The Sn/Pb eutectic alloy system is the most widely used joining material in the electronics industry. In this application, the solder acts as both an electrical and mechanical connection within and among the different packaging levels in an electronic device. Recent advances in packaging technologies, however, driven by the desire for miniaturization and increased circuit speed, result in severe operating conditions for the solder connection. In an effort to improve its mechanical integrity, metallic or intermetallic particles have been added to eutectic Sn/Pb solder, and termed composite solders. It was the goal of this study to investigate the growth and morphology of the two intermetallic phases (Cu6Sn5 and Cu3Sn) that form between a Cu substrate and Sn/Pb solder under different aging and annealing conditions.

No description available.

The FVS-Sn model was developed by the USDA Forest Service to project and report forest growth and yield predictions for the Southern United States. It is able to project forest growth and yield for different forest types and management prescriptions, but it is a relatively new, complex, and untested model. These limitations notwithstanding, FVS-Sn once tested and validated could meet the critical need of a comprehensive growth and yield model for the mixed hardwood forests of the southern Appalachian region. In this study, sensitivity analyses were performed on the FVS-Sn model using Latin hypercube sampling. Response surfaces were fitted to determine the magnitudes and directions of relationships between FVS-Sn model parameters and predicted 10-year basal area increment. Model sensitivities were calculated for five different test scenarios for both uncorrelated and correlated FVS-Sn input parameters and sub-models. Predicted 10-year basal area increment was most sensitive to parameters and sub-models related to the stand density index and, to a lesser degree, the large tree diameter growth sub-model. The testing procedures and framework developed in this study will serve as a template for further evaluation of FVS-Sn, including a comprehensive assessment of model uncertainties, followed by a recalibration for southern Appalachian mixed hardwood forests. / Master of Science

Les organoétains sont parmi les polluants les plus dangereux connus à ce jour à avoir été introduits dans les écosystèmes aquatiques par l'homme. Les lixiviats de décharge sont des sources importantes de ces substances toxiques. Afin de minimiser leur rejet dans l'environnement, il est important de comprendre les transformations que les organoétains subissent dans ces lixiviats et d'appliquer des procédures d'assainissement appropriées. Cette thèse a eu pour objectifs principaux i) de contribuer à une meilleure connaissance des processus de transformation des organoétains dans les lixiviats de décharge et ii) d'évaluer le potentiel d’élimination des organoétains par des nanaoparticules de fer (FeNPs). Dans la première partie, les synthèses de TBT enrichi en 117Sn, DBT enrichi en 119Sn, SnCl2 et SnCl4 enrichi en 117Sn, ont été effectuées à partir d’étain métallique enrichi en Sn. La dégradation et la biométhylation des organoétains dans des lixiviats ont été ensuite suivies pendant six mois, en utilisant des traceurs isotopiques enrichis en Sn. Pour discriminer entre les transformations biotiques et abiotiques des organoétains et de l'étain inorganique, des lixiviats stérilisés et non stérilisés ont été considérés et les concentrations en organoétains, mesurées dans chaque lixiviat, ont été comparées. Par la suite, les procédés pouvant conduire à l'élimination du TBT et du TMeT présents dans les lixiviats de décharge, par traitement du lixiviat par différents type de FeNPs ont été étudiés. Le TBT est plus efficacement éliminé (96%) lorsque un traitement séquentiel des lixiviats avec nZVI (dispersé par agitation) est appliqué, d'abord par mise en contact à pH 8, puis par traitement de la phase aqueuse avec nZVI acidifiée à pH 3 avec de l'acide citrique. Enfin, afin de prendre en compte les effets induits par les procédés de traitement par les nanoparticules de fer, leur comportement a été étudié après leur introduction dans des eaux environnementales (eau de source et lixiviat de décharge) différant par leur force ionique et leur contenu de matière organique. L'efficacité de l'élimination des métaux sélectionnés par les FeNPs a également été évaluée. Les nanoparticules ayant des éléments adsorbés à leur surface peuvent contribuer à une contamination du milieu dans lequel elles ont été introduites. / OTCs are among the most hazardous pollutants known so far to have ever been introduced into aquatic ecosystems by man. Landfill leachates are an important pool of these toxic substances. In order to minimise their release to the nearby environment it is important to understand the transformations that OTCs undergo in landfill leachates and to apply appropriate remediation procedures. This thesis has as main objectives i) to contribute to a better knowledge on transformation processes of OTCs in landfill leachates and ii) to evaluate the potential of OTCs removal by iron nanoparticles (FeNPs). In the first part, ‘‘In house’’ synthesis of individual 117Sn-enriched TBT, 119Sn-enriched DBT, 117Sn-enriched SnCl2 and 117Sn-enriched SnCl4 was performed, starting from Sn-enriched metallic tin. Next, the degradation and biomethylation of OTCs in landfill leachates were investigated over a time span of six months, using Sn-enriched isotopic tracers. To discriminate between biotic and abiotic transformations of OTCs and inorganic tin species, sterilized and non-sterilized leachate samples were investigated and the concentrations of OTCs in each sample were compared. Thereafter, the processes for the removal of TBT and TMeT from landfill leachates by different FeNPs were studied. It was proven that TBT could be the best removed by a sequential treatment procedure by first adding nZVI (dispersed by mixing) at pH 8, and then by treating with nZVI the aqueous phase, which is acidified to pH 3 with citric acid. Last, to take in account the effects that are induced by treatment procedures with FeNPs, their behaviour was studied after their introduction to environmental waters (forest spring water and landfill leachate), which differ in their ionic strength and the content of organic matter. The efficiency of the removal of selected metals by FeNPs was also evaluated. It was observed that elements which are adsorbed on the surface of FeNPs can contribute to the contamination of the environment in which they are introduced.

En tant que nouveau matériau magnétique à mémoire de forme, les alliages basés sur le système Ni-Mn-Sn possèdent de multiples propriétés physiques telles que l'effet de mémoire de forme des alliages polycristallins, l'effet magnétocalorique géant, l'effet de magnétorésistance et l'effet de polarisation d'échange. Jusqu'à présent, la plupart des études ont été axées sur l'amélioration des multifonctionnalités de ces alliages, mais l'information fondamentale qui est fortement associée à ces propriétés n'est toujours pas claire. Ainsi, une étude approfondie sur les structures cristallines de la martensite et de l'austénite, les caractéristiques microstructurales et cristallographiques de la transformation martensitique a été menée dans le cadre du présent travail de doctorat. Il a été confirmé que l'austénite de Ni50Mn37.5Sn12.5 possède une structure cubique L21 (Fm3 ̅m, No.225). Le paramètre de réseau de l'austénite dans Ni50Mn37.5Sn12.5 est aA = 5.9813 Å. La martensite possède une structure orthorhombique (4O) à quatre couches (Pmma, No.51). Les paramètres de réseau de la martensite dans Ni50Mn38Sn12 et Ni50Mn37.5Sn12.5 sont a4O = 8.6068 Å; b4O = 5.6226 Å and c4O = 4.3728 Å, and a4O = 8.6063 Å, b4O = 5.6425 Å, and c4O = 4.3672Å, respectivement. La martensite 4O Ni-Mn-Sn présente une microstructure hiérarchiquement maclée. La martensite est organisée en larges plaques dans le grain d'austénite d'origine. Les plaques contiennent des colonies à forme irrégulière avec deux modèles caractéristiques de microstructures : le motif lamellaire classique et le motif en arête de poisson. Dans chaque colonie, il existe quatre variantes d'orientation (A, B, C et D) et elles forment trois types de macles (Type I, Type II et macles composées). Les interfaces entre les variantes correspondantes sont en coincidence avec leur plan de maclage K1. Les plans d'interface des paires de macles composées A-D et B-C peuvent avoir une ou deux orientations différentes, ce qui conduit aux deux modèles microstructuraux. Les variantes correspondantes dans les colonies voisines dans une même large plaque (colonies intra-plaques) possèdent des orientations proches et le joint de colonie est courbé, tandis que la limite de colonie inter-plaques est relativement droite. La relation d’orientation de Pitsch (Orientation Relation OR), spécifiée comme {1 0 1} A//{22 ̅1}4O and <1 0 1 ̅> A//<1 ̅2 2>4O, a été exclusivement déterminée à être une OR effective entre l'austénite cubique et la martensite modulée 4O. Sous cette OR, 24 variantes peuvent être générées dans un grain d'austénite. Ces 24 variantes sont organisées en 6 groupes et chaque groupe correspond à une colonie de martensite. La structure de martensite finement maclée (microstructure sandwich) est le composant microstructural de base produit par la transformation martensitique. Une telle structure assure une interface de phase invariante (plan d'habitat) pour la transformation. Au cours de la transformation, les variantes de la martensite sont organisées en clusters en forme de diamant composés de colonies de variantes et avec des structures en forme de coin au front de transformation. Chaque coin est composé de deux structures sandwich séparées par un plan de nervure médiane {1 0 1}A. Les paires de variantes dans chaque coin devraient avoir le même type de macles avec une relation de Type I ou de Type II pour garantir de bonnes compatibilités géométriques des variantes à l'interface de phase et au plan de la nervure centrale. Dans les diamants, les colonies sont séparées par des frontières présentant des marches à faible énergie interfaciale qui évoluent vers les joints des colonies intra-plaques et par des joints droits qui deviennent les joints entre les plaques. Les diamants s'allongent le long de la direction presque parallèle aux plans de la nervure centrale des coins et la forme de la plaque de la martensite est finalement formée. [...] / Being a novel magnetic shape memory material, Ni-Mn-Sn based alloy systems possess multiple physical properties, such as shape memory effect of polycrystalline alloys, giant magnetocaloric effect, large magnetoresistance effect and exchange bias effect. So far, most studies have been focused on the improvement of the multifunctionalities of these alloys, but the fundamental information which is highly associated with these properties is still unclear. Thus, a thorough study on the crystal structures of martensite and austenite, microstructural and crystallographic features of martensitic transformation has been conducted in the present PhD work. The austenite of Ni50Mn37.5Sn12.5 was confirmed to possess a L21 cubic structure (Fm"3" ̅m, No.225). The lattice parameter of austenite in Ni50Mn37.5Sn12.5 is aA=5.9813 Å. The martensite possesses a four-layered orthorhombic (4O) structure (Pmma, No.51). The lattice parameters of martensite in Ni50Mn38Sn12 and Ni50Mn37.5Sn12.5 are a4O = 8.6068 Å; b4O = 5.6226 Å and c4O = 4.3728 Å, and a4O = 8.6063 Å, b4O = 5.6425 Å, and c4O = 4.3672Å, respectively. The 4O Ni-Mn-Sn martensite exhibits a hierarchically twinned microstructure. The martensite is organized into broad plates in the original austenite grain. The plates contain irregularly shaped colonies with two characteristic microstructural patterns: classical lamellar pattern and herring-bone pattern. In each colony, there are four orientation variants (A, B, C and D) and they form three types of twins (Type I, Type II and compound twin). The interfaces between the corresponding variants are in coincidence with their twinning plane K1. The interface planes of the compound twin pairs A-D and B-C can have one or two different orientations, which leads to the two microstructural patterns. The corresponding variants in the neighboring colonies within one broad plate (intra plate colonies) possess close orientations and colony boundary is curved, whereas the inter plate colony boundary is relatively straight. The Pitsch OR, specified as "{1 0 1}" A//"{2 " "2" ̅" " "1" ̅"}" 4O and "<1 0 " "1" ̅">" A//"<" "1" ̅" " "2" ̅" 2>" 4O, was uniquely determined to be an effective OR between the cubic austenite and 4O modulated martensite. Under this OR, 24 variants can be generated within one austenite grain. Such 24 variants are organized into 6 groups and each group corresponds to a martensite colony. The finely twinned martensite structure (sandwich microstructure) is the basic microstructural constitute produced by martensitic transformation. Such a structure ensures an invariant phase interface (habit plane) for the transformation. During the transformation, martensite variants are organized into diamond shaped clusters composed of variant colonies and with wedge shaped structures at the transformation front. Each wedge is composed of two sandwich structures separating by a midrib plane {1 0 1}A. The variant pairs in each wedge should have the same twin type with either Type I or Type II relation to ensure good geometrical compatibilities of the variants at phase interface and at the midrib plane. Within the diamonds, colonies are separated by step-like boundaries with low interfacial energy that evolve into the intra plate colony boundaries and by straight boundaries that become the inter plate colony boundaries. The diamonds elongates along the direction nearly paralleled to the midrib planes of the wedges and plate shape of martensite is finally formed. Such features of the diamond structure in Ni-Mn-Sn alloys are realized by self-accommodation of transformation strains for energy minimization. The present work provides comprehensive microstructural and crystallographic information on martensite and on martensitic transforamtion of Ni-Mn-Sn alloys and it is useful for understanding their multi functionalities associated with martensitic transformation and helpful on property optimization

O objetivo do presente trabalho é calcular o fator de utilização térmica através da aplicação do método L TS ,v . Inicialmente definimos o fator de utilização térmica f para reatores heterogêneos e homogêneos, salientando que o problema fundamental do cálculo desse fator para sistemas heterogêneos consiste em determinar os valores do fluxos médios nas regiões do combustível e do moderador. A seguir procedemos a análise do método LTS N e a sua aplicação no cálculo do fator de desvantagem p • bem como na determinação do fator de utilização térmica / The objective of thís work ís to calculate the thermal utilization factor f applying the LTS N method. First, we define the thermal utilization factor f to heterogeneous and homogeneous reactors, observing that the maín problem to calculatefto heterogeneous systems consists in calculating the average flux in the fuel and in the moderator. Afterwards, we apply the LTS N method to obtain the disadvantage factor p and the thennal utilization factor f.

Pure Sn and Sn-alloys are widely used in electrical and microelectronic devices as protective layer to prevent oxidation of Cu conductors and also as a component of Pb-free, Sn-based solders. Sn coatings, typically 0.5-10 μm thick, deposited on substrates, e.g., Cu, brass, etc., are prone to spontaneous growth (i.e., without any external stimuli) of Sn whiskers under ambient conditions. The growth of whiskers from Sn plating has caused numerous failures in micro-electronic devices, mainly due to short-circuiting, leading to failure of components or devices. Whisker growth is, thus especially very critical in aviation, space and defines applications, where the electronic components are designed for longer life span. Furthermore, due to miniaturization of electronic devices, the spacing between adjacent conductors or interconnects can be as small as a few hundred nanometres to a few micrometres, making them more prone to whisker induced short-circuiting. Minor alloying of Sn with Pub was the principle way for mitigating the whisker growth in Sn plated components; however, due to the recent worldwide acceptance of European Union’s Restriction of Hazardous Substances (RoHS) act, enforcing Pub-free manufacturing, whisker growth has re-emerged as a reliability issue in Pub-free solders and the Sn plating finishes. Even after decades of research, a universal whisker growth mechanism and hence effective mitigation technique is still not available in the public domain. This is mainly due to the fact that large number of factors that affect the whisker growth directly or indirectly, making it difficult to devise an experimental procedure, which allows studying effect of one factor at a time while keeping other factors constant. Although many mechanistic models for Sn whispering have been proposed in the past, the experimental evidences to support them are lacking. For example, recrystallization of whisker grain was proposed by various researchers; however, a direct observation confirming whisker grain is indeed a recrystallized grain has never been reported. Nevertheless, it is well understood that whisker growth is a form of stress relaxation process and diffusion plays important role in the formation of whiskers. Since Sn is extremely anisotropic with tetragonal crystal structure, the stress state of Sn coatings, as well as the diffusion needed for mass transport of atoms, varies drastically depending upon the direction of interest. Therefore, it is important to study the role of crystallographic texture (both macroscopic and microscopic) on whisker propensity by systematically varying the crystallographic texture of Sn coating while keeping thickness, grain size, substrate material, and post-deposition storage conditions the same. Better understanding of role of macro- and micro- texture is very crucial before any whispering mechanism can be proposed. Furthermore, recent studies indicate that role of stresses in Sn coatings driving whisker growth is not fully understood. It is generally accepted that compressive stress in Sn coating is the main factor that drives the whisker growth. However, whiskers were also observed when Sn coating was under tensile stress, making the role of stress controversial. Again, the stresses in Sn have multiple origins and need a systematic approach to understand their origin, quantify them and then relate it to whisker growth. Such systematic approach was never adopted in previous works. Hence, the current thesis aims to address the role of macro- and micro- crystallographic texture, stress regeneration mechanism, nature (i.e., magnitude and sign) of stress and stress gradient in the Sn coatings via systematic variation of texture, post-deposition storage conditions and substrate composition, including deposition of an interlayer in between Sn coating and the brass or Cu substrate. Whisker growth was studied from electro-deposited Sn coatings. The deposition parameters were optimized for producing different thickness and grain orientations. X-Ray diffraction (XRD) techniques were used to extract macro-texture of the coatings. The macro-texture measurement using XRD and micro-texture measurement using electron backscatter diffraction (EBSD) showed the same dominant and the second dominant orientations. It was observed that current density and deposition temperature, which are the two main electro-deposition parameters, significantly influence the crystallographic orientation of the grains. Thus, the global or macro-texture can be manipulated by changing the deposition parameters systematically. It was observed that whisker propensity increases drastically by growth of low index planes, such as (100) and (110), during deposition. Hence, proper selection of deposition parameters that lead to growth of high index planes can be used to suppress the whisker growth. Furthermore, micro-texture surrounding whisker grain was studied using EBSD technique by observing the same set of grains surrounding a whisker grain before and after whispering. Orientation imaging microscopy (OIM) maps of several whisker regions clearly indicate that whiskers preferentially grow from low index planes, such as (100), etc. Furthermore, using orientation dependent stiffness mapping (in-plane and out-of-plane), it was noticed that whiskers preferentially grew from regions of soft oriented grains (low modulus) surrounded by hard orientations. In addition, grain boundary disorientation analysis revealed presence of high fraction of high angle grain boundaries (HAGBs) in the vicinity of whisker grain. It was observed that overall fraction of HAGBs in the whispering region was 0.7 while the fraction of HAGBs surrounding and leading to whisker grain was 0.85. In addition, it was observed that whisker grew from pre-existing grain and not from the recrystallized grain. Also, grain boundary sliding was not observed as a pre-requisite for whisker growth in Sn coatings on brass substrate. The local stress field around the whisker grain also plays a crucial role in whisker growth. Therefore, local stress field around whisker site was simulated using crystal plasticity simulation by incorporating grid resolved spatial description of orientation in terms of Euler’s angles. The crystal plasticity model included slip systems of Sn and other material parameters, such as anisotropic elastic stiffness constants, critical resolved shear stresses for different slip systems, etc. Thus, the slip in individual grain was accounted following homogenization to maintain compatibility at grain boundaries. The simulated stress field shows that both in-plane and out-of-plane stresses were highly inhomogeneous without any unique condition around whisker grain. It has been observed that high compressive hydrostatic stresses develop in the vicinity of the whisker grain, while whisker grain is slightly tensile. Therefore, the gradient of hydrostatic stress around the whisker suggests whisker growth is mainly controlled by vacancy transport phenomenon. The stress in Sn coatings may originate from many factors, such as residual stress inherent to electro-deposition, diffusion of substrate atoms (Cu, Zn, etc.) into the coating, formation of interfacial intermetallic compound (IMC) layer, segregation of impurities at Sn grain boundaries, formation of surface oxide layer, and coefficient of thermal expansion (CTE) mismatch between in Sn and substrate as well as between differently orientated grains of Sn. Therefore, it is important to understand the dominant stress regeneration mechanism responsible for whisker growth. To identify dominant mechanism, which can continuously regenerate the compressive stress in Sn, samples deposited under fixed electro-deposition conditions were exposed to different post-deposition storage conditions, such as isothermal aging at room temperature, 50 °C, 150 °C, and thermal cycling from -25 to 85 °C with and without hold time at the highest temperature. It has been observed that Cu6Sn5 IMC growth due to the inter-diffusion of Cu and Sn atoms is the dominant mechanism responsible for whisker growth. Both growth kinetics and morphology of IMC have a significant impact on whisker growth. The role of CTE mismatch in regenerating compressive stresses in Sn coatings on brass substrate for whisker growth is highly limited. The substrate composition as well as the under layer metallization affects the inter-diffusion between Sn and the substrate atoms and therefore IMC growth, which is mainly responsible for whisker growth in Sn coatings on brass or Cu substrates. The effects of substrate composition on whisker growth was studied by using pure Cu, brass (65 wt. % Cu 35 wt. % Zn) and Ni (bulk and electro-deposited under layer) as substrate. Whisker growth was more rapid if brass substrate was used instead of pure Cu. Whiskers were not observed when Sn was deposited on either bulk Ni or when Ni under layer was electro-deposited on brass or Cu substrates prior to Sn deposition. Ni under layer effectively stops the diffusion of Cu into Sn, thus avoiding the growth of Cu6Sn5 (which places Sn coatings under compressive stress). Thus, it is clear that continuous formation of Cu6Sn5 at the interface provides the long-term driving force for whisker growth. Since the whisker growth is a stress driven phenomenon, it is important to understand the stress evolution in Sn coatings. Stress state of the Sn coatings was studied using custom-built laser curvature set-up with multi-beam optical stress sensor (MOSS). This allowed monitoring of curvature change of the coating-substrate system in real time and the bulk average stress was calculated using Stoney’s equation. For multi-layer system such as Sn deposited on pre-deposited Ni under layer on brass substrate modified Stoney’s equation was used. In case of Sn deposited on brass without any under layer, it is known that the Cu6Sn5 IMC do not form a continuous layer at the interface between Sn and substrate under aging at ambient conditions, therefore, the curvature change due to IMC can be neglected. In addition, glancing angle X-ray diffraction was employed to analyse stress in the top surface region of the coating. The variation of glancing angle allowed probing strain at different penetration depths. Both the bulk stress and the stress in only near surface region evolve with time. The residual bulk stresses in Sn coatings are tensile immediately after deposition. The residual stresses relax very quickly upon room temperature aging and become compressive. The bulk of Sn coatings on brass substrate progressively become more compressive upon continued aging. However, stresses in Sn coatings deposited on brass substrate with Ni under layer saturate quickly at low compressive stress. Surprisingly, stress in the top-most region of Sn coating measured using XRD evolve differently. The surface of Sn coating deposited on brass substrate is compressive initially and progressively become more tensile (less compressive), while the initial compressive stress in the sample with Ni under layer saturated at a higher compressive stress than the bulk stress value recorded from curvature measurement. Therefore, the surface of the Sn coatings with Ni under layer is always more compressive than the bulk stress in the Sn coating. Therefore, a negative stress gradient for the diffusion of Sn atoms towards surface is never established and whiskers do not grow in these Sn coatings. Interestingly, through thickness voids are observed in the Sn coatings on Ni. Contrarily, in Sn coatings without Ni under layer after 170 h of aging, the surface stress becomes more tensile than the bulk of the Sn coating, favouring continuous migration of atoms from the highly compressed region near Cu6Sn5 IMC layer to the stress-free whisker root. Aforementioned observation indicates the crucial role of negative stress gradient in the mass transport of atoms required for whispering. The importance of stress and stress gradient was further studied by analysing the effect of externally imposing stress and stress gradient on whisker growth. The stresses were applied using a three-point bend setup. It has been observed that externally applied stress accelerates the whisker growth. This is mainly because applied stress alters the diffusion kinetics and growth of Cu6Sn5 IMC at the interface. However, the coating under tensile stress shows more whisker growth as compared to the coating under high compressive stress. This is attributed to the fact the coating under tensile stress is under higher negative stress gradient. Therefore, it is proposed that out-of-plane stress gradient is more important rather than the sign and the magnitude of stress in determining the propensity of whisker growth in Sn coatings.

Made available in DSpace on 2015-05-14T13:21:38Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 8317996 bytes, checksum: 64db9066ac027260f6795886de515804 (MD5) Previous issue date: 2013-10-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Strontium stannate (SrSnO3) and titanate (SrTiO3) are perovskite type oxides that have orthorhombic (Pbnm) and cubic (Pm3m) structures, respectively. These materials have received much attention due to their interesting physical and chemical characteristics, leading to a variety of technological applications. In this sense, these two materials were combined to each other in order to obtain powders and thin films of a solid solution, SrSn1-xTixO3. In relation to the powders, this solid solution presented successive phase transitions ranging from orthorhombic and tetragonal structures to a cubic one with increasing of Ti4+ amount in the composition. These transitions were observed by XRD Rietveld refinement of the samples and confirmed by Raman spectroscopy. The different crystalline structures of the compositions within the solid solution led to different photoluminescent properties in the visible spectrum varying the range of emission, moving from a lower energy region to a higher one with increasing of Ti4+ in the structure (from orthorhombic (SrSnO3), tetragonal (SrSn0.75Ti0.25O3) to cubic (SrSn0.50Ti0.50O3 ; SrSn0.25Ti0.75O3 and SrTiO3). These emissions were probably favored by specific defects created inside the band gap of these materials. On the other hand, the thin films of this system showed different growth orientations that are associated to the crystalline nature of the substrates, the composition of the thin films and the deposition method (Chemical Solution Deposition - CSD - and Pulsed Laser Deposition - PLD). The films deposited on silica substrate were polycrystalline (random growth of the crystallites), whereas the films deposited on sapphire-R (Al2O3-012) were also polycrystalline, with a preferred orientation (h00) for the films deposited by PLD (textured growth), except SrTiO3 which was rotated 45° epitaxially in the sapphire plane. On the contrary, all of the films deposited on LAO (LaAlO3-100) had an (h00) epitaxial growth. In addition to that, the morphological characteristics and photocatalytic properties were strongly influenced also by the same parameters described above. Regarding the photocatalytic efficiency of the films, those obtained by CSD were more efficient than the ones obtained by PLD. Moreover, the films with Sn4+ richer compositions were the most active in the photodegradation of the azo dye Remazol yellow gold, reaching a maximum efficiency with the polycrystalline SrSnO3 thin film obtained by CSD whose degradation and decolorization percentage were 55 and 90 %, respectively. The type of orientation of the SrSnO3 films showed also a strong influence on the photodegradation of the dye. The polycrystalline films with a random orientation obtained on silica were more efficient than the textured films and these ones were more than the epitaxial films / O estanato (SrSnO3) e o titanato de estrôncio (SrTiO3) são óxidos do tipo perovskita que apresentam estrutura ortorrômbica (Pbnm) e cúbica (Pm3m), respectivamente. Estes materiais têm recebido bastante atenção nos últimos anos devido às suas características físicas e químicas interessantes, levando a diferentes tipos de aplicações tecnológicas. Portanto, estes dois materiais foram combinados com intuito de obter uma solução sólida, SrSn1-xTixO3, na forma de pós e filmes finos. Em relação aos pós, esta solução sólida apresentou transições de fase sucessivas com o aumento da quantidade de Ti4+ no sistema, passando de uma estrutura ortorrômbica à tetragonal levando à cúbica. Estas transições foram observadas através de difração de raios-X e refinamento Rietveld, e confirmadas por espectroscopia vibracional Raman. Os diferentes tipos de estrutura cristalina das composições da solução sólida levaram a diferentes propriedades fotoluminescentes no espectro visível, variando a região de emissão de mais baixa à mais alta energia com o aumento de Ti4+ na estrutura, ou seja, passando da estrutura ortorrômbica (SrSnO3), tetragonal (SrSn0,75Ti0,25O3) até à cúbica (SrSn0,50Ti0,50O3, SrSn0,25Ti0,75O3 e SrTiO3). Estas emissões foram provavelmente favorecidas pelos tipos de defeitos específicos criados dentro do band gap destes materiais. Por outro lado, os filmes finos deste sistema apresentaram diferentes tipos de crescimento os quais são associados à natureza cristalina dos substratos, composição dos filmes e com o método de deposição utilizado (método de deposição química em solução - CSD - e método de deposição por laser pulsado PLD). Os filmes depositados sobre sílica e safira-R (Al2O3-012) apresentaram como policristalinos (crescimento aleatorio dos cristalitos), enquanto os filmes depositados por PLD apresentaram orientação preferencial (h00) (crescimento texturizado), com exceção do filme de SrTiO3 que é epitaxial rotacionado em 45º no plano da safira-R. Todos os filmes depositados através dos dois métodos de deposição sobre LAO (LaAlO3-100) apresentaram um crescimento epitaxial (h00). Além disso, as características morfológicas e as propriedades fotocatalíticas também apresentaram forte influencia dos mesmos parâmetros acima citados. Em relação às propriedades fotocatalíticas, os filmes obtidos pelo método CSD apresentaram maior eficiência que os obtidos por PLD e os filmes com composições mais ricas em Sn4+ foram os mais ativos na fotodegradação do corante azo Remazol amarelo ouro, chegando a uma eficiência fotocatalítica máxima com o filme policristalino de SrSnO3 obtido por CSD com percentagem de degradação e de descoloração de 55 e 90 %, respectivamente. A orientação dos filmes de SrSnO3 também mostrou uma forte influencia na fotodegradação do corante, sendo os filmes policristalinos com orientação aleatória mais eficiente que o texturizado e estes por sua vez mais eficientes que os epitaxiais

O objetivo do presente trabalho é calcular o fator de utilização térmica através da aplicação do método L TS ,v . Inicialmente definimos o fator de utilização térmica f para reatores heterogêneos e homogêneos, salientando que o problema fundamental do cálculo desse fator para sistemas heterogêneos consiste em determinar os valores do fluxos médios nas regiões do combustível e do moderador. A seguir procedemos a análise do método LTS N e a sua aplicação no cálculo do fator de desvantagem p • bem como na determinação do fator de utilização térmica / The objective of thís work ís to calculate the thermal utilization factor f applying the LTS N method. First, we define the thermal utilization factor f to heterogeneous and homogeneous reactors, observing that the maín problem to calculatefto heterogeneous systems consists in calculating the average flux in the fuel and in the moderator. Afterwards, we apply the LTS N method to obtain the disadvantage factor p and the thennal utilization factor f.

O objetivo do presente trabalho é calcular o fator de utilização térmica através da aplicação do método L TS ,v . Inicialmente definimos o fator de utilização térmica f para reatores heterogêneos e homogêneos, salientando que o problema fundamental do cálculo desse fator para sistemas heterogêneos consiste em determinar os valores do fluxos médios nas regiões do combustível e do moderador. A seguir procedemos a análise do método LTS N e a sua aplicação no cálculo do fator de desvantagem p • bem como na determinação do fator de utilização térmica / The objective of thís work ís to calculate the thermal utilization factor f applying the LTS N method. First, we define the thermal utilization factor f to heterogeneous and homogeneous reactors, observing that the maín problem to calculatefto heterogeneous systems consists in calculating the average flux in the fuel and in the moderator. Afterwards, we apply the LTS N method to obtain the disadvantage factor p and the thennal utilization factor f.