No presente trabalho foram desenvolvidos compósitos à base de alumina, com adição de carbetos de metais de transição, NbC, TaC e TiC, como reforço. Os carbetos, na forma de partículas, foram adicionados em 1,5% em volume à matriz de alumina durante a moagem em attritor. O processamento foi realizado por moagem em attritor, secagem em rotoevaporadora e desaglomeração em peneira. A dinâmica de oxidação dos carbetos e das composições dos compósitos foi estudada para a definição de parâmetros de sinterização e processamento dos compósitos. A cinética de sinterização foi estudada por dilatometria, com taxa de 10°C/min. até 1600°C em atmosfera de ar sintético, e até 1800°C, em atmosfera de argônio, com esta etapa foi possível verificar que o NbC e o TiC dificultaram a sinterização da alumina e que o TaC auxiliou nos processos de retração. Nas amostras que foram sinterizadas em dilatômetro ao ar foram detectadas fases resultantes de fusão congruente nos compósitos Al2O3/NbC e Al2O3/TaC, foram também observadas evidências de formação de líquido no compósito com adição de TaC. Com base nesses resultados foram estudadas duas técnicas de produção das ferramentas de corte: prensagem uniaxial seguida de sinterização sem pressão e sinterização por prensagem a quente. Todas as amostras foram caracterizadas microestruturalmente e quanto às propriedades mecânicas, tendo-se determinado que as amostras produzidas por prensagem a quente possuem microestrutura mais controlada e propriedades mecânicas superiores às produzidas por sinterização sem pressão. Pelos processos estudados foi observado que os carbetos influenciam diferentemente a sinterização da alumina. De maneira geral a presença destas fases nos contornos de grãos promove alterações na microestrutura modificando o tamanho de grãos da alumina. Foi proposta a hipótese de que esse comportamento é afetado pela formação de uma camada superficial resultante da oxidação dos reforços, com isto, de acordo com os diagramas de fase é possível a formação de soluções sólidas entre alumina e Ta2O5 e Nb2O5 além da formação de fase líquida, estes mecanismos alterariam a mobilidade dos contornos de grão da alumina. Para o processamento das ferramentas de corte foi utilizada prensagem a quente, escolhido pelo critério da microestrutura e propriedades mecânicas. Os testes de usinagem foram realizados com ferramentas de corte de geometria quadrada, em peças de ferro fundido cinzento e vermicular. O tempo de vida útil da ferramenta produzida com o compósito Al2O3/ NbC foi 13% superior quando comparado à uma ferramenta cerâmica comercial no teste de usinagem de ferro fundido cinzento. / In the present work alumina based composites with addition of transition metal carbides, NbC, TaC and TiC as reinforcement phase were developed. The carbides, in particulate form, were added in 1.5vol.% on the alumina matrix during attritor milling. The processing was conducted by attritor milling, drying in a rotoevaporator and deagglomeration in sieve. The oxidation dynamics of carbides and composities were studied in order to define the sintering and processing parameter of composites. The sintering kinetics was studied by dilatometry at 10° C/min. up to 1600 ° C in synthetic air atmosphere and up to 1800°C in argon, with this step it was possible to verify that the NbC and TiC hindered the sintering of alumina and the TaC helped in the retraction process. In the sintered by dilatometer in air phases resultant from congruent melting on Al2O3/NbC and Al2O3/TaC composites were detected in the composite with TaC addition was also observed evidence of liquid phase. In the samples sintered in dilatometer in air were detected solid solutions on composites CN and CTa and evidence of liquid formation in the composite with TaC addition. Based on these results two techniques were studied in order to produce cutting tools: uniaxial pressing, followed by pressureless sintering and hot pressing. All samples were characterized by microstructure and mechanical properties, and it was shown that samples produced by hot pressing have more controlled microstructure and mechanical properties superior to those produced by pressureless sintering. With the studied processes it was observed that the carbides influence differently alumina sintering. Generally the presence of these phases at the grain boundary causes changes in the microstructure modifying alumina grain size alumina. The proposed hypothesis is that this behavior would be affected by the formation of a surface layer resulting from oxidation of reinforcements with that, according to the phase diagrams, it is possible to find solid solutions between alumina and Ta2O5 and Nb2O5 and possible formation of liquid phase, which alter the mobility of the grain boundary of alumina. Hot pressing was used for the processing of cutting tools, chosen due to the microstructure and mechanical properties. The machining tests were performed with square geometry cutting tools, in samples of gray cast iron and compacted graphite iron. The tool life of cutting tool produced with Al2O3 / NbC composite was 13% higher when compared to a commercial ceramic cutting tool on machining of gray cast iron.

No presente trabalho foram desenvolvidos compósitos à base de alumina, com adição de carbetos de metais de transição, NbC, TaC e TiC, como reforço. Os carbetos, na forma de partículas, foram adicionados em 1,5% em volume à matriz de alumina durante a moagem em attritor. O processamento foi realizado por moagem em attritor, secagem em rotoevaporadora e desaglomeração em peneira. A dinâmica de oxidação dos carbetos e das composições dos compósitos foi estudada para a definição de parâmetros de sinterização e processamento dos compósitos. A cinética de sinterização foi estudada por dilatometria, com taxa de 10°C/min. até 1600°C em atmosfera de ar sintético, e até 1800°C, em atmosfera de argônio, com esta etapa foi possível verificar que o NbC e o TiC dificultaram a sinterização da alumina e que o TaC auxiliou nos processos de retração. Nas amostras que foram sinterizadas em dilatômetro ao ar foram detectadas fases resultantes de fusão congruente nos compósitos Al2O3/NbC e Al2O3/TaC, foram também observadas evidências de formação de líquido no compósito com adição de TaC. Com base nesses resultados foram estudadas duas técnicas de produção das ferramentas de corte: prensagem uniaxial seguida de sinterização sem pressão e sinterização por prensagem a quente. Todas as amostras foram caracterizadas microestruturalmente e quanto às propriedades mecânicas, tendo-se determinado que as amostras produzidas por prensagem a quente possuem microestrutura mais controlada e propriedades mecânicas superiores às produzidas por sinterização sem pressão. Pelos processos estudados foi observado que os carbetos influenciam diferentemente a sinterização da alumina. De maneira geral a presença destas fases nos contornos de grãos promove alterações na microestrutura modificando o tamanho de grãos da alumina. Foi proposta a hipótese de que esse comportamento é afetado pela formação de uma camada superficial resultante da oxidação dos reforços, com isto, de acordo com os diagramas de fase é possível a formação de soluções sólidas entre alumina e Ta2O5 e Nb2O5 além da formação de fase líquida, estes mecanismos alterariam a mobilidade dos contornos de grão da alumina. Para o processamento das ferramentas de corte foi utilizada prensagem a quente, escolhido pelo critério da microestrutura e propriedades mecânicas. Os testes de usinagem foram realizados com ferramentas de corte de geometria quadrada, em peças de ferro fundido cinzento e vermicular. O tempo de vida útil da ferramenta produzida com o compósito Al2O3/ NbC foi 13% superior quando comparado à uma ferramenta cerâmica comercial no teste de usinagem de ferro fundido cinzento. / In the present work alumina based composites with addition of transition metal carbides, NbC, TaC and TiC as reinforcement phase were developed. The carbides, in particulate form, were added in 1.5vol.% on the alumina matrix during attritor milling. The processing was conducted by attritor milling, drying in a rotoevaporator and deagglomeration in sieve. The oxidation dynamics of carbides and composities were studied in order to define the sintering and processing parameter of composites. The sintering kinetics was studied by dilatometry at 10° C/min. up to 1600 ° C in synthetic air atmosphere and up to 1800°C in argon, with this step it was possible to verify that the NbC and TiC hindered the sintering of alumina and the TaC helped in the retraction process. In the sintered by dilatometer in air phases resultant from congruent melting on Al2O3/NbC and Al2O3/TaC composites were detected in the composite with TaC addition was also observed evidence of liquid phase. In the samples sintered in dilatometer in air were detected solid solutions on composites CN and CTa and evidence of liquid formation in the composite with TaC addition. Based on these results two techniques were studied in order to produce cutting tools: uniaxial pressing, followed by pressureless sintering and hot pressing. All samples were characterized by microstructure and mechanical properties, and it was shown that samples produced by hot pressing have more controlled microstructure and mechanical properties superior to those produced by pressureless sintering. With the studied processes it was observed that the carbides influence differently alumina sintering. Generally the presence of these phases at the grain boundary causes changes in the microstructure modifying alumina grain size alumina. The proposed hypothesis is that this behavior would be affected by the formation of a surface layer resulting from oxidation of reinforcements with that, according to the phase diagrams, it is possible to find solid solutions between alumina and Ta2O5 and Nb2O5 and possible formation of liquid phase, which alter the mobility of the grain boundary of alumina. Hot pressing was used for the processing of cutting tools, chosen due to the microstructure and mechanical properties. The machining tests were performed with square geometry cutting tools, in samples of gray cast iron and compacted graphite iron. The tool life of cutting tool produced with Al2O3 / NbC composite was 13% higher when compared to a commercial ceramic cutting tool on machining of gray cast iron.

Les assiettes de fibrage utilisées pour la production de fibres de verre subissent d’importantes contraintes mécaniques, chimiques et thermiques. Par conséquent, cette pièce se dégrade et doit être périodiquement remplacée. Le but de ces travaux est d’augmenter la durée de vie des assiettes de fibrage en améliorant les propriétés mécaniques et chimiques des superalliages qui les constituent. Plus précisément, l’objectif de cette thèse est, dans un premier temps, d’améliorer les alliages utilisés pour le fibrage à 1000°C, puis dans un second temps, de trouver un superalliage pouvant fibrer à 1125°C. Ces travaux ont été menés sur deux familles de superalliages : base nickel et base cobalt. Les propriétés chimiques ont été caractérisées par des essais thermogravimétriques et les propriétés mécaniques par des essais de fluage flexion 3 points. Pour l’alliage base Ni, l’influence des éléments minoritaires subis, Mn et Si, a été étudiée. Les propriétés mécaniques de cet alliage ont fait, ensuite, l’objet d’essais d’amélioration par l’addition de titane, zirconium, tantale, hafnium et de niobium. L’addition d’aluminium a été aussi expérimentée mais ayant pour but d’améliorer les propriétés chimiques de l’alliage. Enfin, des études ont été aussi menées sur l’addition de métaux nobles (Pd et Ru) et de terres rares (Y, La et Ce). Concernant les superalliages base cobalt, l’étude s’est portée sur un alliage base Co qui a antérieurement montré de bonnes propriétés générales pour une utilisation à 1125°C et non à 1000°C. Des variantes avec une teneur abaissée en tantale, sans hafnium et sans tungstène ont été étudiées. Pour clore ces travaux, l’augmentation de la teneur en nickel et un traitement thermique ont été étudiés afin d’améliorer la résistance à l’oxydation de ce second alliage / The fiberizing spinners used to produce the glass fibers undergo sizable mechanical, chemical and thermal solicitations. Therefore, this piece is degraded and must be periodically replaced. The purpose of these works is to increase the lifetime of the fiberizing spinners by improving the mechanical and chemical properties of the superalloys that constitute them. More precisely, the objective of this thesis is, in the first time, to improve the alloys used to fiberize at 1000°C, and in a second time, to find a superalloy that can fiberize at 1125°C. These works are focused on two families of superalloys: nickel-based and cobalt-based. The chemical properties are characterized by the thermogravimetry tests and the mechanical properties by 3 points flexural creep tests. For the Ni-based alloy, the influences of unwanted minority elements, Mn and Si, were studied. The mechanical properties of this alloy are subject to improvement tests by the addition titanium, zirconium, tantalum, hafnium and niobium. The aluminium addition was also experimented but with the aim of improving the chemical properties of the alloy. Finally, the studies were also driven on the addition of noble metals (Pd and Ru) and of rare earths (Y, La and Ce). Concerning the cobalt-based superalloys, the study focused on an alloy which has previously shown good general properties to be used at 1125°C and no at 1000°C. The versius with a lowered content in tantalum, without tungsten and without hafnium were studied. To close this work, the increase of nickel and a heat treatment were studied in order to improve the oxidation resistance of this second alloy

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

The rapid influx of solar energy and the desire to utilize carbon dioxide (CO2) will require large-scale energy storage and CO2 conversion technologies. Electrocatalytic devices can substantially impact both challenges, but improvements to electrocatalyst cost, activity, and selectivity are needed. Transition metal carbides provide a unique framework to reduce the loading of expensive catalyst metals while tuning the electrocatalytic activity and selectivity. Transition metal nitrides have many similar properties as carbides, and their synthesis inherently avoids the unwanted carbonaceous overlayer associated with carbide synthesis. Here it is shown that carbides and nitrides enable lower platinum-group metal (PGM) loadings and improve the activity and selectivity of electrocatalysts for reactions of water electrolysis and electrochemical CO2 reduction. Atom-thick layers of Pt were deposited onto niobium carbide (NbC) thin films to assess hydrogen evolution reaction (HER) activity. The Pt/NbC thin film, with one monolayer of Pt on NbC, performed similarly to bulk Pt. This correlated well with density functional theory (DFT) calculations of the hydrogen binding energy on the Pt/NbC surface. Potential applications of transition metal nitrides as electrocatalyst support materials were explored by synthesizing thin film nitrides of niobium and tungsten. The stability of each nitride was evaluated across broad potential-pH regimes to create a pseudo-Pourbaix diagram for each one. The films were each modified with atom-thick layers of Pt and were evaluated for HER performance in acid and alkaline electrolyte. Thin layers of Pt on WN and NbN showed Pt-like HER performance in acid and are promising candidates for high-surface area catalysts. To address the issue of high iridium (Ir) loading for the oxygen evolution reaction (OER) at the water electrolyzer anode, core-shell Ir-metal nitride particles were synthesized that contained 50% of the Ir mass loading of benchmark IrO¬2 particles. Iridium-iron nitride (Ir/Fe4N) showed increased activity on a mass-Ir basis and on a per-site basis, compared to IrO2. The core-shell morphology and stability under reaction conditions were confirmed with electron microscopy and in-situ X-ray absorption spectroscopy. Electrochemical reduction of CO2 to a mixture of CO and H¬2 (synthesis gas) was achieved on the palladium hydride (PdH) electrocatalyst. The product mixture can then be used as feedstock for the Fischer–Tropsch process and methanol synthesis. The syngas production performance was optimized by evaluating shape controlled PdH particles, bimetallic PdH, and PdH supported on transition metal carbides. At each step, the phase transition from Pd to PdH was monitored under reaction conditions with synchrotron-based X-ray absorption spectroscopy and X-ray diffraction. We also performed an overall carbon balance for catalytic transformation of CO2 to methanol via four reaction schemes, including one relying on electrocatalytic syngas production. The analysis revealed that hybrid electrocatalytic/thermocatalytic processes are most promising for resulting in overall CO2 reduction, but current densities of recently reported electrocatalysts need to increase to make the process economically feasible.

Magnetische Nanopartikel bieten ein großes Potential, da sie einerseits die Eigenschaften ihrer Bulk-Materialien besitzen und anderseits, auf Grund ihrer Größe, über komplett unterschiedliche magnetische Eigenschaften verfügen können; Superparamagnetismus ist eine dieser Eigenschaften. Die meisten etablierten Anwendungen magnetischer Nanopartikel basieren heutzutage auf Eisenoxiden. Diese bieten gute magnetische Eigenschaften, sind chemisch relativ stabil, ungiftig und lassen sich auf vielen Synthesewegen relativ einfach herstellen. Die magnetischen Eigenschaften der Eisenoxide sind materialabhängig aber begrenzt, weshalb nach anderen Verbindungen mit besseren Eigenschaften gesucht werden muss. Eisencarbid (Fe3C) kann eine dieser Verbindungen sein. Dieses besitzt vergleichbare positive Eigenschaften wie Eisenoxid, jedoch viel bessere magnetische Eigenschaften, speziell eine höhere Sättigungsmagnetisierung. Bis jetzt wurde Fe3C hauptsächlich in Gasphasenabscheidungsprozessen synthetisiert oder als Nebenprodukt bei der Synthese von Kohlenstoffstrukturen gefunden. Eine Methode, mit der gezielt Fe3C-Nanopartikel und andere Metallcarbide synthetisiert werden können, ist die „Harnstoff-Glas-Route“. Neben den Metallcarbiden können mit dieser Methode auch die entsprechenden Metallnitride synthetisiert werden, was die breite Anwendbarkeit der Methode unterstreicht. Die „Harnstoff-Glas-Route“ ist eine Kombination eines Sol-Gel-Prozesses mit einer anschließenden carbothermalen Reduktion/Nitridierung bei höheren Temperaturen. Sie bietet den Vorteil einer einfachen und schnellen Synthese verschiedener Metallcarbide/nitride. Der Schwerpunkt in dieser Arbeit lag auf der Synthese von Eisencarbiden/nitriden, aber auch Nickel und Kobalt wurden betrachtet. Durch die Variation der Syntheseparameter konnten verschiedene Eisencarbid/nitrid Nanostrukturen synthetisiert werden. Fe3C-Nanopartikel im Größenbereich von d = 5 – 10 nm konnten, durch die Verwendung von Eisenchlorid, hergestellt werden. Die Nanopartikel weisen durch ihre geringe Größe superparamagnetische Eigenschaften auf und besitzen, im Vergleich zu Eisenoxid Nanopartikeln im gleichen Größenbereich, eine höhere Sättigungsmagnetisierung. Diese konnten in fortführenden Experimenten erfolgreich in ionischen Flüssigkeiten und durch ein Polymer-Coating, im wässrigen Medium, dispergiert werden. Desweiteren wurde durch ein Templatieren mit kolloidalem Silika eine mesoporöse Fe3C-Nanostruktur hergestellt. Diese konnte erfolgreich in der katalytischen Spaltung von Ammoniak getestet werden. Mit der Verwendung von Eisenacetylacetonat konnten neben Fe3C-Nanopartikeln, nur durch Variation der Reaktionsparameter, auch Fe7C3- und Fe3N-Nanopartikel synthetisiert werden. Speziell für die Fe3C-Nanopartikel konnte die Sättigungsmagnetisierung, im Vergleich zu den mit Eisenchlorid synthetisierten Nanopartikeln, nochmals erhöht werden. Versuche mit Nickelacetat führten zu Nickelnitrid (Ni3N) Nanokristallen. Eine zusätzliche metallische Nickelphase führte zu einer Selbstorganisation der Partikel in Scheiben-ähnliche Überstrukturen. Mittels Kobaltacetat konnten, in Sphären aggregierte, metallische Kobalt Nanopartikel synthetisiert werden. Kobaltcarbid/nitrid war mit den gegebenen Syntheseparametern nicht zugänglich. / Magnetic nanoparticles offer a great potential, because they exhibit on the one hand the properties of their bulk materials and on the other hand, because of their size, completely different magnetic properties. The most established applications of magnetic nanoparticles are based on iron oxide. These oxides have good magnetic properties, they are chemical relatively stable, non toxic and easy to prepare. But the magnetic properties are limited. Therefore, we need new materials with improved magnetic properties. Iron carbide (Fe3C) could be one of these materials. Up to now, Fe3C was mainly synthesized in chemical vapor deposition processes (CVD) or was found as side product in the synthesis of carbon structures. A method for the systematical synthesis of metal carbides is the “Urea-Glass-Route”. In addition to the synthesis of metal carbides, this method allows to synthesize metal nitrides, which shows the broad practicability. The “Urea-Glass-Route” is a combination of a sol-gel process with following carbothermal reduction/nitridation at higher temperatures. The method is fast and simple and it is possible to synthesis different metal carbides/nitrides. The main topic of this work is the synthesis of iron carbide/nitride, but also cobalt and nickel is examined. By varying the synthesis parameters, different iron carbide/nitride nanostructures could be synthesized. With the use of iron chloride, Fe3C nanoparticles, in the size range of d = 5 – 10 nm, could be produced. Because of their small size, the particles show superparamagnetism and compared to iron oxide particles (in the same size range) a higher saturation magnetization. In following experiments, the particles could be successfully dispersed in an ionic liquid and with a polymer coating in aqueous medium. Furthermore, via templating with colloidal silica a mesoporous Fe3C structure could be synthesized. The material could be successfully tested in the catalytic ammonia decomposition. By changing the iron source to iron acetylacetonate, Fe7C3 and Fe3N nanoparticles, in addition to Fe3C, could be also synthesized. With nickel acetate it was possible to synthesize nickel nitride (Ni3N) nano crystals. An additional metallic nickel phase in the sample leads to a self organization to disk-like superlattice. Via cobalt acetate, in spheres aggregated, metallic cobalt nanoparticles could be synthesized. Cobalt carbide or nitride was not accessible under these synthesis parameters.

Cellulose is the most abundant biopolymer on earth. In this work it has been used, in various forms ranging from wood to fully processed laboratory grade microcrystalline cellulose, to synthesise a variety of metal and metal carbide nanoparticles and to establish structuring and patterning methodologies that produce highly functional nano-hybrids. To achieve this, the mechanisms governing the catalytic processes that bring about graphitised carbons in the presence of iron have been investigated. It was found that, when infusing cellulose with an aqueous iron salt solution and heating this mixture under inert atmosphere to 640 °C and above, a liquid eutectic mixture of iron and carbon with an atom ratio of approximately 1:1 forms. The eutectic droplets were monitored with in-situ TEM at the reaction temperature where they could be seen dissolving amorphous carbon and leaving behind a trail of graphitised carbon sheets and subsequently iron carbide nanoparticles. These transformations turned ordinary cellulose into a conductive and porous matrix that is well suited for catalytic applications. Despite these significant changes on the nanometre scale the shape of the matrix as a whole was retained with remarkable precision. This was exemplified by folding a sheet of cellulose paper into origami cranes and converting them via the temperature treatment in to magnetic facsimiles of those cranes. The study showed that the catalytic mechanisms derived from controlled systems and described in the literature can be transferred to synthetic concepts beyond the lab without loss of generality. Once the processes determining the transformation of cellulose into functional materials were understood, the concept could be extended to other metals and metal-combinations. Firstly, the procedure was utilised to produce different ternary iron carbides in the form of MxFeyC (M = W, Mn). None of those ternary carbides have thus far been produced in a nanoparticle form. The next part of this work encompassed combinations of iron with cobalt, nickel, palladium and copper. All of those metals were also probed alone in combination with cellulose. This produced elemental metal and metal alloy particles of low polydispersity and high stability. Both features are something that is typically not associated with high temperature syntheses and enables to connect the good size control with a scalable process. Each of the probed reactions resulted in phase pure, single crystalline, stable materials. After showing that cellulose is a good stabilising and separating agent for all the investigated types of nanoparticles, the focus of the work at hand is shifted towards probing the limits of the structuring and pattering capabilities of cellulose. Moreover possible post-processing techniques to further broaden the applicability of the materials are evaluated. This showed that, by choosing an appropriate paper, products ranging from stiff, self-sustaining monoliths to ultra-thin and very flexible cloths can be obtained after high temperature treatment. Furthermore cellulose has been demonstrated to be a very good substrate for many structuring and patterning techniques from origami folding to ink-jet printing. The thereby resulting products have been employed as electrodes, which was exemplified by electrodepositing copper onto them. Via ink-jet printing they have additionally been patterned and the resulting electrodes have also been post functionalised by electro-deposition of copper onto the graphitised (printed) parts of the samples. Lastly in a preliminary test the possibility of printing several metals simultaneously and thereby producing finely tuneable gradients from one metal to another have successfully been made. Starting from these concepts future experiments were outlined. The last chapter of this thesis concerned itself with alternative synthesis methods of the iron-carbon composite, thereby testing the robustness of the devolved reactions. By performing the synthesis with partly dissolved scrap metal and pieces of raw, dry wood, some progress for further use of the general synthesis technique were made. For example by using wood instead of processed cellulose all the established shaping techniques available for wooden objects, such as CNC milling or 3D prototyping, become accessible for the synthesis path. Also by using wood its intrinsic well defined porosity and the fact that large monoliths are obtained help expanding the prospect of using the composite. It was also demonstrated in this chapter that the resulting material can be applied for the environmentally important issue of waste water cleansing. Additionally to being made from renewable resources and by a cheap and easy one-pot synthesis, the material is recyclable, since the pollutants can be recovered by washing with ethanol. Most importantly this chapter covered experiments where the reaction was performed in a crude, home-built glass vessel, fuelled – with the help of a Fresnel lens – only by direct concentrated sunlight irradiation. This concept carries the thus far presented synthetic procedures from being common laboratory syntheses to a real world application. Based on cellulose, transition metals and simple equipment, this work enabled the easy one-pot synthesis of nano-ceramic and metal nanoparticle composites otherwise not readily accessible. Furthermore were structuring and patterning techniques and synthesis routes involving only renewable resources and environmentally benign procedures established here. Thereby it has laid the foundation for a multitude of applications and pointed towards several future projects reaching from fundamental research, to application focussed research and even and industry relevant engineering project was envisioned. / Die vorliegende Arbeit beschäftigt sich mit der Synthese und Strukturierung von Nanokompositen, d.h. mit ausgedehnten Strukturen, welche Nanopartikel enthalten. Im Zuge der Arbeit wurde der Mechanismus der katalytischen Graphitisierung, ein Prozess, bei dem ungeordneter Kohlenstoff durch metallische Nanopartikel in geordneten (graphitischen) Kohlenstoff überführt wird, aufgeklärt. Dies wurde exemplarisch am Beispiel von Zellulose und Eisen durchgeführt. Die untersuchte Synthese erfolgte durch das Lösen eines Eisensalzes in Wasser und die anschließende Zugabe von so viel Zellulose, dass das die gesamte Eisensalzlösung aufgenommen wurde. Die so erhaltene Mischung wurde anschließend unter Schutzgas innerhalb kürzester Zeit auf 800 °C erhitzt. Hierbei zeigte sich, dass zu Beginn der Reaktion Eisenoxidnanopartikel (Rost) auf der Oberfläche der Zellulose entstehen. Beim weiteren Erhöhen der Temperatur werden diese Partikel zu Eisenpartikeln umgewandelt. Diese lösen dann kleine Bereiche der Zellulose auf, wandeln sich in Eisenkarbid um und scheiden graphitischen Kohlenstoff ab. Nach der Reaktion sind die Zellulosefasern porös, jedoch bleibt ihre Faserstruktur vollkommen erhalten. Dies konnte am Beispiel eines Origamikranichs gezeigt werden, welcher nach dem Erhitzen zwar seine Farbe von Weiß zu Schwarz verändert hatte, ansonsten aber seine Form vollkommen beibehält. Aufgrund der eingebetteten Eisenkarbid Nanopartikel war der Kranich außerdem hochgradig magnetisch. Basierend auf dieser Technik wurden außerdem winzige metallische Nanopartikel aus Nickel, Nickel-Palladium, Nickel-Eisen, Kobalt, Kobalt-Eisen und Kupfer, sowie Partikel aus den Verbundkarbiden Eisen-Mangan-Karbid und Eisen-Wolfram-Karbid, jeweils in verschiedenen Mischungsverhältnissen, hergestellt und analysiert. Da die Vorstufe der Reaktion flüssig ist, konnte diese mit Hilfe eines einfachen kommerziellen Tintenstrahldruckers strukturiert auf Zellulosepapier aufgebracht werden. Dies ermöglicht gezielt Leiterbahnen, bestehend aus graphitisiertem Kohlenstoff, in ansonsten ungeordnetem (amorphen) Kohlenstoff zu erzeugen. Diese Methode wurde anschließend auf Systeme mit mehreren Metallen übertragen. Hierbei wurde die Tatsache, dass moderne Drucker vier Tintenpatronen beherbergen, ausgenutzt um Nanopartikel mit beliebigen Mischungsverhältnisse von Metallen zu erzeugen. Dieser Ansatz hat potentiell weitreichende Auswirkungen im Feld der Katalyse, da hiermit hunderte oder gar tausende Mischungen simultan erzeugt und getestet werden können. Daraus würden sich große Zeiteinsparungen (Tage anstelle von Monaten) bei der Entwicklung neuer Katalysatoren ergeben. Der letzte Teil der Arbeit beschäftigt sich mit der umweltfreundlichen Synthese der obengenannten Komposite. Hierbei wurden erfolgreich Altmetall und Holzstücke als Ausgangstoffe verwandt. Zusätzlich wurde gezeigt, dass die gesamte Synthese ohne Verwendung von hochentwickeltem Equipment durchgeführt werden kann. Dazu wurde eine sogenannte Fresnel-Linse genutzt um Sonnenlicht zu bündeln und damit direkt die Reaktionsmischung auf die benötigten 800 °C zu erhitzen. Weiterhin wurde ein selbst gebauter Glasreaktor eingesetzt und gezeigt, wie das entstehende Produkt als Abwasserfilter genutzt werden kann. Die Kombination dieser Ergebnisse bedeutet, dass dieses System sich beispielsweise zum Einsatz in Katastrophenregionen eignen würde, um ohne Strom und besondere Ausrüstung vor Ort Wasserfilter herzustellen.

Further crosslinking of the fluorinated polyimide was examined to separate the cure reactions from degradation and to determine the optimum post curing conditions. Glass transition/melting temperatures were ascertained using DSC, while weight loss during curing and Td were determined using TGA. Furthermore, the mechanical properties were measured using an Instron to relate to the thermal properties to find the optimum curing conditions. The polyimide resin exhibited the best post-curing conditions for further crosslinking for 8 hours at 410 degress C based on Tg, thermal stability, and mechanical properties. Blister temperatures, resulting from rapid heating, were obtained by monitoring changes in transverse thickness expansion using two different techniques. Both techniques employed showed similar blister temperatures in relation to the amount of absorbed moisture, regardless of sample size. The polyimide resin exhibited blister temperatures ranging from 225 - 362 degrees C, with 1.7 - 3.0 wt% absorbed moisture, and the polyimide composite had blister temperatures from 246 - 294 degrees C with 0.5 - 1.5 wt% moisture. Weight loss of the fluorinated polyimide and its corresponding polyimide carbon fiber composite under elevated temperature was examined. Weight loss as a function of exposure temperature and time was measured using TGA and by pre- and post-weighing of specimens treated in an oven. Both techniques showed similar weight loss trends as a function of time and temperature, but TGA showed much greater weight loss due to greater surface area to volume (i.e., small sample size). The neat polyimide resin and carbon fiber composite exhibited negligible weight loss at temperatures below 430 degrees C for exposure times up to 20 minutes. Transition-metal carbides were initially synthesized by carbothermal reduction of transition-metal halides and polymer precursor mixtures, at temperatures that range from 900 to 1500 degrees C in an argon atmosphere. TaC was synthesized from TaBr5, as a model carbide for this process. Significant (> 40 vol%) amounts of TaC were formed at reaction temperatures as low as 900 degrees C for one hour, with greater times and temperatures leading to > 90 vol% yield. Universality of method was also proven by using other various transition-metal halide salts (NbBr5, WCl4, and WCl6) with the polyimide.

Group 3 metal clusters are synthesized by laser vaporization in a pulsed cluster beam source and identified with laser ionization time-of-flight mass spectrometry. The adiabatic ionization energies and vibrational frequencies of these clusters are measured using mass-analyzed threshold ionization (MATI) spectroscopy. Their structures and electronic states are determined by combining the MATI spectra with quantum chemical calculations and spectral simulations. This dissertation focuses on the study of several small molecules, which include LaO2, La2, M2O2, M3O4, M3C2, and La3C2O, where M = Sc, Y, and La. Except for La2, these molecules exhibit strong ionic characters between the metal and oxygen or carbon atoms and can be described as [O-][La2+][O-], [M2+]2[O2-]2, [M8/3+]3[O2-]4, [M2+]3[C3-]2, and [La8/3+]3[C3-]2[O2-]. The interactions between the metal atoms form covalent bonds, which can be described by a triple bond in La2, a two-center two electron bond in M2O2, a three-center one electron bond in M3O4, and a three-center three electron bond in M3C2. In addition, the electron in the non-bonding highest occupied molecular orbital (HOMO) is localized in the La 6s orbital in LaO2 and La3C2O. The ground states of these molecules are all in low electron-spin states with the spin multiplicities of 1 or 2. Although the ground electronic state of LaO2 is a linear structure, the excited quartet state of the molecule is determined to be a bent structure. M2O2 and M3O4 have the planar rhombic and cage-like structures, respectively; whereas M3C2 has a trigonal bipyramid structure. La3C2O is formed by oxygen binding with two La atoms of La3C2. Ionization removes a metal-based (n+1)s electron in all neutral molecules, and the resultant ions have similar geometries to those of the corresponding neutral states. In the case of La2, additional ionization of a La 5d electron is also observed.

No description available.