Neste trabalho, foram estudadas a oxidação do cicloexano e a epoxidação do (Z)- cicloocteno com iodosilbenzeno (PhIO) e H2O2 como oxidantes, comparando as FeIIIclorinas pentafluorossubstituídas com as FeIIIporfirinas, [Fe(TFPCMG)]Cl, [Fe(TFPCMGCH3)]Cl2, [Fe(TFPP)]Cl e [Fe(TF4TMAPP)](CF3SO3)5 como catalisadores em meio homogêneo e suportadas via ligação iônica e/ou covalente em matrizes de sílica quimicamente modificada. No caso do substrato (Z)-cicloocteno, os metalocomplexos utilizados levaram a rendimentos elevados para formação do ciclooctenóxido, tanto em meio homogêneo quanto heterogêneo, quando PhIO foi utilizado como oxidante. A atividade catalítica foi mantida mesmo após três reciclagens sucessivas. Com o H2O2 como oxidante, os rendimentos foram menores exceto com o metanol, quando se observa um aumento nos rendimentos de epoxidação, porque favorece a formação do intermediário ativo FeIIIhidroperóxido. Já os sistemas heterogeneizados apresentam desempenho bastante inferior quando comparado aos catalisadores em solução. Os melhores rendimentos foram observados com DCE um solvente mais viscoso que aumenta o tempo de vida da gaiola do solvente favorecendo o processo biomimético. Os catalisadores imobilizados foram caracterizados por espectroscopias UV-Vis e de RPE. Estas técnicas deram informações do estado de oxidação e de spin do metal, bem como a geometria do macrociclo na superfície da matriz sólida. Os resultados catalíticos puderam ser explicados pela natureza dos grupos funcionais que ligam o metalocomplexo à sílica, bem como, pelas informações fornecidas pela técnica de RPE quanto ao estado de oxidação do ferro e à geometria dos metalocomplexos imobilizados, dando consistência aos mecanismos propostos nos processos de oxidação. / In this work, the cyclohexane oxidation and the (Z)-cyclooctene epoxidation with iodosylbenzene (PhIO) e H2O2 as oxidants were studied. A comparison between fluorinated FeIIIchlorins and FeIIIporphyrins, [Fe(TFPCMG)]Cl, [Fe(TFPCMGCH3)]Cl2, [Fe(TFPP)]Cl, [Fe(TF4TMAPP)](CF3SO3)5 as catalysts was made either in solution or supported in silica matrices via eletrostatic interaction and/or covalent bonds. In the case of (Z)-cyclooctene epoxidation by PhIO, all the studied metallocomplexes achieved high yields for the epoxide production in both homogeneous and heterogeneous systems. The catalytic activity was maintained even after three successive recyclings. On the other hand, when H2O2 was used as oxidant the yields were lower. Differently, raised yields of epoxidation were observed when using methanol as solvent due to favored formation of the active intermediate FeIIIhydroperoxide. The performance of the heterogeneous systems was significantly lower than that of the catalysts in solution. The best yields were observed with DCE, a viscous solvent that probably raises the shelf life of the solvent cage favoring the biomimetic process. The supported systems were characterized by EPR and UV-Vis spectroscopies. These techniques gave information about the oxidation state and the metal spin, as well as the macrocycle geometry on the solid matrix surface. The catalytic results were explained by the nature of the functional groups that bound the metallocomplex to the silica matrix. In addition, the information obtained by the EPR technique regarding the state of oxidation of iron and the geometry of the supported metallocomplexes gave consistence to the proposed mechanisms in the oxidation processes.

Ultradünne Filme der 3d-Metalle auf einem magnetischen Substrat können durch die magnetische Kopplung ebenfalls eine Magnetisierung erfahren. Im allgemeinen ist die Art und Stärke der induzierten magnetischen Momente von der Dicke und der Struktur dieser Filme abhängig. In dieser Arbeit wurden speziell die Wachstumseigenschaften von Fe, Cr, Mn und V auf einem Fe(100)-Substrat bezüglich ihrer Morphologie und der Grenzflächeninter-diffusion sowie die magnetische Kopplung der Filme zum Substrat untersucht. Bei diesen Studien kam primär die streifende Oberflächenstreuung schneller Ionen (H+, He+, Ar+) mit Primärenergien von bis zu 25keV unter typischen Einfallswinkeln von 1..2° zur Oberfläche zum Einsatz. Bei einer solchen Streuung können die Projektile nicht in die Oberfläche eindringen, sondern werden von dieser reflektiert. Insbesondere die Aufnahme der spekularen Streuintensität und die Halbwertsbreite der resultierenden Streuverteilung erlaubten die Beobachtung des Wachstums-pro-zesses in Echtzeit sowie die quantitative Bestimmung von Stufendichten, kritischen Keim-größen, den Füllungsgrad atomarer Filmlagen, Aktivierungsenergien der lateralen Diffusion, die Änderung der Austrittsarbeit, sowie die Größe der thermischen Auslenkungen der Oberflächenatome. Die Anregung von Auger-Elektronen an der Oberfläche bei der streifenden Streuung von Protonen erlaubte in Verbindung mit der konventionellen Auger-Spektroskopie nach Anregung durch steil einfallende Elektronen die Bestimmung der Konzentra-tionsprofile an der Grenzfläche des Films zum Substrat bei unterschiedlich starker Grenzflächeninterdiffusion. Die Charakterisierung der magnetischen Oberflächenmomente des Fe(100) und der darauf gewachsenen 3d-Metallfilme erfolgte indirekt aus der Polarisation des Fluo-res-zenzlichts aus dem Zerfall des HeI3³P-Zustandes nach der Streuung, der durch den Einfang der polarisierten Elektronen von der Oberfläche entsprechend der dort vorhandenen Zustandsdichte besetzt wird. Grundlegende Zusammenhänge zwischen der Spin-Polarisation des HeI3³P-Zustandes und der Magnetisierung der streuenden Oberfläche wurden am Fe(100) studiert. Mittels einfacher Modelle konnte in diesen Studien die extreme Oberflächen-empfindlichkeit der angewendeten Meßmethode wie auch die qualitative Abhängigkeit der Spin-Polarisation von der elektronischen Zustandsdichte der Festkörper-Oberfläche nachgewiesen werden. Für die Interpretation der Polarisationsdaten beim heteroepitaktischen Filmwachstum war es notwendig, das Wachstum möglichst realitätsnah in einem Modell abzubilden. Dazu wurde ein bereits bestehendes Modell zur Beschreibung des homoepitakti-schen Filmwachstums auf niedrigindizierten Oberflächen weiterentwickelt, so daß auch die zeitliche Entwicklung der Interdiffusion bei heteroepitaktischem Wachstum beschrieben werden kann. Die Eichung des Modells erfolgte mit den Ergebnissen aus der Untersuchung des Wachstums mit der streifenden Ionenstreuung und der Auger-Spektroskopie. Damit wurde es erstmals möglich, die Magnetisierung der heteroepitaktisch gewachsenen 3d-Metallfilme bei nicht idealem Filmwachstum und deutlicher Grenz-flächeninterdiffusion anhand experimenteller Ergebnisse von ein und derselben Probe zu beschreiben sowie den Zusammenhang zwischen Struktur, Interdiffusion und Magnetisierung nachzuweisen. / Ultrathin films of 3d-metals on a magnetic substrate can experience a magnetization due to magnetic coupling. Commonly the induced magnetic moments depend on the thickness and the structure of these films. This work is focussed on the growth properties of Fe, Cr, Mn, and V on the Fe(100) surface with respect to the morphology and the interdiffusion at the interface as well as the magnetic coupling of the film to the substrate. In the experiments mainly the grazing surface scattering of fast ions (H+, He+, Ar+) was applied with primary energies up to 25keV and typical incidence angles of 1..2° to the surface. Using this grazing scattering geometry the projectiles cannot penetrate into but are reflected from the surface. Especially the monitoring of the specular intensity and halfwidth of the resulting scattering distribution enabled the observation of growth processes in real time as well as the quantitative determination of step density, critical growth nuclei, filling of atomic layers, activation energy of lateral diffusion on the surface, change of workfunction, and the size of thermal vibrational amplitudes of the surface atoms. The excitation of Auger electrons at the surface on one hand side by grazing scattering of protons and on the other hand side by electrons at large incidence angles was used to determine the concentration profile at the interface between film and substrate at different degrees of interdiffusion. The magnetic moments of the Fe(100) surface and the 3d-metal films grown on it was indirectly characterized by the polarization of fluorescence light from the deexcitation of HeI3³P-state after the scattering. This atomic state was filled by spin polarized electrons from the surface corresponding to the surface state densities. Basic relations between the spin polarization of the HeI3³P-state and the magnetization of the scattering surface was tested at the Fe(100) surface. Applying simple models an extreme surface sensitivity of the method used here as well as the qualitative dependence of the spin polarization from electron density of states of the surface layer was observed. For the interpretation of the polarization data recorded during heteroepitactical film growth it was necessary to model the growth realistically. Therefore an existing model for homoepitactical film growth on low index surfaces was further developed in order to describe the history of interdiffusion during heteroepitactical film growth. The parameters in the model were adjusted by means of the results from the growth studies with grazing surface scattering and Auger spectroscopy. So for the first time the description of the magnetization of heteroepitactically grown 3d-metal films with nonideal layer growth and interdiffusion both related to experimental results at the same specimen was made possible. Furthermore the interaction between film structure, interdiffusion and magnetization was shown.

Magnetos de Nd-Fe-B produzidos por metalurgia do pó são altamente susceptíveis à corrosão devido à porosidade intrínseca e à sua microestrutura complexa. Por outro lado, tais ímãs apresentam excelentes propriedades magnéticas tendo por isso várias aplicações. Na área nuclear, os ímãs permanentes à base de terras raras-metais de transição-boro (Nd-Fe-B) são utilizados na fabricação de suportes magnéticos (levitação magnética) para ultra-centrífugas utilizadas no enriquecimento isotópico do urânio natural de utilização em reatores nucleares. Em Odontologia são utilizados para fixar próteses totais e parciais sobre implantes, em Ortodontia, para corrigir maloclusões e fazer movimentações dentárias e em Cirurgia buco-maxilo-facial para fixar próteses de grandes defeitos da face. Em equipamentos eletrônicos, os magnetos são utilizados em balanças, cadeados, motores elétricos e principalmente na confecção de discos rígidos de computadores.Diante disso, o objetivo deste trabalho foi avaliar o comportamento de corrosão do magneto e testar tratamentos superficiais a fim de substituir principalmente os tratamentos com cromato que hoje em dia não estão sendo mais utilizados principalmente devido à sua toxicidade e altos custos dos tratamentos dos resíduos. A avaliação da resistência à corrosão foi feita através da análise de curvas de polarização potenciodinâmica, espectroscopia de impedância eletroquímica, medidas de potencial de corrosão versus tempo e microscopia eletrônica de varredura a fim de associar a microestrutura ao comportamento de corrosão apresentado pelas amostras. Os resultados obtidos mostram que estes magnetos são altamente susceptíveis à corrosão e esta ocorre preferencialmente na fase rica em Nd, localizada nos contornos da fase matriz e magnética (). Tratamentos para proteção da superfície com revestimento de silano, revestimento de conversão de cério, moléculas auto-organizáveis (SAM), Cr hexavalente, fosfato tricatiônico seguido por passivação em solução de trióxido de cromo, e revestimento de fosfato obtido por imersão por 24 h em solução de NaH2PO4 (pH= 3,8) seguido de imersão em solução de sulfato de zinco não melhoraram a resistência à corrosão do magneto. Dentre os tratamentos utilizados, o de fosfatização por 24h em solução de NaH2PO4 (pH= 3,8) foi muito superior, conferindo maior proteção contra corrosão quando comparado com os outros tipos de tratamentos testados. ABSTRACT Nd-Fe-B magnets produced by powder metallurgy are highly susceptible to corrosion due to their complex microstructure and intrinsic porosity due to their fabrication process. Moreover, these magnets have excellent magnetic properties and find many applications. In the nuclear area, permanent magnets based on rare earth transition-iron-boron (Ne-Fe-B) are used in the manufacture of magnetic media (magnetic levitation) for ultra-centrifuges used for isotopic enrichment of uranium employed in nuclear reactors. In dentistry these types of magnets are used to fix total and partial prostheses on implants; in orthodontics to correct dental malocclusion and make moves; in buco-maxillo-facial surgery for setting facial prostheses of large defects of the face. In electronic equipment, they are used in scales, locks, electric motors and particularly in the manufacturing of hard drives of computers. The objective of this study is to evaluate the corrosion resistance of the magnet tested and surface treatments that could replace chromating that generates toxic residues and present high cost of processing waste with treatments that are environmentally friendly. The evaluation / Nd-Fe-B magnets produced by powder metallurgy are highly susceptible to corrosion due to their complex microstructure and intrinsic porosity due to their fabrication process. Moreover, these magnets have excellent magnetic properties and find many applications. In the nuclear area, permanent magnets based on rare earth transition-iron-boron (Ne-Fe-B) are used in the manufacture of magnetic media (magnetic levitation) for ultra-centrifuges used for isotopic enrichment of uranium employed in nuclear reactors. In dentistry these types of magnets are used to fix total and partial prostheses on implants; in orthodontics to correct dental malocclusion and make moves; in buco-maxillo-facial surgery for setting facial prostheses of large defects of the face. In electronic equipment, they are used in scales, locks, electric motors and particularly in the manufacturing of hard drives of computers. The objective of this study is to evaluate the corrosion resistance of the magnet tested and surface treatments that could replace chromating that generates toxic residues and present high cost of processing waste with treatments that are environmentally friendly. The evaluation of the corrosion resistance was carried out through the analysis potentiodynamic polarization curves, electrochemical impedance spectroscopy, monitoring of corrosion potential as a function of test time and scanning electron microscopy to try to correlate the magnet microstructure with its corrosion resistance. The results show that these magnets are highly susceptible to corrosion that occurs preferentially in the Nd-rich phase, located in the boundaries of the magnetic matrix phase (). Treatment with silane, cerium, sam, Cr 6+, tricationic phosphate followed by bath of chromium trioxide and in NaH2PO4 solution for 24 hours followed by bath of zinc sulphate did not improve the corrosion resistance of the magnet. Among the treatments used, immersion in NaH2PO4 solution for 24 hours pH=3.8 was the one that provided the best corrosion protection against corrosion, when compared with the other types of tested treatments.

Magnetos de Nd-Fe-B produzidos por metalurgia do pó são altamente susceptíveis à corrosão devido à porosidade intrínseca e à sua microestrutura complexa. Por outro lado, tais ímãs apresentam excelentes propriedades magnéticas tendo por isso várias aplicações. Na área nuclear, os ímãs permanentes à base de terras raras-metais de transição-boro (Nd-Fe-B) são utilizados na fabricação de suportes magnéticos (levitação magnética) para ultra-centrífugas utilizadas no enriquecimento isotópico do urânio natural de utilização em reatores nucleares. Em Odontologia são utilizados para fixar próteses totais e parciais sobre implantes, em Ortodontia, para corrigir maloclusões e fazer movimentações dentárias e em Cirurgia buco-maxilo-facial para fixar próteses de grandes defeitos da face. Em equipamentos eletrônicos, os magnetos são utilizados em balanças, cadeados, motores elétricos e principalmente na confecção de discos rígidos de computadores.Diante disso, o objetivo deste trabalho foi avaliar o comportamento de corrosão do magneto e testar tratamentos superficiais a fim de substituir principalmente os tratamentos com cromato que hoje em dia não estão sendo mais utilizados principalmente devido à sua toxicidade e altos custos dos tratamentos dos resíduos. A avaliação da resistência à corrosão foi feita através da análise de curvas de polarização potenciodinâmica, espectroscopia de impedância eletroquímica, medidas de potencial de corrosão versus tempo e microscopia eletrônica de varredura a fim de associar a microestrutura ao comportamento de corrosão apresentado pelas amostras. Os resultados obtidos mostram que estes magnetos são altamente susceptíveis à corrosão e esta ocorre preferencialmente na fase rica em Nd, localizada nos contornos da fase matriz e magnética (). Tratamentos para proteção da superfície com revestimento de silano, revestimento de conversão de cério, moléculas auto-organizáveis (SAM), Cr hexavalente, fosfato tricatiônico seguido por passivação em solução de trióxido de cromo, e revestimento de fosfato obtido por imersão por 24 h em solução de NaH2PO4 (pH= 3,8) seguido de imersão em solução de sulfato de zinco não melhoraram a resistência à corrosão do magneto. Dentre os tratamentos utilizados, o de fosfatização por 24h em solução de NaH2PO4 (pH= 3,8) foi muito superior, conferindo maior proteção contra corrosão quando comparado com os outros tipos de tratamentos testados. ABSTRACT Nd-Fe-B magnets produced by powder metallurgy are highly susceptible to corrosion due to their complex microstructure and intrinsic porosity due to their fabrication process. Moreover, these magnets have excellent magnetic properties and find many applications. In the nuclear area, permanent magnets based on rare earth transition-iron-boron (Ne-Fe-B) are used in the manufacture of magnetic media (magnetic levitation) for ultra-centrifuges used for isotopic enrichment of uranium employed in nuclear reactors. In dentistry these types of magnets are used to fix total and partial prostheses on implants; in orthodontics to correct dental malocclusion and make moves; in buco-maxillo-facial surgery for setting facial prostheses of large defects of the face. In electronic equipment, they are used in scales, locks, electric motors and particularly in the manufacturing of hard drives of computers. The objective of this study is to evaluate the corrosion resistance of the magnet tested and surface treatments that could replace chromating that generates toxic residues and present high cost of processing waste with treatments that are environmentally friendly. The evaluation / Nd-Fe-B magnets produced by powder metallurgy are highly susceptible to corrosion due to their complex microstructure and intrinsic porosity due to their fabrication process. Moreover, these magnets have excellent magnetic properties and find many applications. In the nuclear area, permanent magnets based on rare earth transition-iron-boron (Ne-Fe-B) are used in the manufacture of magnetic media (magnetic levitation) for ultra-centrifuges used for isotopic enrichment of uranium employed in nuclear reactors. In dentistry these types of magnets are used to fix total and partial prostheses on implants; in orthodontics to correct dental malocclusion and make moves; in buco-maxillo-facial surgery for setting facial prostheses of large defects of the face. In electronic equipment, they are used in scales, locks, electric motors and particularly in the manufacturing of hard drives of computers. The objective of this study is to evaluate the corrosion resistance of the magnet tested and surface treatments that could replace chromating that generates toxic residues and present high cost of processing waste with treatments that are environmentally friendly. The evaluation of the corrosion resistance was carried out through the analysis potentiodynamic polarization curves, electrochemical impedance spectroscopy, monitoring of corrosion potential as a function of test time and scanning electron microscopy to try to correlate the magnet microstructure with its corrosion resistance. The results show that these magnets are highly susceptible to corrosion that occurs preferentially in the Nd-rich phase, located in the boundaries of the magnetic matrix phase (). Treatment with silane, cerium, sam, Cr 6+, tricationic phosphate followed by bath of chromium trioxide and in NaH2PO4 solution for 24 hours followed by bath of zinc sulphate did not improve the corrosion resistance of the magnet. Among the treatments used, immersion in NaH2PO4 solution for 24 hours pH=3.8 was the one that provided the best corrosion protection against corrosion, when compared with the other types of tested treatments.

The reaction between aqueous Fe(II) and Fe(III) oxides is extremely complex, and can catalyze Fe(II)-Fe(III) electron transfer, exchange of Fe atoms between the aqueous and solid phases, mineral transformation, and contaminant reduction. Together, these processes represent a phenomenon referred to as Fe(II)-catalyzed Fe oxide recrystallization, which has been observed under controlled conditions in the laboratory for numerous Fe oxides. In the environment, Fe oxides are likely surrounded by organic carbon in various forms, but their potential to interfere with Fe(II)-catalyzed Fe oxide recrystallization, and its subsequent environmental relevance has not been well studied. The Fe(II)-catalyzed recrystallization of stable Fe oxides goethite and magnetite was studied in the presence of several environmentally relevant classes of organic carbon. For both goethite and magnetite, Fe(II)-catalyzed recrystallization continued relatively undeterred in the presence of electron shuttling compounds, natural organic matter isolates, and extracellular polysaccharides. Slight inhibition was observed when spent media from dissimilatory iron-reducing cultures was present, but only by sorbing a long-chain phospholipid to the oxides was significant inhibition observed. The lack of interference by organic carbon indicates that Fe(II)-catalyzed Fe oxide recrystallization is likely to be relevant throughout a wide range of environments, and represents a significant process with regards to the geochemical cycling of Fe atoms, a claim supported by evidence of Fe(II)-driven isotope mixing in real soils. The movement of atoms during Fe(II)-catalyzed Fe oxide recrystallization is not limited to just Fe however. Multiple trace elements have been shown to exchange between the aqueous and solid phases along with Fe during the Fe(II)-catalyzed recrystallization of Fe oxides. The effect of organic carbon, both sorbed to the oxide surface and coprecipitated with the oxide, on Fe(II)-catalyzed atom exchange and transformation of ferrihydrite was studied. Again, the presence of organic carbon did not appear to influence Fe atom exchange kinetics. It also did not appear to influence the rapid transformation of ferrihydrite to lepidocrocite. The presence of organic carbon does appear to ultimately have implications for mineral transformation, as over longer time periods it stabilized lepidocrocite, preventing its subsequent transformation to magnetite or goethite.

Human exposure to arsenic in groundwater is a global concern, and arsenic mobility in groundwater is often controlled by Fe mineral dissolution and precipitation. Additionally, Fe(II)-catalyzed recrystallization of Fe oxides has been shown to enable trace element release from and incorporation into Fe oxides. However, the effect of As(V) on the Fe(II)-catalyzed recrystallization of Fe oxides such as goethite, magnetite, and ferrihydrite remains unclear. Here, we measured the extent of Fe atom exchange between aqueous Fe(II) and magnetite, goethite, or ferrihydrite in the presence of As(V) by reacting isotopically "normal" Fe oxides with 57Fe-enriched aqueous Fe(II). At lower levels of adsorption (≤13.3 μM), As(V) had little influence on the rate or extent of Fe(II)-catalyzed Fe atom exchange in goethite or magnetite. However, Fe atom exchange was increasingly inhibited as As(V) concentration increased above 100 μM. Additionally, adsorbed As(V) may be incorporated into magnetite over time in the presence and absence of added aqueous Fe(II) as indicated by X-ray absorption spectroscopy (XAS) and chemical extraction data, with more rapid incorporation in the absence of added Fe(II). XAS and chemical extraction data are also consistent with the incorporation of As(V) during goethite and magnetite precipitation. Additionally, atom exchange data indicated that low levels of As(V) coprecipitation (As:Fe = 0.0005-0.0155) had little influence on the rate or extent of Fe(II)-catalyzed Fe atom exchange in goethite or magnetite. Atom exchange data indicated that ferrihydrite likely transforms via a dissolution-reprecipitation mechanism both to lepidocrocite at 0.2 mM Fe(II) and to magnetite at 5 mM Fe(II). The presence of 206 μM As(V) slowed the transformation of ferrihydrite to more crystalline iron minerals and slowed the rate of atom exchange between aqueous Fe(II) and ferrihydrite. However, the degree of atom exchange did not directly correlate with the amount of ferrihydrite transformed. In summary, Fe oxide recrystallization processes may affect As(V) uptake and release in the environment, and As(V) may inhibit Fe(II)-catalyzed Fe oxide recrystallization.

Processing of nanostructured WC-Co and W-Co powders,modelling of Fe-Mn-Si alloy, swelling of Fe-Cu alloy, andmechanical properties and sintering of Fe-Mn-Si steels havebeen studied in the present thesis. W-Co precursors made by chemical synthesis were used toproduce nanostructured WCCo and W-Co powders by calcination,reduction and carburization. The phase constituents in thecalcined powders depend on temperature and atmospheres. Cobaltcan accelerate the reduction rate of the W-Co precursors as acatalyst, and cobalt influences the formation of intermediatephases during the reduction of the precursors. The ratio of carbon monoxide to carbon dioxide controlscarburization process, gives different intermediate phases andcarburization rates. There exist several intermediate phases: W6Co6C, W3Co3C, W2C due to varying carbon monoxide content in thecarburization gases. Nanostructured WC-Co powders with aparticle size of 20-50 nm have been obtained. The effect of silicon content on the particle sizedistribution of milled Fe-Mn-Si master alloy powders is muchmore significant than that of manganese content. A finer finalparticle size can be obtained in the alloy powders with highersilicon compositions. Long time milling results in theagglomeration of small particles. The grinding process can bedescribed using classic batch grinding equation based on thepopulation balance model. A swelling model for Fe-Cu alloyssintered at the temperatures above the melting point of copperhas been established based on the penetration mechanism. In themodel, the particle coordination number and heating rate wereused to express the porosity and the thickness of the diffusionlayers between iron and copper particles respectively. The effects of sintering temperature and time on theproperties of sintered steels have been studied. Fe-Mn-Simaster alloys made by cast-milling, atomizing, and acombination of atomization and milling have been covered. Themilled, and atomizationmilled alloy steels showed goodmechanical properties with small dimensional change. Transientliquid phase of the Fe-Mn-Si alloys accelerates densification,and offer fast diffusion of alloying elements. The addition ofa small amount of Fe-Mn-Si master alloy to Astaloy 85Mo powdercan lead to high strength with zero dimensional change. <b>Key words:</b>Processing; Modelling; Nanostructured powder;WC-Co; W-Co; Calcination; Reduction; Carburization; Particlesize; Sintered steel; Fe-Cu alloy; Swelling; Fe-Mn-Si masteralloy; Mechanical properties; Sintering parameters.

The aim of the project presented in this thesis is to demonstrate a modelling method for predicting the variability in the ultimate load of stiffened panel under axial compression due to manufacturing variability. Bulking is sensitive to imperfections. In the case of a post-buckled panel, manu-facturing variability produces a scatter in the ultimate load. Thus, reasonable leeway for imperfections and inherent variability must be allowed in their design. Firstly, a finite element model of a particular stiffened panel was developed, and all nonlinearities within the material, boundary condition and geometry were considered. Verification and validation were performed to examine the accuracy of the buckling behaviour prediction, especially ultimate load. Experiments on 5 identical panels in design were performed to determine the level of panel-panel variation in geometry and collapse load. A data reduction programme based on the practical geometry scanning was developed, in addi-tion to which, the procedure of importing measured imperfection into Finite Ele-ment model was introduced. To identify and apply representative imperfections to the panel model, a double Fourier series representation of the random geometric distributions is attempt-ed, and was used thereby to derive a series of shapes representing random ge-ometry scatters. With these newly generated geometric imperfections, the variation in collapse load was determined, using the validated FE analysis. And also, the probability of these predicted loads was generalized.

El hierro es un elemento imprescindible para los seres vivos. En la naturalezase encuentra fundamentalmente en forma de Fe(lll) formando parte de sales ehidróxidos de muy baja solubilidad, lo que lo hace biológicamente inaccesible para losseres vivos mediante mecanismos simples de asimilación. En su forma reducida, elFe(ll) es mucho más soluble, pero también muy inestable, pasando immediatamentea Fe(lll) en presencia de oxígeno. Por otro lado, el hierro puede resultar tóxico para lacélula a concentraciones superiores a las requeridas por ésta, hecho éste que haforzado en la célula el desarrollo de mecanismos de incorporación del hierroaltamente regulados. El primer paso en la asimilación del hierro por S. cerevisiaeimplica la reducción del Fe(lll) extracitoplasmático a Fe(ll), estado en el cual el hierroes captado y transportado al citoplasma celular. En S. cerevisiae se han descrito dossistemas para la entrada de hierro en la célula. El sistema de baja afinidad, pococaracterizado hasta el momento, funciona cuando el hierro extracelular es abundante,siendo FET4 el gen que codifica para el transportador del hierro en estascondiciones, el único elemento genético de este sistema que ha sido caracterizado.Cuando el hierro es deficiente en el medio entra en funcionamiento el sistema de altaafinidad, en el que intervienen dos ferro-reductasas de membrana, productos de losgenes FRE1 y FRE2, que reducen el Fe(lll) extracitoplasmático a Fe(ll), el cual escaptado por una oxidasa de membrana, producto del gen F£T3, que se encarga depasarlo de nuevo a Fe(lll) y transportarlo al citoplasma. Resultados nuestros y deotros autores demuestran que la expresión de estos tres genes depende del productodel gen RCS1 (también denominado AFT1). RCS1 es un gen de S. cerevisiae quehabía sido parcialmente secuenciado con anterioridad; mutantes con una delecciónparcial en el mismo tenían un tamaño celular superior al de la cepa salvaje. En estetrabajo se ha completado la secuencia del gen RCS1 y se han construido mutantesnulos, esto es, portadores de una delección total del gen. Las células carentes deRCS1 no crecen en fuentes de carbono respirables como el etanol/glicerol, lo cualhizo pensar ¡nicialmente que RCS1 tuviese un papel en la desrepresión por glucosa.El análisis de la expresión de genes como ADH2 e ICL1, sometidos a represión porglucosa y necesarios para el crecimiento en este medio, ha revelado que dichaexpresión no está afectada en el muíante. La identidad de RCS1 con el gen AFT1implicado en la asimilación de hierro por otros autores nos llevó a intentar relacionarla incapacidad de los mutantes RCS1 para crecer sobre fuentes de carbonorespirables con su deficiente asimilación de hierro. Así, se ha comprobado que laausencia de crecimiento del muíante en etanol/glicerol como únicas fuentes decarbono puede suprimirse adicionando hierro en exceso al medio. Por otro lado, elcrecimiento en etanol/glicerol no requiere la inducción del sistema de alta afinidad,hecho que permite sugerir un papel adicional para RCS1 al anteriormente descrito,bien como responsable de mantener unos niveles de actividad ferro-reductasa y deentrada de hierro suficientes para el crecimiento en dicho medio, bien comoresponsable de la inducción de nuevos elementos implicados en la entrada de hierroque serían necesarios en esas condiciones, o bien porque sea necesario para unfuncionamiento eficiente del sistema de baja afinidad. La sobreexpresión de RCS1produce una detención homogénea del crecimiento celular en la fase G1 del ciclocelular, efecto no suprimible ni por privación ni por adición de hierro. El uso de lagenética de dominancia para contrarrestar este efecto podrá dar luz acerca de otrosgenes con interacción funcional con RCS1. En este trabajo se demuestra que Rcs1es o forma parte de un factor transcripcional activo sobre el promotor de FRE1. Así, laproteína Rcs1 unida al dominio de unión a DNA de la proteína Gal4 es capaz detransactivar dos sistemas reporteros (GAL1-HIS3 y GAL1-lacZ). En relación con ello,mediante estudios de retardamiento en gel, se ha podido comprobar que Rcs1 esnecesaria, en condiciones deficitarias de hierro, para la estabilidad del complejo quereconoce la zona del promotor de FRE1 responsable de su regulación por hierro. Laobtención de anticuerpos anti-Rcsl para su immunodetección ha permitido hacer unseguimiento de la proteína en diferentes condiciones. Así, se ha podido comprobarque dicha proteína está sujeta a una modificación postraduccional por fosforilación,que se produce en situaciones de detención del crecimiento celular. Estudios concepas portadoras de mutaciones en diferentes elementos de la vía Ras han permitidodescartar una implicación de la proteína quinasa A dependiente de cAMP en lafosforilación de Rcsl Asimismo, se ha visto que ósta es también independiente delas proteína quinasas producto de los genes YAK1 (que codifica para una quinasaantagónica de la proteína quinasa A) o SNF1 (quinasa necesaria para la desrepresiónpor glucosa). La fosforilación de Rcs1 parece corresponderse con una inactivación dela proteína y podría constituir un mecanismo para adaptar la entrada de hierro alestado metabólico de la célula.

<p>Processing of nanostructured WC-Co and W-Co powders,modelling of Fe-Mn-Si alloy, swelling of Fe-Cu alloy, andmechanical properties and sintering of Fe-Mn-Si steels havebeen studied in the present thesis.</p><p>W-Co precursors made by chemical synthesis were used toproduce nanostructured WCCo and W-Co powders by calcination,reduction and carburization. The phase constituents in thecalcined powders depend on temperature and atmospheres. Cobaltcan accelerate the reduction rate of the W-Co precursors as acatalyst, and cobalt influences the formation of intermediatephases during the reduction of the precursors.</p><p>The ratio of carbon monoxide to carbon dioxide controlscarburization process, gives different intermediate phases andcarburization rates. There exist several intermediate phases: W₆Co₆C, W₃Co₃C, W₂C due to varying carbon monoxide content in thecarburization gases. Nanostructured WC-Co powders with aparticle size of 20-50 nm have been obtained.</p><p>The effect of silicon content on the particle sizedistribution of milled Fe-Mn-Si master alloy powders is muchmore significant than that of manganese content. A finer finalparticle size can be obtained in the alloy powders with highersilicon compositions. Long time milling results in theagglomeration of small particles. The grinding process can bedescribed using classic batch grinding equation based on thepopulation balance model. A swelling model for Fe-Cu alloyssintered at the temperatures above the melting point of copperhas been established based on the penetration mechanism. In themodel, the particle coordination number and heating rate wereused to express the porosity and the thickness of the diffusionlayers between iron and copper particles respectively.</p><p>The effects of sintering temperature and time on theproperties of sintered steels have been studied. Fe-Mn-Simaster alloys made by cast-milling, atomizing, and acombination of atomization and milling have been covered. Themilled, and atomizationmilled alloy steels showed goodmechanical properties with small dimensional change. Transientliquid phase of the Fe-Mn-Si alloys accelerates densification,and offer fast diffusion of alloying elements. The addition ofa small amount of Fe-Mn-Si master alloy to Astaloy 85Mo powdercan lead to high strength with zero dimensional change.</p><p><b>Key words:</b>Processing; Modelling; Nanostructured powder;WC-Co; W-Co; Calcination; Reduction; Carburization; Particlesize; Sintered steel; Fe-Cu alloy; Swelling; Fe-Mn-Si masteralloy; Mechanical properties; Sintering parameters.</p>