Thesis (MPhil (Sociology and Social Anthropology))--University of Stellenbosch, 2010. / ENGLISH SUMMARY: This study focuses on the shortage of labour in the rural areas of the Free State and, in direct contrast to the high unemployment figures and great demand for jobs. The upskilling of unskilled labour is one of South Africa’s biggest social problems. It is becoming ever more pressing given the increasing demand for skilled labour to adapt to technological advancement and the new information era. The South African government has created various initiatives and policies to accommodate and provide previously disadvantaged groups with opportunities for training and better life prospects. Viewing South Africa’s rural areas from a historical perspective may result in scepticism about the success of these training initiatives and question the commitment of private business towards these policies. Policies and regulations increasingly place greater administrative pressure on workplaces, which could lead to the expectation that training in companies would merely be regarded as an extra burden. The VKB, a local agricultural co-operative in the Free State, challenges this assumption. This study investigates the experiences and expectations of employees to determine the impact of training on individuals. Interviews with employees and management in the company show that training plays a crucial role in producing solidarity in a stable workplace environment. For both groups, government-proposed education and training are regarded as very important in their own lives and for the future development of South Africa. / AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die tekort aan arbeid wat in die plattelandse gebiede van die Vrystaat ondervind word, in teenstelling met die hoë werkloosheidsyfer en behoefte aan werksgeleenthede in dié gebied. Die verdere opleiding van ongeskoolde arbeid is een van Suid-Afrika se grootste maatskaplike probleme. Dié kwessie raak al hoe meer relevant gegewe die groter aanvraag na geskoolde arbeid om aan te pas by tegnologiese vooruitgang en die eise van die inligtingsera. Die Suid-Afrikaanse regering het verskeie inisiatiewe en beleide ingestel om opleidingsgeleenthede en beter vooruitsigte vir voorheen benadeelde groepe daar te stel. As die Suid-Afrikaanse platteland vanuit ’n historiese perspektief beskou word, kan ’n mens skepties staan teenoor die wyse waarop sakeondernemings hierdie beleide sal aanvaar en toepas. Hierbenewens plaas beleide en wetgewing ook geweldige administratiewe druk op ondernemings, wat aanleiding kan gee tot die vermoede dat maatskappye opleiding slegs as ’n ekstra las sou beskou. Die VKB, ’n plaaslike landboukoöperasie in die Vrystaat, bewys egter die teendeel van hierdie aanname. Dit bring hierdie studie tot die punt van ondersoek, waar die ervaring en verwagtings van werknemers ondersoek word om vas te stel watter impak opleiding op individue het. Persoonlike onderhoude met werknemers en die bestuur dui daarop dat opleiding ’n belangrike faktor is wat samehorigheid in ’n stabiele werksomgewing in die hand werk. Albei groepe beskou opleiding en onderrig, soos voorgestel deur die regering, as uiters belangrik in hulle eie lewens en vir die algehele ontwikkeling van Suid-Afrika.

La recherche de "solutions aciers" peu coûteuses alliant conjointement allègement pondéral et sécurité passive est au cœur des problématiques actuelles dans l'industrie automobile. C'est pourquoi le développement de nuances à haute résistance s'en trouve fortement accru, en particulier les alliages inoxydables austénitiques qui présentent une transformation induite par la plasticité (effet TRIP), laquelle améliore considérablement les propriétés mécaniques de ces aciers. L'introduction dans les codes de calcul lors du prototypage de véhicules des modèles appropriés, passe par une bonne connaissance des mécanismes de transformation et de déformation se produisant dans ces matériaux. On a étudié le comportement mécanique et la transformation martensitique dans deux aciers inoxydables austénitiques : 301LN et 201. Pour connaître l'influence de la température sur le comportement de ces alliages, des essais de traction ont été réalisés dans le domaine de température [-150°C ; 150°C] couvrant largement les conditions de mise en forme et de crash en zone froide. De même, l'analyse de la résistance des matériaux au crash a été effectuée via l'étude du comportement en traction aux grandes vitesses de déformation s'étendant de 5.10-4 s-1 à 200 s-1. Des mesures de dosage magnétique à saturation ont permis d'évaluer les fractions volumiques de martensite alpha' formée dans les différentes conditions thermomécaniques. Une loi de transformation thermodynamique a été écrite permettant de modéliser les cinétiques de transformation gamma → alpha' obtenues. Les microstructures de déformation ont été identifiées par diffraction des rayons X et par microscopie électronique en transmission. L'établissement de cartographies de ces microstructures en fonction de la température et de la vitesse de déformation a permis de déterminer les modes de transformation et de déformation dans chaque alliage. On montre que l'accroissement de la vitesse de déformation favorise l'apparition de défauts planaires et la formation de martensite alpha' quand la température en cours d'essai est proche de Md. Outre les caractéristiques en traction, l'influence du taux de triaxialité sur la transformation martensitique a été étudiée. Les chargements suivants ont été appliqués : cisaillement simple, traction plane et expansion équibiaxiale. Les fractions volumiques relevées dans ces conditions laissent penser que l'état de déformation local dans les alliages est un paramètre significatif pour décrire la transformation martensitique. L'impact de chargements non proportionnels a été étudié en faisant varier pour un échantillon donné, l'orientation de la sollicitation dans deux directions non parallèles. Les modifications relevées sur les courbes de traction ainsi que les fractions volumiques mesurées font ressortir l'importance de la prise en compte de la transformation martensitique à l'échelle des systèmes de glissement mis en jeu. Il ressort principalement de cette étude : (i) que les deux nuances 301LN et 201 sont substituables pour les applications visées malgré une différence des modes de déformation. (ii) que l'augmentation de la vitesse de déformation favorise la formation de martensites (alpha' et epsilon et de macles. (iii) qu'une bonne représentation des cinétiques de transformation passe par la description de la transformation à l'échelle cristalline. (iv) que les modèles classiques d'homogénéisation de composite sont insuffisants pour rendre compte du caractère adoucissant de la transformation de phase.

Les oxydes à base de Cérium, ont fait l'objet de nombreuses études ces dernières décennies et se sont révélés des matériaux de choix, dans le domaine de la catalyse hétérogène. L'objectif à l'heure actuelle, est donc d'accroître la réactivité de ces oxydes, tout en élargissant leur gamme de températures optimales d'utilisation. Dans ce contexte particulier, il semble possible de moduler les propriétés des oxydes à base de cérium en contrôlant la morphologie des cristallites. Ce travail de thèse a donc été consacré à la détermination, l'élaboration et à la caractérisation de matériaux oxydes à base de cérium de morphologies contrôlées. Nous avons tout d'abord déterminé cristallographiquement et thermodynamiquement les morphologies accessibles au système étudié puis par traitement hydrothermale assistée par chauffage micro-ondes nous avons synthétisé les dites morphologies. Après caractérisation de la réactivité par ATG et thermographie Infrarouge nous avons optimisé ces matériaux par un dopage extrinsèque tout d'abord (dépôt de métaux précieux), puis par un dopage intrinsèque ensuite (Yttrium et Fer). Enfin, l'obtention de morphologies non accessibles cristallographiquement nous a amené à approfondir le(s) processus de germination croissance de ces particules et la forte réactivité des matériaux dopés fer nous a poussé à une caractérisation fine de la microstructure de ces matériaux. Au final nous avons pu corréler l'influence de la morphologie des cristallites sur la réactivité propre de l'ensemble des familles de matériaux étudiés.

Les performances dans les deux principales applications en électrochimie (batterie primaire au lithium) et en tribologie (lubrifiant solide) de carbones fluorés nanostructurés obtenus par fluoration directe sous fluor moléculaire étaient déjà remarquables mais non - optimisées du fait de la présence de défauts structuraux. Ainsi de nouvelles méthodes de synthèse ont été étudiées pour réduire ces défauts. En fonction du matériau à fonctionnaliser, différentes stratégies de synthèse ont été testées telles que la fluoration assistée, la mécanosynthèse sous atmosphère de fluor gazeux et la fluoration par décomposition d'agent fluorant appelée également fluoration contrôlée. La méthode par agent fluorant avec le tetrafluorure de terbium (TbF4) et le difluorure de xénon (XeF2) a été optimisée. Les propriétés électrochimiques, sensiblement améliorées, et tribologiques, maintenues excellentes, des nanocarbones fluorés obtenues par ces méthodes ont été axpliquées par une caractérisation physico-chimique approfondie et une combinaison de techniques (Résonance Magnétique Nucléaire, Résonance Paramagnétique Electronique, Microscopie Electronique à Balayage et à Transmission, Microscopie à Force Atomique, Raman, Diffraction des Rayons X). Les mécanismes se distinguent entre les fluorations directes et contrôlée par la nature de l'espèce réactive, fluor moléculaire ou atomique, respectivement

A series of studies are presented on the genetic evaluation of cultivated potato (Solanum tuberosum L.) to improve the accuracy and efficiency of selection at various stages of a breeding programme. The central theme was the use of correlated data, such as relationship information and spatial and across-trial correlations, within a linear mixed modelling framework to enhance the evaluation of candidate genotypes and to improve the genetic response to selection. Analyses focused on several social and economically-important traits for the enhancement of the nutritional value, disease resistance and yield of potato tubers. At the formative stages of a breeding scheme, devising a breeding strategy requires an improved understanding of the genetic control of target traits for selection. To guide a strategy that aims to enhance the micronutrient content of potato tubers (biofortification), univariate and multivariate Bayesian models were developed to estimate genetic parameters for micronutrient tuber content from a breeding population generated from crosses between Andean landrace cultivars. The importance of the additive genetic components and extent of the narrow-sense heritability estimates indicated that genotypic 'individual' recurrent selection based on empirical breeding values rather than family-based selection is likely to be the most effective strategy in this breeding population. The magnitude of genetic correlations also indicated that simultaneous increases in important tuber minerals, iron and zinc, could be achieved. Optimising selection efficiency is an important ambition of plant breeding programmes. Reducing the level of candidate replication in field trials may, under certain circumstances, contribute to this aim. Empirical field data and computer simulations inferred that improved rates of genetic gain with p-rep (partially replicated) testing could be obtained compared with testing in fully replicated trials at the early selection stages, particularly when testing over two locations. P-rep testing was able to increase the intensity of selection and the distribution of candidate entries across locations to account for G×E effects was possible at an earlier stage than is currently practised. On the basis of these results, it was recommended that the full replication of trials (at the first opportunity, when enough planting material is available) at a single location in the early stages of selection should be replaced with the partial replication of selection candidates that are distributed over two locations. Genetic evaluation aims to identify genotypes with high empirical breeding values (EBVs) for selection as parents. Using mixed models, spatial parameters to target greater control of localised field heterogeneity were estimated and variance models to account for across-trial genetic heterogeneity were tested for the evaluation of soil-borne powdery scab disease and tuber yield traits at the early stages of a selection programme. When spatial effects improved model fit, spatial correlations for rows and columns were mostly small for powdery scab, and often small and negative for marketable and total tuber yield suggesting the presence of interplot competition in some years for tuber yield traits. For the evaluation of powdery scab, genetic variance structures were tested using data from 12 years of long-term potato breeding METs (multi-environment trials). A simple homogeneous correlation model for the genetic effects was preferred over a more complex factor analytic (FA) model. Similarly, for the MET evaluation of tuber yield at the early stages, there was little benefit in using more complex FA models, with simple correlation structures generally the most favourable models fitted. The use of less complex models will be more straightforward for routine implementation of potato genetic evaluations in breeding programmes. Evaluations for (marketable) tuber yield were extended to multi-location MET data to characterise both genotypes and environments, allowing a re-evaluation of New Zealand MET selection strategies aimed at broad adaptation. Using a factor analytic mixed model, results indicated that the programme’s two main trial locations in the North and the South Islands optimised differentiation between genotypes in terms of G×E effects. There was reasonable performance stability of genotypes across test locations and evidence was presented for some, but limited, genetic progress of cultivars and advanced clonal selections for tuber marketable yield in New Zealand over recent years. The models and selection strategies investigated and developed in this thesis will allow an improved and more systematic application of genetic evaluations in potato selection schemes. This will provide the basis for well informed decisions to be made on selection candidates for the genetic improvement of potato in breeding programmes.

Dans le contexte général lié aux économies d’énergie, l’amélioration sensible du rendement des turbines à gaz (aéronautiques ou terrestres), nécessitera d’augmenter notablement la température des gaz de combustion. Cela implique l’emploi de matériaux stables au-delà de 1 500°C. Les céramiques eutectiques préparées par solidification dirigée, à partir des systèmes Al2O3 - Ln2O3 (où Ln représente un élément lanthanide ou l’yttrium) sont une solution envisageable. En effet, leur microstructure, constituée d’un réseau interpénétré 3D de deux phases monocristallines, et exempte de pores, de colonies et de joints de grains, confère à ces systèmes eutectiques des propriétés mécaniques d’un bon niveau, et quasi-constantes jusqu’à des températures proches de leur température eutectique (> 1 700°C). Nos travaux ont consisté à élaborer plusieurs systèmes eutectiques binaires et ternaires, par ajout d’une phase ZrO2 renforçante. Les six systèmes présentant les microstructures les plus prometteuses (3 binaires : Al2O3 - Y3Al5O12, Al2O3 - Er3Al5O12, Al2O3 - GdAlO3, et 3 ternaires : Al2O3 - Y3Al5O12 - ZrO2, Al2O3 - Er3Al5O12 - ZrO2, Al2O3 - GdAlO3 - ZrO2) ont été retenus pour étudier certaines de leurs propriétés mécaniques. Plusieurs modes de fissuration, allant dans le sens de l’augmentation de ténacité détectée dans ces systèmes, ont été décelés après des essais de flexion biaxiale. Ces modes de fissuration ont été corrélés aux caractéristiques microstructurales et à la distribution des contraintes résiduelles, déterminées par le calcul et mesurées par une méthode piézo-spectroscopique. Enfin, l’étude du comportement en fluage à haute température a permis de mettre en évidence une évolution des mécanismes de déformation en fonction des conditions de sollicitation. L’étude MET post mortem a également souligné l’influence marquée du caractère interconnecté de la microstructure sur le comportement en fluage. / In the general context of energy savings at a global scale, the improvement of the thermal efficiency of both terrestrial and aeronautical gas turbines will require to increase the turbine inlet gas temperature. The development of new materials, stable up to 1 500°C, is thus necessary. In this context, Directionally Solidified Eutectic Ceramics (DSEC), prepared from Al2O3 and Ln2O3-based systems, could be a potential solution. Their microstructure consists of two single-crystal phases continuously entangled in a threedimensional interpenetrating network without grain boundaries, pores or colonies. The outstanding stability of these microstructures gives rise to a high strength and creep resistance at high temperature. Our research consisted first in obtaining, by directional solidification, several eutectic systems, either binary or ternary (with addition of a toughening third ZrO2 phase). The six most promising DSEC (3 binary systems: Al2O3 - Y3Al5O12, Al2O3 - Er3Al5O12, Al2O3 - GdAlO3, and 3 ternary systems: Al2O3 - Y3Al5O12 - ZrO2, Al2O3 - Er3Al5O12 - ZrO2, Al2O3 - GdAlO3 - ZrO2) have then been selected to study some of their mechanical properties. Several crack propagation patterns have been detected after biaxial flexure testing, and partially explain the toughening which has been proven for DSEC. Attention has been paid to the possibility of crack deflection in the various phases and in the phase boundaries, a phenomenon which may markedly improve the toughness of these eutectic ceramics. These observations have been correlated to internal stress calculations and piezo-spectroscopic measurements. Finally, the study of the creep behavior showed that the deformation mechanisms evolve with the macroscopic solicitation (temperature and stress). microstructure. Moreover, post mortem TEM observations exhibited that creep mechanisms are strongly dependant on the entangled microstructure.

Entender o clima dos espaços urbanos em suas diversas conformações é objeto de grande interesse para a melhoria da qualidade de vida da população que usufrui desses espaços. Cada microclima requer intervenções específicas para a obtenção de condições favoráveis de conforto higrotérmico tendo em vista a saúde e o bem estar de seus usuários. O objetivo desta pesquisa foi avaliar elementos de vegetação como barreira aos ventos visando o conforto térmico em espaços abertos. O procedimento utilizado foi quantificar a interferência de elementos vegetais na passagem dos ventos, na altura dos pedestres, a partir de configurações de vegetação pré-estabelecidas. O cenário eleito para este estudo foi a área externa do Campus da Universidade Metodista de Piracicaba (UNIMEP), localizado no bairro Taquaral em Piracicaba, SP. Embora trate-se de clima predominantemente quente, há relatos de desconforto no local em dias frios decorrente do excesso de ventos. Foram estudadas três diferentes espécies dispostas em arranjos com intenção de barreira aos ventos: Jasminum mesnyi Hance, Pseudosasa japonica (Steud.) Makino e Pinus caribaea Morelet. As variáveis microclimáticas medidas foram temperatura do ar, umidade relativa do ar e velocidade dos ventos, em três posições distintas por espécie: em um campo aberto próximo, antes e depois da barreira. O período de coleta de dados foi das 9 às 21 horas, em intervalos de 3 minutos, durante três dias por espécie, nos meses de agosto e setembro de 2014. Os resultados obtidos no campo aberto foram comparados aos registrados na estação meteorológica da ESALQ-USP no mesmo período. Foi feita a medição do LAI (Índice de Área Foliar) das espécies. Foram realizadas simulações computacionais em modelagem da área no programa ENVI-met® 3.1, com os dados de Densidade de Área Foliar (LAD) estimados a partir dos valores de LAI obtidos nas medições, como parte dos estudos de viabilidade para adoção do LAI como parâmetro na previsão de resultados, o que permitiria sua aplicabilidade a outras espécies. Os resultados obtidos indicam uma tendência favorável a este princípio, porém estudos com maior intensidade amostral são necessários para obtenção desta correlação. Outras aplicações podem ser beneficiadas com esta linha de estudo, como a previsão do risco de queda de árvores. / Understanding the climate of urban spaces in their various conformations is subject of great interest to improve the quality of life of the population that occupies these spaces. Each microclimate requires specific interventions to obtain favorable terms of hygrothermal comfort owing to health and welfare of its members. The objective of this research was to evaluate plant matter as a barrier to winds targeting the thermal comfort in open spaces. The procedure was quantifying the interference of tree elements in the passage of winds, at a pedestrian level, from pre-established vegetation settings. The chosen scenario for this study was the campus of the Universidade Metodista de Piracicaba (UNIMEP), located in the Taquaral neighborhood in Piracicaba, SP. While dealing is predominantly warm weather, discomfort is reported in cold weather due to the excessive winds in the external areas. We studied three different species placed in arrangements intended as wind barriers: Jasminum mesnyi Hance, Pseudosasa japonica (Steud.) Makino and Pinus caribaea Morelet. Microclimate variables measured were air temperature, relative humidity and wind speed, in three different positions by species: in a nearby open field, before and after the barrier. The data collection period was from 9 to 21 o\'clock, at 3-minute intervals for three days by species, in August and September 2014. Results obtained in open field were compared with those recorded at ESALQ-USP\'s weather station during the same period. The LAI (Leaf Area Index) of the species was measured. Computer simulations were performed by modeling the area in ENVImet® 3.1 program, with the Leaf Area Density data (LAD) estimated from the LAI values obtained in measurements, as part of feasibility studies for the adoption of LAI as a parameter in the forecast results, allowing its applicability to other species. The results indicate a positive trend towards this principle, however, studies with larger sample intensity are required in order to achieve this correlation. Other applications may benefit from this line of study, such as the prediction of falling trees risks.

Este trabalho apresenta resultados de estudos e caracterizações de Conjuntos Eletrodo/Membrana (MEAs) de Células a Combustível a Membrana Polimérica (PEMFC). Algumas condições de operação de células e diferentes processos de produção de MEA foram investigados. A técnica de Espectroscopia de Impedância Eletroquímica (EIE) (em situ - 0 a 16 A) foi usada \"on-line\" como uma ferramenta de diagnóstico, relativa ao desempenho de célula. As medidas de EIE foram feitas através do Sistema de EIE para células a combustível FC350 (GAMRY), junto a um PC4 Potentiostato/Galvanostato e conectado à carga dinâmica (TDI) para experimentos de EIE \"on-line\" (100 mHz - 10 kHz, dU = 5 mV). MEAs com 25 cm2 de área ativa, usando eletrocatalisadores PtM/C 20 % (M = Ru, Sn ou Ni) fabricados usando o Método de Redução por Álcool (MRA). A tinta catalítica foi diretamente aplicada no Tecido de Carbono (GDL) e este prensado na membrana de Nafion® (105). MEAs usando eletrocatalisadores Pt/C e PtRu/C 20 % da E-TEK foram fabricados para comparação. Todos os cátodos foram confeccionados com Pt/C 20% da E-TEK. Foram fixadas as concentrações de metal nobre em 0,4 mg Pt.cm-2 no anodo e 0,6 mg Pt.cm-2 no catodo (E-TEK). Diagramas de Nyquist dos MEAs com Pt/C e PtRu/C da E-TEK ou PtM/C MRA apresentaram as mesmas resistências de ôhmicas para os MEAs. Este fato pode ser explicado por supressão de aglomerados durante o processo de preparação do MEA ou pela homogeneidade do eletrocatalisador ancorado ao carbono. Também pôde ser observado, a baixas densidades atuais que há uma diferença de desempenho significante entre o eletrocatalisadores da ETEK e os preparados pelo MRA. Os resultados das curvas de polarização confirmaram que PtM/C MRA apresentara um aumento de atividade para as células alimentadas com metanol e etanol. A técnica de EIE se mostrou eficiente para a avaliação do método de preparação dos MEAs e do desempenho da célula, os resultados de EIE mostraram uma coerência na escolha do modelo do circuito elétrico para os MEAs utilizando hidrogênio, metanol e etanol. Esta coerência indica que outras resistências não consideradas no modelo não são relevantes na resistência total dos MEAs. / This work reports results of studies and characterization on Membrane Electrode Assemblies (MEAs) for Proton Exchange Membrane Fuel Cell (PEMFC). Some cell operation conditions and different processes of MEA production were investigated. The Electrochemical Impedance Spectroscopy Technique (EIS) (in situ - 0 to 16 A) was used \"on-line\" as a tool for diagnosis, concerning the cell performance. The EIS measurements were carried out with a FC350 Fuel Cell EIS System (GAMRY), coupled to a PC4 Potentiostat/Galvanostat and connected to the electronic load (TDI) for \"on-line\" EIS experiments (100 mHz - 10 kHz, dU = 5 mV). MEAs with 25 cm2 surface area, using PtM/C 20% (M = Ru, Sn or Ni) electrocatalysts were manufactured using the Alcohol Reduction Process (ARP). The catalytic ink was applied directly into the Carbon Cloth (GDL) and pressed in the NafionR membrane (105). MEAs using Pt/C and PtRu/C 20% from E-TEK electrocatalysts were manufactured by comparison. All the cathodes were sprayed with Pt/C 20% from E-TEK. The noble metal concentrations used were set to 0.4 mg Pt.cm-2 at the anode and 0.6 mg Pt.cm-2 at the cathode (E-TEK). Nyquist diagrams of the MEAs with Pt/C and PtRu/C from E-TEK or PtM/C (M = Ru, Sn or Ni) ARP showed essentially the same ohmic resistances for the MEAs. This fact can be explained by suppression of agglomerates during the MEA preparation process or by the homogeneity of the anchored electrocatalysts at the carbon surface. It could also be observed, at low current densities, that there was a significant performance difference between the electrocatalysts from E-TEK and those prepared with the Alcohol Reduction Process. The polarization curves results confirmed that the PtM/C (M = Ru, Sn or Ni) ARP showed an activity increase for the methanol and ethanol fed cells. The technique of EIE was shown efficient for the evaluation of the method preparation of MEAs and the acting of the cell, the results of EIE showed coherence in the choice of the model the electric circuit for MEAs using hydrogen, methanol and ethanol. This coherence indicates that other resistances no considered in the model are not relevant in the total resistance of MEAs.

Les nanomatériaux sont de plus en plus utilisés dans de nombreusesapplications, que cela soit pour la catalyse, la coloration, l’optique, etc. Pour optimiser leurutilisation, il est nécessaire de mieux comprendre les réactions et interactions ayant lieu à ceséchelles. Cette thèse se propose d’essayer d’explorer les liens entre conditions de synthèse,morphologie de particules, et propriétés de celles-ci. En particulier, nous avons opté pourl’étude d’un matériau modèle : l’oxyde de cérium (IV). Les nanoparticules de CeO2 ont étéobtenues par voie de synthèse solvothermale assistée par chauffage micro-ondes. Lesmorphologies des nanoparticules de CeO2 étudiées ont été : les cubes, les octaèdres et lesbâtonnets, et nous avons essayé de fournir une explication à leur obtention par la voie desynthèse utilisée. De l’or a ensuite été déposé en surface des ces nanoparticules de CeO2 etétudié par une combinaison d’études par Microscopie Électronique en Transmission et demodélisations numériques. / Nanomaterials are more and more used in various situations, such as catalysis,color, optics, etc. To optimize their use, it is necessary to better understand reactions andinteractions taking place at these scales. This PhD thesis aims at exploring the links betweensynthesis conditions, particle morphology and their properties. In particular, we chose a tostudy a model-material: cerium (IV) oxide. CeO2 nanoparticles have been obtained bymicrowave-heating assisted solvothermal synthesis. Morphologies obtained and studied havebeen: cubes, octahedrons and rods. We tried to to give an explanation on how these synthesesallowed the formation of such morphologies. Gold has then be deposed on the surface of theseCeO2 nanoparticles, and studied by a combination of Transmission Electron Microscopystudies, and computer modelizations.

Made available in DSpace on 2015-04-14T13:58:26Z (GMT). No. of bitstreams: 1 401359.pdf: 12495534 bytes, checksum: bd668e0363476d80fd75b86b4d4afe67 (MD5) Previous issue date: 2008-03-26 / A Zn-22%Al ? uma liga eutet?ide de zinco sendo o alum?nio o principal elemento de liga, com alta resist?ncia ? corros?o, boa fluidez no estado l?quido, apresentando superplasticidade ap?s tratamento t?rmico. A complexidade das fases presentes na liga bruta de fus?o se deve a forma??o da fase eutet?ide (α+η) por decomposi??o da fase metaest?vel β - rede c?bica de face centrada, no ponto eutet?ide. O eutet?ide possui estrutura lamelar formada pela fase α - rede c?bica de corpo centrado e pela fase η - rede hexagonal compacta. Durante o envelhecimento, ocorre uma mudan?a na microestrutura com libera??o de calor (rea??o exot?rmica). O objetivo deste estudo foi verificar a rela??o entre a taxa de resfriamento (na solidifica??o at? forma??o do eutet?ide) com a morfologia das fases obtidas antes ap?s o tratamento t?rmico e a temperatura alcan?ada na rea??o exot?rmica. Ap?s a obten??o da liga, lingotes de Zn-22%Al foram refundidos sobre arg?nio, em uma barqueta de grafite, em um forno tubular. A solidifica??o e o resfriamento foram monitorados pelo sistema de an?lise t?rmica. No tratamento t?rmico amostras foram aquecidas acima do ponto eutet?ide, resfriadas em uma mistura de ?gua e gelo (em equil?brio) e deixadas envelhecer em repouso, recobertas com manta t?rmica refrat?ria. Para as an?lises metalogr?ficas e os ensaios de dureza foram obtidos quatro diferentes tipos de amostras da parte central do lingote, sendo elas: solidificadas e resfriadas dentro e fora do forno, com e sem tratamento t?rmico. Amostras foram caracterizadas por microscopia ?ptica, microscopia eletr?nica de varredura e microan?lise por EDS (electron dispersive spectroscopy). Com base nos resultados obtidos pode-se verificar que a taxa de solidifica??o e resfriamento apresentam grande influ?ncia na forma??o da macroestrutura, e na microestrutura antes a ap?s tratamento t?rmico. Observou-se que a temperatura atingida pela amostra durante o envelhecimento ? dependente da homogeneidade da composi??o da estrutura lamelar (α+η), isto ?, amostras solidificadas e resfriadas com taxas maiores, atingiram temperaturas maiores. Atrav?s dos ensaios metalogr?ficos, de dureza e microdureza, conclui-se que o aquecimento ocorre durante a mudan?a da morfologia da fase (α+η) de lamelar para quase-globular, que ocorre durante o envelhecimento.