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Tesi sul tema "Ceramics"
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Dobedoe, Richard Simon. "Glass-ceramics for ceramic/ceramic and ceramic/metal joining applications". Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/4217/.
Testo completoAbstract (sommario):
The use of sintered cordierite/enstatite glass-ceramics as interlayers for joining silicon nitride to itself and to metals has been investigated. The role of the additives B203 and P205, which control the dynamics of sintering and crystallisation, has been studied using SEM, XRD and non-isothermal DTA-based measurements of activation energy. The measured activation energies for the crystallisation of μ-cordierite, for compositions with no additives, with B203 only, and with P205 only, did not differ significantly and were in the range 415-460 kJ mol-1. When both B203 and P205 were present this was increased to 503-524 kJ mol-1. The activation energy for α-cordierite formation when no additives were present was 952 ± 57 kJ mol-1. This was substantially reduced by the presence of B203 (540 ± 27 kJ mol-1), P205 (668 ± 41 kJ mol-1) and when both were present (352 ± 26 kJ mol-1). Cordierite/enstatite glass-ceramics have been successfully used to join silicon nitride to itself. Joining at 1050-1100'C in N2 with an applied load of ~ 2.5 MPa, resulted in joint strengths, measured in 4-pt bending, of 110-170 MPa. This is comparable to the intrinsic strength of the glass-ceramic and sufficient for practical applications. These strengths were obtained using an interlayer with a TCE (5.7 MK-1) greater than that of the silicon nitride (3.0 MK-1). Suggestions for further improvements to the joint strength are discussed. The use of a glass-ceramic joint with graded thermal expansion to bridge a TCE mismatch is discussed, and the geometrical restrictions on the joint, which limit possible practical applications, are outlined. The concept of a ceramic/metal compression joint with a glass-ceramic interlayer has been demonstrated for joining silicon nitride to both Nimonic alloy 80A and Ti. The requirements for continuity of electronic structure at the Nimonic 80A/glass-ceramic and the Ti/glass-ceramic interfaces are satisfied by reaction between the glass/glass-ceramic and, the pre-oxidised surface of the Nimonic alloy to form a MgTi205-Al2TiO5 solid solution phase, and the Ti to form Ti5Si3. For the lower WE mismatch (Ti-silicon nitride) the residual joining stresses generated on cooling were marginally too high and need to be further reduced, either by a slight alteration to the joint geometry and/or a smaller WE mismatch.
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Wade, James. "Contact damage of ceramics and ceramic nanocomposites". Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/24932.
Testo completoAbstract (sommario):
Herein, we study the contact damage performance of two armour ceramics, alumina and silicon carbide, with varying microstructures and one particle-reinforced ceramic nanocomposite, alumina/silicon carbide, in an attempt to understand the microstructural mechanisms that affect plasticity and cracking under quasi-static and dynamic conditions. Quasi-static contact damage was imitated using Vickers indentation over a varying load regime. Numerical analysis of the indentation size effect, performed using the proportional specimen resistance model, allowed the contributions of plastic deformation and cracking to be separated into two individual values. In all three samples, higher levels of surface energy were found to correlate with increased amounts of cracking per unit area of indentation impression. Analytical modelling of crack initiation during Vickers indentation together with quantitative measurements of surface flaw populations revealed that such an increase in cracking damage was the result of higher densities of larger flaws. The hardness of the monolithic ceramics was found vary based on grain size and porosity levels, a smaller average grain size and lower porosity levels resulting in higher hardness values. In the nanocomposite materials, hardening was found to occur with further additions of silicon carbide nanoparticles. Such an effect has been attributed to the increased dislocation densities, as measured using Cr3+/Al2O3 fluorescence spectroscopy, and the impedance of dislocation movement within the lattice due to the presence of silicon carbide nanoparticles. In order to simulate dynamic contact damage, a low velocity, scaled-down drop-weight test was designed and developed. The dynamic contact damage resistance was determined based on the depth of penetration of a blunt indenter. In the monolithic ceramics, the indenter penetration was found to be shallower in materials of higher hardness. However, the nanocomposite materials displayed an opposing trend, the indenter penetration becoming deeper in the samples of higher hardness. The macro-scale fracture patterns produced during drop-weight impacts were seen to vary based on flaw populations and indenter penetration. In certain microstructures, extensive micro-cracking was also observed.
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VENTRELLA, ANDREA. "JOINING OF CERAMIC COMPOSITES AND ADVANCED CERAMICS". Doctoral thesis, Politecnico di Torino, 2012. http://hdl.handle.net/11583/2502686.
Testo completoAbstract (sommario):
Ceramics and Ceramic Matrix Composites (CMC) are well known as useful materials for harsh environment applications. Ceramic components have been widely used as abrasives, cutting tools, nuclear fuel elements, catalyst supports and astronomical telescope mirrors. Generally speaking, ceramics and CMC are excellent candidates for high-temperature applications because of their good mechanical properties and thermal stability at elevated temperatures.
However, to produce large-size and complex components, development and testing of joints for ceramics and CMC are fundamental. Joining materials and techniques currently available to join ceramic and CMC include diffusion bonding using various active fillers, transient eutectic phase methods such as nano-infiltration and transient eutectic-phase (NITE), laser joining, selected area chemical vapor deposition , glass-ceramic joining , solid state displacement reactions, preceramic polymer routes, reaction forming, brazing. Adhesive joining materials (e.g. epoxy resins) are used to join ceramics only for applications at temperature lower than 150 °C, i.e. adhesively bonded joints are widely used for automotive, aerospace, electronic and packaging applications.
Together with the need of a reliable joining method, a widely accepted standard to test the mechanical strength of joined ceramics and composites is still unavailable and measuring the shear strength of the same joining material with different test methods could lead to different results.
The aim of this Thesis is to compare and discuss several different shear strength tests used to join ceramics and CMC, with the final goal to provide designers and scientific community a widely accepted, reliable test method.
A homogeneous pure shear stress state is not obtainable with most of the currently used single or double lap tests, which give apparent and not pure shear strength of the joined samples; in addition, the presence of several different apparent shear strength tests in the literature makes comparison quite impossible.
The asymmetrical four point bending test (ASTM C1469-10) is recommended as a standard test by the ASTM to test joined ceramics and composites, but notches have to be cut in the joined area when the joining material strength is high. When the shear strength of the joining material approaches that of the substrate to be joined, ASTM C1469-10 is not suitable.
With torsion tests a pure shear loading strength can be measured without using notches.
One of the very first proposals for torsion test for epoxy bonded aluminum alloy samples was reported by M. Ouddane et al.: as thoroughly discussed there, torsion results were considered more reliable than those obtained by standard lap tests, the improvement mainly due to the fact that lap tests induce non uniform stress concentrations that affect the reliability of results.
Recent papers deal with torsion tests on joined hourglass shaped samples : preliminary results suggest that the torsion test method with a miniature specimen has a potential to evaluate the shear properties of the joint interface, provided that the fracture occurs in the joined area.
Torsion tests have been thoroughly analyzed in this Thesis: a pure non-uniform shear stress distribution is obtained with torsion tests; together with asymmetrical four point bending test (ASTM C1469-10), torsion test is the only one able to measure pure shear strength of joined ceramics and composites.
The torsion test method is proposed in some ASTM standards but none of them is directly applicable to joined ceramics: the main result of this Thesis is to demonstrate the reliability of torsion as a method to measure the shear strength of joined ceramics and CMC.
Two torsion standards have been adapted to joined C/C and ceramics, first by preparing square section samples (TS), rods (TC), tubes (TT), then by mechanically shaping the joined samples as a hourglass in different shapes.
The choice of an epoxy resin (Araldite AV119) to join SiC in this PhD thesis was done in order to have a “model” brittle joining material to obtain a statistically relevant number of joined samples in a reasonable time, to compare shear strength results .
More than one hundred joined samples have been prepared and tested at room temperature by asymmetrical four point bending (A4PB) (ASTM C1469-10), torsion on square section samples (TS), torsion on circular section rods (TC), torsion on hourglass shaped samples (THG, TDHG, TRHG), torsion of tubes (TT), single lap in compression (SL), single lap off set in compression (SLO), double lap off set in compression (DLO), Brazilian test (BT), double notch (DN) methods. A modified ASTM B898 standard has been used as a further example of single lap test in compression to complete the comparison work (B898).
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Mussi, Toschi Vitoria. "Lead-free ferroelectric ceramics for multilayer ceramic capacitors". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC089.
Testo completoAbstract (sommario):
De nos jours, la consommation des condensateurs céramiques multicouches (MLCCs) augmente en raison de leur efficacité et leur fiabilité. La miniaturisation résultant dans une plus grande dissipation volumique de chaleur et les nouvelles applications demandent des MLCCs qui peuvent travailler de 300 à 350°C, au-delà des limites actuelles de 200 – 250°C. De plus, les exigences environnementales augmentent également avec les réglementations REACH et RoHS qui interdisent l'utilisation du plomb en Europe. Il est donc impératif de créer des nouveaux matériaux sans plomb capables de répondre aux nouvelles attentes des MLCC.Cependant, la compatibilité avec les méthodes de production industrielle, ainsi que les prix du marché sont des limites importantes. Trois familles de matériaux sans plomb ont été examinées : celle du BaTiO3 (BT), du K0.5Na0.5NbO3 et du Na0.5Bi0.5TiO3 (NBT). Le NBT-BT à la MPB (6 % BT) a été choisi comme matériau diélectrique de base. Plusieurs méthodes et paramètres de synthèse ont ensuite été étudiés pour déterminer les meilleures conditions de synthèse. La synthèse à l'état solide et le frittage traditionnel ont été choisis pour les échantillons en massif et le coulage en bande a été choisi pour les couches. Pour éviter l'évaporation des espèces volatiles, le frittage a été effectué en couvrant le NBT-BT par une poudre de ZrO2. Tous les échantillons présentaient des phases secondaires contenant du Ba (Ba2TiO4 et Ba2Ti9O20) en raison de l'évaporation du Na pendant le frittage. Un effet de peau créé par la coexistence des phases tétragonale, rhomboédrique et cubique a également été observé, lié à la concentration locale de Ba dans le réseau cristallin du NBT. Les effets des paramètres de synthèse et la stœchiométrie des réactifs sur les propriétés diélectriques, la résistance d'isolement et la séparation des phases ont été analysés. La stœchiométrie nominale Na0.44Bi0.48Ba0.06TiO3 était la plus appropriée pour les MLCC en raison de sa résistance d'isolement élevée, de ses faibles pertes diélectriques et de sa stabilité de la permittivité en température. La présence de phases secondaires est initialement bénéfique en raison de l'élimination des lacunes d'oxygène. Au-delà d'une fraction volumique critique (2.5 à 3.0 %) et d'une taille de grain moyenne critique (0.9 à 3.0 m2), la tendance s'inverse en raison de la nature conductrice des phases secondaires.Pour atteindre la fraction volumique et la taille de grain critiques, un agent dispersant a été utilisé lors du broyage dans la jarre de YSZ, avec du MEK et de l'éthanol comme solvants, et sans sécher les réactifs avant la pesée. Enfin, la relaxation des contraintes a été réalisée à 400°C pendant 3 heures. Trois modèles ont été utilisés pour expliquer la dispersion des propriétés diélectriques en fréquence : le modèle de Maxwell-Wagner, le modèle de Nyquist et la loi de Curie-Weiss modifiée. Les incompatibilités entre les propriétés diélectriques du NBT-BT rapportées dans la littérature ont ensuite été analysées soulignant l'importance d'avoir des méthodes de synthèse et de mesure strictes. Les trois principaux facteurs affectant les propriétés diélectriques induisant ces incompatibilités étaient la stœchiométrie, la méthode de métallisation et la fixation des fils électriques à l'aide de la laque d'argent. Des pertes diélectriques croissantes à haute température a aussi été observée après chaque cycle thermique dépassant les 300°C, indiquant une dégradation thermique des échantillons.Enfin, les monocouches céramiques ont montré une faible densité (62%) après frittage, limitant la plage de température correspondant aux spécifications d'Exxelia. Cependant, en utilisant un pressage des couches avant frittage, l'échantillon multicouche fritté présentait une densité élevée (89%). Une mesure des propriétés diélectriques doit être effectuée sur cet échantillon multicouche synthétisé, afin de déterminer sa compatibilité avec les spécifications d’ExxeliaMLCC consumption is today increasing due to their high efficiency, reliability and frequency characteristics. MLCCs that can work from 300 to 350°C are required both for miniaturization, resulting in greater volume heat dissipation and for new applications. Moreover, environmental requirements are also increasing, the REACH and RoHS regulations prohibiting the use of lead in Europe. It is imperative to create new lead-free materials that are able to meet those requirements.However, the compatibility with the production methods, price, and market are important industrial limitations that need to be considered.Three families of lead-free materials were examined: BaTiO3-based, K0.5Na0.5NbO3-based and Na0.5Bi0.5TiO3-based materials. NBT-BT at the morphotropic phase boundary (6% BT) was chosen as the base dielectric material.Several synthesis methods and parameters were studied to determine the best synthesis conditions. Solid-state synthesis and traditional sintering were chosen for the bulk samples and tape casting was chosen for the layer samples preparation. Sintering was done under ZrO2 powder to prevent the evaporation of volatile species.All samples had secondary Ba-containing phases (Ba2TiO4 and Ba2Ti9O20) formed because of the evaporation of Na during sintering. A skin-effect was observed due to a phase coexistence (tetragonal, rhombohedral, and cubic) due to the local concentration of Ba in the NBT lattice.The effects of the synthesis parameters and the stoichiometry of the reactants on dielectric properties, insulation resistance, and phase separation were analysed.The Na0.44Bi0.48Ba0.06TiO3 nominal stoichiometry was the most suitable for the MLCCs due to its high insulation resistance, low dielectric losses, and stability of permittivity in temperature.The phase separation was initially beneficial, due to the resulting elimination of oxygen vacancies. Above a critical volume fraction (2.5 to 3.0%) and a critical mean surface area (0.9 to 3.0 m2), the trend was reversed due to the conductive nature of the secondary phases.To achieve the critical volume fraction and surface area of the secondary phases, a dispersing agent was used during ball-milling in YSZ jar, with MEK and ethanol as solvents, and without drying the reactants prior to weighing. Finally, a strain relaxation was done at 400°C for 3 hours.Three models explained the frequency dispersion of the dielectric properties: the Maxwell-Wagner model, the Nyquist plot and the modified Curie-Weiss law.Incompatibilities between the dielectric properties of NBT-BT reported in the literature were then analysed, showing the importance of maintaining strict synthesis and measurement methods. The three main factors affected the dielectric properties, creating these incompatibilities in the bulk samples. There were the stoichiometry, the metallization method, and the fixing of the electrical leads using silver paste.An increase of the high-temperature dielectric losses after each thermal cycle reaching more than 300°C was observed, indicating a thermal degradation of the material.Finally, the sintered ceramic monolayers showed a low density (62%), limiting the temperature range corresponding to Exxelia’s specifications. However, after pressing the layers together before sintering, the sintered multilayer sample showed a high density (89%). Dielectric property measurement should be carried out for these synthesized multilayers
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Hill, Arnold Hill. "PRODUCTION OF BULK CERAMIC SHAPES FROM POLYMER DERIVED CERAMICS". Master's thesis, University of Central Florida, 2008. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4248.
Testo completoAbstract (sommario):
A method has been developed to produce bulk ceramic components from a class of ceramics known as polymer derived ceramics. In the past polymer derived ceramics have been limited to thin film applications or in the fabrication of MEMS devices. The reason being that when the polymer is into a ceramic, large quantities of gas are generated which produce internal pressure that fractures the ceramic components. The method developed here solves that issue by casting into the polymer a 3 dimensional network of polymer fibers in the form of a foam which, during pyrolysis, burns out and leaves a network of open channels that allows decomposition gases to escape thus preventing pressure from building up. The inclusion of the polymer foam allows for the formation of strong plastic like green bodies which can be machined into any shape. The green bodies are then pyrolized into ceramic components. This process allows for the simple and inexpensive fabrication of complex ceramic components that have the potential to replace current components that are made with traditional methods.M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE
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Feilden, Ezra. "Additive manufacturing of ceramics and ceramic composites via robocasting". Thesis, Imperial College London, 2017. http://hdl.handle.net/10044/1/55940.
Testo completoAbstract (sommario):
In the last two decades additive manufacturing (AM) has emerged as a highly important and influential technology. A large range of approaches to AM have been developed which give rise to hundreds of distinct techniques. Many of these are specific to one material system, and only a handful have been successful at producing ceramic parts. Robocasting is one such technique, having been used to produce complex ceramic parts with reasonable mechanical properties. In this thesis robocasting is investigated further, firstly by characterising the rheology of the robocasting paste, and then by measuring the strength and reliability of ceramic parts produced by robocasting. The critical defects associated with the process are identified, and efforts have been made to eliminate them. Furthermore, it was possible to produce a new class of ceramic composites consisting of alumina platelets aligned by the shear forces that arise during printing. These platelets themselves and the composites were extensively characterised. A new in-situ double cantilever test was developed in order to study the fracture behaviour of the composites. Lastly, the principle of using the printing process to align platelets was applied to fibres in order to create printed fibre reinforced ceramic matrix composites, and printed carbon fibre reinforced epoxy.
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Santana, Jerusa Góes Aragão [UNESP]. "Desenvolvimento de cerâmicas multicamadas de carbeto de silício destinadas a aplicações térmicas". Universidade Estadual Paulista (UNESP), 2010. http://hdl.handle.net/11449/103760.
Testo completoAbstract (sommario):
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Cerâmicas multicamadas de carbeto de silício foram obtidas por conformação por consolidação ou prensagem e utilizando diferentes técnicas de adesão das camadas. Produzidas com duas ou três camadas e apresentando gradientes de porosidades, a sistemática para obtenção destas cerâmicas teve início com o estudo individual das amostras. Para atender a níveis de porosidades previamente estabelecidos (15, 30 e 50%), foram conformadas amostras com diferentes composições e percentuais de sólidos. Na prensagem uniaxial utilizou-se um aditivo de sinterização (YAG) para controle do nível de porosidade das amostras. Por meio da realização de ensaios físicos, mecânicos, microscópicos e termomecânicos, foi possível conhecer as particularidades e características inerentes ao método de conformação empregado. As cerâmicas conformadas por prensagem apresentaram melhores acabamentos superficiais, poros pequenos, menores incidências de defeitos, porosidade e resistência mecânica influenciada pelo teor de aditivo empregado. Nas cerâmicas conformadas por consolidação, a existência de uma elevada porosidade associada a defeitos como trincas e fissuras, deterioraram a resistência mecânica das amostras. Baseando-se nos resultados obtidos, partiu-se então, para confecção das cerâmicas multicamadas. Na conformação por consolidação foram produzidas cerâmicas com duas ou três camadas, utilizando-se dois métodos: sobreposição direta e sobreposição por meio de sulcos. Na sobreposição direta a constituição das camadas ocorreu por entorno da dispersão sobre uma camada anteriormente processada. Entretanto, as tensões originadas durante as etapas de secagem conduziram a formação de abaulamento no ponto de adesão das camadas, comprometendo a sua resistência. A utilização de um defloculante polietilenimina...
Multilayer ceramics of silicon carbide were obtained by consolidation or pressing by using different techniques for layers adhesion. Produced with two or three layers and showing porosity gradients, the method for obtaining these ceramics began with the individual study of the samples. In order to achieve the porosity levels previously established (15, 30 and 50%), the samples were conformed with different compositions and percentages of solids. A sintering additive (YAG) was used in the uniaxial pressing in order to control the porosity of the samples. Through physical, mechanical, microscopic and thermomechanical tests, it was possible to know the peculiarities and characteristics related to the conforming method that was used. The obtained ceramics by pressing showed better superficial finish, small pores, lower incidence of defects, porosity and mechanical strength, influenced by the percentage of additive employed in the samples. The ceramic samples by consolidation had their mechanical strength damaged due to the high porosity associated with defects such as cracks and fissures. Multilayer ceramics were produced from the obtained results. Ceramic samples were produced by consolidation with two or three layers, by using two methods: direct overlap and overlap through grooves. In the direct overlap, the layer forming was performed by pouring the dispersion over another layer previously processed. However, the arisen tensions during the drying steps, made the interface between the layers become convex, compromising their strength. The use of the dispersant polyethylenimine (Lupasol SK), with high molecular weight, formed a thick film on the sample surface, allowing the production of grooves between the layers. The reduction of tensions on sample layers enabled the ceramic forming without defects on the interface. Samples produced... (Complete abstract click electronic access below)
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Adicks, Michael Kent. "Strength characterization of thin-wall hollow ceramic spheres from slurries". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/9318.
Testo completo
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Katti, Kalpana Shastri. "Microstructure and local dielectric function in barium titanate based electroceramics /". Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10590.
Testo completo
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Sujirot, Kuljira. "Silicate glass-ceramics containing fluoride for application in ceramic-matrix-composites". Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/7435.
Testo completo
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Gopnik, Hilary. "The ceramics of Godin II, ceramic variability in the archaeological record". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0019/NQ53817.pdf.
Testo completo
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Matthews, Stephen John. "Cavitation erosion of aluminium alloys, aluminium alloy/ceramic composites and ceramics". Thesis, Coventry University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317927.
Testo completo
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Sütçü, Mücahit Akkurt Sedat. "Development of Dense Ceramic Tiles From Mixtures of Alumina Powders With Different Psd/". [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/malzemebilimivemuh/T000462.pdf.
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Zhang, Yu 1965. "Erosion behaviour of engineering ceramics". Monash University, School of Physics and Materials Engineering, 2002. http://arrow.monash.edu.au/hdl/1959.1/8404.
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Lee, Shin Steven. "Damage analysis and mechanical response of as-received and heat-treated Nicalon/CAS-II glass-ceramic matrix composites". Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-10032007-171633/.
Testo completo
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Martinez, Tais Cruz [UNESP]. "Avaliação da resistência á flexão de cerâmicas dentais Y-TZP: efeito de material e espessura". Universidade Estadual Paulista (UNESP), 2011. http://hdl.handle.net/11449/89675.
Testo completoAbstract (sommario):
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martinez_tc_me_arafo.pdf: 873272 bytes, checksum: 438b65835375d34883a0dfb0195b8ae2 (MD5)O objetivo deste trabalho foi avaliar a resistência à flexão de cerâmicas de zircônia estabilizada por ítrio em função de marca comercial e espessura. A resistência à flexão (MPa) foi testada pelo método uniaxial de 3 pontos, conforme Norma ISO 6872/2005 em Máquina de Ensaios Universal EMIC DL 2000, usando célula de carga de 5kN, velocidade de 0,5 mm/min. e suporte com 20 mm de distância entre os apoios. Foram testados 2 sistemas cerâmicos de zircônia parcialmente estabilizada por ítrio (Y-TZP) ZirCAD© - Ivoclar Vivadente e LavaTM Framework - 3MESPE e 2 espessuras (norma ISO: 2,00 mm e uso clinico: 0,7 mm): ZC_2; ZC_0,7; LV_2 e LV_0,7. ANOVA one way e post Hoc de Bonferroni foram utilizados com significância para p<0,05. Não houve diferença estatisticamente significativa entre as médias de resistência a flexão entre ZC_2 (Média = 673,62 e dp = 129,95), ZC_0,7 (Média = 533,63 e dp = 129,84), LV_2 (Média = 593,56 e dp = 122,78) e LV_0,7 (Média = 673,02 e dp = 81,36). Conclusão: Os sistemas cerâmicos Y=TZP ZirCAD e Lava apresentam resistência a flexão (MPa) semelhantes independente da espessura. Espessuras de 0,7 mm podem ser utilizadas nos testes de resistência a flexão para melhor simular as situações de uso clinico dos sistemas cerâmicos Y-TZP
The objective of this study was to evaluate the flexural strength of ceramics by Yttrium stabilized zirconia as a function of thickness and trademark. Flexural strength (MPa) was tested by the method of three uniaxial points, in accordance with ISO 6872/2005. The Universal Testing Machine EMIC DL 2000, using a 5 kN load cell, crosshead speed of 0.5 mm / min. and holder with 20 mm distance between supports was used. We tested 2 systems ceramic zirconia partially stabilized by yttrium (Y-TZP) ZirCAD © - Ivoclar Vivadente and LavaTM Framework - 3MESPE and 2 thicknesses (ISO: 2.00 mm and clinical use: 0.7 mm): ZC_2; ZC_0 7; LV_2 and LV_0, 7. One-way ANOVA and post hoc Bonferroni was used with significance for p <0.05. There was no statistically significant difference between the mean flexural strength between ZC_2 (Mean = 673.62 and SD = 129.95), ZC_0, 7 (mean = 533.63 and SD = 129.84), LV_2 (Average = 593 , 56 and SD = 122.78) and LV_0, 7 (mean = 673.02 and SD = 81.36). Conclusion: Y-TZP ceramic systems ZirCAD and Lava have flexural strength (MPa) similar independent of the thickness. Thickness of 0.7 mm can be used in tests of flexural strength for better simulate the clinical conditions of use of Y-TZP ceramic systems
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Paula, Amauri Jardim de [UNESP]. "Síntese de templates para aplicação em piezocerâmicas livre de chumbo". Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/92080.
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paula_aj_me_araiq.pdf: 4248467 bytes, checksum: 8dc95ae46ec5d889f9869c43632e6cd9 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
As piezocerâmicas de chumbo a base de Pb(Zr1-xTix)O3 (PZT) sempre tiveram destaque devido às suas excelentes propriedades piezoelétricas. Suas aplicações como sensores, atuadores e capacitores tornaram essas cerâmicas um alvo de incessantes estudos. Entretanto, cresce a necessidade de substituí-las devido ao impacto ambiental causado pelo chumbo. Com este objetivo, pesquisas em busca de materiais alternativos vêm ganhando destaque na comunidade científica internacional. Nesse contexto, os únicos materiais que apresentaram características equiparáveis ao PZT foram os niobatos alcalinos texturizados. Entretanto, para a obtenção dessas cerâmicas texturizadas foi necessária a produção de templates de niobato de sódio (NaNbO3) por complexos processos de síntese, uma vez que estes não estão disponíveis comercialmente. Nessa linha de estudo, o presente projeto de pesquisa buscou a síntese de moldes (templates) de niobato de sódio e de potássio para texturização de cerâmicas livres de chumbo a base de niobatos alcalinos (NaKLiNbO3) por método “Templated Grain Growth” (TGG) e “Reactive Templated Grain Growth” (RTGG). Os templates foram produzidos por síntese hidrotérmica assistida por microondas (H-M), a 200ºC, e com variações de tempo, tipo de precursor de nióbio e concentração de reagentes. Os templates de NaNbO3 e KNbO3 foram produzidos através da reação entre um precursor de nióbio (Nb2O5 ou NH4.NbO.(C2O4)2.(H2O)2.(H2O)n) e o hidróxido do respectivo metal alcalino (NaOH ou KOH). O NaNbO3 foi produzido com ambos os precursores de nióbio, embora o oxalato amoniacal favoreça a cristalização de partículas cúbicas de maior tamanho (>4μm). Durante a síntese do NaNbO3, as análises de difratometria de raios X (DRX) e de microscopia eletrônica de varredura (MEV) mostraram que as microfibras de Na2Nb2O6.nH2O formadas são uma fase intermediária...
PZT-based materials [Pb(Zr1-xTix)O3] are the most used piezoceramics around the world due to their excellent piezoelectric properties. Their applications as sensors, actuators and capacitors made these ceramics the center of unceasing studies. However, the necessity of substituting these materials has been increased mainly because of the environment impact caused by the lead element. With this objective, new researches aiming the discovery of alternative materials have been growth in the scientific community. In this context, the only materials which presented properties at the level of PZT were the texturized alkalines niobates. Nevertheless, to produce such texturized ceramics, the use of complexes methods of synthesis was necessary to create templates of sodium niobate (NaNbO3), once they are not commercially available. Therefore, this project attempted to produce templates of sodium and potassium niobates intending the texturization of alkaline niobate-based ceramics (NaKLiNbO3) by Templated Grain Growth (TGG) and Reactive Templated Grain Growth (RTGG) methods. The templates were produced by means of a microwave assisted hydrothermal synthesis (M-H), at 200ºC, by varying the time, type of niobium precursor and reactants concentrations. The templates of NaNbO3 e KNbO3 were produced through the reaction between a niobium precursor (Nb2O5 or NH4.NbO.(C2O4)2.(H2O)2.(H2O)n) and the hydroxide of the respective alkaline metal (NaOH or KOH). The NaNbO3 was synthesized by both niobium precursors, though the niobium ammoniacal oxalate promoted the formation of cubic particles of NaNbO3 with greater sizes (>4μm). During the synthesis of the NaNbO3, the analysis of X-ray diffratometry (XRD) and scanning electronic microscopy (SEM) indicated that the microfibers of Na2Nb2O6.nH2O are formed as an intermediary phase towards the NaNbO3 crystallization... (Complete abstract click electronic access below)
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Santana, Jerusa Góes Aragão [UNESP]. "Estudo e desenvolvimento de cerâmicas porosas de dióxido de titânio aditivadas com proteínas de soja". Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/97080.
Testo completoAbstract (sommario):
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santana_jga_me_guara.pdf: 1891764 bytes, checksum: ab046e5fa746569839a1676ec343c884 (MD5)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
Universidade Estadual Paulista (UNESP)
Este trabalho foi realizado com o objetivo de verificar a possível conformação de cerâmicas de dióxido de titânio (TiO2) utilizando proteína vegetal (soja) como agente ligante e elemento formador de poros. Para tanto, foram confeccionados corpos cerâmicos com diferentes composições de sólidos e variações nos percentuais de proteínas (extrato e proteína texturizada de soja). Como auxiliar de defloculação, com o intuito de reduzir as viscosidades das dispersões estudadas, utilizou-se a sacarose. A escolha destes materiais, além da já conhecida propriedade bactericida do dióxido de titânio, deveu-se a características tais como: baixo custo, não toxicidade, facilidade de obtenção e, principalmente, propriedades inertes, que conferiram ao produto final condição de uso, sem prováveis danos a saúde. Para melhor entendimento do comportamento das proteínas de soja, foram estudadas algumas propriedades reológicas destes materiais, puros ou em presença da sacarose. A caracterização das peças cerâmicas constou de medidas de rugosidade superficial e densidade aparente, além da verificação por meio de microscopia óptica. Os resultados obtidos permitiram conhecer as peculiaridades e comportamento das proteínas de soja, mostrando suas capacidades de conformação, além das características distintas que concedem aos materiais utilizados diferentes possibilidades de usos; enquanto as proteínas texturizadas são mais apropriadas para filtros domésticos ou membranas, o extrato de soja apresenta características mais adequadas para o desenvolvimento de cerâmicas utilizadas como isolantes térmicos.
The main purpose of this work was to verify the possible formation of titanium dioxide (TiO2) ceramics by using vegetable protein (soya bean) as a binder and pore forming element. Accordingly, ceramic specimens were made from different compositions of solids as well as variations in the percentage of proteins (soya essence and texturized soya). Saccharose was used as a dispersion agent in order to reduce the viscosities. Titanium dioxide and soya protein were particularly chosen. The former was for its bactericide property; the latter was due to its low cost, no toxicity, besides being easily acquired. However, the utmost feature is its inert property responsible for the perfect condition of use, probably without any health risks. In order to understand the function of soya proteins, some of their reological behavior were studied, either pure or when in presence of saccharose. The specimens studied were characterized by superficial roughness measurements, apparent density and the verification using optical microscopy. The results obtained showed the peculiarities, as well as the behavior of soya proteins, indicating their formation capacity. Besides this, it was also verified distinct properties that allow the use of soya proteins in different ways. Whereas the texturized soya is more appropriate for residencial filters or membranes, the soya essence presents better performance to the development of ceramics used as thermal insulating.
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Herath, Herath Mudiyanselage Thushari Uthpala. "Novel ceramics and ceramic structures : an 'in-vitro' study of osteoblast response". Thesis, Queen Mary, University of London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429185.
Testo completo
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Bleay, S. M. "Microstructure and micromechanics in glass and glass-ceramics reinforced with ceramic fibres". Thesis, University of Bath, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293064.
Testo completo
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Stevenson, Greg. "Ceramic design for modern living : an archaeology of British ceramics 1927-37". Thesis, University of Wales Trinity Saint David, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683311.
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Fu, Yu. "Residual Strength of Metal Particulate Reinforced Ceramic Matrix Composites with Multiple Cracks". Fogler Library, University of Maine, 2008. http://www.library.umaine.edu/theses/pdf/FuY2008.pdf.
Testo completo
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Gonzalez, Sandra C. "Preparation and characterization of new porous ceramic filters for hot gas clean-up". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-12052009-020046/.
Testo completo
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Owate, I. O. "The electrical properties of some alumina ceramics and glass ceramics". Thesis, University of Manchester, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282951.
Testo completo
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Chung, Jae Hoon. "Compressive mechanical behavior of hollow ceramic spheres and bonded-sphere forms". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/9984.
Testo completo
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Laurie, Joyce. "Freeze casting : a modified sol-gel process". Thesis, University of Bath, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.260248.
Testo completo
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Senapati, Rajeev. "Discrete element modelling of silicon nitride ceramics crack formation and propagation in indentation test and four point bending test /". To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Testo completo
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Valente, Rossana. "Utilitarian ceramics in the Byzantine Peloponnese (8th - 13th century) : the economics of the ceramics and ceramic production in the context of economic cycles". Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33048.
Testo completoAbstract (sommario):
Utilitarian unglazed ceramics constitute an important range of evidence for investigating cultural and economic identities. The present research project analyses commonly used, unglazed Byzantine vessels from stratified contexts, excavated in Ancient Corinth (ASCSA), in close comparison with vessels from Sparta and Argos (Peloponnese - Greece). The first goal of this thesis is to provide an updated overview of the specific types of unglazed, utilitarian vessels used in these sites. Through a quantitative analysis, applied to ceramics, this study presents a seriation of specific types of unglazed utilitarian vessels from the Byzantine Period (8th - 13th centuries), which suggests a revised chronology of use for these vessels. Furthermore, this study also provides an analysis of how vessels changed shape and fabric over time and how Byzantine history and related domestic environments influenced the quantity and quality of utilitarian objects. Quantitative studies of unglazed pottery, based upon type and fabric, can produce relevant information for delineating technological, economic and social patterns on a local and a regional scale. Quantifying the presence and the percentage of unglazed pottery types in relation to their contexts makes it possible to identify technological, economic and cultural networks in which those pots were produced, used, reused and discarded. The production of coarse and cooking wares in the 8th century inherited a Late Roman artisanal tradition. Additionally, these wares are also characterized by a changed scale of production and by transformed manufacturing practices, which are further developed in the Byzantine period and cease only some decades after the Frankish conquest of the Peloponnese. Diverse utilitarian vessels were part of a typological koine in the Byzantine period; the same types have been found in stratified deposits excavated in different sites across the Peloponnese and beyond. The appearance of these vessels may be used, primarily, to suggest date ranges and to denote regional and interregional trade. Furthermore, such typological consistency is evidence for connectivity and for exchange, which encompasses not only the exchange of goods, but also of technical know-how. The same types of wares were possibly produced simultaneously in distant sites. For instance, there are striking similarities between the Early and Middle Byzantine coarse and cooking wares produced in Corinth and those produced in Salento (Southern Apulia, Italy). Due to these similarities, utilitarian unglazed wares may be studied as a proxy for patterns of social, cultural and economic networks of exchange in the Byzantine period between these two regions. Finally, this study would like to investigate how the presence or absence, the frequency and the relative proportions of pottery types are determined by socio-economic factors. An analysis of the manufactory tradition, including variations in technology of production and of vessel morphologies, within the appropriate historical context, can be indicative of social and economic patterns. Pottery can demonstrate the components of effective demand and can, therefore, be an important tool for measuring patterns of production and consumption in relation to economic trends. This project tests diverse research methodologies in order to analyse how ceramics, set within a wide and multifocal range of historical and archaeological sources, can be informative of economic patterns and changes.
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Pengpat, Kamonpan. "Ferroelectric glass-ceramics". Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/66934/.
Testo completoAbstract (sommario):
Ferroelectric glass-ceramics have been investigated from the Bi203-Ge02, BiOl.s-Ge02-B0I.5, Bi0I.5-Ge02-Te02, 5PbO-3Ge02, PbO-Ge02-NbzOs, and PbsGe30u-PbNbz06-Si02+15%Ah03 systems. DTA, XRD and SEM analysis were used to obtain crystallographic and microstructural information. The dielectric properties and ferroelectric hysteresis loop behaviour of selected samples were determined. The stoichiometric Bjz03:Ge02 (BjzGeOs) composition devitrified on cooling, giving rise to the investigation of new systems BiO\.S-Ge02-B0I.5 and Bi0I.5-Ge02-Te0 2. It was found that the glass-forming region in Bi0I.5-Ge02-Te02 is narrow and good parent glasses for precipitating BjzGeOs crystals were not obtained. However, pure BizGeOs based glass-ceramic can be successfully formed from BiOl.s-Ge02-BOI.5. SEM backscatter imaging of these glass-ceramics showed surface crystallisation and XRD analysis confirmed that the preferred orientation is perpendicular to (311) planes. The dielectric behaviour and ferroelectric hysteresis loop study of the Bi2GeOs based glass-ceramic heat treated at 475°C for 12 hours, showed that this material can be ferroelectric at room temperature with Ps = 14 flC/cm2 and has Curie temperature at about 407°C. Glasses of compositions PG(PbSGe30I J)-xPN(PbNhz06) (x = 0.5, I, 2 3) were investigated from the PbO-Ge02-NbzOs system. Most of the samples devitrified on cooling and have poor mechanical strength except the sample PG-O.S PN sample which also contains interesting phases: ferroelectric PbSGe3011 and dielectric pyroniobate PhzNhz07. The surface crystallisation of PbSGe3011 with a-axis orientation and the bulk crystallisation of PhzNbz07 phase in this sample could be observed using SEM and XRD analysis. By applying heat treatment at 667°C for 48 hours to this sample, surface crystallisation along the a-axis can be enhanced. The Curie temperature of this heat treated sample is about 166 °C with Ps = 1 flC/cm2 from dielectric measurement and ferroelectric hysteresis loop behaviour. More samples were also investigated but it was difficult to form glass-ceramics containing both PbSGe3011 and PbNbz06 crystals from this PbO-Ge02-NbzOs system. In order to obtain the multiple ferroelectric PbSGe3011 and PbNbz06 based-glass ceramics, six glasses along the tie line from 62.5 mol%PbO: 25 mol%Ge02: 12.5 mol%Si02 to 40 mol%PbNbz06: 60 mol%Si02 were investigated from the PbSGe3011: PbNhz06: Si02+ 15%Ah03 system. Most of the glasses exhibited glass-in glass phase separation. From DT A analysis and subsequent crystallisation information, the most likely possible parameters, which control the glass-in glass phase separation, may be the NbzOslSi02 ratio for the glasses near the PbSGe3011 rich composition and Ah03 for the glasses near the PhzNhz06 rich composition. This system offered many interesting materials such as cubic pyrocWore PhzNbz07 based glass-ceramics and the orthorhombic PbNbz06 based glass-ceramics, and they are also mechanically robust.
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Dy, Yan-ting Dianne, e 戴欣婷. "Land for ceramics". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31985154.
Testo completo
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Cain, Markys G. "Zirconia toughened ceramics". Thesis, University of Warwick, 1990. http://wrap.warwick.ac.uk/35750/.
Testo completoAbstract (sommario):
The objectives for the thesis were to generate tough ceramics utiising the toughening mechanisms inherent to zirconia materials. The aims have been realised with the successful fabrication of hot pressed silicon nitride / zirconia composite ceramics. The zirconia was prestabilised with two different types of dopant additives, yttria and ceria, with the intention of understanding the chemical compatibility with the silicon nitride matrix and the overall effect on the subsequent mechanical properties. The volume fraction of added zirconia was also varied. The increased toughness over silicon nitride materials alone was attributed to the toughening agents inherent to zirconia which existed either in the form of the tetragonal polymorph or the monoclinic variant. The toughening modes were dependent on initial chemistry of the composite system. When the zirconia was prestabilised with yttria the tetragonal polymorph was retained within the composite. The enhanced toughness was attributed to a transformation toughening mechanism. However, when the zirconia was prestabiised with ceria the depletion of Ce from solid solution with the zirconia during processing resulted in the formation of the unstabiised monoclinic variant. The enhanced toughness was attributed, in this case, to a microcrack type energy absorption mechanism, similar to several ZTA composite ceramics. Additionally, an experiment using ultrasound non-destructive testing, indicated that Tetragonal Zirconia Polycrystals (TZP) is ferroelastic and, as such, can provide a significant contribution to enhanced levels of fracture toughness in these materials or composites containing the same. Further work has been conducted to actually observe, as a function of applied unia.xial stress, the crystallographic changes occurring within the bulk of a 3Y-TZP ceramic via neutron elastic scattering at the ILL, Grenoble, France. This experiment has provided clear direct proof of the ferroelastic nature of zirconia. A similar experiment will be carried out at the Rutherford Laboratory, though with significantly improved statistics. An approach to improve the high temperature properties of TZP via the chemical alteration of the grain boundary phase was also considered. As a preliminary step the grain boundary volume was increased through controlled additions of the grain boundary composition in the form of both a premilled and a premelted glass. Poor fired densities were attained, however, due to the solute additive partitioning from the generation of an enhanced grain boundary phase to overstabilisation of the zirconia resulting in the formation of cubic stabilised zirconia. Furthermore, the incorporation of nitrogen within the grain boundary phase, via sintering TZP with sole additions of A1N, resulted in the attainment of poor fired densities and hence was not considered a suitable method for grain boundary modification.
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Dy, Yan-ting Dianne. "Land for ceramics". Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25947588.
Testo completo
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Cho, Man Ho. "Industries/ influence ceramics". Thesis, University of Iowa, 2017. https://ir.uiowa.edu/etd/5440.
Testo completoAbstract (sommario):
Cultivating the spatial relationship in between utility and sculpture generates my process. I deconstruct, reconstruct and assemble objects; bringing to them a new perspective that simplifies the structure while enhancing the surface and the unassuming nature of the forms.
Developing vessels for drinking or pouring serves as the foundation for my study of materials, architectural foundations and elements of utilitarian objects. The functional purpose of the objects becomes minimized due to the structure beneath the surface and the constructed role of the base blurring distinctions between function and form.
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Herlich, Jessica Marie. "Shellfishing, Ceramics, and Gender: Shell Midden Ceramics from the Kiskiak Site". W&M ScholarWorks, 2011. https://scholarworks.wm.edu/etd/1539626649.
Testo completo
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Ramsey, Melissa. "Manufacturing Ceramics: Ceramic Ecology and Technological Choice in the Upper Cumberland River Valley". UKnowledge, 2013. http://uknowledge.uky.edu/anthro_etds/10.
Testo completoAbstract (sommario):
Ceramic material culture recovered from archaeological sites has more to offer the researcher than placing the site or strata into a cultural historic timeline. By examining the characteristics of ceramics manufactured during the Woodland Period in southern Kentucky, this thesis answers questions related to the behavior of the potters who lived and worked there. Using the theoretical basis of ceramic ecology and technological choice, this thesis examines the choices made by the potters of two sites, the Long (15Ru17) and Rowena (15Ru10) sites, located along the Cumberland River in Russell County, Kentucky. The two sites are also compared to one another and similar assemblages in the Upper Cumberland River Valley, in terms of temporal occupation and utilization of tempering resources. Ultimately, the potters who occupied the Long and Rowena sites during the Woodland Period used locally available materials to temper their clay, even as they emulated other ceramic types. In terms of the two sites themselves, it appears that while they were not occupied by the same population of potters, they did employ similar tempering agents and stylistic types. Examining the behavior of potters who occupied these two sites informs the researcher about the behavior of the larger region of the Upper Cumberland Valley.
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Hays, Kelley Ann. "Anasazi ceramics as text and tool: Toward a theory of ceramic design "messaging"". Diss., The University of Arizona, 1992. http://hdl.handle.net/10150/185829.
Testo completoAbstract (sommario):
This study illustrates the importance of finding out whether painted ceramics represent the total repertoire of decorated artifacts that are expected to carry social information. Painted designs on pottery are the focus of study because (1) painted decoration has had great importance in Southwest archaeology for studying social interaction, cultural affiliation, and fine-grained chronology based on stylistic change, and (2) painted decoration is less constrained by technology and intended vessel function than other attributes, and is most free to vary for social or ideological reasons. Two assumptions underlying previous work on ceramic design "messaging" are examined. First, are ceramics the most important medium for carrying social information? Second, is ethnicity the kind of information they are most likely to carry? These questions are addressed in a case study from the American Southwest. Decorated pottery, baskets, textiles, figurines, and rock art from the seventh century Basketmaker III period occupation of rock shelters in the Prayer Rock District, northeastern Arizona are examined. Comparison of design structure and content across these different media reveals two decorative styles, one for the portable household artifacts and one for rock art. In this case, pottery does not carry the full range of potential social information signalled by applied designs. The contexts of these two decorative styles are suggested by considering aspects of artifact function, design visibility, spatial distribution of artifacts, rock art, and architecture, together with hypotheses about gender differentiation and community organization. It is concluded that for the Prayer Rock Basketmakers, pottery decoration may have carried messages that had more to do with gender than ethnicity.
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GIANCHANDANI, PARDEEP KUMAR. "Joining of Ceramics and Ceramic Matrix Composites (CMC) for Aerospace and Energy Applications". Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2711092.
Testo completoAbstract (sommario):
SiC-based ceramics and composites (SiC, C/SiC & SiC/SiC) are more and more extensively used as advanced materials for aerospace and energy applications. Existing applications are expanding continuously and require advanced materials, design and joining technologies.
The objective of this thesis was to join SiC-based ceramic matrix composites (CMC), ceramics (SiC, Mullite, Alumina) and SiC-based ceramic foams for aerospace and energy applications.
The research was aimed to develop strong, oxidation resistant and high temperature stable joints.
A novel joining technique defined “RM-Wrap” (RM=Mo, Nb, Ta, W Refractory Metals) has been developed within this thesis. The developed technique is a novel brazing technology named RM-Wrap after the metal used as a wrap to contain one or more silicon foils (e.g. Mo-Wrap when a Mo wrap is used to contain a Si foil).
It is a pressure-less joining technology performed at 1450 oC, under an inert environment (Argon flow).
Joining materials are in-situ formed composites made of refractory metals silicides (MoSi2, NbSi2, TaSi2 and WSi2) embedded in a silicon matrix.
RM-Wrap is a highly tailorable joining technique: the quantity of each phase can be modified and more than one refractory metals can be used together. RM-Wrap has been very effective in joining both coated and uncoated CMC, porous and non-porous materials: ceramics (oxide and non-oxide), CMC (SiC-based) and highly porous substrates (SiC foams) having porosity higher than 80% have been soundly joined.
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The joint morphology (interphase and interface) and elemental composition of the joining material was investigated in detail using FESEM and EDS which showed uniform, continuous and crack free joints. XRD investigation confirms the formation of metal silicides. Oxidation resistance of joints was carried out at 1100 oC for 30 minutes (for CMC joints) and 6 hours (for monolithic ceramic joints) in the air; prior and post oxidation examination of joint morphology showed no morphological change and joints remained firmly joined.
Sandwich structures have been developed by Mo-wrap joining two C/SiC as “skins” to the “core” SiC foam. Sandwich structures were tested for thermal shock resistance from RT to 1100 oC in the air for 2 minutes. Three cycles on a single sandwich structure were performed, which remained joined and the joining material composition unchanged.
Joints were mechanically tested in three different modes (i) compression, (ii) tensile and (iii) torsion. Joint strength was higher than the interlaminar shear strength of composites as the fracture was always observed in composites.
In case of monolithic ceramic (SiC) a mixed failure (cohesive and adhesive) was found, which suggest that the joint strength is comparable to ceramic one.
Micro- and nanoindentation tests were also carried out on joining materials.
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Marins, Eleasar Martins [UNESP]. "Otimização e caracterização microestrutural de cerâmicas de carbeto de silício obtidas com material nacional para uso em blindagem balística". Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/103735.
Testo completoAbstract (sommario):
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marins_em_dr_guara_prot.pdf: 7283473 bytes, checksum: 080948824f946973e97d101c513ae685 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Armas de fogo têm sido usadas em periódo dificeis da história, nos quais conflitos entre países têm ocorrido, ou no cotidiano cada vez amis violento das grandes cidades. Neste sentido, a blindagem de veículos, aeronaves e de pessoas é uma necessidade cada vez maior. Das cerâmicas utilizadas para esse fim, o carbeto de silício tem um excelente desempenho devido à alta dureza e baixa densidade. O objetivo desse trabalho é otimizar a manufatura de cerâmicas de carbeto de silício feitas de matéria prima nacional, caracterizá-las tanto quanto comparar suas características com aquelas de material importado, visando sua aplicação em blindagem balística pessoal ou de veículos leves. a fim de proporcionar independência tecnológica nessa área. Foram confeccionadas cerâmicas de carbeto de dilício de dois tipos de pós: um nacional Microservice e importado - H. C. Starck. As cerâmicas foram conformadas por prensagem uniaxial, seguida de prensagem isostática e sinterização com fase líquida, utilzando YAG como aditivo de sinterização. A caracterização das cerâmicas foir formada por: ensaios de flexão por quatro pontos, medidas de densidade, testes de dureza e ceramografia. As cerâmicas confeccionadas com o SiC H. C, Starck apresentaram maior densidade e maior resistência mecânica do que as demais. Enquanto que, as amostras nas quais o SIC da Microservice associado a 10% de YAG como aditivo foi usado, demostraram a mais alta homogeneidade e valores de resistência mecânica e dureza os mais próximos aos valores daquelas feitas com matéria-prima importada. Esses resultados mostram que é possível usar cerâmicas feitas com o SIC nacional para propósitos de blindagem balística.
Firearms have beem used either in hard periods of history, in which conflicts between countries have occurred, or in the everyday life of the large cities, wich are more and more violent. Thus, the protection of vehicles, aircraft and people is an increasing need. Among ceramics used for this purpose, silicon carbide has an excellent performane due to its high hardness and low density. The goal of this work is to optimize the manufacture of the silicon carbide ceramics made from Brazilian raw-materials, characteriza them as well as to compares their characteristics with those form imported raw-material, aiming their application in personnel or in light vehicles armor to provide technological independence in this field. Silicon carbide ceramics were made of two kinds of powders: Brazilian - Microservice and importe - H. C. Starck. The ceramics were shaped by uniaxial pressing, followed by isostatic pressing, and liquid phase sintering using YAG as an sintering additive. The characterization of the ceramics was consisted of the four-point flexural tests, measurements of density, hardness testsm and ceramography. The ceramics made of SIC H.C. Starck presentes higher density and higher mechanical resistance than the others. While the samples of ceramicsm in wich the SIC of Microservice and a 10-percent of YAG as an additive was used, presented the highest homogeneity and mechanical resistance and hardness values closets to the values from those made of importes raw-materials. These results show it is possible to use ceramics, made of Brazilian sources for ballistica armor purposes.
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Papageorge, Marc Vasilios. "Characterization of metal/ceramic interfaces on aluminum nitride". Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/9352.
Testo completo
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Shin, Hyunho. "Interface reactions and their influence on properties of SiC fiber-reinforced ceramic matrix composites". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/19122.
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Villalobos, Guillermo Roberts. "Strength enhancement of nicalon reinforced lithium aluminosilicate containing a Ta₂O₅ second phase". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/19969.
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Yang, Quanzu. "Composite sol-gel ceramics". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0019/NQ46453.pdf.
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43
Seerden, Kitty A. M. "Inkjet printing of ceramics". Thesis, University of Oxford, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393981.
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44
Zhu, Zangyuan. "Lead-free piezoelectric ceramics". Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.581971.
Testo completoAbstract (sommario):
Legislation arising from health and environmental concerns has intensified research into finding suitable alternatives to lead-based electroceramics. Lead zirconate titanate (PZT) has been developed over several decades to become the market-leading piezoelectric ceramic. Lead-free solid solutions based on sodium potassium niobate, Na0.5K0.5NbO3 (NKN), show promising dielectric and piezoelectric properties. 1-2 The related (l-x)( Na0.5K0.5NbO3)-xBiScO3 binary system (NKN-BS) has been reported to exhibit maximum d33 values of 200 pCIN at 2 mol% BS.3 Similarly, an optimal d33 value has been reported for the binary NKN-LT system at 5-6 mol% LiTa03.4 In this work, a series of compositions along the compositional join in the ternary NKN-LT-BS system, extending from 0. Na0.5K0.5NbO3 -0.02BiScO3 toward LiTa03 have been prepared and characterized. A 0.98[0.98NKN - 0.02(LiTaO3)] - 0.02[BiScO3] (NKN- 2L T -2BS) composition showed enhanced piezoelectric properties, relative to similar compositions, with d33 values of 215 pCIN. This can be attributed to a phase content of mixed orthorhombic (or monoclinic) and tetragonal phases at ambient temperatures. Variable temperature X-ray diffraction (XRD), and dielectric measurements as a function of temperature, indicated phase transitions (on heating) from an orthorhombic (or monoclinic) crystal system to tetragonal and then cubic crystal systems at ~25°C and ~370°C respectively. Different types of dielectric behaviour were observed on increasing the LT content. A NKN-5%LT-2%BS composition exhibited twin dielectric peaks at high temperatures (~370°C and ~470°C), along with broad X-ray diffraction peaks and a fine grain size, < 0.5 μm. The twin dielectric peaks suggest that chemical inhomogeneities may have been present; this was examined using transmission electron microscopy (TEM) with energy dispersive X-ray analysis (EDX). Elemental segregation was observed within individual grains, such that a core-shell grain structure was evident. The twin high temperature dielectric peaks are attributed to the separate response from the core and shell regions, each of which have a characteristic Curie temperature range. Subsequently, a series of other compositions were prepared in the wider Na0.5K0.5NbO3 - LiTaO3-BiScO3 ternary system. Considering the combined data from XRD, dielectric measurements, SEM, TEM and piezoelectric properties for a wide range of compositions within the NKN-rich region of the NKN-LT-BS system, materials may be grouped into three categories, exhibiting the following defining characteristics. Type I: single, sharp dielectric Curie peak (~ 370°C); single phase by XRD; large grain size (5-10μm); chemically uniform by TEM-EDX. Type II: broad, single dielectric peak (~ 350°C); single phase by XRD; large grain size; no obvious chemical segregation. Type Ila: twin, broad dielectric peak(s) (~ 370°C and ~ 470°C); broad XRD peaks; small grain size (~ O.5μm); chemical segregation (core-shell structure) identified by TEM-EDX. Reasons for the properties of these three classes of material are discussed; comparisons are drawn with other lead-free dielectrics and piezoelectrics; finally, the potential of the materials in future device applications are considered.
45
Cash, M. "Ceramics in reducing environments". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597354.
Testo completoAbstract (sommario):
Coal gasification poses many problems to the materials engineer due to the high temperatures and corrosive gases involved in the process. The main aim of this research is to investigate the influence of a simulated coal gasification environment on the mechanical properties and surface chemistry of a clay bonded SiC filter. This type of material is presently used to filter combustion gases and it is proposed that it may be used in gasification systems between the gasifier and gas turbine to filter particulates that would damage the turbine blades and lining. Three separate gases are used to investigate the corrosive effects of low pO2/high pS2, high pHC1 and increases in water vapour. Corrosion tests are performed at 1273K/1073K/873K at exposure times of 50, 100 and 200 hours. All physical and chemical observations are supported by theoretical modelling. The filter material is first characterised and found to be composed of SiC particles held together in an aluminosilicate clay binder. The only crystalline material identified in the clay is mullite. The 3-point fracture strength of the filter decreases substantially with increases in exposure time and temperature. It is concluded that the fluxing effects of the sodium present in the clay substantially lower its softening temperature. As a consequence, at temperatures of 1073K and above the filter is above its working temperature. Massive reductions in fracture strength of up to 40% seem to reflect this. The cause of the strength loss is believed to be due to both micro-cracking in the clay bond associated with the differential cooling rates of the clay and SiC, and mass loss from the clay bond due to volatile gas formation. The composition of the gas is found to significantly effect the chemistry of the surface reactions.
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Al-Irimi, Ilana. "Freeze gelation of ceramics". Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391130.
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Cheng, Y. "ZrO2̲-toughened glass-ceramics". Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233443.
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48
Mahon, Stephen William. "Magnetic properties of ceramics". Thesis, University of Newcastle Upon Tyne, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358891.
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Dong, Chun. "Binder removal in ceramics". Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/14101.
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Міхно, Світлана Василівна, Свитлана Васильевна Михно, Svitlana Vasylivna Mikhno e M. Bilokur. "Nanopowders for advanced ceramics". Thesis, Вид-во СумДУ, 2011. http://essuir.sumdu.edu.ua/handle/123456789/22616.
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