京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18087号 / 理博第3965号 / 新制||理||1572(附属図書館) / 30945 / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)准教授 三宅 亮, 教授 土`山 明, 准教授 河上 哲生 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

<p dir="ltr">The technological drive of humanity to explore the cosmos, travel at hypersonic speeds, and pursue clean energy solutions requires ceramic scientists and engineers to constantly push materials to their functional, behavioral, and chemical extremes. Ultra-high temperature ceramics, and particularly transition metal carbides, are promising materials to meet the demands of extreme environment materials with their >4000 °C melting temperature and impressive thermomechanical behaviors in extreme conditions. The advent of the 2D version of these transition metal carbides, known as MXenes, added a new direction to design transition metal carbides for energy, catalysis, flexible electronics, and other applications. Toward extreme conditions, although MXenes remain yet unexplored, we believe that the ~1 nm flakes of MXenes gives ceramics scientists and engineers the ability to truly engineer transition metal carbides layer-by-layer at the nanoscale to endure the extreme conditions required by future harsh environment technology. Although MXenes have this inherent promise, fundamental study of their behavior in high-temperature environments is necessary to understand how their chemistry and 2D nature affects the high-temperature stability and phase behavior of MXenes toward application in extreme environments.</p><p dir="ltr">In this dissertation, we investigate the high-temperature phase behavior of 2D MXenes in high temperature inert environments to understand the stability and phase transition behavior of MXenes. In this work, we demonstrate that 1) MXenes’ transition at high-temperatures is to highly textured transition metal carbides is due to the homoepitaxial growth of these phases onto ~1-nm-thick MXenes’ highly exposed basal plane, 2) the MXene to MXene interface plays a major role in the phase behavior of MXenes, particularly toward building layered transition metal carbides using MXenes as ~1-nm-thick building blocks, and 3) Defects are the primary site at which atomic migration begins during phase transition of MXenes into these highly textured transition metal carbides, and these defects can be engineered for different phase stability of MXenes. To do so, we investigate the phase behavior of Ti₃C₂T_<em>x</em>, Ta₄C₃T_<em>x</em>, Mo₂TiC₂T_<em>x</em>, and other MXenes using a combination of <i>in situ</i> x-ray diffraction and scanning transmission electron microscopy and other <i>ex situ</i> methods, such as secondary ion mass spectrometry and x-ray photoelectron spectroscopy, with other methods. By investigating the fundamentals of the high-temperature phase behavior of MXenes, we hope to establish the basic principles behind use of MXenes as the ideal material for application in future extreme environments.</p>

Lithium triborate, (LiB3O5), is a technologically important material for diverse applications, such as nonlinear optical materials and surface acoustic wave devices or, etc. Furthermore, it is suggested as an efficient thermoluminescent material. LiB3O5, suitable to dosimetric usage, was produced by different synthesis methods which were high temperature solid state reaction, microwave solid state reaction, microwave assisted high temperature solid state reaction and precipitation assisted high temperature solid state reaction. After the synthesis, metal oxides were doped into LiB3O5 to enhance its thermoluminescent properties. Identification and characteristics of LiB3O5 were determined by X-ray diffraction (XRD), Fourier Transform Infra red (FTIR) analyses, Differential Thermal Analyses (DTA), Scanning Electron Microscopy (SEM) and Particle Size Analyzer. The glow curves were obtained by using thermoluminescent (TL) reader. Among four different synthesis methods applied, high temperature solid state method needs very high temperatures and long duration of heating. Therefore, the effect of the reaction temperature, the time intervals, and also starting materials on production of LiB3O5 were investigated. Characterization studies indicated that LiB3O5 could be produced at 710 &deg / C for 4 hours. Among the starting materials used, Li2CO3 and H3BO3 combination was found the most suitable for the synthesis of LiB3O5 considering phase impurity as well as cost. LiB3O5 synthesized by microwave energy was unsuccessful. However, LiB3O5 could be synthesized by microwave assisted synthesis method by adding distilled water, urea and sucrose separately as thermal auxiliaries in microwave pre-heating step. The use of microwave and conventional ovens subsequently shortened the duration of heating. The crystallinity of LiB3O5 was the best in 40 % sucrose addition to initial mixture. The best method for synthesis of LiB3O5 has been found as precipitation assisted high temperature solid state method. This method yields LiB3O5 with higher phase purity as compared to these produced by other methods applied in this thesis and reported in the literature. It seems to be rather attractive since it is simple and needs less energy. Rare earth metal oxides, CuO and Al2O3 were added to LiB3O5 as activators to improve its TL properties. LiB3O5 synthesized by precipitation assisted high temperature solid state reaction and doped by 5 % wt Al2O3 showed the best TL property. Its main dosimetric characteristics revealed that LiB3O5 seemed to be suitable to medical and radiotherapy applications, since it was non-toxic, tissue equivalent, and chemically inert to body fluids.

La résistance à l'écaillage d'un système barrière thermique est fonction de la composition et microstructure des matériaux constituant le système, ainsi que des procédés utilisés pour son élaboration. Cette thèse s'intéresse à l'influence d'une couche de platine déposée à la surface du dépôt NiCoCrAlYTa (sous-couche) sur le comportement en oxydation du système barrière thermique. Une étude approfondie est d'abord menée afin d'identifier les atouts et points faibles en oxydation cyclique d'un système comprenant un revêtement NiCoCrAlYTa. La formation d'une couche d'oxyde composée non exclusivement d'alumine et l'importante rugosité de la sous-couche, favorisant les défauts au sein de la barrière thermique, accélèrent l'écaillage de la barrière thermique. Parallèlement, la présence de carbures de tantale au sein du dépôt ne suffit pas à stopper le titane qui diffuse depuis le superalliage jusqu'à la couche d'oxyde et dégrade le système. Le platine ayant déjà démontré son effet très bénéfique sur les dépôts aluminures de nickel, il apparaît comme prometteur pour améliorer le comportement en oxydation du revêtement NiCoCrAlYTa. L'étude de son influence débute par une analyse fine de deux sous-couches NiCoCrAlYTa modifié platine : la première comprend un revêtement NiCoCrAlYTa obtenu par co-dépôt électrolytique, la seconde un dépôt NiCoCrAlYTa élaboré par projection plasma sous vide. Cette caractérisation, par diffraction des rayons X et microscopie électronique à balayage et en transmission, met en évidence la présence de martensite en surface du revêtement, conséquence de la diminution de l'activité de l'aluminium par le platine. Elle révèle également la forte influence du procédé utilisé pour l'élaboration du dépôt NiCoCrAlYTa sur la microstructure obtenue après le traitement thermique de diffusion. Des essais d'oxydation isotherme et de préoxydation sont ensuite réalisés sur la sous-couche dont le revêtement NiCoCrAlYTa est élaboré par co-dépôt électrolytique. Les couches d'oxydes formées sont analysées par diffraction des rayons X, spectroscopie Raman et fluorescence. Grâce à l'ajout de platine, qui entraîne l'augmentation de la teneur en aluminium dans la zone externe du revêtement, l'oxydation sélective de l'aluminium est favorisée. Cela se traduit par une diminution de la cinétique d'oxydation et une augmentation de la résistance à l'écaillage de la couche d'oxyde. Cependant, les carbures de tantale se décomposent lors du traitement thermique de diffusion puis lors de l'oxydation, laissant le titane libre de diffuser depuis le superalliage jusqu'à l'oxyde. De l'oxyde de titane est en effet détecté par spectroscopie Raman en petite quantité dans de la couche d'oxyde (avec l'AM3 comme substrat). Un autre point important sur la composition du superalliage est la présence d'élément réactif qui permet de diminuer la croissance de la couche d'oxyde. Concernant les essais de préoxydation, les résultats obtenus indiquent la nécessité d'une faible pression partielle d'oxygène afin de promouvoir la formation d'alumine-a. Le platine, quant à lui, ne favorise pas la formation d'alumine de transition. Des essais d'oxydation cyclique sur des systèmes barrière thermique sont ensuite menés. L'effet bénéfique du platine sur l'oxydation sélective de l'aluminium est confirmé, ce qui entraîne une augmentation de la durée de vie en cyclage. Cependant, la décomposition des carbures de tantale est de nouveau observée. Une diffusion très importante de titane depuis le superalliage jusqu'à l'oxyde est ainsi notée pour les systèmes barrière thermique comprenant une sous-couche modifiée platine avec un dépôt NiCoCrAlYTa obtenu par projection plasma sous vide. Dans le cas de système avec une sous-couche modifiée platine comprenant un dépôt NiCoCrAlYTa élaboré par co-dépôt électrolytique, le problème majeur est la présence de pores en surface et d'une certaine porosité à l'intérieur du revêtement. L'oxydation des pores en surface ainsi que le cyclage thermique provoque la pénétration de l'oxyde puis sa propagation catastrophique dans le revêtement. Les résultats obtenus permettent de dégager les points importants de l'élaboration d'un système barrière thermique. Il est alors recommandé que le superalliage contienne un élément réactif mais peu de titane. Le dépôt NiCoCrAlYTa nécessaire à la fabrication de la sous-couche doit être dense et la préparation de surface, avant et après le dépôt de platine, doit permettre d'obtenir une faible rugosité de surface avant le dépôt de la barrière thermique. Enfin, les paramètres (température, pression partielle d'oxygène, sablage) lors de la première oxydation du système doivent être contrôlés de manière à favoriser la formation d'alumine-a. / The resistance to spallation of a thermal barrier coating system depends on the composition and the microstructure of the materials constituting the system, as well as on the processes used for its manufacturing. This PhD is interested in the influence of a Pt layer deposited on the surface of the NiCoCrAlYTa coating (bond coating) on the oxidation behavior of the thermal barrier coating system. A thorough study is first carried out in order to define the assets and the weak points under cyclic oxidizing conditions of a system composed of a NiCoCrAlYTa coating. The formation of an oxide layer not only composed of alumina and the great roughness of the bond coating, favoring defects within the thermal barrier, speed up the thermal barrier spallation. At the same time, the presence of tantalum carbides within the coating is not sufficient to prevent titanium from diffusing from the bond coating toward the oxide layer and from degrading the system. Platinum having already demonstrated its beneficial effect on nickel aluminide coatings, it seems promising in order to improve the oxidation resistance of the NiCoCrAlYTa coating. The study of its influence starts by a thorough analyses of two Pt-modified NiCoCrAlYTa bond coatings: the first one is composed of a NiCoCrAlYTa coating made by composite electroplating, the second one is composed of a NiCoCrAlYTa coating manufactured by vacuum plasma spray. This characterization, done using X-ray diffraction and secondary and transmission electron microscopy, highlights the presence of martensite at the coating surface, consequence of the decrease in the aluminium activity by platinum. It also reveals the strong influence of the process used to manufacture the NiCoCrAlYTa coating on the microstructure obtained after diffusion heat treatment. Preoxidation and isothermal oxidation tests are then carried out on the systems for which the NiCoCrAlYTa coating is made by composite electroplating. The oxide layers that formed are analyzed by X-ray diffraction, Raman spectroscopy and fluorescence. With Pt addition, that leads to an increase in the aluminium concentration in the external part of the coating, the selective oxidation of aluminium is favored. This results in a decrease in the oxidation kinetics and an increase in the resistance to spallation of the oxide layer. However, tantalum carbides decompose during the diffusion heat treatment and then during the oxidation, making the titanium free to diffuse from the superalloy toward the oxide. Indeed, titanium oxide is identified in small quantity in the oxide layer by Raman spectroscopy (with AM3 as substrate). Another relevant point on the superalloy composition is the presence of reactive elements that leads to a decrease in the oxide layer growth. Concerning the preoxidation tests, the obtained results indicate the necessity of a low oxygen partial pressure so as to promote the a-alumina formation. As for platinum, it does not favor the formation of transient alumina. Cyclic oxidation tests on thermal barrier coating systems are then carried out. The beneficial effect of platinum on the selective oxidation of aluminum is confirmed, that leads to longer lifetimes under thermal cycling. However, the tantalum carbides decomposition is observed once again. A great titanium diffusion from the superalloy toward the oxide is noticed for the thermal barrier coating systems composed of a platinum modified bond coating with a NiCoCrAlYTa deposit made by vacuum plasma spraying. In the case of systems composed of a Pt modified bond coating with a NiCoCrAlYTa deposit manufactured by composite electroplating, the main issue is the presence of pores at the surface and of a porosity within the coating. The pores oxidation at the surface as well as the thermal cycling result in the oxide penetration and then its disastrous propagation within the coating. The obtained results reveal the relevant points concerning the manufacturing of thermal barrier coating systems. It is recommended to use a reactive element containing superalloy that has very little titanium. The NiCoCrAlYTa coating required for the bond coating manufacturing has to be dense and the surface preparation, before and after the Pt deposit, has to lead to a surface with a low roughness before the deposition of the thermal barrier coating. Finally, the parameters during the first oxidation of the system (temperature, oxygen partial pressure, grit blasting), has to be done in order to favor a-alumina formation.

Aluminium smelting is a high temperature electrometallurgical process, which suffers considerable inefficiencies in power utilization and equipment maintenance. Aluminium smelting cell works in the extreme environments that contain extraordinarily aggressive gases, such as HF, CO and SO2. Mild steel used as a structural material in the aluminium industry, can be catastrophically corroded or oxidized in these conditions. This project was mainly concerned with extending the lifetime of metal structures installed immediately above the aluminium smelting cells. An aluminium-rich coating was developed on low carbon steel A06 using pack cementation technique. Yttria (Y2O3) was also used to improve the corrosion resistance of coating. Kinetics of the coating formation were studied. XRD, FESEM and FIB were employed to investigate the phase constitution and the surface morphology. Together with other potentially competitive materials, aluminium-rich coating was evaluated in simulated plant environments. Results from the long time (up to 2500h) isothermal oxidation of materials at high temperature (800??C) in air showed that the oxidation resistance of coated A06 is close to that of stainless steel 304 and even better than SS304 in cyclic oxidation tests. Coated A06 was also found to have the best sulfidation resistance among the materials tested in the gas mixture contains SO2 at 800??C. Related kinetics and mechanisms were also studied. The superior corrosion resistance of the coated A06 is attributed to the slow growing alpha-Al2O3 formed. Low temperature corrosion tests were undertaken in the gas mixtures containing air, H2O, HCl and SO2 at 400??C. Together with SS304 and 253MA, coated A06 showed excellent corrosion resistance in all the conditions. The ranking of the top three materials for corrosion resistance is: 253MA, coated A06 and SS304. It is believed that aluminised A06 is an ideal and economical replacement material in the severe corrosive aluminium smelting cell environment.

In this experimental investigation, the tensile creep behavior of commercial-purity molybdenum sheet at temperatures between 1300°C and 1700°C is critically evaluated, based upon experimental creep testing and microstructural characterizations. The high-temperature properties of molybdenum are of interest because there are many applications in which molybdenum and molybdenum alloys are used at elevated temperatures. Understanding of the creep mechanisms and the constitutive relations between stress and strain at elevated temperatures is needed in order to determine if molybdenum is an appropriate choice for a given high-temperature design application and to accurately predict its creep life. The creep behavior of two commercially-available grades of molybdenum was determined using short-term creep tests (1/2 to 14 hours) at slow to moderate true-strain rates of 10⁻⁶ to 10⁻⁴ s⁻¹ and temperatures between 1300°C and 1700°C. High-temperature, uniaxial tensile testing was used to produce data defining the relationship between tensile creep strain-rate and steady-state flow stress at four temperatures: 1340°C, 1440°C, 1540°C, 1640°C. Microstructural changes that occurred during creep testing were evaluated and compared to changes resulting from elevated temperature exposure alone. Mechanisms for dynamic abnormal grain growth that occurred during creep testing and the causes of the microstructural changes that occurred as a function of temperature are discussed. / text

Due to the extreme operating conditions present in the combustion sections of gas turbines, designers have relied heavily on specialized engineering materials. For blades, which must retain substantial strength and resistance to fatigue, creep, and corrosion at high temperatures, directionally-solidified (DS) nickel-base superalloys have been used extensively. Complex thermomechanical loading histories makes life prediction for such components difficult and subjective. Costly product inspection and refurbishment, as well as capital expense required in turbine forced outage situations, are significant drains on the resources of turbine producers. This places a premium on accurate endurance prediction as the foundation of viable long-term service contracts with customers. In working towards that end, this work characterizes the behavior of the blade material CM247LC DS subjected to a variety of in-phase (IP) and out-of phase (OP) loading cycles in the presence of notch stress concentrations. The material response to multiaxial notch effects, highly anisotropic material behavior, time-dependent deformation, and waveform and temperature cycle characteristics is presented. The active damage mechanisms influencing crack initiation are identified through extensive microscopy as a function of these parameters. This study consisted of an experimental phase as well as a numerical modeling phase. The first involved conducting high temperature thermomechanical fatigue (TMF) tests on both smooth and notched round-bar specimens to compile experimental results. Tests were conducted on longitudinal and transverse material grain orientations. Damage is characterized and conclusions drawn in light of fractography and microscopy. The influences of microstructure morphology and environmental effects on crack initiation are discussed. The modeling phase utilized various finite element (FE) simulations. These included an anisotropic-elastic model to capture the purely elastic notch response, and a continuum-based crystal visco-plastic model developed specifically to compute the material response of a DS Ni-base superalloy based on microstructure and orientation dependencies. These FE simulations were performed to predict and validate experimental results, as well as identify the manifestation of damage mechanisms resulting from thermomechanical fatigue. Finally, life predictions using simple and complex analytical modeling methods are discussed for predicting component life at various stages of the design process.

Aluminium smelting is a high temperature electrometallurgical process, which suffers considerable inefficiencies in power utilization and equipment maintenance. Aluminium smelting cell works in the extreme environments that contain extraordinarily aggressive gases, such as HF, CO and SO2. Mild steel used as a structural material in the aluminium industry, can be catastrophically corroded or oxidized in these conditions. This project was mainly concerned with extending the lifetime of metal structures installed immediately above the aluminium smelting cells. An aluminium-rich coating was developed on low carbon steel A06 using pack cementation technique. Yttria (Y2O3) was also used to improve the corrosion resistance of coating. Kinetics of the coating formation were studied. XRD, FESEM and FIB were employed to investigate the phase constitution and the surface morphology. Together with other potentially competitive materials, aluminium-rich coating was evaluated in simulated plant environments. Results from the long time (up to 2500h) isothermal oxidation of materials at high temperature (800??C) in air showed that the oxidation resistance of coated A06 is close to that of stainless steel 304 and even better than SS304 in cyclic oxidation tests. Coated A06 was also found to have the best sulfidation resistance among the materials tested in the gas mixture contains SO2 at 800??C. Related kinetics and mechanisms were also studied. The superior corrosion resistance of the coated A06 is attributed to the slow growing alpha-Al2O3 formed. Low temperature corrosion tests were undertaken in the gas mixtures containing air, H2O, HCl and SO2 at 400??C. Together with SS304 and 253MA, coated A06 showed excellent corrosion resistance in all the conditions. The ranking of the top three materials for corrosion resistance is: 253MA, coated A06 and SS304. It is believed that aluminised A06 is an ideal and economical replacement material in the severe corrosive aluminium smelting cell environment.

Orientador: José de Assis Fonseca Faria / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-18T02:06:39Z (GMT). No. of bitstreams: 1 Cardoso_ClaudioFernandes_D.pdf: 26277698 bytes, checksum: d17c520e85b9389e672d2641e795333d (MD5) Previous issue date: 2011 / Resumo: Esta pesquisa teve como objetivo avaliar o desempenho de um sistema asséptico piloto para a produção de leite UHT (Ultra Hight-Temperature), com capacidade de 1.000 L/h, em embalagens flexíveis institucionais do tipo Bag-in-box (BIB). As embalagens estudadas eram compostas de um filme de polietileno de baixa densidade (PEBD) e um filme de polietileno tereftalato metalizado (PETmet), com volume de 2.000 mL, desenvolvido especialmente para o envase asséptico de produtos lácteos. Leite cru refrigerado tipo A foi utilizado como matéria-prima. O envase do leite UHT foi realizado através de uma dosadeira semi-automática dentro de uma Sala Limpa ISO posicionada sobre o bocal de enchimento das embalagens. O sistema foi avaliado através da identificação e monitoramento de pontos de controle do processo, testes de esterilidade comercial, análises sensorial e físico-química do produto, bem como avaliações da embalagem. O desempenho das embalagens BIB foi avaliado através de ensaios de caracterização, integridade do sistema e estudos de estabilidade microbiana e testes de efetividade de esterilização. As embalagens foram esterilizadas com o uso de radiação ionizante (gama), com dose de 15 kGy. Os ensaios foram conduzidos através da produção de 4 lotes experimentais de leite UHT, obtido em trocador de calor a placas (140 °C por 5 s). A taxa de defeito encontrada nos testes de esterilidade comercial variou entre 0 e 6,7%, sendo que a principal causa de defeitos foi associada aos problemas inerentes a operacionalidade da linha, como falhas nas vedações das junções de tubulações e bombas centrífugas. Os resultados da avaliação dos pontos de controle do processo e embalagem indicaram um bom desempenho do sistema, justificado pela ausência de microorganismos viáveis. O leite UHT acondicionado nas embalagens BIB teve sua vida de prateleira estimada em até 27 semanas de estocagem, valor este muito superior quando comparado às amostras controle de leite UHT comercial, acondicionado em embalagens laminadas cartonadas, que teve sua vida de prateleira estimada em 19 semanas. A diferença de estabilidade físico-química, microbiológica e sensorial entre as amostras processadas e a comercial foi associada às propriedades de barreira das estruturas das embalagens à luz e ao oxigênio, bem como pela qualidade da matéria-prima utilizada. O sistema asséptico piloto avaliado correspondeu às expectativas de desempenho e atendeu aos requisitos estabelecidos pelo Codex Alimentarius. Concluiu-se que o sistema apresenta potencial para utilização por indústrias de laticínios visando atender o mercado institucional de leite longa vida / Abstract: The aim of this research was to evaluate the performance of an aseptic pilot system for the production of Ultra High Temperature (UHT) milk, with 1.000 L/h capacity, filled in flexible institutional packages Bag-in-box (BIB) type. The BIB packages were constructed with one layer of low density polyethylene film (LDPE) and another one of metalized polyethylene terephthalate film (PETmet), with 2.000 mL capacity, specially developed for the aseptic filling of dairy products. Type-A milk was used as raw material and the UHT milk filling was made by a semiautomatic machine located inside a ISO Clean room. The system was evaluated by the identification and monitoring of the control points during the process and also by commercial sterility tests, sensorial and physical-chemistry analysis and packages evaluations. The BIB packages were sterilized by gamma radiation with minimum doses of 15 kGy. The assays were conducted by the production of 4 experimental batches processed in a plate heat exchanger (140 °C/5 s). The defect rates founded were between 0 and 6.7% and these values can be explained by problems linked to the pilot plant operation, like failures in the connections of pipes and centrifugal pumps. The results of the control points evaluation and also BIB packages showed a good performance of the entire process, justified by the absence of viable microorganisms. The milk filled in BIB packages targeted until 27 weeks of shelf life, a superior value when it was compared to the commercial UHT samples, which targeted just 19 weeks. The difference of physical-chemistry, microbiology and sensory stability between the processed samples and the commercial one was associated to the oxygen and light barriers properties and also to the raw milk quality used during the processes. The pilot aseptic system evaluated attended to the Codex Alimentarius requirements and it could be concluded that the system showed potential for application in dairy industry in view of the long life milk institutional market / Doutorado / Tecnologia de Alimentos / Doutor em Tecnologia de Alimentos

Hypersonic aerospace vehicles are severely limited by the lack of adequate high temperature materials that can withstand the harsh hypersonic environment. Tantalum carbide (TaC), with a melting point of 3880°C, is an ultrahigh temperature ceramic (UHTC) with potential applications such as scramjet engines, leading edges, and zero erosion nozzles. However, consolidation of TaC to a dense structure and its low fracture toughness are major challenges that make it currently unviable for hypersonic applications. In this study, Graphene NanoPlatelets (GNP) reinforced TaC composites are synthesized by spark plasma sintering (SPS) at extreme conditions of 1850˚C and 80-100 MPa. The addition of GNP improves densification and enhances fracture toughness of TaC by up to ~100% through mechanisms such as GNP bending, sliding, pull-out, grain wrapping, crack bridging, and crack deflection. Also, TaC-GNP composites display improved oxidation behavior over TaC when exposed to a high temperature plasma flow exceeding 2500 ˚C.