<p>Development of products which can be produced from a country’s natural resources is very important as far as the industrialization of a nation and saving foreign exchange is concerned. Presently, industries in Uganda and the other states in the Lake Victoria region import all refractory-related-consumables, as the demand cannot be met locally. Based on the abundance of ceramic raw materials for high temperature applications in the region and the demand for refractories by industries it is pertinent to develop and manufacture firebricks by exploiting the locally available raw materials.</p><p>This thesis thus, concerns the characterisation of ceramic raw mineral powders from the Lake Victoria region, more particularly, Uganda, with the aim of developing firebrick refractories from the minerals. Two main deposits of kaolin and a ball clay deposit were investigated to assess their potential in the manufacture of refractory bricks. Raw- and processed sample powders were investigated by means of X-ray diffraction (XRD), thermal analysis (DTA-TG) and Scanning Electron Microscopy (SEM). In addition, the chemical composition, particle size distribution, density, and surface area of the powders were determined.</p><p>A comprehensive study on beneficiation of Mutaka kaolin was carried out using mechanical segregation of particles. The aim of the study was to explore other potential applications like in paper filling and coating. The beneficiation process improves the chemical composition of kaolin to almost pure, the major impurity being iron oxide.</p><p>A general production process scheme for manufacturing fireclay bricks starting with raw powder minerals (Mutaka kaolin and Mukono ball clay) was used to make six groups of sample fireclay brick. Experimental results from the characterization of formulated sample bricks indeed revealed the viability of manufacturing fireclay bricks from the raw minerals. Based on these results, industrial samples were formulated and manufactured at Höganäs Bjuf AB, Sweden. Kaolin from the Mutaka deposit was used as the main source of alumina while ball clay from Mukono was the main plasticizer and binder material. The formulated green body was consolidated by wet pressing and fired at 1350°C in a tunnel kiln. Characterization of the sintered articles was done by X-ray diffraction, scanning electron microscopy, and chemical composition (ICP-AES). In addition, technological properties related to thermal conductivity, thermal shock, alkali resistance, water absorption, porosity, shrinkage, permanent linear change (PLC), linear thermal expansion, refractoriness under load (RUL), and cold crushing strength were determined. The properties of the articles manufactured from the selected naturally occurring raw minerals reveal that the produced articles compare favourably with those of parallel types. Thus, the raw materials can be exploited for industrial production.</p>

Filmes de carbeto de silício, SiC, cristalinos foram depositados sobre peças de mulita por meio da técnica de deposição química por vapor (CVD) a pressão atmosférica. As características da superfície do substrato determinam se o filme será denso ou poroso, enquanto a temperatura define a cristalinidade e a taxa de nucleação para formação do filme. Durante os procedimentos de preparação do substrato de mulita para a deposição do filme, observou-se o fenômeno da formação de whiskers de mulita quando adicionados 3%mol de terras raras a peça. O fenômeno de crescimento destes whiskers foi sistematicamente estudado para sua caracterização e compreensão do mecanismo de formação. A adição de terras raras promoveu um abaixamento na temperatura de mulitização e a formação de whiskers com uma composição cuja razão alumina / sílica é de 1,3, uma das mais baixas observadas. / Crystalline silicon carbide, SiC, films were deposited on mullite by atmospheric pressure chemical vapor deposition (CVD) method. The characteristic of substrate surface determinate if the film will be dense or porous, while the deposition temperature defines its crystalinity and nucleation rate in film formation. During the mullite substrate preparation process for film deposition, it was observed a whisker formation phenomenon when the piece was doped with 3%mol of rare earth. The growth phenomenon of these whiskers was studied systematically to its characterization and comprehension of its formation mechanism. The addiction of rare earth promote a reduction in mullitization temperature and the formation of whiskers with a composition that alumina / silica ration was 1.3, one of the lowest one ever observed.

Made available in DSpace on 2017-07-21T20:42:36Z (GMT). No. of bitstreams: 1 Guilherme Feitosa.pdf: 8656207 bytes, checksum: 5144b613822296890457a30b8473bd01 (MD5) Previous issue date: 2011-09-13 / Among the ceramic materials, one can highlight the mullite, whose characteristics are of great industrial interest. This material consists of silica and alumina has high mechanical strength, high refractory and chemical inertness, and low coefficients of expansion and thermal conductivity, which makes this material synthesis from Al2O3 e SiO2 mixtures or from material showing Al2O3 - SiO2 even more technology important in traditional and advanced ceramic fields. Nevertheless the synthesis of mullite is hampered by the reaction kinetics is very slow, taking long time and large amount of energy during sintering. It takes temperatures above 1500°C to form mullite oxides via. Techniques that facilitate this process has been developed, but they have disadvantages such as high cost of reagents. This work had as objective produce mullite using the high energy milling. It was used as starting materials aluminum hydroxide, aluminum oxide, quartzite and kaolin. It was prepared two mixtures of oxides, which are: aluminum hydroxide with quartzite and quartzite with aluminum oxide. These two mixed oxides plus kaolin were subjected to high energy milling for different times and then the milled and unmilled powders were sintered at different temperatures. The characterization was made by ray-X diffraction and by scanning electronic microscopy and thermal analysis. The results showed that the mechanical activation of powders allowed the formation of mullite phase in a lower temperature and formation of anisotropic mullite grains. / Dentre os materiais cerâmicos, pode-se destacar a mulita, cujas características são de grande interesse industrial. Este material formado por sílica e alumina apresenta elevada resistência mecânica, alta refratariedade e inércia química, além de baixos coeficientes de expansão e condutividade térmica, o que torna a síntese desse material a partir de misturas de Al2O3 e SiO2 ou a partir de materiais que apresentem Al2O3 e SiO2 cada vez mais importantes tecnologicamente nas áreas de cerâmica tradicional e avançada. Entretanto, a síntese da mulita é dificultada pela cinética da reação que é muito lenta, levando longos tempos e grande gasto energético durante a sinterização. São necessárias temperaturas acima de 1500ºC para se formar mulita via óxidos. Técnicas que facilitam este processo têm sido desenvolvidas, mas possuem desvantagens como alto custo de reagentes. Este trabalho teve como objetivo a obtenção de mulita utilizando a moagem de alta energia. Foram utilizadas como matériasprimas hidróxido de alumínio, óxido de alumínio, quartzito e caulim. Foram preparadas duas misturas de óxidos, sendo elas: hidróxido de alumínio com quartzito e óxido de alumínio com quartzito. Essas duas misturas e o caulim foram submetidos à moagem de alta energia por diferentes tempos e em seguida os pós moídos e não moídos foram conformados e então sinterizados em diferentes temperaturas. A caracterização das amostras foi feita por difratometria de raios X, análise térmica diferencial, análise termogravimétrica e microscopia eletrônica de varredura. Os resultados mostraram que a ativação mecânica dos pós possibilitou a formação da fase mulita numa temperatura mais baixa que as amostras não ativadas e formação de grãos anisotrópicos de muita.

Mulita é um aluminosilicato com aplicações em sistemas de altas temperaturas como filtração de gases, elemento estrutural, suporte catalítico e isolante térmico. Na natureza, a mulita é pouco abundante e por este motivo é sintetizada via reação do estado sólido entre precursores contendo alumina e sílica. Nesta tese foi estudado o efeito de diferentes tipos de sílicas amorfas sintéticas (sílica precipitada, microssílica, sílica da casca de arroz e sílica da cinza da casca de arroz). Resultados obtidos demonstraram que quanto maior for a porosidade interna das partículas maior é o ganho em módulo de ruptura em flexão. No caso da microssílica, a presença de contaminantes foi determinante para obter a formação de fase vítrea viscosa, obtendo um material com baixa porosidade e elevado módulo elástico e de ruptura em flexão. Com o objetivo de aumentar a porosidade das estruturas de mulita, utilizou-se sílica com elevado tamanho médio de partículas (> 5 &mu;m) e com (> 99%). Os resultados demonstraram que a porosidade obteve valor entre 20 a 30%, com ganho em módulo de ruptura em flexão (72 MPa). Apesar dessa baixa porosidade, a vantagem é que estes poros são revestidos pela sílica o que confere controle da microestrutura e estabilidade frente a sinterização, além de ser reprodutível. Diferentes proporções molares de sílica foram estudadas (de 3A-0S até 3A-2S), dois diferentes tamanhos de partículas de alumina calcinada, uma fina e outra grossa. Os resultados mostraram que utilizando alumina grossa é possível obter uma porosidade maior contudo com menores propriedades mecânicas. Diferentemente dos resultados mostrados em outros trabalhos, verificou-se que uma pequena quantidade de sílica (0,25% em mol ou 3A-0,25S), já prejudica a densificação da alumina, tal efeito foi explicado pelo concentração de fase viscosa nos contornos de grão que dificulta a densificação das partículas de alumina. Utilizando hidróxido de alumínio, e fazendo a sua pré-sinterização foi possível obter estruturas de mulita com porosidade de 55%, e com módulo de ruptura em flexão de 16 MPa e com retração linear térmica de 5%, desta forma, aliou alta porosidade com boas propriedades mecânicas, sem necessidade de uso de agentes porogênicos ou geradores de vapores tóxicos, e tecnologicamente formou um produto com grande potencial para uso em isolamento térmico primário. / Mullite is an aluminosilicate with applications in high-temperature systems such as gas filtration, structural element, catalytic support and thermal insulation. In nature, mullite is not abundant and is therefore synthesized via the solid-state reaction between precursors containing alumina and silica. In this thesis, the effect of different types of synthetic amorphous silicas (precipitated silica, microsilica, silica from rice husk and silica from rice husk ash) was studied. Results obtained showed that the larger the internal porosity of the particles, the greater the gain in modulus of rupture in flexion. In the case of the microsilica, the presence of contaminants was determinant to obtain the formation of viscous glassy phase, obtaining a material with low porosity and high elastic modulus and rupture in flexion. In order to increase the porosity of the mullite structures, high particle size (> 5 &mu;m) and (> 99%) silica were used. The results showed that the porosity obtained a value between 20 to 30%, with the gain in modulus of rupture in flexion (72 MPa). In spite of this low porosity, the advantage is that these pores are coated by silica, which gives control of the microstructure and stability to sintering, in addition to being reproducible. Different molar ratios of silica were studied (from 3A-0S to 3A-2S), two different particle sizes of calcined alumina, one fine and one coarse. The results showed that using coarse alumina it is possible to obtain a higher porosity with lower mechanical properties. Differently, from the results shown in other works, it was verified that a small amount of silica (0.25 mol% or 3A-0.25 S), already affects the densification of alumina, this effect was explained by the concentration of viscous phase in the contours of grain which hinders the densification of the alumina particles. Using aluminum hydroxide, it was possible to obtain mullite structures with 55% porosity and with a modulus of rupture in flexion of 16 MPa and linear thermal retraction of 5%, thus allying high porosity with good mechanical properties, no need for porogenic agents or toxic vapors, and technologically formed a product with great potential for use in primary thermal insulation.

Development of products which can be produced from a country’s natural resources is very important as far as the industrialization of a nation and saving foreign exchange is concerned. Presently, industries in Uganda and the other states in the Lake Victoria region import all refractory-related-consumables, as the demand cannot be met locally. Based on the abundance of ceramic raw materials for high temperature applications in the region and the demand for refractories by industries it is pertinent to develop and manufacture firebricks by exploiting the locally available raw materials. This thesis thus, concerns the characterisation of ceramic raw mineral powders from the Lake Victoria region, more particularly, Uganda, with the aim of developing firebrick refractories from the minerals. Two main deposits of kaolin and a ball clay deposit were investigated to assess their potential in the manufacture of refractory bricks. Raw- and processed sample powders were investigated by means of X-ray diffraction (XRD), thermal analysis (DTA-TG) and Scanning Electron Microscopy (SEM). In addition, the chemical composition, particle size distribution, density, and surface area of the powders were determined. A comprehensive study on beneficiation of Mutaka kaolin was carried out using mechanical segregation of particles. The aim of the study was to explore other potential applications like in paper filling and coating. The beneficiation process improves the chemical composition of kaolin to almost pure, the major impurity being iron oxide. A general production process scheme for manufacturing fireclay bricks starting with raw powder minerals (Mutaka kaolin and Mukono ball clay) was used to make six groups of sample fireclay brick. Experimental results from the characterization of formulated sample bricks indeed revealed the viability of manufacturing fireclay bricks from the raw minerals. Based on these results, industrial samples were formulated and manufactured at Höganäs Bjuf AB, Sweden. Kaolin from the Mutaka deposit was used as the main source of alumina while ball clay from Mukono was the main plasticizer and binder material. The formulated green body was consolidated by wet pressing and fired at 1350°C in a tunnel kiln. Characterization of the sintered articles was done by X-ray diffraction, scanning electron microscopy, and chemical composition (ICP-AES). In addition, technological properties related to thermal conductivity, thermal shock, alkali resistance, water absorption, porosity, shrinkage, permanent linear change (PLC), linear thermal expansion, refractoriness under load (RUL), and cold crushing strength were determined. The properties of the articles manufactured from the selected naturally occurring raw minerals reveal that the produced articles compare favourably with those of parallel types. Thus, the raw materials can be exploited for industrial production. / QC 20101029

Made available in DSpace on 2014-06-11T19:23:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-08-15Bitstream added on 2014-06-13T20:30:15Z : No. of bitstreams: 1 carvalho_av_me_bauru.pdf: 971409 bytes, checksum: 84b4af49272f217e0a96b436d7084289 (MD5) / Chave Fusível é um dispositivo instalado na rede de distribuição de energia elétrica, que tem a função de proteger o transformador. O principal componente de uma Chave Fusível é o isolador, que em sua grande maioria é cerâmico, conhecido também como porcelana elétrica. Diversas companhias de eletricidade, que atuam em regiões próximas ao mar, têm problemas relacionados ao envelhecimento e/ou corrosão causadas pela névoa salina nas Chaves Fusíveis. Neste trabalho, apresentamos uma análise mais detalhada das características dos materiais envolvidos no isolador cerâmico, para entender melhor o problema e contribuir na busca de soluções. Para isso foram realizadas análises estruturais e elétricas na cerâmica e no material de junção, principais componentes do isolador cerâmico. Foi empregada a técnica de Difração de Raios X para identificação das fases que constituem esses materiais. Os resultados confirmam a presença de quartzo e mulita na cerâmica, e a presença de quartzo, enxofre e grafite na junção. Foram também observadas alterações na estrutura do material da junção com a elevação da temperatura, principalmente aquelas relacionadas com a eliminação do enxofre a partir de 167°C. A caracterização elétrica foi realizada através de medidas de corrente em função da voltagem para determinação da resistividade dos materiais (e possível comportamento ôhmico), em diferentes condições de temperatura e concentração de névoa salina. A cerâmica quando exposta à névoa salina apresenta uma diminuição significativa na resistividade elétrica, mas volta a aumentar quando a névoa salina é retirada. Já o material da junção também apresenta uma diminuição significativa na resistividade elétrica quando exposta a névoa salina, mas este comportamento se mantém depois de removida a névoa salina. / Fuse cutout is a device installed in the electric energy distribution network, which plays the role of protection to the transformer. The main component of a fuse cutout is the insulator, which usually is made of ceramic, also known as electric porcelain. Several electricity companies, working in regions close to the coast, have problems concerning aging and/or corrosion caused by salt mist on their fuse cutout keys. In this work, a detailed analysis of the characteristics of materials involved in the ceramic insulator is presented, which shall be a good contribution to a better understanding of this problem and to seek for a solution. Aiming to reach this goal, structural and electrical analysis of the ceramic and the junction material have been carried out. X-ray diffraction technique has been used to identify the phases present in these materials, and the result confirms the presence of quartz and mullite in the ceramic, and quartz, sulfur and graphite in the junction. In the junction material, modifications of the structure were also observed with heating, mainly sulfur elimination above 167°C. The electric characterization was done from current as function of applied voltage measurements, for determination of samples resistivity and the possible ohmic behavior, under different temperatures and salt vapor conditions. The ceramic exposed to salt vapor shows a significant decrease in the electrical resistivity, but it turns back to a high resistivity value, when removed from the salt vapor conditions. On the other hand, the junction material also presents a significant decrease in the resistivity when exposed to salt vapor, but this behavior is held after removing the sample from the salt vapor conditions.

Mulita é um aluminosilicato com aplicações em sistemas de altas temperaturas como filtração de gases, elemento estrutural, suporte catalítico e isolante térmico. Na natureza, a mulita é pouco abundante e por este motivo é sintetizada via reação do estado sólido entre precursores contendo alumina e sílica. Nesta tese foi estudado o efeito de diferentes tipos de sílicas amorfas sintéticas (sílica precipitada, microssílica, sílica da casca de arroz e sílica da cinza da casca de arroz). Resultados obtidos demonstraram que quanto maior for a porosidade interna das partículas maior é o ganho em módulo de ruptura em flexão. No caso da microssílica, a presença de contaminantes foi determinante para obter a formação de fase vítrea viscosa, obtendo um material com baixa porosidade e elevado módulo elástico e de ruptura em flexão. Com o objetivo de aumentar a porosidade das estruturas de mulita, utilizou-se sílica com elevado tamanho médio de partículas (> 5 &mu;m) e com (> 99%). Os resultados demonstraram que a porosidade obteve valor entre 20 a 30%, com ganho em módulo de ruptura em flexão (72 MPa). Apesar dessa baixa porosidade, a vantagem é que estes poros são revestidos pela sílica o que confere controle da microestrutura e estabilidade frente a sinterização, além de ser reprodutível. Diferentes proporções molares de sílica foram estudadas (de 3A-0S até 3A-2S), dois diferentes tamanhos de partículas de alumina calcinada, uma fina e outra grossa. Os resultados mostraram que utilizando alumina grossa é possível obter uma porosidade maior contudo com menores propriedades mecânicas. Diferentemente dos resultados mostrados em outros trabalhos, verificou-se que uma pequena quantidade de sílica (0,25% em mol ou 3A-0,25S), já prejudica a densificação da alumina, tal efeito foi explicado pelo concentração de fase viscosa nos contornos de grão que dificulta a densificação das partículas de alumina. Utilizando hidróxido de alumínio, e fazendo a sua pré-sinterização foi possível obter estruturas de mulita com porosidade de 55%, e com módulo de ruptura em flexão de 16 MPa e com retração linear térmica de 5%, desta forma, aliou alta porosidade com boas propriedades mecânicas, sem necessidade de uso de agentes porogênicos ou geradores de vapores tóxicos, e tecnologicamente formou um produto com grande potencial para uso em isolamento térmico primário. / Mullite is an aluminosilicate with applications in high-temperature systems such as gas filtration, structural element, catalytic support and thermal insulation. In nature, mullite is not abundant and is therefore synthesized via the solid-state reaction between precursors containing alumina and silica. In this thesis, the effect of different types of synthetic amorphous silicas (precipitated silica, microsilica, silica from rice husk and silica from rice husk ash) was studied. Results obtained showed that the larger the internal porosity of the particles, the greater the gain in modulus of rupture in flexion. In the case of the microsilica, the presence of contaminants was determinant to obtain the formation of viscous glassy phase, obtaining a material with low porosity and high elastic modulus and rupture in flexion. In order to increase the porosity of the mullite structures, high particle size (> 5 &mu;m) and (> 99%) silica were used. The results showed that the porosity obtained a value between 20 to 30%, with the gain in modulus of rupture in flexion (72 MPa). In spite of this low porosity, the advantage is that these pores are coated by silica, which gives control of the microstructure and stability to sintering, in addition to being reproducible. Different molar ratios of silica were studied (from 3A-0S to 3A-2S), two different particle sizes of calcined alumina, one fine and one coarse. The results showed that using coarse alumina it is possible to obtain a higher porosity with lower mechanical properties. Differently, from the results shown in other works, it was verified that a small amount of silica (0.25 mol% or 3A-0.25 S), already affects the densification of alumina, this effect was explained by the concentration of viscous phase in the contours of grain which hinders the densification of the alumina particles. Using aluminum hydroxide, it was possible to obtain mullite structures with 55% porosity and with a modulus of rupture in flexion of 16 MPa and linear thermal retraction of 5%, thus allying high porosity with good mechanical properties, no need for porogenic agents or toxic vapors, and technologically formed a product with great potential for use in primary thermal insulation.

No description available.

Filmes de carbeto de silício, SiC, cristalinos foram depositados sobre peças de mulita por meio da técnica de deposição química por vapor (CVD) a pressão atmosférica. As características da superfície do substrato determinam se o filme será denso ou poroso, enquanto a temperatura define a cristalinidade e a taxa de nucleação para formação do filme. Durante os procedimentos de preparação do substrato de mulita para a deposição do filme, observou-se o fenômeno da formação de whiskers de mulita quando adicionados 3%mol de terras raras a peça. O fenômeno de crescimento destes whiskers foi sistematicamente estudado para sua caracterização e compreensão do mecanismo de formação. A adição de terras raras promoveu um abaixamento na temperatura de mulitização e a formação de whiskers com uma composição cuja razão alumina / sílica é de 1,3, uma das mais baixas observadas. / Crystalline silicon carbide, SiC, films were deposited on mullite by atmospheric pressure chemical vapor deposition (CVD) method. The characteristic of substrate surface determinate if the film will be dense or porous, while the deposition temperature defines its crystalinity and nucleation rate in film formation. During the mullite substrate preparation process for film deposition, it was observed a whisker formation phenomenon when the piece was doped with 3%mol of rare earth. The growth phenomenon of these whiskers was studied systematically to its characterization and comprehension of its formation mechanism. The addiction of rare earth promote a reduction in mullitization temperature and the formation of whiskers with a composition that alumina / silica ration was 1.3, one of the lowest one ever observed.

Refractory aggregate manufactured from common clays, claystones and shales in Czech Republic are mostly classified as fireclay. For specific applications are these grogs not suitable and there is a need to use grogs with higher content of alumina oxide. Theoretical part of this thesis is focused on the mineral mullite, which is one of the basic minerals in Al2O3 - SiO2 system. Research is focused on methods of mullite production, manufacture of recfractory grog and new possibilities in modification of current raw materials. In experimental part is carried out a verification of possible production of grogs with increased alumina content according to the designed composition.