Neste trabalho foram avaliados os efeitos da adição de polímeros precursores na sinterização, microestrutura, dureza e na tenacidade à natura de materiais cerâmicos à base de carbeto de silício e de AI2O3. As matérias-primas cerâmicas foram caracterizadas por análise semi-quantitativa por espectrometria de fluorescência de raios X, difração por laser, adsorção gasosa e microscopia eletrônica de varredura. Para os polímeros utilizou-se análise termogravimétrica. A cinética de sinterização das amostras compactadas foi estudada por dilatometria. A caracterização dos materiais sinterizados incluiu medidas de densidade aparente pelo princípio de Arquimedes e/ou por picnometria de He, porosimetria por intrusão de Hg, análises de difração de raios X, de carbono total, avaliação da microestrutura e por microscopia eletrônica de varredura e de transmissão, análise por espectrometria de raios X por dispersão de energia, ensaios de impressão Vickers para determinação de dureza e tenacidade à fiatura. No estudo de cerâmica à base de carbeto de silício foram utilizados os aditivos óxidos AI2O3 (4% em peso) e Y2O3 (4% em peso) e os aditivos poliméricos PMHS (polimetilhidrogenossiloxano) e polimetilhidrogenossiloxano com D4Vi. O processamento envolveu a cura do material, pirólise e sinterização (1850 °C e 1950 °C/l h. Ar ou N2). Nas amostras à base de carbeto de silício houve elevada perda de massa, principalmente quando a atmosfera de sinterização foi argônio. As amostras à base de carbeto de silício, com adição de polímeros atingiram densidade de até 3,15 g/cm3 quando pirolisadas a 900 °C em N2 e sinterizadas a 1950 °C, em atmosfera de nitrogênio. Para as amostras à base de alumina foram utilizados os aditivos poliméricos PMHS, PMS (polimetilsilsesquioxano) e PPS (polifenihnetilvinilhidrogenosilsesquioxano) e as sinterizações foram realizadas a 1650 °C e 1700 °C, não havendo variações significativas nas densidades obtidas nas duas temperaturas. Nos materiais com adição de PMHS foram obtidos compósitos de alumina e mulita, sendo que os grãos de mulita foram formados intergranularmente. Nas amostras contendo PMS ou PPS a distribuição das feses formadas, Si2Al4O4N4 e Si2ON2, foi bastante heterogênea, A obtenção de compósitos cerâmicos utilizando pequenas adições de polímeros precursores cerâmicos mostrou-se viável para materiais à base de alumina, sendo uma rota simples de conformação, com grande potencial para a obtenção de peças com geometria complexa. / The effects of the addition of precursor polymers on sintering, microstructure, hardness and fiacture toughness of silicon carbide and alimiina ceramics were studied. The ceramic raw materials were characterized by semi-quantitative analysis by X-ray fluorescence, particle size by laser diffraction, specific surface area by gas adsorption and microstructural analysis by scanning elecfron microscopy. The polymers were analyzed by thermogravimetry. The sintering kinetics of cold-pressed specimens was studied by dilatometry. The sintered materials were characterized by evaluation of apparent density by the Archimedes technique and/or helium picnometry, by mercury porosimetry, by X-ray diflftaction, by evaluation of total carbon content, by scanning and transmission electron microscopy, by enetgy dispersion X-ray spectrometry, and by Vickers indentation analysis for determining hardness and fiacture toughness. AI2O3 (4wt.%) and Y2O3 (4wt.%) and polymetylhydrogenosiloxane and polymetylhydrogenossiloxane with D4Vi were the sintering aids for SiC. The processing procedures were material cure, pyrolysis and sintering (1850 X and 1950 °C/1 h, Ar or N2). High mass loss was measured in silicon carbide based ceramics, mainly under argon. Silicon carbide based ceramics with polymer sintering aids achieved 3.15 g/cm3 density after pyrolysis at 900 °C under N2 and sintering at 1950 °C under nitrogen. PMHS, PMS and PPS polymer sintering aids were used for almnina based ceramics sintering carried out at 1650 °C and 1700 °C, without significant difference in the final density. Addition of PMHS yielded alumina and mullite composites, with intergranular mullite grains. Heterogeneous Si2AI4O4N4 and Si2ON2 phases were obtained in specimens with PMS or PPS, The preparation of ceramic composites using small amounts of precursor polymers showed a suitable process for alumina-based ceramics, a simple forming route, with high potential for the fabrication of complex shape pieces.

La transformation de la biomasse lignocellulosique requiert des conditions opératoires différentes de celles employées dans les procédés du raffinage et de la pétrochimie. Ainsi, certaines transformations de produits bio-sourcés sont opérées en phase aqueuse et en température (« conditions hydrothermales (HT) » : T > 200°C, eau liquide). Les catalyseurs hétérogènes industriels constitués de supports poreux oxydes comme l’alumine se révèlent alors inadaptés. Des modifications structurales et texturales sont observées induisant des performances catalytiques instables et incompatibles avec une viabilité industrielle d’éventuels procédés. La thèse propose de développer des matériaux catalytiques présentant des propriétés de stabilité hydrothermale adaptées au traitement des nouvelles matières premières que sont la biomasse et ses réactifs dérivés. La stratégie consiste à modifier la surface d’alumine afin de la rendre stable en conditions HT. Cette modification de surface est effectuée avec l’aide d’additifs organiques (carbone, polyols) ou inorganiques (silicium).Il est montré que l’alumine devient stable lors de la saturation de certains hydroxyles de sa surface localisés spécifiquement sur les faces basales des cristallites élémentaires. Des stratégies sont développées pour de déposer sélectivement du carbone ou du silicium sur ces sites en question. Une très bonne stabilité HT est ainsi obtenue avec un taux de recouvrement de la surface proche de 20% seulement. Une phase métallique est ensuite déposée sur les matériaux stabilisés et leurs performances catalytiques sont évaluées pour l’hydrogénolyse du glycérol / Biomass transformation reactions are carried under very different conditions from those used in petroleum industry. Some bio-products are transformed in aqueous phase underhigh temperatures (hydrothermal conditions). Heterogeneous catalysts are most likely made with a porous oxide like alumina witch is not suited for such conditions. Its textural and structural properties are modified during the treatment making the material incompatible with any process. The aim of the thesis is to develop new catalytic materials with hydrothermal stability properties adapted to the treatment of biomass products. The strategy is to modify alumina surface in order to make it insensitive to water during a hydrothermal treatment. The surface modification is done with inorganic (silicon) and organic (carbon, polyols) additives.We show here that alumina is stable only if some specific hydroxyls located in basal surfaces of crystallites are saturated. We develop strategy to selectively cover those sites with carbon or silica. A very good hydrothermal stability is obtained with a surface coverage close to 20% only. Then, a metal phase is deposited on the stabilized supports and catalytic performances of the materials are evaluated through the glycerol hydrogenolysis reaction

L’alumine est un support important en catalyse hétérogène. Le contrôle de ses propriétés physiques et texturales permet d’en améliorer les performances comme support pour des applications en catalyse. Les catalyseurs à base de cobalt sont connus pour présenter d’excellentes performances pour la réaction de reformage de l’éthanol (RRE) du fait de leur grande affinité à cliver les liaisons C-H et C-C.De nombreuses études ont visé à corréler les propriétés de l’alumine avec celles des catalyseurs. L’alumine présente une chimie de surface plutôt complexe qui peut être contrôlée par le mode de préparation. Dans ce travail,des alumines possédant des méso- et macropores ont été obtenues par voie sol-gel dans un mode de préparation « one-pot » accompagnée par une séparation de phases. Dans cette stratégie intégrative, les deux procédés,gélification et séparation de phases, surviennent spontanément dans les systèmes contenant un inducteur de séparation de phase.Les différentes alumines ont été synthétisées à partir d’isopropoxyde oude chlorure d’aluminium et de polyethylène oxyde ou polypropylène oxydeutilisés comme inducteur de séparation de phases. Le choix approprié des compositions des réactifs permet le contrôle de la taille et volume des pores. La formation des macropores résulte du processus de séparation de phase après décomposition par calcination de l’inducteur alors que l’espace entre particules formant le squelette du xerogel constitue la structure mésoporeuse.Les différentes alumines poreuses ainsi préparées et une alumine commerciale ont été utilisées comme supports de catalyseurs de cobalt par imprégnation par voie humide. Les précurseurs oxydes du catalyseur obtenu après calcination sont composés de phases de type Co ₃ O ₄ et CoAl₂O ₄ , cette dernière étant en quantité plus importante dans les alumines synthétiques.Comme les alumines sol-gel sont caractérisées par une plus grande proportion d’aluminium en site octaédrique et de groupement hydroxyles de surface que l’alumine commerciale, nous avons proposé que ces caractéristiques facilitent la migration du Cobalt dans le réseau alumine et explique la formation plus importante de phase de type CoAl₂O ₄ .Les catalyseurs ont été caractérisés pendant l’activation et en conditions réelles de fonctionnement RRE par EXAFS rapide pour suivre l’évolution de l’ordre local du cobalt et par spectroscopie Raman et spectrométrie de masse résolues dans le temps pour l’analyse des produits de réaction. Si l’espèce active est indiscutablement Co0, nous avons montré que les performances catalytiques dépendent aussi du rapport Co ² ⁺ /Co ⁰ obtenu après activation, dans le sens où de faibles rapports Co ² ⁺ /Co ⁰ ne permettront pas de nettoyer la surface du catalyseur par oxydation du coke formé lorsque la réaction de reformage de l’éthanol opère. Une conclusion importante de ce travail est la mise en évidence du rôle joué par l’oxyde cobalt (CoO) dans la stabilité du catalyseur à travers la promotion de l’oxydation des espèces carbonées déposées en surface. Ainsi le contrôle du rapport Co ² ⁺ /Co ⁰ apparaît comme un élément capital pour la conception de catalyseurs performants à base de cobalt pour la réaction de reformage de l’éthanol, le choix du support étant essentiel / Alumina is an important support for heterogeneous catalysts. Thematching of appropriate alumina physical properties and controlled texturalproperties can improve its performance as support in catalysis applications.Cobalt based catalysts have been reported to have a good ethanol steamreforming (ESR) performance due to their high activity for the cleavage of C-Hand C-C bonds.Many studies have been conducted about the effects of aluminaproperties on the cobalt catalysts properties. Alumina exhibits a rather complexsurface chemistry which can be controlled by the preparation procedure. In thiswork alumina samples with macro and mesoporous structure were obtainedusing the one-pot sol-gel synthesis accompanied by phase separation. In thisintegrative strategy both processes, gelation and phase separation,spontaneously occur in system containing the presence of the phase separationinducer.The different aluminas were produced by using as aluminum reactants,aluminum isopropoxide and chloride and PolyEthylene Oxide or PolyPropyleneOXide as phase separation inducer. Appropriate choice of the startingcomposition allows the control the pore size and volume. Macroporous areformed as a result of phase separation after burning the phase separationinducer, while voids between particles of the xerogel skeletons form amesoporous structures.The different alumina porous alumina and commercial alumina wereused as supports for preparing by wetness impregnation cobalt-based catalyst.The oxidic catalyst precursors obtained after calcination are composed of Co ₃ O ₄ and CoAl₂O ₄ -like phases, the latter being in higher proportions in the sol-gelalumina than in the commercial one. As the sol-gel alumina presents a largeramount of octahedral AlVI sites and surface hydroxyl groups than thecommercial alumina, it was assumed that these features can facilitate themigration of Co ions into the alumina network leading to formation of thegreatest amount of CoAl₂O ₄ .The catalysts were characterized under realistic activation and reactionconditions by the combination of Quick-XAS (X-ray Absorption Spectroscopy)for monitoring the change of the local order around Co with time-resolvedRaman and Mass spectroscopy for monitoring reaction products. If the Co(0)species is undoubtedly the active species for ESR, the catalytic performancehas been clearly shown to be affected by the Co ² ⁺ /Co ⁰ ratio obtained afteractivation, getting lower Co ² ⁺ /Co ⁰ ratios will not allow to clean the surface of thecatalyst by oxidation of C* as ESR is running. As an important conclusion of thework reported herein, we have evidenced that the cobalt oxide (CoO) plays akey role in the stability over time of the catalyst through oxidation of adsorbedand reactive carbon atoms. Then the control of the Co ²⁺ /Co ⁰ ratio appears to beone of the key issues in the design of efficient cobalt alumina-supported ethanolsteam reforming catalysts and the choice of the support is essential forcontrolling this ratio of active cobalt species.

Le confinement de la matière condensée dans un milieu nanoporeux peut induire à l'échelle nanométrique des changements structurels ou dynamiques drastiques qui conduisent finalement aux propriétés originales. Le confinement des polyélectrolytes, qui sont des polymères porteurs d'une charge électrique, présente un intérêt particulier. Dans ce projet, des membranes d'alumine nanoporeuse auto-ordonnée (nPAAMs), dont les paramètres structuraux sont réglés par la synthèse, ont été choisies comme milieu de confinement et des approches expérimentales ont été proposées pour étudier le confinement d'un polyélectrolyte fort (PE), polystyrène-sulfonate de sodium. Une partie importante de ce travail a été consacrée à la caractérisation des charges structurales et superficielles des nPAAMs. La structure et la composition du nPAAM sont caractérisées par la combinaison de la microscopie électronique à balayage et de la diffusion neutronique à petit angle (SANS). Une stratégie détaillée est proposée pour mesurer les nPAAM dans des conditions optimales en raison de leur forme anisotrope et de leur pouvoir de diffusion élevé ainsi que des informations sur leur composition chimique. La charge superficielle de la membrane a été déterminée par des mesures de potentiel d’écoulement. La charge de la paroi du pore peut être ajustée à une charge positive ou négative et l'étendue des interactions électrostatiques peut être ajustée, ce qui permet d'adapter le milieu aux études de confinement électrostatique. Le comportement de perméation et l'adsorption du polyélectrolyte à l'intérieur des pores sont étudiés par SANS en combinaison avec des mesures de perméabilité. La cinétique de l'adsorption est obtenue par le potentiel d’écoulement et la possibilité d'utiliser la réflectivité neutronique pour ces études est proposée. Ce travail fournit des approches expérimentales sur la caractérisation de l'PE en milieu confiné. / The confinement of condensed matter in nanoporous medium can induce at the nanoscale drastic structural or dynamical changes that ultimately lead to original properties. Of a specific interest is the confinement of polyelectrolytes that are polymers carrying an electrical charge. In this project, self-ordered nanoporous alumina membranes (nPAAMs), whose structural parameters are tuned through the synthesis, have been chosen as a confining medium and experimental approaches have been proposed to study the confinement of a strong polyelectrolyte (PE), sodium polystyrene-sulfonate . An important part of this work has been devoted to the structural and surface charge characterization of nPAAMs. The nPAAM’s structure and composition are characterized by combining scanning electron microscopy and small angle neutron scattering (SANS). A detail strategy is proposed for measuring the nPAAMs under optimal conditions due to their anisotropic shape and high scattering power and information on their chemical composition. The membrane’s surface charge has been determined by streaming potential measurements. The pore’s wall charge can be adjusted to positive or negative charge and the extent of the electrostatic interactions can be tuned, tailoring the medium for electrostatic confinement studies. The permeation behavior and the adsorption of the polyelectrolyte inside the pores is studied by SANS combined with flow measurements. The kinetics of the adsorption is accessed by streaming potential and the possibility to use of neutron reflectivity for such studies is proposed. This work provides experimental approaches insight into the characterization of PE under confinement.

Metal implants are a type of hard tissue replacement currently used. Metals used for implants include: stainless steel, titanium, chrome, and cobalt alloys. Such implants often fail at the interface with bone. Metal implants fail when the surface of the implant is coated with an osteoconductive material. An osteoconductive material provides scaffolding for cellular migration, cellular attachment, and cellular distribution. A reason for metal implant failure could be the vastly different material properties than bone. Motivation for the research was to find a suitable bone substitute other than metal. Materials considered were: zirconia toughened alumina, carbon fiber reinforced epoxy, and glass fiber reinforced epoxy. Those materials have been used in previous biological applications and can be cast into complex configurations. Objectives of the study were to compare material properties of the composites to bone. A method to create porosity was then tested in the material that was similar to bone in critical material property. Some of the materials were statistically similar to bone in yield strength. Method to create interconnected porosity in those materials resulted in 49% void space.

<p>The work presented in this thesis deals with experimental and theoretical studies related to the growth of crystalline alumina thin films. Alumina, Al₂O₃, is a polymorphic material utilized in a variety of applications, e.g., in the form of thin films. Many of the possibilities of alumina, and the problems associated with thin film synthesis of the material, are due to the existence of a range of different crystalline phases. Controlling the formation of the desired phase and the transformations between the polymorphs is often difficult.</p><p>In the experimental part of this work, it was shown that the thermodynamically stable alpha phase, which normally is synthesized at substrate temperatures of around 1000 °C, can be grown using reactive sputtering at a substrate temperature of 500 °C by controlling the nucleation surface. This was done by predepositing a Cr₂O₃ nucleation layer. Moreover, it was found that an additional requirement for the formation of the <em>α</em> phase is that the depositions are carried out at low enough total pressure and high enough oxygen partial pressure. Based on these observations, it was concluded that energetic bombardment, plausibly originating from energetic oxygen, is necessary for the formation of <em>α</em> alumina (in addition to the effect of the chromia nucleation layer). Further, the effects of impurities, especially residual water, on the growth of crystalline films were investigated by varying the partial pressure of water in the ultra high vacuum (UHV) chamber. Films deposited onto chromia nucleation layers exhibited a columnar structure and consisted of crystalline <em>α</em>-alumina if deposited under UHV conditions. However, as water to a partial pressure of 1x10^-5 Torr was introduced, the columnar growth was interrupted. Instead, a microstructure consisting of small, equiaxed grains was formed, and the gamma-alumina content was found to increase with increasing film thickness. When gamma-alumina was formed under UHV conditions, no effects of residual water on the phase formation was observed. Moreover, the H content was found to be low (< 1 at. %) in all films. Consequently, this shows that effects of residual gases during sputter deposition of oxides can be considerable, also in cases where the impurity incorporation in the films is found to be low.</p><p>In the modeling part of the thesis, density functional theory based computational studies of adsorption of Al, O, AlO, and O2 on different alpha-alumina (0001) surfaces have been performed. The results give possible reasons for the difficulties in growing the <em>α</em> phase at low temperatures through the identification of several metastable adsorption sites, and also provide insights related to the effects of hydrogen on alumina growth.</p> / Report code: LiU-TEK-LIC-2007:1.

The use of fly ash as a supplementary cementitious material (SCM) has increased in the last century due to its various environmental benefits as a recycled product. Within the last 60 years, it has been found that it can be used to effectively control damage induced by Alkali-Silica Reaction. However, it is not completely understood how to properly assign a dosage of fly ash to control the reaction. This depends greatly on the fly ash characteristics (e.g. composition, particle size, and reactivity), the reactivity of the aggregate (e.g. high to low reactivity level) and the environmental exposure conditions. The characteristics of the fly ash depend on the coal source being burned and the burning conditions that result in the fly ash formation. A major concern when supplementing cement with fly ash for ASR mitigation is the effect of the alkali contribution of the fly ash to the concrete pore solution. Current test methods cannot accurately determine the alkali contribution of fly ashes and there is no standardized test method to doing so. When contributed by the implementation of a SCM, alumina has been found to play a role in the ability of an SCM to mitigate ASR-induced damage. It has been observed that fly ashes containing higher levels of alumina (18-25%) tend to improve concrete durabilty more effectively when compared to fly ashes with lower levels of alumina. Additionally, the use of metakaolin, which is composed of 45-50% alumina, has been found to lessen expansion with a lower percentage of cement replacement than would be required if fly ash is used. Furthermore, the use of fly ash with another SCM material, a high quality ultra-fine fly ash or alumino-siliceous metakaolin, in ternary blends may improve the performance of fly ash resulting in a broadening of the spectrum of SCMs usable for ASR mitigation. For successful use of SCMs, it is important to develop an understanding of the alkalisilica reaction and the ability of such SCMs to control expansion. This report provides an overview of alkali-silica reaction and the use of fly ash and metakaolin as SCMs to mitigate expansion due to the reaction, with an emphasis on the role of alumina when contributed from the two materials. / Graduation date: 2012

A highly self-ordered hexagonal array of cylindrical pores has been fabricated by anodizing a thin film of Al on substrate and subsequent growth of GaN and InGaN in these nanoholes has been performed. This AAO template-based synthesis method provides a low cost process to fabricate GaN-based nanomaterials fabrication. / Singapore-MIT Alliance (SMA)

Thesis (M. Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2008.

This document describes work performed related to the determination of how elemental additions affect the interfacial fracture toughness of thermal barrier coatings at the bond coat/thermally grown oxide interface in gas turbines. These turbines are exposed to cyclical thermal loading, therefore a simulation was designed to model this interface in a temperature cycle between 200 K and 1000 K that included oxide growth between 2 μm and 27 μm. The fracture toughness of this interface was then determined to elucidate the function of elemental additions. It was shown that minimal concentrations of atomic species, such as hafnium and yttrium cause notable increases in the toughness of the bond coat/thermally grown oxide interface, while other species, such as sulphur, can dramatically reduce the toughness. Furthermore, it was shown that, contrary to some empirical results, the addition of platinum has a negligible effect on the fracture toughness of this interface.