Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-04-28T15:47:19Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_RobertoAlécio_Digital.pdf: 2746118 bytes, checksum: 727a29b8a8ea3f688e67892861afbb5b (MD5) / Made available in DSpace on 2016-04-28T15:47:19Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese_RobertoAlécio_Digital.pdf: 2746118 bytes, checksum: 727a29b8a8ea3f688e67892861afbb5b (MD5) Previous issue date: 2015-11-13 / Uma previsão das propriedades mecânicas de sub-regiões da ZTA de uma junta soldada de aço API 5L X80 foi feita a partir de uma metodologia teórica e experimental. Para isso, foi utilizado um simulador termomecânico capaz de reproduzir ciclos térmicos com condições termodinâmicas de pontos discretos, semelhante à da ZTA de uma junta soldada produzida pelo processo GMAW, com um único passe, para comparação. No simulador termomecânico, três diferentes ciclos térmicos foram produzidos, a temperaturas de 900°C, 1000°C e 1100°C. Para cada temperatura foram produzidos três corpos de provas. As diferentes condições termodinâmicas impostas aos CPs reproduz a microestrutura de pontos ZTA de uma junta soldada. Em paralelo com a simulação, uma junta soldada do referido aço foi produzida para correlacionar a microestrutura de pontos discretos dessa junta. As amostras com a pseudo ZTA foram submetidos a ensaios mecânicos de tensão uniaxial e a caracterização microestrutural. Uma macrografia da ZTA da junta soldada foi realizada e esta, dividida em cinco sub-regiões e depois caracterizadas as microestruturas. As microestruturas das amostras simuladas foram comparadas com a microestrutura de ZTA das sub-regiões da junta soldada. Com base no valor das propriedades mecânicas das amostras simuladas e o tamanho do grão em ambas as microestruturas (soldada e simuladas) foram desenvolvidas um modelo numérico baseado na equação empírica de Hall-Petch, o que permitiu a determinação indireta da resistência ao escoamento de pontos discretos das sub-regiões do ZTA da junta soldada. / A prediction of the mechanical properties of the HAZ in sub-regions of a welded joint of API 5L X80 steel was made from a theoretical and experimental methodology. For this, it was used a thermomechanical simulator (TS) capable of reproducing thermal cycles with thermodynamic conditions of discrete points, similar to the HAZ of a real welded joint produced by GMAW, with a only pass, for comparations. In thermomechanical simulator, three different thermal cycles were produced at temperatures of 900°C, 1000°C and 1100°C. For each temperature three specimens were produced. The different thermodynamic conditions imposed on CPs reproduced microstructure of HAZ points of a welded joint. Parallel to the simulation, a welded joint of said steel was produced to facilitate the correlation between the microstructure of discrete points of this joint. The specimens with the so-called HAZ were subjected to mechanical tests in uniaxial tension and a microstructural characterization. A macrograph of the HAZ of the welded joint was made and divided into five sub-regions, later characterized microstructurally. The microstructures of the simulated test specimens were compared with the microstructure of HAZ sub-regions of the weld joint. Based on the value of the mechanical properties of the simulated test specimens and the grain size in both microstructures (Welded and simulated) was developed a numerical model based on the empirical equation of Hall-Petch, which enabled the indirect determination of the yield strength of discrete points of the sub-regions of the HAZ of the welded joint.

Orientador: Maria Isabel Felisberti / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-12T12:37:28Z (GMT). No. of bitstreams: 1 Lima_JulianaAristeiade_D.pdf: 4425741 bytes, checksum: e0c47d6335f66cc31a0fe6e5ac1c0457 (MD5) Previous issue date: 2008 / Resumo: Neste trabalho foram estudadas blendas de poli(etileno-co-álcool vinílico) (EVOH), um copolímero semicristalino que combina segmentos hidrofílicos e hidrofóbicos e poli(metacrilato de metila) (PMMA), um polímero amorfo e hidrofílico. As blendas de EVOH, com teor de etileno variando de 27 a 44 mol %, e PMMA foram preparadas por casting a partir de soluções em DMF, e por mistura mecânica em um mini-misturador, objetivando: i) avaliar o comportamento de fases e a morfologia das blendas, EVOH/PMMA, em função da composição das misturas, do teor de etileno nos copolímeros de EVOH e do método de preparação; ii) obter os diagramas de fases das soluções binárias, EVOH/DMF, e ternárias, EVOH/PMMA/DMF, através do processo de separação de fases induzido termicamente (TIPS). O comportamento de fases das blendas, EVOH/PMMA, foi estudado através de Calorimetria Diferencial de Varredura (DSC) e Análise Dinâmico-Mecânica (DMA). A morfologia das blendas foi investigada por Microscopia Eletrônica de Varredura (SEM). As blendas independentemente do modo de preparação e da composição são imiscíveis. Como conseqüência desta imiscibilidade, as temperaturas de fusão (Tf) e cristalização (Tc) não são afetadas pela presença de PMMA. A morfologia das blendas varia com a composição e método de preparação. As blendas obtidas pelo método mecânico são compactas, apresentando morfologia de fase dispersa em uma matriz, com inversão de fases em aproximadamente 50 % em massa de cada componente. As soluções binárias, EVOH/DMF, e ternárias, EVOH/PMMA/DMF, foram submetidas a ensaios para a determinação das temperaturas de turvamento (Tturv) por microscopia ótica, e de cristalização dinâmica (Tcd), por DSC. As soluções binárias apresentaram comportamento UCST (upper critical solution temperature), sendo que a separação de fases L-L ocorre a temperaturas superiores à separação de fases S-L. O modelo de interações binárias prevê que a curva de separação L-L para as soluções EVOH- 38/DMF esteja situada a temperaturas superiores em relação às soluções EVOH-32/DMF e indica que a separação de fases resulta da baixa afinidade entre segmentos hidrofóbicos do EVOH com os segmentos do polímero contendo hidroxila e com o solvente, DMF, concordando com os dados obtidos experimentalmente. Filmes de EVOH obtidos pela evaporação do solvente mostraram-se densos, sem a presença de poros. As soluções ternárias também apresentaram comportamento UCST, resultando em duas fases macroscópicas, F1 e F2, à temperatura ambiente. A composição destas fases foi determinada por Análise Termogravimétrica (TGA), e os resultados mostraram que uma das fases macroscópicas é rica em EVOH e outra fase é rica em PMMA. As blendas resultantes da secagem dos sistemas ternários apresentaram duas camadas: uma densa e rica em PMMA e outra porosa e rica em EVOH. A presença de PMMA foi decisiva à formação de estruturas porosas / Abstract: In this work blends of poly (ethylene-co-vinyl alcohol) (EVOH), a semicrystalline copolymer which combines hydrophobic and hydrophilic segments and poly (methyl methacrylate) (PMMA), an amorphous and hydrophilic polymer were studied. EVOH blends, with ethylene content ranging from 27 to 44 mol% and PMMA were prepared by casting from solutions in DMF, and by mixing into a mini-mixer, with the objective of: i) evaluate the phase behavior and the morphology of the blends, EVOH/PMMA, depending on the composition of mixtures, the ethylene contents in the copolymers of EVOH and the conditions of mixing; ii) obtain the phase diagrams of the binary and ternary solutions, EVOH/DMF and EVOH/PMMA/DMF, respectively, by the process of thermally induced phase separation (TIPS). The phase behavior of the blends, EVOH / PMMA, was investigated by Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Analysis (DMA). The morphology of the blends was investigated by Scanning Electron Microscopy (SEM). The blends independently of the method of preparation and of the composition are immiscible. As a result of immiscibility, the melting temperature (Tm) and the crystallization temperature (Tc) are not affected by the presence of PMMA. The morphology of the blends varies with the composition and with the method of preparation. The blends produced by the mechanical method is compact, showing morphology of dispersed phase in a matrix, with inversion of phases in about 50% by weight of each component. The binary solutions, EVOH-38/DMF and EVOH-32/DMF, were submitted to experiments to determine the cloud temperature (Tcloud) by optical microscopy, and the dynamic crystallization (Tcd), by DSC. The binary solutions show UCST behavior (upper critical solution temperature), and the L-L phase separation occurs at higher temperatures than the S-L phase separation. The binary interaction model provides the L-L line to the EVOH-38/DMF, solutions which was situated at higher temperatures than the EVOH-32/DMF solutions and indicates that the phase separation results from the low affinity between the hydrophobic segments of EVOH with the segments of the polymer containing hydroxyl and the solvent, DMF, which agrees with the data obtained experimentally. Films of EVOH obtained by the solvent evaporating seemed to be dense, without the presence of pores. The ternary solutions also had UCST behavior, resulting in two macroscopic phases, F1 and F2, at room temperature. The phase compositions were determined by Thermogravimetric Analysis (TGA), and the results showed that one of the macroscopic phases is rich in EVOH and the other phase is rich in PMMA. The blends resulting from drying of ternary systems had two layers: a dense and rich in PMMA and another porous and rich in EVOH. The presence of PMMA was crucial to the formation of porous structures / Doutorado / Físico-Química / Doutor em Ciências

Le but de ce travail de thèse est le développement d'un outil miniaturisé basé sur la millifluidique en goutte qui permet de synthétiser et d'étudier en toute sécurité des réactions de polymérisation dans des conditions difficiles ou «extrêmes».À cette fin, le réacteur de polymérisation a été réduit à la taille d'une gouttelette de quelques microlitres. A cette échelle, le microréacteurs goutte a un rapport surface sur volume plus élevé que ceux qui sont couramment obtenus avec des réacteurs discontinus classiques (~ 1500 par rapport à 10). Cette surface importante permet le transfert de chaleur efficace entre le milieu intérieur de la gouttelette (où la réaction chimique a lieu) et le milieu externe, qui est chimiquement inerte. Ici, contrairement à une approche monophasique, les caractéristiques clés d'une goutte miniaturisés permettent : (1) les gouttelettes de haute viscosité interne peuvent circuler normalement sans boucher le canal et (2) la dispersion due à la convection et la diffusion est éliminé car les réactifs sont compartimentées dans les gouttelettes. Comme toutes les gouttelettes se déplacent à la même vitesse, elles ne coalescent pas et il n'y a pas de distribution du temps de résidence. Ceci est particulièrement important étant donné que la viscosité dans des réactions de polymérisation peut augmenter à des milliers de centipoises ou même plus dans le cas des processus de gel.L'utilisation de gouttes comme microréacteurs circulant dans un tube chauffé (1/8’’ dext et 1/16’’ dint) peut permettre d’observer rapidement et en toute sécurité des réactions de polymérisation à différentes conditions. Nous avons choisi d'utiliser des conditions expérimentales où le processus de polymérisation est rapide et exothermique et/ou la viscosité peut être un problème. L'acide acrylique à faible pH et à concentrations élevées est donc un bon candidat pour obtenir un tel comportement. La composition des gouttelettes dépendant uniquement des débits, il est facile d’étudier différentes conditions expérimentales, y compris celles qui ne pouvaient pas être observées dans des réacteurs discontinus conventionnels (i.e. les concentrations de monomère et températures élevées, 40% massique et 90°C).Par ailleurs, couplé avec des systèmes appropriés d'analyse, des données cinétiques de base peuvent être obtenus en ligne à travers la paroi du tube transparent. En utilisant la spectrométrie Raman et l'équivalence temps-espace qui est spécifique à l'utilisation de dispositifs micro-et millifluidique à base de gouttes, nous avons été capables de suivre la conversion du monomère en fonction du temps. Ainsi, nous avons obtenu une cinétique d'ordre 4/3 en fonction de la concentration initiale en monomère et une demi-dépendance avec la concentration initiale de l'amorceur. Nous avons également pu mesurer une énergie d'activation globale de la vitesse de polymérisation entre 68°C et 90°C.En conclusion, la millifluidique et goutte semble être une approche prometteuse pour le criblage haut débit, l’analyse, et l’obtention de données cinétique de base en synthèse de polymères. / The aim of this thesis work is the development of a miniaturized droplet-based millifluidic tool which allows to safely synthesize and investigate polymerization reactions in harsh or “extreme” conditions.For this purpose, the polymerization reactor was reduced to the size of a droplet of a few microliters. At this scale, the droplet microreactor has a surface to volume ratio higher than those commonly obtained with conventional batch reactors (~1500 compare to 10). This important surface allows efficient heat transfer between the internal medium of the droplet (where the chemical reaction takes place) and the external one, which is chemically inert. Here, in contrast to single-phase flows, other key characteristics to a miniaturized droplet-based approach consist in: (1) droplets can manage high internal viscosity issues without plugging the channel and (2) dispersion due to convection and diffusion is eliminated because the reactants are compartmentalized within droplets. Since all droplets move at the same speed, they do not coalesce and there is no residence time distribution. This is particularly important since viscosity in polymerization reactions can increase to thousand of centipoises or even higher in the case of gel processes.The use of droplets as batch microreactors flowing within a heated tube (1/8 in. o.d. and 1/16 in. i.d.) can allow investigating quickly and safely polymerization reactions at different conditions. We choose to use experimental conditions where fast and exothermic polymerization process occurs and/or viscosity can be an issue. Acrylic acid at low pH and high concentrations is hence a good candidate to obtain such behavior. Since droplet composition depends only on flow rates, it was easy to screen different experimental conditions, including those which could not be used in conventional batch reactors (i.e., high monomer concentrations and temperatures; 40% w/v and 90 °C).Moreover, coupled with appropriate and sensitive analytical systems, basic kinetic data can be obtained in line through the wall of the transparent tube. By using Raman spectrometry and the time-space equivalence which is specific to the use of droplet-based micro- and millifluidic devices, we were capable to monitor molar conversions and monomer concentrations as a function of time. Thus, we verified the 4/3 order kinetics in initial monomer concentration and a 1/2 dependence in initial initiator concentration. We also able measured the overall activation energy for the rate of polymerization between 68°C to 90°C.In conclusion, droplet-based millifluidics seems to be a promising high throughput screening approach for investigating kinetics and possibly tailoring polymer properties.

Acrylamide is an undesirable carcinogenic component of thermally processed foods being formed from reducing saccharides and asparagine. In this work, the effect of ammonium and sodium raising agents themselves or in their combination with L-asparaginase enzyme catalyzing the conversion of asparagine into aspartic acid resulting in the reduction of acrylamide in gingerbreads was studied. Also, the influence of selected inorganic salts on the content of acrylamide in a model matrix simulating a composition of cereal products was observed. Simultaneously, the impact of these salts on activity of L-asparaginase was examined to find optimal conditions for its application in cereal technology. Based on experiments it was found, that addition of L-asparaginase reduces acrylamide content by 40 % while inorganic salts addition decreases acrylamide content in the range of 30 - 99 % when the most effective compounds were NH4Cl and CaCl2.

Acrylamide (AA) is a probable human carcinogen and undesirable contaminant which is produced by the reaction of reducing sugars with asparagine in plant foods during their thermal treatment above 120 °C. AA is most often determined by GC-MS and LC-MS/MS in isolates from the matrix in a wide range of foods. According to our observations, AA intake from food is higher among young people (from 1.8 to 3.8 µg/kg bw/day), which is consistent with the estimations of JECFA FAO/WHO from the year 2006. Considering the health risk, it is recommended to reduce AA formation in food during its processing, in particular exploiting the available experience. The aim of this thesis was to extend the knowledge of the possibility of AA elimination in selected types of thermally processed foods. The study was focused on cereal foods that contribute significantly to AA exposure, especially bread and sweet biscuits. The whole AA content in the bread is in the crust, which represents 5-15% of the bread. Crust of home-made bread contains approximately 30-75 µg/kg, however the marketed bread contains 2 to 10 times more of AA. This is due to the composition of bread mix, preparation conditions and baking. For maintaining the quality of home-made bread during the dry mixture shelf-life, optimization of bread mixtures was designed by increasing of yeast content, which proved positive effect on the reduction of AA content at sufficiently high activity of the yeast. Monitoring of AA content in assortment of sweet bakery products showed higher levels of AA in diabetic biscuits containing fructose instead of sucrose. Three of them even exceeded the reference value (500 µg/kg) more than 1.5 times for commodity "cookies". Elimination of AA by applications of the enzyme asparaginase has been designed for minimal interference in technology of their production. The concentration of the enzyme and the appropriate method of its use in industrial environment have been tested previously in model systems. In optimized conditions of the enzyme application, AA content in diabetic biscuits was reduced by more than 40% without affecting the organoleptic properties of the final product. Effect of the antioxidants on AA formation was also part of the study. AA content in gingerbread was reduced efficiently by the use of fennel, anise, cloves, vanilla and white pepper (by about 9-21%). Conversely, coriander and cinnamon significantly increased its content (by 18-54%). Since correlations between the DPPH• radical quenching activity of the spice extracts and AA content was not observed, the final content of AA was probably influenced by the chemical composition of spices and reactivity of the individual components in the matrix. Investigated methods appear to be suitable ways of elimination AA in some foods; however their specific use must be optimized with regard to the composition of the food, processing and the technology used. Estimated impact of application of the above-mentioned methods to the overall elimination of AA exposure showed that its intake in high school students from the Czech and Slovak Republic can be reduced on average by 10%. This decrease is a success to reduce the possible risk of cancer disease by eating foods with a high AA content. It is also important piece of information for food producers for further development of relevant methods for AA elimination which would help to reduce the AA intake from foods even more.

Die Bildung von Dampfphasen in Fernwärmesystemen während des instationären Übergangs vom Umlaufbetrieb in den Ruhezustand wird zugelassen, sofern adiabate Randbedingungen im Hochpunkt und thermisch gesteuertes Kondensationsverhalten der Dampfblase sichergestellt sind. Zur physikalischen Beschreibung wird ein Modell entwickelt, welches von einer zusammenhängenden Dampfblase im Hochpunkt ausgeht und das thermisch gesteuerte Rückbildungsverhalten während des Füll- bzw. Nachspeisevorganges abbildet. Die Rohrgeometrie im Hochpunkt sowie Wärmetransportvorgänge werden dabei berücksichtigt. Der Gesamtwärmeverlust aus dem Dampfraum setzt sich im Wesentlichen aus der Aufheizung der dampfbenetzten Rohrwand und der instationären Wärmeleitung in der angrenzenden Flüssigkeitsschicht zusammen. Mit Simulationsrechnungen werden das thermisch gesteuerte Blasenverhalten demonstriert und die Haupteinflussgrößen benannt. Die Verdichtung der Dampfmasse während des Füllvorgangs bewirkt einen Temperatur- und Druckanstieg in der Blase. Die Modellvalidierung erfolgt mit veröffentlichten Messdaten und anhand eines Versuches, welcher im Anlagenhochpunkt einer Fernwärmepumpstation durchgeführt wurde. Das Dampfvolumen im Versuch beträgt 30 m³. Die Temperatur-, Druck- und Füllstandsverläufe werden qualitativ und quantitativ wiedergegeben. Die Tolerierung der Dampfbildung erfordert die messtechnische Überwachung der Hochpunkte und eindeutige Handlungsanweisungen, wie im Störfall die Dampfblase zurückgebildet wird. / In district heating systems, the existence of vapour bubbles is tolerated during transition from regular heat supply to a non-operating state. The main requirements to ensure grid and plant safety are the adiabatic conditions within the pipe and the thermally controlled behaviour of the vapour bubble. For the description of the phenomenon, a model for the thermally controlled condensation phase of a concentrated vapour bubble is developed including the pipe geometry and heat losses. The total heat transfer consists of two main parts: the heating of the steel material wetted by the vapour and the unsteady heat conduction in the liquid water layer below the vapour. Test calculations demonstrate the behaviour of the vapour bubble, specifically the compression of the bubble contents and the accompanying increase in temperature and pressure. Furthermore, the main factors influencing the results are identified. Comparisons between simulation results and published measurement data show qualitatively and quantitatively good agreement. For the purpose of validation, own experiments with a large 30 m³ bubble were conducted in a pump station without any signs of condensation induced water hammer. The existence of vapour in district heating system requires measurements at the highest points within the grid in order to detect the vapour bubble and to monitor the condensation process safely. Furthermore, in case of pump failures or other incidents, operators need safety instructions on how to act to re-establish single phase flow before restarting heat supply.

Konventionelle Wärmedämmschichtensysteme bestehen aus einer Yttriumoxid-stabilisierten Zirkoniumdioxid-Deckschicht auf einer MCrAIY Haftschicht; wobei M für Co, Ni oder CoNi steht. Während der Nutzung bildet sich durch die Kombination von Wärme und Sauerstoff die Reaktionszone in der BC/TC-Grenzfläche. Diese Reaktionszone besteht aus thermisch wachsenden Übergangsmetalloxiden. In dieser Dissertation wurde das Phänomen der Bildung von TGO in TBC-Systemen betrachtet. Co32Ni21Cr8Al0.5Y Haftschichten wurden mithilfe des Verfahrens des atmosphärischen Plasmaspritzens (APS) auf Inconel 600 Substrate aufgebracht. Jm nächsten Schritt wurden durch DC-Magnetronsputter dünne Aluminumschichten auf die Oberfläche aufgetragen. Schließlich wurde YSZ TC mittels APS auf die Oberfläche gespritzt. Die beiden TBC-Systeme wurden zur Unterscheidung des Einflusses der thermischen Auslagerung unterschiedlich lange ausgelagert, um das thermochemischen Transformationsverhalten der Al-Zwischenschicht zu bestimmen. Die Schichtlebensdauer wurde unter thermischer Zyklierung mit einer definierten Verweilzeit untersucht. Das veränderte TBC-System mit der Al-Zwischenschicht (Al TBC) wurden mit dem TBC-System ohne Al-Zwischenschicht (R TBC) verglichen. Die Ergebnisse zeigen, dass das Hinzufügung der Al-Schichte in der BC/TC Grenzfläche nützlich für die Bildung der kontinuierlichen α Al2O3-Schicht während der Vorbereitungsphase der Wärmebehandlung ist. Diese dichte α Al2O3-Schicht bildet offensichtlich eine Durchgangsbarriere für den Sauerstoff während des Lebensdauertests. Dies hat Potential für die Verringerung der Bildung schädlicher Oxide. Der Ansatz ist nützlich für die Verlängerung der stabilen Wachstumsphase von TGO. In der Folge ermöglicht dies eine höhere Lebensdauer von Al-TBC-Systemen im Vergleich zu R-TBC-Systemen für die betrachteten thermischen Bedingungen und Zyklierungen.:Table of contents 1 Introduction 1 2 Motivation and overall interest 3 3 State of science and technology 5 3.1 Thermal barrier coating (TBC) systems 5 3.1.1 Substrate material 6 3.1.2 Ceramic top coating 6 3.1.3 Metallic bond coating 8 3.1.4 Thermally grown oxides (TGO) 12 3.1.5 Approaches on controlled TGO formation 15 3.1.6 Failure modes of TBC systems 17 3.2 Thermal spray technology 20 3.2.1 Atmospheric plasma spray (APS) technique 20 3.2.2 Formation sequence of the coating 21 3.2.3 Structure of the coating 22 3.3 Technology of thin layer deposition 23 3.4 Conclusions from the state of science and technology 24 4 Scientific objectives and work program 26 5 Experimental procedure 30 5.2 Material selection 30 5.3 Feedstock materials and thermal spray powders 32 5.4 Process selection 33 5.5 Specification of the scientific instruments 33 5.6 Detailed experimental procedure 34 5.6.1 Characterization of thermal spray powders 34 5.6.2 Preparation and characterization of overlaid coatings 35 5.6.3 Thermal treatment of TBC systems 39 5.6.4 Characterization of heat treated coating systems 40 5.6.5 Evaluation of TGO thickness and crack propagation 41 6 Results and discussions 43 6.1 Thermal spray powders and as sprayed coatings 43 6.1.1 Thermal spray powders 43 6.1.1.1 CoNiCrAlY thermal spray powder 43 6.1.1.2 ZrO2 – 8 %Y2O3 thermal spray powders 47 6.1.2 As-sputtered Al layer 50 6.1.2.1 Microstructure features 50 6.1.2.2 Elemental and phase composition analyses 50 6.1.3 As-sprayed coating systems 51 6.1.3.1 Bare and Al-covered CoNiCrAlY coatings 51 6.1.3.2 As-sprayed TBC systems 55 6.2 TBC systems after thermal treatment with different spans of dwell time 58 6.2.1 Thermal treatment with 5 and 30 min dwell time 58 6.2.2 Thermal treatment with 60 and 120 min dwell time 67 6.3 Lifetime test of TBC systems 68 6.3.1 Features in the cross section microstructure 68 6.3.2 Phase composition analyses 71 6.3.3 Elemental and Raman analyses 72 6.3.4 Features in the BC/TC of TBC systems after 80 thermal cycles 87 6.4 Thickness of TGO in the TBC systems 89 6.5 Length of cracks in the TC of the TBC systems 91 6.6 Relation between thickness of TGO and length of cracks 93 6.7 Discussion of loading condition and failure mode 95 6.8 Lifetime prediction of the TBC systems 97 6.9 Oxidation model of the TBC systems 98 7 Complementary work with discussion 100 7.1 Oxidation behavior of the TBC systems based on slow heating and cooling rates 100 7.1.1 Thickness of TGO and length of cracks 108 7.1.2 Raman analyses 112 7.1.3 Oxidation model of the TBC systems 116 7.2 Effect of Al content in the metallic coating 118 8 Complementary discussion 121 8.1 Effect of temperature on the oxidation behavior 121 8.2 Effect of deposition technique for metallic coating on the oxidation behavior 122 8.3 Effect of deposition technique for ceramic coating on the oxidation behavior 122 9 Summary and conclusion 124 10 References 128 / Conventional thermal barrier coating (TBC) systems consist of yttria-stabilized zirconia (YSZ) top coat (TC) on a MCrAlY bond coat (BC), where “M” stands for Co, Ni or CoNi. During their service under a combined heat and oxygen load, a reaction zone forms in the BC/TC interface. This reaction zone consists of thermally grown transition metal oxides (TGO). In the present thesis work, a phenomena related to the TGO formation is introduced. Co32Ni21Cr8Al0.5Y BC was overlaid by atmospheric plasma spraying (APS) technique on Inconel 600 substrates. Thin Al layers were deposited subsequently by DC-Magnetron sputtering on top. Finally, YSZ TC was sprayed by APS technique on the Al layers. The TBC systems were subjected to different thermal treatment procedures in order to investigate the thermo-chemical transformation behaviour of the Al-interlayer. The lifetime of the coatings was investigated under thermal cycling loading with dwell time. The altered TBC systems with Al interlayers (Al-TBC) were compared with the reference TBC systems without Al interlayers (R-TBC). The results show, that the addition of Al layers in the BC/TC interfaces is useful to form a continuous α-Al2O3 layer during the preliminary stage of heat treatment. The in-situ formed dense α-Al2O3 layer obviously acts as a diffusion barrier for oxygen during lifetime test. This has the potential to reduce the formation rate of detrimental oxides. This approach is beneficial to prolong the steady-state growth stage of the TGO, hence allows a higher lifetime for the Al-TBC systems in comparison to the R-TBC systems for the applied thermal loads.:Table of contents 1 Introduction 1 2 Motivation and overall interest 3 3 State of science and technology 5 3.1 Thermal barrier coating (TBC) systems 5 3.1.1 Substrate material 6 3.1.2 Ceramic top coating 6 3.1.3 Metallic bond coating 8 3.1.4 Thermally grown oxides (TGO) 12 3.1.5 Approaches on controlled TGO formation 15 3.1.6 Failure modes of TBC systems 17 3.2 Thermal spray technology 20 3.2.1 Atmospheric plasma spray (APS) technique 20 3.2.2 Formation sequence of the coating 21 3.2.3 Structure of the coating 22 3.3 Technology of thin layer deposition 23 3.4 Conclusions from the state of science and technology 24 4 Scientific objectives and work program 26 5 Experimental procedure 30 5.2 Material selection 30 5.3 Feedstock materials and thermal spray powders 32 5.4 Process selection 33 5.5 Specification of the scientific instruments 33 5.6 Detailed experimental procedure 34 5.6.1 Characterization of thermal spray powders 34 5.6.2 Preparation and characterization of overlaid coatings 35 5.6.3 Thermal treatment of TBC systems 39 5.6.4 Characterization of heat treated coating systems 40 5.6.5 Evaluation of TGO thickness and crack propagation 41 6 Results and discussions 43 6.1 Thermal spray powders and as sprayed coatings 43 6.1.1 Thermal spray powders 43 6.1.1.1 CoNiCrAlY thermal spray powder 43 6.1.1.2 ZrO2 – 8 %Y2O3 thermal spray powders 47 6.1.2 As-sputtered Al layer 50 6.1.2.1 Microstructure features 50 6.1.2.2 Elemental and phase composition analyses 50 6.1.3 As-sprayed coating systems 51 6.1.3.1 Bare and Al-covered CoNiCrAlY coatings 51 6.1.3.2 As-sprayed TBC systems 55 6.2 TBC systems after thermal treatment with different spans of dwell time 58 6.2.1 Thermal treatment with 5 and 30 min dwell time 58 6.2.2 Thermal treatment with 60 and 120 min dwell time 67 6.3 Lifetime test of TBC systems 68 6.3.1 Features in the cross section microstructure 68 6.3.2 Phase composition analyses 71 6.3.3 Elemental and Raman analyses 72 6.3.4 Features in the BC/TC of TBC systems after 80 thermal cycles 87 6.4 Thickness of TGO in the TBC systems 89 6.5 Length of cracks in the TC of the TBC systems 91 6.6 Relation between thickness of TGO and length of cracks 93 6.7 Discussion of loading condition and failure mode 95 6.8 Lifetime prediction of the TBC systems 97 6.9 Oxidation model of the TBC systems 98 7 Complementary work with discussion 100 7.1 Oxidation behavior of the TBC systems based on slow heating and cooling rates 100 7.1.1 Thickness of TGO and length of cracks 108 7.1.2 Raman analyses 112 7.1.3 Oxidation model of the TBC systems 116 7.2 Effect of Al content in the metallic coating 118 8 Complementary discussion 121 8.1 Effect of temperature on the oxidation behavior 121 8.2 Effect of deposition technique for metallic coating on the oxidation behavior 122 8.3 Effect of deposition technique for ceramic coating on the oxidation behavior 122 9 Summary and conclusion 124 10 References 128

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The discovery of the ferroelectric orthorhombic phase in doped hafnia films has sparked immense research efforts. Presently, a major obstacle for hafnia's use in high-endurance memory applications like nonvolatile random-access memories is its unstable ferroelectric response during field cycling. Different mechanisms are proposed to explain this instability including field-induced phase change, electron trapping, and oxygen vacancy diffusion. However, none of these is able to fully explain the complete behavior and interdependencies of these phenomena. Up to now, no complete root cause for fatigue, wake-up, and imprint effects is presented. In this study, the first evidence for the presence of singly and doubly positively charged oxygen vacancies in hafnia–zirconia films using thermally stimulated currents and impedance spectroscopy is presented. Moreover, it is shown that interaction of these defects with electrons at the interfaces to the electrodes may cause the observed instability of the ferroelectric performance.