤1.0) were synthesized. In the former series the effect of simultaneous site dilution by Zn or Cd and Ai atoms on tetrahedral (A) and octahedral (B) sites is investigated and in the latter the effect of single site dilution by Zn or Cd is also studied. The Mossbauer spectra show that the compounds transform with increase in x from ordered to disordered magnetic states. Systematic decrease in the hyperfine fields indicating weakening of the magnetic coupling with an increase in x is observed. We report the presence of a cross over effect with respect to the hyperfine fields on A and B sites at low concentration of diamagnetic ions in the simultaneously diluted series. Both series of compounds show no significant changes in isomer shifts with x. Differences in the evolution of Fe atoms on A and B sites between Zn and Cd based compounds are observed. The results of our analysis show that Zn and Cd ions occupy both tetrahedral and octahedral sites. The spinel structure of the compounds studied in this work is confirmed by X-ray diffraction (XRD). The lattice parameters derived from XRD show systematic change with x consistent with Vergard's law. In Cd based samples an increase of the lattice parameter with x is explained on the basis of the size difference of the cations involved. However, an anomalous behavior of the lattice parameter is observed in Zn based samples. The average grain sizes of the samples were determined from the line width of the (311) XRD intensity lines using the Scherrer formula. These vary between 50 nm and 70 nm for all the samples except for Zn and Al substituted samples which show a systematic anomalous reduction for x ≥ 0.4 in grain size. The porosity, x-ray and bulk densities of the samples are also presented.
Thesis (M.Sc.)-University of Natal, Durban, 2002.
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50

LIU, JIN-XUAN, and 劉景軒. "Study on manganese zinc ferrite." Thesis, 1986. http://ndltd.ncl.edu.tw/handle/03941836239459423379.

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