Atmospheric plasma sprayed (APS) thermal barrier coatings (TBCs) are commonly used for thermal protection of components in modern gas turbine application such as power generation, marine and aero engines. TBC is a duplex material system consisting of an insulating ceramic topcoat layer and an intermetallic bondcoat layer. TBC microstructures are highly heterogeneous, consisting of defects such as pores and cracks of different sizes which determine the coating's final thermal and mechanical properties, and the service lives of the coatings. Failure in APS TBCs is mainly associated with the thermo-mechanical stresses developing due to the thermally grown oxide (TGO) layer growth at the topcoat-bondcoat interface and thermal expansion mismatch during thermal cycling. The interface roughness has been shown to play a major role in the development of these induced stresses and lifetime of TBCs.The objective of this thesis work was two-fold for one purpose: to design an optimised TBC to be used for next generation gas turbines. The first objective was to investigate the relationships between coating microstructure and thermal-mechanical properties of topcoats, and to utilise these relationships to design an optimised morphology of the topcoat microstructure. The second objective was to investigate the relationships between topcoat-bondcoat interface roughness, TGO growth and lifetime of TBCs, and to utilise these relationships to design an optimal interface. Simulation technique was used to achieve these objectives. Important microstructural parameters influencing the performance of topcoats were identified and coatings with the feasible identified microstructural parameters were designed, modelled and experimentally verified. It was shown that large globular pores with connected cracks inherited within the topcoat microstructure significantly enhanced TBC performance. Real topcoat-bondcoat interface topographies were used to calculate the induced stresses and a diffusion based TGO growth model was developed to assess the lifetime. The modelling results were compared with existing theories published in previous works and experiments. It was shown that the modelling approach developed in this work could be used as a powerful tool to design new coatings and interfaces as well as to achieve high performance optimised morphologies.

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The utilization of thermal fluctuations or Johnson/Nyquist noise as a spectroscopic method to determine transport properties in conductors or semiconductors is developed in this paper. The autocorrelation function is obtained from power spectral density measurements thus enabling electronic transport property calculation through the Green-Kubo formalism. This experimental approach is distinct from traditional numerical methods such as molecular dynamics simulations, which have been used to extract the autocorrelation function and directly related physics only. This work reports multi-transport property measurements consisting of the electronic relaxation time, resistivity, mobility, diffusion coefficient, electronic contribution to thermal conductivity and Lorenz number from experimental data. Double validation of the experiment was accomplished through the use of a standard reference material and a standard measurement method, i.e. four-probe collinear resistivity technique. The advantages to this new experimental technique include the elimination of any required thermal or potential gradients, multi-transport property measurements within one experiment, very low error and the ability to apply controlled boundary conditions while gathering data. This research has experimentally assessed the gas pressure and flow effects of helium and argon on 30 nm Au and Cu thin films. The results show a reduction in Au and Cu electronic thermal conductivity and electrical resistivity when subjected to helium and argon pressure and flow. The perturbed electronic transport coefficients, attributed to increased electron scattering at the surface, were so dominant that further data was collected through straight-forward resistance measurements. The resistance data confirmed the thermal noise measurements thus lending considerable evidence to the presence of thin film surface scattering due to elastic and inelastic gas particle scattering effects with the electron ensemble.

Dans les applications nucléaires, les propriétés des matériaux peuvent subir des modifications importantes en raison de l'interaction destructive avec l'irradiation de particules au niveau des microstructures, qui affectent les propriétés globales. L'un des défis associés aux études de matériaux irradiés par des ions, c'est que la couche concernée, ou la profondeur de pénétration, est généralement très mince (0,1-100 um). Cette étude élargit la base des connaissances actuelles en matière de transport thermique dans les matériaux irradiés par des ions, en utilisant une approche expérimentale multiéchelles avec des méthodes basées sur des ondes thermiques. D'une manière pas encore explorée auparavant, quatre méthodes sont utilisées pour caractériser la couche irradiée par des protons dans ZrC : la microscopie thermique à balayage (SThM), la radiométrie photothermique (PTR) avec détection sur la face avant et balayage spatial, la thermographie infrarouge lock-In (IRT), et la PTR tomographique avec balayage en fréquence. Pour la première fois, le profil de conductivité thermique en profondeur d'un échantillon irradié est mesuré directement. Les profils obtenus par chacune des méthodes d'analyse spatiale sont comparés les uns aux autres et à la prévision numérique du profil endommagé. La nature complémentaire des différentes techniques valide le profil mesuré et la dégradation constatée de la conductivité thermique de l'échantillon de ZrC. / In nuclear applications, material properties can undergo significant alteration due to destructive interaction with irradiating particles at microstructural levels that affect bulk properties. One of the challenges associated with studies of ion-Irradiated materials is that the affected layer, or penetration depth, is typically very thin (~0.1-100 μm). This study expands the current knowledge base regarding thermal transport in ion-Irradiated materials through the use of a multiscaled experimental approach using thermal wave methods. In a manner not previously explored, four thermal wave methods are used to characterize the proton-Irradiated layer in ZrC including scanning thermal microscopy (SThM), spatial-Scanning front-Detection photothermal radiometry (PTR), lock-In IR thermography (lock-In IRT), and tomographic, frequency-Based PTR. For the first time, the in-Depth thermal conductivity profile of an irradiated sample is measured directly. The profiles obtained by each of the spatial scanning methods are compared to each other and the numerical prediction of the ion-Damage profile. The complementary nature of the various techniques validates the measured profile and the measured degradation of thermal conductivity in the ZrC sample.

[pt] A presente tese tem por objetivo o estudo teórico e experimental, seguindo as boas práticas metrológicas, de um método baseado em uma fonte esférica de calor para medição da condutividade térmica de líquidos, com foco em soluções aquosas de etanol, e posterior determinação do teor de água da substância. O estudo e o desenvolvimento de métodos de medição de condutividade térmica são essenciais em diversas aplicações de engenharia, visto que, em consequência das justificadas demandas atuais de economia e uso racional de energia térmica, a transferência de calor com a máxima eficiência possível é de extrema relevância. A medição do teor de água também é um relevante parâmetro em muitas áreas de pesquisa e nos setores industriais, pois a quantidade de água nas substâncias influencia vários processos físicos, químicos e biológicos. Contudo, a quantidade de equipamentos disponíveis no mercado para a medição de ambas as grandezas não é vasta. O método da esfera quente, em principio, é um método absoluto de medição da condutividade térmica, o que significa que o sensor pode fornecer um resultado sem ser calibrado. Porém, alguns parâmetros do modelo precisam ser analisados isoladamente ou obtidos por meio de calibração. Embora haja alguns estudos sobre este método, poucos têm os meios líquidos como foco principal. Ademais, tais estudos não correlacionam a condutividade térmica do material com o seu teor de água e nem realizam uma análise metrológica mais criteriosa, de modo a determinar minuciosamente as incertezas de medição. A aplicabilidade do método para medição da condutividade térmica e do teor de água das soluções analisadas mostrou-se bastante satisfatória, pois os resultados obtidos neste estudo apresentaram muito boa concordância com os valores propostos por vários pesquisadores e com as medições realizadas no Inmetro por outros métodos. / [en] The aim of this thesis is the experimental and theoretical study, following the good metrological practices, of a method based on a spherical heat source in order to measure thermal conductivity of liquids, focusing on aqueous solutions of ethanol, with later determination of the water content of the substance. The study and the development of measuring methods of thermal conductivity are essentials in several engineering applications, since as a consequence of the current justified demands on saving and rational use of thermal energy, the heat transfer with the maximum efficient as possible is of great relevance. The measurement of the water content is also a relevant parameter in several research areas and industrial sectors, since the quantity of water in the substances influences several biological, chemical and physical processes. However, the amount of equipment available on the market for the measurement of both quantities is not vast. The heated sphere method, in principle, is an absolute one for the measurement of the thermal conductivity, which means that the sensor may furnish a result without a calibration. Nevertheless, some parameters of the model need to be analyzed separately or obtained by means of calibration. Although there are some studies on this method, few of them have liquids as the main focus. Moreover, these studies do not correlate the thermal conductivity of the material with its water content, and they do not perform a more careful metrological analysis in order to determine the measurement uncertainties. The applicability of the method to measure the thermal conductivity and the water content of the analyzed substances proved to be satisfactory, because the obtained results of this study presented a very good agreement with the values proposed by several researches and with the measurements performed at Inmetro by other methods.

<p>Cellulose nanocrystals (CNCs) and its composite coatings may impart many benefits in packaging, electronic, optical, etc. applications; however, large-scale coating production is a major engineering challenge. To fill this knowledge gap, a potential large-scale manufacturing technique, roll-to-roll reverse gravure processing, has been described in this work for the manufacture of CNC and CNC-poly(vinyl alcohol) (PVA) coatings on a flexible polymer substrate. Various processing parameters which control the coating structure and properties were examined. The most important parameters in controlling liquid transfers were gravure roll, gravure speed, substrate speed, and ink viscosity. After successful fabrication, coating adhesion was investigated with a crosshatch adhesion test. The surface roughness and morphology of the coating samples were characterized by atomic force microscopy and optical profilometer. The Hermans order parameter (S) and coating transparency were measured by UV–Vis spectroscopy. The effect of viscosity on CNC alignment was explained by the variation of shear rate, which was controlled by the micro-gravure rotation. Finally, the CNC alignment effect was investigated for gas barrier and thermal management applications.</p> <p>In packaging applications, cellulose nanomaterials may impart enhanced gas barrier performance due to their high crystallinity and polarity. In this work, low to superior gas barrier pristine nanocellulose films were produced using a shear-coating technique to obtain a range of anisotropic films. Induction of anisotropy in a nanocellulose film can control the overall free volume of the system which effectively controls the gas diffusion path and hence, controlled anisotropy results in tunable barrier properties. The highest anisotropy materials showed a maximum of 900-fold oxygen barrier improvement compared to the isotropic arrangement of nanocellulose film. The Bharadwaj model of nanocomposite permeability was modified for pure nanoparticles, and the CNC data were fitted with good agreement. Overall, the oxygen barrier performance of anisotropic nanocellulose films was 97 and 27 times better than traditional barrier materials such as biaxially oriented poly(ethylene terephthalate) (BoPET) and ethylene vinyl alcohol copolymer (EVOH), respectively, and thus could be utilized for oxygen-sensitive packaging applications. </p> The in-plane thermal conductivity of CNC - PVA composite films containing different PVA molecular weights, CNC loadings and varying order parameters (S) were investigated for potential application in thermal management of flexible electronics. Isotropic CNC - PVA bulk films with 10-50 wt% PVA solid loading showed significant improvement in thermal conductivity compared to either one component system (PVA or CNC). Furthermore, anisotropic composite films exhibited in-plane thermal conductivity as high as ~ 3.45 W m-1 K-1 in the chain direction, which is higher than most polymeric materials used as substrates for flexible electronics. Such an improvement can be attributed to the inclusion of PVA as well as to a high degree of CNC orientation. The theoretical model was used to study the effect of CNC arrangement (both isotropic and anisotropic configurations) and interfacial thermal resistance on the in-plane thermal conductivity of the CNC-PVA composite films. To demonstrate an application for flexible electronics, thermal images of a concentrated heat source on both neat PVA and CNC-PVA composite films were taken that showed the temperature of the resulting hot spot was lower for the composite films at the same power dissipation.

A utilização de novas tecnologias associada a novos materiais é uma contribuição para a indústria da construção civil diminuir o déficit habitacional e reduzir os impactos ambientais gerados pelas técnicas construtivas tradicionais. Esses novos materiais estão entre as alternativas para enfrentar a atual escassez de materiais para construção, que tem pressionado os índices de preços da construção civil em nosso país. O novogesso está entre as novas tecnologias que disputarão espaço nesse vasto mercado, em função do que oferece. A contribuição desse trabalho está centrada no estudo da condutividade térmica desse novo material e no compósito novogesso celulose, obtido a partir do gesso, produzido através de tecnologia originalmente desenvolvida no LCM / IFSC / USP. O gesso é um material com grande abundância em nosso país: jazidas minerais no Norte e Nordeste e de fosfogesso estocadas no centro-sul. O processo inovador utilizado para preparação de peças do novogesso para componentes construtivos consiste em empregar a menor quantidade de água necessária para a hidratação do gesso, o que corresponde a cerca de 20% da massa do hemihidrato. O pó umedecido é submetido à compactação por compressão uniaxial, que por sua vez, resulta em peças com propriedades mecânicas elevadas. O conhecimento da condutividade térmica desse material foi de grande importância para a avaliação do seu desempenho na construção da habitação experimental. A condutividade térmica foi medida pelo método do fio quente. Estudamos placas do novo material, tendo como variáveis o nível de compactação e o teor de fibras de celulose. A baixa condutividade térmica dessas placas influenciou o comportamento térmico dos ambientes da habitação experimental, montada por um sistema construtivo inovador. Outro aspecto avaliado foi o isolamento acústico dos ambientes da habitação experimental, que de acordo com os materiais empregados se mostrou bastante adequado. Portanto, podemos concluir pela viabilidade da construção da habitação experimental tanto do ponto de vista dos materiais empregados quanto do conforto termo-acústico e do seu baixo custo. / The use of new technologies associated with new materials is a contribution to the building industry, decreasing the housing deficit and reducing the environmental impacts generated by traditional design techniques. These new materials are alternatives to the current shortage of materials for construction, which has raised the prices of construction in our country. The novogesso is among the new technologies that will be included in the vast market in function of the offers. In this context, the present thesis focuses on the study of the thermal conductivity of this new material and the novogesso cellulose composite obtained from gypsum and produced using a technology originally developed in LCM / IFSC / USP. Gypsum is an abundant material in our country, as there are mineral deposits in the North and Northeast and phosphogypsum stored in the center-south. The innovative process used for the preparation of parts of novogesso for building components is the employment of the smallest amount of water needed for the hydration of plaster, which represents approximately 20% of the hemihydrates weight. The moistened powder is subjected to compaction by uniaxial compression, which results in parts with high mechanical properties. The Knowledge of the thermal conductivity of this material was of great importance for the assessment of its performance in the construction of an experimental prototype of housing. Its thermal conductivity was measured by hot wire technique. Plates of this new material were studied, considering the level of compaction and the content of cellulose fibers. The low thermal conductivity of the plates influences the thermal behavior of the environments of the experimental house built by an innovative constructive system. Another aspect evaluated was the acoustic behavior of the experimental environments of the house, which, according to the material used, was quite appropriate. It was possible to conclude that the experimental house is feasible for construction taking into account the materials used in its thermo-acoustic comfort and low-cost.

A presente dissertação desenvolve um estudo numérico em duas direções espaciais com o objetivo de encontrar a configuração de geometrias acopladas a aletas de alta condutividade térmica em forma de “T” que resultam na menor resistência ao fluxo de calor utilizando o método Design Construtal. Como restrição as áreas de ambos os componentes, o corpo sólido onde há geração de calor e a aleta, são mantidas constantes. A equação diferencial da difusão do calor bidimensional, em regime permanente e propriedades constantes, com as condições de contorno, foram solucionadas pelo método dos elementos finitos utilizando o programa MATLAB ®, mais precisamente a ferramenta PDETOOL, Partial Differential Equations Tool. Em outras palavras, minimizar a resistência térmica ao fluxo de calor gerado para uma melhora na refrigeração, variando somente os comprimentos e larguras que formam o sólido de baixa condutividade térmica e a aleta composta por material de alta condutividade térmica. Para cada geometria proposta foram avaliadas todas as possibilidades geométricas dentro do domínio estabelecido Três geometrias foram propostas para os sólidos geradores de calor: retangular, trapezoidal e semicircular, todas acopladas com a aleta na forma de T. Além dos graus de liberdade, também foram avaliados o efeito dos seguintes parâmetros adimensionais: (condutividade térmica da aleta), (fração de área), (fração de área auxiliar) e ℎ . O melhor design encontrado é aquele que distribui melhor as imperfeições, ou seja, a geometria que distribui melhor os pontos de temperatura máxima. Os resultados reforçam, ainda, o entendimento de que sistemas multicomponentes devem ser estudados globalmente e não cada componente individualmente. Para a geometria retangular houve uma melhora de 66% no desempenho quando comparados os desempenhos da primeira para a última otimização. O melhor desempenho obtido para a geometria trapezoidal superou em aproximadamente 3,5% o desempenho da geometria retangular. Por fim a geometria semicircular atingiu o melhor desempenho entre as geometrias estudadas, superando em 40% o resultado atingido pela geometria trapezoidal. / This work used the method Construtal Design to develop a numerical study trying to find out the best configuration of geometries coupled to T-shaped materials of high thermal conductivity to improve the heat transfer between the heat generating body, which is a low heat conductor, and the environment. As a restriction, both areas are kept constant. The differential equations of heat diffusion, steady state and constant properties, and their boundary conditions were solved numerically using the MATLAB ® software, specifically the PDETOOL tool. The objective of this work is to improve the flux of heat through the Tshaped materials of high thermal conductivity, in other words, minimize the thermal resistance to improve the refrigeration, changing only the values of the lengths and widths that setup the solid of low thermal conductivity and the T-shaped materials of high thermal conductivity. All geometric possibilities were evaluated, respecting the domain. The optimal geometry was that which resulted in lower thermal resistance. Three geometries have been proposed for solid heat generators: rectangular, trapezoidal and semicircular. All coupled with the T-shaped materials of high thermal conductivity Besides the degrees of freedom were also evaluated the effect of the following dimensionless parameters: (thermal conductivity), (area fraction), (auxiliary area fraction) and ℎ . The best design found is that better distributes the imperfections, in other words, it is the geometry that better distributes the points of maximum temperature. The results reinforce also the understanding that multicomponent systems should be studied globally rather than each component individually. For the rectangular geometry there was an improvement of 66% in performance when comparing the performances of the first to the last optimization. The best performance obtained for the trapezoidal geometry exceeded by approximately 3.5% performance of the rectangular geometry. Finally the semicircular geometry achieved the best performance among the studied geometry, exceeding by 40% the result achieved by the trapezoidal geometry.

Du fait leur conductivité thermique élevée, les matériaux composites à matrice métallique et renfort carbone possèdent un fort potentiel d’application pour la gestion thermique en électronique. Ces travaux présentent le développement d’un nouveau procédé pour la synthèse de matériaux composites Ag/rGO (argent / « reduced Graphene Oxide ») et Ag/GF (argent / « Graphite Flakes ») par métallurgie des poudres. Ce procédé, inspiré des méthodes de « molecular level mixing », permet d’obtenir des poudres composites Ag/rGO dans lesquelles les nano-renforts sont individualisés jusqu’à une concentration volumique de 1 %. Lorsqu’il est appliqué à la synthèse de matériaux composites Ag/GF, ce dernier permet l’élaboration de matériaux composites denses avec une concentration volumique en graphite jusqu’à 70 % et une conductivité thermique jusqu’à 675 W.m-1.K-1 (426 W.m-1.K-1 pour l’argent pur). En outre, il a été montré que le procédé d’élaboration des poudres composites Ag/GF a une forte influence sur l’anisotropie structurale des matériaux massifs ainsi que sur la résistance thermique d’interface extrinsèque Ag-graphite. Le procédé d’élaboration développé dans ces travaux permet ainsi d’obtenir des matériaux ayant une conductivité thermique jusqu’à 19 % supérieure à celle des matériaux obtenus par un procédé de mélange conventionnel. Néanmoins, comme la plupart des matériaux composites métal/GF (à matrice Cu, Al, Mg et Fe), la dilatation thermique des matériaux composites Ag/GF présente des « anomalies ». En effet, l’anisotropie de leur coefficient d’expansion thermique (CTE) est opposée à leur anisotropie structurale, leur CTE a une dépendance anormalement élevée vis-à-vis de la température et ces matériaux présentent une instabilité dimensionnelle en cyclage thermique. S’il est communément admis dans la littérature que ces anomalies sont la conséquence des contraintes internes générées lors de l’élaboration des matériaux (du fait de la différence de CTE entre matrice et renfort), ce phénomène reste mal compris et difficile à maitriser. Une part importante de ces travaux est consacrée à l’étude de ces « anomalies » et en particulier à l’étude de l’influence des propriétés mécaniques de la matrice d’argent sur la dilation thermique des matériaux composites. Grâce à la combinaison des caractérisations d’EBSD, de DRX, de microdureté instrumentée et de microscopie, des phénomènes clés responsables des propriétés thermomécaniques des matériaux composites Ag/GF ont pu être identifiés. En particulier, il a été montré qu’une part importante des contraintes internes est relaxée via la déformation plastique de la matrice d’argent et la déformation pseudo plastique du graphite lors du refroidissement post-densification des matériaux composites. Ainsi, le contrôle des propriétés mécaniques de la matrice métallique (en particulier de sa limite d’élasticité) permet d’atténuer les anomalies en CTE et confère une meilleure stabilité dimensionnelle aux matériaux composites Ag/GF lors d’un cycle thermique. L’addition de rGO dans la matrice d’argent des matériaux composites Ag/GF a également permis de réduire l’instabilité dimensionnel des matériaux jusqu’à 50 % grâce aux propriétés d’amortissement du rGO. / Due to their high thermal conductivity, metal matrix composite materials reinforced with carbon allotropes exhibit a high potential application for thermal management in electronics. This work deals with the elaboration of new synthesis process to produce Ag/rGO (silver/reduced Graphene Oxide) and Ag/GF (silver/Graphite Flakes) composite materials. This process, based on “molecular level mixing” methods, makes it possible to obtain Ag/rGO composite powders with individualized nano-reinforcements up to a concentration of 1 % in volume. Applied to the synthesis of Ag/GF composite materials, it allows to synthesize dense composite materials with a graphite concentration up to 70 % in volume and with a thermal conductivity up to 675 Wm-1.K-1 (426 Wm-1.K-1 for pure silver). Moreover, it has been shown that Ag/GF powders elaboration process has a strong influence on the structural anisotropy of bulk materials as well as on the extrinsic thermal boundary resistance Ag-graphite. The process developed in this work allows Ag/GF composite materials to reach thermal conductivity up to 19 % higher than the same materials synthesized by conventional mixing powder process. However, like most metal/GF composite materials (with Cu, Al, Mg and Fe matrix), thermal expansion of Ag/GF composite materials shows “anomalies”. Indeed, the anisotropy of their coefficient of thermal expansion (CTE) is opposed to their structural anisotropy, their CTE has an abnormally high dependence on temperature and these materials exhibit dimensional instability during thermal cycling. While it is commonly admit in literature that these “anomalies” are the consequence of internal stresses generated during materials densification (because of CTE mismatch between matrix and reinforcement), this phenomenon remains poorly understood and difficult to control. A significant part of this work is devoted to the study of these anomalies and especially to the study of the influence of matrix mechanical properties on composite materials thermal expansion. Thanks to EBSD, XRD, instrumented microhardness and microscopy analysis, key phenomena responsible of thermomechanical behavior of Ag/GF composite materials have been identified. Especially, it has been shown that a large part of the internal stresses is relaxed by plastic deformation of silver matrix and pseudo-plastic deformation of graphite during the post-densification cooling step of the materials. Thus, the control of mechanical properties of metallic matrix (especially of its elastic limit) makes it possible to attenuate the anomalies in CTE and confers a better dimensional stability to Ag / GF composite materials during thermal cycling. Finally, the addition of rGO in silver matrix of Ag/GF composites materials has also reduced material dimensional instability by up to 50 % thanks to the damping properties of rGO.

Zirconium alloys (zircaloy) have been widely used in light water reactors due to their good thermomechanical properties, corrosion resistance, and low thermal neutron absorption rate. As one of the most important safety barriers, cladding is not only used to encapsulate nuclear fuel, but also to prevent the nuclear fission products from leaking into the coolant. During the operation of nuclear reactors, hydride will form in zircaloy and significantly degrade the tensile strength, ductility, fracture toughness, and creep behavior of the cladding, and eventually leading to the failure of cladding. Therefore, understanding the material properties of zircaloy and its hydrides is crucial to the safety of power plants. In this study, the mechanical Raman spectroscopy and nano-mechancial testing techniques were used to perform thermomechanical measurements and damage analysis of zircaloy-4. The Raman thermometry method was used to measure localized spatially resolved thermal conductivity and establish the potential linkage of microstructure to thermal and mechanical properties of zircaloy-4. The local thermal conductivity values showed to increase with increase in grain size. Nanoindentation and nano-scale impact techniques were used to obtain the viscoplastic constitutive relation of hydrides at elevated temperatures. Based on the obtained viscoplastic model, fracture strength of hydrides was predicted by using finite element method (FEM) simulations. An extended Gurson-Tvergaard-Needleman (GTN) model was used to study the macro-scale fracture behavior of hydrided zircaloy-4 structures. Good agreement between calculated and experimental results was obtained for various boundary conditions.