A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel. The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen. Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS. Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM. Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.

L’impact énergétique de la tribologie sur la vie économique et industrielle est important ; diminuer le frottement et l’usure des pièces mécaniques est un véritable enjeu pour des secteurs industriels très divers. Cette étude s’inscrit dans le cadre de la prévention de l’usure d’éléments mécaniques pouvant être soumis à des conditions sévères d’utilisation telles que les hautes températures. La réalisation de revêtements protecteurs céramique-métal est alors particulièrement indiquée afin d’apporter respectivement la résistance à la corrosion induite par les hautes températures avec un alliage adapté, et la résistance à l’usure grâce à la dureté des céramiques. D’autre part, le développement des recherches dans le domaine nanométrique a montré l’intérêt de la diminution de l’échelle sur l’amélioration des propriétés tribologique globales des revêtements. La projection thermique regroupe alors les procédés les plus adaptés à la réalisation de tels revêtements. Dans ce travail, des revêtements multi-composants (céramique-métal) et multi-échelles (micrométrique-nanométrique) sont développés par projection plasma afin de répondre à la problématique de résistance tribologique à haute température. La réalisation des dépôts est mise en œuvre à l’aide d’une torche tri-cathodes (TriplexPro-200) avantageuse pour sa stabilité et les larges possibilités laissées par sa fenêtre opératoire étendue. Les spécificités de cette torche seront étudiées afin d’adapter au mieux le procédé à la réalisation complexe de dépôts à composante multi-échelle. Une démarche innovante de projection hybride associant projection de poudres micrométriques et de suspensions de poudres nanométriques sera alors développée. Les étapes ayant amenées à la réalisation de ces revêtements sont détaillées dans ce travail puis les caractéristiques et le comportement tribologique des dépôts sont finalement étudiés. / Nowadays, tribology has a high energetic impact on economic and industrial areas. Thus, reducing wear and friction of mechanical parts has become a real stakes for various industries. This study is focused on the wear prevention of mechanical parts subjected to severe operating conditions like high temperatures.The realization of protective ceramic-metal coatings is thus particularly appropriated to improve corrosion resistance induced by the high temperatures, with a suitable alloy, and the wear resistance, thanks to the ceramics hardness. Furthermore, researches development in the nanoscale field have shown the interest of scale reduction on the improvement of coatings tribological properties. Thermal spraying is then the most appropriate process for the realization of such coatings.In this work, multi-components (ceramic-metal) and multi-scales (micrometric-nanometric) coatings are developed by plasma spraying in order to give an answer to the high temperature tribological resistance issue. Coatings are realized using a three-cathodes plasma gun (TriplexPro-200) which provides a more stable plasma jet and offers wide possibilities by an extended operating window. First, the special features of this kind of plasma gun will be studied in order to adjust the process to the complex realization of multi-scale coatings. An innovative approach using a hybrid spraying process was thus developed, combining conventional micrometric powder spraying and suspension of nanoscale powders spraying. In a second time, the steps leading to the production of such coatings will be detailed, and finally, their main properties and their tribological behavior will be studied.

A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel. The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen. Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS. Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM. Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.

No description available.

Dans la recherche de nouveaux matériaux d'anode inerte pour l'électrolyse de l'aluminium, les cermets sont de bons candidats grâce à leurs propriétés conductrices et leur résistance à la corrosion. À une température de 960°C, ce matériau ne doit pas seulement résister à la corrosion du bain d'électrolyse, mais aussi à la corrosion par l'oxygène et des espèces fluorées de l'atmosphère gazeuse. Cette étude est consacrée à la cinétique de corrosion par O2 et HF d'un cermet composé de ferrite de nickel (NixFe3-xO4), d'oxyde de nickel (NiyFe1-yO) et d'un alliage de cuivre-nickel (CuzNi1-z).<br />Dans un premier temps, nous présentons les mesures thermogravimétriques à 960°C et à une pression partielle d'oxygène comprise entre 1 - 1000 hPa ainsi que les observations MEB des échantillons oxydés. L'influence de la pression d'oxygène sur la vitesse d'oxydation est déterminée par des " décrochements ", c'est-à-dire des sauts de pression pendant la réaction d'oxydation. Les résultats montrent qu'au-dessus d'une pression partielle de 51 hPa (PCu), la pression d'oxygène n'a pas d'influence sur la cinétique d'oxydation. La présence des deux oxydes, CuO et Cu2O explique cette indépendance. En effet, la pression partielle d'oxygène en dessous de l'interface CuO/Cu2O est imposée par l'équilibre entre les deux oxydes. Pour PO2 inférieur à PCu, seul Cu2O a été détecté dans la couche en croissance externe sur les échantillons oxydés, et la vitesse d'oxydation dépend de la pression partielle d'oxygène. Des analyses par microsonde électronique montrent la formation d'une sous-couche contenant une phase " monoxyde " notée (NiCuFe)O, ainsi que la consommation de la phase métallique initialement présente dans le matériau cermet et la formation d'oxyde de nickel en périphérie de la phase métallique. En plus de ces modifications, nous avons observé la dissolution d'une partie du cuivre dans les phases de ferrite de nickel et de monoxyde.

Zugl.: Karlsruhe, Univ., Diss.

No description available.

No / This paper investigates the sliding wear performance of two types of co-electrodeposited cermet coatings com- posed of nano-sized tungsten carbide (WC) and combined tungsten carbide and alumina (Al2O3) particles incor- porated in a nickel matrix. For this purpose, the effects of alternating the ceramic particle concentration in the electrolyte solutions on microhardness of the coatings and also the effect of applied loads on wear performance of the coatings have been studied using ball-on-flat sliding wear tests. The wear track volumes and the progres- sion of wear depths as a function of time and at three applied loads were recorded and wear track morphologies were investigated using FE-SEM and microhardness testing. The results showed that microstructure, microhard- ness and wear performance of the coatings composed of WC improved when Al2O3 particles were introduced into the matrix. It was also found that the rule of mixtures for composite materials provides a good explanation for microhardness behaviour while Archard equation can explain the changes in wear performance due to the hardness and microstructural changes. / Alberta Innovates Future Technologies (Nanoworks) Canada

Made available in DSpace on 2016-12-08T15:56:17Z (GMT). No. of bitstreams: 1 TESE_ ELIANA FRANCO.pdf: 10762116 bytes, checksum: 0473839f89cd4764137c8cf282af6c0d (MD5) Previous issue date: 2014-06-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Materials or coatings for tools are of primary importance for industrial development. This work proposes the development of tools materials through two routes, one of them using cermets based Fe-NbC as a raw material and the other through thermochemical treatments in steel tool substrates. The specific objectives were planning the processing, manufacture and analyze of Fe-NbC cermets; and to develop a coating composed by B, Nb and C by diffusion thermoreactive in solid-state in M2 high speed steel substrates. There are some studies, even applications of cermets using iron as a matrix, such as cermets with TiC or Ti (C, N) carbides. The Brazilian Society of Mining and Metallurgy (Companhia Brasileira de Metalurgia e Mineração - CBMM) produced the Fe-NbC cermets with different contents of Al and other elements added during the obtaining of cermets. In this work thermal analyzes and calculations of phases equilibrium were performed through ThermoCalc® software to study the thermal behavior of these materials. Also, C and Fe were added to these materials and consolidations by conventional powder metallurgy and by Field Assisted Hot Pressing (FAHP). The results showed that these cermets had a temperature of formation of liquid phase around 1200o C. The Fe and C addition resulted in the disappearance of undesirable phases. The cermet FeNbC5Al exhibited higher hardness with or without additions, 820 HV10 without additions elements and after consolidation by FAHP and annealing. For the development of surface coatings, multicomponent boriding with Nb treatments were performed on substrates of M2; treatments in stages, with diffusion of Nb and B separately; and simultaneous treatments, with diffusion of Nb and B at the same time. Treatments were carried out by the thermoreactive diffusion method on solid-state; calculations were made by ThermoCalc® to estimate the pack composition and treatment temperature. The results showed that by the treatment performed in stages, a coating formed by NbB and NbC phase with hardness 2300 HV was obtained. The wear volume of the material showed high dispersion of results, which can be improved by producing a more homogeneous niobized layer; a suggestion to obtain that layer is using a substrate with a small addition of alloying elements or niobizing in liquid bath. / O interesse por materiais ou recobrimentos para ferramentas é de suma importância para o desenvolvimento industrial. Este trabalho propõe o desenvolvimento de ferramentas através de duas rotas, uma utilizando como matéria prima cermets a base de Fe-NbC e outra por meio de tratamentos termoquímicos em substratos de aço ferramenta. Os objetivos específicos foram planejar o processamento, fabricar e analisar cermets Fe-NbC; e desenvolver um recobrimento a base de B, Nb e C por difusão termorreativa em meio sólido, em substratos de aço rápido M2. Há alguns estudos, e até mesmo aplicações de cermets que utilizam ferro como matriz, como os cermets com carbonetos de TiC ou Ti(C,N). A Companhia Brasileira de Metalurgia e Mineração (CBMM) produziu os cermets Fe-NbC com diferentes teores de Al, bem como outros elementos, adicionados durante a obtenção dos cermets. Neste trabalho realizaram-se análises térmicas e cálculos de equilíbrio de fases através do software ThermoCalc® para estudar o comportamento térmico destes materiais. Também se fizeram adições de C e Fe a esses materiais e consolidações por metalurgia do pó convencional e por compactação a quente assistida por campo (FAHP). Os resultados mostraram que esses cermets apresentaram uma temperatura de formação de fase líquida em torno de 1200o C. A adição de C e Fe resultou no desaparecimento de fases indesejáveis. O cermet FeNbC5Al exibiu maior dureza com ou sem adições, 820 HV10 sem adição de elementos e após consolidação assistida por campo e recozimento. Para desenvolvimento dos recobrimentos de superfície, realizaram-se tratamentos de boretação multicomponente com Nb sobre substratos de M2; tratamentos em etapas, com difusão de B e Nb separadamente; e tratamentos simultâneos, com difusão de B e Nb ao mesmo tempo. Realizaram-se os tratamentos pelo método de difusão termorreativa em meio sólido, se fizeram cálculos por ThermoCalc® para a estimativa da composição da mistura e temperatura de tratamento. Os resultados mostraram que através do tratamento em etapas, se obteve um recobrimento formado por fases de NbB e NbC com dureza de 2300 HV. O volume de material removido desse material apresentou alta dispersão de resultados, o que pode ser melhorado através da produção de uma camada niobizada mais homogênea; uma sugestão para obtenção de uma camada mais homogênea é através da utilização de um substrato com pouca adição de elementos de liga ou da realização de niobização em banho líquido.

In der vorliegenden Arbeit wird erstmals systematisch der Einfluss von gasförmigen und festen Verunreinigungen auf das O2, Pt│YSZ- Elektrodensystem am praxisnahen Beispiel der Lambdasonde untersucht. Dazu wurden Festelektrolyt- und Elektrodenmaterialien unterschiedlicher Zusammensetzung und Morphologie den realen Abgasbedingungen nachempfundenen, chemischen und physikalischen Einflüssen ausgesetzt und in Bezug auf Langzeitstabilität, Sensitivität und Wirkmechanismen untersucht. Im Einzelnen lag der Fokus der Untersuchungen auf zwei Ausführungsformen von Elektroden, die sich vor allem durch mikro- bzw. nanoskalige Partikelgrößenverteilungen sowie der Platin/YSZ-Zusammensetzung unterschieden und als Mikro- bzw. Nano-Elektrode bezeichnet wurden. Der Einfluss von Siliciumdioxid als gezielt dem Festelektrolyten beigemischte intrinsische Vergiftung sollte in Wechselwirkung zu den extrinsischen Verunreinigungen wie Natriumionen, Wasserdampf und Phosphorpentoxid untersucht werden. Im Unterschied zu den in der Literatur betrachteten, vereinfachten Modellsystemen konnten damit erstmals Wechselwirkungen beschrieben werden, die zu einem tieferen Verständnis des realen Sensorverhaltens, vor allem der Degradation beitragen. Insbesondere ist es gelungen, ein Modell für die Sauerstoffreaktion an geschädigten Elektroden aufzustellen. Neben der bekannten elektrochemischen Reduktion von Sauerstoff spielen die Transportvorgänge an der Elektrodenoberfläche eine entscheidende Rolle, über die in der Literatur bisher nur wenig bekannt war.