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Ferro, Alberto Eduardo Morao Cabral. "Aluminium brazes for silicon carbide ceramics." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317212.
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Maensiri, Santi. "Thermal shock resistance of sintered alumina/silicon carbide nanocomposites." Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365329.
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Ren, Zheng Materials Science & Engineering Faculty of Science UNSW. "Mechanical properties of 7075 aluminium matrix composites reinforced by nanometric silicon carbide particulates." Awarded by:University of New South Wales, 2007. http://handle.unsw.edu.au/1959.4/34742.
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Aluminium composites reinforced by particles have received considerable attention because of their superior mechanical properties over monolithic aluminum matrix. Over the last ten years, nanocomposites with nano-sized reinforcements have become a revolutionary progress for composites because they have different strengthening mechanisms as compared to that in composites with micro-sized reinforcements. Consequently novel properties can be expected from the nanometric particulate reinforced composites. The aim of this project was to fabricate SiC (50nm)/7075 aluminium composites via a modified powder metallurgy and extrusion route. Ageing treatment was used to increase the strength of the composites and mechanical tests, including tensile test and abrasive wear test, were performed. The effects of nanometric silicon carbide particulates to the ageing behaviours and mechanical properties of the composites have been studied by optical metallography, scanning electron microscopy and transmission electron microscopy. It was found that the dispersion of nanometric silicon carbide was not homogeneous, but tended to disperse along grain boundaries. Clustering of these nano-reinforcements was also found within the grains. This was particular true when the amount of nano-reinforcement increased to 5%. Compared with the monolithic 7075 alloy, the 1 vol.% SiC (50nm)/7075 aluminium had a higher strength because of effective dislocation pinnings by the reinforcements, while 5% SiC (50nm)/7075 had a much lower strength and ductility because of severe aggregation of nanometric particulates. Nanometric silicon carbide was not as effective as the micro ones in improving abrasive wear resistance of aluminium, this was because of micro-cracking in the aggregation and relatively large abrasive grit. In summary, the addition of a small amount of SiC nanoreinforcements has a high potential to further strengthen 7xxx aluminium alloy. However, the clustering of reinforcements in the matrix will detrimentally affect the strength and ductility of the alloy. The wear resistance of nanometric particulate reinforced composites was inferior to those with micrometric reinforcements. It is suggested that by improving the dispersion of nanometric reinforcements, as well as putting in reinforcememts with different sizes, the mechanical properties and wear resistance can both be increased.
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Jammula, Chaitanya Krishna. "Correlating the microstructure with wear properties of aluminium silicon carbides." Thesis, Tekniska Högskolan, Högskolan i Jönköping, JTH, Industriell produktutveckling, produktion och design, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-45820.
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Aluminium is one of the metals playing a prominent role in automobile industry after cast iron. Because of its light weight property and good mechanical properties. When aluminium reinforced with silicon carbide showing good tribological properties and improved strength. Aluminium silicon carbide needs some good wear and frictional properties to use it as break disc. Aluminium reinforced with 15% and 20% silicon carbide and casted in two different ways, liquid casting and stir casting. Four different composites are compared in this paper. Hardness test was carried out on the samples. Increase in the Vickers hardness with increase in silicon carbide reinforcement for both the castings is observed. Rockwell C hardness is showing decreasing trend with increase in SiC reinforcement. The scratch resistance of the surface under micro level was analysed with the help of nano scratch test. The SiC particles in the aluminium matrix are resisting the indenter from deep deformation of the surface. Frictional forces are dropped whenever the indenter met the SiC particles. In other cases, SiC particles are deforming the aluminium matrix in the form of broken particles. The plastic deformation of aluminium is observed, and material is piled up on sideways of groove at high load.Sliding wear behaviour of the composites are investigated by means of reciprocating pin on plate wear rig. The test was carried out at load of 20N for five different sliding duration. Aluminium with 20% silicon carbide of liquid casting is used as a base metal. The worn-out surface of the samples is analysed in SEM. The metallography of the worn-out samples is showing some deep grooves and abrasion of the material. Wear debris from both the surfaces are forming into a cluster of layers. These layers are protecting the surface from wear in some areas were observed. Composition of tribo layer formed during the test was investigated with the help of EDS analysis. The tribo layer are rich in aluminium and silicon elements because both the samples are made of aluminium silicon carbide.
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Sparks, Christopher Nigel. "Hot formability and microstructural development of spray-deposited Al-Li alloy and composite." Thesis, University of Sheffield, 1994. http://etheses.whiterose.ac.uk/1805/.
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The deformational and microstructural behaviour of the commercial Al-Li alloy 8090 and an 8090 based composite containing silicon carbide particulate has been investigated. The materials were deformed at elevated temperature by the test methods of plane strain compression (PSC) and torsion to provide stress-strain data for the formulation of constitutive relationships. Torsion testing also provided high temperature ductility data. Isothermal annealing of rolled samples was carried out at the solution temperature of 530°C to investigate the recrystallisation kinetics and microstructures produced, with particular emphasis on the effect of the inclusion of reinforcement particles on the behaviour of the matrix alloy. Hyperbolic sine forms of constitutive equation have been produced and are found to provide good agreement with the experimental data. High values of the activation energy are calculated for the deformation of both the alloy and composite from the PSC test data. The equations obtained from the two different test methods are found to be comparable for the composite material, but a discrepancy is found for the monolithic alloy, where apparently less hardening results from torsion testing. A distinct transition in microstructure from recrystallised equiaxed grains when deformed at low temperature to an elongated, sometimes partially recrystallised, structure for material rolled at high temperature is present in the monolithic material. This is attributed to the balance of recrystallisation driving force and the Zener pinning force exerted by the 13' (A1 3Zr) phase. The composite material exhibited greatly enhanced recrystallisation kinetics in agreement with the theory of particle stimulated nucleation (PSN) of recrystallisation.
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Zetterling, Carl-Mikael. "Silicon dioxide and aluminium nitride as gate dielectric for high temperature and high power silicon carbide MOSFETs." Doctoral thesis, KTH, Electronic Systems Design, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2514.
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Silicon carbide (SIC) is a wide bandgap semiconductor thathas been suggested as a replacement for silicon in applicationsusing high voltages, high frequencies, high temperatures orcombinations thereof. Several basic process steps need to bedeveloped for reliable manufacturing of long-term stableelectronic devices. One important process step is the formationof an insulator on the silicon carbide surface that may be usedas a) a gate dielectric, b) for device isolation or c) forpassivation of the surface. Silicon dioxide and aluminumnitride have been suggested for these purposes. This thesiscovers the investigation of some formation methods for boththese materials on 4H and 6H silicon carbide, and theelectrical characterisation of the resulting films.
Commercially available n-type and p-type 4H and 6H SICwafers have been used, and both the silicon face and the carbonface have been investigated. Silicon dioxide has been formed byseveral methods: a) dry thermal oxidation with or without theaddition of TCA (trichloroethane), b) wet oxidation inpyrogenic steam or with awater bubbler, c) oxide deposition byPECVD (plasma enhanced chemical vapor deposition) or LPCVD (lowpressure chemical vapor deposition) and d) oxidation of aevaporated or LPCVD deposited sacrificial layer of silicon. Theinfluence of various cleaning methods prior to oxidation hasbeen studied, as well as post-oxidation and post-metallisationannealing. The aluminum nitride films were grown by MOCVD(metal organic chemical vapor deposition) under various processconditions.
Oxidation kinetics have been studied for dry thermaloxidation at 1200 0C. The redistribution of aluminum (p-typedopant in SiC) during dry thermal oxidation has beeninvestigated using SIMS (secondary ion mass spectrometry). Themorphology of the aluminum nitride was determined using x-raydiffraction rocking curves, RHEED (reflection high energyelectron diffraction) and AFM (atomic force microscopy). Thequality of the silicon dioxide used as gate dielectric has beendetermined using breakdown field measurements. High frequencycapacitance-voltage measurements have been used on bothinsulators to a) verify thickness measurements made with othermethods, b) to determine fixed oxide charges by measuring theflatband voltage shifts and c) to quantitatively compare theamount of interface states.
For electrical characterisation either aluminum, titanium ordoped polysilicon circular gate contacts of various sizes wereformed on the insulator surface. Flat MOS capacitors weremainly used for the electrical characterisation. U-grooved MOScapacitors, manufactured by RIE (reactive ion etching), wereused to test the quality of oxides grown on vertical surfaces.Two types of MOSFETs (metal oxide semiconductor field effecttransistors) have been fabricated: vertical U-grooved andlateral devices.
Keywords:silicon carbide, thermal oxidation, silicondioxide, metal organic chemical vapor deposition (MOCVD),aluminum nitride, capacitance-voltage measurements, MOSFET.
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Kaminski, Piotr M. "Remote plasma sputtering for silicon solar cells." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13058.
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The global energy market is continuously changing due to changes in demand and fuel availability. Amongst the technologies considered as capable of fulfilling these future energy requirements, Photovoltaics (PV) are one of the most promising. Currently the majority of the PV market is fulfilled by crystalline Silicon (c-Si) solar cell technology, the so called 1st generation PV. Although c-Si technology is well established there is still a lot to be done to fully exploit its potential. The cost of the devices, and their efficiencies, must be improved to allow PV to become the energy source of the future. The surface of the c-Si device is one of the most important parts of the solar cell as the surface defines the electrical and the optical properties of the device. The surface is responsible for light reflection and charge carrier recombination. The standard surface finish is a thin film layer of silicon nitride deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). In this thesis an alternative technique of coating preparation is presented. The HiTUS sputtering tool, utilising a remote plasma source, was used to deposit the surface coating. The remote plasma source is unique for solar cells application. Sputtering is a versatile process allowing growth of different films by simply changing the target and/or the deposition atmosphere. Apart from silicon nitride, alternative materials to it were also investigated including: aluminium nitride (this was the first use of the material in solar cells) silicon carbide, and silicon carbonitride. All the materials were successfully used to prepare solar cells apart from the silicon carbide, which was not used due to too high a refractive index. Screen printed solar cells with a silicon nitride coating deposited in HiTUS were prepared with an efficiency of 15.14%. The coating was deposited without the use of silane, a hazardous precursor used in the PECVD process, and without substrate heating. The elimination of both offers potential processing advantages. By applying substrate heating it was found possible to improve the surface passivation and thus improve the spectral response of the solar cell for short wavelengths. These results show that HiTUS can deposit good quality ARC for silicon solar cells. It offers optical improvement of the ARC s properties, compared to an industrial standard, by using the DL-ARC high/low refractive index coating. This coating, unlike the silicon nitride silica stack, is applicable to encapsulated cells. The surface passivation levels obtained allowed a good blue current response.
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Lopes, Nuno Filipe Ferreira. "Development and implementation of strategies for the incorporation of reinforcing elements in aluminium alloys by solid state processing." Master's thesis, Faculdade de Ciências e Tecnologia, 2012. http://hdl.handle.net/10362/7809.
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Dissertação para obtenção do Grau de Mestre em
Engenharia MecânicaThis investigation aimed to study new surface processing strategies to produce reinforced surface metal matrix composites by Friction Stir Processing. The first consisted on pre-placing reinforcing particles over the surface, while the second used consumables drilled holes filled with reinforcing particles. Each strategy was investigated using an electric current in a process under patenting. Aluminium AA5083-H111 plates were used as base material. Silicon carbide and alumina particles with median sizes of 35 and 45 μm, respectively, were used. Pre deposition of reinforcing particles proved to be more effective than the use of consumable tools packed with particles. The last ones produced coatings with a non homogeneous distribution and poor bonding between the substrate and the reinforcing coating. The pre deposition of alumina produced a higher extension and depth of reinforced layer and an increase in hardness of 60%, while silicon carbide produced an increase in hardness of 300 %, though in a smaller extension and depth than alumina under the same processing conditions. Using the electric current a significant raise of 500% and 40% was observed in extension and depth respectively, but hardness decreased by 10 %.
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Suvanam, Sethu Saveda. "Radiation Hardness of 4H-SiC Devices and Circuits." Doctoral thesis, KTH, Integrerade komponenter och kretsar, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199907.
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Advances in space and nuclear technologies are limited by the capabilities of the conventional silicon (Si) electronics. Hence, there is a need to explore materials beyond Si with enhanced properties to operate in extreme environments. In this regards, silicon carbide (4H-SiC), a wide bandgap semiconductor, provides suitable solutions. In this thesis, radiation effects of 4H-SiC bipolar devices, circuits and dielectrics for SiC are investigated under various radiation types. We have demonstrated for the first time the radiation hardness of 4H-SiC logic circuits exposed to extremely high doses (332 Mrad) of gamma radiation and protons. Comparisons with previously available literature show that our 4H-SiC bipolar junction transistor (BJT) is 2 orders of magnitude more tolerant under gamma radiation to existing Si-technology. 4H-SiC devices and circuits irradiated with 3 MeV protons show about one order of magnitude higher tolerance in comparison to Si. Numerical simulations of the device showed that the ionization is most influential in the degradation process by introducing interface states and oxide charges that lower the current gain. Due to the gain reduction of the BJT, the voltage reference of the logic circuit has been affected and this, in turn, degrades the voltage transfer characteristics of the OR-NOR gates. One of the key advantages of 4H-SiC over other wide bandgap materials is the possibility to thermally grow silicon oxide (SiO2) and process device in line with advanced silicon technology. However, there are still questions about the reliability of SiC/SiO2 interface under high power, high temperature and radiation rich environments. In this regard, aluminium oxide (Al2O3), a chemically and thermally stable dielectric, has been investigated. It has been shown that the surface cleaning treatment prior to deposition of a dielectric layer together with the post dielectric annealing has a crucial effect on interface and oxide quality. We have demonstrated a new method to evaluate the interface between dielectric/4H-SiC utilizing an optical free carrier absorption technique to quantitative measure the charge carrier trapping dynamics. The radiation hardness of Al2O3/4H-SiC is demonstrated and the data suggests that Al2O3 is better choice of dielectric for devices in radiation rich applications.QC 20170119
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Ferreira, Lygia Maria Policarpio 1987. "Fabricação de materiais compósitos por tixoconformação de misturas de cavacos de alumínio com pós cerâmicos." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263611.
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Orientador: Maria Helena RobertDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Este trabalho explora a aplicação da tecnologia de metais semi-sólidos para a fabricação de compósitos de matriz metálica (CMM), e ainda a possibilidade de reciclagem de cavacos de usinagem para a produção destes materiais, buscando o desenvolvimento de uma engenharia de baixo custo. São empregados como matriz a liga AA7075, dada a grande geração de cavacos de usinagem na indústria aeronáutica, e SiC ou NiAl2O4 particulados como reforços. O processo é baseado na tixoconformação de misturas de cavacos e partículas de reforço; é esperada a penetração destas últimas em contornos de glóbulos, contendo líquido, no interior do cavaco no estado semi-sólido. São avaliados parâmetros de processo e sua influência na qualidade do produto, em particular na distribuição de reforço na matriz e interação matriz/reforço. Compósitos tixoconformados contendo 10, 20 e 30% em peso de SiC são avaliados mecanicamente através de ensaios de microindentação instrumentada e desgaste micro-abrasivo. Os resultados mostraram, de modo geral, a viabilidade do processo proposto para a fabricação de diferentes tipos de compósitos, o qual envolve procedimento simples e de reduzido custo, além de mostrar a possibilidade de produção de materiais com boas propriedades mecânicas a partir da reciclagem de cavacos, particularmente importante em uma indústria que envolve elevada demanda de energia, como a do Al. Os resultados indicaram que a qualidade geral do produto, em termos de distribuição do reforço e interação reforço/matriz dependem da adequada seleção dos parâmetros de processo: temperatura, tempo de aquecimento, pressão de tixoconformação. Entre as várias condições estudadas, as composições nas quais foi utilizado NiAl2O4 como reforço apresentaram melhores características microestruturais, com melhor interface entre matriz e reforço e baixa porosidade. Boa dispersão das partículas de reforço e baixa porosidade também foram observados para compósitos reforçados com SiC nos quais foram adicionadas partículas finas de silício e alumina
Abstract: This work explores the application of semi-solid technology to produce metal matrix composites, and also the possibility of using machining chips as raw material. The main aim is to develop a process inserted in a low cost engineering concept. To achieve this general objective, the alloy AA7075 is used as matrix, once a significant amount of rejected chips of this high resistance, low weight alloy is generated in the aeronautical industry. As reinforcing material, SiC or NiAl2O4 particles are used. The proposed process is based on the thixoforming of pre-compacted mixtures of chips and reinforcing particles; it is expected the penetration of reinforcing particles within the semi-solid, thixotropic material. It is analyzed the influence of processing parameters in the final quality of products, particularly in the reinforcement dispersion in the matrix and matrix/reinforcement interface. Thixoformed composites containing 10, 20 and 30% weight SiC are produced and evaluated concerning mechanical properties through indentation tests and micro wear. Results showed the general viability of producing composites by the proposed technique, based on a simple and low cost procedure. It was also shown the possibility of producing materials with good mechanical properties from recycled chips, which is particularly important in the high energy demanding Aluminium industry. Results showed the importance of choosing appropriate processing parameters (temperature, heating rate / soaking time and thixoforming pressure), to achieve desired product quality. Among the various conditions studied, the compositions in which NiAl2O4 was used as reinforcement showed better microstructural characteristics with better interface between matrix and reinforcement, and lower porosity. Good dispersion of the reinforcement particles and low porosity were also observed for SiC reinforced composites in which fine particles of silicon and alumina were added
Mestrado
Materiais e Processos de Fabricação
Mestra em Engenharia Mecânica
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Carminati, Paul. "Composites SiC/SiC à interphase de type BN de compositions variables et réactivité optimisée." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0248/document.
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Les composites SiC/SiC à renfort fibreux à base de SiC, et à matrice SiC sont développés pour applications aéronautiques. En vue d’améliorer leur durée de vie en atmosphère oxydante à haute température, l’utilisation d’interphase BN est préconisée,puisque l’oxyde de bore liquide permet de protéger le matériau. Cependant, sous atmosphère humide, la volatilisation de B2O3 sous forme d’hydroxyde HxByOz est non négligeable. L’objectif de ce travail est d’optimiser l’organisation structurale de BN élaboré par CVD/CVI, pour améliorer sa résistance à l’oxydation, et d’évaluer l’intérêt de l’ajout d’élément(s) au nitrure de bore permettant la stabilisation thermodynamique de B2O3 à haute température, en présence d’humidité. Ce travail a permis d’établir des liens entre composition chimique de la phase gazeuse, cinétique et mécanisme de dépôt, et degré d’organisation du nitrure de bore. Malheureusement, si la résistance à l’oxydation de BN augmente perpendiculairement à ses plans (002) avec son organisation structurale, elle est à peine améliorée le long des plans (002). Néanmoins, l’intérêt de l’ajout d’aluminium à l’interphase BN pour améliorer la stabilité chimique de B2O3 en présence d’humidité a été démontré à une température suffisamment élevée pour permettre la formation de cristauxAl4B2O9. Ainsi, il semble que ces cristaux permettent une cicatrisation efficace des fissures matricielles dans des composites SiC/SiC. Des essais supplémentaires d’oxydation dans des conditions plus complexes, comme sous cyclage thermique, sont nécessaires pour conclure catégoriquement en faveur de l’amélioration de la durée de vie de ces matériauxSiC/SiC composites with SiC-based fibres and SiC matrix are developed for aeronautic applications. In order to improve their life time in an oxidizing atmosphere at high temperature, the use of BN interphase is recommended, as far as liquid boron oxide can protect the material. However, this glassy material is known to be very sensitive to moisture because boron oxide volatilizes quickly under high temperature. The aims of this work are (i) to maximise the structural organization of BN deposited by CVD/CVI to improve its oxidation resistance and (ii) to assess the interest of elemental addition to boron nitride allowing thermodynamic retention for B2O3 under wet air. Relationships between gas phase composition, deposition rates, and microstructure have been established in this work. Unfortunately, if the oxidation resistance of BN perpendicular to its (002) crystal planes increases with its structural organization, it appears to be hardly improved along the (002) planes. Nevertheless, aluminium addition to BN has led to Al4B2O9 crystals generation, asAl2O3 reacts together with B2O3 under high temperature. These materials therefore appear tobe able to seal SiC matrix cracks. As a result, the global oxidation resistance under wet air of SiC/SiC composites with B(Al)N interphases can been significantly improved. Additional oxidation tests, especially under thermal cycling, are needed to definitively conclude about this point
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Jesus, Edilson Rosa Barbosa de. "OBTENÇÃO, USINAGEM E DESGASTE DE MATERIAIS COMPÓSITOS DE MATRIZ METÁLICA PROCESSADOS VIA METALURGIA DO PÓ." Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/85/85132/tde-25052007-163032/.
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O objetivo deste trabalho foi a obtenção de compósitos de matriz metálica (CMM) pela rota da metalurgia do pó, e a avaliação destes quanto às suas características de usinagem e desgaste. Inicialmente foram obtidos materiais compósitos de matriz de alumínio comercialmente puro, com frações volumétricas de partículas de reforço de carboneto de silício iguais a 5, 10 e 15 %. Foi obtida também uma quantidade de material somente com o material da matriz (sem partículas de reforço) para que se pudesse durante o trabalho, verificar por comparação a influência da adição de material de reforço na matriz. O material obtido foi caracterizado física (densidade hidrostática), mecânica (dureza, ensaios de tração) e microestruturalmente (microscopia óptica e microscopia eletrônica de varredura). Os resultados mostraram para os materiais compósitos uma distribuição homogênea das partículas de reforço e melhoria das propriedades mecânicas principalmente o limite de resistência (LR) em relação ao material sem reforço. Na etapa seguinte foram realizados ensaios para verificação do comportamento dos materiais frente à usinagem, e avaliação de desempenho de diversos materiais de ferramenta (carboneto cementado, cerâmica e diamante policristalino). Nestes ensaios foram coletados valores de força de corte a partir de porta-ferramentas instrumentados com medidores de deformação. Fenômenos tais como desgaste da ferramenta, formação ou não de aresta postiça de corte e formação de cavaco também foram observados e avaliados. Os resultados encontrados nos ensaios com ferramenta de carboneto duro sinterizado foram utilizados para a determinação dos índices de usinabilidade de cada material; estes valores foram ainda aplicados na equação de Taylor e as constantes da equação para os materiais e condições de ensaio foram também determinadas. Os resultados mostraram que a inclusão de partículas de reforço cerâmico torna extremamente difícil a usinagem desses materiais e, somente com ferramenta de diamante foi possível obter resultados satisfatórios. Na fase final foram realizados testes de desgaste de efeito comparativo para verificação da influência da adição de partículas de reforço nas características de resistência ao desgaste do material. Neste caso a adição de partículas de reforço mostrou ser eficiente na melhoria da resistência ao desgaste de todos os materiais compósitos em relação ao material sem reforço.The aim of this investigation was the obtainment of metal matrix composites (MMC) by the route of powder metallurgy, and the valuation of these materials with relation to their machining and wear characteristics. Firstly, were obtained pure comercial aluminium matrix composites materials, with 5, 10 and 15% volumectric fraction of silicon carbide particles. Was also obtained a material without reinforcement particles in order to verify by comparison, the influence of adittion of reinforcement particles. The obtained materials were characterized physics (hidrostatic density), mechanics (hardness and tensile tests) and microstructurally (optical microscopy and scanning electron microscopy). The results showed a homogeneous distribution of reinforcement particles in the composite, and improvement in the mechanical properties, mainly tensile strength (UTS) in comparison to the unreinforced material. After, tests were made to verify the materials behavior during machining and to check the performance of several tool materials (cemented carbide, ceramics and polycrystalline diamond). In these tests, values of the cutting force were measured by instrumented tool-holders. Phenomena such as tool wear, built-up edge formation and mechanism of chip formation were also observed and evaluated. The results from the cemented carbide tool tests, were utilisated for the machinability index determination of each material. These results were applied to the Taylor equation and the equation constants for each material and test conditions were determinated. The results showed that the inclusion of silicon carbide particles made extremely difficult the machining of the composites, and only with diamond tool, satisfactory results were obtained. At last, wear tests were performed to verify the influence of the reinforcement particles in the characteristics of wear resistance of the materials. The results obtained were utilized in the wear coefficient determination for each material. The results showed an improvement in wear resistance, with the increase in volume fraction of reinforcement particles.
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Johnson, Peter Kenneth. "The interaction between liquid aluminium and silicone carbide in metal composites." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46370.
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Penugonda, Madhusudhan R. "Alumina - silicon carbide composites from kaolinite-carbon precursors by hot-pressing." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/28509.
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The system kaolinite - carbon black consisting of cheap precursors has been investigated, in terms of its potential to form A1₂ O₃ - SiC composites. The carbothermal reduction process of mullite and silica was studied, in detail, in the range 1275° to 1810° C and over different periods, both under sintering as well as hot-pressing conditions. It was established that the reduction of mullite and silica starts around 1450° C, where the rate of reaction is very slow. Until about 1800° C during the reduction of mullite, SiO₂ gets preferentially reduced, thus forming a composite ceramic consisting of SiC and A1₂ O₃ phases.
The kinetics of the formation of SiC + A1₂ O₃ were followed in the range 1590° - 1660° C and it was noted that under hot-pressing conditions they follow a contracting cylinder model. The rate of reaction increased with the increase in temperature and followed a parabolic path with time because of the geometry of the hot-pressed specimens at each temperature. This indicated that the gas diffusion in and out of the system along the edges of the cylindrical specimens is the rate controlling step. The activation energy of the reduction process was calculated to be 922 KJ/mole. The application of pressure prior to the carbothermal reduction process seemed to be not favourable for the formation of SiC and A1₂ O₃, however, when applied after the beginning of soaking period, this greatly improved the densities and formation of SiC and A1₂ O₃.
The microstructure of the samples was analysed using SEM and TEM. It was found that the grain size of the composite ceramic was of the order of 0.2μm. SiC was present mainly in the form of fine platelets.
Finally, the isothermal compaction behaviour of the system was studied under a constant pressure in the temperature range 1200° C - 1800° C, during which the formation and carbothermal reduction of mullite and silica took place. A mathematical model based on the least squares fitting was used to fit the compaction curves. Due to the complex nature of the compaction data an empirical approach was used to interpret the data and a viscoelastic model was developed. It was found that the interactive-double-Kelvin unit having two elastic and two viscous components explained the type of compaction behaviour observed in the kaolinite + C system. One of the viscous components (η₁) and one of the elastic components (M₁) were found to be temperature sensitive.
It is concluded that starting from the cheap precursors (kaolinite and carbon black) a particulate composite of A1₂ O₃,-SiC can be produced by hot-pressing technique. SiC-whisker formation is not encountered in this system. The very fine grain size of the paniculate composite, resulting in a small flaw size, should provide the composite ceramic with good mechanical properties.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Yilmaz, Hamdi Sencer. "Characterization Of Silicon Carbide Particulate Reinforced Squeeze Cast Aluminum 7075 Matrix Composite." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605261/index.pdf.
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The aim of this study is to investigate the mechanical behavior and its relation with processing and microstructure of the silicon carbide particulate (SiCp) reinforced aluminum matrix composite. Aluminum 7075 alloy is chosen as matrix alloy, in which zinc is the main alloying element. Four different additions of SiCp were used and the weight fractions were 10%, 15%, 20% and 30%. Composites were processed by with squeeze casting and the applied pressure during casting was 80 MPa. The mould is specially designed to produce both specimens ready for tensile and three point bending tests.
Both as-cast and heat treated aluminum composites were examined and T6 heat treatment was applied. Three point bending tests were performed to reveal the fracture strength of aluminum composites. 10wt% SiCp aluminum composites showed the maximum flexural strength in both as-cast and heat treated composites. The mechanical test results revealed that precipitated phases in heat treated composites, behaved like fine silicon carbide particulates and they acted as barriers to dislocation motion. Maximum flexural strength increased about 40 MPa (10%) in as-cast and 180 MPa (44%) in heat treated composites. Tensile testing was also conducted to verify the results of the three point bending tests.
Hardness tests were done to find the effect of silicon carbide addition and to find the peak hardness in heat treatment. For as-cast specimens hardness values increased from 133 to 188 Vickers hardness (10 kg.) with increase in SiCp content from 0 to 30wt% and for heat treatment specimens hardness values increased from 171 to 221 Vickers hardness (10 kg.). The peak hardness values were obtained at 24 hours precipitation heat treatment. SEM studies were carried out to examine the heat treated composites, to take SEM photographs and to obtain a general elemental analysis. Theoretical volume percentage addition of SiCp was checked with Clemex Image Analyzer program. Distribution of SiCp was determined by mettalographic examination. Second phases that were formed during heat treatment was searched by x-ray analysis.
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Cernyar, Jeffery. "Fatigue and fracture behavior of a 2124 aluminum alloy reinforced with silicon carbide whiskers." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/20053.
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Morgan, Andrew. "JOINING AND HERMETIC SEALING OF SILICON CARBIDE USING IRON, CHROMIUM, AND ALUMINUM ALLOYS." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3529.
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Silicon Carbide (SiC) is increasingly gaining attention as a potential fuel cladding material, on account of its favorable thermo-mechanical and neutronic properties. The major limitations of such a cladding is currently associated with joining and hermetic sealing. The work presented here investigated the use of Al, Cr and Fe metals and a specialized alloy (FeCrAl) to achieve hermetic sealing of SiC tubes as well as a joining technology of SiC. Major part of solving this issue requires addressing joining of ceramic and metallic components, which are largely dissimilar in both thermal and mechanical properties. Preliminary experiments to bond SiC with FeCrAl resulted in adverse separation partially attributed to the differences in thermal expansion mismatch. To alleviate these problems, thin and thick coatings of the metals and alloys were applied to SiC. Qualitative microstructural characterization of the final product indicated satisfactory bonding between the materials.
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Rao, Shailaja P. "Implant annealing of al dopants in silicon carbide using silane overpressure." [Tampa, Fla.] : University of South Florida, 2005. http://purl.fcla.edu/fcla/etd/SFE0001213.
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Zaman, Farhana. "Characterization of selective epitaxial graphene growth on silicon carbide: limitations and opportunities." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43624.
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The need for post-CMOS nanoelectronics has led to the investigation of innovative device structures and materials. Graphene, a zero bandgap semiconductor with ballistic transport properties, has great potential to extend diversification and miniaturization beyond the limits of CMOS. The goal of this work is to study the growth of graphene on SiC using the novel method of selective graphitization. The major contributions of this research are as follows - First, epitaxial graphene is successfully grown on selected regions of SiC not capped by AlN deposited by molecular beam epitaxy. This contribution enables the formation of electronic-grade graphene in desired patterns without having to etch the graphene or expose it to any detrimental contact with external chemicals. Etching of AlN opens up windows to the SiC in desirable patterns for subsequent graphitization without leaving etch-residues (determined by XPS). Second, the impact of process parameters on the growth of graphene is investigated. Temperature, time, and argon pressure are the primary growth-conditions altered. A temperature of 1400oC in 1 mbar argon for 20 min produced the most optimal graphene growth without significant damage to the AlN capping-layer. Third, first-ever electronic transport measurements are achieved on the selective epitaxial graphene. Hall mobility of about 1550 cm2/Vs has been obtained to date. Finally, the critical limitations of the selective epitaxial graphene growth are enumerated. The advent of enhanced processing techniques that will overcome these limitations will create a multitude of opportunities for applications for graphene grown in this manner. It is envisaged to be a viable approach to fabrication of radio-frequency field-effect transistors.
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Kothari, Mitul Arvind. "Welding of cast A359/SiC/10p metal matrix composites." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2699.
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Welding of metal matrix composites (MMCs) is an alternative to their
mechanical joining, since they are difficult to machine. Published literature in fusion
welding of similar composites shows metallurgical problems. This study investigates the
weldability of A359/SiC/10p aluminum SiC MMC. Statistical experiments were
performed to identify the significant variables and their effects on the hardness, tensile
and bending strengths, ductility, and microstructure of the weld. Finite Element
Analysis (FEA) was used to predict the preheat temperature field across the weld and the
weld pool temperature.
Welding current, welding speed, and the preheat temperature (300-350??C)
affected the weld quality significantly. It was seen that the fracture of the welded
specimens was either in the base MMC or in the weld indicating a stronger interface
between the weld and the base MMC. Oxides formation was controlled along the weld
joint. Low heat inputs provided higher weld strengths and better weld integrity. It was
found that the weld strengths were approximately 85% of the parent material strength.
The weld region had higher extent of uniform mixing of base and filler metal when
welded at low currents and high welding speeds. These adequate thermal conditions
helped the SiC particles to stay in the central weld region. The interface reaction
between the matrix and SiC particles was hindered due to controlled heat inputs and
formation of harmful Al4C3 flakes was suppressed. The hardness values were found to
be slightly higher in the base metal rich region. There was no significant loss in the
hardness of the heat affected zone. The ductility of the weld was considerably increased
to 6.0-7.0% due to the addition of Al-Si filler metal.
21
May, Christopher William. "Effect of thermomechanical treatments on the aging response of centrifugally cast silicon carbide/aluminum composites." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23871.
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Vargas, Alexandro. "Machinability Study on Silicon Carbide Particle-Reinforced Aluminum Alloy Composite with CVD Diamond Coated Tools." Scholarly Commons, 2017. https://scholarlycommons.pacific.edu/uop_etds/215.
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Particle-reinforced MMCs (pMMC) such as aluminum alloys reinforced with ceramic silicon carbide particles (AlSiC) require special cutting tools due to the high hardness and abrasive properties of the ceramic particles. Diamond coated cutting tools are ideal for machining this type of pMMC. Previous research studies focus on the machinability of pMMCs with low ceramic content. The aim of this research is to determine the optimal cutting parameters for machining AlSiC material containing high silicon carbide particle reinforcement (>25%). The optimal cutting parameters are determined by investigating the relationship between cutting forces, tool wear, burr formation, surface roughness, and material removal rate (MRR). Experimental milling tests are conducted using CVD diamond coated end mills and non-diamond tungsten carbide end mills. It was found that low tool rotation speeds, feed rates and depths of cut are necessary to achieve smoother surface finishes of R a < 1 μm. A high MRR to low tool wear and surface roughness ratio was obtainable at a tool rotation speed of 6500 r/min, feed rate of 762 mm/min and depth of cut of 3 mm. Results showed that a smooth surface roughness of the workpiece material was achieved with non-diamond tungsten carbide end mills, however, this was at the expense of extreme tool wear and high burr formation. The use of coolant caused a 50% increase in tool wear compared to the dry-cutting experiments which had lower cutting tool forces.
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SETHI, VARUN. "Effect of Aging on Abrasive Wear Resistance of Silicon Carbide Particulate Reinforced Aluminum Matrix Composite." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1191951786.
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MAKUNTUALA, KEVA. "Desenvolvimento de compositos refratarios SiC-AlN e SiC-SiAlON." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9274.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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JESUS, FILHO EDSON S. de. "Obtencao e avaliacao do comportamento a fadiga de compositos de matriz de aluminio submetidos a diferentes tratamentos superficiais mecanicos." reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9273.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
26
Drehmann, Rico. "Haftmechanismen kaltgasgespritzter Aluminiumschichten auf keramischen Oberflächen." Doctoral thesis, Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-229668.
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Aluminiumschichten werden durch Kaltgasspritzen auf fünf verschiedene poly- und monokristalline keramische Werkstoffe (Al2O3 , AlN, SiC, Si3N4 , MgF2 ) appliziert. Dabei erfolgt eine Variation der Substrattemperatur und der Partikelgröße. Ausgewählte Proben werden einer nachfolgenden Wärmebehandlung unterzogen. Die im Fokus der Arbeit stehende Erforschung der an der Grenzfläche zwischen Aluminium und Keramik wirkenden Haftmechanismen erfolgt sowohl mithilfe einer mechanischen Charakterisierung (Stirnzugversuche) als auch durch verschiedene mikroskopische, spektroskopische und hochauflösende Methoden. Die Bewertung der Untersuchungsergebnisse zeigt, dass im Allgemeinen ein Anstieg der Haftzugfestigkeit mit steigender Substrat- und Wärmebehandlungstemperatur sowie mit zunehmender thermischer Effusivität des Substratwerkstoffs zu verzeichnen ist. Eine vergleichbare Auswirkung hat innerhalb bestimmter Grenzen die Zunahme der Partikelgröße. Mit der Heteroepitaxie wird neben der mechanischen Verklammerung ein weiterer wichtiger Haftmechanismus kaltgasgespritzter metallischer Schichten auf keramischen Substraten identifiziert. Die Ausbildung von quasiadiabatischen Scherbändern und statische Rekristallisationsprozesse wirken dabei als wichtige begleitende Mechanismen. Als Nachweis für heteroepitaktisches Wachstum ist die Existenz von (annähernd) parallelen, senkrecht oder geneigt zur Grenzfläche stehenden Ebenenpaaren, die eine geringe Gitterfehlanpassung aufweisen, zu werten. Der Vergleich mit PVD-Schichten zeigt, dass in Bezug auf die Orientierung von Gitterebenen verschiedene Mechanismen der Heteroepitaxie existieren, die von der atomaren Mobilität des Beschichtungswerkstoffs bestimmt werden.
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Muller, Kurt Alwin. "Effect of post-fabrication processing on the tensile properties of centrifugally cast silicon carbide particulate reinforced aluminum composites." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1993. http://handle.dtic.mil/100.2/ADA274865.
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Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, September 1993.Thesis advisor(s): Dutta, Indranath. "September 1993." Cover title: Effect ... cast SiC particulate ... Include bibliographical references. Also available online.
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Bindas, Erica Bindas. "EFFECT OF TEMPERATURE, STRAIN RATE, AND AXIAL STRAIN ON DIRECT POWDER FORGED ALUMINUM-SILICON CARBIDE METAL MATRIX COMPOSITES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case1530871866585058.
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Kaneko, Mitsuaki. "Strain-Controlled AlN Growth on SiC Substrates." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217172.
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GODOY, ANA L. E. "Estudo da influência da adição de polímeros precursores cerâmicos na sinterização de SiC e Alsub(2)Osub(3)." reponame:Repositório Institucional do IPEN, 2005. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9288.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
31
Sánchez, Sovero Luis Francisco. "Effect of thermal annealing treatments on the optical and electrical properties of aluminum-doped, amorphous, hydrogenated silicon carbide thin films." Master's thesis, Pontificia Universidad Católica del Perú, 2019. http://hdl.handle.net/20.500.12404/14529.
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In this work, a systematic study of the structural, optical and electrical properties of aluminum doped hydrogenated amorphous silicon carbide (Al-doped a-SiC:H) thin films grown by radio frequency magnetron sputtering is presented. The samples were grown using a high purity Al and SiC targets in a hydrogen-rich atmosphere and then were subjected to a rapid thermal annealing processes with temperatures of up to 600 °C. The film thickness ranged from 321 nm to 266 nm. The amorphous nature of the thin films was confirmed by X-ray diffraction measurements before and after the annealing treatments. Fourier transform infrared spectroscopy analysis revealed the different heteronuclear bonds present in the samples, whilst Raman spectroscopy showed the different homonuclear bonds present in the material. The evolution of the latter bonds with annealing temperature was assessed, showing a change in the structure of the thin film. Energy-dispersive X-Rays Spectroscopy confirmed the incorporation of aluminum in the amorphous silicon carbide matrix. UV-VIS Transmittance spectra revealed optical parameters such as Tauc energy bandgap, Iso-absorption energy bandgap and refractive index. Furthermore, the bandgap is also determined by means of a recently developed band-fluctuation model. In addition, electrical resistivity is determined by means of a four-probe Van Der Pauw method. Only the samples annealed at 600 °C exhibited contacts with an Ohmic behavior. The annealed films exhibited lower resistivities than the as-deposited ones, probably due to a thermal-induced reordering of the atoms. This reordering is shown in the variation of the Urbach energy which is related to an increase in the Si-C bond density, due to the dissociation of the hydrogen-related bonds.En este trabajo de tesis se presenta el estudio las propiedades estructurales y optoelectrónicas de carburo de silicio amorfo hidrogenado dopado con aluminio fabricado mediante pulverización catódica de radio frecuencia. Las muestras se fabricaron usando target de SiC y Al de alta pureza en atmosfera de hidrogeno. Luego las películas fueron calentadas hasta la temperatura de 600°C en un horno de rápido procesamiento térmico. La difracción de rayos X confirma la naturaleza amorfa de las películas. Los espectros de absorción infrarroja muestran los diferentes enlaces hetero-nucleares mientras que la espectroscopia Raman nos muestra los diferentes enlaces hononucleares presentes en la muestra. Se evaluó la evolución de los últimos enlaces con el tratamiento térmico, mostrando un cambio en la estructura del material. Espectroscopía de dispersión de energía de rayos X nos muestra la incorporación de aluminio en la matriz de carburo de silicio amorfo. Los espectros de transmitancia UV-VIS revelan parámetros ópticos tales como energía de Tauc, energía de Iso- absorción, energía de Tauc e índice de refracción. Además, el modelo de fluctuación de bandas desarrollado recientemente nos permite determinar los bordes de movilidad y energía de Urbach. Adicionalmente, el método de Van Der Pauw nos permite determinar el valor de la resistividad eléctrica de la muestra, solo a 600°C, donde se obtuvo un comportamiento óhmico mostrando baja resistividad eléctrica, probablemente debido a un reordenamiento de los átomos inducidos térmicamente. Este reordenamiento estructural se muestra en la variación de la energía de Urbach que está asociada con el aumento de la densidad de enlaces Si-C, debido a la disociación de los enlaces relacionados con el hidrogeno.
Tesis
32
Ison, Stephen John. "Interfacial reactions between PbO-rich glasses and aluminium composites." Thesis, University of Warwick, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364605.
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Lu, Peng. "Sublimation growth of ALN bulk crystals and high-speed CVD growth of SiC epilayers, and their characterization." Diss., Manhattan, Kan. : Kansas State University, 2006. http://hdl.handle.net/2097/242.
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Baker, Victoria Isabelle. "3D Commutation-Loop Design Methodology for a SiC Based Matrix Converter run in Step-up mode with PCB Aluminum Nitride Cooling Inlay." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/104361.
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This work investigates three-dimensional power loop layout for application to a SiC based matrix converter, providing a symmetric, low-inductance solution. The thesis presents various layout types to achieve this design target, and details the implementation of a hybrid layout to the matrix converter phase-leg. This layout is more easily achievable with a surface-mount device package, which also offers benefits such as ease in manufacturing, and a compact package. In order to implement a surface-mount device, a PCB thermal management strategy should be utilized. An evaluation of these methods is also presented in the work. The final power loop solution that implements an aluminum nitride inlay is evaluated through simulated parasitic extraction and experimental double pulse tests. The layout achieves small, symmetric loop inductances. Finally, the full power, three-phase matrix converter demonstrates the successful implementation of this power loop layout.Master of Science
In the United States, 40% primary energy consumption comes from electricity generation, which is the fastest growing form of end-use energy. Industries such as commercial airlines are increasing their use of electric energy, while phasing out the mechanical and pneumatic aircraft components, as they offer better performance and lower cost. Thus, implementation of high efficiency, electrical system can reduce energy consumption, fuel consumption and carbon emissions [1]. As more systems rely on this electric power, the conversion from one level of power (voltage and current) to another, is critical. In the quest to develop high efficiency power converters, wide bandgap semiconductor devices are being turned to. These devices, specifically Silicon Carbide (SiC) devices, offer high temperature and high voltage operation that a traditional Silicon (Si) device cannot. Coupled with fast switching transients, these metal oxide semiconductors field effect transistors (MOSFETs), could provide higher levels of efficiency and power density. This work investigates the benefits of a three-dimensional (3D) printed circuit board (PCB) layout. With this type of layout, a critical parasitic – inductance – can be minimized. As the SiC device can operate at high switching speeds, they incur higher di/dt, and dv/dt slew rates. If trace inductance is not minimal, overshoots and ringing will occur. This can be addressed by stacking PCB traces on top of one another, the induced magnetic field can be reduced. In turn, the system inductance is lowered as well. The reduction of this parameter in the system, reduces the overshoot and ringing. This particular work applies this technique to a 15kW matrix converter. This converter poses a particular design challenge as there are a large number of devices, which can lead to longer, higher inductance PCB traces. The goal of this work is to minimize the parasitic inductance in this converter for high efficiency, high power density operation.
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GOMES, EDSON G. "Caracterizacao microestrutural mecanica e tratamentos termicos de material composito Al/SiC obtido por conformacao por 'spray'." reponame:Repositório Institucional do IPEN, 1998. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10718.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
36
Uribe, Restrepo Catalina. "Process-dependent microstructure and severe plastic deformation in SiCp?? reinforced aluminum metal matrix composites." Master's thesis, University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4712.
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Discontinuously reinforced MMCs with optimized microstructure are sought after for exceptional high strain rate behavior. The microstructure evolution of a stir-cast A359 aluminum composite reinforced with 30 vol.% SiCsubscript p] after isothermal anneal, successive hot-rolling, and high strain rate deformation has been investigated. Quantitative microstructural analysis was carried out for the as-cast, annealed (470??C, 538??C and 570??C) and successively hot rolled specimens (64, 75, 88, and 96% rolling reductions). Selected composites were also examined after high strain rate deformation. X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy were employed for microstructural characterization. The strength and ductility of the A359 Al alloys, and the composite, were greatly influenced by the brittle eutectic silicon phase and its morphology. Lamellar eutectic silicon spheroidized with isothermal anneal and successive hot rolling with a corresponding decrease in hardness. The hot rolling process also considerably decreased the SiC particle size (approximately 20% after 96% reduction) by breaking-up the hard SiC particles. However, this break-up of particles increased the homogeneity of SiCsubscript p] size distribution. Successive hot rolling also healed voids due to solidification shrinkage, incomplete infiltration of molten Al and defects originating from fractured particles. Four selected specimens of composites were examined after high strain rate deformation. Fractography and metallographic analysis for the craters, voids, and relevant regions affected by the high velocity impact were carried out. The deposition of impact residuals was frequently observed on the exposed fracture surfaces. These residuals were typically observed as "molten-and-solidified" as a consequence of excessive heat generated during and after the damage.; Particularly in regions of entry and exit of impact, intermixing of residuals and composite constituents were observed, demonstrating that the Al matrix of the composite also had melted. In all samples examined, cracks were observed to propagate through the eutectic Si network while a small number of broken reinforcement particles were observed. A slight variation in failure mechanisms was observed (e.g., radial, fragmentation, petalling) corresponding to the variation in ductility against high strain rate deformation. In selected specimens, parallel sub-cracks at the exit were observed at 45?? and 30??. These sub-cracks were again filled with intermixed constituents from projectile residuals and composites. This observation suggests that the melting of composite constituents that leads to intermixing occured after the crack propagation and other damage.ID: 030646232; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; On t.p. "p??" is subscript.; Thesis (M.S.M.S.E.)--University of Central Florida, 2011.; Includes bibliographical references (p. 86-88).
M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Godoy, Ana Lúcia Exner. "Estudo da influência da adição de polímeros precursores cerâmicos na sinterização de SiC e Al2O3." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-18052012-141434/.
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Neste trabalho foram avaliados os efeitos da adição de polímeros precursores na sinterização, microestrutura, dureza e na tenacidade à natura de materiais cerâmicos à base de carbeto de silício e de AI2O3. As matérias-primas cerâmicas foram caracterizadas por análise semi-quantitativa por espectrometria de fluorescência de raios X, difração por laser, adsorção gasosa e microscopia eletrônica de varredura. Para os polímeros utilizou-se análise termogravimétrica. A cinética de sinterização das amostras compactadas foi estudada por dilatometria. A caracterização dos materiais sinterizados incluiu medidas de densidade aparente pelo princípio de Arquimedes e/ou por picnometria de He, porosimetria por intrusão de Hg, análises de difração de raios X, de carbono total, avaliação da microestrutura e por microscopia eletrônica de varredura e de transmissão, análise por espectrometria de raios X por dispersão de energia, ensaios de impressão Vickers para determinação de dureza e tenacidade à fiatura. No estudo de cerâmica à base de carbeto de silício foram utilizados os aditivos óxidos AI2O3 (4% em peso) e Y2O3 (4% em peso) e os aditivos poliméricos PMHS (polimetilhidrogenossiloxano) e polimetilhidrogenossiloxano com D4Vi. O processamento envolveu a cura do material, pirólise e sinterização (1850 °C e 1950 °C/l h. Ar ou N2). Nas amostras à base de carbeto de silício houve elevada perda de massa, principalmente quando a atmosfera de sinterização foi argônio. As amostras à base de carbeto de silício, com adição de polímeros atingiram densidade de até 3,15 g/cm3 quando pirolisadas a 900 °C em N2 e sinterizadas a 1950 °C, em atmosfera de nitrogênio. Para as amostras à base de alumina foram utilizados os aditivos poliméricos PMHS, PMS (polimetilsilsesquioxano) e PPS (polifenihnetilvinilhidrogenosilsesquioxano) e as sinterizações foram realizadas a 1650 °C e 1700 °C, não havendo variações significativas nas densidades obtidas nas duas temperaturas. Nos materiais com adição de PMHS foram obtidos compósitos de alumina e mulita, sendo que os grãos de mulita foram formados intergranularmente. Nas amostras contendo PMS ou PPS a distribuição das feses formadas, Si2Al4O4N4 e Si2ON2, foi bastante heterogênea, A obtenção de compósitos cerâmicos utilizando pequenas adições de polímeros precursores cerâmicos mostrou-se viável para materiais à base de alumina, sendo uma rota simples de conformação, com grande potencial para a obtenção de peças com geometria complexa.The effects of the addition of precursor polymers on sintering, microstructure, hardness and fiacture toughness of silicon carbide and alimiina ceramics were studied. The ceramic raw materials were characterized by semi-quantitative analysis by X-ray fluorescence, particle size by laser diffraction, specific surface area by gas adsorption and microstructural analysis by scanning elecfron microscopy. The polymers were analyzed by thermogravimetry. The sintering kinetics of cold-pressed specimens was studied by dilatometry. The sintered materials were characterized by evaluation of apparent density by the Archimedes technique and/or helium picnometry, by mercury porosimetry, by X-ray diflftaction, by evaluation of total carbon content, by scanning and transmission electron microscopy, by enetgy dispersion X-ray spectrometry, and by Vickers indentation analysis for determining hardness and fiacture toughness. AI2O3 (4wt.%) and Y2O3 (4wt.%) and polymetylhydrogenosiloxane and polymetylhydrogenossiloxane with D4Vi were the sintering aids for SiC. The processing procedures were material cure, pyrolysis and sintering (1850 X and 1950 °C/1 h, Ar or N2). High mass loss was measured in silicon carbide based ceramics, mainly under argon. Silicon carbide based ceramics with polymer sintering aids achieved 3.15 g/cm3 density after pyrolysis at 900 °C under N2 and sintering at 1950 °C under nitrogen. PMHS, PMS and PPS polymer sintering aids were used for almnina based ceramics sintering carried out at 1650 °C and 1700 °C, without significant difference in the final density. Addition of PMHS yielded alumina and mullite composites, with intergranular mullite grains. Heterogeneous Si2AI4O4N4 and Si2ON2 phases were obtained in specimens with PMS or PPS, The preparation of ceramic composites using small amounts of precursor polymers showed a suitable process for alumina-based ceramics, a simple forming route, with high potential for the fabrication of complex shape pieces.
38
BOARI, ZOROASTRO de M. "Modelo matematico da influencia da distribuicao de particulas de SiC nas tensoes termicas em compositos de matriz metalica." reponame:Repositório Institucional do IPEN, 2003. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11105.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
39
Dagher, Roy. "Croissance directe de graphène par dépôt chimique en phase vapeur sur carbure de silicium et nitrures d'éléments III." Thesis, Université Côte d'Azur (ComUE), 2017. http://www.theses.fr/2017AZUR4068/document.
Full textAbstract:
Le graphène est un matériau bidimensionnel appartenant à la famille des allotropes du carbone. Il consiste en une couche atomique restant stable grâce à des liaisons chimiques fortes dans le plan entre les atomes de carbone. C'est un semi-conducteur sans bande interdite (gap) avec une dispersion d'énergie linéaire près des points de Dirac, ce qui facilite le transport balistique des porteurs de charge. De plus, tout comme n'importe quel semi-conducteur, il est possible de contrôler ses propriétés électriques sous l'influence d'un champ électrique externe, ce qui permet de modifier la densité de porteurs et leur type (électrons ou trous). Le graphène peut être élaboré par différentes techniques, mais nous avons considéré la croissance directe sur le carbure de silicium (SiC) par dépôt chimique en phase vapeur (CVD) avec une source de carbone externe, technique développée dans notre laboratoire depuis 2010. Cette approche est attrayante car elle permet de contrôler les propriétés du graphène en modifiant les paramètres de croissance. Notre objectif dans ce manuscrit est de donner une idée plus approfondie de cette technique de croissance et d'étudier son potentiel pour la croissance du graphène. À cette fin, nous avons discuté en détail de différents aspects de la croissance, en commençant par des simulations thermodynamiques pour comprendre la chimie gouvernant cette méthode. Nous avons également étudié l'influence des différents paramètres de croissance sur la formation du graphène et sur ses propriétés, tels que le temps de croissance, le débit de propane et d'autres paramètres. Cependant, nous nous sommes principalement concentrés sur deux paramètres majeurs : la quantité d'hydrogène dans le mélange gazeux, surtout que la croissance se fait sous hydrogène et argon, et la désorientation du substrat. Nos recherches ont révélé que la structure du graphène peut être modifiée en fonction de la proportion de l’hydrogène dans le mélange des gaz utilisé pour la croissance. Pour une faible proportion d’hydrogène, la croissance du graphène est associée à une reconstruction d'interface de (6√3×6√3), alors que pour une proportion élevée d’hydrogène, la couche de graphène est désordonnée dans le plan. Ces observations sont liées à l'intercalation de l'hydrogène à l'interface entre la couche de graphène et le substrat SiC, ce qui peut favoriser ou interdire la formation de la reconstruction (6√3×6√3) comme nous l'avons discuté dans le manuscrit. On s'attend à ce que la présence des deux structures de graphène ait un effet sur la contrainte dans la couche de graphène. Pour cette raison, nous avons discuté en détail les origines de la contrainte dans le graphène et tenté de corréler l'intercalation de l'hydrogène à l’interface avec la contrainte. Aussi, nous avons montré que l'angle de désorientation du substrat a une influence directe sur la croissance du graphène, affectant principalement la morphologie mais également la contrainte dans la couche du graphène. Enfin, nous avons pu produire du graphène de haute qualité, tout en démontrant la possibilité de contrôler ses propriétés électriques avec les conditions de croissance. Dans la deuxième partie de ce travail, nous avons étendu notre étude à la croissance du graphène sur les semi-conducteurs de type nitrures d’éléments III et en particulier le nitrure d’aluminium (AlN) massif ainsi que des couches hétéroépitaxiées d’AlN/SiC et AlN/Saphir, ce qui ouvre de nouvelles opportunités pour des applications innovantes. La croissance du graphène a été précédée d'une étude de recuit sur les différents échantillons d’AlN, dans le but d'améliorer leur qualité de surface, mais aussi pour tester leur stabilité à la température nécessaire pour la croissance du graphène. Bien que le film d’AlN ait été incapable de résister à la température élevée dans certains cas, une amélioration de la qualité cristalline a été détectée, attribuée à l'effet de recuitGraphene is a two-dimensional material belonging to the family of carbon allotropes, consisting of a stable single atomic layer owing to strong in-plane chemical bonds between carbon atoms. It can be identified as a gapless semiconductor with a linear energy dispersion near the Dirac points, which facilitates ballistic carrier transport. In addition, similarly to any semiconductor, it is possible to control its electrical properties under the influence of an external electric field, resulting in the tuning of its carrier density and doping type, i.e. electrons or holes. Graphene can be elaborated by different techniques and approaches. In this present work, we have considered the direct growth on silicon carbide (SiC) by chemical vapor deposition (CVD) with an external carbon source. This approach which has started to be developed in our laboratory since 2010 is very promising since it allows to control the graphene properties by manipulating the growth parameters. Our objective in this manuscript is to give further insights into this growth technique and to study its potential for the growth of graphene. For this purpose, we have discussed in details different aspects of the growth, starting with thermodynamic simulations to understand the chemistry behind our distinct growth approach. We have also investigated the influence of the different growth parameters, such as the growth time, the propane flow rate and other parameters on the growth of graphene and its properties. However, we mainly focused on two major factors: the hydrogen amount in the gas mixture, especially since the growth is carried out under hydrogen and argon, and the substrate’s miscut angle. Our investigations revealed that the graphene structure can be altered depending on the hydrogen percentage in the gas mixture considered for the growth. For low hydrogen percentage, the graphene growth is associated with a (6√3×6√3) interface reconstruction, whereas for high hydrogen percentage, the graphene layer is dominated by in-plane rotational disorder. These observations are related to the hydrogen intercalation at the interface between the graphene layer and the SiC substrate, which can allow or prohibit the formation of the (6√3×6√3) interface reconstruction as we have discussed thoroughly in this manuscript. The presence of two graphene structures was expected to impact the strain within the graphene layer. For this reason, we have discussed in details the origins of the strain in graphene and attempted to correlate the hydrogen intercalation at the interface to the strain amount. Furthermore, the substrate’s miscut angle was also found to have a direct influence on the growth of graphene, mainly affecting the morphology but also the strain within the graphene layer. In light of the different studies and results, we were able to combine the ideal growth parameters to produce state-of-the art graphene, while demonstrating the possibility of tuning its electrical properties with the growth conditions. In a second part of this work, we extended our study to the growth of graphene on III-nitrides semiconductors. We have considered substrates and templates such as bulk aluminum nitride (AlN), AlN/SiC and AlN/sapphire, which opens new opportunities for innovative applications. The growth of graphene was preceded by an annealing study on the different AlN substrates, in an attempt to enhance their surface quality, but also to test their stability at the temperatures necessary for the growth of graphene. Although the AlN film was found to be unable to withstand the high temperature in some cases, an enhancement of the crystalline quality was detected, attributed to the annealing effect
40
Kavalco, Patrícia Mariane. "Caracterização de material composto de matriz metálica a partir de um liga de alumínio aeronáutico." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/18/18150/tde-27012012-172742/.
Full textAbstract:
Materiais compostos de matriz metálica (CMM) vêm sendo estudados para diversas aplicações. Entretanto, pouco estudo é apresentado na sua confecção a partir de materiais reciclados. Este trabalho teve como objetivo a caracterização de um material composto de matriz metálica (CMM), utilizando material reciclado como matéria prima. Foram usados aparas de chapas de liga de alumínio 2024 descartados para a matriz e carbeto de silício (SiC) como reforço, sendo a produção realizada através do processo de fabricação com base na técnica de conformação por spray para possível aplicação em componentes automotivos. Foi realizado o tratamento térmico do material e a caracterização, determinando as propriedades de dureza, resistência mecânica, resistência ao desgaste, MEV e EDS. Foram ensaiadas amostras do material composto fundido e extrudado, bem como de ferro fundido de uma peça automotiva e da liga de alumínio 2024. Observou-se que o CMM ainda precisa de melhorias no processo de produção para obter propriedades de dureza e resistência que permitam que ele possa ser usado como um substituto para o ferro fundido, porém o mesmo apresentou melhores propriedades quando comparado com o material da matriz.Metal matrix composites (MMC) have been studied for several applications. However, little study is presented in its manufacture from recycled materials. This study aimed to characterize a metal matrix composite (MMC), using recycled material as raw material. Were used aluminum alloy 2024 plates clippings discarded for the matrix and silicon carbide (SiC) as reinforcement, being the production accomplished through the manufacturing process based on the technique of spray forming for possible application in automotive components. The thermal treatment and the characterization of the materia was accomplished, determining the properties of hardness, mechanical strength, wear resistance, SEM and EDS. Were tested samples of the cast and extruded composite material, as well as cast iron of an automotive part and aluminum alloy 2024. It was observed that the MMC still needs improvements in the production process to obtain properties of hardness and strength that allows it to be used as a substitute forcast iron, but it presented better properties when compared with the matrix material.
41
Crane, Samantha. "High resolution transmission electron microscopy analysis of the influence of grain boundary and triple grain junction crystallinity and chemistry on silicon carbide-based armor with small additions of aluminum, boron, and carbon." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0010845.
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Kang, Min. "Alkali/steam corrosion resistance of commercial SiC products coated with sol-gel deposited Mg-doped Al₂TiO₅ and CMZP." Thesis, Virginia Tech, 1994. http://hdl.handle.net/10919/42006.
Full textAbstract:
The corrosion resistance of two commercially available SiC filter materials coated with Mg-doped
Al2 Ti05 and (Ca 0.6.6' Mg0.52)
Zr4P6024 (CMZP) was investigated in high-temperature high pressure
(HTHP) alkali-steam environments. Coated specimen properties, including cold and hot
compressive strengths, bulk density, apparent porosity, permeability, and weight change,
dete~ed after exposure to 92% air-S% steam 10 ppm Na at 8OO°C and 1.8 MPs for 500 h were
compared with those of uncoated specimens. Procedures for applying homogeneous coatings of
Mg-doped Al2 Ti05 and CMZP to porous SiC filters were established and coating of the materials
was successfully accomplished. Efforts to stabilize the Al2 Ti05 coating composition at elevated
temperature were successful. Coatings show promise for providing improved corrosion resistance
of the materials in pressurized fluidized bed combustion (PFBC) environments as evidenced by
higher compressive strengths exhibited by coated SiC specimens than by uncoated SiC specimens
following HTHP alkali-steam exposure.
Master of Science
43
Krishnan, Bharat. "DEVELOPMENT OF SIMULATION FRAMEWORK FOR THE ANALYSIS OF NON-IDEAL EFFECTS IN DOPING PROFILE MEASUREMENT USING CAPACITANCE ? VOLTAGE TECHNIQUE." MSSTATE, 2005. http://sun.library.msstate.edu/ETD-db/theses/available/etd-04082005-092339/.
Full textAbstract:
Silicon Carbide devices are proving to be most promising for high power and high-temperature application in recent times. Efficient and accurate characterization of the device characteristics is key to the fabrication of high quality devices and reproduction of the quality of the devices fabricated. Capacitance-Voltage profiling is one of the most commonly used techniques to measure the doping profiles of semiconductors. However, interpretation of C-V profiling in the presence of traps in the material becomes complicated. Various complications arising from compensation between donors and acceptors, partial ionization of dopants and presence of deep level impurities could yield anomalous measured profile. Silicon Carbide being a wide bandgap semiconductor, many impurities commonly found such as Boron and Aluminum are not completely ionized at Room temperature. This leads to complications in calculating doping profiles when the trap levels are deeper. Other complications arising due to series resistance effect and diode edge effect may also affect the measured profile. Accounting for these complications may be difficult by mere observation of the measured profile. Simulation can be an excellent tool to extract parameters of interest from experimental results that are influenced by non-ideal effects. Fitting of the experimentally obtained data with simulated profile using specific models may be a useful technique to quantitatively account for the deviations from the actual profiles.
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MACHADO, GLAUSON A. F. "Recobrimentos à base de mulita em refratário de carbeto de silício obtidos a partir de PMSQ [POLI (METILSILSESQUIOXANO)] e alumínio." reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/27969.
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O carbeto de silício (SiC) é um material que apresenta baixa expansão térmica, altas resistências mecânica e ao choque térmico e alta condutividade térmica. Em razão disto é empregado na confecção de mobília de fornos de sinterização. O SiC no entanto sofre degradação a altas temperaturas quando submetido a atmosferas agressivas. A utilização de recobrimentos protetores evita a exposição direta da superfície do material à atmosfera dos fornos; a mulita pode ser um recobrimento protetor apropriado em razão de sua alta estabilidade em temperaturas elevadas e seu coeficiente de expansão térmica compatível com o do SiC (4x10-6/°C e 5,3x10-6/°C, respectivamente). No presente trabalho foi estudada a obtenção de recobrimento de mulita, para refratário de SiC, a partir da utilização de polímero precursor cerâmico e alumínio particulado. Foram preparadas composições com 10, 20, 30 e 50% (vol.) de alumínio adicionado ao polímero, sendo utilizados pós de alumínio de diferentes distribuições de tamanhos de partículas. As composições foram submetidas a diversos ciclos térmicos para determinação da condição mais adequada à obtenção de alto teor de mulita. A composição que apresentou melhor resultado foi a contendo 20% do pó de Al de menor tamanho de partículas. A partir desta, foi preparada e aplicada suspensão para ser aplicada sobre o refratário de SiC. A suspensão aplicada, após seca, reticulada e tratada termicamente a 1580°C, originou um recobrimento de mulita. Foram realizados ciclos de choque térmico em amostras com e sem recobrimento para comparação, num total de 26 ciclos. As condições foram 600°C/30 min. seguida de resfriamento ao ar até a temperatura ambiente. Após cada choque térmico, as amostras foram caracterizadas por microscopia óptica e eletrônica e determinado o módulo de elasticidade. Os recobrimentos apresentaram boa adesão e não foram detectados danos significativos após os choques térmicos.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
45
RAMBO, CARLOS R. "Sintese e caracterizacao de ceramicas biomorficas." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10973.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
46
Djenkal, Djamal. "Al2O3-AlON-SiC, composite céramique pour la coupe : élaboration et caractérisations mécaniques." Grenoble INPG, 1996. http://www.theses.fr/1996INPG4207.
Full textAbstract:
Les outils de coupe ceramiques permettent, par l'augmentation des vitesses de coupe, l'amelioration des rendements d'usinage. Ce travail a consiste a developper un composite a matrice alumine 80- oxynitrure d'aluminium 20 vol. Pourcents renforce par du carbure de silicium sous deux morphologies: poudre et plaquette. Les etudes ont porte sur les ameliorations du procede de fabrication et l'evaluation du comportement en frottement et en coupe d'un acier dur (z38cdv5) et un superalliage base nickel (inconel 718). Outre l'interet de la formation in situ de l'oxynitrure d'aluminium (reaction alumine-nitrure d'aluminium) au cours du frittage sur la densification finale, il est montre qu'une homogeneisation par attrition conduit a un certain renforcement de la matrice. Les proprietes mecaniques du materiau a poudre optimise sont maintenues jusqu'a 1000c. Concernant le composite a plaquette, on observe une reactivite identique a celle du composite a poudre, mais a une temperature plus basse. On obtient les valeurs maximales de tenacite (7 mla. M) pour un diametre de moyen de 8 microns et une teneur en plaquettes de 20 vol. Pourcents. Dans les conditions de frottement testees (faible pression), l'usure des composites face a l'acier est negligeable, face a l'inconel l'usure n'est plus negligeable et depend de la granularite de sic et du taux d'oxynitrure. Les essais de coupe, realises a l'ecole centrale de nantes, laboratoire materiaux, montrent l'interet des composites renforces par la poudre pour le tournage d'acier de haute dureté
47
Hégr, Ondřej. "Charakterizace nanostruktur deponovaných vysokofrekvenčním magnetronovým naprašováním." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-233428.
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This thesis deals with the analysis of nano-structured layers deposited by high-frequency magnetron sputtering on the monocrystalline silicon surface. The content of the work focuses on the magnetron sputtering application as an alternative method for passivation and antireflection layers deposition of silicon solar cells. The procedure of pre-deposite silicon surface cleaning by plasma etching in the Ar/H2 gas mixture atmosphere is suggested. In the next step the silicon nitride and aluminum nitride layers with hydrogen content in Ar/N2/H2 gas mixture by magnetron sputtering are deposited. One part of the thesis describes an experimental pseudo-carbide films deposition from a silicon target in the atmosphere of acetylene (C2H2). An emphasis is placed on the research of sputtered layers properties and on the conditions on the silicon-layer interface with the help of the standard as well as special measurement methods. Sputtered layers structure is analyzed by modern X-ray spectroscopy (XPS) and by Fourier infrared spectroscopy (FTIR). Optical ellipsometry and spectrophotometry is used for the diagnostic of the layers optical properties depending upon the wavelength of incident light. A special method of determining the surface lay-out of the charge´s carrier life in the volume and on the surface of silicon is employed to investigate the passivating effects of the sputtered layers.
48
Sobola, Dinara. "Nedestruktivní lokální diagnostika optoelektronických součástek." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2015. http://www.nusl.cz/ntk/nusl-233678.
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Chceme-li využít nové materiály pro nová optoelektronická zařízení, potřebujeme hlouběji nahlédnout do jejich struktury. K tomu, abychom toho dosáhli, je však nutný vývoj a aplikace přesnějších diagnostických metod. Předložená disertační práce, jako můj příspěvek k částečnému dosažení tohoto cíle, se zabývá metodami lokální diagnostiky povrchu optoelektronických zařízení a jejich materiálů, většinou za využití nedestruktivních mechanických, elektrických a optických technik. Tyto techniky umožňují jednak pochopit podstatu a jednak zlepšit celkovou účinnost a spolehlivost optoelektronických struktur, které jsou obecně degradovány přítomností malých defektů, na nichž dochází k absorpci světla, vnitřnímu odrazu a dalším ztrátovým mechanismům. Hlavní úsilí disertační práce je zaměřeno na studium degradačních jevů, které jsou nejčastěji způsobeny celkovým i lokálním ohřevem, což vede ke zvýšené difúze iontů a vakancí v daných materiálech. Z množství optoelektronických zařízení, jsem zvolila dva reprezentaty: a) křemíkové solární články – součástky s velkým pn přechodem a b) tenké vrstvy – substráty pro mikro optoelektronická zařízení. V obou případech jsem provedla jejich detailní povrchovou charakterizaci. U solárních článků jsem použila sondovou mikroskopii jako hlavní nástroj pro nedestruktivní charakterizaci povrchových vlastností. Tyto metody jsou v práci popsány, a jejich pozitivní i negativní aspekty jsou vysvětleny na základě rešerše literatury a našich vlastních experimentů. Je také uvedeno stanovisko k použití sondy mikroskopických aplikací pro studium solárních článků. V případě tenkých vrstev jsem zvolila dva, z hlediska stability, zajímavé materiály, které jsou vhodnými kandidáty pro přípravu heterostruktury: safír a karbid křemíku. Ze získaných dat a analýzy obrazu jsem našla korelaci mezi povrchovými parametry a podmínkami růstu heterostruktur studovaných pro optoelektronické aplikace. Práce zdůvodňuje používání těchto perspektivních materiálů pro zlepšení účinnosti, stability a spolehlivosti optoelektronických zařízení.
49
Etzion, Ron. "Degradation mechanisms and development of silicon carbide refractories." 2008. http://hdl.handle.net/2292/4531.
Full textAbstract:
The lifetime of aluminium reduction cells is of considerable importance in the operating economics of an aluminium smelter. Not only are the cell materials costly, but cell life is also key in minimizing production downtime and the waste material generated in the cutting-out and relining of a reduction cell. This lifetime is increasingly driven by two components of the cell lining: the carbon cathode and the sidewall refractories which are the primary containment of the metal and electrolyte. Silicon nitride bonded silicon carbide (SNBSC) refractories are the current state-of-the-art sidewall materials. These materials are formed by encapsulation of SiC particles in a silicon nitride matrix, by nitridation of silicon at high temperatures under a nitrogen atmosphere. In this study the mechanisms of the corrosion of silicon nitride bonded silicon carbide refractories in an aluminium reduction cell environment were examined. Microstructural analysis of SNBSC materials by: X-ray diffraction, solid state NMR, Raman spectroscopy, XPS, and SEM, identified variations in α/β Si3N4 ratio and porosity in the binder phase, with higher porosity levels and β Si3N4 content found in the interior part of the brick. Unreacted metallic silicon was observed only as a crystalline phase inside SiC grains and is not associated with the binder phase. SNBSC samples from eight different commercial refractory manufacturers were tested in an industrial aluminium cell environment, both by immersion in industrial cells and in the laboratory. The samples showed extensive attack and considerable differentiation between the samples. The effects on the corrosion rate of porosity levels, amount of binder, α/β Si3N4 ratio, free Si content in the binder, and different factors in the environment were examined in the laboratory scale trials. A laboratory scale testing rig with some novel features, such as a rotating anode, was developed to examine corrosion resistance of samples under electrolysis conditions in molten cryolite at up to 1000oC. Corrosion test results, supported by thermodynamic calculations, identified the Si3N4 binder as the reactive phase in SNBSC materials, especially in the gas phase above the bath level. High porosity levels and high β Si3N4 fraction in the binder showed a statistically significant contribution to the corrosion rate in lab-scale corrosion trials. Commercial materials are also highly inhomogeneous in the distribution of the β Si3N4 phase as mentioned above, which complicates sample selection and the interpretation of corrosion test results. The crystal morphology of β Si3N4 is suggested as the reason for the high reactivity of these materials. This morphology characterised by elongated rod-like shape crystals with hexagonal cross section, presents a higher surface area compared to α Si3N4 crystals containing mainly flat matte crystals. In the light of this observation, the binder phase in selected samples was deliberately modified to convert a significant fraction of the α Si3N4 to β Si3N4. Corrosion rates measured from these modified samples in general support the argument that the crystallographic form of silicon nitride contributes to corrosion rate. The proposed corrosion mechanism for SNBSC materials in the aluminium reduction cell atmosphere is based on combination of oxidation of the binder followed by attack of corrosive gases to produce volatile SiF4. Thus the binder phase is initially passivated below the electrolyte level on the sidewall, where exposure to corrosive gases is limited, but occurs more rapidly in the area above the electrolyte/air interface. The intrusion of electrolyte into the refractory and capillary transport up the sidewall is a key in accelerating this reaction.
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Ghosh, Kunal. "Aluminum-silicon carbide composite coatings by plasma spraying." Thesis, 1996. http://hdl.handle.net/2429/6003.
Full textAbstract:
The use of aluminum in the automobile engines and other critical parts require a
superior surface property of the same. This has led to the development of plasma
sprayable surface coatings for the components. To impart the maximum bonding
strength, along with hardness to the coatings an aluminum based composite (Al-SiC) was
found to be the most suitable. The presence of a hard ceramic second phase within a soft
metallic matrix greatly improves the wear resistance of the composite material. The
powders for spraying were prepared by mechanical agglomeration of 6061 Al alloy
(particle size between 40 and 60 um) with fine SiC particles ( « 8 um) by using high
energy vibratory mills. The concentration of SiC was varied from 20-75 vol%, the
balance being the matrix A l alloy. The size of the reinforcement was varied from 8 to 37
um in the Al-50vol%SiC composite coatings. A Process Control Agent (PCA) was used
to modify the morphology of the powders during the process of mechanical alloying.
Mechanical alloying produced composite powders in a size range between 40 and 120 u.m
with the SiC phase uniformly dispersed within the matrix. The powders used for
spraying were fractionated between the size range of 44 and 149 um by sieving.
The powders were sprayed using two types of axial feed plasma torches.
Coatings were sprayed on mild steel coupons, rods and thin foils of A l , Ni, plain carbon
steel and stainless steel, which were used for conducting tests to assess the physical
properties of the coatings. The cross sections of the coatings sprayed on the coupons
were observed under an SEM and optical microscope. The hardness, porosity and SiC
distribution of the coatings were assessed on these cross sections. The coatings were
tested for different physical and mechanical properties like adhesion and wear strength.
Adhesion was tested on the mild steel rods using the standard ASTM C633 pull
tests but the results were mostly inconclusive. Adhesion strength on the foils was also
measured by peel tests which is a modification of the ASTM D-3167 tests. The coatings
showed high adhesion strength compared to the other commercially available coatings
reported in a recent work [40]. Adhesion strength was found to decrease with the
increase in the SiC content and decrease in SiC particle sizes.
Erosive wear of the coatings was assessed using a dry erosion test which is a
modification of the ASTM G76-83 test. The increase in the SiC content and decrease in
the reinforcing particle size improved the wear resistance of the coatings. The abrasive
wear resistance was found to improve with the increase in SiC particle size and also with
the SiC content in the composite powders (or coatings).