Soldering results from the interfacial interactions between the die and the casting alloy during high pressure die casting and is one of the major die failure modes. To prevent this occurring, lubricant layers and surface coatings are used to act as a barrier between the die and the casting alloy. The microstructures of a series of soldered layers on H13 tool steel core pins were examined after conducting high pressure die casting experiments with a specially designed die using removable core pins and Al-11Si-3Cu casting alloy. This showed that first, a casting alloy build-up layer formed, and then intermetallic phases nucleated at the die steel interface and grew to cover the entire surface in subsequent casting cycles. The structures of intermetallic layers formed during immersion of H13 tool steel into an Al-11Si-3Cu casting alloy melt were studied by X-ray diffraction and energy dispersive spectroscopy (EDS). A thick composite layer away from the H13 steel substrate consisted of irregular intermetallic phases and solidified casting alloy. A thin intermetallic layer was present between the composite layer and an inner compact layer next to the steel substrate. The irregular intermetallic phase in the thick composite layer away from the H13 steel substrate was identified to have a body centre cubic (bcc) structure, abcc-( FeSiAlCrMnCu). The thin and continuous intermetallic layer between the composite layer and the inner compact layer was found to be structurally isomorphous with aH-Fe2SiAl8. The compositional differences observed between aH and abcc phases indicated that the latter consisted of a higher amount of chromium, manganese, copper, and a lower amount of iron. It was likely that the presence of chromium, manganese and copper in the H13 tool steel caused the transformation of aH®abcc. The inner compact layer next to the steel substrate was identified to be orthorhombic h-Fe2Al5 containing silicon and chromium. An examination of lubricants to prevent soldering in high pressure die casting in conjunction with Nissan Casting Australia Pty Ltd. found that soldering was reduced by using a suitable lubricant. The chemistry of the lubricant, spray parameters, and die surface temperature were important factors in producing a protective lubricant layer. It was found that lubricant containing polypropylene waxes prevented soldering significantly better than lubricant containing polyethylene waxes. It was also found that the lubricant containing polypropylene waxes had lower surface tension. An examination of the use of iron oxide layers to prevent soldering in high pressure die casting was performed. H13 tool steel was oxidised in air and produced porous iron oxide with a mixture of haematite (Fe2O3) and magnetite (Fe3O4). These porous iron oxides did not completely prevent the H13 steel from soldering in immersion tests as intermetallic cones formed at the surface of the steel. Commercial steam tempering of H13 steel produced more compact iron oxide layers with magnetite (Fe3O4) and haematite (Fe2O3) structures. It was found that these compact iron oxide layers offered better protection against soldering than the porous layers created in air. Pure iron oxidised in a CO2/H2 gas mixture at a ratio of 95:5 at 550°C produced structurally pure, compact magnetite (Fe3O4) layers. H13 steel oxidised in a CO2/H2 gas mixture at a ratio of 95:5 at 550°C produced compact iron oxide layers that showed only magnetite (Fe3O4) structure. The magnetite (Fe3O4) layer containing chromium, manganese, silicon and vanadium formed next to the H13 substrate was found to be a very adherent layer and protected H13 steel from soldering in high pressure die casting experiments with a specially designed die using removable core pins and Al-11Si-3Cu casting alloy. An examination of aluminium oxide layers to prevent soldering in high pressure die casting was performed. Incoloy MA956 containing 4.5 wt.% aluminium, oxidised in air at 1100°C, produced a single, compact, adherent oxide layer with a-alumina (Al2O3) structure, that prevented the formation of intermetallic phases between aluminium alloy and Incoloy MA956 during high pressure die casting. However, non-reactive casting alloy build-up formed on the oxide coatings, similarly to physical vapour deposition (PVD) and vanadium carbide coatings. It was found that the thickness of the non-reactive casting alloy build-up was reduced by decreasing the roughness of the oxide coatings by lightly grinding of the surface of the coatings. The industrial application of these findings are discussed and directions for further research are presented.

Made available in DSpace on 2014-12-17T14:07:14Z (GMT). No. of bitstreams: 1 TharsiaCCC_TESE.pdf: 4165596 bytes, checksum: b73b464d52ff23430b153992ec45405a (MD5) Previous issue date: 2013-04-25 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work aims at obtaining nanoparticles of iron oxide, the magnetite one (Fe3O4), via synthesis by thermal decomposition through polyol. Thus, two routes were evaluated: a simple decomposition route assisted by reflux and a hydrothermal route both without synthetic air atmosphere using a synthesis temperature of 260?C. In this work observed the influence of the observe of surfactants which are generally applied in the synthesis of iron oxide nanoparticles decreasing cluster areas. Further, was observed pure magnetite phase without secondary phases generally found in the iron oxide synthesis, a better control of crystallite size, morphology, crystal structure and magnetic behavior. Finally, the introduction of hydroxyl groups on the nanoparticles surface was analyzed besides its employment in the polymer production with OH radicals. The obtained materials were characterized by XRD, DLS, VSM, TEM, TG and DSC analyses. The results for the magnetite obtainment with a particle size greater than 5 nm and smaller than 11 nm, well defined morphology and good magnetic properties with superparamagnetic behavior. The reflux synthesis was more efficient in the deposition of the hydroxyl groups on the nanoparticles surface / O objetivo desse trabalho foi a obten??o de nanopart?culas de ?xido de ferro, a magnetita (Fe3O4), via s?ntese por decomposi??o t?rmica via poliol, avaliando assim duas rotas: a rota simples decomposi??o assistida por refluxo e a rota hidrot?rmica, ambas sem atmosfera de ar sint?tico e usando a temperatura de s?ntese de 260?C. Observou-se nesse trabalho a influ?ncia da aus?ncia de surfactantes, comumente utilizados em s?nteses de ?xidos de ferro, com a finalidade de promover uma melhor dispers?o das nanopart?culas, diminuindo assim as ?reas de aglomerados. Al?m disso, visou-se: a obten??o de uma fase puramente de magnetita, sem a forma??o de fases secund?rias comumente encontradas nas s?nteses dos ?xidos de ferro; um melhor controle do tamanho de cristalito; da morfologia; da estrutura cristalina e do comportamento magn?tico. Por fim, analisou-se a introdu??o dos grupos hidroxilas na superf?cie das nanopart?culas, e sua empregabilidade na produ??o de pol?meros com radicais (OH). Os materiais obtidos foram caracterizados por an?lises de DRX, DLS, VSM, TEM, TG e DSC. Os resultados foram satisfat?rios quanto ? obten??o da magnetita, com tamanho de part?cula maior que 5 nm e menor que 11 nm, de morfologia bem definida e com boas propriedades magn?ticas com comportamento superparamagn?tico. Quanto ? deposi??o dos grupos de hidroxilas na superf?cie das nanopart?culas, a s?ntese com refluxo mostrou-se mais eficiente

The current proposed method for the long-term management of intermediate and high level radioactive waste in the UK is via geological disposal. It is known that redox sensitive elements such as uranium and neptunium will significantly contribute to the total waste inventory. Recently, studies have indicated that both U and Np can be stabilised by interaction with minerals. Over long periods of time (1000’s -10,000’s years) steel canisters that encase radioactive waste in geodisposal systems will undergo anaerobic corrosion, potentially leading to the release of radionuclides, including U and Np. Anaerobic corrosion will also result in the formation of a number of oxide phases, including iron (oxyhydr)oxides e.g. magnetite and green rust. The interaction of U and Np with such forming iron (oxyhydr)oxides may lead to the sequestering of radionuclides in the environment through a range of processes such as adsorption to a mineral surface and incorporation into a mineral structure. Therefore the interactions between iron (oxyhydr)oxides and radionuclides are important to determine their fate if potentially released within the wider environment. In this study, the fate of U(VI) and Np(V) when in contact with a range of iron (oxyhydr)oxides was considered. These systems were selected to help understand the detailed mechanisms that may occur between radionuclides and iron (oxyhydr)oxides. XRD and TEM were used to characterise mineralogy, whilst acid digestions determined the distribution of U within the mineral phase. Synchrotron based XAS was used to determine oxidation state, site geometry and local bonding environment of the radionuclides associated with the mineral phases. The data suggests that: U(V) is stabilised and incorporated in octahedral coordination into both the magnetite and green rust structure in a uranate-like coordination; with increasing U concentration mineral formation favours uraninite and Fe(III) (oxyhydr)oxides; the limit of U incorporation into magnetite is 0.45 mol % U ± 0.23; Np(V) is reduced to Np(IV) on the iron (oxyhydr)oxide surface forming a bidentate binuclear complex; and that upon reoxidation, Np(IV) is partially reoxidised back to Np(V) but not released back into solution. These results highlight the significance in understanding the mechanisms when both Np and U are in contact with iron (oxyhydr)oxides which can contribute towards site environmental clean-up and waste management in the nuclear industry.

We have performed detailed measurements of magnetic and dielectric properties of high quality magnetite (Fe3O4) single crystals in weak magnetic and electric fields. These measurements can reveal details of phase transitions and other features that are not yet fully understood. We focused not only at the Verwey transition - a well known phase transition taking place at about 120 K in stoichiometric samples - but we also explored and described new relaxation effects in magnetite at low temperatures. The low-temperature properties were also found to be exceptionally sensitive to sample quality, stoichiometry and homogeneity. The results presented in this thesis were acquired on sensitive non-commercial SQUID magnetometer complemented by four-probe dielectric spectroscopy and dc conductivity measurements.

Le générateur de vapeur est un composant essentiel du réacteur à eau pressurisée. Après 15 à 20 ans de fonctionnement du GV, un phénomène de colmatage est observé, qui induit le bouchage du passage folié entre les tubes GV et la plaque entretoise. Ce phénomène peut avoir de graves conséquences pour le fonctionnement de la centrale nucléaire. L’objectif majeur de cette thèse est d’approfondir les connaissances des mécanismes responsables de la formation du colmatage en identifiant et hiérarchisant les processus prépondérants. L’installation COLENTEC est un outil expérimental conçu pour reproduire des dépôts dans des conditions représentatives d’un GV. La post-caractérisation microscopique a permis d’identifier la contribution du phénomène de précipitation et le rôle d’initiation de la passivation du matériau. Les formes spécifiques du colmatage, lipping à l’entrée et rides le long de la plaque entretoise, n’ont pas été observées dans les essais COLENTEC. Cela peut être provoqué par l’absence de particules dans la section d’essai ou une vitesse insuffisante du fluide. Le flashing et le phénomène électrocinétique ont été supposés contribuer à la formation du colmatage. Une collaboration avec l’Université de Manchester a été établie au cours de ce travail afin d’étudier expérimentalement le phénomène électrocinétique. Les travaux effectués ont permis de mieux comprendre ce phénomène et de suggérer son influence considérable dans la formation du colmatage. Des quantifications numériques de chaque phénomène ont été réalisées, prédisant un rôle prédominant du phénomène électrocinétique. / The steam generator is an essential component in PWR. After 15-20 years of functioning, an obstruction by deposits of flow holes between Tube Support Plate (TSP) and primary tubes is observed, called TSP clogging. This phenomenon may lead to dramatic consequences for nuclear power plant operation. The aim of this thesis is to deepen the understanding of the mechanisms responsible for TSP clogging by identifying and prioritizing the preponderant processes. COLENTEC is an experimental facility designed to reproduce TSP clogging deposits under representative conditions. Microscopic characterizations allowed revealing the deposit formation by precipitation and the initiation role of material passivation in deposit formation. Lipping and ripple forms, specifying TSP clogging, were not observed in COLENTEC tests. This is suggested to be caused by insufficient concentration of suitable particles at the test section. Particle deposition is supposed to be essential for the formation of lipping deposits. Electrokinetic and flashing phenomena are supposed to contribute to TSP clogging formation. An experimental collaboration with the University of Manchester was established to better understand the clogging formation by investigating the role of electrokinetic phenomenon. This study allowed reforming deposits with lipping and ripple forms as observed in EDF steam generators. Electrokinetic involvement, strongly affected by flow velocity, was considerably suggested in TSP clogging formation. Numerical quantification of deposit formation by each phenomenon was performed and compared to EDF feedbacks. Electrokinetic phenomenon was found to play a predominant role.

A presença da pirita (FeS2) em depósitos de rejeitos de carvão mineral pode causar danos ambientais. A pirita oxida e proporciona a geração da drenagem ácida de minas (DAM). Uma possível maneira de se evitar tal problema é separando a pirita e empregando-a para algum fim. Assim, o objetivo do presente trabalho foi desenvolver uma rota para sintetizar óxidos magnéticos a partir de um concentrado de pirita oriundo de rejeito de carvão. Experimentalmente, utilizou-se 300 kg de um concentrado com 73,2% de pirita em escala piloto. Realizou-se uma etapa de lixiviação aeróbica com água, em circuito fechado, com o intuito de se obter um extrato aquoso rico em íons férricos. A seguir, procederam-se mudanças no sistema de forma a estabelecer uma condição anaeróbia e redutora ao meio para obterem-se íons ferrosos. O lixiviado, rico em íons Fe2+ e SO4 2-, foi misturado com etanol para a precipitação do ferro como melanterita. Duas rotas para a produção de óxidos ferromagnéticos foram avaliadas. Primeiro, para a síntese de ferritas, utilizou-se o direto ajuste de pH da solução lixiviada reduzida até 10,5 durante 4 dias e posterior precipitação do material magnético. Segundo, para a síntese da magnetita, os cristais de melanterita, obtidos pela precipitação com etanol, foram dissolvidos em água deionizada e procedeu-se o mesmo ajuste de pH e tempo reacional para a cristalização do ferro na forma de óxido. Os cristais foram separados por precipitação, lavados com água deionizada, secos e caracterizados em relação à composição elementar, cristalinidade, distribuição granulométrica, forma, termodecomposição e magnetização. Pode-se concluir que os procedimentos empregados resultaram na obtenção de ferritas e cristais de magnetita na faixa granulométrica entre 0,1 e 10,0 μm. As ferritas apresentaram medidas de magnetização de saturação e coercividade de 29 emu/g e 33,4 Oe e a magnetita de 86,6 emu/g e 75,2 Oe. Os rendimentos em relação ao Fe presentes no lixiviado reduzido (síntese da ferrita de zinco) e melanterita (síntese da magnetita) foram de 34,9% e 93,2%, respectivamente. A produção de reagentes e materiais com valor agregado a partir de concentrados de pirita, oriundo de um rejeito mineral é tecnologicamente viável. O custo estimado para a produção de nano e microgrãos de magnetita foi calculado em R$ 136,29/kg. O processo reduz o desperdício de materiais, minimiza impactos de descarte de resíduos ao meio ambiente e pode tornar-se uma fonte de recursos alternativa dentro da cadeia de produção de carvão. Deve-se ressaltar que os óxidos magnéticos encontram aplicações como pigmentos, em suspensões de meio denso, suporte magnético, agente de contraste em medicina e como material adsorvente. / The presence of pyrite (FeS2) in coal tailings deposits can cause environmental damage. Pyrite oxidizes and generates acid mine drainage (AMD). One possible way to avoid such a problem is by separating the pyrite and employing it for some purpose. Thus, the aim of the present work was to develop a route to synthesize magnetic oxides from a pyrite concentrated from coal rejects. Experimentally, it was carried out in a pilot leaching unit with 300 kg of a pyrite concentrate with of 73.2% FeS2. A step of aerobic leaching with closed circuit water was carried out in order to obtain an aqueous extract rich in ferric ions. Next, changes were made in order to establish an anaerobic and reductive condition in the medium to obtain ferrous ions. The leachate, rich in Fe2+ and SO4 2- ions, was mixtured with different proportions of ethanol to precipitate the iron as melanterite. Two procedures to produce ferromagnetic oxides were investigated. First, for ferrite synthesis, the reduced leachate had the pH adjusted to 10.5 and this condition was kept for a period of 4 days for crystallization of the magnetic material. Second, for magnetite synthesis, melanterite crystals obtained by the precipitation with ethanol (A.P) were dissolved in deionized water and the same pH adjustment and reaction time for the crystallization of the iron as ferrites was carried out. The crystals were separated by precipitation, washed with deionized water, dried, and characterized in relation to elemental composition, crystallinity, particles size distribution, shape, thermo-decomposition, and magnetization. The procedures applied resulted in ferrites and magnetite particles in particle size between 0.1 and 10.0 μm. Ferrite particles presented magnetization saturation and magnetization coercivity of 29 emu/g and 33,4 Oe and magnetite particles of 86.6 emu/g e 75.2 Oe. The yields, from the reduced leachate, were 34.9% for ferrites and 93.2% for magnetite. The production of reagent and materials with aggregate values from pyrite concentrates is viable. The estimated cost for nano and micro particles of magnetite synthesis was estimated in R$ 136.29/kg. The process reduces the waste of materials, minimize the discharge of wastes in the environment and could be source of resource in coal production chain. It should be noted that magnetic oxides find applications as pigments, in dense media suspensions, magnetic support, contrast agent in medicine, and as adsorbent material.

Nanoparticulas magnéticas (NPMs) de óxido de ferro tem sido amplamente utilizadas em diversas áreas da biotecnologia e biomedicina, tais como no tratamento de câncer, na entrega controlada de fármacos e como agentes de contraste em imagem por ressonância magnética. O intuito deste trabalho foi sintetizar nanopartículas magnéticas com magnetização de saturação intensificadas via processo do poliol modificado e modificar sua superfície afim de promover a biocompatibilização dos sistemas. Além da funcionalização de nanopartículas previamente biocompatibilizadas utilizando dois métodos: via ligação amida com moléculas de ácido fólico (AF) e com a encapsulação das nanopartículas com quitosana. A modificação de superfície deu-se via procedimentos de lavagem de superfícies, adição e/ou troca de ligantes utilizando moléculas de ácido ?- aminocapróico (EACA), aminopropiltrimetoxisilano (APTMS) e ácido dimercaptosuccínico (DMSA). Através da microscopia eletrônica de transmissão (TEM), foi obtido que as nanopartículas magnéticas de magnetita obtiveram um diâmetro médio de 8 nm, em uma estreita distribuição de tamanho. A difração de raios-X (DRX) indicou a formação de magnetita em todos os sistemas em que o método do poliol modificado foi utilizado. As medidas de espectroscopia vibracional na região do infravermelho (FTIR) evidenciaram a presença de modos de vibração relacionados às macromoléculas e compostos inorgânicos utilizados na modificação de superfície das nanopartículas magnéticas e/ou funcionalização. A TEM das diferentes modificações de superfície mostram a formação de aglomerados dependendo da molécula utilizada. Os estudos de estabilidade coloidal foram necessários para que o meio biológico fosse simulado para uma possível aplicação destes sistemas como carreadores para tratamento via magnetohipertermia ou entrega controlada de NPMs para tratamento de câncer. A nanopartícula recoberta com DMSA apresentou melhores resultados de estabilidade coloidal. Com os sistemas funcionalizados com ácido fólico, o procedimento via ligação com carbodiimida na presença de NHS demonstrou ser eficaz na formação de ligação amida, confirmada por FTIR e quantificação de ligantes. A funcionalização com quitosana necessita de alguns ajustes, visto ser um novo procedimento, porém alguns sistemas em que foi utilizado o método da gelificação iônica possuíram bons resultados de nanocápsulas de quitosana formadas com nanopartículas biocompatibilizadas em seu interior. / Magnetite, iron oxide, is a type of magnetic nanoparticles (NPMs) that is a widely adopted in several areas of biotechnology and biomedicine, such as in the treatment of cancer, controlled delivery of drugs and as contrast agents in magnetic resonance imaging. The purpose of this work is to synthesize magnetic nanoparticles with enhanced saturation magnetization via modified polyol process and modify its surface to promote a biocompatibilization in these systems. In addition, there was the aim to functionalize nanoparticles with modificate surfaces, using two methods: via amide bonding with folic acid molecules (AF) and encapsulation of nanoparticles with chitosan. Surface modification was done via surface washing, addition and / or exchange ligands using ?-aminocaproic acid (EACA), aminopropyltrimethoxysilane (APTMS) and dimercaptosuccinic acid (DMSA) molecules. By transmission electron microscopy (TEM), it was obtained that the magnetite nanoparticles had an average diameter of 8 nm, in a narrow size distribution. X-ray diffraction (XRD) indicated formation of magnetite in all systems where modified polyol method was used. Infrared spectroscopy (FTIR) showed the presence of vibration modes related to macromolecules and inorganic compounds used in the surface modification of magnetic nanoparticles and / or functionalization. The TEM of different surface modifications showed the formation of agglomerates, depending on the molecule used. Colloidal stability studies were necessary to simulate a biological medium for a possible application of these systems as carriers for treatment via magnetohyperthermia or controlled delivery of NPMs for cancer treatment. Nanoparticles coated with DMSA showed better colloidal stability results. With folic acid functionalized systems, the procedure via carbodiimide linkage in the presence of NHS had been shown to be effective in FTIR-confirmed amide bond formation and ligand quantification. The functionalization with chitosan requires some adjustments, since it was a new procedure, however some systems using the ionic gelation method had good results of chitosan nanocapsules formed with biocompatibilized nanoparticles in structure.

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