To see the other types of publications on this topic, follow the link: Aluwia.
Dissertations / Theses on the topic 'Aluwia'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Aluwia.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Castro, Pedro Afonso de. "Pares cerâmicos homólogos alumina/alumina para anéis de empanque." Master's thesis, Universidade de Aveiro, 2006. http://hdl.handle.net/10773/4692.
Full textAbstract:
Mestrado em Engenharia de MateriaisO propósito do presente trabalho é a produção, caracterização mecânica, microestrutural e avaliação do comportamento tribológico de pares homólogos de anéis vedantes (empanques) de alumina (Al2O3). Os anéis de empanque têm por função garantir a vedação em veios rotativos de equipamentos nos quais circulam fluidos. Dadas as solicitações tribológicas extremas a que os materiais constituintes dos anéis são sujeitos, por vezes em ambientes altamente corrosivos, a alumina apresenta-se como uma excelente alternativa aos materiais tradicionalmente usados na produção destes vedantes (metal duro, carbono grafitizado, ligas ferrosas, etc.) devido à combinação das suas propriedades mecânicas e inércia química. Foram sinterizados três lotes de alumina a diferentes velocidades de aquecimento do forno, mantendo constantes as restantes condições de processamento. O aumento do valor deste parâmetro traduziu-se num incremento da taxa de densificação, resultando a densidade relativa de r=97,2% para a velocidade de aquecimento mais elevada (Vaq=20ºC/min). Este lote apresenta valores de dureza e tenacidade à fractura de HV=15,4GPa e KIc=3,7MPa.m1/2 respectivamente, resistência à flexão σF=279MPa e módulo de elasticidade E=322GPa. Os ensaios tribológicos anel/anel realizaram-se com diferentes velocidades de rotação (w), no intervalo 500 a 2000rpm, pressão de fluido (PL, água destilada) entre 0,5 e 2bar, sob carga normal (Nt) variando até ao valor necessário para a vedação plena. Os vedantes de alumina apresentaram valores de coeficiente de atrito extremamente reduzidos (<0,05), impossibilitando mesmo em alguns casos a sua determinação por se localizarem abaixo do limite de sensibilidade da máquina. Para w=2000rpm e PL=2bar conseguiu-se a estanquicidade total em dois dos três lotes ensaiados, com cargas totais de Nt=0,438kN (lote menos denso) e Nt=0,420kN (lote com maior densidade), obtendo-se para o produto PV, onde P representa a pressão efectiva e V a velocidade linear, PV=1,523MPa.m/s e PV=1,324MPa.m/s respectivamente. No primeiro caso determinou-se ainda o limite máximo de funcionamento em vedação plena, registando-se para Nt=0,900kN o valor de PV=4,200MPa.m/s. A análise posterior dos anéis revelou superfícies polidas por acção do movimento relativo entre os anéis, com rugosidade inferior à medida previamente à realização dos testes, sem delaminação ou fractura, não evidenciando qualquer tipo de destruição. Foi ainda testado o comportamento tribológico com azeite, meio potencialmente mais agressivo, corroborando a capacidade de funcionamento deste sistema vedante.
The purpose of the present work is the production, microstructural and mechanical characterization, and evaluation of the tribological behaviour of self-mated pairs of alumina mechanical seals. These components are used to ensure sealing in rotating shafts in equipments where a fluid is flowing. Due to the drastic tribological solicitations that seal rings are usually exposed to, sometimes in highly corrosive environments, alumina is a potential alternative to the commonly used materials (hardmetal, graphitized carbon, nonferrous alloys, etc.) due to the good combination of mechanical properties and chemical inertness. Three grades of alumina were sintered using different heating rates, keeping constant the remaining processing conditions. The increase of this parameter lead to a higher densification rate, the highest density (r=97,2%) being achieved when using the highest heating rate (Vaq=20ºC/min). The main mechanical properties were the following: HV=15,4GPa, KIc=3,7MPa.m1/2, σF=279MPa and E=322GPa. Ring-on-ring tribological tests were conducted using different rotational speeds (w) from 500 to 2000rpm, fluid pressure (PL, distilled water) between 0,5 and 2bar, under a normal load (Nt) varying until the complete sealing. The tests showed that the alumina mechanical seals could guarantee full sealing conditions, with extremely low values of friction coefficient (<0.05), sometimes turning impossible the recording of the results, as they were below the equipment sensitivity. Using w=2000rpm and PL=2bar, full sealing was achieved in two of the three grades of the tested seals, under applied loads of Nt=0.438kN (grade with the lowest density) and Nt=0.420kN (grade with the highest density). PV (being P the effective pressure and V the linear speed) lower limiting conditions were PV=1.523MPa.m/s and PV=1.324MPa.m/s, respectively. For the first of the previous mentioned grades, the upper limit was also determined, being PV=4.200MPa.m/s with Nt=0.900kN. The surface analysis of the tested seals showed a well polished surface, due to the relative motion between the rings, with a lower roughness when compared to the nominal finishing. No delamination, fracture or any kind of destruction were observed. The tribological behaviour of the alumina rings was also characterized using olive oil, potentially more aggressive fluid, corroborating the adequateness of the present system. These results, combined to some of the intrinsic properties of alumina (corrosion resistance, chemical inertness, low density when compared with that of the most traditionally materials used in seals production) create the expectation that alumina could be a feasible alternative to the most widely used materials used in this kind of application.
2
Kayiplar, Burcu. "Microwave Sintering And Characterization Of Alumina And Alumina Matrix Ceramic Nanocomposites." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611854/index.pdf.
Full textAbstract:
ABSTRACT
MICROWAVE SINTERING AND CHARACTERIZATION OF ALUMINA
AND ALUMINA MATRIX CERAMIC NANOCOMPOSITES
Kayiplar, Burcu
M.S., Department of Metallurgical and Materials Engineering
Supervisor: Assist. Prof. Dr. Arcan F. Dericioglu
April 2010, 106 pages
Efficiency of microwave heating on the sintering of ceramic materials has been
investigated in comparison to conventional processing. Monolithic alumina with or
without sintering additives such as MgO, CaO, Y2O3 were fabricated by both
conventional and microwave sintering at temperatures ranging from 1000°C to 1600°
C with a constant soaking time of 1 hour. Based on the densification results on monolithic alumina, nanometer-sized SiC or stabilized ZrO2 particle-dispersed alumina matrix ceramic nanocomposites were sintered by both methods at 1300°
C and 1500°
C for 1 hour. Sintered ceramic materials were characterized in terms of densification, microstructural evolution, chemical composition and mechanical properties such as hardness and indentation fracture toughness. Microwave sintering was determined to be a remarkably effective method in the production of Al2O3 ceramics at considerably low temperatures (&
#8804
1400°
C) compared to conventional sintering in achieving enhanced relative densities reaching to ~97% with improved microstructural characteristics and mechanical properties. Usage of sintering additives at temperatures higher than 1400°
C was determined to be effective in densifiying Al2O3 by both methods. Second phase particle incorporation yielded poor densification resulting in a decrease of hardness of the fabricated ceramic nanocomposites
however, their fracture toughness improved considerably caused by the crack deflection at the dispersed particles and grain boundaries reaching to ~4 MPa·
m1/2 in the case of SiC particledispersed nanocomposites. Compared to conventional sintering, microwave sintering is more effective in the processing of alumina and alumina matrix nanocomposites leading to similar densification values along with improved microstructural and mechanical characteristics at lower temperatures in shorter soaking periods.
3
Meoto, Silo, and Marc-Olivier Coppens. "Anodic alumina-mesoporous silica hybrid membranes: a systematic study of alumina filling." Diffusion fundamentals 16 (2011) 34, S. 1-2, 2011. https://ul.qucosa.de/id/qucosa%3A12715.
Full text
4
Franco, Jr Adolpho. "Erosive wear of alumina." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320591.
Full text
5
He, Jingyan. "Processing and characterisation of submicron/nanometre alumina ceramics and alumina matrix nanocomposite ceramics." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633127.
Full textAbstract:
The microstructure and properties of alumina and alumina-matrix nanocomposites are strongly affected by the raw powders and the processing route. The significant effect of hydrothermal synthesis condition on the morphology of boehmite particle was observed. UF-SiC has more controllable oxidation behaviour for the preparation of nanometer SiC/mullite/alumina composites than P-SiC. Due to the crystallization and agglomeration of SiC at high temperature, oxidation at low temperature is suggested. The properties of the compacts prepared by pressure filtration were closely related to the state of the starting slurry, the particle size and morphology and the applied pressure. A desired slurry can be obtained by the controlling of pH value, the ionic strength and the addition of suitable dispersant. Due to the non-uniform distribution of the liquid pressure and solid pressure across the compact during pressure filtration, the density of the compacts is not uniform as well. Gradually increasing the pressure to the desired level is suggested in order to obtain a more homogeneous compact density. Cracking upon unloading after pressure filtration and during drying became severe for mono and binary boehmite system due to the high stress caused by its very small particle size. Drying rate and stress, hence cracking can be somehow controlled by the drying condition. All the sintered materials from the pressure filtered compacts of submicron/nanometer alumina and alumina-matrix composite show very homogeneous microstructures with fine grain size, confirming that colloidal pressure filtration is a good way to produce advanced materials
6
Griffin, Jack M. "Combustion chemical vapor deposition of α-alumina, YSZ and multilayer α-alumina/YSZ films." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/20047.
Full text
7
Mubarak, Ahmed T. A. "Transition metals promoted alumina catalysts." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312197.
Full text
8
Oliveira, Ricardo Vinicius Bof de. "Moldagem de alumina por injeção." Florianópolis, SC, 2004. http://repositorio.ufsc.br/xmlui/handle/123456789/87484.
Full textAbstract:
Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matermáticas. Programa de Pós-Graduação em QuímicaMade available in DSpace on 2012-10-21T20:48:56Z (GMT). No. of bitstreams: 1 211337.pdf: 3803188 bytes, checksum: fdfc18812ee709aa25e1af365ff772ce (MD5)
Atualmente, a moldagem de pós por injeção tem se tornado um processo de transformação altamente atrativo, por aliar as propriedades inerentes aos materiais metálicos e cerâmicos à versatilidade da moldagem por injeção. Neste processo, o material na forma de pó é misturado ao veículo orgânico (ligante), o qual possibilita a moldagem por injeção da mistura. Neste trabalho, avaliou-se a utilização de componentes poliméricos e surfactante na fabricação de peças de alumina por moldagem de pós por injeção, sendo as propriedades micro e macroscópicas caracterizadas. A temperatura do solvente produziu diferentes velocidades de remoção, devido a mudanças no parâmetro de solubilidade e difusividade dos componentes solúveis. Um modelo matemático foi proposto para o processo de remoção por solvente, apresentando boa correlação com os valores obtidos experimentalmente. O processo subseqüente de remoção térmica foi facilitado pela porosidade formada na solubilização, resultando em peças livres de defeitos. As decomposições do PP e do PVB produziram hidrocarbonetos alifáticos, compostos com insaturações, e aldeídos. A sinterização mostrou que as peças de alumina não possuíam defeitos grosseiros, sugerindo que o amplo conhecimento das etapas do processo pode tornar a moldagem de pós por injeção mais interessante economicamente.
9
Tuttle, Richard W. "ELECTROSPUN ALUMINA FIBERS:SYNTHESIS AND CHARACTERIZATION." University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1164040902.
Full text
10
Xu, Chen. "Alumina based nanocomposites by precipitation." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:2bc4b631-6b5e-4536-b842-63c591df2832.
Full textAbstract:
This project addressed two main problems pertaining to Al2O3-FeAl2O4 nanocomposites developed via solid state precipitation: the mechanisms for precipitation in ceramic solid solution via reduction reaction, and the mechanisms for the improved mechanical properties and wear resistance of the developed Al2O3-FeAl2O4 nanocomposites. A model was proposed for precipitation in ceramic solid solutions via reduction reactions (the PRCS model). The thermodynamics of reduction reactions during aging treatments under various atmospheres were calculated and discussed relative to the second phase precipitate formation. Attempts were made to measure the corresponding diffusion kinetics using a new theory developed here based on volume fraction profiles of second phase particles in the aged samples. It was found that the measured apparent oxygen vacancy diffusivities conform well to the oxygen vacancy grain boundary diffusion coefficients reported in the literature, and the measured apparent matrix diffusivity conforms well to the Fe3+ ion matrix diffusion coefficients reported in literature. Based on the thermodynamics calculations, diffusion kinetics and some essential mechanisms that were discussed, the PRCS model was proposed. This has two aspects: macroscopic and microscopic. The macroscopic aspect of PRCS model was mainly used to explain the general aspects of microstructure and the distribution of intergranualar second phase particles. The microscopic aspect of the PRCS model was mainly used to explain the precipitation of intragranualar nanoparticles. The mechanical properties, thermal residual stress and wear resistance of selected Al2O3-FeAl2O4 nanocomposites were measured. The results revealed that the Al2O3-FeAl2O4 possessed improved fracture toughness (by around 46%), flexural strength (by around 30%) and abrasive wear resistance (by a factor of around 5) with respect to monolithic alumina. Several mechanisms were proposed to explain the improvements in both mechanical properties and wear resistance. Compressive residual stress was found in the surface layer of Al2O3-FeAl2O4 nanocomposites due to the thermal expansion coefficient mismatch between surface layer and bulk parts. Such residual stress was also interpreted as the main reason for the improvements in both mechanical properties and wear resistance.
11
Lamas, Juliana Colombo. "Carboximetilquitosanas: preparação, caracterização e aplicação como agentes de estabilização de suspensões aquosas de alumina." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-02092008-160622/.
Full textAbstract:
Suspensões coloidais encontram um grande interesse prático e apresentam aplicações na área de material cerâmico. No processamento deste material, a qualidade do produto final depende das propriedades iniciais da suspensão. Portanto, a desaglomeração e dispersão do pó cerâmico são cruciais para que os defeitos sejam minimizados. Para isto, estabilizantes eficientes devem ser utilizados. A carboximetilquitosana (CMQ) é a uma cadeia macromolecular, que apresenta grupos funcionais (carboximetila e amino) que podem adquirir cargas quando dissolvidos em meio aquoso e, por isso, pode ser usada no controle de propriedades de suspensões em que a presença de grupos com cargas seja importante para os mecanismos de estabilização. Neste trabalho, a CMQ foi preparada pela reação entre quitosana e diferentes proporções de ácido monocloroacético. A reação foi realizada em dois meios, um em que ocorreu previamente a dissolução da quitosana em um sistema de solventes (dimetilacetamida/cloreto de lítio) e outro em meio heterogêneo, no qual o material permaneceu em suspensão. A carboximetilação com prévia dissolução da quitosana pode levar a uma distribuição mais homogênea dos grupos carboximetila, quando comparado à preparação em meio heterogêneo, o que poderá influenciar na eficiência da CMQ como estabilizante. As amostras de CMQ foram caracterizadas pelas técnicas de espectroscopia na região de infravermelho (IV), ressonância magnética nuclear (RMN) e análise termogravimétrica (TGA). A técnica de IV, aplicada também para as amostras na forma ácida, permitiu a determinação do grau de substituição médio (GS ), sendo encontrado valores que variaram de 0,6 a 1,1. A eficiência da CMQ como dispersante foi avaliada por meio de medidas viscosimétricas, de potencial zeta e diâmetro médio de partícula. Em geral, houve uma diminuição da viscosidade da suspensão de alumina com a adição da CMQ, com certo destaque para as amostras com GS em torno de 1,0. As medidas de potencial zeta mostraram um aumento da magnitude das cargas superficiais, quando na presença de CMQ, o que proporciona repulsão eletrostática entre as partículas. As medidas de diâmetro de partícula mostraram que, além da diminuição do valor médio na região do ponto de carga zero (pcz), em que a agregação é máxima, ocorreu uma diminuição na distribuição dos diâmetros das partículas, em todos os pHs considerados. Estes resultados confirmam a eficiência das amostras de CMQ como estabilizantes para suspensões aquosas de alumina.Colloidal suspensions are of great practical interest, including applications in ceramic materials. In colloidal ceramic processing, the quality of the final product will depend on the properties of the initial powder suspension. Thus, an efficient deagglomeration and dispersion of the ceramic powder in a solvent is crucial for minimizing defects. This requires efficient dispersants. Carboxymethylchitosan (CMCh) corresponds to macromolecular chains containing groups carboxymethyl and amino, that can acquire charges when dissolved in water. Then, it can be used for the control of the properties of surface, when the presence of charged groups is important to the mechanisms of particles dispersion. In this work, carboxymethylchitosan was prepared reacting chitosan and different amount of monochloroacetic acid, in two different media. In the first one, chitosan was previously dissolved in a solvent system (dimethylacetamide/ lithium Chloride) and in the second one, corresponding to heterogeneous media, the reactants and products remained suspended during the whole process. The reaction with previous dissolution of chitosan may generate a more homogeneous distribution of carboxymethyl groups, which in turn can influence the CMCh efficiency as dispersant. The CMCh sample was characterized by infrared spectroscopy (IR), nuclear magnetic resonance (NMR) and thermogravimetric analyses (TGA). The obtainment of IR spectra considering the samples of CMCh in their acid form, also allowed determining the average degree of substitution (DS), that ranged from 0.6 to 1.1. These samples were used as dispersants for aqueous alumina suspensions. In this work the efficiency of the carboxymethylchitosans as stabilizing agents was analyzed considering rheological, zeta potential and average particle size measurements. The addition of CMCh, mainly that with DS near 1.0, led to a suspension with lower viscosity. Zeta potential measurements show that the addition of CMCh results in an increase in the absolute value of zeta potential at the point of zero charge (pzc), what promote the electrostatic repulsion between the particles. The presence of CMCh led also to a suspension with lower average diameter of particles and narrow particle size distribution in all pH values considered in the present work. The results showed that the charged macromolecules (CMCh) obtained from a renewable source (chitosan), present a good performance as deflocculating agents of alumina suspensions.
12
Tonello, Karolina Pereira dos Santos. "Compósitos à base de Al2O3, com adições de NbC e de MgO." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-15102009-153306/.
Full textAbstract:
Avanços tecnológicos geram a necessidade de materiais com propriedades cada vez melhores, de acordo com a sua aplicação final. Compósitos de alumina com adição de partículas de carbeto são uma opção promissora de aplicação estrutural. Neste trabalho foi estudada a influência da diferença de distribuição e tamanho de partículas de duas aluminas comerciais, a adição de 1,5 e 6% em volume de carbeto de nióbio e a adição de 500 ppm de óxido de magnésio, nas propriedades microestruturais e mecânicas de compósitos à base de alumina. Foram preparados corpos de prova por prensagem uniaxial e isostática, sinterizados em forno de resistência de grafite a temperaturas de 1600, 1650, 1700 e 1750°C, por trinta minutos, em atmosfera com pressão positiva de argônio. As amostras obtidas foram avaliadas quanto à densidade, microestrutura e propriedades mecânicas. Também foram realizados ensaios de difusão para verificar a reatividade química entre pares formados por amostras de alumina e ferro fundido cinzento. As características físicas e químicas das aluminas comerciais utilizadas acarretaram diferenças nos materiais finais; os compósitos produzidos com alumina A16 apresentaram densidade maior do que os produzidos com alumina A1000, nas mesmas condições; assim como os valores de dureza também foram maiores. A adição de 6vol% de carbeto de nióbio à matriz de alumina retarda o início da sinterização, enquanto que a adição de 1,5vol% não provoca mudanças sensíveis na cinética de densificação em relação aos materiais sem adição. Os valores de densidade e dureza dos compósitos contendo 1,5vol% de NbC foram superiores nas menores temperaturas de sinterização utilizadas. Os melhores resultados de densificação (>96% Dt) e dureza (>15GPa) foram obtidos para compósitos produzidos com alumina A16 e adição de 1,5% de NbC.The worldwide technological advances generate the needs of improved materials with better properties, according to its final purpose. Alumina composites with the addition of carbide particles have become an interesting option for structural applications. This work studies the influence of two commercial aluminas with different particle size and the adding of 1.5 and 6% in volume of niobium carbide and MgO 500 ppm in microstructural and mechanical properties of the composite. Samples were prepared by uniaxial and isostatic pressing and sintering was carried out in a graphite resistance furnace at 1600, 1650, 1700 and 1750°C for thirty minutes in Ar atmosphere. The obtained samples were evaluated sintering behavior, density, microstructure and mechanical properties, diffusion tests were realized to verify chemical reactivity between pairs formed by alumina and gray cast iron samples. The differences between aluminas caused some changes on the composites final properties. The composites produced with A16 alumina presented density about 2% higher than those produced with A1000 alumina. Similarly, the hardness also showed higher values. The carbide niobium added to the matrix of alumina delayed the sintering start, with an increase of about 30% in shrinkage initial states, when 6% of NbC was added. Composite with addition of 1,5% of NbC have higher density and hardness, even at lower sintering temperatures. The adding of niobium carbide to the alumina matrix and higher sintering temperatures provided higher density, hardness and fracture toughness to the composite. The best densification and hardness results of were obtained for composites produced with alumina A16 and when 1.5% of NbC was added.
13
Fernandes, Rodrigo Sampaio [UNESP]. "Desenvolvimento de processo alternativo para a fabricação de materiais cerâmicos envolvendo as técnicas de conformação por consolidação com amido e colagem." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/103733.
Full textAbstract:
Made available in DSpace on 2014-06-11T19:32:50Z (GMT). No. of bitstreams: 0
Previous issue date: 2008-12-01Bitstream added on 2014-06-13T19:03:29Z : No. of bitstreams: 1
fernandes_rs_dr_guara.pdf: 3696333 bytes, checksum: 967ad7b5dd1ef455a42e079e5e339fe8 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
A conformação por consolidação com amido é uma técnica que utiliza o amido como ligante e elemento formador de poros e é usada geralmente para confecção de cerâmicas porosas. Essa técnica pertence à família dos métodos de conformação direta que utilizam moldes impermeáveis. Por outro lado, a obtenção de cerâmicas pelo método da colagem de barbotinas é extremamente conhecido e amplamente utilizado na indústria. Baseia-se no ato de verter a barbotina em moldes porosos de gesso. O objetivo deste trabalho foi desenvolver um novo método para a obtenção de cerâmicas de alumina, que consiste na junção dos processos de colagem e de conformação com amido. Ou seja, suspensões contendo amido foram vertidas em moldes porosos de gesso e submetidas ao processo de gelatinização, visando a consolidação das peças e futura sinterização. Para atingir esta meta, o trabalho foi dividido em três etapas: a primeira, um estudo detalhado da conformação por consolidação com amido; posteriormente, uma análise de peças cerâmicas produzidas com a utilização de um molde com base porosa e laterais impermeáveis, a fim de gerar um gradiente de porosidade; por fim, um estudo das cerâmicas obtidas a partir do vertimento de suspensões contendo amido no teor de 10% a 40%, em moldes de gesso de consistência 70 e 90. As cerâmicas produzidas na primeira e terceira etapas foram caracterizadas por meio do ensaio de flexão por três pontos, e em determinados casos os resultados foram tratados estatisticamente pelo método de Weibull, pela determinação da porosidade aparente, baseado no Princípio de Arquimedes, por microscopia óptica e microscopia eletrônica de varredura. Uma análise comparativa mostrou que as cerâmicas produzidas por este novo método proposto apresentaram maior resistência mecânica que as obtidas somente por conformação por consolidação amido ou somente por colagem.
The formation by starch consolidation is a technique which uses the starch as a binder and porous form element and is generally used to make porous ceramics. This technique belongs to the direct consolidation methods that use mould impermeable. On the other hand, the ceramic obtained by the slip casting method is extremely known and largely used in the industry. It is based on the act of pouring the slip in cast porous moulds. This work was intended to develop a new method for obtaining alumina ceramics, that consists on joining of slip casting processes and starch consolidation, that is, suspensions containing starch were poured in cast porous moulds and submitted to the gelling process, in order to obtain the sample consolidation and future sintering. For reaching this purpose, the work was divided in three stages: the first one, a detailed study of the starch consolidation; later, an analysis of ceramic samples produced by using a mould porous base and impermeable laterals, in order to generate a porosity gradient; finally, a study of the ceramics obtained from suspension flowing containing starch of 10% to 40% content in cast mould of 70 and 90 consistence. The ceramics produced in the first and third stage were characterized by means of threepoint flexural test and in certain cases the results were statistically treated by the Weibull method, by the determination of the apparent porosity, based on Archimedes principle, by optical microscopy and scanning electronic microscopy. The comparative analysis showed that the ceramics produced by this new proposed method presented better mechanical resistance than the ones obtained only by starch consolidation or only by slip casting.
14
Blaese, Diego. "Processing and characterization of monoclinic-zirconia fibre-matrix interfaces in dense matrix alumina-alumina composites." reponame:Repositório Institucional da UFSC, 2013. https://repositorio.ufsc.br/handle/123456789/107283.
Full textAbstract:
Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2013.Made available in DSpace on 2013-12-05T23:42:12Z (GMT). No. of bitstreams: 1 318449.pdf: 2754019 bytes, checksum: d73daae4512a7cb151813f0d7e905cae (MD5) Previous issue date: 2013
Interfaces fibra-matriz tem um papel muito importante no desempenho de compósitos de matriz cerâmica. Sendo a interação entre fibra e matriz for muito forte, o compósito se comportará como uma cerâmica monolítica, e sendo muito fraca, o compósito perderá sua integridade estrutural e suas propriedades interlaminares. Zircônia monoclínica (não-estabilizada) tem mostrado ser uma boa alternativa na produção de interfaces fibra-matriz para compósitos cerâmicos à base de alumina devido à sua baixa interação química durante a sinterização e também devido ao fenômeno de microtrincamento causado pela transformação tetragonal-monoclínica durante o resfriamento. Interfaces porosas à base de zircônia monoclínica, as quais apresentam baixa tenacidade devido à sua porosidade e microtrincamento, haviam sido usadas no passado para criar interfaces com baixa interação entre fibras de safira e matrizes de alumina. Neste sistema, as interfaces se mostraram quimicamente estáveis mesmo acima de 1300 °C. Compósitos tenazes à base de alumina haviam sido fabricados com zircônia monoclínica como interface. Entretanto, a porosidade da matriz era ? 13%, o que dificulta a interpretação dos resultados, pois as propriedades mecânicas do compósito não podem ser claramente atribuídas às propriedades da zircônia monoclínica. Neste trabalho, compósitos-modelo com matriz densa e fibras individuais de alumina foram produzidos. A interface fibra-matriz foi produzida através de recobrimento por dip-coating das fibras em suspensões cerâmicas de zircônia monoclínica. Diferentes tamanhos de partícula foram utilizados no processo de dip-coating com o objetivo de variar a porosidade e assim, as propriedades das interfaces. A tensão de cisalhamento interfacial foi determinada através do teste de pushin nas fibras. O fenômeno de deflexão de trincas foi avaliado através de trincas criadas por indentação Vickers e o fenômeno de pullout das fibras através de observações nas superfícies de fratura. Propriedades como tenacidade à fratura, dureza e módulo de elasticidade da matriz e interface foram avaliadas para determinar os parâmetros de deflexão de trincas propostos por He e Hutchinson.
Abstract : Fibre-matrix interface properties play an important role on the performance of ceramic matrix composites. Being the fibre-matrix interaction too strong, the composite will behave such as a monolithic ceramic and being too weak, the composite will lose its structural integrity and its interlaminar properties. Monoclinic (unstabilized) zirconia has shown to be a suitable alternative for the production of fibre-matrix interfaces for alumina ceramic matrix composites due to its low chemical interaction during sintering and due to the microcracking phenomenon caused by the tetragonal-monoclinic transformation during cooling. Porous oxide coatings of monoclinic zirconia, which have low toughness because of their porosity and microcracking, have been used in the past to achieve debonding between sapphire fibres and alumina matrices and were to be chemically stable with sapphire above 1300 °C. Tough alumina matrix composites have been fabricated using monoclinic zirconia as fibres coating. However the matrix porosity was = 13%, which makes it difficult to interpret the results, because the toughness cannot be unambiguously attributed to the properties of the unstabilized zirconia interfaces. In this work, model composites with dense alumina matrix and single alumina fibres were fabricated. The fibre-matrix interface was produced via dip-coating single fibres in monoclinic zirconia suspensions. Different particle sizes were used for the dip-coating in order to vary the coating porosity. The interfacial sliding stress was determined via a modified fibre pushin test. The crack deflection behaviour was analysed from cracks created via Vickers indentations and the fibre pullout via surface fracture observations. Properties such as fracture toughness, hardness and elastic modulus for the interface and matrix were also evaluated in order to determine the crack deflection parameters established by He and Hutchinson.
15
Sparrapan, Regina. "Estudo das reações da monotosil-hidrazona de furila e compostos analogos na presença de alumina basica." [s.n.], 1989. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250103.
Full textAbstract:
Orientador : Concetta KascheresDissertação (mestrado) - Universidada Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-07-17T02:11:33Z (GMT). No. of bitstreams: 1 Sparrapan_Regina_M.pdf: 3785732 bytes, checksum: e1888af62a381b1d1ace322ee945e0f3 (MD5) Previous issue date: 1989
Mestrado
16
Marcos, Kelly Nanci Pinto. "Área específica, morfologia e estrutura de aluminas obtidas a partir de alguns precursores." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-18082008-145838/.
Full textAbstract:
As características das matérias-primas particuladas como tamanho, forma, área específica, entre outras, determinam não somente o desempenho final de um produto, mas também o processo de sua fabricação. Neste sentido, matérias-primas sintéticas são produzidas por meio de conversões químicas que têm como finalidade o controle da reprodutibilidade de características. Esta tese tem como objetivo o estudo de precursores sintetizados com matérias-primas nacionais de elevada pureza, quanto à área específica (AE), estrutura cristalina e morfologia das fases formadas durante as transformações térmicas de alguns hidróxidos (gibsita e pseudoboemita), sais (acetato e formato) e sulfatos duplos (de amônio e de sódio) de alumínio. As amostras sintetizadas e aquecidas foram caracterizadas por DRX, MEV, BET e análise térmica (TG, DTA e DSC), a fim de que fossem observadas as variações nas características das fases formadas. Observou-se que todos os precursores, à exceção do \"sulfato-Na\", evoluem termicamente resultando como produto final somente a a-alumina. No caso particular do \"sulfato-Na\", em que se apresenta resultados preliminares, verifica-se a formação, além da a- alumina, de B-alumina. Os hidróxidos e os sais de alumínio passam por uma seqüência de aluminas de transição que exibem valores de área específica elevados. Com relação à pseudoboemita, além da caracterização proposta no trabalho, foi estudada a influência do método de secagem e do tempo de envelhecimento da pseudoboemita nas características dos materiais sintetizados. Verificou-se que o método de secagem pode influenciar as temperaturas de transformações de fases das aluminas. Precursores secos por nebulização podem formar a fase a concomitantemente com a fase 0, o que não ocorre com os materiais secos ao ar. Já o tempo de envelhecimento influenciou no tamanho final das fibrilas de pseudoboemita. Tanto o método de secagem quanto o tempo de maturação afetam de forma determinante a organização das fibrilas que, por sua vez, estabelecem a distribuição de poros nos materiais produzidos.Features of powdered raw materials like size, morphology, specific area, determine the product performance, besides the fabrication process product. In this direction, the synthetic raw materials are produced by means of chemical conversion to control the characteristics reprodutibility. This thesis has as objective the study of precursor\'s synthesized with national raw materials of raised pureness, by the study if the specific area (AE), crystalline structure and morphology of the phases formed during thermal transformation of some hydroxides as (aluminum hydroxides- gibbsite and pseudoboehmite; aluminum salts - acetate and formate and aluminum sulphates - sodium and amonium) produzed by high pure nacional raw materials. The sythetized and heated samples are examined by DRX, MEV, BET and thermal analysis (TG, DTA e DSC) to verify the characteristics variations in the formed phases. It\'s can be seen that every thermal treated precursors evolve to a-alumina. In the particular case of \"Na-sulfate\", the preliminary results present also B-alumina. The hydroxides and salts pass by a sequence of alumina transition, that show high specific area. In the case of pseudoboehmite, was also studied the influence of dried method and the aging of aqueous aluminum hydroxide gels in the characteristic of synthesized materials. It verified that the dried method can influence the temperature of the alumina phase\'s transitions. Dried precursors by spray drier can form the phase a and 0 together, this not occur with the others. The aging can influence in the pseudoboehmite microfibrils size. The dried method and the aging influence the organization microfibrils, and this one determines the pore distribution from the produced materials.
17
Edelstein, Sergio Gavalas George R. "Adsorption of sulphur dioxide and reduction of sulphate on alumina and alkali-alumina at high temperatures /." Diss., Pasadena, Calif. : California Institute of Technology, 1987. http://resolver.caltech.edu/CaltechETD:etd-05052006-082025.
Full text
18
Sartori, Thauane Aparecida Inácio da Costa. "Biocerâmicas porosas de alumina e de alumina-zircônia recobertas com fosfatos de cálcio para implantes ósseos." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/74/74133/tde-17092015-092938/.
Full textAbstract:
A utilização de biocerâmicas de natureza inerte, como a alumia e zircônia, têm ao longo dos últimos anos, estimulado grande interesse científico no entendimento dos mecanismos biológicos dos biomateriais. Por sua vez, cerâmicas bioativas (a base de fosfatos de cálcio) apresentam uma melhor estabilidade química superficial e biocompatibilidade, entretanto, suas limitações estão relacionadas a baixos valores de propriedades mecânicas. Assim, a técnica de recobrimento de alumina-zircônia, em soluções de concentrações semelhantes ao fluido corpóreo, possibilita o desenvolvimento de uma camada bioativa, que induz uma melhor interação osso-implante. Além disso, cerâmicas porosas (arcabouços) com morfologia e distribuição bem definida são reconhecidamente empregadas como suporte para o crescimento, fixação e desenvolvimento de tecido no interior do implante. Neste sentido, o objetivo deste trabalho foi obter corpos de prova porosos de alumina e alumina contendo 5% em volume de inclusões nanométricas de zircônia. A obtenção dos corpos porosos se baseou no processo gelcasting de espumas, sem atmosfera controlada, seguido pelo tratamento químico de superfície com ácido fosfórico e finalmente, pelo recobrimento biomimético para o período de 7, 14 e 21 dias de incubação. As caracterizações dos corpos de prova foram realizadas através de porosidade aparente, microscopia eletrônica de varredura (MEV) aliada à espectroscopia por dispersão de energia (EDS) e ensaio de compressão diametral. Os resultados indicaram a obtenção de corpos porosos de alumina e alumina-zircônia com alta homogeneidade de poros em toda a estrutura com elevada interconectividade. O método de recobrimento biomimético promoveu uma formação efetiva de apatita na superfície e no interior dos poros dos corpos porosos em todas as composições e condições estudadas, contudo, essa formação se apresentou mais uniformemente distribuída na superfície dos nanocompósitos porosos de alumina-zircônia tratados com ácido fosfórico, indicando que a presença da zircônia nanométrica estimula a formação da nucleação da apatita a partir das interações entre os grupos (Zr-OH). Além disso, bons valores de resistência mecânica à compressão da matriz foram alcançados, potencializando a aplicação dos corpos porosos de alumina e de alumina-zircônia recobertos com fosfato de cálcio como bons substitutos ósseos.The use of naturally inert bioceramics as alumina and zirconia has over the last few years spurred great scientific interest in understanding the biological mechanisms of biomaterials. In turn, ceramic biactive (by calcium phosphate), have a better surface biocompatibility and chemical stability. However, their limitations are related to low values of mechanical properties. Thus, the alumina-zirconia coating technique, in similar concentrations to the body fluid solutions, enables the development of a bioactive layer, which induces a better implantbone interaction. Furthermore, porous ceramic (scaffolds) with a defined morphology and distribution are known by using it as support for the growth, attachment and tissue development within the implant. In this sense, the objective of this study was to obtain porous bodies of alumina and alumina containing 5%vol. nanometric zirconia inclusions. The obtaining of porous bodies based on the gelcasting foams process without controlled atmosphere, followed by chemical surface treatment with phosphoric acid, and finally the biomimetic coating to the period of 7, 14 and 21 days of incubation. The characterizations of the samples were performed by apparent porosity, scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and diametrical compression test. The results indicated porous bodies of alumina and alumina-zirconia with high homogeneity throughout the pore structure with high interconnectivity. The biomimetic coating method promoted effective formation of apatite on the surface and within the pores of the porous bodies in all investigated compositions and conditions, however, such a formation is presented more evenly distributed on the surface of porous alumina-zirconia nanocomposite acid-treated phosphoric, indicating that the presence of nano-zirconia stimulates the formation of nucleation of apatite from interactions between groups (Zr-OH). Furthermore, good values of compressive strength of the matrix that have been achieved, enhancing the application of the porous bodies of alumina and alumina-zirconia coated with calcium phosphate bone substitutes as well.
19
Soares, Robson de Miranda. "Membranas suportadas de alumina, obtidas pelo método da sedimentação gravitacional." Universidade de São Paulo, 1998. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-10092008-110844/.
Full textAbstract:
Este trabalho trata da preparação de membranas suportadas em substratos com alta permeabilidade, alta porosidade e razoável resistência mecânica., pelo método da sedimentação gravitacional. Os substratos foram obtidos através da prensagem de composições contendo poli(metacrilato de metila) e ácido esteárico dissolvidos no dicloro metano e alumina APC-SG (d50 = 3 μm ) calcinada a 1600°C durante 1h. As partículas de alumina após calcinação são classificadas em peneiras da série Tyler e utilizadas aquelas cuja distribuição se encontravam na faixa granulométrica de 250 a 500 μm. Os substratos após a prensagem a 33 MPa são calcinados e sinterizados a 1600°C durante 3h e apresentam \"alta resistência mecânica\", taxa de fluxo de 404 m3/m2h , porosidade de 59 % e distribuição de poros nas faixas de 10 a 100 μm e de 0.4 a 2.0 μm. Devido a grande diferença entre os diâmetros dos poros do substrato e o tamanho das partículas de alumina AKP-50 (d50 = 0.3 μm), utilizada para a obtenção da membrana, foi necessário acrescentar uma camada intermediária de alumina APC-SG entre o substrato e a membrana para viabilizar o processo de sedimentação. A camada intermediária foi depositada por sedimentação gravitacional e sinterizada a 1500°C durante 1h. A porosidade do substrato/camada intermediária é igual a 56 %, taxa de fluxo de 10 m3/m2h e distribuição de poros estreita na faixa de 0.4 a 2 μm. As membranas foram sinterizadas a 100°C durante 0.5h e se caracterizam por possuir uma distribuição de poros estreita na faixa de 0.04 a 0.09 μm, espessura média de 57 μm e taxa de fluxo de 0.4 m3/m2h.This work is concerned with ceramic membrane preparation supported on a ceramic substrate having high permeability, high porosity and reasonable mechanical strength. Membranes were prepared from AKP-50 alumina by the gravitational sedimentation method followed by sintering at 1000°C for 0.5 h. Membranes showed a unimodal narrow pore size distribution in the 0.04 to 0.09 range, thickness of 57 μm and 0.4 m3/m2h. flow rate. Substrates were prepared by uniaxial compression, at 33 MPa, of alumina PMMA stearic acid powder composites followed by organic burning and final sintering at 1600°C for 3h. In order to increase alumina APC-SG grain size distribution to 250- 500 μm range, alumina was previously calcined at 1600°C for 1h. Substrates show high mechanical strength, 4.0 to 2 m3/m2h flow rate, 60% porosity and pore size distribution in the range of 10-100 μm and from 0.4 to 2.0 μm. Due to the large difference between the substrate pore diameter and the AKP-50 alumina grain size distribution (d50 = 0.3 μm) used in the membrane preparation, it was necessary to add an intermediary APC-SG layer. This layer was prepared also by the gravitational sedimentation method and sintered at 1500°C for 1h. The intermediary layer/substrate showed 56% porosity, 10 m3/m2h flow rate and a narrow pore sue distribution in the 0.4-2.0 μm range.
20
Pope, Stephen Gerard. "Mechanical properties of ion implanted alumina." Diss., Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/19544.
Full text
21
Negahdari, Zahra. "Reaction sintered alumina-lanthanum hexaaluminate composites." Aachen Shaker, 2009. http://d-nb.info/1000213897/04.
Full text
22
To, Lap C. "Nonlinear control techniques in alumina refineries." Curtin University of Technology, School of Chemical Engineering, 1996. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=12276.
Full textAbstract:
Nonlinearities exist in all process control systems. The use of linear control techniques is valid only in a narrow range of operation. Therefore, in this thesis, multivariable nonlinear control techniques are considered. The target process is the single effect evaporative process of the liquor burning unit in Alcoa's alumina refinery in Kwinana and the proposed triple effects unit in the Wagerup refinery. Two types of nonlinear control strategies using differential geometry were studied, namely, the input output linearization (Kravaris and Soroush, 1990) and the input state linearization (Hunt et al, 1983a). The research has successfully demonstrated the superiority and simplicity of the nonlinear controller through simulations and plant implementations. An integrated software package using MAPLE V.3 as the computing environment was developed to automate the solution algorithms and to graphically simulate the closed loop dynamics of different processes using the two nonlinear control strategies.The issue of robustness of the nonlinear controller was addressed by developing a procedure called uncertainty vector adjustment. The effectiveness of the new strategy was successfully demonstrated on the simulated liquor burning process. Furthermore, the stability of the adjustment technique was proved and its theoretical bounds were established using Lyapunov function analysis.A comparative study of geometric nonlinear filter and extended Kalman filter was conducted to reduce the requirement of full state feedback necessary for nonlinear control using either input output linearization or input state linearization. The simulation of the single effect evaporation unit of the liquor burning process showed that the geometric nonlinear filter is superior to the extended Kalman filter in terms of nonlinear tracking performances.The plant trials of the input output linearization ++in Alcoa's Kwinana alumina refinery demonstrated the practicability and feasibility of implementing nonlinear control in an industrial setting and also fostered a closer gap between academia and industry. The trials established guidelines for implementing a global linearizing controller on site, including conversion of the relevant constraints and the output of an industrial proportional and integral controller to the equivalent proportional and integral action required by the nonlinear controller. The results showed that the performance of the nonlinear controller was better than the current linear controller on site in terms of responsiveness and resistance to disturbances. Hence, the nonlinear control strategy enables the process to settle faster.All in all, efforts have been made in this thesis to minimise the use of abstract mathematical language and, in some cases, simplify the language so that nonlinear control theory can be understood by a wider range of audience, especially industrial practitioners. It is hoped that the insights provided in the dissertation will encourage more industrial implementations of nonlinear controllers and forge more interaction to close the widening gap between academic and industrial practice in process control.Keywords: nonlinear control, differential geometry, symbolic algebra, evaporator process, uncertainty vector adjustment, geometric nonlinear filter.
23
Tuttle, Richard W. "Electrospun alumina fibers synthesis and characterization /." Akron, OH : University of Akron, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=akron1164040902.
Full textAbstract:
Thesis (M.S.)--University of Akron, Dept. of Physics, 2006."December, 2006." Title from electronic thesis title page (viewed 05/28/2008) Advisor, Rex D. Ramsier; Committee members, Matthew P. Espe, Sasa V. Dordevic; Department Chair, Robert R. Mallik; Dean of the College, Ronald F. Levant; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
24
Meoto, Silo, and Marc-Olivier Coppens. "Anodic alumina-mesoporous silica hybrid membranes." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184904.
Full text
25
Morsi, Khaled M. B. E. "Mechanical properties of particle reinforced alumina." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320644.
Full text
26
Schneider, Jochen Michael. "Formation and properties of alumina coatings." Thesis, University of Hull, 1997. http://hydra.hull.ac.uk/resources/hull:10469.
Full textAbstract:
Investigations concerning the microstructure and mechanical properties, composition and chemical bonding of alumina coatings have been performed. Alumina coatings have been deposited by both ionized reactive magnetron sputtering (IMS) and conventional reactive magnetron sputtering (CMS) in an argon/oxygen discharge onto stainless steel coated silicon substrates. X-ray diffraction (XRD) was used for the phase analysis, and nanoindentation was used to evaluate the mechanical properties. Substrate temperature during deposition was <500°C, which is the technologically interesting temperature range to coat temperature sensitive substrates such as tool steels. Formation of the x-phase was observed at 472°C. At substrate temperatures <472°C evidence for the formation of the amorphous alumina phase was found. Films containing a mixture of K and θ-alumina phases was grown at 430°C. The crystalline film hardness was 22+-1 GPa, which is equivalent to values reported for alumina films deposited by Chemical Vapor Deposition (CVD). Films grown at the same temperature by conventional magnetron sputtering were X-ray amorphous, and the hardness was found to be strong function of the substrate temperature. Furthermore, a novel, very high rate reactive magnetron sputtering deposition process for alumina hard coatings at substrate temperature ≤250°C has been developed. Utilizing pulsed D.C. power to sputter A1+A1Ox off the target surface and partial pressure control of the reactive gas to maintain a certain partial pressure value (accuracy of better than 0.005 mTorr), fully dense, transparent alumina coatings could be produced at 76% of the metal deposition rate. The coatings have an elastic modulus of,140 GPa, a hardness of 12 GPa, a chemical composition close to stoichiometric, and a refractive index of 1.65.
27
Ntalkiwa, J. W. "Electrochemical characterisation of colloidal alpha-alumina." Thesis, Swansea University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638342.
Full textAbstract:
In this work, average particle size and distribution, specific surface area, density, electrophoretic mobility, zeta potential and surface charge density of colloidal α-alumina are reported. These properties are necessary in describing the surface characteristics and stability towards aggregation of a colloid material when suspended in various conditions. It was recommended that, in order to describe adequately the stability of α-alumina suspensions in various conditions, rheological and sedimentation studies performed over the same range of conditions are required.
28
Bennett, Ian John. "Development and evaluation of alumina calcination." Thesis, University of Bath, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340929.
Full textAbstract:
This thesis focuses on a number of aspects governing the transformation of gibbsite, via intermediate phases, to a-alumina. These aspects include the size and morphology of the gibbsite grains, the influence of additions of foreign elements, the effect of a mechanical treatment of the gibbsite prior to calcination, and combinations of these factors. The materials were characterisedb y scanninge lectron microscopy, X-ray diffraction and surfacea rea measurementsF. or someo f the calcined materials an attempt was made to sinter the powders to a dense body to investigate if any of the treatments during calcination had an effect on this process. The literature review covers the current state of understanding of the production of bulk alumina powder by the Bayer process and the phase changes seen on calcination of precursors to the stable a-alumina phase. A detailed description of the phase changes is given and the various routes and conditions necessary for the transformations to occur are considered. The transformations are examined in relation to the morphology of the crystals and the variables controlling the phase transformation route are discussed. Calcination in air showed that the size of the gibbsite grain governs the calcination route taken to reach a-alumina. The standard gibbsites used in this work show a mixed calcination sequence transforming both via the boehmite phase, followed by the y, 8 and 0 phases, and via the x and K phases. The formation of boehmite is attributed to retention of water vapour within the grainDifferences in morphology of the starting materials showed that for the range of materials seen, the morphology of the grain is less important than its size. The super fine material confirmed that a small grain size transforms via the non-boehmite route only, with the other gibbsites taking intermediate routes as for the standard gibbsites. Of the additions made prior to calcination, aluminium fluoride was found to reduce the transformation temperature to a-alumina by approximately 300°C. Other additions had little effect on the transformation temperature although a reduction in grain size was seen with aluminium chloride. It was found that good mixing of the alumina fluoride was essential to obtain reliable and reproducible results. This is due to the small amounts of additive that are needed and the sensitivity of the process to concentration variations. Mineralisation of a range of gibbsites showed that the presence of sodium in the starting material was crucial in reducing the calcination temperature. This led to the conclusion that the sodium and fluoride react to form a liquid phase. The presence of a liquid phase increases the mobility of the aluminium and oxygen atoms resulting in a reduction of the transformation temperature. Fluoride additions to the gibbsites with different morphologies showed that the presence of sodium was the governing factor in reduction of the transformation temperature. Milling of the starting materials showed that there was a small reduction in the transformation temperature between some of the phases. The energy involved in milling leads to activation of the gibbsite. This activation takes the form of a reduction in the grain size and in a reduction of the crystallinity seen in the XRD patternFluoride additions during the calcination of sapphire with a standard gibbsite powder showed preferential grain growth. It was possible to initiate growth of small plate-like crystals on the polished surface of a piece of sapphire parallel to the basal plane. Crystal growth was also seen in scratches on a polished surface perpendicular to the basal plane
29
Wang, Shuo, and 王硕. "Tribological behaviour of anodised alumina nanohoneycombs." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B49618131.
Full textAbstract:
Anodic alumina nanohoneycombs (AAO) have been widely used because of its convenient fabrication and controllable pores’ geometry. A lot of investigations have been conducted to study its physical and chemical properties. However, the mechanical properties, especially tribological properties, of such a popular nanomaterial still remain almost unknown.
In this project, a series of scratch experiments were conducted on AAO films fabricated by a two-step anodisation method. The testing system is a G200 Nanoindenter provided by Agilent Corporation. A standard diamond Berkovich tip is used as the scratch tip. A scanning electron microscope was used to image the microstructure of the material deformation after scratching. Strengths of AAO domains with different pore regularities were compared by performing the scratch tests at constant normal loads crossing the boundaries separating these domains. Ramping load tests were carried out to show the effects of the normal load on the deformation and friction of the AAO. Scratch cycles and velocities were also varied to see their influence on friction and wear.
The results show that the more ordered AAO structure has higher strength than disordered counterparts under scratch testing. The friction coefficient reduces rapidly on increasing normal load, and an explanation of this unusual behaviour is offered by considering the row-by-row deformation of the AAO structure. In multicycle scratch tests, the friction reaches a maximum at the fourth cycle. A step-like deformation behaviour was observed when the scratch velocity became extremely large, and this is probably due to the dynamic response of the instrument.published_or_final_version
Mechanical Engineering
Master
Master of Philosophy
30
Abdul-Kader, Oras Khalid. "Liquid-phase sintering of alumina ceramics." Thesis, University of Leeds, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417339.
Full text
31
Fletcher, Helen Lucy. "Hydratable alumina for refractory castable systems." Thesis, University of Leeds, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.400262.
Full text
32
Gilmour, Alison. "The electrochemical breakdown of beta alumina." Thesis, Glasgow Caledonian University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379150.
Full text
33
Couroyer, Charlotte G. M. "Attrition of alumina catalyst carrier beads." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/843669/.
Full textAbstract:
Attrition of alumina catalyst carrier beads in reforming units causes operational problems and the loss of the catalyst particles due to the formation of fines and small fragments. This thesis addresses the characterisation and optimisation of the mechanical strength of these beads in collaboration with Institut Francais du Petrole (IFP) and Rhodia. A methodology was devised to test and improve the particle strength at various strain rates using both single particle and multiple particle tests by considering the mechanical stresses prevailing in industrial units. This methodology was tested with a commercial sample and then used to assess the strength of new samples for which the bead structure was modified by changing the filler concentration and type, the macroporosity, the drying regime and the surfactant concentration. A significant increase in the particle strength was achieved in comparison with the commercial samples. The mean crushing strength increased by a factor of about three and the extent of impact attrition was significantly decreased, e.g. by a factor of 30 for normal impacts at 20 m s-1. For single particle testing, a relationship between quasi-static and impact results was obtained when the impact breakage was compared with the percentage of weak particles obtained from the side crushing strength (SCS) test. This suggests that for this type of material the particle strength is not sensitive to the strain rate. Multiple particle tests confirmed the results obtained by single particle tests for two samples for which sufficient quantity of test material was available. In order to relate the extent of attrition in a particle assembly under compressive loading to the single particle properties, the BCS test was simulated by distinct element analysis using the TRUBAL code. Trends similar to the experimental work were obtained for the simulation of the attrition. However, the simulations tend to underestimate slightly the extent of attrition, which is highly dependent on the particle strength distribution and on the contact force distribution within the particle assembly. As a result of this work, the manufacture of the alumina catalyst carrier beads used in reforming units has been significantly improved.
34
Miller, Jerry Wayne. "The adsorption of phosphate on alumina /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487259580262193.
Full text
35
Van, Zyl Arnold. "The synthesis of beta alumina powders." Doctoral thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/17648.
Full textAbstract:
Bibliography: pages 83-90.Beta alumina solid electrolyte material is conventionally synthesized by the high temperature solid state reaction of α-Al₂O₃ with soda and a stabilizer ion such as lithia or magnesia. This reaction requires a reconstructive transformation of the α-Al₂O₃ oxygen sublattice and results in a two-phase mixture of β and β"-Al₂O. In order to maximize the preferred β"-Al₂O₃ phase an additional peak heat treatment schedule is required. This work investigated the replacement of the α-Al ₂O₃ component of the reaction mixture with a range of synthetic aluminium hydroxide precursor materials. Four different aluminium hydroxide precursors were synthesized by the controlled hydrolysis of a common aluminium isopropoxide parent material. The oxygen sublattice of each aluminium hydroxide precursor was engineered by varying the alkoxide hydrolysis conditions. These precursors were used to synthesize beta alumina powders by the high temperature solid state reaction with soda and lithia, resulting in powders with a nominal composition of Li₀.₃₈Na₁.₆₅Al₁₀.₆₆O₁₇. The solid state reactions were monitored by differential thermal analysis and thermogravimetric analysis. The structural development of the reaction products with increasing temperature, was monitored by powder X-ray diffraction. A significant observation was the direct formation of single phase β"-Al₂O₃ at 1200 °C by the solid state reaction of soda and lithia with certain aluminium hydroxides. The work concludes with the proposal of a generalized mechanism relating the aluminium hydroxide precursor oxygen sublattice to the nature of the beta alumina reaction product.
36
Gahanbani, Ardakani Mahmoud. "Deformation of copper containing alumina particles." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46309.
Full text
37
Zeng, Peng. "Wear mechanisms of alumina hip prostheses." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489871.
Full textAbstract:
Although extensive research has been undertaken on wear of alumina there is still poor understanding about the mechanisms which can take place during the ill vivo wear of alumina, such as found in alumina hip prostheses. In particular, the origin of 'stripe' wear, a region of high wear dominated by fracture that is observed widely from retrieved ill vivo alumina hip prostheses, has not been clearly determined. Moreover, it has not been completely validated that laboratory hip simulators reproduce the same wear mechanisms as found in the body, although it is known that the stripe wear can only be replicated by the introduction of microseparation during the simulated walking cycle. The current study presents detailed analysis of the worn surface of alumina acetabular cup and alumina femoral head following ill vitro testing incorporating microseparation at the University of Leeds, as well as retrieved ill vivo alumina hip prostheses. Four different wear zones were identified on both the acetabular cup and femoral head for both ill vitro and ill vivo specimens, defined as: mild wear, wear transition, stripe boundary and stripe wear zones. Although sequence of events cannot be verified, the available evidence indicated the following wear process of alumina hip prostheses: rather than the final stage of the wear process, fracture occurred in the early stages due to the local impact associated with microseparation, leading to the region of stripe wear. FIB cross-section investigations showed that fracture was predominantly intergranular, with some transgranular fracture, and that in both cases, fracture was restricted to the outer layer of grains. In addition, plastic deformation and a 3rd body abrasion were also observed, with the dislocation activity also restricted to the outer grains. The wear debris liberated from the stripe wear region was believed to subsequently have resulted in wear in other parts of the joint that would otherwise have shown little evidence of damage. The stripe boundary zone, immediately adjacent to the stripe wear region, exhibited minimal wear, with a remarkably sharp boundary between the stripe wear and mild wear. The explanation for such an abrupt change from mild to severe wear were possibly abrupt change in lubrication from microseparation or small changes in the height of the alumina surface. Most of the remaining surface on the worn alumina-on-alumina THRs had experience only mild wear. Detailed analysis of this region showed that it contained extensive fine scale 3rd body abrasion, presumably from wear debris that had become much finer due to attrition between the articulating surfaces, originally coming from the stripe wear region. Cross-sectional TEM indicated that the abrasive grooves did result in surface dislocation activity which was restricted to the outer 100nm of the surface. In addition, differential wear between grains was observed in the mild wear zone, which was believed to be evidence of tribochemical wear. Some small additional wear scars, similar to the observations of the morphology of stripe wear and parallel to the stripe wear occurred near the stripe wear region on ill vitro and retrieved ill vivo alumina femoral heads in the mild wear zone. A wear transition zone outside the stripe wear zone was identified, comprising a highly pitted surface and an amount ofwear debris. The pits had largely arisen from intergranular fracture. The extent of this region was limited compared with other wear zones and was more obvious on the alumina acetabular cup than on the alumina femoral head. Detail TEM analysis showed of this region showed extensive dislocation activity on the pyramidal system. Three types of wear debris were observed: globular wear debris, nanocrystalline wear debris and needle shaped wear debris. The globular wear debris is most likely to have come from grains been pulled out and covered by tribochemical film as it rolls over the surface. The nanocrystalline wear debris was believed to arise from 3rd body microabrasion during the normal articulation and the needle shaped wear debris is believed to be a direct product of tribochemical wear.
38
Marshall, Peter R. "Potassium promotion of nickel alumina catalysts." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/12572.
Full textAbstract:
The chemical and physical effects of potassium promotion on prepared nickel-alumina catalysts have been examined using "in-situ" Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Temperature Programmed studies and X-ray Powder Diffraction (XRPD). Various preparative methods were explored to obtain catalyst samples with a high metallic surface area. A sequential precipitation technique was employed, yielding a highly loaded nickel alumina catalyst (56 %wt Ni) with the hydrotalcite structure, typical of other industrial catalysts. Subsequent potassium promotion of this initial catalyst was achieved by impregnation. X.R.P.D. studies showed no observable changes in the bulk structure of the catalyst at room temperature or during calcination with low loadings of potassium (≤ 1 %wt). However, at higher loadings, potassium carbonate/oxide peaks became apparent but there was no indication of any other potassium derivatives. The presence of potassium both inhibited the reduction of the catalyst and brought about a reduction of the nickel surface area in the final reduced catalyst. Infrared studies showed definite changes in the surface chemistry of the catalyst with potassium promotion. Adsorption of carbon monoxide showed a downward shift in the wavenumber of the characteristic bands together with an apparent change in the relative proportions of the different carbon monoxide adsorbed species. Temperature dependent adsorption studies further indicated the formation of an activated species which was increasingly stable as a function of potassium promotion. The same species was observed in analogous carbon dioxide experiments. The effect of potassium on the infrared spectra from adsorbed ethene, propene and but-1-ene was more subtle.
39
Souza, Adriane Damasceno Vieira de. "Evolução microestrutural e de propriedades físicas de cerâmicas porosas moldáveis de alta alumina durante calcinação e sinterização." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-25102016-110245/.
Full textAbstract:
A combinação de óxido de alumínio (Al2O3) com hidróxido de alumínio (Al(OH)3) resulta numa maneira interessante de produzir cerâmicas porosas com baixa condutividade térmica, alta área superficial específica, elevada refratariedade e estabilidade química, com custos competitivos. Devido a essas características, esse sistema tem grande potencial de aplicação tecnológica em catalisadores, isolantes térmicos e filtros para altas temperaturas. Apesar do bom desempenho, essas cerâmicas ainda apresentam limitações tais como a baixa resistência termomecânica, devido à elevada porosidade (principalmente, naqueles materiais com fração volumétrica de poros acima de 50%) e redução de porosidade causada pelos fenômenos de sinterização e crescimento de grãos que se intensificam acima de 1100°C. Por esse motivo, investigações adicionais são necessárias a fim de minimizar esses aspectos negativos. Este trabalho teve como objetivo desenvolver estruturas porosas moldáveis (porosidade acima de 50%) de alta alumina, com adequada resistência mecânica (acima de 10 MPa em compressão) e que fossem resistentes à densificação, para uso em temperaturas acima de 1100°C. Inicialmente foi realizado um estudo sobre a decomposição térmica (temperatura variando de 300°C a 1500°C) de três tipos de hidróxidos de alumínio com diferentes granulometrias (1, 10 e 100 µm) a fim de avaliar seus potencias como agentes porogênicos. Em seguida, por meio de ensaios reológicos, determinou-se as condições ideais de dispersão e mistura das partículas de alumina calcinada, hidróxido de alumínio e alumina hidratável. Em uma segunda etapa do trabalho, suspensões aquosas de alumina calcinada (D50: 1 µm ou 2,5 µm) consolidadas com alumina hidratável foram preparadas com diferentes proporções (0 - 67,5% vol.) de Al(OH)3 (D50: 1 µm ). Para os tipos de Al(OH)3 com partículas maiores foram preparadas somente as composições contendo 22,5% vol. de alumina calcinada (2,5 µm), 67,5% de hidróxido de alumínio e 10% vol. de alumina hidratável. As amostras foram submetidas a tratamentos térmicos em 1100°C, 1300°C e 1500°C durante 3 h. O comportamento durante a sinterização foi acompanhado por meio de dilatometria e as estruturas verdes/secas e sinterizadas foram caracterizadas em relação à porosidade total e tamanho médio dos poros, resistência à compressão e módulo elástico. A evolução da microestrutura foi avaliada usando microscopia eletrônica de varredura. Comprovou-se a ação porogênica do Al(OH)3 em matrizes de alumina calcinada. Essa ação depende de diversos fatores como teor adicionado, temperatura máxima de sinterização e da relação entre as granulometrias da matriz e do Al(OH)3. Variando-se esses parâmetros, estruturas com elevada porosidade (acima de 50%) e resistência à ruptura por compressão (acima de 10 MPa) foram obtidas. Foi observado que a alumina hidratável, utilizada como ligante, desempenha papel de grande importância no desenvolvimento da microestrutura desses materiais, particularmente em temperaturas abaixo de 1000°C.The combination of aluminum oxide (Al2O3) and aluminum hydroxide (Al(OH)3) results in an interesting way of producing porous ceramics of low thermal conductivity, high specific surface area, high refractoriness, and chemical stability at competitive costs. Consequently, such a system shows great potential for technological applications in catalysts, thermal insulators and filters for high temperatures. Despite the good performance of those ceramics, they still have limitations, as low thermomechanical strength, due to high porosity (especially materials whose volume fraction of pores exceeds 50%) and reduced porosity caused by the sintering phenomena and grain growth intensified above 1100°C. Therefore, further research is required for the minimization of such negative aspects. This thesis addresses the development of moldable porous structures (porosity higher than 50%) of high alumina with proper mechanical strength (above 10 MPa in compression) and densification resistance, for use at temperatures above 1100°C. First, a study on the thermal decomposition (temperatures ranging from 300°C to 1500°C) of three types of aluminum hydroxides of different granulometries (1, 10 e 100 µm) was conducted for the evaluation of their potential as porogenic agents. Rheological measurements enabled the determination of the optimal conditions for the dispersion and mixing of the calcined alumina particles, hydratable alumina and aluminum hydroxide. In a second stage of the study, aqueous suspensions of calcined alumina (D50: 1 µm ou 2.5 µm) consolidated with hydratable alumina were prepared with different proportions (0 - 67.5 vol.%) of Al(OH)3 (D50: 1 µm ). However, for Al(OH)3 with larger particles, were only prepared compositions with 22.5 vol.% of calcined alumina (2.5 µm), 67.5 vol.% of aluminum hydroxide, and 10 vol.% of hydratable alumina. The samples were heat treated at 1100, 1300 and 1500°C for 3 h. The behavior during sintering was studied by dilatometry and the green/dried and sintered structures were characterized regarding the total porosity and average pore size, compressive strength and elastic modulus. The evolution of the microstructure was evaluated by scanning electron microscopy. The porogenic action of Al(OH)3 on a calcined alumina matrix was proved and showed to depend on several factors, as content added, maximum sintering temperature and relationship between the grain size of the matrix and Al(OH)3. Variations in those parameters yielded structures of high porosity (higher than 50%) and resistance to compression fracture (above 10 MPa). The hydratable alumina used as a binder played a major role in the development of the microstructure of such materials, particularly at temperatures below 1000°C.
40
Baker, Alexander Roberts. "Proton and metal ion interactions of fulvic acid solution and of alumina and alumina/fulvic acid suspensions." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314936.
Full text
41
Bittencourt, Evandro. "Elaboração e caracterização de um cerâmico de alumina pura e de compósitos de alumina/carbeto de Silício." Universidade do Estado de Santa Catarina, 1997. http://tede.udesc.br/handle/handle/1797.
Full textAbstract:
Made available in DSpace on 2016-12-08T17:19:39Z (GMT). No. of bitstreams: 1
Evandro Bittencourt - Resumo.pdf: 66194 bytes, checksum: 5fcb96b474c22c7b95869e391ce30e24 (MD5)
Previous issue date: 1997-02-09Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Um estudo bibliográfico preliminar permitiu estabelecer um estado de conhecimento sobre as técnicas de elaboração e de reforçamento de materiais cerâmicos. Foram elaborados via técnicas barbotina um cerâmico de alumina, compósito alumina/SiCm e nanocompósito alumina/SiCn, com 5% EM VOLUME DE SiC. Os pós-obtidos da mistura mecânica foram pré compactados dentro de uma matriz em grafite à 40MPa, após a matriz foi colocada dentro de um forno de prensagem à quente para realização de sinterização a uma temperatura T2 = 1550 oC para alumina e a 1600 oC para o compósito e nanocompósito Al2O3/SiC. A incorporação de 5% em volume do pó de SiC nanométrico (d=20 30mm), conduziu a uma estabilização térmica da alumina, isto é, permitiu uma limitação do crescimento dos grãos de alumina alfa da matriz. Tendo sido levado em conta as observações, para os cerâmicos nanocompósitos Al2O3/SiC a prensagem à quente foi realizada a uma temperatura T2 = 1600 oC. As características mecânicas obtidas mostram que os valores do nanocompósito e compósito se apresentam superiores aos valores da alumina, embora, esta superioridade provavelmente foi devida a uma melhora na densificação, devido as diferenças na realização da sinterização do compósito e nanocompósito. Estes resultados foram explicados pelo estudo, através da técnica de microscopia eletrônica de varredura. As propriedades baixas obtidas, resultam em particular da má dispersão das partículas nanométricas de SiC na matriz e da contaminação dos pós ocorrida durante a preparação, resultado da fragmentação das esferas utilizadas no moinho de bolas.
42
Kassam, Tahsin Ali. "The effects of Alumina purity, TICUSIL® braze preform thickness and post-grinding heat treatment on the microstructure, mechanical and nanomechanical properties of Alumina-to-Alumina brazed joints." Thesis, Brunel University, 2017. http://bura.brunel.ac.uk/handle/2438/15311.
Full textAbstract:
Alumina-to-alumina brazed joints were formed using 96.0 and 99.7 wt.% Al2O3 ceramics in as-ground and in ground and heat treated conditions using TICUSIL® (68.8Ag-26.7Cu-4.7Ti wt.%) braze preforms of thicknesses ranging from 50 to 250 μm. Brazing was conducted in a vacuum of 1 x 10-5 mbar at 850 °C for 10 minutes. Joint strengths were evaluated using four-point bend testing and were compared to the flexural strengths of standard test bars according to ASTM C1161-13. Post-grinding heat treatment, performed at 1550 °C for 1 hour, did not affect the average surface roughness or grain size of either grade of alumina but affected their average flexural strengths, with a small increase for 96.0 wt.% Al2O3 and a small decrease for 99.7 wt.% Al2O3. Post-grinding heat treatment led to secondary phase migration, creating a fissured 96.0 wt.% Al2O3 surface. This affected the reliability of 96.0 wt.% Al2O3 brazed joints, in which braze infiltration was observed. As the TICUSIL® braze preform thickness was increased from 50 to 150 μm, the average strengths of both 96.0 and 99.7 wt.% Al2O3 brazed joints improved. This occurred due to a microstructural evolution, in both sets of joints, which was studied using SEM, TEM and nanoindentation techniques. An increase in the TICUSIL® braze preform thickness increased the amount of Ti which was available to diffuse to the joint interfaces. This led to increases in both, reaction layer and braze interlayer thicknesses. Excess Ti in joints that were made using TICUSIL® braze preforms thicker than 50 μm, led to relatively hard Cu-Ti phases in an Ag-Cu braze interlayer. Cu-Ti phase formation, which may have reinforced joint strength whilst also reducing CTE mismatch at the joint interface, also led to Ag-rich braze outflow at the joint edges. Brazed joints made using as-ground 96.0 wt.% Al2O3 consistently outperformed brazed joints made using as-ground 99.7 wt.% Al2O3, due to the formation of Ti5Si3 phases at locations where the Ti-rich reaction layer intersected with the triple pocket grain boundary regions of the as-ground 96.0 wt.% Al2O3 surface.
43
Rodrigues, Michelle Fernanda Faita. "Hidrogenação parcial do benzeno em fase liquida : influencia da natureza e da morfologia dos suportes alumina e niobia no desempenho de catalisadores de rutenio." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266248.
Full textAbstract:
Orientador: Antonio Jose Gomez CoboDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-11T16:03:38Z (GMT). No. of bitstreams: 1 Rodrigues_MichelleFernandaFaita_M.pdf: 1374459 bytes, checksum: ee724b305981f732c54098cdcd569738 (MD5) Previous issue date: 2008
Resumo: No presente trabalho, tem-se por objetivo estudar os efeitos da morfologia do suporte, notadamente do diâmetro da partícula e da área específica, sobre o desempenho de catalisadores de Ru/Al2O3 e Ru/Nb2O5 destinados à reação de hidrogenação parcial do benzeno em fase líquida. Para tanto, catalisadores de Ru/Al2O3 e Ru/Nb2O5 foram preparados através de impregnação incipiente, a partir de uma solução aquosa do precursor RuCl3.xH2O, empregando-se os respectivos suportes com granulometrias e áreas específicas diversas. Após impregnação, os sólidos foram secos a 358 K, por um período de cerca de 24 h. A seguir, os sólidos foram submetidos a um tratamento de redução direta sob H2, à temperatura de 573 K. Os sólidos obtidos foram caracterizados através das técnicas Mastersizer-Distribuição do Tamanho de Partícula, Difração de Raios-X, Adsorção de N2 (método B.E.T.), Microscopia Eletrônica de Varredura com Microssonda para Análise Espectrométrica de Raios-X e Redução à Temperatura Programada. Os desempenhos catalíticos foram avaliados na reação de hidrogenação do benzeno, empregando-se um reator Parr do tipo ¿slurry¿. A reação foi conduzida sob pressão constante de 5,0 MPa de H2 e à temperatura de 373 K, em meio reacional trifásico contendo água. Para as condições empregadas neste estudo, os resultados obtidos mostram que praticamente não há influência da natureza dos suportes Al2O3 e Nb2O5 sobre a seletividade de cicloexeno. No entanto, o aumento do diâmetro de partícula ou da área específica do suporte diminui o rendimento do produto desejado
Abstract: The principal aim of the present work is to study the effects of the morphology of supports, especially the particle diameter and the specific area on the performance of catalytic Ru/Al2O3 and Ru/Nb2O5 for partial hydrogenation reaction of benzene in liquid phase. Therefore, Ru/Al2O3 and Ru/Nb2O5 catalysts were prepared by incipient wetness impregnation, from an aqueous solution of RuCl3.xH2O chlorinated precursor, using supports with several granulometries and specific areas. After impregnation, the solids were dried at 358 K, for a period of 24 h. Then the solid underwent a treatment to direct reduce under H2, at the temperature of 573 K. The solid results were characterized by technical Mastersizer-Particle size Analysis, Diffraction of X-rays, adsorption of N2 (BET method), Electronic Scanning Microscopy and Temperature Programmed Reduction (TPR). The performances were evaluated in the catalytic reaction of benzene hydrogenation, using a reactor Parr of the "slurry". The reaction was conducted under constant pressure of 5.0 MPa of H2 and a temperature of 373 K, in a three-phase reactional medium with water. For the conditions employed in this study, the results show that virtually no influence the nature of the Al2O3 and Nb2O5 supports on the ciclohexene selectivity. However, the increase in the diameter of particle or the specific area of support decreases the yield of the desired product
Mestrado
Sistemas de Processos Quimicos e Informatica
Mestre em Engenharia Química
44
Silva, Helder Augusto da. "Sintese e propriedades de alumoxanos : modificações de superficie e aplicações." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249987.
Full textAbstract:
Orientador: Celso Aparecido BertranDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
Made available in DSpace on 2018-08-13T00:01:52Z (GMT). No. of bitstreams: 1 Silva_HelderAugustoda_M.pdf: 1759666 bytes, checksum: 1f953c93a8e5d84755e3ca468dca7818 (MD5) Previous issue date: 2008
Resumo: Alumoxanos são materiais cujos cernes são idênticos aos da alumina, constituídos por ligações do tipo Al-O-Al e grupos pendentes como alquil, aril, haletos ou quaisquer grupos funcionais ligados aos átomos de alumínio. As primeiras sínteses desses compostos envolviam as reações de organoalumínios com água, ou com compostos contendo oxigênio. Nesse trabalho de mestrado, a síntese de alumoxanos foi realizada a partir da reação da superfície sólida de óxidos e oxihidroxidos de alumínio com soluções cujos solutos deram origem aos grupos pendentes. Os alumoxanos obtidos por essa rota de síntese, as quais os reagentes que originaram os grupos pendentes eram ácidos carboxílicos são denominados alumoxanos carboxilatos. A modificação da superfície de um óxido de alumínio, como a alumina, por exemplo, com um ácido carboxílico altera significativamente as suas propriedades químicas, mantendo-se as suas propriedades mecânicas. Nesse trabalho, foram sintetizados os alumoxanos benzoato, oxalato, vinil-acetato, succinato e adipato. Com o sucesso das sínteses, algumas aplicações para os produtos formados puderam ser investigadas, como o estudo da energia superficial do alumoxano benzoato através de medidas de ângulo de contato e a biocompatibilidade apresentada pelos alumoxanos sintetizados a partir de ácidos dicarboxílicos. As aluminas cujas superfícies foram modificadas pela reação com ácido benzóico, resultando na formação do alumoxano benzoato, mostraram um expressivo aumento de hidrofobicidade, indicado pelo ângulo de contato dessas superfícies com água de cerca de 70o. As aluminas cujas superfícies foram modificadas pela reação com ácidos dicarboxílicos, resultando na formação de alumoxano oxalato, succinato e adipato, foram analisadas segundo o teste de imersão em SBF, quanto à potencialidade de uso como biocerâmicas biocompatíveis. Apenas o alumoxano oxalato apresentou resultados satisfatórios, ocorrendo uma intensa precipitação de fosfato de cálcio na superfície desse material, o que possibilitou a realização de experimentos de adesão celular e testes in vivo para esse alumoxano. Os resultados desses experimentos foram concordantes com o teste de imersão em SBF, indicando uma forte possibilidade de uso do alumoxano oxalato como biomaterial
Abstract: Alumoxanes are materials which their cores are identical to alumina's core, consisting of an Al-O-Al backbone with a variety of pendant groups, such as alkyl, aryl, halides or any functional groups bonded with aluminum atoms. The first synthesis of these compounds had been made by reacting organoaluminum and water or other compounds cointaining oxygen. In this mastering work, alumoxanes were synthesized by reactions between solid surfaces from aluminum oxides or aluminum oxihydroxide and solutions which solutes originated pendant groups. The alumoxanes made from this kind of synthesis and which reactants were carboxylic acids are named carboxylatoalumoxanes. This reaction causes drastic changes in chemical properties of an aluminum oxide, such as alumina, but keeps its mechanical properties. In this work, benzoatoalumoxane, oxalatoalumoxane, vinil-acetatoalumoxane, succinatoalumoxane and adipatoalumoxane were synthesized. After the successful synthesis of these materials, some applications involving alumoxanes were investigated. For example: the benzoatoalumoxane surface energy, studied by contact angle experiments and the biocompatibility of alumoxanes from dicarboxylic acids. The alumina's surface modified by reaction with benzoic acid, resulting in benzoatealumoxane, showed an expressive rise about its hydrofobicity. This fact was supported by the contact angle around 70o between benzoatealumoxane surface and a drop of water. The alumina's surface which were modified by reaction with dicarboxylic acids, resulting in oxalatoalumoxane, succinatoalumoxane and adipatoalumoxane, were analyzed by SBF test, about using them as biocompatible bioceramics. Among these materials, only oxalatoalumoxane had shown good results because a lot of calcium phosphate crystals had been formed on its surface. Supported by this result, this material could be tested in cell adhesion and in vivo tests. Their results agreed with SBF test, showing a considerable possibility of using oxalatoalumoxane as a biomaterial
Mestrado
Físico-Química
Mestre em Química
45
Christe, Charles de Miranda. "Efeitos de variáveis do processo de gelificação interna nas propriedades físicas e químicas de microesferas de alumina." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-07032013-094320/.
Full textAbstract:
Microesferas cerâmicas vêm sendo utilizadas em diferentes aplicações, relacionadas à área nuclear, farmacêutica, química, médica, ambiental, biotecnológica, etc. É possível a obtenção, pelo método da gelificação interna, de microesferas de diferentes materiais cerâmicos, densas ou porosas (com porosidade controlada) e com diferentes tamanhos. No entanto o grande obstáculo é a formação de trincas na secagem e/ou calcinação, que podem inviabilizar a aplicação das mesmas. Este trabalho tem como objetivo a produção de microesferas a base de alumina (Al2O3) pelo processo de gelificação interna, variando-se parâmetros de processamento de forma a se controlar as características físicas e químicas das mesmas, como tamanho, porosidade, superfície específica, etc., além de características específicas que viabilizem a aplicação das mesmas no preenchimento de colunas de eluição de geradores de 99Mo-99mTc. Foi desenvolvida uma metodologia simples e eficiente de tratamento de lavagem das microesferas, que possibilita a extração de uma porção significativa da fase orgânica presente antes da secagem e calcinação; desta forma elimina-se praticamente todas as trincas que surgiriam durante a secagem, e principalmente na etapa de calcinação. Além disso, foram variados parâmetros de processo que permitem controlar a porosidade e superfície específica das microesferas. Foram também caracterizadas em paralelo, duas aluminas de transição na forma de pós, utilizadas atualmente no preenchimento de colunas do gerador de 99Mo-99mTc de modo a se ter uma noção das atuais exigências quanto às propriedades fisicas do material de preenchimento.Ceramic microspheres have been used in various applications, related to the nuclear, pharmaceutical, chemical, medical, environmental, biotechnology, etc. It is possible to obtain, by internal gelation method, microspheres of different ceramic materials, dense or porous (with controlled porosity) and different sizes. However, the major obstacle is the formation of cracks on drying and / or calcination, which can hinder their use. This study have an objective at the production of alumina (Al2O3) based microspheres by internal gelation process, varying processing parameters in order to control the chemical and physical characteristics such as size, porosity, specific surface area, etc., in addition to specific characteristics that enable their application in filling of the elution columns of 99Mo-99mTc generators. It was developed a simple and efficient method of washing treatment of the microspheres, which enables the extraction of a significant portion of the organic phase present prior to drying and calcination; thus virtually eliminates all cracks that arise during drying, and particularly in calcination step. In addition, process parameters were varied for controlling the porosity and specific surface of the microspheres. Were also characterized in parallel, two transition aluminas in the form of powders currently used in filling of elution columns of 99Mo-99mTc generator so as to get an idea of the current requirements for physical properties of the filling material.
46
Santos, Thais da Silva. "Micro-nanocompósitos de Al2O3/ NbC/ WC e Al2O3/ NbC/ TaC." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-10022015-104122/.
Full textAbstract:
Cerâmicas à base de alumina pertencem à classe de materiais denominados estruturais, muito utilizados em ferramentas de corte. A alumina possui boas propriedades para uso como cerâmica estrutural e com o objetivo de melhorar suas tenacidade à fratura e resistência mecânica, são produzidos compósitos com diferentes aditivos. Novos estudos apontam para os micro-nanocompósitos, onde a adição de partículas micrométricas deve auxiliar no aumento da resistência mecânica, e de partículas nanométricas, no aumento da tenacidade à fratura. Neste trabalho foram obtidos micro-nanocompósitos à base de Al2O3 com inclusão de partículas nanométricas de NbC e micrométricas de WC com proporções de 2:1, 6:4, 10:5 e 15:10 e micro-nanocompósitos à base de Al2O3 com inclusão de partículas nanométricas de NbC e micrométricas de TaC com proporção de 2:1 em relação à alumina. Para o estudo de densificação, os micro-nanocompósitos foram sinterizados em dilatômetro com taxa de aquecimento de 20 °C / min até a temperatura de 1800 °C, em atmosfera de argônio. Com base nos resultados de dilatometria, corpos de prova foram sinterizados entre 1500°C e 1700°C, com patamar de 30 minutos, em forno resistivo de grafite e atmosfera de argônio. Foram determinadas as densidades, fases cristalinas formadas, durezas e tenacidades, e analisadas as microestruturas dos micro-nanocompósitos. As amostras Al2O3:NbC:TaC sinterizadas a 1700°C atingiram as maiores densidades aparentes (~95%DT) e a amostra sinterizada a 1600°C apresentou microestrutura homogênea e valor de dureza (15,8 GPa) em comparação à alumina pura. As composições com 3% de inclusões são as mais promissoras para aplicações futuras como ferramentas de corte.Alumina based ceramics belong to a class of materials designated as structural, which are widely used in cutting tools. Although alumina has good properties for application as a structural ceramics, composites with different additives have been produced with the aim of improving its fracture toughness and mechanical strength. New studies point out micro-nanocomposites, wherein the addition of micrometric particles should enhance mechanical strength, and nano-sized particles enhance fracture toughness. In this work, alumina based micro-nanocomposites were obtained by including nano-sized NbC and micrometer WC particles at 2:1, 6:4, 10:5 and 15:10 vol% proportions, and also with the inclusion of nano-sized NbC and micrometer TaC particles at 2:1 vol% proportion. For the study of densification, micro-nanocomposites were sintered in a dilatometer with a heating rate of 20°C/min until a temperature of 1800°C in argon atmosphere. Based on the dilatometry results, specimens were sintered in a resistive graphite furnace under argon atmosphere between 1500°C and 1700°C by holding the sintering temperature for 30 minutes. Densities, crystalline phases, hardness and tenacity were determined, and micro-nanocomposites microstructures were analyzed. The samples Al2O3: NbC: TaC sintered at 1700 ° C achieved the greater apparent density (~ 95% TD) and the sample sintered at 1600 ° C showed homogeneous microstructure and increased hardness value (15.8 GPa) compared to the pure alumina . The compositions with 3% inclusions are the most promising for future applications.
47
Machado, Glauson Aparecido Ferreira. "Desenvolvimento de compósito cerâmico a partir de mistura de alumina e polímero pecursor cerâmico polissilsesquioxano." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-13102009-154057/.
Full textAbstract:
O processamento de materiais cerâmicos, a partir de pirólise de polímeros precursores, tem sido intensivamente pesquisado no decorrer das últimas décadas, devido às vantagens que esta via proporciona, como: temperaturas de processo inferiores as das técnicas convencionais; controle da estrutura em nível molecular; possibilidade de síntese de grande variedade de compostos cerâmicos; obtenção de peças semi-acabadas; etc. O processo de pirólise controlada de polímero e carga ativa (AFCOP-active filler controlled polymer pyrolysis) possibilita a síntese de compósitos cerâmicos, por meio de reação entre cargas adicionadas (óxidos, metais, intermetálicos, etc.) e produtos sólidos e gasosos, provenientes da decomposição polimérica. Com base neste processo, no presente trabalho foram confeccionadas amostras de alumina, contendo adições de 10 e 20% em massa, de polímero precursor polissilsesquioxano. Estas foram pirolisadas a 900°C e tratadas termicamente em temperaturas de 1100, 1300 e 1500ºC, empregando-se taxa de aquecimento de 5°C/ min. e atmosfera de N2. As amostras foram caracterizadas em relação à densidade aparente, porosidade e dureza, após cada etapa de tratamento térmico. As transformações estruturais foram analisadas por difração de raios X, microscopia eletrônica de varredura e espectroscopia de infravermelho. As amostras tratadas até 1300°C resultaram em compósitos de alumina e oxicarbeto de silício, enquanto as tratadas a 1500°C, formaram compósitos de mulita e alumina. Na amostra da composição com 20% de polímero, se observou início de densificação em torno de 800°C e alta taxa de retração foi obtida a 1400°C.Processing of ceramics materials, by polymer precursors pyrolysis, has been intensively researched over the past decades, due to advantages that this path provides, such as: lower temperature process compared to conventional techniques; structure control at molecular level; synthesis possibility of a wide range of ceramic compounds; obtaining parts with dimensions of the final product etc. The active filler controlled polymer pyrolysis (AFCOP) process, enables the synthesis of ceramic composites, by reaction between added filler (oxides, metals, intermetallic etc.) and solid and gaseous products, from polymer decomposition. In this study, based on this process, samples of alumina, with addition of 10 and 20 mass% of poly silsesquioxane polymer precursor, were manufactured. These samples were pyrolyzed at 900 °C and thermal treated at temperatures of 1100, 1300 and 1500 °C. The samples were characterized for bulk density, porosity and hardness, after each stage of thermal treatment. Structural transformations were analyzed by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. Samples treated until 1300 °C resulted in composites of alumina and silicon oxicarbide, while those treated at 1500 °C, formed composites of mullite and alumina. The samples with 20% of polymer added started to densify around 800°C and high retraction rate was observed at 1400°C.
48
Ma, Jan. "Constitutive modelling of the densification of porous ceramic components." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286645.
Full text
49
Payne, David Robert. "Mineralogical changes during the hydration and firing of refractory calcium aluminate cements." Thesis, University of Sheffield, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311975.
Full text
50
Gomez, Cobo Antonio José 1957. "Desidratação catalitica do etanol a eter etilico em alumina." [s.n.], 1985. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267102.
Full textAbstract:
Orientador: Mario de Jesus MendesDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Campinas
Made available in DSpace on 2018-07-15T19:05:47Z (GMT). No. of bitstreams: 1 GomezCobo_AntonioJose_M.pdf: 2514396 bytes, checksum: bb32692e47ed8181e5d8333ab160835e (MD5) Previous issue date: 1985
Resumo: Alguns aspectos termodinâmicos das reações de desidratação do etanol a etileno e a éter etílico, em fase gasosa, são discutidos. A partir de uma revisão da estrutura das aluminas, com base nas informações sobre as formas de adsorção do etanol nesse catalisador, e tendo em conta as diversas versões sugeridas para os mecanismos das reações de desidratação do etanol , é extraida uma proposta de mecanismo, e deduzida a respectiva equação da taxa para a reação de desidratação do etanol a éter etílico em catalisadores de alumina. A validade do modelo cinético proposto foi testada com um conjunto de dados cinéticos, obtidos num reator tubular integral contendo catalisador de alumina, para uma faixa de temperatura entre 212 e 2420C. A concentração do vapor de etanol alimentado, ao reator foi variada pela sua diluição com nitrogênio, e alguns ensaios foram realizados com etanol hidratado. A composição da corrente efluente do reator determinou-se vés da técnica de cromatografia gasosa com DCT. A otimização dos parimetros cinéticos foi feita por um método integral de análise, usando os valores experimentais de conversão versus o tempo espacial modificado. Os resultados obtidos na análise cinética mostram não só um bom ajuste dos dados cinéticos pela equação da taxa usada, como também uma significancia no comportamento dos parâmetros cinéticos otimizados.
Abstract: Some thermodynamic aspects about ethanol dehydration reactions to ethylene and diethyl ether, in gas phase, are discussed. From a review of aluminasstructure, based on information about ethanol adsorption forms in this catalyst, and considering the various suggested versions for the mechanisms of ethanol dehydration rections, it is extracted a proposal mechanism , and deducted the respective rate equation for the ethanol dehydration reaction to diethyl ether in alumina catalysts. The validity of the proposed kinetic model was tested with a group of kinetic data, obtained in an integral tubular reactor with alumina catalyst, at the temperature range between 212 and 242ºC. The concentration of ethanol vapour in the reactor feeding was varied by nitrogen dilution, and some laboratory tests were done with hydrated ethanol.. The composition of effluent current of the reactor was determined by gas chromatography technic with TCD (thermal conductivity detector). The kinetic parameters optimization was done by a integral method of analysis, using the conversion experimental values versus space time. The results obtained in the kinetic analysis show not only a good adjustement of the kinetic data by the rate equation used but also a significance in the behaviour of the optimized kinetic parameters.
Mestrado
Mestre em Engenharia Química