Dissertations / Theses on the topic 'Manganese ferrite'

Les conditions d'elaboration a basses temperatures de particules aciculaires de differents ferrites substitues au cuivre ont ete determinees en vue de l'etude de leurs proprietes physico-chimiques. La caracterisation structurale des ferrites peu riches en cuivre a permis de reveler les valences mixtes du cuivre et du fer. Dans ces phases stoechiometriques les ions cuivreux et ferriques sont localises en sites tetraedriques et octaedriques et les ions cuivriques et ferreux uniquement en sites octaedriques. Compte tenu des basses temperatures utilisees pour leur elaboration ces ferrites possedent une reactivite vis-a-vis de l'oxygene suffisante pour faire apparaitre des phases lacunaires. L'oxydation des ions cuivreux a ete mise en evidence de maniere originale puisque le ferrite stoechiometrique riche en cuivre (21% massique) de symetrie cubique possede apres oxydation une maille quadratique. Le ferrite cuivrique (26,5% massique) possede lorsqu'il est refroidi lentement a partir de sa temperature de preparation une symetrie quadratique. Pour cette composition, l'association de l'anisotropie de structure (deformation de la maille) et de l'anisotropie de forme due a l'acicularite des particules permet d'atteindre des champs coercitifs de l'ordre de 1600 oe. Par ailleurs, si l'on substitue les ions cobalt (cations a forte anisotropie magnetocristalline) aux ions cuivre le champ coercitif de ces ferrites atteint une valeur de 4000 oe environ pour une teneur massique relativement faible de 3,7%. L'incidence de la deformation de la maille spinelle sur le champ coercitif a egalement ete observee pour le ferrite substitue au manganese (un manganese pour deux fer). En effet, a l'etat stoechiometrique le ferrite possede une symetrie cubique, mais au terme d'un traitement d'oxydation faisant apparaitre une quantite importante d'ions manganese trivalents la maille cristalline devient quadratique. Cette evolution structurale et chimique se traduit par un tres fort accroissement du champ coercitif qui passe de 180 oe pour le ferrite stoechiometrique a 500 oe apres oxydation

All weld metal test pieces were produced from two commercial and six experimental 7016 type electrodes, each having different contents of manganese and nickel. These were tested in three point bending over a range of depressed temperatures in a cryostatic cell of the author’s devising. Notched samples were used to obtain values for the cleavage fracture strength. This was calculated by reference to slip line field theory from the fracture load at the test temperature where fracture was first coincident with general yielding. The commercial electrodes were first tested in the as welded condition and all eight electrodes were then tested after a heat treatment designed to give a microstructure similar to that found in re-heated weld metal. Notched and pre-cracked samples were then tested in the heat treated condition to determine KI values. Fracture surfaces were examined by scanning electron microscope and grain size measurements made by optical microscopy. Lower shelf impact energy measurements were also made. The results show that both manganese and nickel individually increased the cleavage fracture strength. In combination the best cleavage properties were given by alloying contents of 1.0% manganese and 1.5% nickel increasing alloying beyond this level had a detrimental effect. The mechanism for this was a combination of grain size effects, changes in the slip characteristics of the material, the size, distribution and nature of inclusions and the effects of alloying on grain boundary and matrix/inclusion cohesion. In re-heated material at test temperatures studied the plane strain fracture toughness is influenced by similar factors to those which determine cleavage fracture strength.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
In this work, we developed a multifunctional nanocarrier that has diagnostics and therapeutic applications in oncology, and evaluated the magnetothermal efficiency (SLP) properties in a comparative manner with respect to magnetic fluids. The nanocarrier consists of Mn-ferrite magnetic nanoparticles, a near-infrared fluorescent molecule IR-780, that are surface-coated with albumin proteins (BSA). The samples were characterized by dynamic light scattering (DLS), electron microscopy (TEM and MEV-FEG), vibrating sample magnetometer (VSM), fluorescence molecular tomography (FMT). FMT data proved the coupling of IR-780 to the protein allowing the fabrication of a magnetofluorescent nanostructure. Magnetic hyperthermia data as function of field amplitude (60-200 Oe) and frequency (170-990 kHz) were obtained for all samples containing the same magnetic particle volume fraction in the liquid carrier, but with distinct agregate sizes. The sizes were controlled by tuning the ionic force, and monitored experimentally using DLS. Magnetization curves revealed a (quasi-static) superparamagneticlike behavior, and was used to extract the particle concentration. The hyperthermia efficiency SLP of the magnetic fluids decreased increasing the hidrodynamic diameter. On the contrary, the nanocarrier showed a maximum of SLP, that can be optimized for hyperthermia and is more efficient than the ferrofluid. SLP data as function of frequency revealed a relaxation time of the order of 10-7 s and an equilibrium susceptibility lower than the Langevin value. A theoretical analysis of SLP at the linear responde regime was developed taking into account the dipolar interaction of nanoparticles organized in distinct arrangements. In magnetic fluids we considered a linear chain using the longitudinal configuration (anisotropy axis aligned), while for the nanocarriers we considered spherical agregates where the anisotropy axis of the nanoparticles are arranged randomly. The theoretical analysis indicate that the relaxation time cannot be explained by brownian relaxation or the Néel relaxation of single particle (even considering the dipolar effect). But instead, a mechanism of collective relaxation, mediated by dipolar interaction, is responsible for heat generation. It also indicates that only a fraction of agregates in the colloid is responsible for heating. In addition, the theoretical model revealed the existence of a transition from single particle relaxation to collective relaxation only if the dipolar interaction for the aggregate is higher than a critical value, which depends on material parameters, as for instance anisotropy field and saturation magnetization. Indeed, the model indicates that collective states are more easily achieved on soft magnets, and therefore suggests enhanced magnetothermal properties for this kind of materials.
Neste trabalho desenvolvemos um nanocarreador multifuncional, que possui aplicações diagnósticas e terapêuticas para tratamento oncológico, e avaliamos sua eficiência magnetotérmica (SLP) de forma comparativa com fluidos magnéticos. O nanocompósito contém nanopartículas magnéticas à base de ferrita de manganês, molécula fluorescente na faixa do infravermelho próximo IR-780, sendo recobertas por proteínas de albumina (BSA). As amostras foram caracterizadas por diversas técnicas experimentais, entre elas: espalhamento dinâmico de luz (DLS), microscopia eletrônica (TEM e MEV-FEG), magnetometria de amostra vibrante (VSM), tomografia por fluorescência molecular (FMT). Dados de FMT provaram o acoplamento do IR-780 à proteína e a construção de nanoestrutura magnetofluorescente. Dados de hipertermia magnética em função da amplitude do campo magnético (60-200 Oe) e frequência (170-990 kHz) foram obtidos para diversas amostras contendo a mesma fração de partículas magnéticas, mas tamanho de agregados distintos. O tamanho dos agregados foi controlado variando a força iônica, e monitorados experimentalmente por DLS. Curvas de VSM revelaram comportamento tipo superparamagnético (quasi-estático) e foram usadas para determinar a concentração de partículas. A eficiência magnetotérmica (SLP) revelou, para os fluidos magnéticos, que o SLP diminui aumentando o diâmetro hidrodinâmico. Ao contrário, no nanocarreador, o SLP apresentou um máximo indicando uma hipertermiaotimizada e mais eficiente que o fluido magnético. Os dados de SLP em função da frequência revelaram um tempo de relaxação da ordem de 10-7 s e susceptibilidade de equilíbrio menor que a de Langevin. Aavaliação teórica do SLP foi feita no regime da teoria de resposta linear e baseou-se no cálculo do efeito dipolar de nanopartículas organizadas de forma distinta. No caso do fluido magnético cadeias lineares na configuração longitudinal, enquanto os nanocarreadores consistiram de agregados esféricos com eixos de anisotropia organizados de forma randômica. A análise teórica indicou que o tempo de relaxação não pode ser explicado pela relaxação browniana, tão pouco por uma relaxação de Néel de partícula simples (mesmo considerando efeito dipolar). De fato, demonstramos teoricamente que o mecanismo de relaxação coletivo, mediado pela interação dipolar, é responsável pela geração de calor. A análise indica ainda que somente uma fração de partículas dos colóides, formando agregados específicos, é responsável pelo aquecimento.O modelo teórico revelou que existe uma transição entre o regime de relaxação de partícula isolada (mesmo interagente) para o regime coletivo apenas se a interação dipolar da configuração do agregado magnético for maior que um valor crítico, o qual depende de parâmetros como campo de anisotropia e magnetização de saturação das nanopartículas. Tal teoria indica que a transição ocorre mais facilmente para amostras magnéticas macias, sugerindo maior potencial magnetotérmico para estes materiais.

This study evaluated alternative sulfide treatment processes for potable water systems that rely on groundwater supplies. Research for this study was conducted at the Imperial Lakes (IL) and Turner Road (TR) water treatment plants (WTPs) in Polk County, Florida. These WTPs are in the process of refurbishment and expansion, and will require the installation of a new groundwater well. The IL and TR WTPs both rely upon groundwater sources that contain total sulfide at concentrations ranging from 1.4 to 2.6 mg/L. Sulfide is a concern because if left untreated it can impact finished water quality, corrosivity, create undesirable taste and odor, and oxidize to form visible turbidity. For this reason, the raw water will require treatment per Florida Department of Environmental Protection (FDEP) "Sulfide Rule" 62-555.315(5)(a). This rule does not allow the use of conventional tray aeration (currently in use at the IL and TR WTPs) for wells that have significant total sulfide content (0.6 to 3.0 mg/L). This research was commissioned because the potential water treatment method identified in the Sulfide Rule (i.e. forced-draft aeration) would not adequately fit within the confines of the existing sites and would pose undue burden to neighboring residents. In addition, an effective sulfide treatment process was desired that offered a low profile, did not necessitate the need for additional complex chemical feed systems, minimized the extent of electrical infrastructure upgrades, and was inexpensive to construct and operate. To meet these goals, several alternative technologies were evaluated at the desktop and bench-scale; these included anion exchange, various oxidation methods, and alternative media filtration processes. From that effort, several processes were selected for evaluation at the pilot scale: bleach (NaOCl) oxidation preceding electromedia filtration; manganese (IV) oxide (MnO2) filtration continuously regenerated with bleach; and ferrate (Fe(VI)) oxidation. Electromedia and MnO2 filtration were shown to be effective for total sulfide treatment. Both processes reduced total sulfide content to below detection levels (< 0.1 mg/L) for groundwater supplies containing as much as 2.6 mg/L of total sulfide. The use of bleach oxidation ahead of media filtration also produced finished water with low turbidity (< 1.0 NTU) as compared to conventional tray aeration and chlorination processes (6-16 NTU, as observed in this study). It was determined that the media filtration approach (electromedia and MnO2) was effective for sulfide treatment and met the County's site objectives established at the outset of the project. Ferrate was also shown to reduce total sulfide content to below detection levels (< 0.1 mg/L) for groundwater supplies containing as much as 2.6 mg/L of total sulfide. An opinion of probable capital costs for installing a sulfide oxidation/filtration process at either the Imperial Lakes or Turner Road WTP was estimated to range from roughly $830,000 to $1,100,000. That equates to a $/kgal capital cost of $0.10 to $0.32 (at 8% for 20 years). An opinion of annual probable bleach chemical costs was estimated to range from $3,500 to $9,800 for the IL WTP and $3,500 to $5,800 for the TR WTP.
M.S.Env.E.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Environmental Engr MSEnvE

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No presente estudo, foram sintetizadas ferritas sem dopagem (Fe2O3/Fe3O4) e ferritas dopadas com manganês (MnFe2O4(R)) a partir de reagentes comerciais, bem como (MnFe2O4(B)) a partir de manganês recuperado de pilhas de Zn-MnO2 exauridas. O cátodo de pilhas Zn-MnO2 utilizado é constituído principalmente por MnO2 e Mn3O4, de acordo com análises de difratometria de raios-X (DRX). Análise por espectrometria de emissão óptica com plasma indutivamente acoplado (ICP OES) detecta a presença de zinco advindo do ânodo das pilhas. O manganês do cátodo foi lixiviado com ácido nítrico 0.5 molL-1 e utilizado como dopante na síntese de ferritas MnFe2O4(B). Os materiais sintetizados apresentaram características de MnFe2O4, de acordo com a difratometria de raios-X (DRX). As ferritas foram caracterizadas por microscopia eletrônica de varredura (MEV) e microscopia eletrônica de transmissão (MET). Nas micrografias verificou-se que os materiais apresentaram partículas e aglomerados em escala nanométrica com geometria variada e irregular. Pela análise de espectrometria de energia dispersiva de raios-X (EDS) acoplada ao MEV pôde-se observar a composição das partículas da ferritas sintetizadas. Obteve os picos de Fe e O na amostra de Fe2O3/Fe3O4 e de Fe, Mn e O nas mostras de MnFe2O4(R) e MnFe2O4(B). A composição química das ferritas foi determinada por dicromatometria para ferro e espectrometria de absorção atômica de chama (F AAS) para manganês, sendo de 66,6 % de Fe para a Fe2O3/Fe3O4, 56,6 % de Fe e 11,5 % de Mn para MnFe2O4(R) e 61,5 % de Fe e 4,5 % de Mn para MnFe2O4(B). As ferritas foram avaliadas cataliticamente na descoloração do corante azul de metileno através do processo foto Fenton heterogêneo, obtendo-se 15,6 %, 98 % e 92 % de descoloração do corante usando Fe2O3/Fe3O4, MnFe2O4(R) e MnFe2O4(B) respectivamente, em 120 minutos de reação.

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

>Magister Scientiae - MSc
Lithium iron manganese phosphate (LiFe0.5Mn0.5PO4), is a promising, low cost and high energy density (700 Wh/kg) cathode material with high theoretical capacity and high operating voltage of 4.1 V vs. Li/Li+, which falls within the electrochemical stability window of conventional electrolyte solutions. However, a key problem prohibiting it from large scale commercialization is its severe capacity fading during cycling. The improvement of its electrochemical cycling stability is greatly attributed to the suppression of Jahn-Teller distortion at the surface of the LiFe0.5Mn0.5PO4 particles. Nanostructured materials offered advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. The LiFe0.5Mn0.5PO4 nanoparticles were synthesized via a simple-facile microwave method followed by coating with multi-walled carbon nanotubes (MWCNTs) nanoparticles to enhance electrical and thermal conductivity. The pristine LiFe0.5Mn0.5PO4 and LiFe0.5Mn0.5PO4-MWCNTs composite were examined using a combination of spectroscopic and microscopic techniques along with electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Microscopic results revealed that the LiFe0.5Mn0.5PO4-MWCNTs composite contains well crystallized particles and regular morphological structures with narrow size distributions. The composite cathode exhibits better reversibility and kinetics than the pristine LiFe0.5Mn0.5PO4 due to the presence of the conductive additives in the LiFe0.5Mn0.5PO4-MWCNTs composite. For the composite cathode, D = 2.0 x 10-9 cm2/s while for pristine LiFe0.5Mn0.5PO4 D = 4.81 x 10-10 cm2/s. The charge capacity and the discharge capacity for LiFe0.5Mn0.5PO4-MWCNTs composite were 259.9 mAh/g and 177.6 mAh/g, respectively, at 0.01 V/s. The corresponding values for pristine LiFe0.5Mn0.5PO4 were 115 mAh/g and 44.75 mAh/g, respectively. This was corroborated by EIS measurements. LiFe0.5Mn0.5PO4-MWCNTs composite showed to have better conductivity which corresponded to faster electron transfer and therefore better electrochemical performance than pristine LiFe0.5Mn0.5PO4. The composite cathode material (LiFe0.5Mn0.5PO4-MWCNTs) with improved electronic conductivity holds great promise for enhancing electrochemical performances and the suppression of the reductive decomposition of the electrolyte solution on the LiFe0.5Mn0.5PO4 surface. This study proposes an easy to scale-up and cost-effective technique for producing novel high-performance nanostructured LiFe0.5Mn0.5PO4 nano-powder cathode material.
2023-12-01

Des particules submicroniques de ferrites substituees par le molybdene et des ferrites mixtes de cobalt et de molybdene ont ete synthetisees par chimie douce. L'etude structurale de ces nouvelles phases spinelles, a permis de determiner leur repartition cationique ainsi que leur processus d'oxydation. Dans les phases stchiometriques, les ions molybdene, situes principalement en sites octaedriques, presentent les etats de valence +3 et +4. L'oxydation de ces phases conduit a l'apparition d'ions ferriques et d'ions molybdene +6. Les ferrites lacunaires, ainsi obtenus ont un taux de lacunes croissant avec la teneur en molybdene; il peut atteindre 0,77 par unite formulaire. La substitution des ions molybdene aux ions fer accroit la teneur des ions ferreux et, de ce fait, contribue a l'obtention de coercivites elevees. Par ailleurs les champs coercitifs des ferrites de cobalt et de molybdene sont maximaux lorsque la valence des cations du molybdene est elevee. La coercivite des echantillons oxydes peut etre exaltee (jusqu'a des valeurs proches de 4000oe) par un refroidissement lent depuis la temperature d'oxydation. Ce comportement est associe a l'etablissement de l'ordre directionnel. Les mesures des effets magneto-optiques de poudres de ferrites, ont permis de mettre en evidence deux compositions (cobalt/molybdene et cobalt/manganese) presentant des rotations faraday meilleures que celle du ferrite de cobalt. Nous n'avons pu toutefois elaborer, sous forme de couches minces, que le ferrite de cobalt et de manganese. Celui-ci se caracterise par une rotation faraday (26000degre/cm) et une carrure (0,75) de cycle magneto-optique deux fois plus importantes que celles du ferrite de cobalt. Les resultats des premiers tests d'ecriture statique, realises sur des structures verre/ferrite/reflecteur, ont revele d'importants signaux de lecture (superieurs a ceux de disques commerciaux). La sensibilite a l'ecriture reste toutefois faible pour permettre l'inscription de bits magneto-optiques dans des conditions standards d'ecriture

Le ferrite de cuivre en couche mince a ete elabore par pulverisation cathodique radiofrequence sous argon pur avec magnetron. Sa sensibilite a la teneur en oxygene de l'enceinte de pulverisation rend son elaboration delicate. Neanmoins, il presente apres un recuit de cristallisation une structure cristalline de symetrie quadratique (c/a > 1). Cette anisotropie de structure, associee a une forte anisotropie perpendiculaire, permet d'atteindre des champs coercitifs d'environ 1700 oe. La variation thermique du champ coercitif met en evidence la transition quadratique-cubique a 380c. Une rotation faraday maximale de 20000 degre/cm a 440 nm associee a une carrure de 0,8/0,9 revele un materiau a fortes potentialites pour l'enregistrement magneto-optique et magnetique. Les ferrites de manganese lacunaires mn#1#,#1#8fe#1#,#8#2o#4#+# en couche mince presentent egalement une deformation quadratique au terme d'un traitement d'oxydation faisant apparaitre une quantite importante d'ions manganese trivalents. Ces couches minces, constituees de cristallites de faibles dimensions (< 50 nm) presentent en effet une reactivite suffisante par rapport a l'oxygene pour faire apparaitre des phases lacunaires dont les proprietes magnetiques, magneto-optiques et electriques dependent fortement de leur etat d'oxydation. En vue de leur application a l'enregistrement magneto-optique, des ferrites ternaires de cuivre, cobalt et manganese a faibles temperatures de curie ont ete elaborees en couche mince. De structure cubique, ces films minces possedent des proprietes magneto-optiques interessantes a 650 nm et 1650 nm (respectivement 18000 et 22000 deg. /cm) dues a la presence de cobalt en sites tetraedriques. Par ailleurs, des proprietes semi-conductrices ont ete mises en evidence dans ces phase. Elles resultent de la presence de deux couples (cu#+/cu#2#+ et mn#3#+/mn#4#+) en sites octaedriques permettant la conduction electrique par sauts d'electrons.

Dissertação (mestrado)—Universidade de Brasília, Instituto de Física, 2011.
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Neste trabalho, investigamos as propriedades estruturais locais de fluidos magnéticos à base de nanopartículas de ferritas de manganês. Tais nanopartículas são obtidas durante a etapa de coprecipitação hidrotérmica e são dispersas em meio ácido graças à estratégia núcleo-superfície, o que impede que os nanogrãos sofram a ação corrosiva do ácido. Este tratamento modifica a composição química que pode ser descrita por um núcleo de ferrita estequiométrica e uma camada superficial de composição química γ-Fe2O3 num modelo “core-shell”. Dosagens químicas permitem determinar a fração volumétrica em nanopartículas assim como a espessura da camada superficial. A espectroscopia de absorção de raios x é utilizada para determinar o estado de oxidação médio do átomo absorvedor. Os resultados obtidos pela análise na região de XANES mostram a presença de íons Mn3+ e a presença destes induz distorções chamadas de efeito Jahn-Teller. Difração de raios x e de nêutrons é utilizada a fim de se obter informações sobre a estrutura local dos nanocristais, em particular a distribuição catiônica nos sítios intersticiais da estrutura espinélio. Os resultados apresentados indicam uma inversão catiônica diferente daquela encontrada para a ferrita maciça. O refinamento de Rietveld dos difratogramas de raios x e nêutrons é utilizado para determinar o tamanho médio e o parâmetro de malha das nanopartículas com qualidade e precisão. ______________________________________________________________________________ ABSTRACT
We investigate the local structure of magnetic fluids based on nanosized particles of manganese. These nanoparticles were obtained by soft chemistry method and they are dispersed thanks a core-shell strategy which prevents the acid attack. This treatment modifies the chemical composition of the particles and they can be described as a core of stoechiometric ferrite surrounded by a surface layer with a mean composition of maghemite γ-Fe2O3 in a “core-shell” strategy. Chemical titration allows us to determine the thickness of this surface layer. X-ray absorption spectroscopy is used to determine the mean oxidation state of the absorber atom. The results obtained by XANES analysis shows the presence of Mn3+ ions and such presence induces some distortions known by Jahn-Teller effect. X-ray and neutron diffractions were used to obtain information about the local structure of the nanosized particles, in particular the cation distribution. The results indicate an inversion degree that is different of the bulk ferrite. Rietveld refinement of the x-ray and neutron diffractograms is used to determine the size and lattice parameter with precision and quality.

Cette etude presente la mise au point de particules ferro ou ferrimagnetiques submicroniques dans le but d'ameliorer les performances a l'enregistrement magnetique haute densite (numerique). Tout d'abord, on a etudie les conditions de precipitations des precurseurs oxaliques a base de fer permettant d'obtenir des particules aciculaires dont les dimensions moyennes sont 0,2 mu m pour la longueur et 0,05 mu m pour le diametre. Par traitement thermique, on transforme ces precurseurs en ferrites lacunaires, en cherchant a obtenir des particules monocristallines monodomaines. En jouant sur l'anisotropie magnetocristalline grace a la substitution des ions fe**(3+) et des lacunes de gamma -fe::(2)o::(3) par des ions cobalt et du manganese, on a reussi a regler les proprietes magnetiques des particules (champ coercitif, aimantation remanente, aimantation saturation) de facon a les rendre compatibles avec les exigences de l'enregistrement magnetique haute densite

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Nanoparticles based on Mn-ferrite, Mn1−xAxFe2O4, doped with copper, magnesium and cobalt (A = Cu, Mg ou Co) were synthesized by hydrothermal method under pressure, with X varying from 0 to 0, 5. Magnetic fluids stable in physiological conditions were obtained surface-coating the nanoparticle with citric acid. X-ray diffraction confirmed the spinel structure. Energy dispersive spectroscopy (EDS) confirmed the success of the synthesis of the mixed ferrite, where the element composition agreed with the value expected within an error of 10%. Transmission electron microscopy showed sphericalshaped nanoparticles, while magnetization data at room temperature allowed the analysis of the coercivity field (Hc) and the saturation magnetization (Ms). Ms decreased with the increase of X for the Cu and Mg doped samples, while the opposite effect was observed for Co doped nanoparticles. Hc increased the higher the X value for all the samples. The effect on the Cu and Mg-doped ferrites are explained by the increase in particle size. However, the Co-doped samples, showed a diameter increasing the higher X, but Hc also increased. In this case the Hc behavior is explained by the increase concentration of Co and its effect on the magnetic anisotropy which increases for higher Co content. The magnetic hyperthermia efficiency of the magnetic fluids, for all samples, were investigated in a field amplitude ranging from 50 Oe to 170 Oe and frequencies from 110 kHz up to 990 kHz. The hyperthermia efficiency decreased with X increasing, considering the case of 130Oe and 333 kHz, which indicates that at this experimental condition undoped Mnferrite nanoparticles are better for hyperthermia. In most of the samples it was observed that the efficiency scaled with the square of the field amplitude, which is in accordance with Linear Response Theory (LRT). In addition, the hyperthermia frequency dependence study showed a saturation effect, for some samples, at a frequency higher than 600 kHz. The experimental data as function of frequency were susccessfully curve fitted with the LRT model using 2 free parameters related to the effective relaxation time ( ef ) and the equilibrium susceptibility ( 0). In particular, for theMn-ferrite sample for a field of 130Oe it is found ef = 5, 2 · 10−7s and 0 = 0, 028. The value of ef can be explained using an effective magnetic anisotropy value of 2·105 erg/cm3. The value is one order of magnitude higher than the bulk value, and allowed one to estimate the surface anisotropy contribution to in the order of 0, 04 erg/cm2. On the other hand, a linear chain formation model, for this sample consisted of a trimer (3 nanoparticles), can also explain the increase of the effective anisotropy. Moreover, we found a 0 value lower than the estimated Langevin susceptibility. In order to explain this, a new model, valid in the linear regime, was developed considering the contribution from blocked nanoparticles. Indeed, the analysis of hyperthermia data using this model indicates that the contribution to heat generation spans from 34.7% of the nanoparticles for a field of 110 Oe up to 52.5% at 170 Oe.
Nanopartículas à base de ferrita de Mn, Mn1−xAxFe2O4, dopadas com cobre, magnésio ou cobalto (A = Cu, Mg ou Co) foram sintetizadas pelo método hidrotermal sob pressão, com X variando de 0 até 0, 5. Posteriormente, fluidos magnéticos estáveis em pH fisiológico foram obtidos recobrindo a superfície das nanopartículas com ácidocítrico. A caracterização estrutural por raios-X confirmou a fase cristalina do tipo espinélio. A técnica de espectroscopia de energia dispersiva confirmou o sucesso da síntese de ferrita mista, quanto a sua composição, com um erro de até 10%. Microscopia eletrônica de transmissão revelou formação de nanopartículas esféricas, enquanto medidas de magnetização a temperatura ambiente permitiram uma análise do campo coercitivo (Hc) e da magnetização de saturação (Ms). Ms caiu com aumento de X para amostras dopadas com Cu e Mg, enquanto o oposto foi observado para Co. O Hc cresceu com o aumento de X para todas as amostras. Para as amostras dopadas com Cu e Mg tal efeito é explicado pelo aumento do diâmetro das nanopartículas. No caso das amostras dopadas com Co, o diâmetro caiu com X crescendo, mas Hc aumentou. Neste caso o comportamento do Hc é explicado pela maior contribuição a anisotropia magnética aumentando a proporção de Co na ferrita. A eficiência da hipertermia magnética (EHM) dos fluidos magnéticos, de todas as amostras, foi avaliada numa faixa de amplitude de campo de 50 Oe à 170 Oe para frequências variando entre 110 kHz à 990 kHz. A EHM caiu com X aumentando para H0 = 130 Oe e f = 333 kHz, o que indica, nesta condição experimental, que a ferrita de Mn é a amostra mais eficiente para hipertermia. A maior parte das amostras apresentou um EHM escalando com o quadrado da amplitude de campo magnético, em concordância com o esperado pela Teoria do Regime Linear (TRL). O estudo da EHM em função da frequência (f) revelou que algumas amostras apresentam saturação para f > 600 kHz. Os dados experimentais de hipertermia em função da frequência foram ajustados com sucesso, para todas as amostras, usando apenas 2 parâmetros livres relacionados ao tempo de relaxação efetivo ( ef ) e a susceptibilidade de equilíbrio ( 0). Em particular, para a amostra de ferrita de Mn e H0 = 130 Oe encontramos ef = 5, 2 · 10−7 s e 0 = 0, 028. O valor obtido para ef pode ser explicado para uma anisotropia magnética efetiva com 2 · 105 erg/cm3. Este valor é uma ordem de grandeza maior que o do bulk, e permite estimar uma anisotropia de superfície da ordem de 0, 037 erg/cm2. Por outro lado, a formação de cadeias lineares, contendo 3 partículas, também é capaz de explicar o aumento da anisotropia. O valor encontrado para 0 é menor que aquele estimado para a susceptibilidade de Langevin. Para explicar tal resultado, um novo modelo, válido no regime linear, foi desenvolvido considerando a contribuição de partículas bloqueadas. Neste caso, foi possível estimar, pela análise da EHM em função da frequência, que a fração de partículas contribuindo para a geração de calor sobe de 34, 7% em H0 = 110 Oe para 52, 5% em 170 Oe.

Les relations structure-proprietes au sein de fines particules et de couches minces de ferrites spinelles lacunaires cobalt-manganese sont etudiees en vue de l'application de ces materiaux a l'enregistrement magneto-optique. Dans les particules acidulaires submicroniques, les ions du manganese initialement au degre d'oxydation +3, dans les sites octaedriques, peuvent etre oxydes partiellement. Les ions cobalt a l'etat de valence +2, peuvent etre situes dans les deux types de sites. Les proprietes magnetiques et magneto-optiques dependent de la composition, et des traitements thermiques qui modifient le degre d'oxydation, la coordinence des cations et leur rearrangement a courte distance (ordre directionnel). Ces phenomenes se traduisent par un accroissement du champ coercitif. La microstructure des couches minces, deposees par pulverisation cathodique radio-frequence de cibles de ferrite, est caracterisee par des cristallites de faible dimension. La reactivite des films est semblable a celle revelee dans les particules. Les traitements thermiques analogues a ceux effectues sur les poudres, ont permis la creation d'un ordre directionnel pour la premiere fois dans les films. Ces rearrangements cationiques locaux ne semblent pas modifier la rotation magneto-optique. Lorsque la teneur en manganese augmente, une decroissance de l'effet faraday est observee a 780 et 630 nm. En raison de l'analogie du comportement physico-chimique des ferrites sous leurs deux formes macroscopiques la methode de mesure de l'effet faraday de poudres, de differentes compositions, permet d'estimer par avance les performances magneto-optiques des films

La proteine fur (ferric uptake regulation), homodimere de 2 fois 17 kda, est impliquee dans le controle de la concentration intracellulaire du fer chez les bacteries gram negative telle que escherichia coli. Ce controle est essentiel car, bien que necessaire a la croissance de pratiquement toutes les cellules, le fer est aussi un element potentiellement toxique puisqu'il peut catalyser la formation de radicaux libres. Un mecanisme est propose selon lequel fur lie l'ion fe(ii) et, ainsi activee, peut se fixer sur la region promotrice de genes impliques dans le transport du fer, inhibant de ce fait la transcription. La presence du metal est essentielle a l'activite. In vitro, plusieurs cations divalents comme mn(ii) ou co(ii) peuvent remplacer fe(ii) pour conduire a la fixation specifique de fur sur l'adn. Toutefois, la stoechiometrie metal/monomere et l'environnement du metal n'ont pas ete jusque la clairement identifies. Notre objectif est de caracteriser les sites metalliques de la proteine et d'identifier les ligands du metal. Pour cela les proteines fur substituees au manganese et au cobalt ont ete preparees et etudiees par plusieurs techniques spectroscopiques et magnetiques, chaque metal representant une sonde structurale interessante grace a ses proprietes spectroscopiques. L'incorporation du metal, suivie par spectroscopie d'absorption electronique pour le co(ii) et rpe a temperature ambiante pour le mn(ii), a permis de montrer la presence d'un site metallique principal par monomere. La rpe et les mesures d'aimantation montrent que l'ion metallique est present a l'etat haut spin dans un environnement hexacoordonne deforme pour l'ion co(ii) (s = 3/2) et peu ou pas deforme dans le cas de l'ion mn(ii) (s = 5/2). Un site secondaire a zinc de type structural a egalement ete caracterise par ailleurs. Les experiences rmn de la forme co(ii)-fur ont permis d'identifier les protons n-h echangeables d'histidines et egalement des signaux correspondant a des protons ch#2 de ligands carboxylates. Au moins deux histidines (peut-etre trois) et au moins un aspartate ou glutamate sont ligands, la sphere de coordination est complete par des atomes n/o mais il n'y a pas de cysteine ligand du cobalt.

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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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

Water from Mantua reservoir has, during some years, exhibited reddish-brown staining when used by Brigham City for irrigation. I propose that seasonal fluctuations in the reservoir chemistry create an environment conducive to dissolving iron from the iron-rich sediments, which subsequently precipitate during irrigation, resulting in a staining event. These conditions are produced by chemical and biological decomposition of organic matter, coupled with isolation of the hypolimnetic waters, which results in seasonal low concentrations of dissolved oxygen in these waters. Under these specific circumstances, anaerobic conditions develop creating a geochemical environment that causes iron and manganese reduction from Fe(III) to Fe(II) and Mn(IV) to Mn(II), respectively. These reducing conditions facilitate reduction-oxidation (redox) chemical reactions that convert insoluble forms of iron and manganese found in the reservoir sediments into more soluble forms. Consequently, relatively high amounts of dissolved iron and manganese are generated in the bottom waters immediately adjacent to the benthic sediments of the reservoir. Water withdrawn from a bottom intake pipe during these periods introduces iron-rich water into the distribution system. When this water is exposed to oxygen, reoxidation shifts redox equilibrium causing precipitation of soluble Fe(II) and Mn(III) back to highly insoluble Fe(III) and Mn(IV). The precipitant appears on contact surfaces as the aforementioned ferric stain. This research focuses specifically on the iron chemistry involved and evaluates this hypothesis using various measurements and models including field data collection, computer simulations, and bench-scale testing to validate the processes proposed.

This thesis aims to provide adequate analytical information on the spade shaped iron bars of Norrland and central Sweden. While their significance has been thoroughly debated for decades, analytical research on them has been confined to cases of single artefacts or theoretical interpretations of their value, meaning and origin. In this study a comprehensive approach is taken into consideration. Based on X-Ray fluorescence (XRF), scanning electron microscopy (SEM) and metallographical analysis this thesis seeks to facilitate new interpretations on quality, production centres and usage based on analytical results. Aiming to settle some of the long lasting questions regarding the artefacts while producing results which can further the discussion by raising new questions, previously unasked.

碩士
大同大學
材料工程研究所
89
In order to enhance the application properties of Mn-Zn ferrite, the improvement of its high permeability and low power loss are needed. Although,magnetic properties are highly influenced by the process of sintering and the variation of chemical composition. The could be enhanced with several ways included control proper grain size, avoid the formation of pores in the grains, decrease the temperature sensitivity, and etc. This is the main cause in order to have high permeability Mn-Zn ferrite. The composition of Mn-Zn ferrite in this study is formed with the molar ratio Fe2O3:MnO:ZnO=52.5:24.5:23.The initial permeability is from 3200 to 11599,depends on sintering processing.The magnetic properties are enhanced under the control of proper sintering atmosphere and the initial permeability could be reached from 9000 to 20000. The additive of CaCO3 is doped to improve the magnetic properties at higher frequency.

碩士
國立中興大學
化學系所
104
Abstract Analysis of biological samples frequently has accompanied with the complex matrices that impacts the identification and quantification of biological analytes. Therefore, a powerful mass spectrometry-based tool for research is necessary, due to its high sensitivity and high selectivity. Protein phosphorylation is one of the most important post-transitional modifications (PTMs), which plays a key role in the regulation of many cellular processes, such as phosphorylation enzymes, kinase and phosphatase are critical in the modulation of cellular transduction pathway. Over the past decade, the investigation of protein phosphorylation have been one of most popular research topics. However, the major challenges for phosphoproteomic analysis include the low abundance of phosphoproteins in biological samples and the ion suppression of phosphopeptide signals due to the large amount of non-phosphoryated peptides. For this reason, a sensitive and selective pretreatment method is essential for the facile and rapid analysis of protein phosphorylation. In this study, MnFe2O4 magnetic nanoparticles (MNPs) were synthesized by using one-pot hydrothermal method for the rapid and selective enrichment of phosphorylated peptides. MnFe2O4 MNPs possessed high selectivity and high selectivity for the isolation of phosphopeptides based on chelation interaction. The phosphopeptides derived from ultralow concentration β-casein (500 attomol) could be captured with MnFe¬2O4 MNPs and even in a mixture of BSA peptides and β-casein peptides mixture at molar ratio 10:1, the phosphopeptides were still isolated as well. The bind capacity and recovery for this method are 3.6 μg/mg (amount of proteins/amount of MNPs) and over 85%, respectively. To demonstrate the performance of MnFe2O4 MNPs, tryptic digests of milk, human serum and total cell lysate were employed as the complex mixture. We successful enriched 18 phosphopeptides from milk, and identified 3 endogenous phosphopeptides from human serum, 1331 phosphopeptides from total cell lysate as well. The workflow for the enrichment is similar to solid phase extraction (SPE) but the procedure is more convenient than traditional SPE. In brief, strong points of MnFe2O¬4 MNPs are the facile fabrication, durable and inexpensiveness, and possess high sensitivity and high specificity for the isolation of low concentration of phosphopeptides from the complex biological samples.

Τα δομικά χαρακτηριστικά των μαγνητικών κολλοειδών με βάση το οξείδιο του σιδήρου είναι ιδιαίτερα σημαντικά κατά την χρήση τους σε βιοϊατρικές εφαρμογές όπως η απεικόνιση σε μαγνητικό τομογράφο (MRI), η μεταφορά φαρμάκων, η μαγνητική υπερθερμία και στόχευση. Ιδιαίτερα για την μαγνητική στόχευση, η αύξηση της μαγνήτισης κορεσμού των κολλοειδών είναι ιδιαίτερης σημασίας. Συνεπώς, η μελέτη της σχέσης δομής-ιδιοτήτων είναι απαραίτητη για την περαιτέρω βελτίωση της απόδοσης των εν λόγω συστημάτων στις προαναφερθείσες εφαρμογές. Με στόχο τη βελτίωση της μαγνήτισης κορεσμού αυτών των υλικών έχει μελετηθεί στο παρελθόν μια στρατηγική αντικατάστασης ενός ποσοστού ιόντων σιδήρου στη δομή του νανοκρυστάλλου με άλλα μεταλλικά ιόντα. Οι μελέτες αυτές έχουν δείξει πως αναλόγως της συνθετικής πορείας άλλοτε επιτυγχάνεται το επιθυμητό αποτέλεσμα και άλλοτε όχι. Σε αυτά τα πλαίσια, σκοπός της παρούσας εργασίας ήταν η εφαρμογή αυτής της στρατηγικής σε μία συνθετική πορεία ανάπτυξης μαγνητικών νανοκολλοειδών στην οποία δεν έχει εκτιμηθεί μέχρι τώρα η επιτυχία της. Το ενδιαφέρον έγκειται στο γεγονός ότι η συγκεκριμένη συνθετική πορεία οδηγεί σε νανοκρυσταλλίτες οξειδίου του σιδήρου με αυξημένες μαγνητικές ιδιότητες σε σχέση με τη βιβλιογραφία, οι οποίες θα μπορούσαν (πιθανώς) να βελτιωθούν ακόμα περισσότερο με μερική ιοντική αντικατάσταση. Τα νανοκολλοειδή παρασκευάστηκαν με την μέθοδο της υδρολυτικής αλκαλικής καταβύθισης από μία πρόδρομη ένωση σιδήρου (FeCl2 ή FeSO4), με προσμίξεις διαφόρων αναλογιών με Zn(Cl2/SO4) ή Mn(Cl2/SO4). Η χημική τροποποίηση της επιφάνειας των μαγνητικών νανοκολλοειδών έγινε με στοχευμένη προσθήκη του φυσικού βιοπολυμερούς του αλγινικού νατρίου κατά τη διαδικασία κρυστάλλωσης του ανόργανου μαγνητικού πυρήνα. Η μελέτη των φυσικοχημικών χαρακτηριστικών και της δομής των νανοφορέων πραγματοποιήθηκε με την χρήση των παρακάτω αναλυτικών τεχνικών: Ηλεκτρονική Μικροσκοπία Σάρωσης (SEM) σε συνδυασμό με Φασματομετρία Ενεργειακής Διασποράς Ακτινοβολίας-X (EDS), Περίθλαση Ακτινοβολίας-X (XRD), Θερμοσταθμική Ανάλυση (TGA), Δυναμική Σκέδαση Φωτός (DLS), Ηλεκτροκινητικές Μετρήσεις, Μαγνητομετρία Δονούμενου Δείγματος (VSM), Μαγνητοφόρηση και Μαγνητική Υπερθερμία Δείγματος.
Structural characteristics of magnetic ferrite nanocolloids are particularly important in biomedical applications such as magnetic resonance imaging (MRI), drug delivery, magnetic hyperthermia and targeting. Particularly about magnetic targeting, increasing saturation magnetization is crucial. Therefore, studying the structure-properties relation of colloids is necessary, in order to improve further the performance of these systems in the above applications. In order to enhance the saturation magnetization of those materials, substitution of a percentage of iron ions in the structure of the nanocrystal with other metal ions has been previously studied. Results have shown that the desired properties are obtained under certain circumstances, depending on the synthetic route. Within this frame, the goal of the present work is to test this strategy on a synthetic route which has not been so far evaluated. The interest lies in the fact that this synthetic route leads to iron oxide nanocrystallites with increased magnetic properties compared to the literature, which could (possibly) be further improved with partial ionic replacement. Nanocolloids were synthesized by hydrolytic alkaline precipitation from a single iron molecular precursor (FeCl2 or FeSO4), doped at different ratios with Zn(Cl2/SO4) or Mn(Cl2/SO4). The surface modification of the magnetic nanocolloids was performed by in-situ grafting of the natural biopolymer of sodium alginate, during the crystallization process of the inorganic magnetic core. The evaluation of the structural, magnetic and physicochemical characteristics of the nanocarriers was performed with the use of the following analytical techniques: Scanning Electron Microscopy (SEM) in conjunction with Energy-Dispersive X-Ray Spectrometry (EDS), X-Ray Diffraction (XRD), Thermal Gravimetric Analysis (TGA), Dynamic Light Scattering (DLS), Electrokinetic Measurements, Vibrating Sample Magnetometer (VSM), Magnetophoresis and Magnetic Hyperthermia of the Sample.

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.

碩士
中國文化大學
化學工程與材料工程學系奈米材料碩士班
104
Mn0.1Mg0.9CrxFe2-xO4 (x=0, 0.1, 0.2, 0.3, and 0.5) ceramics have been synthesized with the solid state method to study the frequency and temperature dependent of the Neel relaxation behavior in these compounds. All un-dopant and Cr-doping samples were formed spinel cubic structure, which has been checked by powder X-ray diffraction. The OM images in the Mg-Mn ferrite samples are shown that the grain size is increasing with sintering temperature increasing, but decreasing with Chromium concentration increasing. The grain size has been counted by the intercept technique through the OM images. Room temperature AC magnetic susceptibility measurement is showed that all samples obey Neel magnetic relaxation behavior. The real part of magnetic susceptibility is gradually decreasing around the magnetic resonance frequency and the imaginary part of magnetic susceptibility is appeared a broad magnetic resonance peak due to magnetic loss. Low temperatures AC magnetic susceptibility has been measured vary temperature, which was fitted the Debye relaxations model to calculate the resonance frequency (f0), and the magnetic anisotropy energy can be computed by the lnf0 versus reciprocal temperature plot. The maximum magnetic anisotropy energy of 1300oC sintering temperature samples is x=0.3, but the anisotropy energy is gradually decreasing with Cr doping level x increasing except x=0.2 and 0.3 samples. In this work, we reported that bulk or powder samples can measure the magnetic anisotropy energy by temperature dependent AC susceptibility method to compares with Magneto Optical Kerr Effect measurement, which is more convenient way to measure the magnetic anisotropy energy and doesn’t limit to thin films.

碩士
嘉南藥理科技大學
環境工程與科學系暨研究所
99
The synthesis of ferrate (FeO4-2) from field waste sludge using the wet oxidation process was investigated and evaluated. Ferrate as an oxidant is now being considered as one of the new powerful oxidizing and coagulating agent can be synthesized from Fe(III) under alkaline conditions. Simulated sludge was first synthesized using analytical grade FeCl3 and NaOH to yield Fe(OH)3. Nitric acid (HNO3) is used to leach out Fe (III) from Fe(OH)3 at different acid concentrations. The maximum amount of Fe (III) from the sample was obtained using 1.0 M HNO3. The impact of the presence manganese ions (Mn+2), manganese oxide (MnO2) and Fe2O3 is also evaluated by injecting a known amount of the three substances to the simulated sludge sample. Results showed that the presence of MnO2 significantly enhance the yield of ferrate and no significant effect was observed in ferrate yield in the presence of Mn+2 ions.In addition,no significant improvement on ferrate yield was observed in the presence of Fe2O3. Experiments on actual field waste sludge for the synthesis of ferrate showed a higher ferrate yield compare to the simulated sludge.The increased yield of ferrate from actual waste sludge can be attributed to the presence of other substance,such as Mn oxide and hydroxide.

碩士
國立中正大學
化學工程研究所
99
In this study, MnO2-carbon black-Fe2O3 supercapacitors were prepared by electrochemical deposition method and the impregnation method. The supercapacitors were examined capacitance and cycle stability by electrochemical methods. Crystal structure and surface morphology of the deposited oxide were examined by XRD and SEM. The results showed that capacitance was higher 13~20% by impregnation method than electrochemical deposition method and the capacitance can reach 317.4F/g. Because using impregnation method, the carbon black will assemble spherical carbon black on surface. Then the spherical carbon black specific surface area is higher than flat, so the capacitance will be higher. As for cycle stability, the stability can reach 89.0% by impregnation method, reach 70~80% by co-deposition Fe2O3-MnO2-carbon black, and reach 75.1% by co-deposition MnO2-carbon black. The cycle stability is better by impregnation method than the others because the capacitance made by impregnation method have higher capacitance which produces more active sites to react. All of the results reveal disordered peaks when analyzing the supercapacitors made by three different methods with XRD, the grain size is about 21.8~22.9nm by impregnation method, 26.8nm by co-deposition of Fe2O3-MnO2-carbon black, and 28.5nm by co-deposition of MnO2-carbon black. It is found that capacitance become larger, grain size become smaller. Besides, the morphology is also observed. It’s clear to see MnO2 in lines or Fe2O3 particles on the face of the supercapacitors by co-deposition. The specific surface area of the supercapacitors is smaller by electrochemical deposition than by the impregnation method which makes carbon black in spherical shape. The phenomenon can confirm results in previous.

碩士
國立成功大學
化學工程學系
107
This study reports that the Lewis acid-base properties of peroskite-type LaMnO3 and LaFeO3 can be adjusted by immobilizing them on silica. Bulk LaMnO3 and LaFeO3 were strong base catalyst due to unsaturated-coordinated oxygen on the surface, While, after supported them on silica, the basic properties of bulk materials were diluted and simultaneously acidities improved due to the increased amounts of tetravalent B-site cations. Ethanol reactivity was performed to reflect the different acid-base properties of bulk and silica-supported LaMnO3 and LaFeO3. Under differential analysis conditions, bulk perovskites were active in base-catalyzed reactions such as reverse aldolization and Tishchenko reaction, while silica-supported perovskites were active in aldolization and dehydration. We also notice the higher aldolization activity over LaMnO3/SiO2 than that of LaFeO3/SiO2, the different activity was attributed to existence of excess mobile oxygen on the surface of LaMnO3/SiO2, forming aldolization-active Lewis acid (Mn4+)-base (nonstoichiometric oxygen) pair sites while these sites were absent in LaFeO3/SiO2 which was enriched with oxygen vacancies.

This thesis presents the results of investigations of the synthesis, structure and physical properties of multiferroic materials. Multiferroics are materials in which two or all three of ferroelectricity, ferromagnetism and ferroelasticity occur in the same phase. Such materials have the potential applications of their parent materials, as well as new ones because of the interaction between the order parameters. The thesis is organized into four sections. Section 1 gives an overview of multiferroics, explaining the origin of mul-tiferroicity , occurrence of magnetoelectric coupling, their possible technological ap-plications and the challenges involved. Section 2 gives the scope of the investigations. The specific objectives of the present research on yttrium chromite, heavy rare earth chromites, solid solutions of yttrium chromite, rare earth manganites doped with alkaline earth metals, charge-ordered rare earth ferrites and indium manganite are outlined. Experimental aspects of the work carried out are discussed in section 3. It gives details of the experimental set up and the basic operation principles of various structural and physical characterizations of the materials prepared. In section 4, results of the investigations are discussed. Magnetic and di-electric properties of yttrium chromite (YCrO3), heavy rare earth chromites and YCr1-xMnxO3 are reported in section 4.1. These materials show canted antiferro-magnetic behavior below the Nel transition temperatures and dielectric transitions at high temperatures. Role of local non-centrosymmetry is discussed based on high-resolution neutron powder diffraction data. In 4.2 we discuss the results of charge-ordered rare earth ferrites which show good magnetoelectric effect. Magnetic, dielectric and magneto-dielectric properties of YCr1-xMnxO3 (Ln = rare earth) are discussed in 4.3. These materials show magneto-dielectric effect. In 4.4 we discuss the near normal incidence far infrared reflectivity spectra of a single crystal of TbMnO3, in the spectral range of 50cm−1 to 700 cm−1 from 10 K to 300 K. Finally in 4.5, magnetic and dielectric properties of bulk and thin films of indium manganite are discussed.