O presente trabalho descreve os processos de preparação do aluminato de bário e cálcio, material emissor de elétrons, empregados nos catodos do tipo impregnado para utilização em uma válvula de microondas do tipo TWT. Os catodos investigados constituem-se de uma pastilha de tungstênio porosa impregnada com aluminato de bário e cálcio com proporção molar 5:3:2. Para a síntese do aluminato, utilizaram-se três diferentes métodos: reação em estado sólido, precipitação e cristalização. A termogravimetria auxiliou na consolidação dos procedimentos de preparação dos aluminatos de modo a definir os parâmetros de pirólise/calcinação. Verificou-se que a técnica que apresentou melhores características de síntese foi o método da cristalização, pois esta apresentou uma menor temperatura de formação do aluminato (800ºC) em atmosfera oxidante (O2), quando comparada às técnicas de reação em estado sólido e de precipitação (temperatura de 1000ºC em atmosfera redutora – H2). Utilizou-se o conceito da distribuição da função trabalho prática (PWFD) de Miram para a caracterização termiônica dos catodos impregnados. Empregando-se este método, foi possível traçar o perfil termiônico do catodo com aluminato de bário e cálcio. As curvas PWFD apresentaram a função trabalho média do catodo aluminato de, aproximadamente, 2,00 eV. / In the present work it is described the barium calcium aluminate manufacture processes employed to produce impregnated cathodes to be used in a traveling-wave tube (TWT). The cathodes were developed using a tungsten body impregnated with barium and calcium aluminate with a 5:3:2 proportion (molar). Three different processes were investigated to obtain this material: solid-state reaction, precipitation and crystallization. Thermal analysis, thermogravimetry specifically, supported to determine an adequate preparation procedure (taking into account temperature, time and pirolisys atmosphere). It was verified that the crystallization showed a better result when compared to those investigated (solid-state reaction and precipitation techniques – formation temperature is about 1000ºC in hydrogen atmosphere), whereas it presented the lower formation temperature (800ºC) in oxidizing atmosphere (O2). It was used the practical work function distribution theory (PWFD) of Miram to characterize thermionic impregnated cathode. The PWFD curves were used to characterize the barium-calcium aluminate cathode. PWFD curves shown that the aluminate cathode work function is about 2,00 eV.

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.

A constante busca por redução de custos e alternativas estratégicas por abastecimento de insumos refratários, tem levado as usinas siderúrgicas à buscar novos fornecedores para atender suas necessidades. Com base na necessidade da Companhia Siderúrgica Nacional (CSN), firmou-se uma parceria entre universidade e empresa, com intuito de desenvolver um novo fornecedor para um insumo refratário o qual só era fornecido por uma empresa. Foi então iniciado um trabalho de investigação das propriedades físico-químicas do material utilizado pela CSN (material de referência), utilizando-se a análise da distribuição granulométrica, composição mineralógica e propriedades mecânicas. A partir deste ponto, convidouse uma empresa genuinamente nacional, para desenvolver um novo produto, com matérias primas nacionais, que tivesse as mesmas propriedades mecânicas do material de referência. O concreto nacional foi caracterizado da mesma forma que o material de referência, em suas propriedades físico-químicas e ensaios mecânicos. Com base nos resultados foi realizado um teste em escala piloto, com aprovação do material. A empresa parceira passou a ter um novo material em sua carteira de produtos comercializado no mercado nacional e a CSN está realizando testes em escala industrial para aprovar um novo fornecedor de concreto refratário de alta resistência mecânica. / The constant search for cost reduction and strategic alternatives for refractory raw materials supply, has led the steelplants to look for new suppliers to meet its needs. Companhia Siderurgica Nacional (CSN) has signed a partnership between universities and companies, aiming to develop a new supplier for a refractory raw material which was only supplied by one company. Then a research based on chemical-physical properties of material used by CSN (reference material) was started, using the analysis of particle size distribution, mineralogical composition and mechanical properties. From this point, a genuine national company was invited, to develop a new product, with national raw materials, which had the same mechanical properties of the reference material. The national castable was characterized in the same way as the reference material in their chemical-physical properties and mechanical tests. Based on the results a test was performed on a pilot scale, with the approval of the material. The partner company has taken on a new material in its portfolio of products marketed in the domestic market and CSN is conducting tests on an industrial scale to approve a new supplier of refractory concrete with high mechanical strength.

A constante busca por redução de custos e alternativas estratégicas por abastecimento de insumos refratários, tem levado as usinas siderúrgicas à buscar novos fornecedores para atender suas necessidades. Com base na necessidade da Companhia Siderúrgica Nacional (CSN), firmou-se uma parceria entre universidade e empresa, com intuito de desenvolver um novo fornecedor para um insumo refratário o qual só era fornecido por uma empresa. Foi então iniciado um trabalho de investigação das propriedades físico-químicas do material utilizado pela CSN (material de referência), utilizando-se a análise da distribuição granulométrica, composição mineralógica e propriedades mecânicas. A partir deste ponto, convidouse uma empresa genuinamente nacional, para desenvolver um novo produto, com matérias primas nacionais, que tivesse as mesmas propriedades mecânicas do material de referência. O concreto nacional foi caracterizado da mesma forma que o material de referência, em suas propriedades físico-químicas e ensaios mecânicos. Com base nos resultados foi realizado um teste em escala piloto, com aprovação do material. A empresa parceira passou a ter um novo material em sua carteira de produtos comercializado no mercado nacional e a CSN está realizando testes em escala industrial para aprovar um novo fornecedor de concreto refratário de alta resistência mecânica. / The constant search for cost reduction and strategic alternatives for refractory raw materials supply, has led the steelplants to look for new suppliers to meet its needs. Companhia Siderurgica Nacional (CSN) has signed a partnership between universities and companies, aiming to develop a new supplier for a refractory raw material which was only supplied by one company. Then a research based on chemical-physical properties of material used by CSN (reference material) was started, using the analysis of particle size distribution, mineralogical composition and mechanical properties. From this point, a genuine national company was invited, to develop a new product, with national raw materials, which had the same mechanical properties of the reference material. The national castable was characterized in the same way as the reference material in their chemical-physical properties and mechanical tests. Based on the results a test was performed on a pilot scale, with the approval of the material. The partner company has taken on a new material in its portfolio of products marketed in the domestic market and CSN is conducting tests on an industrial scale to approve a new supplier of refractory concrete with high mechanical strength.

The ever increasing global demand for materials has placed aluminium as the world’s second most used metal, with world annual production currently >24 million tons. Consequently, the global alumina industry is perpetually striving to meet demands in conjunction with research, development and implementation of more efficient and sustainable processes and practises. Of specific concern for many proponents within the industry is that increased alumina production inadvertently results in increased Bayer Process-derived alkaline solid and liquid waste loads. Furthermore, in-house power generation at all Australian alumina refineries contributes to acid gas emissions, particularly SOx and NOx, both of which have environmental and anthropogenic impacts of global concern. The focus of this work is SO2 emission. SOx emission control measures can be achieved before, during or after combustion; the latter is termed flue gas desulphurisation (FGD). Commercially available FGD systems are dominated by once-through wet processes whereby the flue gas passes up through an absorbtion tower. The most favourable medium for industrial use is seawater, followed by limestone, and in some cases, a combination of both. However, the ever-increasing stringency of environmental emission legislation continues to inflict tighter controls on power production and is forcing industry to investigate alternative cost-effective FGD mediums. Therefore much research is currently dedicated to the utilisation of high volume, alkaline waste streams over manufactured sorbents. Modern environmental engineering approaches to waste product minimisation, neutralisation and/or reuse have lead to many new processes which change the view of many materials from waste product to environmental resource. Subsequently, this work examines the application of an isolated Bayer Process waste product, tricalcium aluminate hexahydrate (TCA6), as a FGD medium. Initial research assessed the dissolution behaviour and performance of the proposed medium with sulphuric acid, followed by batch reactor trials with a simulated flue gas. Data derived from this research indicated the suitability of TCA6 as a FGD medium and was subsequently applied to a preliminary model and proposed design parameters required for further pilot scale investigations. This work provides strong support for an economically viable and more sustainable approach to FGD for the alumina industry.

Biomaterials used for stabilization of compressed vertebraes due to osteoporosis, have mainly been based on resin materials, like PMMA (polymethyl methacrylate), but have recently expanded to consist of injectable ceramics, such as calcium-aluminate. In this in vitro study human osteoblast-like cells, MG-63, were cultured on three different injectable biomaterials based on: Ca-aluminate, Bis-GMA (bisphenol A-glycidylmethacrylate) and PMMA, to investigate the cellular response elicited by these materials. Cell proliferation was measured by the NucleoCounter® system, cell viability was investigated by LDH (lactate dehydrogenase) analysis, cell differentiation and mineralization was evaluated by mRNA gene expression of the osteoblastic markers: ALP (alkaline phosphatase), OC (osteocalcin) and COLL-I (collagen type I) by qPCR (quantitative polymerase chain reaction) analysis. Two control materials were used: TCP (tissue culture polystyrene, negative control) and PVC (polyvinyl chloride, positive control). The results showed that all the bone cement materials were non-toxic and biocompatible, i.e. they provided good cell viability and proliferation of the MG-63 cells. They are specific for bone cells, since they expressed high values of the osteoblast-specific differentiation markers, and are thus promising as injectable bone cement materials. Among the bone cements, Xeraspine appears to be the most biocompatible material for bone cells. It is followed by Cortoss and then Vertebroplastic.

<p>Biomaterials used for stabilization of compressed vertebraes due to osteoporosis, have mainly been based on resin materials, like PMMA (polymethyl methacrylate), but have recently expanded to consist of injectable ceramics, such as calcium-aluminate. In this in vitro study human osteoblast-like cells, MG-63, were cultured on three different injectable biomaterials based on: Ca-aluminate, Bis-GMA (bisphenol A-glycidylmethacrylate) and PMMA, to investigate the cellular response elicited by these materials. Cell proliferation was measured by the NucleoCounter® system, cell viability was investigated by LDH (lactate dehydrogenase) analysis, cell differentiation and mineralization was evaluated by mRNA gene expression of the osteoblastic markers: ALP (alkaline phosphatase), OC (osteocalcin) and COLL-I (collagen type I) by qPCR (quantitative polymerase chain reaction) analysis. Two control materials were used: TCP (tissue culture polystyrene, negative control) and PVC (polyvinyl chloride, positive control). The results showed that all the bone cement materials were non-toxic and biocompatible, i.e. they provided good cell viability and proliferation of the MG-63 cells. They are specific for bone cells, since they expressed high values of the osteoblast-specific differentiation markers, and are thus promising as injectable bone cement materials. Among the bone cements, Xeraspine appears to be the most biocompatible material for bone cells. It is followed by Cortoss and then Vertebroplastic.</p>

The objective of this thesis is to study the effects of flux deposition non uniformity on spreading of molten metal. Flux deposition non-uniformity here means as to whether the amount of flux deposited in a non-uniform or uniform pattern helps in the better wetting and spreading characteristics of the molten metal or is detrimental to the process. The material selection constraint to the study was imposed by selecting brazing of aluminum i.e., aluminum alloy melting and flow over an aluminum alloy substrate. The study was carried out by conducting a number of Hot Stage microscopy tests using aluminum silicon alloy as the filler metal and Potassium Fluoro Aluminate (Nocolok) as the flux. The flux was applied in different spatial distribution patterns to uncover the varying effects of its distribution on spreading. The uneven pattern of flux deposition indicates the influence on spreading but due to the efficient spreading of flux prior to aluminum melting and associated fuzziness of the achieved coverage distribution the effects are not always conclusive. It has been concluded that non uniform flux deposition does not necessarily mean uneven or less uniform spreading of the molten liquid metal if the spreading of the molten flux is beyond the distance of ultimate metal spreading. This is because, in spite of uneven flux deposition, the flux melts approximately at 560C-570C and spreads on the surface of the metal thereby promoting appreciable spreading and wetting of the molten liquid metal that happens at temperatures above 577C.

In this thesis different aspects of calcium-aluminate (CA) as biomaterial are presented. Calcium aluminate is a chemically bonded ceramic with inherent properties making it suitable for use as biomaterial in some applications. In this thesis the emphasis is put on the basic chemical, physical and mechanical properties that may be achieved using the CA system as well as synthesis of the CA raw material. The basis for using CA in any application is the synthesis of the raw material. Different synthesis routes for producing CA are presented with focus on high temperature routes and the micro-structural and phase development during synthesis. As a base for further understanding of the CA properties a thorough outline of the reaction chemistry for CA is presented also including a description of how the reactions may be controlled and how formulations can be designed. The surface reactions of CA when subjected to simulated body fluid showed that CA is in vitro bioactive. An in vivo study in teeth also indicates that CA produces apatite at the tooth material interface. Dental materials are subjected to a harsh environment in the mouth with high mechanical forces, erosion and thermal changes. Also the demands on precise handling characteristics are high. For these reasons the in vitro evaluation of physical and mechanical properties are important. In this work several mechanical and physical properties of Ca-based formulations for dental applications has been tested using different methods. Some attention is also put on the specific characteristics of CA and the difficulties that arise when new material classes needs to be tested according to consensus standard methods. Finally studies on a CA-based formulation intended for Vertebroplasty is presented. The studies include basic mechanical properties as well as testing the material in an in vitro model utilising synthetic cancellous bone.

The ever increasing global demand for materials has placed aluminium as the world’s second most used metal, with world annual production currently >24 million tons. Consequently, the global alumina industry is perpetually striving to meet demands in conjunction with research, development and implementation of more efficient and sustainable processes and practises. Of specific concern for many proponents within the industry is that increased alumina production inadvertently results in increased Bayer Process-derived alkaline solid and liquid waste loads. Furthermore, in-house power generation at all Australian alumina refineries contributes to acid gas emissions, particularly SOx and NOx, both of which have environmental and anthropogenic impacts of global concern. The focus of this work is SO2 emission. SOx emission control measures can be achieved before, during or after combustion; the latter is termed flue gas desulphurisation (FGD). Commercially available FGD systems are dominated by once-through wet processes whereby the flue gas passes up through an absorbtion tower. The most favourable medium for industrial use is seawater, followed by limestone, and in some cases, a combination of both. However, the ever-increasing stringency of environmental emission legislation continues to inflict tighter controls on power production and is forcing industry to investigate alternative cost-effective FGD mediums. Therefore much research is currently dedicated to the utilisation of high volume, alkaline waste streams over manufactured sorbents. Modern environmental engineering approaches to waste product minimisation, neutralisation and/or reuse have lead to many new processes which change the view of many materials from waste product to environmental resource. Subsequently, this work examines the application of an isolated Bayer Process waste product, tricalcium aluminate hexahydrate (TCA6), as a FGD medium. Initial research assessed the dissolution behaviour and performance of the proposed medium with sulphuric acid, followed by batch reactor trials with a simulated flue gas. Data derived from this research indicated the suitability of TCA6 as a FGD medium and was subsequently applied to a preliminary model and proposed design parameters required for further pilot scale investigations. This work provides strong support for an economically viable and more sustainable approach to FGD for the alumina industry.