Estudo dos sistemas binários Fe-Pr e Fe-Nd em torno de suas respectivas regiões eutéticas

Orientador: Sergio GamaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: O objetivo desta tese é tentar resolver melhor os dois eventos térmicos seqüenciais, que aparecem na análise térmica diferencial de ligas com composições em torno das regiões eutéticas dos sistemas Fe-Pr e Fe-Nd. Pretendemos verificar se esses eventos possuem alguma relação com as fases magnéticas metaestáveis que são observadas em ligas como fundidas de ambos os sistemas, e tentar descobrir que fases realmente participam do diagrama de equilíbrio dos sistemas. Para isto lançamos mão da técnica de Solidificação Direcional para a obtenção de amostras com microestruturas segregadas espacialmente. Esta técnica é similar à técnica de crescimento de cristais conhecida como método Bridgman, e nos proporciona um método para a obtenção de fases estáveis dos sistemas estudados. As amostras obtidas com esta técnica foram analisadas pelas técnicas de análise térmica diferencial, análise calorimétrica, metalografia óptica, microanálise eletrônica e análise termomagnética. Da correlação de todos os dados experimentais obtidos nesses estudos chegamos às seguintes conclusões: No sistema Fe-Pr confirmamos a existência da fase Fe2Pr, que se forma periteticamente a 669 °C e provavelmente decompõe-se através de uma reação eutectóide a uma temperatura superior a 600 °C, e que possui temperatura de Curie de 44 ºC. A fase de estequiometria Fe3Pr13 não foi observada. As amostras do sistema Fe-Nd, obtidas da solidificação direcional, apresentaram características semelhantes às do sistema Fe-Pr. Nesse sistema identificamos uma fase nova, com estequiometria Fe2Nd, que se forma periteticamente a 688 ºC e provavelmente decompõe-se através de uma reação eutectóide na temperatura de 663 ºC, e que possui temperatura de Curie de 251 ºC. Observamos que essa fase deve ser magneticamente anisotrópica, pois apresenta domínios magnéticos a temperatura ambiente. Para cada sistema, é proposto um novo diagrama de fases. Estes diagramas foram construídos com base em nossos dados e nos diagramas apresentados por Hoyos e Landgraf, respectivamente. No diagrama do sistema Fe-Pr foi retirada a fase Fe3Pr13 e no diagrama do sistema Fe-Nd foi incluída a nova fase Fe2NdAbstract: The aim of this thesis is to better resolve the two sequencial thermal events, which appear in the differential thermal analysis of alloys, with compositions around the eutectic regions of the Fe-Pr and Fe-Nd systems. We intend to verify if these events have relation with metastable magnetic phases which are observed in as-cast alloys in both systems, and to disçover which phases really belong to the equilibrium phase diagrams of these systems. To carry out this purpose we used the direcional solidification technique for obtain samples with spacially segregated microestructures. This technique is similar to that of crystal growth technique, known as Bridgman method, and provide us with a method to obtain stable phases of the studied systems. The samples obtained by means of this technique have been studied with the techniques of differential thermal analysis, calorimetry , metallography, electron probe microanalysis and thermomagnetic analysis. The correlation of all experimental data obtained from these studies, lead us to the following conclusions: In the Fe-Pr system we confirm the existence of the phase Fe2Pr, that is formed peritectically at 669 °C, and decomposes through an eutectoid reaction a temperature above 640 °C, and have Curie Temperature of 44 °C. The phase with stoichiometry Fe3Pr13 has not been observed. The samples of the system Fe-Nd, obtained by direcional solidification, presented similar feature as the system Fe-Pr. We have identified a new phase, with stoichiometry Fe2Nd, that is formed peritectically at 689 °C, and that decomposes through na eutectoid reaction at 659 °C, and has Curie Temperature of 251 °C, and presents magnetic domains at room temperature. For each system is proposed a new phase diagram. These diagrams have been constructed based on our experimental data and on diagrams presented by Hoyos and Landgraf, respectivelly. In the diagram of the system Fe-Pr, the phase Fe3Pr13 was dropped out, and in the diagram of the system Fe-Nd, the new phase Fe2Nd was includedMestradoFísicaMestre em Físic

Magnetic Nanorings for Biomedical Applications

In this work we investigate the characteristics and feasibility of a new class of magnetic particles that are optimized for possible biological applications as magnetic hyperthermia. These new nanostructures have the nanoring shape, being composed of iron oxides (magnetite or hematite). Such morphology gives the nanoparticles a peculiar magnetic behavior due to their magnetic vortex state. The iron oxide nanorings were obtained using hydrothermal synthesis. X-ray Diffraction confirmed the existence of the desired crystal structure and Scanning Electron Microscopy shows that the magnetite particles had nanometric dimensions with annular morphology (diameter ~250 nm). The nanorings also show intensified magnetic properties and a transition to a vortex state. This study showed that it is possible to obtain magnetic nanorings with properties that can be used in nanotechnological applications (mainly biotechnological ones aimed at the treatment and diagnosis of cancer), in large quantities in a simple synthesis route

Magnetic Nanorings for Biomedical Applications

In this work we investigate the characteristics and feasibility of a new class of magnetic particles that are optimized for possible biological applications as magnetic hyperthermia. These new nanostructures have the nanoring shape, being composed of iron oxides (magnetite or hematite). Such morphology gives the nanoparticles a peculiar magnetic behavior due to their magnetic vortex state. The iron oxide nanorings were obtained using hydrothermal synthesis. X-ray Diffraction confirmed the existence of the desired crystal structure and Scanning Electron Microscopy shows that the magnetite particles had nanometric dimensions with annular morphology (diameter ~250 nm). The nanorings also show intensified magnetic properties and a transition to a vortex state. This study showed that it is possible to obtain magnetic nanorings with properties that can be used in nanotechnological applications (mainly biotechnological ones aimed at the treatment and diagnosis of cancer), in large quantities in a simple synthesis route

Magnetic Nanorings for Biomedical Applications

In this work we investigate the characteristics and feasibility of a new class of magnetic particles that are optimized for possible biological applications as magnetic hyperthermia. These new nanostructures have the nanoring shape, being composed of iron oxides (magnetite or hematite). Such morphology gives the nanoparticles a peculiar magnetic behavior due to their magnetic vortex state. The iron oxide nanorings were obtained using hydrothermal synthesis. X-ray Diffraction confirmed the existence of the desired crystal structure and Scanning Electron Microscopy shows that the magnetite particles had nanometric dimensions with annular morphology (diameter ~250 nm). The nanorings also show intensified magnetic properties and a transition to a vortex state. This study showed that it is possible to obtain magnetic nanorings with properties that can be used in nanotechnological applications (mainly biotechnological ones aimed at the treatment and diagnosis of cancer), in large quantities in a simple synthesis route

On the Distribution of Magnetic Moments in a System of Magnetic Nanoparticles

Particle size distribution carries out a substantial role in the magnetic behavior of nanostructured magnetic systems. In fact, a vast literature on superparamagnetism has been reported, suggesting that the particle size distribution in a system of magnetic nanoparticles (MNPs) corresponds to a lognormal probability density function, and several works have properly considered their magnetic moments following a similar distribution, as a universal rule. In this manuscript, it is demonstrated that alternative probability distribution functions, such as the gamma and Weibull ones, can be used to obtain useful parameters from the analysis of the magnetization curves, indicating there is no universal model to represent the actual magnetic moment distribution in a system of magnetic nanoparticles. Inspired by this observation, a reliable method to properly identify the actual magnetic moment distribution in a given nanostructured magnetic system is proposed and discussed