Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Neste trabalho, foram estudadas as caracterÃsticas estruturais de nanopartÃculas de Ãxidos semicondutores SnO2 dopadas com ferro, atravÃs de difraÃÃo de raios-x e espectroscopia MÃssbauer. O composto em estudo (Sn1−xFexOy) foi preparado por moagem mecÃnica de altas energias e sol-gel proteico. As amostras preparadas por moagem apresentaram aumento de dopagem na matriz semicondutora como funÃÃo do tempo de moagem, mas tambÃm apresentaram impurezas indesejÃveis provenientes do recipiente e das esferas que foram utilizadas na sÃntese. Uma sÃrie de amostras com concentraÃÃes variadas de ferro foram lavadas com HCl e reanalisadas. Resultados obtidos dessas medidas mostram que o ferro entra na rede do SnO2 substituindo o Sn de forma aleatÃria independente da concentraÃÃo de ferro. TambÃm foi observado a formaÃÃo de um sÃtio de ferro com deficiÃncia de oxigÃnio que à atribuÃdo ao desbalanÃo estequiomÃtrico dos compostos precursores usados na moagem. Amostras de SnO2 nanoparticuladas foram sintetizados pelo mÃtodo sol-gel proteico com trÃs temperaturas de calcinaÃÃo. Foi observado que o tamanho de partÃcula à diretamente proporcional à temperatura de calcinaÃÃo. TambÃm por sol-gel proteico foram preparadas amostras de Sn0,90Fe0,10O2 nanoparticulado. Foi identificado que a temperatura de calcinaÃÃo de 400ÂC hà formaÃÃo de Fe2O3 espÃrio. Jà a 300ÂC a Ãnica fase presente à a de SnO2 dopada com ferro. Assim como nas amostras produzidas por moagem, essa amostra apresentou dois sÃtios de ferro como valores de quadrupolo menor do que na moagem indicando menor distorÃÃo da rede cristalina. A quantidade relativa de sÃtios com deficiÃncia de oxigÃnio à bem menor nas amostras preparadas por sol-gel mostrando que o composto produzido por sol-gel proteico possui uma concentraÃÃo mais estequiomÃtrica do que os preparados por moagem. / In this work structural characterization by x-ray diffraction and MÂossbauer spectroscopy of Fe-doped semiconducting oxide SnO2 nanoparticles is reported. The compound under study (Sn1−xFexOy) was prepared by high energy ball milling and proteic sol-gel. The samples prepared by ball milling showed an increase of Fe-doping in the semiconducting matrix as a function of milling time, as well as amounts of undesirable metallic iron impurities from the milling tools. A series of samples with various Fe concentrations were HCl-washed in order to eliminate the impurities. Results obtained from measurements on these samples showed that Fe enters the host matrix randomly replacing Sn in octahedral sites regardless of iron concentration. It was also showed the presence of oxygen deficient iron sites attributed to the stoichiometric unbalance of precursor materials used in the milling process. Samples of nanosized SnO2 were prepared by proteic sol-gel with three calcination temperatures. It was found that average particle sizes are directly proportional to the temperature. Nanostructured Sn90Fe10O2 was also synthesized by proteic sol-gel. Formation of spurious Fe2O3 was found at calcination temperature of 400ÂC. At 300ÂC, on the other hand, monophased Fe-doped SnO2 was achieved. Likewise the milled samples, this sample presented two different octahedral iron sites, although with quadrupole splitting slightly smaller than those for the milled samples indicating a less distorted crystal structure. The significantly smaller relative number of oxygen-deficient sites in the proteic sol-gel sample shows that this compound has a more stoichiometric concentration of Fe, Sn and O than those prepared by ball milling.

Neste trabalho investigou-se a obtenção do composto TiFe a partir da moagem de alta energia de misturas de pós de TiH2 e Fe, seguida de aquecimento sob vácuo para a reação de síntese. No lugar do Ti, o TiH2 foi escolhido como precursor em razão de sua fragilidade, benéfica para a diminuição da aderência dos pós ao ferramental de moagem. Foram preparados dois lotes de misturas obedecendo-se a relação Ti:Fe de 50:50 e 56:44. Ambos foram processados em um moinho do tipo planetário por tempos que variaram de 5 até 40 horas, sob atmosfera de argônio de elevada pureza. Em todos os experimentos foram mantidos constantes a velocidade de rotação do prato do moinho, a quantidade de amostra, o diâmetro e o número de bolas. As amostras moídas foram caracterizadas por calorimetria exploratória diferencial (DSC), termogravimetria (TG), microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e fluorescência de raios X por dispersão de energia (EDXRF). Apenas TiH2 e Fe foram observados nas amostras moídas, com um grau crescente de mistura em função do tempo de moagem. O composto TiFe nanoestruturado (12,5 a 21,4nm) foi obtido de forma majoritária em todas as amostras após a reação de síntese promovida pelo tratamento térmico a 600ºC (873K). As amostras reagidas foram caracterizadas por microscopia eletrônica de transmissão (MET) e DRX. Um equipamento do tipo Sievert, operando sob um fluxo constante (modo dinâmico), foi utilizado para levantar as curvas termodinâmicas de absorção e dessorção de hidrogênio. Todas as amostras absorveram hidrogênio à temperatura ambiente (~298K) sem a necessidade de ciclos térmicos de ativação. Os melhores resultados foram obtidos com as amostras moídas por 25 e 40 horas, de composição não estequiométrica 56:44. Tais amostras absorveram e dessorveram hidrogênio à temperatura ambiente, sob os platôs de aproximadamente 6,4 e 2,2bar (~0,6 e 0,2MPa), respectivamente. A capacidade máxima de armazenamento foi de 1,06% em massa de hidrogênio (H:M~0,546), sob pressão de até 11bar (1,1MPa), com reversão de até 1,085% em massa de hidrogênio (H:M~0,559), sob pressão de até 1bar (0,1MPa). Estas amostras também apresentaram maior cinética de absorção e dessorção de hidrogênio com fluxos de 1,23 (25h) e 2,86cm3/g.min. (40h). Tais resultados são atribuídos à variação composicional da fase TiFe e à maior quantidade de TiH2 livre. / In this work high-energy ball milling from TiH2 and Fe powder mixtures, followed by post-heating under vacuum, were performed for the reaction synthesis of TiFe compound. TiH2 was used instead of Ti due to its brittleness, preventing strong particles adhesion to the grinding balls and vial walls. Two mixtures batches were prepared following Ti:Fe ratios of 50:50 and 56:44. Both of them were dry-milled in a planetary mill for times ranging from 5 to 40 hours, under high purity argon atmosphere. The speed of main disk rotation, the amount of sample, number and diameter of the balls were kept constant in all experiments. As-milled samples were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TG), scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray fluorescence (EDXRF). As-milled materials presented only Fe and TiH2 phases showing increased mixture degree with the milling time. After heat treatment at 600ºC (873K), nanostructured TiFe compound (12.5 to 21.4nm) was mostly formed in all samples. Reacted samples were characterized by transmission electron microscopy (TEM) and XRD. Hydrogen absorption and desorption thermodynamics curves were determined in a Sievert-type apparatus operating at constant flow (dynamic mode). All samples absorbed hydrogen at room temperature (~298K) requiring no thermal activation cycles. Best results were seen on samples milled at 25 and 40 hours, with non-stoichiometric composition 56:44. Those samples absorbed and desorbed hydrogen at plateaus of 6.4 and 2.2bar (~0.6 and 0.2MPa), respectively. Maximum hydrogen storage capacity was 1.06 wt% (H:M~0,546) at 11bar (1.1MPa), with reversion of 1.085 wt% (H:M~0,559) at 1bar (0.1MPa). Higher hydrogen absorption and desorption kinetics were observed in those samples, as well, with flows of 1.23 (25h) and 2.86cm3/g.min. (40h). Such results were assigned to the compositional variation of TiFe phase and to the largest amount of free TiH2.

Le travail de thèse est consacré à la synthèse, l’élaboration et à l’étude des propriétés physiques d’une famille d’oxydes semi-conducteurs BiVO4 sous formes de nanostructures et de films minces incluant un dopage métallique (Metal = Cu, Mo et Ag) dans le but de réaliser des photocatalyseurs efficaces sous irradiation en lumière visible. La synthèse de nanopoudres dopées a ainsi été effectuée par la technique de broyage planétaire à haute énergie ainsi que par la méthode sol-gel. Les matériaux obtenus et les effets de dopage ont été étudiés sur les caractéristiques structurales, électroniques et optiques. En conjuguant des études par XPS, Raman et RPE, nous avons montré que le dopage substitutionnel est effectivement réalisé pour les ions (Cu, Mo) localisés dans les sites cristallins des ions vanadium alors que le dopage par l’élément Ag contribue à former des clusters métalliques localisés à la surface de nanoparticules de BiVO4 formant ainsi des nanocomposites. Les réactions photocatalytiques ont été étudiées par la dégradation de colorants organiques (Acide bleu 113, méthyle orange (MO)) dans des solutions faiblement concentrées. Parmi les ions dopants substitués dans les matrices hôtes, le dopage au cuivre (Cu2+) a montré de meilleures performances en raison d'une augmentation de la densité de charges photo-générées et de la conductivité électrique par rapport au cas du dopage au molybdène. Pour le dopage à l’argent, la formation de clusters métalliques donnent lieu à des effets de résonances plasmoniques qui améliorent l'efficacité photocatlytique à un niveau équivalent à celui du dopage substitutionnel au cuivre. La deuxième contribution de ce travail a porté sur la réalisation par pulvérisation cathodique rf-magnétron de films minces BiVO4 dopés par des éléments Mo et Cu dans des conditions définies par l'atmosphère de dépôt à base de pressions partielles d’un gaz Ar ou d’un mélange Ar / O2 et des températures de substrats variables jusqu'à 450 ° C. Les paramètres optimaux de dépôt ont été identifiés pour réaliser des films cristallins à faible rugosité de surfaces ou à morphologies en nano-îlots. Des études photocatalytiques utilisant des films minces dopés ont été effectuées par la dégradation des colorants organiques (MO) sous rayonnement visible. Ces études montrent que la morphologie des films avec des surfaces spécifiques importante est aussi un facteur d’amplification des performances photocatalytiques des films minces dopés Me-BiVO4. / The thesis work is devoted to the synthesis and investigations of the physical properties of a family of semiconducting oxides based on BiVO4 as nanostructures or thin films including a metal doping (Metal = Cu, Mo and Ag) in order to achieve effective photocatalysts under visible light irradiation. The synthesis of doped nanopowders was carried out by the techniques of high-energy ball milling and sol-gel. The resulting materials and doping effects were characterized on the structural, electronic and optical properties. By combining XPS, Raman and EPR studies, it was shown that the substitutional doping is achieved for the doping ions (Cu, Mo) being located in the lattice sites of the vanadium ions. Oppositely, Ag doping contributes to form Ag metal clusters located on the surface of nanoparticles of BiVO4 thereby forming nanocomposites. Photocatalytic reactions were studied by the degradation of organic dyes (Acid Blue 113, methyl orange (MO)) in low concentrated solutions. Among the doping ions substituted in the host matrices, Cu2+ showed better photocatalytic performances because of an increase in the density of photo-generated charges and similar effect on the electrical conductivity compared to the case of Mo doping. In the Ag based nanocomposites, the formation of metal clusters seems to induce surface resonance plasmonic effects that improve the efficiency of photocatalytic reactions with respect to the activity demonstrated for substitutional doping. The second contribution of the thesis work was devoted to BiVO4 thin films deposition by rf sputtering process with Mo and Cu doping under defined synthesis conditions such as the partial pressures of Ar gas or an Ar / O2 mixture and varying the substrate temperatures up to 450 ° C. The optimal deposition parameters have been identified to achieve crystalline films with low roughness surface or alternatively with nano-islands morphologies. Photocatalytic studies using doped thin films were carried out through the degradation of organic dyes (MO) under visible light irradiation. The performed measurements show that the film morphology with high specific surface is also a key factor in the amplification of photocatalytic reactions in metal doped thin films.

Le couplage covalent sur surface métallique en UHV (Ultra High Vacuum) est une technique émergente permettant de synthétiser des structures moléculaires impossibles à obtenir par la chimie en solution (nanorubans de graphène, polymères 2D par exemple). Aujourd'hui, le plus grand défi reste le développement de ces réactions sur des surfaces isolantes pour différentes applications comme, par exemple, l'électronique moléculaire. En particulier, le couplage de dérivés d'acides benzoïques, greffés sur les surfaces de carbonate de calcium en UHV par des groupes carboxyliques, a été démontré récemment pour la première fois. Lors de ces travaux, nous avons dans un premier temps synthétisé des molécules précurseurs de réactions de couplage (homo-couplage d'éthyne, photopolymérisation, polycondensation et réaction d'Ullmann) sur des surfaces de carbonate de calcium en UHV. Par la suite, nous avons mené cette étude à l'échelle macroscopique (semi-préparatoire), par greffage de molécules sur des microparticules de carbonate de calcium, puis activation de la réaction, et enfin dissolution du substrat afin d'extraire le produit final. Les microparticules ont été obtenues par broyage de produit commercial ainsi que par spray pyrolyse et complètement caractérisées par FTIR, ATG/DTG, DRX, MEB et BET. Les réactions de couplage ont été activées par deux méthodes sans solvant: par broyage dans une broyeuse planétaire ou par traitement thermique sous vide. Alors qu'en UHV le couplage de l'acide 4-iodobenzoïque donne l'acide biphenyldicarboxylique, en mécanochimie nous avons obtenu l'acide benzoïque et par activation thermique l'éther dibenzoïque. / Covalent coupling on metallic surfaces in UHV (Ultra High Vacuum) conditions is a new method for preparing molecular structures otherwise impossible to achieve in solution (graphene nanoribbons, 2D polymers for instance). The major challenge is now to extend these reactions from metallic to insulating surfaces, for future applications as, for instance, in molecular electronics. In particular, the coupling reaction of benzoic acid derivatives, grafted on calcite via carboxylic groups, has been demonstrated for the first time in UHV conditions. In the first part of this work, we synthesized precursor molecules for specific reactions (homocoupling of ethynes, photopolymerization, polycondensation and Ullmann reaction) on calcium carbonate in UHV conditions. In the second part of this work we extended this investigation up to the macroscale level (semi-preparative) by grafting molecules on calcium carbonate microparticles, followed by reaction activation and finally by dissolution of the substrate in order to recover the coupling products. The calcium carbonate microparticles were prepared by grinding commercial product or by spray pyrolysis and were fully characterized by FTIR, TG/DTG, XRD, SEM and BET techniques. Then, after grafting of organic reactant, the reactions were activated with two different solvent-free methods: by grinding in a planetary milling machine or by heating the samples in a furnace under vacuum. Whereas in UHV conditions, 4-iodobenzoic acid affords biphenyldicarboxylic acid, mechanochemical condition gives benzoic acid and thermal activation the dibenzoic acid ether.

This diploma thesis deals with milling of dispersed particles of WO3 using low-cost wet ball milling. Thin layers of WO3 were formed from them. These layers were characterized by profilometry, turbidity measurements, XRD and SEM. The photocatalytic activity was studied by the electrocatalytic properties of these layers. Profilometric measurements showed declining trends with milling time. XRD measurements confirmed the milling process and revealed a change in the crystalline phase during this process. Electrophotocatalytic measurements confirmed the photocatalytic activity of these layers and revealed its trends.

Metallic glasses exhibit many attractive attributes such as outstanding mechanical, magnetic, and chemical properties. Due to the absence of crystal defects, metallic glasses display remarkable mechanical properties including higher specific strength than crystalline alloys, high hardness and larger fracture resistance than ceramics. The technological breakthrough of metallic glasses, however, has been greatly hindered by the limited plastic strain to failure. Thus, several strategies have been employed to improve the intrinsic and extrinsic effects on the flow behavior of metallic glasses with respect to their fracture toughness and overall plastic strain. One of the suggested strategies is the production of a composite consisting of the brittle metallic glass along with a ductile second phase that either acts as an active carrier of plastic strain or passively enhances the multiplication of shear bands via shear-band splitting . Another approach for increasing plastic deformation consists of introducing pores as a gaseous second phase into the material. The pores are similarly effective in delaying catastrophic failure resulting from shear band localization. In metallic glasses with high porosity, propagation of shear bands can even become stable, enabling macroscopic compressive strains of more than 80 % without fracture. In this thesis, Ni59Zr20Ti16Si2Sn3 glass and its composites have been fabricated using mechanical milling and consolidation by hot pressing followed by extrusion of Ni59Zr20Ti16Si2Sn3 metallic glass powder or Ni59Zr20Ti16Si2Sn3 metallic glass powder reinforced with 40 vol.% of brass particles to obtained bulk composite materials with high strength and enhanced compressive plasticity and to generate porous structure in Ni59Zr20Ti16Si2Sn3 metallic glass using selective dissolution. The brass–glass powder mixtures to be consolidated were prepared using two different approaches: manual blending and ball milling to properly vary size and morphology of the second phase in the composites. Powder consolidation was carried out at temperatures within the supercooled Liquid (SCL) region, where the glassy phase displays a strong decrease of viscosity, with using the sintering parameters which were chosen after analysis of the crystallization behavior of the glassy phase to avoid its crystallization during consolidation. Ball milling has a significant effect on the microstructure of the powder mixtures: a refined layered structure consisting of alternating layer of glass and brass is formed as a result of the mechanical deformation. However, ball milling reduces the amorphous content of the composite powders due to mechanically induced crystallization and reaction of the glass and brass phases during heating. In addition, the milling of the composite powders and the following consolidation step reduces the amorphous content by about 50 %. The bulk amorphous Ni59Zr20Ti16Si2Sn3 alloy synthesized by hot pressing exhibits higher strength (2.28 GPa) than that of the as-cast bulk amorphous Ni59Zr20Ti16Si2Sn3 alloy (2.2 GPa). The mechanical behavior of the glass-brass composites is significantly affected by the control of the microstructure between the reinforcement and the nano-grained matrix phase through the different methods used for the preparation of the powder mixtures. The strength of the composites increases from 500 MPa for pure brass to 740 and 925 MPa for the composites with 40 and 60 vol.% glass reinforcement prepared by manual blending. The strength further increases to 1240 and 1640 MPa for the corresponding composites produced by ball milling caused by the remarkable effect of the matrix ligament size on the strengthening of the composites. The porous metallic glass was obtained by the selective dissolution in a HNO3 solution of the fugitive brass phase in the Ni59Zr20Ti16Si2Sn3 composite. The microstructure of the porous samples consists of highly elongated layered pore structures and/or irregularly shaped pores. The average size of the pores depends on the processing parameters and can be varied in the range of 0.4–15 µm. Additional porous samples were prepared from different extruded composite precursors of blended and milled powder mixtures. This leads to customized hybrid porous structures consisting of a combination of large and small pores. The specific surface area of the porous Ni-based metallic glass powder measured by the BET method is 16 m2/g, while the as-atomized Ni59Zr20Ti16Si2Sn3 powder has a specific surface area of 0.29 m2/g. This indicates a mechanical milling induced enhancement in surface area by refinement of the fugitive brass phase. However the specific surface area of the porous Ni-based metallic glass obtained from as-extruded precursors is 10 m2/g caused by a breakdown of the porous structure during selective dissolution of the nano-scale fugitive phase. Although milling of the present composite powders and the following consolidation step reduces the amorphous content by about 50 %, through the use of glassy phases with improved stability against mechanically induced crystallization along with reduced affinity with the fugitive phase to avoid unwanted reactions during processing, this approach using powder metallurgical offers the possibility to produce highly active porous bulk materials for functional applications, such as catalysis, which require the fast transport of reactants and products provided by the large pores along with high catalytic activity ensured by the large surface area characterizing the small pores. Accordingly, gas absorption ability tests of porous Ni-based metallic glass powders have been performed in order to evaluate the possibility of replacement of conventional support materials. From these first tests it can be conclude that additional opportunities should exist for nano-porous MGs with designed architecture of porous structures that are tailored to specific functional applications. / Metallische Gläser weisen viele attraktive mechanische, magnetische und chemische Eigenschaften auf. Aufgrund der fehlenden Kristallstruktur zeigen metallische Gläser bemerkenswerte mechanische Eigenschaften, einschließlich höherer spezifischer Festigkeit, höherer Härte und größerer Bruchfestigkeit als Keramik. Der technologischen Durchbruch metallischer Gläser wird jedoch bis heute stark von ihremspröden Bruchverhalten behindert. Deshalb wurden verschiedene Herstellungsverfahren entwirkt, um sowohl die plastische Verformung der metallischer Massivgläser zu erhöhen, als auch um die mechanischen Eigenschaften generell zu verbessern. Eine mögliche Methode, zur Erhöhung der Plastizität und zur Beeinflussung der mechanischen Eigenschaften der metallischen Gläser ist der Einbau zweiter Phasen, wie z.B. durch Fremdpartikel Verstärkung oder Poren in Kompositen. Die Scherband bewegung wird durch die Wechselwirkung mit zweiten Phasen behindert, und gleichzeitig werden durch die in den Grenzflächen entstehenden Spannungsspitzen zwischen der zweiten Phase und der Matrix neue Scherbänder initiert. Dies führt zur Bildung einer Vielzahl von Scherbändern, was eine höhere plastische Dehnung zur Folge hat, da die Deformationsenergie auf ein größeres Volumen verteilt wird. In der vorliegenden Arbeit wurden Ni59Zr20Ti16Si2Sn3 Massivglas und mit Messing- verstärkte Komposite durch Kugelmahlen und Heißpressen mit anschließender Extrusion von Ni59Zr20Ti16Si2Sn3 Pulver oder Ni59Zr20Ti16Si2Sn3 Pulver mit 40 vol.% Messing Partikeln hergestellt. Neben der Herstellung der Ni59Zr20Ti16Si2Sn3 Komposite mit Messing Partikeln, wurden auch Ni59Zr20Ti16Si2Sn3 Komposite mit definierter Porösität durch die selektive Auflösung der zweiten Phase erzeugt. Die verwendete Mischung von Messing und metallischem Glaspulver wurde über zwei verschiedene Ansätzen hergestellt: die Pulver wurden manuell gemischt oder gemahlen, um die optimale Größe und Morphologie der zweiten Phase in den Komositen zu erzeugen. Das Sintern der Pulver erfolgte bei Temperaturen im Bereich der unterkühlten Schmelze, wobei die Legierung eine starke Abnahme der Viskosität zeigte, mit Hilfe optimierter Sinterparameter, die nach der Analyse des Kristallisationsverhaltens der gläsernen Phase ausgewählt wurden, um deren Kristallisation während der Konsolidierung zu vermeiden. Kugelmahlen hat einen signifikanten Einfluss auf die Mikrostruktur der gemahlenen Pulver: Eine verfeinerte Lamellare Struktur, teils bestehend aus Glas und teils aus Messing, wird durch mechanische Verformung gebildet. Kugelmahlen reduziert jedoch den amorphen Anteil der Komposite durch mechanische induzierte Kristallisation und die Reaktion der Glas- und Messing- Phasen durch Erwärmung. Das Kugelmahlen der Komposite (Pulver) und das darauf folgende Sintern führte zur eine Absenkung der freien Enthalpie der amorphen Phase um ca. 50%. Ni59Zr20Ti16Si2Sn3 metallische Massivgläser, welche durch Heißpressen hergestellt werden, weisen eine höhere Streckgrenze von 2.28 GPa als das gegossene Ni59Zr20Ti16Si2Sn3 Massivglas (2.2 GPa) auf. Die mechanischen Eigenschaften der mit Messing Ni59Zr20 Ti16Si2Sn3 verstärkten Komposite sind abhängig von der Kontrolle der Mikrostruktur zwischen den zweiten Phasen und der Matrixphase durch die verschiedenen Verfahren zur Herstellung von Pulvermischungen. Die Festigkeiten der Komposite, welche durch Handmischen und Heißpressen mit nachfolgender Extrusion hergestellt wurden, erhöhten sich von 500 MPa für reines Messing bis auf 740 und 925 MPa für die Komposite mit 40 und 60 Vol. % Glaspartikel- Verstärkung durch Handmischen. Die Festigkeiten erhöhten sich nochmals auf 1240 und 1640 MPa für die Komposite mit 40 und 60 Vol. % an Glaspartikel-Verstärkung mit lamellare Stuktur, die durch Kugelmahlen hergestellt würden. Die Ursache hier für liegt in der Wirkung der Ligamentabmessungen zwischen den Matrixbestandteilen hinsichtlich der Verfestigung der Komposite. Die Porösität im metallischen Glas wurde durch die selektive Auflösung der flüchtigen Messingphasen in den Kompositen mit Salpetersäure-Lösung erhalten. Die Mikrostuktur der porösen metallischen Gläser besteht aus stark elongiert geschichteten Porenstrukturen und/oder unregelmäßig geformten Poren. Die durchschnittliche Größe einer Pore hängt von den behandelnden Parametern ab und kann von 0.4–15 µm variieren. Weitere poröse Proben wurden ausgehend von verschiedenen extrudierten Komposit-Precursoren aus handgemischten und kugelgemahlenen Pulvermixturen erzeugt. Dies führte zu angepassten hybrid-porösen Strukturen bestehend aus einer Kombination von großen und kleinen Poren. Die spezifische Oberfläche des porösen Glaspulvers gemessen mit Hilfe der BET- Methode, beträgt 16m2/g, wohingegen das atomisierte Ni59Zr20Ti16Si2Sn3 MG Ausgangspulver eine spezifische Oberfläche von 0.29 m2/g besitzt. Dies weist darauf hin, dass das Mahlen eine Vergrößerung der Oberfläche durch die Verfeinerung der flüchtigen Messingphase induziert. Die spezifische Oberfläche der porösen-metallischen Gläser beträgt 10 m2/g und entsteht durch die Zerstörung der porösen Struktur während der selektiven Auflösung der nanoskaligen flüchtigen Phase. Obwohl das Kugelmahlen der Komposite (Pulver) und die darauf folgende Konsolidierung zwar den amorphen Anteil um etwa 50% reduziert, bietet die Pulvermetallurgische Herstellung durch die Verwendung von gläsernen Phasen mit verbesserter Stabilität gegenüber mechanisch induzierter Kristallisation, sowie einer reduzierten Affinität mit der flüchtigen Messingphase zur Vermeidung von unerwünschten Reaktionen während des Prozesses eine Möglichkeit, hochaktive poröse metallische Gläser für funktionelle Anwendungen, wie z.B. Katalyse, zu entwickeln. Hier ist eine schnelle Transport von Reaktanten und Produkten, welcher von den großen Poren, sowie eine hohe katalytische Aktivität, die von kleinen Poren und einer großen Oberfläche sichergestellt wird wesentlich. Daher wurden Untersuchungen zur Gasabsorptionsfähigkeit von porösem metallischen Glaspulver durchgeführt, um die Möglichkeit der Ersetzung von konventionellen Trägermaterialen bewerten zu können. Diese ersten Versuche zeigen die grundsäLzliche Eignung nano poröse metallischer Gläser zur Herstellung von porösen Strukturen mit einstellbarer Porenarchitektur auf die Langfristig für spezifische funktionelle Anwendungen von Interesse sein könnten.

The process of milling drugs to obtain samples with a desirable particle size range has been widely used in the pharmaceutical industry, especially for the production of drugs for inhalation. However by subjecting materials to milling techniques surfaces may become thermodynamically activated which may in turn lead to formation of amorphous material. Polymorphic conversions have also been noted after milling of certain materials. Salt and cocrystal formation is a good way of enhancing the properties of an API but little or no work has been published which investigates the stability of these entities when subjected to milling. Different milling techniques (ball and jet) and temperatures (ambient and cryogenic) were used to investigate the milling behaviour of polymorphs, salts and cocrystals. All materials were analysed by XRPD and DSC to investigate any physical changes, i.e. changes in melting point and by inverse gas chromatography (IGC) to investigate whether any changes in the surface energetics occurred as a result of milling. Another aim of this thesis was to see if it was possible to predict the milling behaviour of polymorphs by calculating the attachment energies of the different crystal facets using Materials Studio 4.0. These results were compared to the IGC data to see if the predicted surface changes had occurred. The data collected in this study showed that different milling techniques can have a different effect on the same material. For example ball milling at ambient temperature and jet micronisation of the SFZ tosylate salt caused a notable increase in the melting point of the material whereas ball milling at cryogenic temperatures did not cause this to happen. The IGC data collected for this form also showed a contrast between cryomilling and the other two techniques. The study also showed that the formation of salts and cocrystals does not necessarily offer any increased stability in terms of physical properties or surface energetics. Changes in melting point were observed for the SFZ tosylate salt and the IMC:Benzamide cocrystal. Changes in the specific surface energies were also observed indicating that the nature of the surfaces was also changing. The materials which appeared to be affected the least were the two stable polymorphs, gamma IMC and SFZ III. The computational approach used has many limitations. The software does not allow for conversion to the amorphous form or polymorphic conversions. Such conversions were seen to occur, particularly for the metastable polymorphs used, meaning that this computational approach may only be suitable for stable polymorphs.

Made available in DSpace on 2017-07-24T19:38:04Z (GMT). No. of bitstreams: 1 Alan Rogerio Ferreira Lima.pdf: 4210754 bytes, checksum: 82a7a7898a00633ad3aa474df848f207 (MD5) Previous issue date: 2011-02-28 / This work aimed the study of the effect of transition metals (Ni, Fe, Co) on the spontaneous polarization of the ferroelectric oxides of tetragonal tungsten bronze (TTB)-type structure of potassium strontium niobate (KSr2Nb5O15) and of the KSr2(FeNb4)O15-d, KSr2(NiNb4)O15-d and KSr2(CoNb4)O15-d solid solutions. All systems investigated were prepared by mechanical mixture of oxide/carbonates by high-energy ball milling. The calcination temperature was performed to obtain nanoparticles and the nanostructured particles were evaluated. The evolution of mass loss, chemical bonds, crystalline structure and the electrical behavior were evaluated using the thermal analysis (thermogravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC), infrared absorption spectroscopy (FTIR), X-ray diffraction (XRD) and impedance spectroscopy, respectively. From the impedance spectroscopy technique were studied the dielectric properties of the nanoparticles and the dielectric permittivity of the KSr2Nb5O15, KSr2(FeNb4)O15-d, KSr2(NiNb4)O15-d and KSr2(CoNb4)O15-d systems was determined. The highest permittivity value was obtained for KSr2(FeNb4)O15-d. The determination of crystallographic parameters of nanopowders was performed using the Rietveld method. From the crystallographic parameters was simulated the crystalline structure and determined the spontaneous polarization for KSr2Nb5O15, KSr2(FeNb4)O15-d, KSr2(NiNb4)O15-d and KSr2(CoNb4)O15-d systems based on the atomic displacement (Dz) of Nb (niobium) atom, in the z plane, from the central position of the [NbO6] octahedron. The variation of spontaneous polarization of the nanoparticles with the addition of transition metals in the KSr2Nb5O15 host structure confirmed the existence of ferroelectricity in the systems investigated. / O objetivo deste trabalho foi estudar o efeito de metais de transição (Ni, Fe, Co), sobre a polarização espontânea, dos óxidos ferroelétricos de estrutura tungstênio bronze (TB) de niobato de potássio e estrôncio (KSr2Nb5O15) e das soluções sólidas de KSr2(FeNb4)O15-d, KSr2(NiNb4)O15-d e KSr2(CoNb4)O15-d. Todos os sistemas investigados foram preparados por mistura de óxidos/carbonatos pelo do método de ativação mecânica por moagem de alta energia. A temperatura de calcinação necessária à obtenção de nanopartículas foi otimizada e as partículas nanoestruturadas foram avaliadas. A evolução dos parâmetros de perda de massa, ligações químicas, estrutura cristalina e o comportamento elétrico, foram avaliados utilizando as técnicas de análise térmicas (análise termogravimétrica (ATG) e calorimetria diferencial exploratória (DSC), espectroscopia de absorção na região do infravermelho, difração de raios X e espectroscopia de impedância, respectivamente. A partir da técnica de espectroscopia de impedância foram estudadas as propriedades dielétricas das nanopartículas em suspensão, determinando a permissividade dielétrica dos sistemas KSr2Nb5O15, KSr2(FeNb4)O15-d, KSr2(NiNb4)O15-d e KSr2(CoNb4)O15-d. O maior valor de permissividade foi obtido para o KSr2(FeNb4)O15-d. A determinação dos parâmetros cristalográficos dos nanopós foi realizada utilizando o método de Rietveld de refinamento e/ou ajuste de estrutura cristalina. A partir dos parâmetros cristalográficos foi simulada a estrutura cristalina e determinada a polarização espontânea para os sistemas KSr2Nb5O15, KSr2(FeNb4)O15-d, KSr2(NiNb4)O15-d e KSr2(CoNb4)O15-d com base no deslocamento atômico (Dz) do átomo de Nb (nióbio), no plano z, da posição central do octaedro [NbO6]. A variação da polarização espontânea das nanopartículas, com a adição de metais de transição na estrutura hospedeira do KSr2Nb5O15, confirmou a existência de ferroeletricidade nos sistemas investigados.

Le stockage d'hydrogène en phase solide sous forme d'hydrures, est l'une des solutions non-polluantes futures pour le stockage et le transport de l'énergie. Parmi les matériaux candidats, LiBH4 a été sélectionné vu sa capacité gravimétrique élevée en hydrogène (jusqu'à 13,6 % H2 en masse). Ce matériaux possède des propriétés thermodynamiques et cinétiques insuffisamment établies pour comprendre son comportement dans les applications futures. Sa décomposition peut être facilitée en présence de l'hydrure MgH2. Ainsi, le composite MgH2-xLiBH4 / Hydrides for solid-state hydrogen storage are one of the future solutions - pollutant free - for the storage and the transport of energy. Among the candidates, LiBH4 was selected considering its high gravimetric hydrogen capacity (up to 13.6 wt.% H2). This material has thermodynamic and kinetic properties insufficiently established to be included in future applications. Its decomposition can be facilitated within the presence of the hydride MgH2. Thus, the composite MgH2-xLiBH4 (0< x< 3.5) reactivated by high energy ball-milling, was studied regarding its microstructural properties and stability of the phases. The desorption reaction of hydrogen, with or without additives, shows the appearance of additional phases accompanying the principal reaction. Heat capacity measurements of LiBH4 revealed the presence of an abnormal behaviour before the polymorphous transition (Ttrs = 386 K), attributed to the increase of crystal defects in agreement with the existence of a hypo-stoichiometric domaine LiBH4-ε observed at higher temperatures. The stability of the three-phase system LiBH4-LiH-B was studied resulting to the principal reaction of decomposition: LiBH4(s,l) → LiH(s) + B(s) + 1,5H2(g). Vapour pressure measurements of LiBH4 showed that H2 is the major component of decomposition with minor species such as B2H6 and BH3. The thermodynamic properties of LiBH4 were critically assessed, gathering the new data with those existing in the literature, in the aim of modelling of reactions occurring in hydride mixtures.

This study investigated the influence of the attainable region technique to ball milling as applied in reactor technology. Flow rate, ball filling, mill speed, ball size and mill density were varied. When each was varied, the rest of the parameters were kept constant in-order to determine the influence of each parameter on the process of milling. Selection function and breakage function parameters were selected for the mill model. These were kept constant for all four circuit configurations: open milling circuit, normal closed circuit, reverse closed circuit, and combined closed circuit. Flow rate was varied from 10 tph to 150 tph. It was observed that in all circuit configurations the optimum results were obtained from 90 tph upwards. When ball filling was varied, the optimum results were obtained between 30 % and 40 % of ball filling. At this range the mill is neither experiencing under-filling nor over-filling. When the mill speed was varied, at 60 – 80 % of critical speed the product specification was achieved and for grinding balls, sizes of between 60 mm and 90 mm yielded the optimum results. Varying the mill density resulted in insignificant changes. From the results, the combined closed circuit produced more of the product specification. / School of Engineering / M. Tech. (Engineering: Chemical)