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Effective application of thermal interface materials (TIM) sandwiched between silicon and a heat spreader in a microelectronic package for improved heat dissipation is studied through thermal and mechanical characterization of high thermally conductive carbon nanotubes (CNTs) integrated into eutectic gallium indium liquid metal (LM) wetting matrix. Thermal conductivity data from Infrared microscopy tool reveals the dependence of experimental factors such as matrix types, TIM contacting interfaces, orientation of CNTs and wetting of CNTs in the matrix on the thermal behavior of TIM composite. Observed generalized trend on LM-CNT TIM shows progressive decrease in effective thermal conductivity with increasing CNT volume fractions. Further thermal characterizations LM-CNT TIM however show over 2x increase in effective thermal conductivity over conventional polymer TIMs (i.e. TIM from silicone oil matrix) but fails to meet 10x improvement expected. Poor wetting of CNT with LM matrix is hypothesized to hinder thermal improvement of LM-CNT TIM composite. Thus, wetting enhancement technique through electro-wetting and liquid crystal (LC) based matrix proposed to enhance CNT-CNT contact in LM-CNT TIM results in thermal conductivity improvement of 40 to 50% with introduction of voltage gradient of 2 to 24 volts on LM-CNT TIM sample with 0.1 to 1 percent CNT volume fractions over non voltage LM-CNT TIM test samples. Key findings through this study show that voltage tests on LC- CNT TIM can cause increased CNT-CNT networks resulting in 5x increase in thermal conductivity over non voltage LC-CNT TIM and over 2x improvement over silicone-CNT TIMs. Validation of LM wetting of CNT hypothesis further shows that wetting and interface adhesion mechanisms are not the only factors required to improve thermal performance of LM-CNT TIM. Anisotropic characteristic of thermal conductivity of randomly dispersed CNTs is a major factor causing lower thermal performance of LM-CNTs TIM composite. Other factors resulting in LM-CNT TIM decreasing thermal conductivity with increasing CNT loading are (i) Lack of CNT-CNT network due to large difference in surface tension and mass density between CNTs and LM in TIM composite (ii) Structural stability of MWCNT and small MFP of phonons in ~5um MWCNTs compared to the system resulted in phonon scattering with reduced heat flow (iii) CNT percolation threshold limit not reached owing to thermal shielding due to CNT tube interfacial thermal resistance. While mixture analytical models employed are able to predict thermal behaviors consistent with CNT-CNT network and CNT- polymer matrix contact phenomenon, these models are not equipped to predict thermo-chemical attributes of CNTs in LM-CNT TIM. Extent of LM-CNT wetting and LM-solid surface interfacial contact impacts on interfacial thermal resistance are investigated through LM contact angle, XPS/AES and SEM-EDX analyses on Au/Ni and Ni coated copper surfaces. Contact angle measurements in the range of 120o at both 55oC and 125oC show non wetting of LM on CNT, Au and Ni surfaces. Interface reactive wetting elemental composition of 21 days aged LM on Au/Ni and Ni surfaces reveals Ga dissolution in Au and Ni diffusion of ~0.32um in Au which are not present for similar analysis of 1 day LM on Au/Ni surface. Formation of Au-Ni-Ga IMC and IMC-oxide iono-covalency occurrence at the interface causes reduction in surface tension and reduction in interfacial contact resistance.

Many materials are made up of small crystals, or grains. Grain boundaries are the interfaces between two grains and affect the flow of heat through the material. These interfaces serve to interfere with the energy carriers by scattering or disrupting them. Because of the negative effect these interfaces have on these energy carriers, they inhibit heat flow and act as thermal resistors. The thermal boundary resistance between two grains of the same material is sometimes referred to as the Kapitza resistance, although this term is also used to describe the thermal resistance between solid/solid interfaces of different materials or solid/liquid interfaces. A better understanding of the heat transport process on a micro-scale is especially relevant to nuclear energy applications. Nuclear fuels are polycrystalline materials that experience large heat differences over small distances. An improved understanding of these grain boundaries and the role they play in transferring heat can help better predict nuclear fuel performance and improve nuclear reactor efficiency and safety. The study of the thermal resistance across crystal interfaces and their potential influence on nuclear fuels is a topic that has received relatively little attention. While the thermal resistance across a single grain boundary is rather small, the total resistance generated from many grain boundaries can have a big impact on the material. Smaller grains mean there are more interfaces, which will result in a lower overall thermal conductivity. For this study, Kapitza resistance across individual grain boundaries was measured using a laser-based measurement technique. The sample material was Cerium Oxide. It was used because of its similar properties to Uranium Oxide, which is a popular material used in nuclear fuel. The average interfacial thermal resistance measured at room temperature in this thesis study was 9.88∙10-9 �2�/�. The average measured value fit in an accepted range from other results found in similar studies.

[pt] A presente pesquisa trata da avaliação da resistência ao arrancamento de grampos em solo residual de gnaisse. Foram realizados ensaios de arrancamento em uma obra de solo grampeado executada em um maciço de solo residual de gnaisse. A resistência ao arrancamento foi avaliada em 4 cotas diferentes ao longo do perfil de escavação. Foram realizados 8 ensaios de arrancamento em grampos de 4m de comprimento. Quatro ensaios foram executados em grampos instrumentados com strain-gages, para avaliar a distribuição das cargas de tração durante os estágios de carregamento. Foram também realizados ensaios de cisalhamento direto no solo e na interface solo/cimento para avaliação das propriedades mecânicas destes materiais. Amostras indeformadas foram coletadas imediatamente à frente dos furos de instalação dos grampos ensaiados garantindo uma maior representatividade dos materiais. Uma relação semi-empírica é proposta para se avaliar a resistência do solo e da interface solo/nata de cimento, obtidos em ensaios de cisalhamento direto no laboratório. Os resultados obtidos nesta pesquisa são comparados com ensaios realizados por outros autores, em encostas de solos residuais de gnaisse e empregados para validação da relação desenvolvida. / [en] The present research presents an evaluation of the pullout resistance of nails in residual gneissic soil. Pullout tests were carried out in 4 different levels of the nailed wall with nails 4m long. Four tests were carried out in strain-gauged nails for evaluating the tension distribuition along the nail. A series of direct shear tests in soil specimens and in the soil/grout interface were also performed for obtaining the mechanical properties of these materials. Undisturbed samples had been collected very close to the pull-out test locations. A semi-empirical relation is proposed for evaluating the pullout resistance of nails, based on the shear strenghth parameters of the soil and of the soil/grout interface from laboratory direct shear tests.

[pt] Em obras ambientais, onde geossintéticos são utilizados como sistema de proteção e de cobertura de taludes, é de extrema importância o conhecimento do mecanismo de interação solo-geossintético, através da obtenção dos parâmetros de resistência da interface (adesão e ângulo de atrito da interface). O ensaio de laboratório mais adequado para a obtenção desses parâmetros, nestas condições, é o de cisalhamento em plano inclinado ou ensaio de rampa, pois permite simular a condição de campo onde o cisalhamento ocorre em um plano inclinado sob baixas tensões. Assim, este trabalho apresenta um estudo sobre a interação sologeossintético através de ensaios de rampa, executados em um equipamento de grandes dimensões, visando analisar a influência de alguns fatores, tais como, tipo de geossintético, tipo de solo, densidade relativa do solo e tensão confinante. Foram utilizados dois tipos de geossintéticos, uma geomembrana de PVC e uma geogrelha uniaxial e dois tipos de solo, areia e pedregulho (brita). A análise da influência da densidade relativa do solo foi realizada através de ensaios na interface areia-geossintético em duas densidades relativas diferentes (35 e 100%). A influência da tensão confinante foi estudada através de ensaios com três tensões confinantes distintas (2,1; 3,2 e 5,1 kPa). Os resultados mostram que a influência de fatores como densidade relativa do solo, tensão confinante e tipo de solo, dependem do tipo do geossintético. O aumento da densidade relativa do solo promove um acréscimo de resistência na interface para a geogrelha e uma redução para a geomembrana. O aumento da tensão confinante reduz o ângulo de rampa na ruptura, sendo este efeito mais pronunciado na interface areia-geogrelha. Em relação ao tipo de material, a interface brita-geogrelha é a que apresenta maior resistência. / [en] In environmental works, where geosynthetics are used as protection system and of slope covering, it is of extreme importance the knowledge of the interaction mechanism soil-geosynthetic, through the obtaining of the parameters of resistance of the interface (adhesion and interface friction angle). The laboratory test more appropriate for the obtaining of those parameters, in these conditions, is it the inclined plane test or ramp test, because it allows to simulate the field condition where the shearing happens in inclined plane under low tensions. Like this, this work presents a study about the interaction soilgeosynthetic through ramp tests, executed in an equipment of great dimensions seeking to analyze the influence of some factors, such as, geosynthetic type, soil type, relative density of the soil and confinement pressure. Two geosynthetics types, a PVC geomembrane and a uniaxial geogrid, two soil types, it sand and gravel (break). The analysis of the influence of the relative density of the soil was accomplished through tests in the interface sand- geosynthetic in two different relative densities (35 and 100%). The influence of the confinement pressure was studied through tests with three different confinement pressures (2,1; 3,2 and 5,1 kPa). The results show that the influence of factors as relative density of the soil, pressure confinement and soil type, they depend on the type of the geosynthetic. The increase of the relative density of the soil promotes an increment in the interface resistance for the geogrid and a reduction for the geomembrana. The increase of the confinement pressure reduces the ramp angle in the rupture, being this more pronounced effect in the interface sand-geogrid. In relation to the material type, the interface gravel-geogrid presents larger resistance.

Die fortschreitende Miniaturisierung von elektronischen Systemen begleitet von steigender Leistung und Funktionalität führt zur Erhöhung der Leistungsdichte. Um diesem Trend zu entsprechen, werden neue Entwärmungskonzepte benötigt, die wiederum neuartige Materialien und Materialverbünde fordern. Ein wichtiger Aspekt dieser Arbeit ist deshalb die Konzentration auf die für den Wärmetransport entscheidenden Materialien. Diese Arbeit befasst sich mit der Entwicklung von Methoden für die umfassende thermische Charakterisierung von den verschiedenen Materialien und Materialklassen, die in der Elektronikindustrie verwendet werden. Die Messsysteme wurden so entworfen und entwickelt, dass spezifische Anwendungsbedingungen berücksichtigt werden können, keine aufwändige Probenherstellung notwendig ist und gleichzeitig eine hohe Messgenauigkeit gewährleistet ist. Es wurden vier verschiedene Messsysteme innerhalb dieser Arbeit entwickelt und realisiert, die in ihrer Gesamtheit die Charakterisierung von fast allen Package-Materialien unter gewünschten Randbedingungen ermöglichen. Zahlreiche Materialien und Effekte wurden daraufhin im Rahmen dieser Arbeit mit den entwickelten Messsystemen untersucht und diskutiert. / The continuous miniaturization of electronic systems accompanied by increasing performance and functionality leads to an increase in power density. In order to comply this trend, new heat dissipation concepts are needed which demand new materials and material composites. An important aspect of this work is therefore the concentration on the materials that are decisive for the heat flow. This thesis deals with the development of Methods for comprehensive thermal characterization of the different materials and material classes used in the electronics industry. The measuring systems have been designed and developed in such a way that they enable to take into account specific application conditions, no costly sample preparation is necessary and at the same time high measuring accuracy is ensured. Four different measuring systems were developed and realized within this work, which, in their entirety, enable the characterization of almost all package materials under desired boundary conditions. Based on this, numerous materials and effects were investigated and discussed in the context of this work with the developed measurement systems.