Dissertationen: „Ultra High Temperature Materials“

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Petla, Harita. „Computational design of ultra-high temperature ceramic composite materials“. To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.

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Walker, Luke Sky. „Processing of Ultra High Temperature Ceramics“. Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228496.

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For hypersonic flight to enable rapid global transport and allow routine space access thermal protection systems must be developed that can survive the extreme aerothermal heating and oxidation for extended periods of time. Ultra high temperature ceramics (UHTCs) are the only potential materials capable of surviving the extreme hypersonic environment however extensive research in processing science and their oxidation properties are required before engineering systems can be developed for flight vehicles. Investigating the role of oxides during processing of ultra high temperature ceramics shows they play a critical role in both synthesis of ceramic powders and during densification. During spark plasma sintering of UHTCs the oxides can result in the formation of vapor filled pores that limit densification. A low temperature heat treatment can remove the oxides responsible for forming the vapor pores and also results in a significant improvement of the densification through a particle surface physical modification. The surface modification breaks up the native continuous surface oxide increasing the surface energy of the powder and removing the oxide as a barrier to diffusion that must be overcome before densification can begin. During synthesis of UHTCs from sol-gel the B₂O₃ phase acts as the main structure of the gel limiting the transition metal oxide network. While heat treating to form diborides the transition metal oxide undergoes preferential reduction forming carbides that reduce B₂O₃ while at high temperature encourage particle growth and localized extreme coarsening. To form phase pure borides B₂O₃ is required in excessive quantities to limit residual carbides, however carbide reduction and grain growth are connected. When the UHTC systems of ZrB₂-SiC are exposed to oxidation, either as dense ceramics or coatings on Carbon-Carbon composites, at high temperatures they undergo a complex oxidation mechanism with simultaneous material transport, precipitation and evaporation of oxide species that forms a glass ceramic protective oxygen barrier on the surface. The composite effect observed between the oxides of ZrB₂-SiC enables them to survive extreme oxidizing environments where traditional SiC oxidation barrier coatings fail.

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Miller-Oana, Melia. „Oxidation Behavior of Carbon and Ultra-High Temperature Ceramics“. Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/605121.

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Hypersonic vehicles require material systems that can withstand the extreme environment they experience during flight. Carbon-based materials and ultra-high temperature ceramics are candidates for materials systems that will protect hypersonic vehicles. In order to study the material response, an oxyacetylene torch facility and thermal gravimetric analysis are used to investigate the gas-solid interactions under conditions that simulate aspects of flight. The oxyacetylene torch facility is characterized as a function of position from the tip for heat flux and oxygen content. By understanding the local heat flux and oxygen conditions, experiments are designed so that graphite ablation rates can be measured as a function of heat flux and partial pressure of oxygen. Further investigation shows that composition of the material influences the temperature response where ultra-high temperature ceramics exhibit the lowest surface temperatures. Using thermal gravimetric analysis, the isothermal oxidation behavior of ultra-high temperature ceramics from 1000-1600°C is investigated using a Dynamic Non- Equilibrium method in order to understand the reaction kinetics of ZrB₂-SiC where parabolic rate constants are determined. Isothermal oxidation behavior is compared to non-isothermal mass gain and oxide scale formation where specimens oxidized isothermally gain 3 times more mass and have oxide scales 4 times as thick. Finally, the effect of SiC content in ZrB₂ on temperature during oxyacetylene torch testing is determined. Increasing the amount of SiC results in lower front face temperatures because more heat is absorbed due to the endothermic reactions of evaporation of SiO₂.

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Pham, David, und David Pham. „Processing High Purity Zirconium Diboride Ultra-High Temperature Ceramics: Small-to-Large Scale Processing“. Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621315.

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Next generation aerospace vehicles require thermal protection system (TPS) materials that are capable of withstanding the extreme aerothermal environment during hypersonic flight (>Mach 5 [>1700 m/s]). Ultra-high temperature ceramics (UHTC) such as zirconium diboride (ZrB₂) are candidate TPS materials due to their high-temperature thermal and mechanical properties and are often the basis for advanced composites for enhanced oxidation resistance. However, ZrB₂ matrix impurities in the form of boron trioxide (B₂O₃) and zirconium dioxide (ZrO₂) limit the high-temperature capabilities. Electric based sintering techniques, such as spark plasma sintering (SPS), that use joule heating have become the preferred densification method to process advanced ceramics due to its ability to produce high density parts with reduced densification times and limit grain growth. This study focuses on a combined experimental and thermodynamic assisted processing approach to enhance powder purity through a carbo- and borocarbo-thermal reduction of oxides using carbon (C) and boron carbide (B₄C). The amount of oxides on the powder surface are measured, the amount of additive required to remove oxides is calculated, and processing conditions (temperature, pressure, environment) are controlled to promote favorable thermodynamic reactions both during thermal processing in a tube furnace and SPS. Untreated ZrB₂ contains 0.18 wt%O after SPS. Additions of 0.75 wt%C is found to reduce powder surface oxides to 0.12 wt%O. A preliminary Zr-C-O computational thermodynamic model shows limited efficiency of carbon additions to completely remove oxygen due to the solubility of oxygen in zirconium carbide (ZrC) forming a zirconium oxycarbide (ZrCₓOᵧ). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with atomic scale elemental spectroscopy shows reduced oxygen content with amorphous Zr-B oxides and discreet ZrO₂ particle impurities in the microstructure. Processing ZrB₂ with minimal additions of B₄C (0.25 wt%) produces high purity parts after SPS with only 0.06 wt%O. STEM identifies unique “trash collector” oxides composed of manufacturer powder impurities of calcium, silver, and yttrium. A preliminary Zr-B-C-O thermodynamic model is used to show the potential reaction paths using B₄C that promotes oxide removal to produce high-purity ZrB₂ with fine grains (3.3 𝜇m) and superior mechanical properties (flexural strength of 660MPa) than the current state-of-the-art ZrB₂ ceramics. Due to the desirable properties produced using SPS, there is growing interest to advance processing techniques from lab-scale (20 mm discs) to large-scale (>100 mm). The advancement of SPS technologies has been stunted due to the limited power and load delivery of lab-scale furnaces. We use a large scale direct current sintering furnace (DCS) to address the challenges of producing industrially relevant sized parts. However, current-assisted sintering techniques, like SPS and DCS, are highly dependent on tooling resistances and the electrical conductivity of the sample, which influences the part uniformity through localized heating spots that are strongly dependent on the current flow path. We develop a coupled thermal-electrical finite element analysis model to investigate the development and effects of tooling and current density manipulation on an electrical conductor (ZrB₂) and an electrical insulator, silicon nitride (Si₃N₄), at the steady-state where material properties, temperature gradients and current/voltage input are constant. The model is built based on experimentally measured temperature gradients in the tooling for 20 mm discs and validated by producing 30 mm discs with similar temperature gradients and grain size uniformity across the part. The model aids in developing tooling to manipulate localize current density in specific regions to produce uniform 100 mm discs of ZrB₂ and Si₃N₄.

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He, Junjing. „High temperature performance of materials for future power plants“. Doctoral thesis, KTH, Materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-191547.

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Increasing energy demand leads to two crucial problems for the whole society. One is the economic cost and the other is the pollution of the environment, especially CO2 emissions. Despite efforts to adopt renewable energy sources, fossil fuels will continue to dominate. The temperature and stress are planned to be raised to 700 °C and 35 MPa respectively in the advanced ultra-supercritical (AUSC) power plants to improve the operating efficiency. However, the life of the components is limited by the properties of the materials. The aim of this thesis is to investigate the high temperature properties of materials used for future power plants. This thesis contains two parts. The first part is about developing creep rupture models for austenitic stainless steels. Grain boundary sliding (GBS) models have been proposed that can predict experimental results. Creep cavities are assumed to be generated at intersection of subboundaries with subboundary corners or particles on a sliding grain boundary, the so called double ledge model. For the first time a quantitative prediction of cavity nucleation for different types of commercial austenitic stainless steels has been made. For growth of creep cavities a new model for the interaction between the shape change of cavities and creep deformation has been proposed. In this constrained growth model, the affected zone around the cavities has been calculated with the help of FEM simulation. The new growth model can reproduce experimental cavity growth behavior quantitatively for different kinds of austenitic stainless steels. Based on the cavity nucleation models and the new growth models, the brittle creep rupture of austenitic stainless steels has been determined. By combing the brittle creep rupture with the ductile creep rupture models, the creep rupture strength of austenitic stainless steels has been predicted quantitatively. The accuracy of the creep rupture prediction can be improved significantly with combination of the two models. The second part of the thesis is on the fatigue properties of austenitic stainless steels and nickel based superalloys. Firstly, creep, low cycle fatigue (LCF) and creep-fatigue tests have been conducted for a modified HR3C (25Cr20NiNbN) austenitic stainless steel. The modified HR3C shows good LCF properties, but lower creep and creep-fatigue properties which may due to the low ductility of the material. Secondly, LCF properties of a nickel based superalloy Haynes 282 have been studied. Tests have been performed for a large ingot. The LCF properties of the core and rim positions did not show evident differences. Better LCF properties were observed when compared with two other low γ’ volume fraction nickel based superalloys. Metallography study results demonstrated that the failure mode of the material was transgranular. Both the initiation and growth of the fatigue cracks were transgranular.

QC 20160905

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Lipke, David William. „Novel reaction processing techniques for the fabrication of ultra-high temperature metal/ceramic composites with tailorable microstructures“. Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/43750.

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Ultra-high temperature (i.e., greater than 2500°C) engineering applications present continued materials challenges. Refractory metal/ceramic composites have great potential to satisfy the demands of extreme environments (e.g., the environments found in solid rocket motors upon ignition), though general scalable processing techniques to fabricate complex shaped parts are lacking. The work embodied in this dissertation advances scientific knowledge in the development of processing techniques to form complex, near net-shape, near net-dimension, near fully-dense refractory metal/ceramic composites with controlled phase contents and microstructure. Three research thrusts are detailed in this document. First, the utilization of rapid prototyping techniques, such as computer numerical controlled machining and three dimensional printing, for the fabrication of porous tungsten carbide preforms and their application with the Displacive Compensation of Porosity process is demonstrated. Second, carbon substrates and preforms have been reactively converted to porous tungsten/tungsten carbide replicas via a novel gas-solid displacement reaction. Lastly, non-oxide ceramic solid solutions have been internally reduced to create intragranular metal/ceramic micro/nanocomposites. All three techniques combined have the potential to produce nanostructured refractory metal/ceramic composite materials with tailorable microstructure for ultra-high temperature applications.

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WU, QUANYAN. „MICROSTRUCTURAL EVOLUTION IN ADVANCED BOILER MATERIALS FOR ULTRA-SUPERCRITICAL COAL POWER PLANTS“. University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1154363707.

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Audouard, Lisa. „Conception et caractérisation de matériaux ultra haute température à gradient de propriétés“. Electronic Thesis or Diss., Bourgogne Franche-Comté, 2023. http://www.theses.fr/2023UBFCA019.

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Le développement d’un nouveau prototype d’ergol vert destiné aux moteurs de repositionnement de satellites implique des conditions thermiques et environnementales plus sévères pour les matériaux de la chambre de combustion, par rapport aux conditions actuelles. De ce fait, des matériaux alternatifs dits Matériaux à Gradient de Propriétés (MGP) sont développés depuis plusieurs années dans le cadre d’une étude ONERA-CNES-ICB. Cette thèse a pour objectif de poursuivre le développement de ce type de matériau à gradient céramique/métal afin d’optimiser sa conception et d’assurer ainsi sa mise en œuvre jusqu’à 2400 °C en présence de vapeur d’eau. Premièrement, différentes configurations de MGP élaborés par projection thermique plasma sous air (APS) ont été testées sous flux thermique laser sous vide jusqu’à 2350 °C. La mise en place d’une modélisation de la fissuration de ces matériaux soumis à un choc thermique a permis de mieux faire le lien entre les dégradations observées et les configurations de MGP. En particulier, il a été montré que l’augmentation de l’épaisseur de la céramique à la surface du MGP est responsable de l’apparition et de la propagation de fissures plus profondes et déviées.Dans un second temps, la possibilité d’utiliser les MGP élaborés dans une ambiance oxydante à ultra haute température a été étudiée au moyen de deux bancs d’essais expérimentaux. Le premier d’entre eux est un banc laser qui a permis de tester les matériaux face à des chocs thermiques répétés jusqu’à 1800 °C et en présence de vapeur d’eau. Les matériaux testés ont présenté une bonne résistance et les mécanismes de dégradation relatifs à l’oxydation du MGP ont pu être identifiés et reliés à aux différentes configurations de MGP et aux conditions d’essai testées. Dans ces conditions, l’augmentation de l’épaisseur de la couche céramique assure une meilleure protection contre l’oxydation. Le second moyen d’essai a permis de qualifier les MGP dans la flamme H2/O2 d’une chambre de combustion. De ce fait, les conditions d’essais étaient relativement proches des conditions réelles visées. Aucune dégradation majeure n’a été relevée à la suite de ces essais en chambre de combustion, ce qui démontre le potentiel de ce type de MGP pour l’application visée.En parallèle, un travail a été mené sur l’amélioration de la partie en céramique du MGP. En effet, le métal utilisé a un coefficient de dilatation thermique deux fois inférieur à celui de la céramique choisie. De ce fait, et malgré la présence du gradient, de fortes contraintes thermomécaniques s’exercent au niveau des interfaces entre les différentes couches du MGP. Ainsi, un point clé de cette étude a consisté à comprendre l’influence de la composition de la céramique et en particulier du taux et de la nature de l’oxyde de terre rare utilisé sur le coefficient de dilatation thermique. De plus, des mesures de conductivité ionique et de conductivité thermique ont permis de rendre compte du rôle de barrière thermique et environnemental de la couche en céramique pure à la surface du MGP. Il a été montré que des compositions à base de forts taux de Lu2O3 étaient les plus prometteuses. Enfin, une dernière partie de cette thèse était consacrée à étudier la possibilité de cicatriser les fissures observées au sein de la couche céramique, apparues à la suite du traitement thermique ou à la suite d’un essai sous flux thermique. Pour cela, un disilicate d’yttrium a été introduit dans la couche en céramique pure du MGP directement au cours de l’élaboration par APS. Son influence sur la résistance des échantillons dans des conditions sévères de température et d’atmosphère a été reportée. En particulier, la présence de ce disilicate est responsable de transformations chimiques au sein du MGP au cours des essais à haute température
The development of a new green ergol prototype for satellite repositioning engines requires more severe thermal and environmental conditions for combustion chamber materials than is currently the case. As a result, alternative materials known as functionally graded materials (FGM) have been developed for several years as part of an ONERA-CNES-ICB study. The aim of this thesis is to pursue the development of this type of ceramic/metal gradient material, in order to optimize its design and ensure that it can be used up to 2400 °C in the presence of water vapor. Firstly, different configurations of FGM developed by air plasma thermal spraying (APS) were tested under vacuum laser heat flux up to 2350 °C. By modelling the cracking of these materials when subjected to thermal shock, the link between the observed degradations and the FGM configurations was better established. In particular, it has been shown that increasing the thickness of the ceramic on the FGM surface is responsible for the appearance and propagation of deeper, deviated cracks.Secondly, the possibility to use such FGM under an oxidising atmosphere at ultra-high temperature was studied through two experimental set ups. The first one is a laser test bench which allowed to assure the resistance of the materials submitted to repeated thermal schocks up to 1800 °C in presence of water vapour. The tested materials presented an appropriate behaviour under the tested conditions. The degradation mechanisms related to FGM oxidation have been identified and compared from one FGM configuration to another and linked to the tested conditions. The second one permits to qualify the behaviour of FGM in the H2/O2 flame of a combustion chamber. Thus, the tested conditions were relatively close to the ones of the intended application. No major degradation was observed after the combustion chamber tests, which demonstrates the potential of this type of FGM for the application.In parallel, a study was carried out about the improvement of the ceramic part of the FGM. Indeed, the thermal expansion coefficient of the chosen metal is twice lower than the one of the chosen ceramic. Thus, and despite the presence of graded layers in-between the metal and the ceramic, high thermomechanical stresses occur at the interfaces between the different layers of the FGM. Thus, a key point of this study consisted in the understanding of the influence of the ceramic composition, and in particular of the amount and nature of the rare earth oxide, on the thermal expansion coefficient. In addition, ionic conductivity and thermal conductivity measurements most accurately reflect the role of thermal and environmental barrier coating of the pure ceramic layer upon the FGM. It has been shown that high content Lu2O3 based compositions are the most promising to be used for the ceramic composition of the FGM. The last part of this thesis was dedicated to study the possibility to heal the cracks observed in the ceramic, which came either from the thermal treatment, either from the thermal tests. Thus, an yttrium disilicate was introduced in the pure ceramic layer of the FGM directly during the elaboration process with APS. Its influence on the resistance of FGM under harsh thermal and environmental conditions was finally reported. In particular, the presence of this disilicate is responsible of chemical transformations in the FGM during high temperature tests

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UHLMANN, FRANZISKA JOHANNA LUISE. „Protective Ultra-High Temperature Coatings/ Ceramics (UHTCs) for Ceramic Matrix Composites in Extreme Environments“. Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2644372.

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This thesis is focused on the development of a protective coating system for Cf/SiC SiCARBONTM (Airbus trademark) materials against very high temperatures in extreme environment. Here, we concentrate on the application of this technology in combustion chambers, for example in orbital thrusters. During combustion, the composite material needs to be protected against oxidation caused by the extreme conditions. With the aim to increase the combustion performance using higher temperatures (up to 1850 °C), this thesis deals with the replacement of the current Environmental Barrier Coating (EBC) solution (CVD-SiC coating, Chemical Vapor Deposition) by an Ultra High Temperature Ceramic (UHTC) based coating system. Different challenges of this approach are, for instance, the CTE mismatch between Cf/SiC and UHTC materials and the feasibility to create a dense, thick and adherent UHTC based coating on the hot gas wall (inner wall) of a small combustion chamber. In this work, a suitable coating process (High Performance Plasma Coating process, HPPC) for inner wall coatings is selected and further developed to create ZrB2 based coatings on Cf/SiC based substrate materials. Based on a parameter study, the coating quality of HPPC based ZrB2 coatings is optimized depending on plasma current, chamber pressure, powder flow rate, preheating and cooling rate. HPPC coatings with different material combinations (ZrB2, ZrB2-SiC, ZrB2-TaC, ZrB2-LaB6) are investigated regarding coating adhesion, voids, composition and thermo-chemical behavior within a combustion chamber-like environment. To decrease the CTE mismatch between Cf/SiC substrate and a ZrB2 based coating and to increase the thermo-chemical resistance of the composite, the SiC matrix material is modified by ZrB2 and Ta additions. Cf/SiC-ZrB2-TaC composites with different SiC/ZrB2-TaC ratios are fabricated and investigated regarding microstructure, chemical composition and material properties (physical, thermo-physical, mechanical and thermo-chemical). The adhesion of HPPC based ZrB2 coatings on Cf/SiC composites is enhanced by a ZrB2 and TaC matrix modification. Based on the results, interactions between process parameters, coating composition and substrate material are analyzed and provide the base for ZrB2 based EBCs of the inner wall coatings on Cf/SiC based components. By means of the obtained findings, the potential of several material systems is derived in order to develop a protective coating for long-term applications in combustion chamber environments.

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Krossa, Alexander. „Material characteristics of new ultra high-strength steels manufactured by Giflo Steels“. Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/236243/1/Alexander%2BKrossa%2BThesis%281%29.pdf.

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This thesis has investigated the material characteristics of the new high-strength steel (HSS) produced by Giflo Steels (F-series steel) using detailed experimental studies involving ambient and elevated temperature mechanical property tests, post-fire mechanical property tests and V-Charpy notch tests for hardness. Its findings have shown that the new F-series steel has an advantage over similar HSS as it has superior post-fire mechanical properties, while retaining also the other mechanical properties within the requirements of relevant design standards.

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Jahani, Babak. „Development of an Advanced Composite Material Consisting of Iron Matrix Reinforced with Ultra High Temperature Ceramic Particulate (TiB2) with Optimum Properties“. Thesis, North Dakota State University, 2016. https://hdl.handle.net/10365/28089.

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This study was intended to investigate the mechanical properties and microstructure of iron based composite reinforced by ultra high temperature ceramics fabricated by powder metallurgy technique. The fabrication parameters were optimized and composite samples with different volume fraction of TiB2 were fabricated and were subjected to different mechanical tests. The results indicated improving in mechanical properties of Fe-TiB2 composites by increasing the volume fraction of TiB2 up to 20 vol%. More TiB2 particles didn?t improve the mechanical properties of composite, instead adversely affected it due to increasing the chance of agglomeration and porosity in entire microstructure. Another finding showed the twofold characteristic of TiB2 on mechanical properties of composite via increasing the hardness and decreasing the bulk density of composite. Finite Element Analysis (FEA) have also been performed on microstructural based developed models to simulate failure of composites. Numerical simulation results could verify the experimental results.

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Cattelan, Mattia. „Graphene and beyond: development of new two-dimensional materials“. Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424752.

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During the three years of my PhD project, I explored part of the world of two-dimensional materials. My activity has been focused on the growth and analysis of two-dimensional materials by means of Surface Science techniques. For the growth both chemical methods, such as decomposition of gaseous precursors, as well as physical methods, such as evaporation of metals under ultra-high vacuum conditions, were used. The main method for studying the properties of these materials was photoemission spectroscopy from core levels and valence band. The materials were mostly grown and analysed directly in-situ, avoiding air exposure, which is known to alter their properties. Taking the cue from the results on single materials, I further widened my investigation toward complex heterostructures, i.e. artificial architectures of two-dimensional materials. Systems stemming from different combinations among graphene, hexagonal boron nitride and two-dimensional chalcogenides were produced and investigated with the aim to unravel the structure-activity relationships in heterostructures. The thesis is divided into four main chapters. The first is an introduction to the world of two-dimensional materials and summarized the main themes and the general structure of the thesis. The second chapter is dedicated to the growth and study of graphene, which is the archetype of this class of materials. After an introduction on its electrical properties and on its growth on conventional metal single crystals, the chapter is divided into four sections that cover specific issues. Paragraphs 2.1.1 and 2.1.2 examine the properties of graphene and nitrogen doped graphene in contact with ultra-thin layers of iron. The section 2.2 studies the reaction of water with graphene grown on nickel single crystal, for the production of hydrogen. The paragraph 2.3 describes the growth of graphene on an unconventional substrate: platinum nickel alloy (Pt3Ni). The third chapter is devoted to the study of other two-dimensional materials firstly introducing the studied materials: hexagonal boron nitride, transition metals dichalcogenides, other layered chalcogenides and heterostructures. Afterward, this chapter continues with three specific sections: paragraphs 3.1.1 and 3.1.2 are dedicated to two innovative methods for preparing heterostructures under ultra-high vacuum conditions. The section 3.1.1 presents a new strategy to synthesize monolayer in-plane heterostructure composed by graphene and hexagonal boron nitride, the 3.1.2 discusses a versatile route to create vertically stacked heterostructures of various two-dimensional materials. The last paragraph, 3.2, reports a detailed investigation of the electronic and chemical properties of a bulk layered chalcogenide, indium selenide. The fourth chapter summarizes the main conclusions of the work.
In questi tre anni di progetto di dottorato ho esplorato parte del mondo dei materiali bidimensionali. Il mio lavoro si è concentrato sull’analisi e la crescita di materiali bidimensionali con tecniche della Scienza delle Superfici. Per la crescita sono stati utilizzati sia metodi chimici, come la decomposizione di precursori gassosi, che fisici, come l’evaporazione di metalli in condizioni di ultra alto vuoto. Il metodo principale usato per studiare le proprietà di questi materiali è stata la fotoemissione da livelli di core e dalla banda di valenza. I materiali sono stati in gran parte cresciuti e analizzati direttamente in-situ, cioè evitando l’esposizione all’aria che ne altera le loro proprietà. Prendendo spunto dai risultati sui singoli materiali ho ulteriormente ampliato le mia ricerca verso complesse eterostrutture, ossia delle architetture artificiali di materiali bidimensionali. I sistemi derivanti da diverse combinazioni di grafene, nitruro di boro esagonale e calcogenuri bidimensionali sono stati prodotti e analizzati con lo scopo di rivelare la relazioni tra struttura e attività nelle eterostrutture. La tesi è divisa in quattro capitoli principali. Il primo è un’introduzione al mondo dei materiali bidimensionali e riassume i temi principali e la struttura generale della tesi. Il secondo capitolo è dedicato alla crescita e allo studio del grafene, archetipo di questa classe di materiali. Dopo un’introduzione sulle sue proprietà elettriche e sulla sua crescita su monocristalli metallici convenzionali il capitolo si suddivide in quattro sezioni che trattano tematiche specifiche. I paragrafi 2.1.1 e 2.1.2 esaminano le proprietà di grafene e grafene drogato azoto in contatto con strati ultrasottili di ferro. La sezione 2.2 studia la reazione dell’acqua con grafene cresciuto su monocristallo di nickel, per la produzione di idrogeno. Il paragrafo 2.3 descrive la crescita di grafene su un substrato non convenzionale: una lega di platino e nickel (Pt3Ni). Il terzo capitolo è rivolto allo studio di altri materiali bidimensionali, innanzitutto introduce i materiali trattati: nitruro di boro esagonale, dicalcogenuri di metalli di transizione, altri calcogenuri stratificati e le eterostrutture. Poi prosegue con tre sezioni specifiche; i paragrafi 3.1.1 e 3.1.2 sono dedicati a due metodi innovativi per formare eterostrutture in condizioni di ultra alto vuoto. La sezione 3.1.1 presenta un nuovo metodo per sintetizzare l’eterostruttura nel piano composta da grafene e nitruro di boro esagonale, la 3.1.2 propone un metodo versatile per creare eterostrutture impilate verticalmente di vari materiali bidimensionali. L’ultimo paragrafo, 3.2, riporta una ricerca dettagliata sulle proprietà elettroniche e chimiche di un calcogenuro stratificato massivo, l’indio seleniuro. Il quarto capitolo riassume le conclusioni del lavoro.

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Radmanesh, Seyed Mohammad Ali. „Ultra-low Temperature Properties of Correlated Materials“. ScholarWorks@UNO, 2018. https://scholarworks.uno.edu/td/2511.

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Abstract After the discovery of topological insulators (TIs), it has come to be widely recognized that topological states of matter can actually be widespread. In this sense, TIs have established a new paradigm about topological materials. Recent years have seen a surge of interest in topological semimetals, which embody two different ways of generalizing the effectively massless electrons to bulk materials. Dirac and, particularly, Weyl semimetals should support several transport and optical phenomena that are still being sought in experiments. A number of promising experimental results indicate superconductivity in members of half-Hesuler semimetals which realize the mixing singlet and triplet pairing symmetry. We now turn to results we got through the work on topological semimetals. This work presents quantum high field transports on Dirac and Weyl topological semimetals including Sr1-yMn1-zSb2 (y, z < 0.1), YbMnBi2 and TaP. In case of Sr1-yMn1-zSb2 (y, z < 0.1), massless relativistic fermion was reported with m* = 0.04-0.05m0. This material presented a ferromagnetic order for in 304 K < T < 565 K, but a canted antiferromagnetic order with a net ferromagnetic component for T < 304 K. These are considered striking features of Dirac fermions For YbMnBi2, we reported the unusual interlayer quantum transport behavior in magnetoresistivity, resulting from the zeroth LL mode observed in this time reversal symmetry breaking type II Weyl semimetal. Also, for Weyl semimetal TaP the measurements probed multiple Fermi pockets, from which nontrivial π Berry phase and Zeeman splitting were extracted. Our ultra-low penetration depth measurements on half-Heuslers YPdBi and TbPdBi revealed a power- law behavior with n= 2.76 ± 0.04 for YPdBi samples and n=2.6 ± 0.3 for TbPdBi sample. We may conclude the exponent n > 2 implies nodless superconducting gap in our samples. Also, we found that despite the increase in magnetic correlations from YPdBi to TbPdBi, superconductivity remains robust in both systems which indicates that AF fluctuations do not play a major role in superconducting mechanism.

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Waheed, Qari Muhammad Khalid. „Ultra-high temperature steam gasification of biomass“. Thesis, University of Leeds, 2013. http://etheses.whiterose.ac.uk/5852/.

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In this research, hydrogen production from conventional slow pyrolysis, flash pyrolysis, steam gasification and catalytic steam gasification of various biomass samples including rice husk, wood pellets, wheat straw and sugarcane bagasse was investigated at ultra-high temperature (~1000 °C). During flash pyrolysis of the waste wood, the gas yield was improved to ~78 wt.% as compared to ~25 wt.% obtained during slow pyrolysis. The addition of steam enhanced the hydrogen concentration from 26.91 vol.% for pyrolysis to 44.13 vol.% for steam gasification. The comparison of pyrolysis, steam gasification and catalytic steam gasification in a down-draft gasification reactor at 950 °C using rice husk, bagasse and wheat straw showed a significant increase in gas yield as well as hydrogen yield. The hydrogen yield was enhanced from ~2 mmoles g-1 for pyrolysis to ~25 mmoles g-1 during steam gasification using a 10 wt.% Ni-dolomite catalyst. The higher hydrogen yield was due to the enhanced steam reforming of hydrocarbons and thermal cracking of tar compounds at higher temperature. When compared with the other catalysts such as 10 wt.% Ni-dolomite, 10 wt.% Ni-MgO, and 10 wt.% Ni-SiO2, the 10 wt.% Ni-Al2O3 catalyst showed the highest hydrogen yield of 29.62 mmoles g-1. The investigation on gasification temperature showed that the hydrogen yield was significantly improved from 21.17 mmoles g-1 at 800 °C to 35.65 mmoles g-1 at 1050 °C. The hydrogen concentration in the product gas mixture was increased from 50.32 vol.% at 800 °C to 67.41 vol.% at 1050 °C. The increase in steam injection rate from 6 to 35 ml hr-1 enhanced the hydrogen yield from 29.93 mmoles g-1 to 44.47 mmoles g-1. The hydrogen concentration increased from 60.73 to 72.92 vol.%. The increase was mainly due to the shift in the equilibrium of the water gas shift reaction as H2:CO ratio increased from 2.97 to 7.78. The other process variables such as catalyst to sample ratio, carrier gas flow rate showed little or no influence on the gas yield and hydrogen yield. The steam gasification of residual biomass char was performed at 950 °C to recover extra hydrogen. The presence of 10 wt.% Ni-Al2O3 in the gasifier improved the hydrogen yield to ~47 mmoles per gram of biomass as compared to the other catalysts such as 10 wt.% Ni-dolomite and 10 wt.% Ni-MgO. The gasification temperature showed a positive influence on hydrogen yield from 750 °C to 950 °C. The increase in steam injection rate from 6 ml hr-1 to 15 ml hr-1 enhanced the hydrogen yield from 46.81 to 52.10 mmoles g-1 of biomass.

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Benning, Rainer. „Novel process synthesis in ultra high temperature plants“. [S.l. : s.n.], 2003. http://deposit.ddb.de/cgi-bin/dokserv?idn=969425066.

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Ersson, Anders. „Materials for High-Temperature Catalytic Combustion“. Doctoral thesis, KTH, Chemical Engineering and Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3501.

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Catalytic combustion is an environmentally friendlytechnique to combust fuels in e.g. gas turbines. Introducing acatalyst into the combustion chamber of a gas turbine allowscombustion outside the normal flammability limits. Hence, theadiabatic flame temperature may be lowered below the thresholdtemperature for thermal NO_Xformation while maintaining a stable combustion.However, several challenges are connected to the application ofcatalytic combustion in gas turbines. The first part of thisthesis reviews the use of catalytic combustion in gas turbines.The influence of the fuel has been studied and compared overdifferent catalyst materials.

The material section is divided into two parts. The firstconcerns bimetallic palladium catalysts. These catalysts showeda more stable activity compared to their pure palladiumcounterparts for methane combustion. This was verified both byusing an annular reactor at ambient pressure and a pilot-scalereactor at elevated pressures and flows closely resembling theones found in a gas turbine combustor.

The second part concerns high-temperature materials, whichmay be used either as active or washcoat materials. A novelgroup of materials for catalysis, i.e. garnets, has beensynthesised and tested in combustion of methane, a low-heatingvalue gas and diesel fuel. The garnets showed some interestingabilities especially for combustion of low-heating value, LHV,gas. Two other materials were also studied, i.e. spinels andhexaaluminates, both showed very promising thermal stabilityand the substituted hexaaluminates also showed a good catalyticactivity.

Finally, deactivation of the catalyst materials was studied.In this part the sulphur poisoning of palladium, platinum andthe above-mentioned complex metal oxides has been studied forcombustion of a LHV gas. Platinum and surprisingly the garnetwere least deactivated. Palladium was severely affected formethane combustion while the other washcoat materials were mostaffected for carbon monoxide and hydrogen.

Keywords:catalytic combustion, catalyst materials,palladium, platinum, bimetallic, garnet, spinel, hexaaluminate,deactivation, sulphur, poisoning, diesel, methane,hydrocarbons

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Mills-Brown, Joseph. „High temperature composite materials and structures“. Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.617589.

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The recent resurgence and growing interest in high temperature structures to maximise design space and performance in motorsport applications, led to the need for greater understanding of high temperature composite materials. This study aimed to investigate suitable materials for high temperature structures with application to the motorsport environment. Composite materials were quickly identified as the most appropriate materials given the needs of motorsport, with polysialate composites championed after a thorough review of available materials. A commercially available composite reinforced with silicon carbide fibres was selected to meet the study requirements. This led to the need for thermal and mechanical characterisation in order to provide temperature dependant data suitable for accurate design of high temperature structures. The result of .this was a full engineering dataset for the most widely used polysialate composites, filling In significant gaps in the literature, whilst simultaneously producing a novel and unique high temperature tensile testing rig for this composite laminates. In turn, this new data was exploited with application to a polysialate composite case study structure; an exhaust liner used on current Formula One vehicles. This required full understanding of the thermal and mechanical load cases experienced by the liner, in order to accurately simulate the liner and environment using finite element analysis. Not only did this provide an application of the newly acquired temperature dependant material properties, but it also highlighted the need for temperature dependant properties in the design of high temperature structures. The study, its aims and approach, were validated through comparison of simulation failure predictions against component failed in service.

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Thomas, Rachel Elizabeth. „High temperature processing of kaolinitic materials“. Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/6075/.

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Calcination, is the process of heating a substance, to a temperature below its fusing point, with a resultant loss of water. It is one of the most important techniques currently used to enhance the properties, and therefore value, of kaolin. The overall aim of this project was to provide a better understanding of the principles of the kaolin calcination reaction in order to enhance the efficiency, quality and sustainability of the Imerys calcining operations. This research has shown a strong correlation between the chemistry of kaolin and the colour of the calcined product. This is due to the influence of contaminant materials on the colour of the hydrous kaolin, which in turn affects the calcined material. The strongest colour influencing factor is the presence of iron, particularly if it is present on the surface of the kaolin. Surface iron is currently reduced using a reductive bleaching process. This has an improving influence on even the most contaminated kaolins, however there can be quite a lot of interbatch variability. Despite its effect on colour the chemistry of kaolin has little influence on post calcination reactivity. Reactivity is due to physical factors such as particle and agglomerate size and the penetration of heat into the material. Any kaolin will calcine to produce a low reactivity product; provided the heat is able to penetrate into the bed and that the material is able to remain at temperature for sufficient time for the calcination reaction to occur. Another outcome of the research was the discovery that a higher temperature and shorter time period has little on the end calcined product but has implications for lower energy usage.

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Huang, Chen. „Ultra high resolution imaging of radiation-sensitive materials“. Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:837c7c40-ecce-4ff1-ac98-1491b67518db.

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Electron radiation damage is an important topic in electron microscopy. A large proportion of materials or biological structures are still unable to be directly imaged by electron microscopes at high resolutions due to their radiation sensitivity, instead of by the instrumental resolution capacity of the microscopes. In fact, as the availability of aberration correctors was rapidly increased in the past decade, as well as the emergence of the next generation of chromatic aberration correctors, attention has been again focused on the control and reduction of radiation damage. This thesis proposes a complete low-dose high resolution imaging strategy for characterising radiation-sensitive materials using an aberration-corrected transmission electron microscope. The microscope was quantitatively calibrated for electron dose and was operated under a strict low-dose condition to ensure maximum protection for the radiation-sensitive samples. Time series and focal series imaging were employed to allow other data processing techniques to be applied. During the course of pursuing higher resolutions using low-dose imaging and data processing, several side problems have been explored. Image registration of low-dose image series was first tested using a variable dose time series of human tooth tissue. The impact of excessive image noise was reduced by modification of the registration algorithm. In the case of focal series image registration, a simulation-assisted registration procedure was developed. This demonstrated the ability to register focal series of cerium dioxide and silicon nitride at various doses, despite the contrast reversal problem when the series defoci moved from under focus to over focus. A quantitative evaluation metric, the IQ factor, was implemented to assess the signal-to-noise ratio in the power spectrum of an image and has proved to be a useful indirect criterion for measuring the quality of registration and that of exit wave reconstruction. Exit wave reconstruction from low-dose HRTEM was investigated using this improved image registration and the resultant exit waves were quantitatively compared using the IQ factor. The influence of noise on exit wave reconstruction was an intertwined problem with the low electron dose and has also been addressed in this work. By combining improvements in the various aspects of low-dose imaging and data processing, time/focal series of ZSM-5, an important type of zeolitic catalyst, was acquired. The low-dose time series of ZSM-5 was aligned by both the traditional rigid XCF image registration and a more sophisticated non-rigid image registration method. The low-dose focal series of ZSM-5 was used to restore the electron wave function at the exit plane of the sample. The restored exit wave was able to resolve the fine structure inside the ZSM-5 framework, which was not clearly resolved in the individual images of the focal series.

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Gai, Fangyuan, und Fangyuan Gai. „Processing and Microstructural Characterization of Ultra-High Temperature Ceramics“. Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626334.

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Spark plasma sintering (SPS), also known as direct current sintering (DCS) is an advanced sintering technique that and uses a continuous pulsed direct current to rapidly process materials through Joule heating and offers significant advantages and versatility over conventional sintering methods. The technique features in energy saving owing to high heating rates and is very suitable for consolidation as well as diffusion bonding of electrical conductive advanced ceramic materials such as ultra high temperature ceramics (UHTCs). However, cooling rate in SPS also plays an important role as it directly influences the generation of residual stress especially for specimens consist of dissimilar phases such as composites and laminates primarily due to CTE mismatch. Therefore, in order to produce high quality materials, a zirconium diboride with addition of silicon carbide (ZrB2-SiC) ultra high temperature ceramic composite is selected to investigate the effect of cooling rate in SPS on microstructure and mechanical properties. After being densified at the target temperature, ZrB2-25vol%SiC specimens are cooled from 1800°C using controlled cooling rates of 10 °C/minute to ~225.5 °C/minute (free cooling). A time dependent finite element analysis (FEA) model is used to simulate the temperature gradients across the specimens at dwell times and during the cooling processes. The residual stress within the specimens are experimentally verified using X-ray diffraction (XRD) and Raman spectrometry, and found maximum residual stress within the specimen cooled at 225.5 °C/minute. Peak Hardness and moderate elastic modulus is found for specimen sintered at 1800 °C and cooled at 100 °C/minute, which make this temperature and cooling rate appropriate conditions for future fabrication of UHTCs with similar thermal and electrical properties. These materials are of great interest for their excellent high-temperature capabilities, wear and corrosion resistance, and are regarded as material candidates for engineering applications in extreme environments. Therefore, development of an effective joining technique is important since near-net shape fabrication is challenging, and joints formed by brazing or conventional solid-state diffusion bonding limit the mechanical strength and high temperature applications of the base materials. Using SPS we have rapidly and successfully joined ZrB2 to hafnium diboride (HfB2) at 1750 and 1800 °C within a minute through electric current assisted solid-state diffusion bonding. The electric current enables localized Joule heating as well as plastic deformation of the mating surface asperities, and enhances the elemental interdiffusion process at the HfB2/ZrB2 interfaces owing to electromigration, which leads to the formation of ZrxHf1-xB2 solid solution. A series of characterization and analytical techniques including scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (S/TEM) are employed to study the microstructure and chemical composition at of the HfB2/ZrB2 interfaces. Apart from enhanced diffusion as a result of electromigration, the applied electric current can also be use to promote plastic deformation in ZrB2, which does not go through gross plastic deformation due to its extremely high melting point and brittle nature even when elevated temperature and pressure are applied. Through “electroplastic effect” (an effect based on electromigration) the mobility and multiplication of the existing dislocations in ZrB2 is enhanced, and a “metal-like” primary recrystallization phenomenon in the ZrB2 is observed meaning the material has experienced a sufficient amount of plastic deformation and reached the critical dislocation density and configuration for nucleation of “strain-free” grains. The average grain size of the recrystallized grain is only ½ of its original value. These findings suggest great potentials in microstructural tailoring and grain refinement of conductive advanced ceramics using SPS, and provide promising ideas for future fabrications and applications.

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Suen, Timothy W. (Timothy Wu). „Temperature response of the ultra-high throughput mutational spectrometer“. Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32960.

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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.
Includes bibliographical references (p. 43-44).
The Ultra-High Throughput Mutational Spectrometer is an instrument designed to separate mutant from wild type DNA through capillary electrophoresis. Since this technique uses the melting point of the molecule to distinguish between sequences of base pairs, temperature control is crucial to the success of the device. The purpose of this analysis is to characterize the temperature response of the instrument, taking into account the heat dissipated by the 10,000 capillaries in the system during electrophoresis. Analytical models, finite element analysis, and physical models were used to predict the steady state response of the system to heat generated by capillary electrophoresis. The analytical models estimated a steady state offset of 0.2 K for water at 3.3x 10Ì⁴ m³/s (20 L/min) and 1.0 K for water at 6.7x 10Ì⁵ m³/s (4.0 L/min) and predicted that the system would reach steady state within several seconds. Finite element analysis determined that the gel inside the capillaries would have a steady state offset of 0.24 K. The physical system, which simulated the Joule heating of the capillaries using an immersion heater, yielded a steady state offset of 0.24 K at 3.3x 10Ì⁴ m³/s and 0.65 K at 6.7x 10Ì⁵ m³/s, but the settling time in both cases was on the order of 500 s.
(cont.) This discrepancy is due to the fact that many aspects of the physical system, including the thermal mass of the instrument, heat loss through convection, and the PID temperature controller in the circulator, were not taken into consideration in the theoretical analysis. Pressure drop and vortex shedding were also calculated for the instrument. Finite element analysis determined the pressure drop to be 18.55 Pa. Vortex shedding does not occur, because the operating conditions of this instrument are below the critical Reynolds number.
by Timothy W. Suen.
S.B.

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Hollis, Julie Alison. „Natural and experimental constraints on ultra-high temperature metamorphism“. Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/15035.

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Independent determination of the heat capacity of the sapphirine used in this study is currently underway. It is expected that extrapolation of this data to the results of this study will result in the derivation of a heat capacity function for natural sapphirine from 0-1573K. Incorporation of this into existing thermodynamic datasets should allow the quantitative determination of the position of sapphirine-bearing reactions in petrogenetic grids relevant to ultra-high temperature metamorphism in natural systems. The Archean Napier Complex of Antarctica is one of the best documented UHT terrains, long recognised as having experienced temperatures in excess of 1000°C followed by a long period of near-isobaric cooling at deep crustal levels. However, the early history of the terrain, the timing of deformation and metamorphism, and the tectonic processes responsible for the generation of the extreme temperatures of metamorphism, have not been resolved (e.g. Ellis, 1987; Harley, 1989; Sandiford, 1989; Hensen and Motoyoshi, 1992). Mineral textural relationships linked to deformation features from a range of localities in and around Amundsen Bay are consistent with peak metamorphic conditions of 900-1100°C at 0.8-1.1 GPa during intense lower crustal extension. Rare decompression textures from widely spaced localities attest to decompression of the whole terrain to depths equivalent to the base of a normal thickness crust after peak metamorphism, while still under UHT conditions, and indicate that intense lower crustal extension and UHT metamorphism occurred synchronously with crustal thickening. Retrograde reactions textures may have been produced either by isobaric cooling, or by later granulite facies metamorphic event/s, or both. Mineral reaction textures and structural features support a tectonic model of lithosphere delamination for the development of UHT metamorphism, in the Napier Complex. This model involves the detachment of the lower part of the mantle lithosphere during continental collision, allowing upwelling of hot asthenosphere material directly beneath the crust, which in turn results in intense extensional deformation of the lower crust and lateral expulsion of melts.

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Almström, Linda, und Camilla Söderström. „Alternative materials for high-temperature and high-pressure valves“. Thesis, Karlstads universitet, Fakulteten för teknik- och naturvetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-7393.

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AB SOMAS Ventiler manufactures valves for different applications. A valve of type DN VSSL 400, PN 100, used in high-temperature and high-pressure applications was investigated in this thesis. This type of valve is coated with high cobalt alloys to achieve the tribological properties needed for this severe condition. However there is a request from AB Somas Ventiler to find another solution. This request is based on the fact that demands on higher temperatures, from customers, yields higher requirements on the material. It is also a price issue since cobalt is quite expensive. Materials investigated were high-nitrogen steel, Vanax 75, nickel-based superalloy Inconel 718 and hardened steels, EN 1.4903 and EN 1.4923 presently used as base material in the valve. Calculation of contact pressure that arises when the valve is closed was first approached by using finite element method (FEM). Several models were constructed to show the behavior of the valve during closing in terms of deformation. Hot wear tests, in which a specimen was pressed against a rotating cylinder, were performed to be able to compare the materials to the solution of today and among each other. Data extracted from the tests were compiled in the form of coefficients of friction. Profilometer examinations were used to reveal the volumes of worn and adhered material and together with scanning electron microscopy (SEM) the wear situation for each material couple could be assessed. Wear mechanisms detected in SEM were adhesive and abrasive and the results clearly showed that the steels were not a good solution because of severe adhesive wear due to the similarity of mating materials creating a more efficient bonding between the asperities. Vanax 75 showed much better performance but there was still an obvious difference between the steels and the superalloy in terms of both coefficient of friction and amount of wear. On this basis, Inconel 718 was selected as the most suitable material to replace the high cobalt alloys used in the valves today.
AB Somas ventiler är ett företag som tillverkar ventiler för ett brett spann av applikationer. I det här examensarbetet har undersökningar genomförts på en ventil av modell DN VSSL 400, PN 100, som normalt används i applikationer för höga tryck och höga temperaturer. Ventilen beläggs i dagsläget med höghaltiga koboltlegeringar för att uppnå de tribologiska egenskaper som krävs i de påfrestande arbetsförhållanden som råder. AB Somas Ventiler har dock framfört en förfrågan om att hitta en alternativ lösning, en förfrågan som grundar sig i att kundernas ständiga önskemål på att ventilerna ska klara högre arbetstemperaturer också medför högre krav på ventilmaterialen. Det är även en prisfråga, då kobolt är en dyr legering att använda sig av. De material som inkluderades i undersökningen var det kvävelegerade stålet Vanax 75, nickelbaserade superlegeringen Inconel 718 samt de två stålen EN 1.4903 och EN 1.4923 i härdat tillstånd. De två sistnämnda används idag som basmaterial i ventilen. Genom att använda den finita element metoden (FEM) kunde en första beräkning göras av det kontakttryck som uppstår då ventilen stängs. Flera modeller konstruerades för att simulera ventilens deformation vid stängning. Där efter utfördes nötningstester i hög temperatur på de alternativa materialen, genom att låta en provbit pressas mot en roterande cylinder, för att sedan kunna göra en jämförelse mellan materialen och även med den nuvarande lösningen. Från nötningstesterna erhölls data som kunde användas för att ta fram friktionskoefficienter för de olika materialparen. Med hjälp av undersökningar med profilometer och svepelektronmikroskop (SEM) kunde värden på nötta och vidhäfta volymer erhållas tillsammans med information om nötningssituationer för ytorna mellan de olika materialparen. De nötningsmekanismer som påvisades med hjälp av SEM-undersökningen var adhesiv och abrasiv nötning, och resultaten visade tydligt att nötningen av stålen var omfattande, på grund av att lika material i kontakt med varandra skapar starkare band mellan ytorna, och att de därför inte var en intressant lösning. Det kvävelegerade Vanax 75 uppförde sig visserligen bättre men en tydlig skillnad mot superlegeringarna kunde dock fortfarande konstateras, sett till både friktionskoefficient och mängden slitage. Baserat på dessa resultat valdes Inconel 718 som det bäst lämpade materialet att ersätta de höghaltiga koboltlegeringarna som idag används i ventilen.

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Elm, Svensson Erik. „Nanotemplated High-Temperature Materials for Catalytic Combustion“. Doctoral thesis, KTH, Kemiteknik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4800.

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Catalytic combustion is a promising technology for heat and power applications, especially gas turbines. By using catalytic combustion ultra low emissions of nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional combustion technologies. Besides achieving low emission levels, catalytic combustion can stabilize the combustion and thereby be used to obtain stable combustion with low heating-value gases. This thesis is focused on the high-temperature part of the catalytic combustor. The level of performance demanded on this part has proven hard to achieve. In order to make the catalytic combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity have to be developed. The objective of this work was to develop catalysts with higher activity and stability, suitable for the high-temperature part of a catalytic combustor fueled by natural gas. Two template-based preparation methods were developed for this purpose. One method was based on soft templates (microemulsion) and the other on hard templates (carbon). Supports known for their stability, magnesia and hexaaluminate, were prepared using the developed methods. Catalytically active materials, perovskite (LaMnO3) and ceria (CeO2), were added to the supports in order to obtain catalysts with high activities and stabilities. The supports were impregnated with active materials by using a conventional technique as well as by using the microemulsion technique. It was shown that the microemulsion method can be used to prepare catalysts with higher activity compared to the conventional methods. Furthermore, by using a microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using the conventional impregnation technique. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed on selected catalysts prepared by the microemulsion technique. The stability of the catalysts was assessed by measuring the activity before and after aging at 1000 C in humid air for 100 h. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparative purposes. The results showed that LMHA deactivated much more strongly compared to several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the developed microemulsion method. Carbon templating was shown be a very good technique for the preparation of high-surface-area hexaaluminates with excellent sintering resistance. It was found that the pore size distribution of the carbon used as template was a crucial parameter in the preparation of hexaaluminates. When a carbon with small pores was used as template, the formation of the hexaaluminate crystals was strongly inhibited. This resulted in a material with poor sintering resistance. On the other hand, if a carbon with larger pores was used as template, it was possible to prepare materials with hexaaluminate as the major phase. These materials were, after accelerated aging at 1400 C in humid air, shown to retain surface areas twice as high as reported for conventionally prepared materials.
QC 20100719

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Ren, Xinhua. „High Temperature Materials Characterization and Sensor Application“. Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5456.

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This dissertation presents new solutions for turbine engines in need of wireless temperature sensors at temperatures up to 1300oC. Two important goals have been achieved in this dissertation. First, a novel method for precisely characterizing the dielectric properties of high temperature ceramic materials at high temperatures is presented for microwave frequencies. This technique is based on a high-quality (Q)-factor dielectrically-loaded cavity resonator, which allows for accurate characterization of both dielectric constant and loss tangent of the material. The dielectric properties of Silicon Carbonitride (SiCN) and Silicoboron Carbonitride (SiBCN) ceramics, developed at UCF Advanced Materials Processing and Analysis Center (AMPC) are characterized from 25 to 1300oC. It is observed that the dielectric constant and loss tangent of SiCN and SiBCN materials increase monotonously with temperature. This temperature dependency provides the valuable basis for development of wireless passive temperature sensors for high-temperature applications. Second, wireless temperature sensors are designed based on the aforementioned high-temperature ceramic materials. The dielectric constant of high-temperature ceramics increases monotonically with temperature and as a result changes the resonant frequency of the resonator. Therefore, the temperature can be extracted by measuring the change of the resonant frequency of the resonator. In order for the resonator to operate wirelessly, antennas need to be included in the design. Three different types of sensors, corresponding to different antenna configurations, are designed and the prototypes are fabricated and tested. All of the sensors successfully perform at temperatures over 1000oC. These wireless passive sensor designs will significantly benefit turbine engines in need of sensors operating at harsh environments.
Ph.D.
Doctorate
Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering

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Antunes, Isabel Alexandra Gonçalves. „Mechanochemistry of high temperature fuel cell materials“. Doctoral thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/18657.

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Doutoramento em Ciência e Engenharia de Materiais
Nos últimos anos, a mecanoquímica tem sido uma temática muito abordada na formação de materiais, motivada pelo grande interesse na preparação de nanopós. A sobressaturação estrutural de lacunas e a heterogeneidade química dos pós preparados por via mecanoquímica permitem melhoria na sinterabilidade, enquanto a elevada densidade dos agregados e a reduzido tamanho de cristalite produzem densidade em verde elevada. Estes fatores são extremamente atrativos na preparação de materiais cerâmicos óxidos densos, como é requerido na preparação de membranas eletroquímicas. Além disso, o processamento cerâmico por via mecanoquímica possibilita a síntese de novos materiais, que não conseguem ser sintetizados por outros métodos. Esta tese apresenta um estudo detalhado do processamento por via mecanoquímica de potenciais materiais de eletrólito e elétrodo para pilhas de combustível de óxido sólido de alta temperatura, e sua caracterização estrutural e eletroquímica. Por manipulação das variáveis do processo mecanoquímico pretende-se melhorar a capacidade de processamento e desenvolver novos materiais para aplicação em tecnologias de pilhas de combustível. A investigação foca-se, especificamente, no desenvolvimento de materiais de estrutura perovesquite à base de BaZrO3 e BaPrO3, com possíveis aplicações como condutores protónicos e condutores mistos, eletrónicos e protónicos, respetivamente.
In recent years, mechanochemistry has become an increasingly hot topic for the formation of materials, motivated by an explosion of interest in the preparation of nanopowders. The structural supersaturation by vacancies and chemical non-uniformity of mechanochemical powders promote enhanced sinterability, while the high density of aggregates and reduced crystallite density produce high green-densities. Such factors are highly attractive for preparation of dense ceramic oxide materials, as required for the formation of electrochemical-membranes. Additionally, mechanochemical ceramic processing may allow the synthesis of novel materials, which cannot be synthesized by other methods. In this thesis one offers a detailed study of mechanochemical processing for important potential electrolyte and electrode materials for high temperature solid oxide fuel cells and their subsequent structural and electrochemical characterisation. By mechanochemical manipulation one aims to improve the processing ability and to develop novel materials for fuel cell technologies. The research work is focused specifically on the development of perovskite materials based on BaZrO3 and BaPrO3, with potential applications as proton and mixed proton-electron conductors, respectively.

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27

Wan, Jun. „Iron-platinum granular films for ultra-high density recording“. Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 178 p, 2009. http://proquest.umi.com/pqdweb?did=1674099591&sid=2&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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28

Soignard, Emmanuel. „High pressure - high temperature synthesis and studies of nitride materials“. Thesis, University College London (University of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407347.

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29

Woodburn, Charles N. „Development of low-temperature, ultra high vacuum, scanning tunnelling microscope“. Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.264506.

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30

Dorfler, Kristin Marie. „On Ultra-High Temperature Metamorphism in the Mid-Lower Crust“. Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/48927.

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The Cortlandt Complex in New York is a composite intrusion of six mafic plutons and contains pelitic xenoliths that experienced extensive interaction with Mg-rich basaltic melt. The complex is an excellent natural example of ultra-high temperature (UHT) metamorphic processes and country rock-magma interaction due to mappable units of hybrid igneous rocks and the presence of large, partially melted, politic "emery" xenoliths. Previous attempts to understand the formation of the UHT xenoliths in the Cortlandt have provided the petrologic foundation for more rigorous thermodynamic modeling to determine the petrogenesis of these materials and to ultimately contribute to the understanding of UHT metamorphism in the Earth's crust. This work focuses on the development of hybrid monzonorites and emery at Salt Hill, located in the southeasternmost edge of the Cortlandt Complex. First, a thermobarometric study focuses on the P-T conditions of the country rock into which the Complex intruded. Pelitic schists from contact aureoles around a nearby pluton chemically and chronologically related to the complex, record high-P (~ 0.9 GPa, ~ 32 km depth) crustal conditions during pluton emplacement. This is interpreted to reflect loading due to the emplacement of Taconic allochthons during the waning stages of regional metamorphism before emplacement of the plutons. The second study uses thermodynamic heating calculations of pelitic schist to determine the production of norite and emery. Modeling results produce (i) an initial melt that produces a monzonorite composition when mixed with a mafic melt, (ii) a high-T melt that is texturally and compositionally homologous with quartzofeldspathic veins retained in the emery, and (iii) a residual mineral assemblage that, when oxidized, closely resembles the emery assemblage. Finally, focus is given to understanding the relationship between norite and emery and reflection on the mineralogy and structure of the lower crust-mantle boundary. Density calculations of the emery estimate values comparable to mantle densities, implying that rare exposure of UHT assemblages may be due to the fact the material stays at lower crustal (upper mantle?) depths. Therefore, the less-rare norite and other hybrid igneous rock occurrences may be the traces of deep, unexposed, UHT metamorphic assemblages.
Ph. D.

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31

Haj-Taieb, Manel Bade Klaus Aktaa Jarir. „Development of high temperature electrodeposited LIGA MEMS materials“. Eggenstein-Leopoldshafen Forschungszentrum Karlsruhe GmbH, 2009. http://d-nb.info/1002906997/34.

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32

Lee, Elaine Tse Ching. „Synthesis and characterisation of high-temperature superconducting materials“. Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624888.

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33

Vedula, Ramakrishna. „Materials for High Temperature Thin Film Thermocouple Applications“. Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/46493.

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The thermocouple systems used for the measurement of surface temperature in high temperature applications such as advanced aerospace propulsion systems and diesel engine systems are expected to perform in rapidly fluctuating and extremely high heat fluxes corresponding to high temperatures (in excess of 1400 K) and high speed flows. Traditionally, Pt/Pt-Rh based thin film thermocouples have been used for surface temperature measurements. However, recent studies indicated several problems associated with these thermocouples at temperatures exceeding 1000 K, some of which include poor adhesion to the substrate, rhodium oxidation and reaction with the substrate at high temperatures. Therefore, there is an impending demand for thermoelectric materials that can withstand severe environments in terms of temperature and heat fluxes. In this study, thin films of titanium carbide and tantalum carbide as well as two families of conducting perovskite oxides viz., cobaltites and manganates (La(1-x)SrxCoO3, M(1-x)Cax MnO3 where, M=La,Y) were investigated for high temperature thin film thermocouple applications as alternate candidate materials. Thin films of the carbides were deposited by r.f. sputtering while the oxide thin films were deposited using pulsed laser ablation. Sapphire (1102) was used as substrate for all the thin film depositions. All the thin films were characterized for high temperature stability in terms of phase, microstructure and chemical composition using x-ray diffraction, atomic force microscopy and electron spectroscopy for chemical analysis respectively. Electrical conductivity and seebeck coefficients were measured in-situ using a custom made device. It was observed that TiC/TaC thin film thermocouples were stable up to 1373 K in vacuum and yield high and fairly stable thermocouple output. The conducting oxides were tested in air and were found to be stable up to at least 1273 K. The manganates were stable up to 1373 K. It was observed that all the oxides studied crystallize in a single phase perovskite structure. This phase is stable up to annealing temperatures of 1373 K. The predominant electrical conduction mechanism was found to be small polaron hopping. Stable and fairly high electrical conductivities as well as seebeck coefficients accompanied with phase, structure, composition and microstructure stability indicate that these materials hold excellent promise for high temperature thin film thermocouple applications.
Master of Science

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34

Li, Junyue. „Perovskite thermoelectric materials for high-temperature energy conversion“. Thesis, Boston University, 2014. https://hdl.handle.net/2144/21206.

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Thesis (M.Sc.Eng.)
Despite of recent success in achieving the figure of merit ZT > 1 based on the nanoscale patterned thermoelectric structures, there have been few stable n-type materials with attractive thermoelectric responses for high temperature applications at T > 800K. In this thesis, we applied the first-principles density functional theory (DFT) calculations to probe the structure and thermoelectric properties relationship of a comprehensive series of perovskite materials. The density of states (DOS), Seebeck coefficient S, electric conductivity σ, and electronic contribution of the thermal conductivity Ke were obtained directly from the first-principles DFT calculations. In particular, Lanthanum (La), Gadolinium (Gd), Samarium (Sm), Yttrium (Y) doped MU+2093SrU+2081U+208BU+2093TiOU+2083 and Niobium (Nb) doped SrNbyTi1-yOU+2083 and doubly doped LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083 systems were studied. The change of the power factor S^2σ corresponding to the different dopant concentration had a good agreement with the experimental data. Our computed power factors S^2σ as a function of the dopant con- centration agree well with the available experimental data, and at the same time provide new insights for the optimal compositions. In the low doping region (x U+003E 12:5%), gadolinium and niobium are the best candidates of perovskite thermoelectric materials while at high doping level (x U+003E 25%), lanthanum and yttrium are the best options. In the case of doubly doped perovskites LaU+2093SrU+2081U+208BU+2093NbyTi1-yOU+2083, our calculations predict that the x= 12.5% and y= 12.5% is the best choice.

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35

Fang, Xiaojun. „Sapphire fiber based high temperature extensometer“. Master's thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-01262010-020150/.

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36

Wang, Cai Johnson R. Wayne. „High temperature high power SiC devices packaging processes and materials development“. Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/doctoral/WANG_CAI_24.pdf.

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37

Smith, Mark H. „Manufacture of a Dairy Dessert from Ultra-High Temperature Milk Concentrate“. DigitalCommons@USU, 1994. https://digitalcommons.usu.edu/etd/5424.

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The purpose of this project was to initiate development of a nonrefrigerated dairy dessert product. Milk was concentrated by pressure-driven filtration and then sterilized using ultra-high temperature (UHT) processing. Following sterilization, samples were aseptically inoculated with rennet to coagulate the milk, which was then stored at room temperature. These processing steps produced a dairy dessert that did not require refrigeration. I investigated the influence of total solids, milk fat, rennet dosage, storage temperature, and storage time on curd firmness and syneresis. I investigated the effect on curd firmness and syneresis of giving the concentrate a heat treatment prior to UHT processing. Chocolate and vanilla dairy desserts were prepared, and a taste panel was conducted to compare the dairy dessert with a ready-to- eat starch-based pudding. Milk concentrate obtained by reverse osmosis did not form a gel, whereas concentrate obtained by ultrafiltration did gel. Increasing the solids content of the milk concentrate increased curd firmness, but increasing the fat content of the concentrate decreased curd firmness. Curd firmness and syneresis increased as the concentration of rennet was increased. Products stored at 21°C yielded firmer gels with more syneresis than products stored at 4°C. Moreover, products stored for longer periods of time produced firmer gels and greater amounts of syneresis. Concentrate that received a batch heat treatment prior to sterilization reduced syneresis. The addition of cocoa to the concentrate inhibited coagulation. Taste panelists preferred the commercial pudding over the dairy

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38

Foroughi, Paniz. „Synthesis & Fundamental Formation Mechanism Study of High Temperature & Ultrahigh Temperature Ceramics“. FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3730.

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Borides and carbides of tantalum and hafnium are of great interest due to their ultrahigh temperature applications. Properties of these ceramics including oxidation resistance and mechanical properties might be further improved through solid solution/composite formation. Synthesis of single-phase TaxHf1-xC and TaxHf1-xB2 solid solution powders including nanopowders via carbothermal reduction (CTR) is complicated due to noticeable difference in reactivity of parent oxides with carbon, and also the low solubility of those oxides in each other. Moreover, for TaC-HfC system the solid solution may go through phase separation due to the presence of a miscibility gap at temperatures below 887°C.In this study, a method of low-cost aqueous solution processing followed by CTR was used to synthesize TaxHf1-xC and TaxHf1-xB2 solid solution powders. In fact, method was first used to synthesize boron carbide (B4C) powders as it paves the way for a detailed study on the synthesis of TaxHf1-xC and TaxHf1-xB2 solid solutions powders considering the fact that B4C contains both carbon and boron in its structure. Particular emphasis was given to investigate the influences of starting compositions and processing conditions on phase separation during the formation of both carbide and boride phase(s). It was found that individual TaC-HfC and TaB2-HfB2 phases always form quickly but separately during the CTR process (e.g., at 1600 °C within a few minutes). Those carbides and borides remain phase-separated unless heated to much higher temperatures for long time due to the slow inter-diffusion between them. It was also found that for TaxHf1-xC applying a DC electric field through the use of spark plasma sintering (SPS) system significantly accelerates the inter-diffusion of Ta and Hf leading to formation of a single-phase TaxHf1-xC solid solution at 1600 °C for 15 minutes. On the other hand, for borides alkali metal reduction reaction (AMR) method appears to be an excellent alternative to CTR-based method for formation of a single-phase TaxHf1-xB2 solid solution. In this method, chlorides of tantalum and hafnium are directly reduced using sodium borohydride (NaBH4) giving rise to formation of a single-phase Ta0.5Hf0.5B2 solid solution nanopowders in one step at much lower temperatures (e.g., 700 °C) by avoiding the oxides formation and the associated phase separation of individual borides as observed in the CTR-based process.

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39

Boontongkong, Yot. „Orientation of channel die-compressed ultra-high molecular weight polyethylene“. Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/46093.

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40

Chen, Xin. „High temperature performance of glass fabric/polyimide composites“. Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/11165.

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41

Liddicott, Katherine Mary. „High temperature materials chemistry of doped cerium oxide ceramics“. Thesis, Imperial College London, 1994. http://hdl.handle.net/10044/1/8619.

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42

Lawrie, David Dickson. „Isotope effects in high-temperature superconductors and related materials“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape9/PQDD_0033/NQ46870.pdf.

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43

Naylor, Matthew J. „Development of high temperature superconducting materials for power applications“. Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301420.

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44

Hudelson, George David Stephen III. „High temperature investigations of crystalline silicon solar cell materials“. Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/50568.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.
Includes bibliographical references (p. 74-78).
Crystalline silicon solar cells are a promising candidate to provide a sustainable, clean energy source for the future. In order to bring about widespread adoption of solar cells, much work is needed to reduce their cost. Herein, I discuss the development of a new experimental technique to investigate solar cell materials under simulated processing conditions. I present the first applications and results using this technique, including observations of novel impurity interactions at elevated temperatures, and discuss their importance to the solar cell manufacturing process. One of the key drivers for reducing solar cell cost is developing a fundamental understanding of the behavior of defect and impurities in solar cell materials. Since solar cell processing occurs at high temperatures, experiments are needed that allow characterization of solar cell materials at high temperatures representative of manufacturing conditions, at the length-scales of the defects that are present. To achieve this, I have developed a novel in situ high temperature sample stage for measuring samples via synchrotron-based X-ray microprobe. This technique allows for mapping and chemical state determination of metal impurity clusters on the order of 100 nm to 100 [mu]m, over sample areas of several square millimeters, at temperatures in excess of 1200°C and under controlled ambient atmosphere. The application of this technique has yielded novel insights concerning the behavior of metal impurities at high temperature.
(cont.) For the first time, the phenomenon of retrograde melting (i.e. melting on cooling) has been observed in a semiconductor material. Internal gettering of dissolved metal to liquid metal-silicon droplets within the silicon matrix is observed. Understanding of this phenomenon provides the potential to improve solar cell devices by reducing the more-detrimental dissolved metal content within the material by concentrating it into precipitates. Finally, I provide results and a model that explains the formation and resulting morphology of mixed-metal silicide precipitates in multicrystalline silicon.
by George David Stephen Hudelson, III.
S.M.

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Mazánová, Veronika. „Short Crack Growth in Materials for High Temperature Applications“. Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-409084.

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Pokročilá vysoce legovaná austenitická nerezová ocel Sanicro 25 s Fe-Ni-Cr matricí byla studována za podmínek nízkocyklové únavy za pokojové a vysoké teploty 700 °C. Široká škála moderních experimentálních technik byla použita ke studiu vzájemně souvisejících efektů chemického složení slitiny, mikrostrukturních změn a deformačních mechanismů, které určují odolnost materiálu vůči poškození. Hlavní úsilí bylo zaměřeno na studium iniciace únavových trhlin a růstu krátkých trhlin, tedy dvě stádia, která hrají zásadní roli ve výsledné celkové délce únavového života materiálu v provozu. • Vnitřní deformační mechanismy byly korelovány s vývojem povrchového reliéfu, který je pozorován ve formě persistentních skluzových stop na povrchu. Bylo zjištěno, že vysoce planární charakter dislokačního skluzu způsobuje vysokou lokalizaci cyklické plastické deformace do persistentních skluzových pásů, což v důsledku vede k nukleaci “Stage I” trhlin, která je spojena s přítomností persistentních skluzových stop na povrchu ve všech studovaných vzorcích. Bylo zjištěno, že praskání dvojčatových hraníc je taktéž spojeno s přítomností persistentních skluzových stop podél povrchové stopy dvojčatové roviny. • Interkrystalická iniciace únavové trhliny byla pozorována pouze zřídka, a to za podmínek zatěžování amplitudami vysoké deformace. Bylo zjištěno že interkrystalická iniciace je spojena s přítomností persistentních skluzových stop na hranicích zrn. Hranice zrn praskají za podmínek externího tahového zatížení zejména z důvodu vysokého počtu nekompatibilit na hranicích zrn, které jsou způsobené tvarem persistentních skluzových stop. • Mechanismy růstu přirozených krátkých trhlin byly studovány na vzorcích vystavených nízkocyklove únava s nízkou i vysokou deformací. Role mikrostruktury byla analyzována pomocí experimentálních technik a diskutována. • Rychlosti šíření nejdelších trhlin byly měřeny na vzorcích s mělkým vrubem. Výsledky byly analyzovány použitím přístupů lomové mechaniky založených na amplitudě KI a J-integrálu stejně jako na amplitudě plastické deformace. Všechny přístupy byly diskutovány v souvislosti s Mansonovými-Coffinovými křivkami únavové životnosti. Jednoduchý mocninový zákon růstu krátkých trhlin založený na amplitudě plastické deformace ukazuje velice dobrou korelaci se zákonem únavové životnosti. • Byla studována role oxidace v podmínkách cyklického zatěžování za vysokých teplot. Bylo zjištěno, že křehké praskání zoxidovaných hranic zrn hraje hlavní roli v počátečních stádiích nukleace trhlin. Později po iniciaci se dráha růstu trhliny mění preferenčně na transkrystalickou. Dráha šíření trhlin je velmi podobná dráze zjištěné při cyklování za pokojové teploty.

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46

Bateman, Joseph A. „High temperature fracture toughness of Cr-Mo-V welds“. Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/15025.

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47

Lee, Te-Hao. „Silicon Carbide High Temperature Logic“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1283437983.

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48

Peters, Sarah June. „Fracture Toughness Investigations of Micro and Nano Cellulose Fiber Reinforced Ultra High Performance Concrete“. Fogler Library, University of Maine, 2009. http://www.library.umaine.edu/theses/pdf/PetersSJ2009.pdf.

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49

Suckling, Martin Brian. „High temperature erosive wear of a boiler tube steel“. Doctoral thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/22485.

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This work is an attempt to evaluate the influence of critical operational parameters on the high temperature erosion of a 1Cr½Mo boiler tube steel. Erosion testing has been carried out in a specially designed and developed unique laboratory apparatus capable of simulating the conditions of temperature, particle velocity and flux as found in the economiser region of pulverised fuel boiler combustors in electricity generation power plants. The work has encompassed the effects of particle type, size, velocity and flux on the erosive wear rates of the 1Cr½Mo boiler tube steel at temperatures of up to 600°C. The response of the target to impacting erodent particles has been analysed using scanning electron and optical microscopy, transmission electron microscopy (TEM) as well as conducting cross-sectional microhardness tests. The change in the mechanical properties of the steel was determined by conducting tensile tests over a range of temperatures from 20°C to 565°C.

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50

Liu, Yi Johnson R. Wayne. „Packaging of silicon carbide high temperature, high power devices processes and materials /“. Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Spring/doctoral/LIU_YI_31.pdf.

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Dissertationen zum Thema „Ultra High Temperature Materials“

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