In this study, the wear behaviour of a powder metallurgically produced AlCoCrFeNiTi0.5 high-entropy alloy (HEAs) is investigated at elevated temperatures. Spark plasma sintering (SPS) of inert gas atomised feedstock enables the production of dense bulk material. The microstructure evolution and phase formation are analysed. The high cooling rate in the atomisation process results in spherical powder with a microstructure comprising two finely distributed body-centred cubic phases. An additional phase with a complex crystal structure precipitates during SPS processing, while no coarsening of microstructural features occurs. The wear resistance under reciprocating wear conditions increases at elevated temperatures due to the formation of a protective oxide layer under atmospherical conditions. Additionally, the coefficient of friction (COF) slightly decreases with increasing temperature. SPS processing is suitable for the production of HEA bulk material. An increase in the wear resistance at elevated temperature enables high temperature applications of the HEA system AlCoCrFeNiTi0.5.

Ce manuscrit de thèse porte sur l'élaboration de nouveaux matériaux pour la protection balistique grâce à l'apport du procédé de frittage flash. Il s'agit, en effet, d'associer deux composés possédant des températures de frittage éloignées, tels que l'alumine et l'aluminium, matériaux de référence utilisés dans la protection balistique.La première voie testée était un assemblage bi-matériau, réalisé par frittage d'une poudre d'aluminium sur un plot d'alumine préalablement fritté. Cette étude a permis d'observer la formation de la liaison alumine/aluminium par microscopie électronique à balayage et en transmission et d'optimiser les paramètres d'assemblage pour l'obtention d'un bi-matériau possédant une forte cohésion interfaciale. Des outils de caractérisation adaptés (diffraction des rayons X et indentation Vickers) ont mis en évidence des contraintes résiduelles dans la céramique qui résultent de la différence de coefficients de dilatation thermique entre les deux composés lors du refroidissement du bi-matériau. Ces assemblages ont également fait l'objet d'essais statiques (essais de traction indirects) et d'essais dynamiques (tirs balistiques). Ces essais ont démontré la très grandec ohésion des assemblages et ont permis de valider la pertinence de l'étude de matériaux de protection balistique par des essais statiques, qui sont plus faciles à mettre en oeuvre.L'autre voie envisagée était de fritter en une seule étape un matériau à gradient de composition, de l'alumine pure à l'aluminium pur avec une interphase constituée de mélanges alumine/aluminium. D'un point de vue technique, le frittage flash a démontré sa capacité à générer un gradient de température de plusieurs centaines de degrés à l'intérieur d'un échantillon de quelques millimètres de haut, grâce à l'utilisation d'un moulede forme spécifique. Malheureusement, la mauvaise mouillabilité de l'alumine par l'aluminium n'a pas permis d'abaisser la température de frittage des mélanges alumine/aluminium par rapport à l'alumine pure. Elle a au contraire conduit à augmenter la température de frittage des mélanges de ~200 °C, empêchant l'élaboration du matériau à gradient de composition. Cette voie a tout de même permis l'élaboration de composites denses (>99 %) à matrice d'alumine avec de faibles quantités d'aluminium, de l'ordre de 5 % en masse.

In this thesis, the focus is on studying BaZrO3-BaCeO3 based proton conductors due to that they represent very promising proton conductors to be used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs). Here, dense BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) ceramics were selected as the major studied materials. These ceramics were prepared by different sintering methods and doping strategies. Based on achieved results, the thesis work can simply be divided into the following parts: 1) An improved synthesis method, which included a water-based milling procedure followed by a freeze-drying post-processing, was presented. A lowered calcination and sintering temperature for a Hf0.7Y0.3O2-δ (YSH) compound was achieved. The value of the relative density in this work was higher than previously reported data. It is also concluded that this improved method can be used for mass-production of ceramics. 2) As the solid-state reactive sintering (SSRS) represent a cost-effective sintering method, the sintering behaviors of proton conductors BaZrxCe0.8-xLn0.2O3-δ (x = 0.8, 0.5, 0.1; Ln = Y, Sm, Gd, Dy) during the SSRS process were investigated. According to the obtained results, it was found that the sintering temperature will decrease, when the Ce content increases from 0 (BZCLn802) to 0.3 (BZCLn532) and 0.7 (BZCLn172). Moreover, the radii of the dopant ions similar to the radii of Zr4+ or Ce4+ ions show a better sinterability. This means that it is possible to obtain dense ceramics at a lower temperature. Moreover, the conductivities of dense BZCLn532 ceramics were determined. The conductivity data indicate that dense BZCY532 ceramics are good candidates as either oxygen ion conductors or proton conductors used for ITSOFCs. 3) The effect of NiO on the sintering behaviors, morphologies and conductivities of BZCY532 based electrolytes were systematically investigated. According to the achieved results, it can be concluded that the dense BZCY532B ceramics (NiO was added during ball-milling before a powder mixture calcination) show an enhanced oxygen and proton conductivity. Also, that BZCY532A (NiO was added after a powder mixture calcination) and BZCY532N (No NiO was added in the whole preparation procedures) showed lower values. In addition, dense BZCY532B and BZCY532N ceramics showed only small electronic conductivities, when the testing temperature was lower than 800 ℃. However, the BZCY532A ceramics revealed an obvious electronic conduction, when they were tested in the range of 600 ℃ to 800 ℃. Therefore, it is preferable to add the NiO powder during the BZCY532 powder preparation, which can lower the sintering temperature and also increase the conductivity. 4) Dense BZCY532 ceramics were successfully prepared by using the Spark Plasma Sintering (SPS) method at a temperature of 1350 ℃ with a holding time of 5 min. It was found that a lower sintering temperature (&lt; 1400 ℃) and a very fast cooling rate (&gt; 200 ℃/min) are two key parameters to prepare dense BZCY532 ceramics. These results confirm that the SPS technique represents a feasible and cost-effective sintering method to prepare dense Ce-containing BaZrO3-BaCeO3 based proton conductors. 5) Finally, a preliminary study for preparation of Ce0.8Sm0.2O2-δ (SDC) and BZCY532 basedcomposite electrolytes was carried out. The novel SDC-BZCY532 based composite electrolytes were prepared by using the powder mixing and co-sintering method. The sintering behaviors, morphologies and ionic conductivities of the composite electrolytes were investigated. The obtained results show that the composite electrolyte with a composition of 60SDC-40BZCY532 has the highest conductivity. In contrast, the composite electrolyte with a composition of 40SDC-60BZCY532 shows the lowest conductivity. In summary, the results show that BaZrO3-BaCeO3 based proton-conducting ceramic materials represent very promising materials for future ITSOFCs electrolyte applications. / <p>QC 20150423</p>

Am Beispiel von ferroelektrischen Systemen auf Bismut-Basis (Bismutmolybdat, Bismutwolframat und Bismuttitanat) und von Strontiumbariumniobat werden neue Möglichkeiten zur Synthese solcher Nanopartikel aufgezeigt. Die Integration der Nanopartikel in transparente Nanokompositmaterialien und die Entwicklung neuer Precursoren für die Herstellung von Dünnschichtproben gehen den Untersuchungen zur Anwendung als elektrooptische aktive Materialien voraus. Durch weitere Anwendungsmöglichkeiten in der Photokatalyse, dem Test dampfadsorptiver Eigenschaften mit Hilfe eines neuartigen Adsorptionstesters (Infrasorb) und auch mit Hilfe der Ergebnisse der ferroelektrischen Charakterisierung von gesinterten Probenkörpern aus einem Spark-Plasma-Prozess wird ein gesamtheitlicher Überblick über die vielfältigen Aspekte in der Arbeit mit nanoskaligen, ferroelektrischen Materialien gegeben.

High hardness and good wear resistance have been revealed for the high-entropy alloy (HEA) system AlCoCrFeNiTi, confirming the potential for surface protection applications. Detailed studies to investigate the microstructure and phase formation have been carried out using different production routes. Powder metallurgical technologies allow for much higher flexibility in the customisation of materials compared to casting processes. Particularly, spark plasma sintering (SPS) enables the fast processing of the feedstock, the suppression of grain coarsening and the production of samples with a low porosity. Furthermore, solid lubricants can be incorporated for the improvement of wear resistance and the reduction of the coefficient of friction (COF). This study focuses on the production of AlCoCrFeNiTi composites comprising solid lubricants. Bulk materials with a MoS2 content of up to 15 wt % were produced. The wear resistance and COF were investigated in detail under sliding wear conditions in ball-on-disk tests at room temperature and elevated temperature. At least 10 wt % of MoS2 was required to improve the wear behaviour in both test conditions. Furthermore, the effects of the production route and the content of solid lubricant on microstructure formation and phase composition were investigated. Two major body-centred cubic (bcc) phases were detected in accordance with the feedstock. The formation of additional phases indicated the decomposition of MoS2.

[ES] Los avances tecnológicos se encuentran, en algunas ocasiones, limitados debido a la imposibilidad de combinar las excelentes prestaciones de los materiales conocidos con algunas funcionalidades críticas necesarias para desarrollar nuevas aplicaciones tecnológicas. Estos nuevos materiales con un diseño a la carta resultan extremadamente interesantes ya que permiten combinar propiedades y funcionalidades actualmente inalcanzables. La circona, u oxido de zirconio (ZrO2), es un sólido cristalino blanco con enlaces iónicos altamente estables que es principalmente obtenido en forma de polvo para aplicaciones tecnológicas. Debido a sus propiedades física y químicas, la circona es un material cerámico que posee una serie de características excepcionales, que incluyen una dureza, tenacidad y fractura relativamente altas en comparación con otros materiales cerámicos, bajo coeficiente de fricción y alto punto de fusión. Además, es un material relativamente no reactivo cuando se expone a ambientes húmedos y corrosivos en comparación con otros materiales como metales y polímeros, con buena resistencia a altas temperaturas y abrasión. Todas estas propiedades posicionan a la circona como un material muy versátil con un amplio espectro de aplicaciones que abarca intercambiadores de calor, celdas de combustible, componentes de turbinas para sistemas aeronáuticos y generación de electricidad, así como para medicina, odontología y otras aplicaciones. El propósito de esta tesis doctoral es la obtención de materiales base circona que puedan ser empleados en la fabricación de nuevos composites con funcionalidades a la carta en sectores tecnológicos como el transporte, energía, medicina, etc. Para ello se utilizarán técnicas de sinterización no-convencionales: Microondas (MW) y Spark Plasma Sintering (SPS). Para este trabajo se plantea el estudio de distintos composites base circona: circona reforzada con óxido de niobio (Nb2O5), Titania (TiO2) y composites de circona reforzados con manganita de lantano dopada con estroncio (LSM). El resultado final de esta investigación permitirá determinar si las técnicas rápidas de sinterización no-convencional, permiten mejoran las propiedades mecánicas, eléctricas y magnéticas de los materiales obtenidos en comparación con la sinterización por métodos convencionales. / [CA] Els avenços tecnològics són, en algunes ocasions, limitats per la impossibilitat de combinar l'excel·lent comportament dels materials coneguts amb algunes funcionalitats crítiques necessàries per desenvolupar noves aplicacions tecnològiques. Aquests nous materials amb disseny a la carta resulten summament interessants ja que permeten combinar propietats i funcionalitats actualment inabastables. La circonia, o òxid de zirconi (ZrO2), és un sòlid cristal·lí blanc amb enllaços iònics altament estables que s'obté principalment en forma de pols per a aplicacions tecnològiques. A causa de les seves propietats físiques i químiques, la zircònia és un material ceràmic que posseeix una sèrie de característiques excepcionals, que inclouen duresa, tenacitat i fractura relativament altes en comparació amb altres materials ceràmics, baix coeficient de fricció i alt punt de fusió. A més, és un material relativament no reactiu quan s'exposa a ambients humits i corrosius en comparació amb altres materials com metalls i polímers, amb bona resistència a altes temperatures i abrasió. Totes aquestes propietats posicionen a la zircònia com un material molt versàtil amb un ampli espectre d'aplicacions que inclou intercanviadors de calor, piles de combustible, components de turbines per a sistemes aeronàutics i generació d'electricitat, així com per a medicina, odontologia i altres aplicacions. L'objectiu d'aquesta tesi doctoral és l'obtenció de materials base de zircònia que puguin ser utilitzats en la fabricació de nous compòsits amb funcionalitats sota demanda en sectors tecnològics com transport, energia, medicina, etc. Per a això, s'utilitzaran tècniques de sinterització no convencionals utilitzat: microones (MW) i sinterització per plasma d'espurna (SPS) Per a aquest treball es proposa l'estudi de diferents composites a força de zircònia: zircònia reforçada amb òxid de niobi (Nb2O5), titanat (TiO2) i composites de zircònia reforçats amb manganita de lantani dopat amb estronci (LSM). El resultat final d'aquesta investigació permetrà determinar si les tècniques de sinterització ràpida no convencional permeten millorar les propietats mecàniques, elèctriques i magnètiques dels materials obtinguts en comparació amb la sinterització per mètodes convencionals. / [EN] Technological advances are, on some occasions, limited due to the impossibility of combining the excellent performance of known materials with some critical functionalities necessary to develop new technological applications. These new materials of great design are extremely interesting since they allow combining properties and functionalities currently unattainable. Zirconia, or zirconium oxide (ZrO2), is a white crystalline solid with highly stable ionic bonds that is mainly obtained in powder form for technological applications. Due to its physical and chemical properties, zirconia is a ceramic material that possesses several exceptional characteristics, including relatively high hardness, toughness and fracture compared to other ceramic materials, low coefficient of friction, and high melting point. Furthermore, it is a relatively non-reactive material when exposed to humid and corrosive environments compared to other materials such as metals and polymers, with good resistance to high temperatures and abrasion. All these properties position zirconia as a very versatile material with a wide spectrum of applications that includes heat exchangers, fuel cells, turbine components for aeronautical systems and electricity generation, as well as for medicine, dentistry, and other applications. The purpose of this doctoral thesis is to obtain zirconia base materials that can be used in the manufacture of new composites with on-demand functionalities in technological sectors such as transport, energy, medicine, etc. For this, non-conventional sintering techniques will be used: Microwaves (MW) and Spark Plasma Sintering (SPS) For this work, the study of different zirconia-based composites is proposed: zirconia reinforced with niobium oxide (Nb2O5), titania (TiO2) and zirconia composites reinforced with strontium-doped lanthanum manganite (LSM). The result of this research will make it possible to determine whether rapid non-conventional sintering techniques allow the mechanical, electrical, and magnetic properties of the materials obtained to be improved compared to sintering by conventional methods. / El autor agradece a la Generalitat Valenciana por la ayuda económica recibida para la beca del programa Santiago Grisolía (GRISOLIAP/2018/168) / Guillén Pineda, RM. (2021). Desarrollo de materiales cerámicos base circona sinterizados mediante técnicas rápidas no convencionales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/180231 / TESIS

Thermoelectric generators (TEG) are re-emerging technology that can be used to recover heat waste from commercial and industrial processes to generate electricity, enhancing fuel utilization and lowering greenhouse gas emissions. TEG modules are solid-state heat engines that produce no noise or vibration during operation. Notably, TEG modules are also able to operate at low-temperature differences, which makes them ideal for a wide range of heat waste recovery applications. Annular thermoelectric generator (ATEG) modules are optimal in applications where either the heat source or sink are round in shape. Bi2Te3 solution-based compounds are of significant interest in the application of thermoelectric materials (TE) used in low-temperature cooling and power generation applications. The main objective of the current work is to design a mechanically reliable ring-shaped ATEG module with a predictable performance using spark plasma sintered Bi2Te3 TE material for low temperature waste heat recovery applications. In terms of structure, this work is divided into two parts. The first part investigates how the use of a powder pre-treatment technique affects the mechanical and thermoelectric properties of P- and N-type Bi2Te3. In addition, part one also presents the measurements of these materials’ mechanical and thermoelectric properties, which serve as inputs for the finite element models used to design thermoelectric modules with parallel and perpendicular configurations vis-a-vis the sintering pressing direction. The second part evaluates the thermoelectric performance and thermal stresses of a ring-shaped ATEG couple that has been integrated between hot-side and cold-side heat exchangers. To this end, two configurations are compared with respect to their heat/electrical current flow paths: one that allows for radial flow (radial configuration), and one that allows for axial flow (axial configuration). The P- and N-type Bi2Te3 powder was treated using a mechanically agitated fluidized powder reduction facility that was built in-house. The characteristic uniaxial tensile strength of the P-type Bi0.4Sb1.6Te3 increased from 13.9 MPa to 26.3 MPa parallel to the sintering pressure, and from 16.3 MPa to 30.6 MPa perpendicular to the sintering pressure following oxide reduction using 5% H2 ˗ 95% Ar at 380 ℃ for 24 h. The figure of merit, ZT, increased from 0.35 to 0.80 and from 0.42 to 1.13 at room temperature (25 ℃) in the parallel and the perpendicular directions, respectively, after the surface oxide reduction treatment. On the other hand, the annealing effects of the oxide reduction pr-treatment of the N-type (Bi0.95 Sb0.05)2(Se0.05 Te0.95)3 using 5% H2 ˗ 95% Ar at 380 ℃ for 24 h were found to be responsible for the majority of the mechanical properties and ZT enhancement. Additionally, the characteristic uniaxial tensile strengths for this material increased from 30.4 to 34.1 MPa and from 30.8 to 38 MPa in the parallel and the perpendicular directions, respectively. The ZTmax (150 ℃) increased from 0.54 to 0.63 in both the parallel and perpendicular directions due to oxide reduction, while annealing led to an increase to 0.58 and 0.62 in the parallel and the perpendicular directions, respectively. An analytical model was constructed to compare the thermoelectric performance of the two configurations under three different hot-side thermal resistances, and a 3D coupled finite element ANSYS model was constructed to study and compare the thermal stresses of the two configurations at different dimensions. The two models were then used to create 2D maps in order to investigate the effects of ATEG couple configuration and dimensions, as well as the hot-side thermal resistance, with the goal of identifying the optimum design. The optimization of module geometry requires a trade-off between performance and mechanical reliability. The results of these investigations showed that increases in the temperature difference across the ATEG couple (ΔT) led to increases in both power and thermal stresses in both configurations. When both configurations were generating the same power at ΔT = 105 ℃, the thermal stresses in the radial configuration were as much as 67 MPa higher than those in the axial configuration due to the formation of additional tensile hoop stresses. The lowest thermal stress obtained for the axial couple configuration was 67.8 MPa, which was achieved when the couple had an outer diameter of 16 mm, an axial thickness of 1 mm, a ΔT of 14.8 ℃, and power generation of 10.4 mW per couple. The maximum thermal stress values were located at the corners of the interface between the solder and the TE rings due to the mismatched coefficient of thermal expansion. This thesis makes a novel contribution to the state-of-the-art literature in ring-shaped ATEG modules, as it details a well-characterised spark plasma sintered Bi2Te3 TE material and a methodology for designing a ring-shaped ATEG module with reliable, robust, and predictable thermoelectric and mechanical performance. The details of the contribution made by this work have been disseminated in the form of three journal publications, which have been integrated into this sandwich Ph.D. thesis. / Thesis / Doctor of Science (PhD)

L’amélioration des systèmes électroniques pour le déploiement de l'avion tout électrique dépend de la capacité des composants passifs, tels que les condensateurs, à réduire leur volume, leur masse et leur coût, et augmenter leurs performances et leur fiabilité, particulièrement dans l’environnement aéronautique. Dans ce contexte, cette thèse a eu pour objectif l’étude et le développement de nouvelles technologies de condensateurs pour des applications avioniques. Dans la première partie des travaux, nous abordons l’évaluation de condensateurs céramique de puissance. La technologie céramique constitue, en effet, l’une des rares solutions matures capables de répondre aux exigences des équipementiers. La caractérisation, l’analyse des mécanismes de défaillance, de leurs effets et de leur criticité (AMDEC) ainsi que l’étude de fiabilité et de robustesse de composants commerciaux présentant des architectures originales (condensateurs multi-chips) ont été réalisées. Ces résultats ont été complétés par une étude plus amont sur la caractérisation de céramiques frittées par frittage flash (SPS). Les permittivités colossales de ces matériaux permettraient d’accroitre la fiabilité et la miniaturisation des condensateurs tout en conservant de fortes valeurs de capacité et de tension nominale. La seconde partie, plus fondamentale, a été consacrée au développement de nanoparticules céramique/polymère coeur-écorce pour des applications de condensateurs enterrés, opérant aux radiofréquences. La synthèse et les caractérisations physico-chimiques des nanocomposites ainsi que les procédés de fabrication de condensateurs en couches épaisses sont, en premier lieu, décrits. Une méthode de caractérisation électrique large bande a été mise au point pour permettre l’analyse des propriétés diélectriques et des mécanismes de conduction des nanoparticules. Les performances des dispositifs ont été recherchées en fonction de la température et des procédés de mise en forme. En outre, la durabilité en température de ces derniers a été évaluée. / The improvement of electronic systems for the deployment of all-electric aircrafts depends on the ability of passive components, such as capacitors, to reduce their volume, weight and cost, and to increase their performance and reliability, particularly in the aeronautical environment. In this context, the objective of this thesis was to study and develop novel capacitor technologies for avionics. In the first part of this work, the evaluation of power ceramic capacitors has been discussed. Indeed, the ceramic technology appeared to be one of the few mature solutions meeting the requirements of OEMs. The characterization, the failure mode, effects and criticality analysis (FMECA) and reliability and robustness assessment of commercial components using original architectures (multi-chip capacitors) have been performed. These results have been completed by a more advanced study on the characterization of new ceramics sintered by spark plasma sintering (SPS). The colossal permittivity of these materials could allow to increase reliability and miniaturization of capacitors while maintaining high values of capacitance and voltage rating. The second part, more fundamental, is devoted to the development of core-shell ceramic/polymer nanoparticles for embedded capacitors operating at radiofrequencies. The synthesis and the physicochemical characterization of the nanocomposites as well as the manufacturing processes of the thick film capacitors are first described. A new broadband electrical characterization methodology has been developed to analyze the dielectric properties and the conduction mechanisms of the nanoparticles. The effects of the temperature and the manufacturing process on the device performance have been investigated. In addition, the durability was evaluated.

Am Beispiel von ferroelektrischen Systemen auf Bismut-Basis (Bismutmolybdat, Bismutwolframat und Bismuttitanat) und von Strontiumbariumniobat werden neue Möglichkeiten zur Synthese solcher Nanopartikel aufgezeigt. Die Integration der Nanopartikel in transparente Nanokompositmaterialien und die Entwicklung neuer Precursoren für die Herstellung von Dünnschichtproben gehen den Untersuchungen zur Anwendung als elektrooptische aktive Materialien voraus. Durch weitere Anwendungsmöglichkeiten in der Photokatalyse, dem Test dampfadsorptiver Eigenschaften mit Hilfe eines neuartigen Adsorptionstesters (Infrasorb) und auch mit Hilfe der Ergebnisse der ferroelektrischen Charakterisierung von gesinterten Probenkörpern aus einem Spark-Plasma-Prozess wird ein gesamtheitlicher Überblick über die vielfältigen Aspekte in der Arbeit mit nanoskaligen, ferroelektrischen Materialien gegeben.:Inhaltsverzeichnis...........................................................................................................5 Abkürzungsverzeichnis ...................................................................................................9 1. Motivation....................................................................................................................11 2. Stand der Forschung und theoretischer Teil ...............................................................14 2.1. Nanoskalige Materialien...........................................................................................15 2.1.1. Nanopartikel und Nanokompositmaterialien ....................................................... 15 2.1.2. Dünnschichten..................................................................................................... 21 2.1.3. Anwendungen in der Photokatalyse.................................................................... 22 2.1.4. Anwendungen in der Gas- und Dampfsensorik.................................................... 24 2.2. Ferroelektrika .........................................................................................................26 2.2.1. Bismutmolybdat................................................................................................... 32 2.2.2. Bismutwolframat.................................................................................................. 34 2.2.3. Bismuttitanat ....................................................................................................... 36 2.2.4. Strontiumbariumniobat......................................................................................... 37 2.3. Verwendete Methoden.............................................................................................40 2.3.1. Spark-Plasma-Sintering ........................................................................................40 2.3.2. Bestimmung ferroelektrischer Eigenschaften ...................................................... 42 2.3.3. Charakterisierung nichtlinearer, elektrooptischer Eigenschaften......................... 43 3. Experimenteller Teil ....................................................................................................51 3.1. Synthesevorschriften................................................................................................52 3.1.1. Verwendete Chemikalien und Substrate.............................................................. 52 3.1.2. Solvothermalsynthese von Bi2MO6 (M = Mo, W)................................................... 55 3.1.3. Phasentransfersynthese von Bi2MO6 (M = Mo, W)............................................... 56 3.1.4. Präparation von Bi2MO6/PLA Nanokompositmaterialien (M = Mo, W) ................... 57 3.1.5. Sol-Gel-Synthese von Bi2MO6 (M = Mo, W), Bi4Ti3O12 und Ba0.25Sr0.75Nb2O6 und Dünnschichten..................... 57 3.1.6. Mikroemulsionssynthese von Bi4Ti3O12 ............................................................... 59 3.1.7. Sol-Gel-Synthese von Bi2Ti2O7............................................................................. 60 3.1.8. Synthese von BiOH(C2O4), BiOCH3COO und Bi(CH3COO)3................................... 61 3.2. Vorschriften zur Durchführung und Charakterisierung...............................................62 3.2.1. Verwendete Geräte und Einstellungen ................................................................ 62 3.2.2. Spark Plasma Sintering von Bi2MO6 (M = Mo,W) und Bestimmung ferroelektrischer Eigenschaften ........................ 65 3.2.3. Prüfung elektrooptischer Eigenschaften, Präparation der Bauteile und Messaufbau .............................................. 67 3.2.4. Durchführung photokatalytischer Messungen ....................................................... 69 3.2.5. Messung der Dampfadsorption an Nanopartikeln mit Hilfe berührungsloser Detektion ........................................... 70 4. Ergebnisse und Diskussion...........................................................................................71 4.1. Synthese und Eigenschaften von nanoskaligen Materialien......................................72 4.1.1. Synthese von Bi2MO6 (M = Mo, W) Nanopartikeln................................................. 72 4.1.2. Nanokompositmaterialien mit Bi2MO6 (M = Mo, W)................................................ 81 4.1.3. Synthese der Bismuttitanate Bi4Ti3O12 und Bi2Ti2O7 .......................................... 84 4.1.4. Herstellung von Dünnschichten der Systeme Bi2MO6 (M = Mo, W), Bi4Ti3O12 und Sr0.75Ba0.25Nb2O6 ................. 88 4.2. Funktion der nanoskaligen Materialien .....................................................................100 4.2.1. Bismuthaltige Nanopartikel in der Photokatalyse ..................................................100 4.2.2. Spark-Plasma-Sintern von Bi2MO6-Nanopartikel (M = Mo, W)................................103 4.2.3. Elektrooptische Eigenschaften von Dünnschichten und Kompositmaterialien ............................................................108 4.2.4. Messung der Dampfadsorption an Bi2MO6 (M = Mo, W)-Nanopartikeln mit Hilfe berührungsloser Detektion ............114 4.3. Synthese von BiOH(C2O4), BiO(CH3COO) und Bi(CH3COO)3....................................118 5. Zusammenfassung ......................................................................................................127 6. Ausblick .......................................................................................................................131 7. Literatur ......................................................................................................................132 8. Abbildungs- und Tabellenverzeichnis ..........................................................................146 8.1. Abbildungsverzeichnis...............................................................................................146 8.2. Tabellenverzeichnis...................................................................................................152 9. Anhang ........................................................................................................................154 9.1. Synthese und Eigenschaften von nanoskaligen Materialien......................................155 9.1.1. Solvothermalsynthese von Bi2MO6 (M = Mo, W).....................................................155 9.1.2. Phasentransfersynthese von Bi2MO6 (M = Mo, W).................................................156 9.1.3. Synthese der Bismutmolybdate Bi4Ti3O12 und Bi2Ti2O7 .......................................156 9.1.4. Herstellung von Dünnschichten der Systeme Bi2MO6 (M = Mo, W), Bi4Ti3O12 und Sr0.75Ba0.25Nb2O6 .................159 9.2. Funktion der nanoskaligen Materialien ......................................................................164 9.2.1. Spark-Plasma-Sintern..............................................................................................164 9.2.2. Elektro-optische Eigenschaften von Dünnschichten und Kompositmaterialien .........................................................166 9.2.3. Messung der Dampfadsorption an Bi2MO6 (M = Mo, W)-Nanopartikeln mit Hilfe berührungsloser Detektion ...........174 9.3. Synthese von BiOH(C2O4), BiO(CH3COO) und Bi(CH3COO)3.....................................175 9.3.1. DTA-TG-Ergebnisse .................................................................................................175 9.3.2. Kristalldaten und Strukturverfeinerung ...................................................................177 9.4. Quelltexte ..................................................................................................................181 9.4.1. MATLAB-Skript zur Auswertung elektrooptischer Koeffizienten................................181 9.4.2. MATLAB-Skript zur Auswertung dampfadsorptiver Eigenschaften............................182

L'élaboration de composites à matrice céramique denses et à fibres continues multidirectionnelles par de nouveaux procédés hybrides a été étudiée. Les procédés développés reposent sur le dépôt d'interphases autour des fibres par Infiltration Chimique en phase Vapeur (CVI) puis sur l'introduction de poudres céramiques au sein de préformes fibreuses par infusion de suspensions aqueuses colloïdales concentrées et stables, et enfin sur la consolidation des préformes soit par frittage flash, soit par imprégnation réactive de métaux liquides.La consolidation des composites par frittage flash est très rapide (palier de maintien en température inférieure à 5 minutes) et permet d'obtenir des composites denses. Durant le frittage, la dégradation des fibres de carbone a pu être évitée en adaptant le cycle de pression afin de limiter l'évolution des gaz au sein du système.La densification totale des composites par imprégnation de métaux liquides a été obtenue en contrôlant attentivement les paramètres d'imprégnation afin d'éviter de piéger des espèces gazeuses au sein des préformes fibreuses.Les composites à fibres de carbone consolidés par frittage flash ou par imprégnation réactive de métaux liquide possèdent un comportement mécanique de type élastique endommageable ainsi qu'une contrainte à rupture en flexion voisine de 300 MPa. Ces composites ont montré leur capacité à s'autocicatriser dans des conditions oxydantes. Comparés aux composites à matrice céramiques élaborés par CVI, les composites densifiés par imprégnation de métaux liquide sont eux parfaitement denses et ont un comportement mécanique en traction à température ambiante similaire avec notamment une contrainte à rupture en traction de 220 MPa. / The fabrication of multidirectional continuous carbon fibers reinforced dense self healing Ceramic Matrix Composites by new short time hybrid processes was studied. The processes developed are based, first, on the deposition of fiber interphase and coating by chemical vapor infiltration, next, on the introduction of ceramic powders into the fibrous preform by Slurry Impregnation and, finally, on the densification of the composite by liquid-phase Spark Plasma Sintering (SPS) or by Reactive Melt Infiltration of silicon (RMI).The homogeneous introduction of the ceramic particles into the multidirectional fiber preforms was realized by slurry impregnation from highly concentrated (> 32 %vol.) and well dispersed aqueous colloid suspensions. The densification of the composites by spark plasma sintering was possible with a short (< 5 minutes) dwelling period in temperature. The chemical degradation of the carbon fibers during the fabrication was prevented by adapting the sintering pressure cycle to inhibit gas evolution inside the system. The composites elaborated are dense. The fully densification of the composites by RMI was realised by carefully controlling the impregnation parameters to avoid to entrap some gaseous species inside the fiber preforms. Our carbon fiber reinforced ceramic matrix composites processed by Spark Plasma Sintering or Reactive Melt Infiltration have a damageable mechanical behaviour with a room temperature bending stress at failure around 300 MPa and have shown their ability to self-healing in oxidizing conditions. Compared to the CMC processed by CVI, the composites processed with a final consolidation step by RMI are fully dense and have a similar room temperature tensile test behaviour with an ultimate tensile stress around 220 MPa.