O aluminato de magnésio (MgAl2O4; espinélio) apresenta propriedades mecânicas superiores quando comparado aos materiais cerâmicos tradicionais, tais como elevados módulo elástico (273 GPa) e resistência à flexão (110 MPa), associadas à baixa densidade (3,58 g/cm3), baixo índice de reflexão (1,736), índice de transmissão óptica elevado no espectro visível e espectros no infravermelho com comprimentos de onda médios (0,2 - 5,5 µm), além da ausência de anisotropia óptica, devido à sua estrutura cúbica. No entanto, MgAl2O4 é utilizado principalmente como material refratário, apesar de possuir grande potencial em aplicações que exijam blindagem transparente leve. Nanopartículas de espinélio já foram preparadas anteriormente por diferentes métodos. Contudo, o domínio de um processo industrial contínuo, escalonável e versátil para a preparação de MgAl2O4 dopado ainda permanece como um desafio para expandir as aplicações deste material. Dentre as vias de síntese habituais utilizadas para produzir nano-óxidos, a Pirólise de Spray gerado por Pulverização Ultrassônica (PSPU) tem sido utilizada com sucesso para sintetizar nanopartículas esféricas, nanofios, nanofitas e nanovaretas. Neste contexto, o presente trabalho confirma o potencial da PSPU para produzir espinélio dopado em um processo contínuo. A influência dos parâmetros envolvidos na síntese do aluminato de magnésio por meio desta técnica, assim como o efeito da presença do cálcio e do fluoreto de lítio sobre a morfologia e a estrutura das partículas, foram investigadas por fluorescência de raios X, difração de raios X, espectroscopia no infravermelho, granulometria por difração laser, microscopia eletrônica de varredura e adsorção de N2. Finalmente, as propriedades mecânicas do produto final sinterizado foram avaliadas visando estabelecer uma correlação com as condições de síntese. O processo de síntese de aluminato de magnésio por meio do sistema de PSPU desenvolvido nas dependências do Departamento de Engenharia Metalúrgica e de Materiais da Escola Politécnica da Universidade de São Paulo demostrou-se eficaz para a produção de amostras de aluminato de magnésio puro após a etapa de sinterização, desde que respeitada a estequiometria do composto após a etapa de síntese. Por meio desta técnica, esferas micrométricas de MgAl2O4 dopadas com Ca(NO3)2 e LiF, apresentando tamanhos médios de cristalito na faixa de 3,5 - 7,0 nm e áreas de superfície específicas de 20 a 40 m2/g, foram produzidas como aglomerados esféricos de aproximadamente 2,5 µm. Durante o processo, as partículas permaneceram a temperaturas elevadas durante um curto período de tempo (de 35 a 70 segundos), permitindo a estabilidade de fases e aumento do tamanho de grãos limitado. Destaca-se ainda que as condições de síntese e/ ou incorporação de aditivos devem ser ajustados para a obtenção de amostras com maior área de superfície específica após a PSPU, o que acarretará em um produto final sinterizado com maior teor de densificação e dureza. Dessa forma, os melhores resultados foram obtidos a maiores temperaturas de pirólise e com incorporação do aditivo LiF, demonstrado a necessidade de futuros estudos mais aprofundados a respeito dos limites máximos destas variáveis para a obtenção de um produto final otimizado. Finalmente, as propriedades balísticas das amostras também foram analisadas através da aplicação de fórmulas empíricas para avaliação da fragilidade (B) e da habilidade do material dissipar energia balística (critério D), onde se observou que as amostras sintetizadas sem aditivos apresentaram boa concordância em relação aos valores reportados na literatura para a alumina. A amostra aditivada com LiF, no entanto, apresentou um incremento no critério D de cerca de 43% em relação à alumina com 99,7% de pureza, evidenciando o efeito deste aditivo nas propriedades balísticas do aluminato de magnésio produzido pela PSPU. / Magnesium aluminate (MgAl2O4; spinel) possesses superior mechanical properties when compared to traditional ceramic materials, such as high elastic modulus (273 GPa) and flexural strength (110 MPa), associated with low density (3.58 g/cm3), low reflection index (1.736), high optical transmission in visible and mid-wavelength infrared spectra (0.2 - 5.5 µm), and no optical anisotropy due to its cubic structure. However, MgAl2O4 is primarily used as a refractory material, despite its great potential as a transparent lightweight armor. Spinel nanoparticles have been previously prepared by different methods. Nevertheless, a continuous, scalable, and versatile process for the preparation of doped MgAl2O4 still remains a challenge for expanding applications. Among the usual synthesis routes used to produce nano-oxides, Ultrasonic Spray Pyrolysis (USP) has been successfully employed to synthesize nanoparticles as spheres, nanowires, nanoribbons and nanorods. In this context, the present work confirms the potential of USP to produce doped spinel in a continuous setup. The influence of the parameters involved in the synthesis of magnesium aluminate through this technique, as well as the effect of the presence of calcium and lithium fluoride on the morphology and structure of the particles, were investigated by X-ray fluorescence, X-ray diffraction, infrared spectroscopy, laser diffraction for particle size analysis, scanning electron microscopy and N2 adsorption. Finally, the mechanical properties of the sintered product were evaluated in order to establish a correlation with the synthesis conditions. The magnesium aluminate synthesis process through the USP system developed at the Department of Metallurgical and Materials Engineering of the Polytechnic School of the University of São Paulo was effective for the production of pure magnesium aluminate samples after the sintering stage, if the stoichiometry of the compound after the synthesis step is observed. Through this technique, micrometric spheres of Ca(NO3)2 and LiF doped MgAl2O4 with crystallite size in the range from 3.5 - 7.0 nm and specific surface areas varying from 20 to 40 m2/g, were produced as spherical agglomerates of approximately 2.5 µm. During the process, the particles stay at high temperatures for a short period (from 35 to 70 seconds), allowing phase stability and limited coarsening. It should also be noted that the synthesis conditions and / or the incorporation of additives must be adjusted in order to obtain samples with greater specific surface area after the USP, which will result in a sintered final product with a higher densification and hardness. Therefore, the best results were obtained at higher pyrolysis temperatures and with the incorporation of LiF additive, demonstrating the need for further studies on the maximum limits of these variables to obtain an optimized final product. Finally, the ballistic properties of the samples were also analyzed by the application of empirical formulas to evaluate the brittleness (B) and the ability of the material to dissipate ballistic energy (criterion D), where it was observed that the samples synthesized without additives showed good agreement with the values reported in the literature for alumina. The sample containing LiF additive, however, showed an increase in the D criterion of about 43% in relation to alumina with 99.7% purity, evidencing the effect of this additive on the ballistic properties of magnesium aluminate produced by USP.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present work strontium aluminate powders (Sr1-a-bAl2O4:EuaDyb) with different dopant concentrations were prepared by Pechini’s method. All compositions presented the expected crystalline phase when calcined at 800ºC. Three distinct methodologies were employed to obtain the luminescent ceramics. The first one was the laser sintering method, where a CO2 laser is the heating source for sintering. Translucent ceramics were obtained using this sintering method, with 40% of transmittance in visible region. Even without controlling atmosphere, it was possible to reduce the Eu ion from valence III to II during this process, a necessary condition to achieve the persistent luminescence property in strontium aluminate. The other sintering method was vacuum sintering. This method didn’t provide well defined a microstructure, and presenting high porosity been opaque. Nevertheless, XANES results showed a more efficient reduction process in this case. A third methodology used was a vacuum treatment of previously laser-sintered ceramics. These samples presented a well-defined microstructure and high Eu reduction rate. Performing MEV, EDS and XANES measurements it was possible study the reduction process of Eu in the strontium aluminate and suggest some defect equations that describe this process. It was also observed that this reduction process depends on the Dy content and the used method. To characterize the luminescent properties of the samples were used photoluminescence and lifetime measurements. Two main influences were investigated: i) the sintering method; ii) the dopant concentration. The results showed that the photoluminescence is highly influenced by the Eu2+ concentration, and the persistent luminescence is more influenced by the Dy concentration. Finally it was created an illustrative scheme that describes the persistent luminescence in the strontioum aluminate. / No presente trabalho pós de aluminato de estrôncio (Sr1-a-bAl2O4:EuaDyb) com diversas concentrações de dopantes foram preparados utilizando o método Pechini. Todas as composições apresentaram fase cristalina desejada quando calcinadas a 800ºC. Para a obtenção das cerâmicas luminescentes foram escolhidas três metodologias distintas de sinterização. Inicialmente foi utilizado o método de sinterização a laser, que tem como fonte de aquecimento um laser de CO2. Este método proporcionou a obtenção de cerâmicas densas com boa transmitância óptica, chegando a 40% na região visível. Também foi observado que durante o processamento a laser mesmo sem controle de atmosfera ocorreu a redução do európio III para a valência II, condição exigida para a obtenção da luminescência persistente no aluminato de estrôncio. Outro método de sinterização utilizado foi em forno resistivo com ambiente a vácuo. Durante esse processamento foram obtidas cerâmicas com propriedades microestruturais inferiores às anteriores, porém de acordo com os resultados de XANES foi observada uma redução mais eficiente do európio neste caso. Também foi realizado um tratamento em forno a vácuo de cerâmicas previamente sinterizadas a laser. Estas apresentaram uma microestrutura bem definida e elevada eficiência na redução do európio. Realizando medidas de XANES, EDS e MEV foi possível estudar o processo de redução do európio no sistema, apresentando as possíveis equações de defeitos que governam esse processo. Também foi encontrada uma dependência do processo de redução com a concentração dos dopantes, principalmente de Dy. As características luminescentes das cerâmicas foram estudadas através de medidas de fotoluminescência e tempo de luminescência, analisando principalmente dois fatores: i) Influência da metodologia de processamento; ii) influência da concentração de dopantes. Os resultados mostraram que a propriedade fotoluminescente apresenta forte influência da concentração de Eu2+ presente no material enquanto que a propriedade de luminescência persistente apresenta maior influência da concentração de Dy. Por fim foi montado um esquema ilustrativo que descreve o modelo de luminescência persistente para o aluminato de estrôncio.

L’emploi d’adjuvants fluidifiants est courant pour tout béton. Ceci permet d’améliorer les propriétés rhéologiques à l’état frais: la fluidité initiale et son maintien pendant les 2-3 premières heures de la vie d’un béton. La compréhension de ce mécanisme d’action est encore partielle pour les PCP (copolymères greffés). Ici, le but a été de tester l’hypothèse selon laquelle l’évolution de la quantité de PCP adsorbé par unité de surface minérale instantanée explique quantitativement l’évolution temporelle de la fluidité au cours de la période d’ouvrabilité.Sur un système inerte (calcite), nous avons confirmé que la fluidité est bien gouvernée par l’adsorption: à même adsorption surfacique, la fluidité de la pâte est quasiment identique quelle que soit la structure du PCP. Par ailleurs sur un système inerte (calcite ou ettringite), la modification de la fonction ionique du PCP fournit une solution pour améliorer la résistance de l’adsorption à la variation de la concentration en sulfates.Deux techniques ont été utilisées pour mesurer l’aire interfaciale au cours de l’hydratation d’un système réactif modèle (aluminate tricalcique, gypse, hémihydrate et calcite): l’adsorption de N2 et la relaxométrie du proton de l’eau. L’adsorption du PCP par unité de surface réelle a été calculée et corrélée à la fluidité de la pâte. La relation simple fluidité/adsorption n’est plus vérifiée ici. La présence de PCP a un impact sur l’hydratation du système et l’augmentation de l’étendue de la surface minérale associée. Les PCP vont augmenter la surface spécifique de l’ettringite qui précipite en modifiant sa morphologie. Cet effet est plus marqué quand la densité de greffage du PCP diminue. / Nowadays the use of superplasticizers admixtures becomes unavoidable for concrete. It allows enhancing the rheological properties at the fresh state: the initial flow and slump retention during the 2-3 first hours of the life of a concrete. The understanding of this mechanism is still partly elucidated for PCE (grafted copolymers). The aim of this thesis was to challenge the assumption of the evolution of the adsorbed amount of PCE per instantaneous mineral surface unit as origin of the fluidity temporal evolution during the workability period.On an inert system (calcite), we confirmed that the fluidity is mainly governed by the adsorption level. Thus for a same surface adsorption density, the fluidity of the paste is roughly similar whatever the structure of the PCE. On an inert system also (calcite or ettringite), the modification of the anionic function provides a technological way to improve the resistance of the adsorption against the variation of the sulfate ions concentration.The surface area of a reactive model system (tricalcium aluminate, gypsum, hemihydrate and calcite) has been measured by two techniques during the workability period: the N2 adsorption (BET) and the water proton relaxometry (RMN). The PCE adsorption per surface unit has been calculated and analysed in link with the fluidity of the paste. In that case, the simple relation, shown on the inert system, is not verified because the presence of PCE has also an impact on the hydration and on the extent of the surface area. Especially PCE lead to increase the surface by changing the morphology of ettringite. The specific surface area of ettringite increases when the grafting density of PCE decreases.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work, the synthesis of the oxide zinc aluminate spinel (ZnAl2O4) was realized by the metal-chitosan complexation method in different calcinations temperatures with the purpose of studying their influence in the physical properties of the material. The powders obtained were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), nitrogen adsorption-dessorption by the Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM) and differential thermal analysis (DTA). This material was used as catalyst and its activity was investigated in the photodegradation reaction of an organic textile dye under ultraviolet irradiation. In order to do this research, aqueous solutions of the dye were used in different initial concentrations and different amounts of catalyst. In the photocatalytic tests, parameters like the influence of the dye s calcinations temperature, the influence of the dye s initial concentration and the effect of the catalyst concentration. The rates constants of photocatalytic reactions were determined. The summary of the results demonstrated the obtainment of mesoporous particles with high surface area. The photocatalytic tests indicated that the material prepared in this work shows satisfactory photocatalytic activity for the degradation of the organic pollutant. The initial concentration of the dye as well as the catalyst mass had significant influence in the photocatalytic process. / Neste trabalho foi realizada a síntese do óxido espinélio aluminato de zinco (ZnAl2O4) pelo método de complexação metal-quitosana em diferentes temperaturas de calcinação, a fim de estudar a influência das mesmas sobre as propriedades físicas do material. Os pós obtidos foram caracterizados por difração de raios-X (DRX), espectroscopia no infravermelho (FTIR), adsorção-dessorção de nitrogênio pelo método Brunauer-Emmett-Teller (BET), microscopia eletrônica de varredura (MEV) e análise térmica diferencial (ATD). Este material foi usado como catalisador e sua atividade foi investigada na reação de fotodegradação de um corante orgânico têxtil (Vermelho Procion H-E7B) sob irradiação ultravioleta. Para tal estudo, foram utilizadas soluções aquosas do corante em diferentes concentrações iniciais e diferentes quantidades de catalisador. Nos testes fotocatalíticos foram analisados parâmetros como influência da temperatura de calcinação do catalisador, influência da concentração inicial de corante e efeito da concentração de catalisador. As constantes de velocidade das reações fotocatalíticas foram determinadas. Os resultados da síntese demonstram a obtenção de partículas mesoporosas e com alta área superficial. Os testes fotocatalíticos indicaram que o material preparado neste trabalho apresenta satisfatória atividade fotocatalítica para a degradação do poluente orgânico. A concentração inicial do corante bem como a massa do catalisador influenciaram significativamente no processo fotocatalítico.

The aim of this research project was to synthesise both the normal and inverse cobalt aluminate spinels by various methods and characterise them mainly by Raman spectroscopy with the support of X-ray powder diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR), energy disperse spectroscopy (EDS), and scanning electron microscopy (SEM). Four different synthesis methods (glycine-gel, citrate-gel, polyol and solid-state) were used to synthesise the cobalt aluminate powders with the general formula CoIICoIIIxAl2-xO4 (where x = 0-2). The gel or powder precursors were annealed at various temperatures ranging from 350ºC - 1000ºC. The properties of the intermediate and final products, influenced by the synthesis method, processing temperature, processing time and particle size, were compared. Raman spectra and XRD patterns indicating the presence of both normal and inverse cobalt aluminate spinel were observed. The inverse spinel was identified both as a transitional phase as well as a final phase, depending on the synthesis method and annealing temperature used. The various synthesis methods were also used to gain further insight into the crystal chemistry of cobalt aluminate. The solid-state method is the more traditional synthesis method. Solution techniques (glycine-gel, citrate-gel and polyol) were used in an attempt to synthesise blue cobalt aluminate at relatively low temperatures and processing times in order to obtain homogeneous, nanosized crystals with broad applicability. The polyol method was found to be most favourable for the synthesis of blue cobalt aluminate with regard to processing temperature and processing time. The various characterisation methods used, show that the intensity of the colour of the powders produced are strongly related to the degree of material crystallinity as well as Al/Co ratio. Inverse (Co2AlO4) and Co3O4 spinels are formed at lower temperatures or when the Co/Al ratio is greater than 0.5. The normal spinel (CoAl2O4) is produced at higher temperatures or when the Co/Al ratio is 0.5. The XRD patterns of CoAl2O4, Co2AlO4 and Co3O4, are very similar because they share the same spinel cubic structure (space group Fd3m) differing only slightly in the lattice size. It has been demonstrated that Raman and XRD can be used to distinguish between inverse and normal spinels while FT-IR and EDS are useful for assessing the purity of the powders produced. As predicted by group theory, five Raman and four IR active vibrations were evident in the results. / Dissertation (MSc)--University of Pretoria, 2009. / Chemistry / unrestricted

This diploma thesis deals with the preparation of modified tricalcium aluminate phases using sodium ions, and the study of their hydration processes and products. The X-ray diffraction analysis, isothermal calorimetry, laser diffraction, and scanning electron microscopy with energy dispersion analysis were used to solve this task. The preparation of modified tricalcium aluminate phases using high temperature methods has been described in the experimental section. Furthermore, the X-ray diffraction analysis was used to determine the purity of the prepared phases and the scanning electron microscopy with energy dispersion analysis was used to define the volume of sodium. Laser diffraction was used to measure a particle size distribution in the individual phases. Subsequently, hydration of the pure phases was performed in an isothermal calorimeter. It was followed by hydration of phases in the presence of different gypsum content and then in the presence of saturated portlandite solution. Hydration of some samples was stopped in order to better understand the hydration process. Hydration products were studied by X-ray diffraction analysis. The obtained results were compared with each other and the influence of sodium ions on both the structure of the prepared phases and the course of hydration and its products has been discussed. The effect of adding different volumes of gypsum and portlandite on the course of hydration of the individual phases was also compared.

Ceramic materials are in general characterized by high hardness, high modulus of elasticity, excellent abrasion resistance, etc. These properties make ceramics among others useful in optically transparent applications. An ideal form of optically transparent ceramic material is monocrystalline. However, the monocrystalline fabrication is expensive and/or time consuming. From this point of view polycrystalline ceramics is preferred. But the polycrystalline transparent ceramics fabrication is fraught with complications such as porosity, inappropriate grain size and insufficient purity. These circumstances could be solved by using sintering additives. This master’s thesis compiles literature research summarizing modern technologies of advanced ceramics sintering and ceramic polycrystalline microstructure dependence on its optical properties. The experimental part of this thesis focuses on the fabrication parameters of polycrystalline advanced ceramics based on Al2O3MgO and evaluation of their optical properties. Polycrystalline magnesium-aluminate spinel with sintering additive contents 0; 0.3 and 0.6 weight % LiOH was fabricated by optimalisation of Spark Plasma Sintering cycle. Fully dense ceramic samples of polycrystalline magnesium-aluminate spinel with favourable optical properties in visible spectrum radiation were achieved. Real In-line Transmission RIT and Total Forward Transmittance TFT were analysed. RIT exceeded 84 % at wavelength of 633 nm and TFT exceeded 83 % at wavelength above 860 nm. The decisive factors in terms of the optical properties of ceramics sintered with sintering additives were the amount of time-spending at high temperatures and the purity of ceramic powders.

This diploma thesis deals with non-traditional binder, which is strontium aluminate, with his preparation and hydration. The behaviour of binary and ternary mixtures of strontium-calcium-barium aluminates was also studied. These aluminates were prepared by firing an equimolar mixture of aluminum oxide and the appropriate carbonate. Samples prepared this way, including their mixtures, were characterized by analytical methods such as X-ray diffraction analysis (XRD), thermal analysis with evolved gas analysis (TG-DTA and EGA), scanning electron microscopy (SEM), infrared spectroscopy (IR) and calorimetry, with the greatest importance for the study of the hydration process.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第20635号 / 農博第2242号 / 新制||農||1052(附属図書館) / 学位論文||H29||N5079(農学部図書室) / 京都大学大学院農学研究科食品生物科学専攻 / (主査)教授 入江 一浩, 教授 平井 伸博, 教授 田中 千尋 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

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