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.

Bayer processing of bauxite employed for production of alumina yield a residue red-mud. The worldwide annual-rate of red-mud generation is approximately 120 million tons, and most of this is stockpiled. Red mud is rich in elements like aluminum, titanium and rare earths, in addition to the major iron-bearing constituents. The objective of this research is to explore such a strategy to extract Iron as fine particulate magnetite. Pyrometallurgical reduction experiments using carbon mixtures and a novel hydrometallurgical route are experimented. Reduction experiments performed with petroleum coke as a reductant resulted in incomplete reduction. The ‘optimal conditionsÂ’ for gaseous state reduction are determined to be: a processing temperature of 540oC ± 10oC, partial pressures CO (g) and CO2 (g) each of 0.070atm (bar) ± 0.001atm.(bar)/ inert diluent-gas: N2 (g), for a conversion-time of 30min. A mathematical-model was developed on the basis of unidirectional-diffusion of CO2 (g) within the CO2 (g)–CO (g)–N2 (g) gas-phase of the porous product-layer. Magnetic separation applied to the optimally reduced sample in: obtaining a magnetic portion with high iron and non-magnetic portion containing nonferrous (Al, Ti) is not successful. This finding was subsequently attributed to the nanometer length-scales crystallites of the predominant iron-containing phase, hydrated ferric-oxide(s) as determined by STEM micrographs. In addition, the presence of substitution for Fe3+ by Al3+ and Ti3+/4+ are determined with the help of MÖssbauer spectrograms. A hydrometallurgical route involving selective leaching and precipitation of iron in red-mud is tried. Red-mud is leached in oxalic acid at: 95˚C, 15 % Pulp density, 2.5 h leaching time, 1.5 pH. Kinetic studies yielded the leaching mechanism to be predominantly fluid film control. Ferric oxalate in the leach liquor is reduced to insoluble ferrous oxalate selectively using Iron powder. The ferrous oxalate formed is ~98 % pure. The precipitated ferrous oxalate is magnetically separated and reduced in Nitrogen atmosphere to form fine particulate magnetite. Additionally an economic feasibility study was conducted for the hydro and pyro alternatives to produce magnetite using Monte Carlo Simulations by imparting uncertainties in various input cost components. A traditional process was also compared to the proposed approaches for Total Capital Investment (TCI), Total Product Cost (TPC), Net Present Value (NPV) and sensitivity analysis. ~52 % reduction in Total product cost, 46 % reduction in Total Capital Investment was achieved for the hydrometallurgical process when compared to the traditional approach.

Este trabalho descreve o estudo da geração eletroquímica do H2O2 em eletrólito ácido (H2SO4 (0,1 mol L-1) + K2SO4 (0,1 mol L-1)) e eletrólito alcalino (KOH 1,0 mol L-1) utilizando eletrodo de difusão gasosa (EDG), sendo este fabricado com carbono Printex 6L e modificado com 3,0; 5,0 e 10,0% de ftalocianina de cobalto (II) ou cobre (II). Os experimentos foram realizados em uma célula eletroquímica de compartimento único contendo eletrodo de referência Ag/AgCl, contra eletrodo de Pt e como eletrodo de trabalho foi utilizado o EDG. Nos testes de eletrólise a potencial constante (-0,4 V ≤ E ≤ -1,4 V) durante 90 minutos com O2 pressurizado a 0,2 Bar, a concentração de H2O2 alcançou valor máximo de 178 mg L-1 a - 1,0 V (vs. Ag/AgCl) para o EDG não modificado em eletrólito ácido e em eletrólito alcalino, o valor máximo foi de 3.370 mg L-1 a -1,1 V (vs. Ag/AgCl). Quando incorporada a porcentagem de 5,0% de ftalocianina de cobalto (II) à massa do EGD verificou-se que a concentração de H2O2 alcança valor máximo em 331 mg L-1 a -0,7 V (vs. Ag/AgCl), o que representa um aumento de 86,0% no rendimento da produção de H2O2 em meio ácido, além de uma diminuição de 300 mV no potencial aplicado para formação da espécie oxidante. Para o estudo da degradação eletroquímica foram utilizados os corantes amaranto e tartrazina com concentração de 100 mg L-1. Para o estudo do processo eletro-Fenton homogêneo foram utilizados 0,05; 0,1 e 0,15 mmol de Fe2+ ou Fe3+ e para o processo eletro-Fenton heterogêneo em meio alcalino foi utilizado 0,15 mmol das nanopartículas do tipo Fe3-xCuxO4 (0 ≤ x ≤ 0,25). As eletrólises foram realizadas a potencial constante em -0,7 V (vs. Ag/AgCl) no EDG modificado com 5,0% de ftalocianina de cobalto (II) sob fluxo constante de O2 durante 90 minutos no processo eletro-Fenton homogêneo enquanto no processo eletro-Fenton heterogêneo o EDG não modificado foi utilizado e as eletrólises foram realizadas a -1,1 V (vs. Ag/AgCl). Todos os ensaios eletroquímicos foram realizados em um potenciostato PGSTAT- 302 acoplado a um com módulo de alta corrente BSTR-10A e controlado por meio do software GPES (Metrohm Autolab). As nanopartículas Fe3-xCuxO4 (0 ≤ x ≤ 0,25) foram caracterizadas por Análise de Ativação de Neutrons (AAN), DRX, BET, XPS e MET. As amostras dos corantes foram analisadas por espectrofotometria UV/Vis, cromatografia líquida de alta eficiência (CLAE) e teor de carbono orgânico total (COT). Em termos de descoloração, houve uma pequena diminuição no espectro dos corantes quando utilizado H2O2 eletrogerado em meio ácido o que não ocorre na degradação quando utilizado o processo eletro-Fenton homogêneo sendo mais evidente quando utilizado Fe2+, alcançando uma descoloração máxima de 80,0 e 99,2% respectivamente para os corantes amaranto e tartrazina. O decaimento da concentração por CLAE foi bastante eficiente quando utilizado o processo eletro-Fenton, com melhores resultados para Fe2+ e Fe3-xCuxO4 (x= 0,25) sendo a cinética dos processos de pseudo-primeira ordem. Foram identificados os subprodutos formados durante a degradação dos corantes durante o processo eletro-Fenton homogêneo. Os maiores valores de remoção de COT (67,3%) e consumo energético (CE) (370 kwh kg-1 foram obtidos para o processo utilizando íons Fe2+ e as nanopartículas Fe3-xCuxO4 (x=0,25) respectivamente para o corante amaranto. Os valores da concentração de ferro residual solúvel estão dentro do limite permitido segundo a Resolução CONAMA nº 430/2011. Para o processo eletro-Fenton heterogêneo, a concentração de H2O2 residual e consumida diminuiu e aumentou respectivamente com o aumento do valor de \"x\" na espinela da Fe3-xCuxO4 (0 ≤ x ≤ 0,25). / This work describes the electrogeneration of H2O2 study in acidic medium (H2SO4 (0.1 mol L-1) + K2SO4 (0.1 mol L-1)) and alkaline medium (KOH 1.0 mol L-1) using gas diffusion electrode (GDE), being these GDE manufactured with the Printex 6L carbon and modified with percentages of 3.0, 5.0 and 10.0% of cobalt (II) phthalocyanine or copper (II) phthalocyanine. The experiments were performed in an electrochemical cell single compartment containing the reference electrode Ag/AgCl, platinum counter electrode and the working electrode was used the GDE. In tests electrolysis at constant potential (-0.4 V ≤ E ≤ - 1.4 V) for 90 minutes pressurized with O2 at 0.2 Bar, H2O2 concentration reached a maximum value at 178 mg L-1 to -1.0 V (vs. Ag/AgCl) for GDE unmodified in acid electrolyte and alkaline electrolyte, the maximum value was 3,370 mg L-1 at potential -1.1 V (vs. Ag/AgCl).When incorporated percentage of 5.0% of cobalt (II) phthalocyanine to mass GDE, it is verified that the concentration of H2O2 reaches maximum value at 331 mg L-1 at -0.7 V (vs. Ag/AgCl), which represents increase in yield of 86.0% relative to Printex 6L carbon in acidic medium, addition to a decrease of 300 mV at potential applied to the formation of oxidizing species. To study the electrochemical degradation were amaranth and tartrazine dyes with concentration of 100 mg L-1. To study the homogeneous electro-Fenton process were used 0.05; 0.1 e 0.15 mmol de Fe2+ or Fe3+ and to heterogeneous electro-Fenton process in alkaline medium was used 0.15 mmol of Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles. The electrolysis were performed at constant potential -0.7 V (vs. Ag/AgCl) in the GDE modified with 5.0% of cobalt (II) phthalocyanine under constant flow of O2 for 90 minutes in the homogeneous electro-Fenton process while in the heterogeneous electro-Fenton process, GDE unmodified was used and the electrolysis were performed at -1.1 V (vs. Ag/AgCl). All electrochemical tests were performed using a potentiostat/galvanostat model PGSTAT 302 coupled to a BSTR-10A current booster and controlled by GPES software (Metrohm Autolab). The Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles were characterized by Neutron Activation Analysis (NAA), XRD, BET, XPS and TEM. The samples of the dyes were analyzed by spectrophotometry UV/Vis, high performance liquid chromatography (HPLC) and total organic carbon (TOC). In terms of discoloration, was a small decrease in the spectrum of the dye when used H2O2 in acidic medium which doesn\'t occur in the degradation when used homogeneous electro-Fenton process being more evident when used Fe2+, reaching a maximum discoloration of 80.0 and 99.2% respectively for amaranth and tartrazine dyes. The decay concentration by HPLC was very efficient when using the electro-Fenton process with better results for Fe2+ and Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles being the kinetics of the process of pseudo-first order. Were identified by-products formed during the degradation of dyes during the homogeneous electro-Fenton process. The higher values of TOC removal (67.3%) and energy consumption (EC) (370 kWh kg-1) were obtained to process using Fe2+ ions and Fe3-xCuxO4 (x= 0.25) nanoparticle respectively for amaranth dye. The values of residual soluble iron concentrations are within the permissible limit according to CONAMA Resolution nº 430/2011. To the heterogeneous electro-Fenton process, the residual and consumed concentration of H2O2 decreased and increased respectively with increasing value of \"x\" in the spinel of Fe3-xCuxO4 (0 ≤ x ≤ 0.25).

Este trabalho descreve o estudo da geração eletroquímica do H2O2 em eletrólito ácido (H2SO4 (0,1 mol L-1) + K2SO4 (0,1 mol L-1)) e eletrólito alcalino (KOH 1,0 mol L-1) utilizando eletrodo de difusão gasosa (EDG), sendo este fabricado com carbono Printex 6L e modificado com 3,0; 5,0 e 10,0% de ftalocianina de cobalto (II) ou cobre (II). Os experimentos foram realizados em uma célula eletroquímica de compartimento único contendo eletrodo de referência Ag/AgCl, contra eletrodo de Pt e como eletrodo de trabalho foi utilizado o EDG. Nos testes de eletrólise a potencial constante (-0,4 V ≤ E ≤ -1,4 V) durante 90 minutos com O2 pressurizado a 0,2 Bar, a concentração de H2O2 alcançou valor máximo de 178 mg L-1 a - 1,0 V (vs. Ag/AgCl) para o EDG não modificado em eletrólito ácido e em eletrólito alcalino, o valor máximo foi de 3.370 mg L-1 a -1,1 V (vs. Ag/AgCl). Quando incorporada a porcentagem de 5,0% de ftalocianina de cobalto (II) à massa do EGD verificou-se que a concentração de H2O2 alcança valor máximo em 331 mg L-1 a -0,7 V (vs. Ag/AgCl), o que representa um aumento de 86,0% no rendimento da produção de H2O2 em meio ácido, além de uma diminuição de 300 mV no potencial aplicado para formação da espécie oxidante. Para o estudo da degradação eletroquímica foram utilizados os corantes amaranto e tartrazina com concentração de 100 mg L-1. Para o estudo do processo eletro-Fenton homogêneo foram utilizados 0,05; 0,1 e 0,15 mmol de Fe2+ ou Fe3+ e para o processo eletro-Fenton heterogêneo em meio alcalino foi utilizado 0,15 mmol das nanopartículas do tipo Fe3-xCuxO4 (0 ≤ x ≤ 0,25). As eletrólises foram realizadas a potencial constante em -0,7 V (vs. Ag/AgCl) no EDG modificado com 5,0% de ftalocianina de cobalto (II) sob fluxo constante de O2 durante 90 minutos no processo eletro-Fenton homogêneo enquanto no processo eletro-Fenton heterogêneo o EDG não modificado foi utilizado e as eletrólises foram realizadas a -1,1 V (vs. Ag/AgCl). Todos os ensaios eletroquímicos foram realizados em um potenciostato PGSTAT- 302 acoplado a um com módulo de alta corrente BSTR-10A e controlado por meio do software GPES (Metrohm Autolab). As nanopartículas Fe3-xCuxO4 (0 ≤ x ≤ 0,25) foram caracterizadas por Análise de Ativação de Neutrons (AAN), DRX, BET, XPS e MET. As amostras dos corantes foram analisadas por espectrofotometria UV/Vis, cromatografia líquida de alta eficiência (CLAE) e teor de carbono orgânico total (COT). Em termos de descoloração, houve uma pequena diminuição no espectro dos corantes quando utilizado H2O2 eletrogerado em meio ácido o que não ocorre na degradação quando utilizado o processo eletro-Fenton homogêneo sendo mais evidente quando utilizado Fe2+, alcançando uma descoloração máxima de 80,0 e 99,2% respectivamente para os corantes amaranto e tartrazina. O decaimento da concentração por CLAE foi bastante eficiente quando utilizado o processo eletro-Fenton, com melhores resultados para Fe2+ e Fe3-xCuxO4 (x= 0,25) sendo a cinética dos processos de pseudo-primeira ordem. Foram identificados os subprodutos formados durante a degradação dos corantes durante o processo eletro-Fenton homogêneo. Os maiores valores de remoção de COT (67,3%) e consumo energético (CE) (370 kwh kg-1 foram obtidos para o processo utilizando íons Fe2+ e as nanopartículas Fe3-xCuxO4 (x=0,25) respectivamente para o corante amaranto. Os valores da concentração de ferro residual solúvel estão dentro do limite permitido segundo a Resolução CONAMA nº 430/2011. Para o processo eletro-Fenton heterogêneo, a concentração de H2O2 residual e consumida diminuiu e aumentou respectivamente com o aumento do valor de \"x\" na espinela da Fe3-xCuxO4 (0 ≤ x ≤ 0,25). / This work describes the electrogeneration of H2O2 study in acidic medium (H2SO4 (0.1 mol L-1) + K2SO4 (0.1 mol L-1)) and alkaline medium (KOH 1.0 mol L-1) using gas diffusion electrode (GDE), being these GDE manufactured with the Printex 6L carbon and modified with percentages of 3.0, 5.0 and 10.0% of cobalt (II) phthalocyanine or copper (II) phthalocyanine. The experiments were performed in an electrochemical cell single compartment containing the reference electrode Ag/AgCl, platinum counter electrode and the working electrode was used the GDE. In tests electrolysis at constant potential (-0.4 V ≤ E ≤ - 1.4 V) for 90 minutes pressurized with O2 at 0.2 Bar, H2O2 concentration reached a maximum value at 178 mg L-1 to -1.0 V (vs. Ag/AgCl) for GDE unmodified in acid electrolyte and alkaline electrolyte, the maximum value was 3,370 mg L-1 at potential -1.1 V (vs. Ag/AgCl).When incorporated percentage of 5.0% of cobalt (II) phthalocyanine to mass GDE, it is verified that the concentration of H2O2 reaches maximum value at 331 mg L-1 at -0.7 V (vs. Ag/AgCl), which represents increase in yield of 86.0% relative to Printex 6L carbon in acidic medium, addition to a decrease of 300 mV at potential applied to the formation of oxidizing species. To study the electrochemical degradation were amaranth and tartrazine dyes with concentration of 100 mg L-1. To study the homogeneous electro-Fenton process were used 0.05; 0.1 e 0.15 mmol de Fe2+ or Fe3+ and to heterogeneous electro-Fenton process in alkaline medium was used 0.15 mmol of Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles. The electrolysis were performed at constant potential -0.7 V (vs. Ag/AgCl) in the GDE modified with 5.0% of cobalt (II) phthalocyanine under constant flow of O2 for 90 minutes in the homogeneous electro-Fenton process while in the heterogeneous electro-Fenton process, GDE unmodified was used and the electrolysis were performed at -1.1 V (vs. Ag/AgCl). All electrochemical tests were performed using a potentiostat/galvanostat model PGSTAT 302 coupled to a BSTR-10A current booster and controlled by GPES software (Metrohm Autolab). The Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles were characterized by Neutron Activation Analysis (NAA), XRD, BET, XPS and TEM. The samples of the dyes were analyzed by spectrophotometry UV/Vis, high performance liquid chromatography (HPLC) and total organic carbon (TOC). In terms of discoloration, was a small decrease in the spectrum of the dye when used H2O2 in acidic medium which doesn\'t occur in the degradation when used homogeneous electro-Fenton process being more evident when used Fe2+, reaching a maximum discoloration of 80.0 and 99.2% respectively for amaranth and tartrazine dyes. The decay concentration by HPLC was very efficient when using the electro-Fenton process with better results for Fe2+ and Fe3-xCuxO4 (0 ≤ x ≤ 0.25) nanoparticles being the kinetics of the process of pseudo-first order. Were identified by-products formed during the degradation of dyes during the homogeneous electro-Fenton process. The higher values of TOC removal (67.3%) and energy consumption (EC) (370 kWh kg-1) were obtained to process using Fe2+ ions and Fe3-xCuxO4 (x= 0.25) nanoparticle respectively for amaranth dye. The values of residual soluble iron concentrations are within the permissible limit according to CONAMA Resolution nº 430/2011. To the heterogeneous electro-Fenton process, the residual and consumed concentration of H2O2 decreased and increased respectively with increasing value of \"x\" in the spinel of Fe3-xCuxO4 (0 ≤ x ≤ 0.25).

The foci of this thesis are the metal oxides Cu2O, ZnO and Fe3O4 and their interaction with water and sulfur dioxide (SO2). The intention is to study SO2-induced atmospheric corrosion on a molecular level. All studies are based on photoelectron spectroscopy (PES) and scanning tunneling microscopy (STM) measurements. The band structure of Cu2O in the Γ-M direction has been probed by angle-resolved PES (ARPES). It reveals a more detailed picture of the bulk band structure than earlier data and gives the first experimental evidence of a dispersive hybridized Cu 3d-Cu 4s state. The experimental data is compared to band structure calculations. The structure of clean metal oxide surfaces and impact of sample preparation have been studied. Oxygen vacancies can form a (√3x√3)R30° reconstruction on Cu2O(111). Oxygen atoms adjacent to copper vacancies, steps or kinks are shown to be adsorption sites for both water and SO2. Annealing temperature influences the defect density and hydrogen content in ZnO, which can have large impact on the surface properties of ZnO(0001). Water is shown to adsorb dissociatively on ZnO(0001) and partly dissociatively on Cu2O(111). The dissociation occurs at undercoordinated oxygen sites on both surfaces. Water stays adsorbed on ZnO(0001) at room temperature but on Cu2O(111), all water has desorbed at 210 K. SO2 interacts with one or two undercoordinated O-sites on all studied oxide surfaces forming SO3 or SO4 species respectively. SO4 on Fe3O4(100) follows the (√2x√2)R45° reconstruction. On Cu2O(111) and ZnO(0001), SO2 adsorbs on defect sites. An SO3 to SO4 transition is observed on Cu2O(111) when heating an SO3 adsorbate layer from 150 K to 280K. Coadsorption of water and SO2 on ZnO(0001) and Fe3O4(100) has been studied briefly. Water blocks SO2 adsorption sites on ZnO(0001). On Fe3O4(100) and on one type of reduced ZnO(0001) sample, SO2 dissociation to atomic sulfur or sulfide occurs to a higher extent on water exposed surfaces than on clean surfaces. Water thus appears to increase the charge density on some surfaces. Further studies are needed to reveal the cause of this unexpected effect. / <p>QC 20110516</p>

Bentonite is the most preferred silicate-based binder in iron ore pelletizing. However, it is considered as an impurity due to its high SiO2 and Al2O3 content. The iron-making economy is adversely affected by the addition of bentonite or other silicate-based binders. In recent years, impurity-free alternative binders have been tested in order to replace bentonite or to lower the bentonite dosage. Organic binders yield good quality green and dry pellets. However, they fail to impart enough mechanical strength to the preheated and fired pellets as a result of insufficient slag bonding. Thus, they have not found widespread application in the industry. The addition of boron compounds into pellet mix is proposed as a potential solution to overcome the insufficient compressive strengths of preheated and fired pellets produced with organic binders. During the experiments, some organic binders and boron compounds were tested as alternative binders to bentonite either alone or in combination, for both magnetite and hematite pellets. The performances of the tested binders on pellet qualities: balling, wet pellet moisture content, drop number, pellet compressive strengths (wet - dry - preheated - fired), dustiness, porosity, mineralogy, morphology, chemical contents, reducibility and swelling index have been compared with the performances of reference bentonite binder. The results of the tests showed that, the quality of pellets are insufficient when organic binders or calcined colemanite used as binder alone. The former failed to provide sufficient preheated and fired pellet strengths, the latter failed in terms of wet and dry pellet quality. However, good quality wet, dry, preheated and fired pellets could be produced with combination of these two binders. Calcined colemanite addition into pellets made with organic binders was tested in different dosages (0.25-1.00%). Results showed that with increasing dosage of calcined colemanite both strengths of preheated and fired pellets increased linearly. It was found that as low as 0.50% calcined colemanite addition equally-performed on magnetite fired magnetite pellets at 1300oC when compared with the performance of the reference bentonite binder. However, its performance was better on hematite pellets in order to improve the pellet compressive strengths. In addition, stronger pellets could be produced at lower firing temperatures like 1100oC with the addition of calcined colemanite. The reason of the improved preheated and fired compressive strengths of pellets bonded with calcined colemanite was due to the physical melting of calcined colemanite at the contact point of iron oxide grains during thermal treatment. It was found that bentonite bonded pellets fired at 1300oC were more reducible than those of produced with calcined colemanite addition. Swelling indices of these pellets were determined in the industrially acceptable limits. The chemical and mineralogical analyses results showed that the combined binders did not contaminate the pellet composition since the organic binders burnt-out without residue and colemanite does not contain much impurity.

In der vorliegenden Arbeit soll das weit gefächerte Thema der chemischen Nanotechnologie um neue Resultate bereichert werden. Im Einzelnen handelt es sich um neue Synthesemethoden für magnetische Nanorods (Nanoteilchen mit länglicher Form) und Nanoshells (oxidische Nanokristalle mit einer Hülle aus Edelmetall), ein Verfahren zur Modifizierung diverser Oberflächen mit heterogenen Polymerbürsten durch kontrollierte binäre radikalische Polymerisation, neuartige Copolymere zur Stabilisierung und Funktionalisierung von Nanopartikeln und Herstellung von amphiphilen Nanopartikeln durch Oberflächenbehandlung mit Niotensiden. Es sollen ferner die möglichen Anwendungen diskutiert werden. Die Abb. 1 illustriert die Zusammenhänge der bearbeiteten Thematik.

This work details the synthesis and growth mechanisms of 1D magnetic and semiconducting nanostructures. Specifically, magnetic iron oxide and ZnS-SiO2 nanowires are examined. These materials are chosen due to their promise for biomedical and electronic applications and the perceived need to both create these structures as tools for these applications and to understand their formation processes so that they can be manufactured at a scale and efficiency suitable for commercialization. The current state and impact of nanotechnology is discussed through the lens of continuing technological advances and environmental factors, and the term is defined according to a specific set of criterion involving size, utility, and uniqueness. Details of synthesis and characterization of Fe3O4, ε-Fe2O3, and ZnS-SiO2 core-shell nanowires are presented. Observations regarding the growth of these structures are paired with additional experiments, simple simulations, and other literature to discuss the classical VLS growth process in general, and its applicability to these structures in particular. Finally, some exciting future applications are discussed, with details for initial experimental work presented in the appendix.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Foram sintetizadas microesferas poliméricas com propriedades magnéticas e morfologia casca-núcleo por meio da técnica de polimerização em suspensão em duas etapas. O núcleo foi constituído por poli(estireno-co-divinilbenzeno) e magnetita modificada com ácido oleico. Foi avaliada a influência da velocidade de agitação e da concentração de iniciador sobre as características das microesferas utilizadas como núcleo (morfologia, tamanho de partículas, propriedades magnéticas e estabilidade térmica). A casca foi constituída por poli(estireno-co-divinilbenzeno) sem material magnético. Foi avaliado o método de adição da emulsão dos monômeros formadores da casca e o tempo de inchamento dos núcleos na emulsão. As microesferas casca-núcleo foram caracterizadas quanto ao seu aspecto morfológico e à estabilidade térmica. Os núcleos não apresentaram ciclos de histerese, estando assim próximos de um material com propriedades superparamagnéticas. O copolímero sintetizado com a maior velocidade de agitação e a menor concentração de iniciador foi o que apresentou o maior teor de ferro incorporado (3,317 %), a maior magnetização de saturação (2,99 emu/g) e o menor diâmetro médio de partículas (81 &#61549;m). As microesferas casca-núcleo apresentaram apenas um estágio de degradação e as suas Tmáx foram menores do que a do núcleo. O mapa composicional de ferro confirmou a presença de magnetita na superfície das microesferas casca-núcleo / Polymeric microspheres with magnetic properties and core-shell morphology were synthesized by the technique of suspension polymerization in two stages. The core was constituted by poly(styrene-co-divinylbenzene) and magnetite coated with oleic acid. The influence of stirring rate and initiator concentration on microspheres characteristics (morphology, particle size, magnetic properties and thermal stability) was studied. The shell was constituted by poly(styrene-co-divinylbenzene) without magnetic material. It was also evaluated the methods of the monomers emulsion addition and the coress swelling time in the emulsion.. The microspheres were characterized by morphologic aspect and thermal stability. The cores did not presented hysteresis cycles, thus proving the superparamagnetic properties. Copolymer synthesized with the higher stirring rate and lower initiator concentration presented the higher incorporated iron content (3.317 %), higher saturation magnetization (2.99 emu/g) and the lower average particle diameter (81 &#61549;m). Core-shell microspheres presented only one stage of degradation and the Tmáx were smaller than temperature of the cores. Iron compositional map confirmed the presence of magnetite on the surface of core-shell microspheres

L’objectif principal de cette étude est d’évaluer le rôle de l’activité de bactéries hydrogénotrophes et ferri-réductrices sur le processus de corrosion anoxique en utilisant des indicateurs géochimiques. Il est considéré que le couple redox H2/Fe(III) est un moteur important pour les activités bactériennes qui peuvent ainsi affecter les vitesses de corrosion par la déstabilisation des couches de passivation (i.e. magnétite, Fe3O4). Les résultats indiquent que la magnétite de synthèse est déstabilisée en présence de bactéries hydrogénotrophes et ferri-réductrices due à la réduction du Fe(III) structural couplée à l’oxydation de l’H2. La quantité de Fe(III) bioréduit est augmentée en présence de concentrations croissantes en H2 dans le système: 4% H2 < 10% H2 < 60% H2. De plus, les résultats indiquent que la réaction de corrosion est différente selon la composition de la solution et la surface de contact de l’échantillon métallique (poudre de fer ou coupon en acier au carbone). Les produits de corrosion solides sont différents pour chaque échantillon étudié: vivianite, sidérite et chukanovite sont les principales phases minérales identifiées dans les expériences avec de la poudre de fer, tandis que vivianite et magnétite sont identifiées en présence de coupons en acier au carbone. Les résultats montrent que la vitesse de corrosion est quasiment deux fois plus importante en présence de bactéries après 5 mois de réaction. Cette étude apporte une nouvelle approche sur la compréhension des phénomènes de biocorrosion, l’identification des mécanismes physico-chimiques et la détermination des paramètres contrôlant la vitesse de corrosion. / The main objective of this study is to evaluate the role of hydrogenotrophic and IRB activities on anoxic corrosion process by using geochemical indicators. It is assumed that the redox couple H2/Fe(III) is an important driver for bacterial activities potentially affecting the corrosion rate by destabilization of passive layers (i.e. magnetite, Fe3O4). Our results indicate that synthetized Fe3O4 is destabilized in the presence of hydrogenotrophic IRB due to structural Fe(III) reduction coupled to H2 oxidation. The extent of Fe(III) bioreduction is notably enhanced with the increase in the H2 concentration in the system: 4% H2 < 10% H2 < 60% H2. Moreover, the results indicate that corrosion extent changes according to the solution composition and the surface of metallic sample (iron powder and carbon steel coupon). The solid corrosion products are different for each sample: vivianite, siderite and chukanovite are the main mineral phases identified in the experiments with iron powder, while vivianite and magnetite are identified with carbon steel coupons. Our results demonstrate that corrosion rate is increased almost two-fold in the presence of bacteria after 5 months of reaction. This study gives new insights regarding the understanding of biocorrosion phenomena, identification of physicochemical mechanisms, and determination of key parameters controlling the corrosion rate.