Дисертації: "Magnesian"

1

Ellis, Sam. "Ecological studies of the butterflies of magnesian limestone grassland." Thesis, University of Sunderland, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295744.

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2

Riley, James D. "Restoration of magnesian limestone grassland on former quarry sites." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.246688.

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3

Deknatel, William Brockway. "A theoretical model of component activities in magnesian calcites." Diss., The University of Arizona, 1991. http://hdl.handle.net/10150/185369.

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Calcium carbonate, calcite, and magnesium carbonate, magnesite, form a series of solid solutions with compositions ranging 0 to 50% magnesite which is dolomite the end member of the series. The calcite magnesite solid solutions are called magnesian calcites (Mg-calcites). Mg-calcites exist in nature, in soils, in marine skeletal materials, in some marine cements, etc., and their existence has been associated with the supersaturation of calcite in sea water and the soil solution of some calcareous soils. They are clearly more soluble than calcite, but their chemical properties has not been defined. This paper examines the basic chemistry of the Mg-calcites and develops a theoretical model derived from the regular solution model and based on classical equilibrium thermodynamics. This model can be used to predict solubility and explain the behavior of the Mg-calcites.

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4

Mitchell, David Norman. "The plant ecology and conservation of magnesian limestone sea cliffs, County Durham." Thesis, University of Sunderland, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295771.

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5

Laycock, Elizabeth Anne. "Frost degradation and weathering of the Magnesian Limestone building stone of the Yorkshire province." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267105.

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6

Deknatel, William Brockway. "USE OF THE SOLUTION MODELS TO CALCULATE THE ACTIVITY COMPOSITION RELATIONS OF MAGNESIAN CALCITES (SOLID, CARBONATES)." Thesis, The University of Arizona, 1985. http://hdl.handle.net/10150/291512.

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7

Coles, Geraint. "Aspects of the application of palynology to cave deposits in the magnesian limestone region of North Nottinghamshire." Thesis, University of Sheffield, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285562.

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8

Buggakupta, Wantanee. "Microstructure and thermal expansion behaviour of magnesia-magnesium aluminate composites." Thesis, University of Surrey, 2008. http://epubs.surrey.ac.uk/713/.

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Knowledge of the coefficient of thermal expansion (CTE) of a ceramic material is important in many application areas. Whilst the CTE can be measured, it would be useful to be able to predict the expansion behaviour of multiphase materials. There are several models for the CTE, however, most require a knowledge of the elastic properties of the constituent phases and do not take account of the microstructural features Ã‚Â·of the material. If the CTE could be predicted on the basis ofmicrostructural information, this would then lead to the ability to engineer the microstructure of multiphase ceramic materials to produce acceptable thermal expansion behaviour. To investigate this possibility, magnesia-magnesium aluminate spinel (MMAS) composites, consisting of a magnesia matrix and magnesium aluminate spinel (MAS) particles, were studied. Having determined a procedure to produce MAS from alumina and magnesia, via solid state sintering, magnesia-rich compositions with various magnesia contents were prepared to make the MMAS composites. Further, the MMAS composites prepared from different powders (i.e. from an alumina-magnesia mixture and from a magnesia-spinel powder) were compared. Com starch was added into the powder mixtures before sintering to make porous microstructures. Microstructural development and thermal expansion behaviour of the MMAS composites were investigated. Microstructures of the MAS and the MMAS composites as well as their porous bodies were quantified from backscattered electron micrographs in terms of the connectivity of solids i.e. solid contiguity by means of linear intercept counting. Solid contiguity decreased with increasing pore content and varied with pore size, pore shape and pore distribution whereas the phase contiguity depended strongly on the chemical composition and was less influenced by porosity. The thermal expansion behaviour of the MAS and the MMAS composites between 100 and 1000 Ã‚Â°C was determined experimentally. Variation in the CTE of the MAS relates to the degree of spinel formation while the thermal expansion of the MMAS composites depends strongly on phase content. However, the MMAS composites with similar phase compositions but made from different manufacturing processes showed differences in microstructural features and thermal expansion behaviour. Predictions of the CTE values for composites based on a simple rule-of-mixtures (ROM) using volume fraction were compared with the measured data. A conventional ROM accurately predicted the effective CTE of a range of dense alumina-silicon carbide particulate composites but was not very accurate for porous multiphase structures. It provided an upper bound prediction as all experimental values were lower. Hence, the conventional ROM was modified to take account of quantitative microstructural parameters obtained from solid contiguity. The modified ROM predicted lower values and gave a good agreement with the experimental data. Thus, it has been shown that quantitative microstructural information can be used to predict the CTE of multiphase ceramic materials with complex microstructures.

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9

Unluer, Cise. "Enhancing the carbonation of reactive magnesia cement-based porous blocks." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610879.

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10

Arruda, Cezar Carvalho de. "Processos de hidroxilação do óxido de magnésio (MgO): sínter e magnésia cáustica." Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/18/18158/tde-14072014-112443/.

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A principal limitação do uso de MgO em refratários é a facilidade com que reage com água formando hidróxido de magnésio (Mg(OH)2) que, devido à sua menor densidade, causa tensões destrutivas nesses materiais. Para outras aplicações, no entanto, a reação de hidroxilação do MgO é necessária, como em produção de agentes antichamas, em compósitos poliméricos e na correção de pH de solos. Observações empíricas na literatura demonstraram que diferentes fontes de MgO possuem reatividades e sensibilidades à hidroxilação distintas. Este estudo analisou o impacto de variáveis externas (por exemplo, a liberação de calor que ocorre durante a reação ou o volume das amostras) que ainda não foi completamente compreendido. O impacto auto-catalítico da temperatura reacional e da exotermia da reação foi avaliado. Por meio de medidas de temperatura in situ e de grau de hidroxilação termogravimétrico, também foram estudados os impactos do volume das amostras testadas e da concentração de sólidos nas suspensões, por meio de medidas de temperatura in situ e termogravimetria. Analisou-se também as principais diferenças estruturais entre duas principais fontes de MgO (sínter de MgO e magnésia cáustica): morfologia de partículas, densidade e área superficial específica. Em seguida, os mecanismos de hidroxilação em suspensões aquosas e seus efeitos foram avaliados por meio de testes de hidroxilação seguidos de termogravimetria, difração de raios-X, medidas de condutividade iônica, densidade, área superficial específica e microscopia eletrônica, e relacionado com as características físico-químicas e morfológicas das respectivas fontes de MgO. Pôde-se constatar que diferenças significativas entre a temperatura nominal do meio reacional e no interior da amostra podem afetar a cinética de hidroxilação do material. O volume e a concentração de sólidos variáveis também podem acentuar consideravelmente os efeitos da exotermia e gerar gradientes de hidroxilação. Também se verificou que a morfologia e a quantidade do Mg(OH)2 formado mudam significativamente dependendo do precursor e em função das condições de tempo-temperatura.
The use of MgO in refractories is restrict due to the easy reaction with water forming magnesium hydroxide (Mg(OH)2). Its lower density causes compressive stresses that can crack their structure. On the other hand, for applications such as the production of flame retardant agents for polymer composites and pH correcting of contaminated soil, this reaction is necessary. Empirical observations in the literature have shown that different sources of MgO have district levels of chemical reactiveness. The present study analyzed the main structural differences between the two main sources of MgO (magnesia sinter and caustic magnesia): particle morphology, density and specific surface area. The mechanisms of hydroxylation of these raw materials in aqueous suspensions and their effects were followed by hydroxylation tests, X-ray diffraction, ionic conductivity, density, specific surface area and scanning electron microscopy. They were associated with the physical characteristics morphological, chemical of these MgO sources. The impact of external variables (e.g., heat release during the reaction or the sample volume), that was not yet completely understood, was also evaluated through temperature measurements carried out in situ and hydroxylation degree accessed by thermogravimetry. The effects of samples volume and solid concentration in aqueous suspension were also investigated. The results showed that differences between the ambient temperature and reaction inside sample temperature can affect the kinetics of hydroxylation of the material. The samples volume and solids concentration can also enhance significantly the effects of heat release and generate gradients of hydroxylation. It was also found out that the morphology and the amount of Mg(OH)2 formed can change depending on the precursor and on the time-temperature conditions.

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11

Fernández, Renna Ana Inés. "Procedimiento para la obtención de hidromagnesita: estudio cinético." Doctoral thesis, Universitat de Barcelona, 2000. http://hdl.handle.net/10803/667560.

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El procedimiento que se estudia para la obtención de carbonato básico de magnesio consta de dos etapas: la lixiviación en CO2 de una pulpa que contienen MgO, y la precipitación del producto utilizando la solución de bicarbonato de magnesio de la etapa anterior y MgO como agente precipitante. Se realiza el estudio cinético de ambas etapas separadamente. En la primera etapa, la etapa de lixiviación se forma una solución de bicarbonato de magnesio y, según las condiciones experimentales, un precipitado de hidroxicarbonato de magnesio. En ausencia de precipitado, el proceso de carbonatación cumple el modelo cinético para control químico. La energía de activación calculada tiene un valor de 29.1 kJ/mol. Se propone un mecanismo acorde con los resultados. El método descrito es válido para la obtención de soluciones de bicarbonato de magnesio y podría ser utilizado para obtener carbonato de magnesio si la pureza del óxido de magnesio lo justificase. La segunda etapa, de precipitación de carbonato básico de magnesio, se verifica el adicionar MgO a una solución de bicarbonato de magnesio de forma que la relación (MgO adicionado/Mg2+ inicial) (g/L) no exceda el valor de 2.5, y la suspensión continuamente agitada. La reactividad del óxido de magnesio utilizado tiene un papel primordial en la cinética difusivo. A partir del diagrama de Arrenhius se ha observado que existe una transición de un proceso por control difusivo hacia uno químico o mixto. Se sugiere un mecanismo acorde con los resultados obtenidos en esta etapa. Los rendimientos del orden del 90%, permiten afirmar que el procedimento descrito es válido para la obtención de carbonato básico de magnesio a partir de compuestos de baja ley de magnesio. La pureza de éste último dependerá del óxido de magnesio empleado para precipitar y de la materia prima utilizada.

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12

Belluci, Marina Montosa [UNESP]. "Efeito da deficiência de magnésio na dieta sobre a densidade e o metabolismo ósseo ao redor de implantes com osseointegração estabelecida: estudos em ratos." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/96190.

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Introdução: O magnésio (Mg+2) é essencial para a vida, sendo importante em reações enzimáticas de vários tipos celulares, além de ter um papel importante no tecido ósseo e na homeostase mineral, podendo afetar diretamente a função das células ósseas e a formação da hidroxiapatita. O entendimento de fatores associados à modificação do metabolismo ósseo é de extremo interesse na reabilitação oral com implantes osseointegrados. O contato íntimo entre o metal do implante e o tecido ósseo é fundamental para o sucesso desta forma de tratamento. Diversas alterações sistêmicas, dentre elas a deficiência de Mg, podem representar um risco à osseointegração, podendo afetar a remodelação e diminuir o contato osso-implante. Objetivo: Avaliar, em animais com diferentes idades, o efeito da deficiência de magnésio na dieta sobre o metabolismo ósseo ao redor de implantes de Ticp (titânio comercialmente puro) com osseointegração estabelecida Material e Método: Foram utilizados 90 ratos machos, divididos em 2 grupos de acordo com a idade, sendo constituídos por animais jovens (60 dias) e adultos (150 dias). Após adaptação ao ambiente do biotério, todos os animais foram submetidos à cirurgia de instalação dos implantes nas tíbias direita e esquerda (dia 0). Decorrido um período de 60 dias, necessário à osseointegração dos implantes, os animais de cada grupo foram então subdivididos em 3 subgrupos conforme a dieta que iriam receber (dieta padrão, dieta com redução de 75% do magnésio necessário diariamente e dieta com redução de 90% do magnésio necessário diariamente), a qual foi administrada por mais 90 dias para instalação da deficiência mineral. No período de 24 horas antes do sacrifício foram coletadas amostras de urina. Após o sacrifício, foram coletadas amostras de soro para determinação da concentração de magnésio (Mg) e cálcio (Ca).
Introduction: Magnesium (Mg+2) is essential for life, it is important for many enzymatic reactions of several kinds of cells. Magnesium is very important for bone and mineral homeostasis; it can directly affect bone cell functions and crystal formation (hydroxyapatite). The factors associated to the modification of bone metabolism are extremely important in oral rehabilitation of osseointegrated implants. The intimate bone to implant contact is fundamental for the success of this kind of treatment. Several systemic alterations, like magnesium deficiency, can represent a risk factor to implants osseointegration, it could affect bone remodeling and reduce the bone-implants contact. Objective: This study evaluated, in animals with different ages, the effect of magnesium deficiency in diet on bone metabolism around integrated implants. Methods: Ninety male Holtzman rats were divided in 2 groups by the age, young animals were 60 days years old and adult animals were 150 days years old. After acclimation to the vivarium, all the animals were submitted to a titanium implant at right and left tibias (day 0). After a healing period of 60 days the animals were ramdonly divided into 3 subgroups: rats were fed either normal control magnesium diet (CTL), a reduction of 75% of magnesium diet (Mg1) and a reduction of 90% of magnesium diet (Mg2). After 90 days on the experimental diet the animals were sacrificed. In order to confirm the systemic deficiency of magnesium the serum and urine were colleted for determination of magnesium and calcium concentration. In order to confirm the systemic osteopenia, a dual-energy X-ray absorptiometry (DEXA) was performed in lombar vertebra and femur. For evaluation of bone density around integrated implants, radiographs were taken. And for evaluation of magnesium deficiency in osseous metabolism, mRNA levels of RANKL and OPG were quantified.

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13

Santos, Emanuel Ernesto Fernandes [UNESP]. "Acúmulo de nutrientes e relação Ca:Mg no cultivo da cebola, no submédio São Francisco." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/103219.

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A cebola apesar de ser a hortaliça de maior expressão econômica no Submédio São Francisco, seu cultivo apresenta baixo nível tecnológico, tomando como exemplo seu sistema de fertilização. Foram instalados dois experimentos no Submédio São Francisco com o objetivo de avaliar o acúmulo de nutrientes pela cultura da cebola, assim como a influência de diferentes relações Ca:Mg no seu desenvolvimento. No primeiro experimento foram avaliados o acúmulo e o teor de nutrientes em duas cultivares de cebola - Alfa São Francisco e Franciscana IPA - 10. Para tanto foram coletadas plantas transplantadas, em áreas de produtores em duas ordens de solo: Vertissolo no município de Juazeiro - BA e um Argissolo no município de Casa Nova - BA. Para essa situação, os tratamentos correspondentes a datas de coleta de material vegetal, foram dispostos em blocos ao acaso com três repetições, sendo colhidas oito plantas competitivas, por repetição. No Vertissolo, o material vegetal foi colhido aos 20, 40, 60, 80 e 94 dias após o transplante - DAT e no Argissolo aos 20, 40, 60 e 80 DAT. As plantas foram separadas em folhas e bulbos para determinação da matéria seca e posterior determinação do teor e acúmulo de nutrientes. No segundo experimento foi avaliada a influência da relação Ca:Mg em amostras de um Argissolo Amarelo Eutrófico, em vasos com capacidade de 13 dm3, sem controle das condições ambientais. Os tratamentos foram dispostos em delineamento inteiramente casualizado, com quatro repetições, constaram das seguintes relações Ca:Mg, dados em percentual: 95:5, 80:20, 50:50, 20:80, 5:95 e um tratamento sem correção do solo. Para essa situação foram coletadas amostras de solo para análises químicas após o processo de incubação e por ocasião da colheita. Nesse experimento as plantas foram mantidas até a colheita...
Despite being the vegetable crop of highest economical value in the middle lower São Francisco river basin the onion crop has a low technological asset, as it can be seen in the fertilizing system. Two experiments were set in the middle lower São Francisco river basin to evaluate nutrient accumulation by the onion crop and the influence of different rations Ca: Mg for the onion development. In the first experiment the nutrient content of two different onion cultivars were evaluated (Alfa São Francisco and Franciscana IPA - 10). Then transplanted plants were collected from farmers with two orders of soils in their farms: Vertisol in the town of Juazeiro-BA and Argisol in the town of Casa Nova-BA. For the first experiment the treatments, regarding the vegetal material collecting date, were done in randomized blocks with three replications, where eight plants were collected per replication. In the Vertisol the vegetal material was collected 20, 40, 60, 80 and 94 days after transplanting - DAT, and in the Argisol 20, 40, 60 and 80 DAT. The plants were sorted in leaves and bulbs to determine dry matter weight as well as accumulation and nutrient content. In the second experiment the influence of the Ca: Mg ration was evaluated in Yellow Eutrophic Argisol, in 13 dm3 vases, with no control of environmental conditions. The treatments were set in a completely randomized design, with four replications, with the following Ca: Mg relations in percentages: 95:5, 80:20, 50:50, 20:80, 5:95 and one treatment was the check. For this experiment soil samples were collected for chemical analyses after the incubation process e during the harvest. In this experiment the plants were kept until harvest and the nutrient content was evaluated in the bulbs and leaves and the productivity was also evaluated. The highest macronutrient accumulation in the Vertisol was for N followed by... (Complete abstract click electronic access below)

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14

Belluci, Marina Montosa. "Efeito da deficiência de magnésio na dieta sobre a densidade e o metabolismo ósseo ao redor de implantes com osseointegração estabelecida : estudos em ratos /." Araraquara : [s.n.], 2008. http://hdl.handle.net/11449/96190.

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Resumo: Introdução: O magnésio (Mg+2) é essencial para a vida, sendo importante em reações enzimáticas de vários tipos celulares, além de ter um papel importante no tecido ósseo e na homeostase mineral, podendo afetar diretamente a função das células ósseas e a formação da hidroxiapatita. O entendimento de fatores associados à modificação do metabolismo ósseo é de extremo interesse na reabilitação oral com implantes osseointegrados. O contato íntimo entre o metal do implante e o tecido ósseo é fundamental para o sucesso desta forma de tratamento. Diversas alterações sistêmicas, dentre elas a deficiência de Mg, podem representar um risco à osseointegração, podendo afetar a remodelação e diminuir o contato osso-implante. Objetivo: Avaliar, em animais com diferentes idades, o efeito da deficiência de magnésio na dieta sobre o metabolismo ósseo ao redor de implantes de Ticp (titânio comercialmente puro) com osseointegração estabelecida Material e Método: Foram utilizados 90 ratos machos, divididos em 2 grupos de acordo com a idade, sendo constituídos por animais jovens (60 dias) e adultos (150 dias). Após adaptação ao ambiente do biotério, todos os animais foram submetidos à cirurgia de instalação dos implantes nas tíbias direita e esquerda (dia 0). Decorrido um período de 60 dias, necessário à osseointegração dos implantes, os animais de cada grupo foram então subdivididos em 3 subgrupos conforme a dieta que iriam receber (dieta padrão, dieta com redução de 75% do magnésio necessário diariamente e dieta com redução de 90% do magnésio necessário diariamente), a qual foi administrada por mais 90 dias para instalação da deficiência mineral. No período de 24 horas antes do sacrifício foram coletadas amostras de urina. Após o sacrifício, foram coletadas amostras de soro para determinação da concentração de magnésio (Mg) e cálcio (Ca).
Abstract: Introduction: Magnesium (Mg+2) is essential for life, it is important for many enzymatic reactions of several kinds of cells. Magnesium is very important for bone and mineral homeostasis; it can directly affect bone cell functions and crystal formation (hydroxyapatite). The factors associated to the modification of bone metabolism are extremely important in oral rehabilitation of osseointegrated implants. The intimate bone to implant contact is fundamental for the success of this kind of treatment. Several systemic alterations, like magnesium deficiency, can represent a risk factor to implants osseointegration, it could affect bone remodeling and reduce the bone-implants contact. Objective: This study evaluated, in animals with different ages, the effect of magnesium deficiency in diet on bone metabolism around integrated implants. Methods: Ninety male Holtzman rats were divided in 2 groups by the age, young animals were 60 days years old and adult animals were 150 days years old. After acclimation to the vivarium, all the animals were submitted to a titanium implant at right and left tibias (day 0). After a healing period of 60 days the animals were ramdonly divided into 3 subgroups: rats were fed either normal control magnesium diet (CTL), a reduction of 75% of magnesium diet (Mg1) and a reduction of 90% of magnesium diet (Mg2). After 90 days on the experimental diet the animals were sacrificed. In order to confirm the systemic deficiency of magnesium the serum and urine were colleted for determination of magnesium and calcium concentration. In order to confirm the systemic osteopenia, a dual-energy X-ray absorptiometry (DEXA) was performed in lombar vertebra and femur. For evaluation of bone density around integrated implants, radiographs were taken. And for evaluation of magnesium deficiency in osseous metabolism, mRNA levels of RANKL and OPG were quantified.
Orientador: Silvana Regina Perez Orrico
Coorientador: Elcio Marcantonio Junior
Banca: Maria Lúcia Rubo de Menezes
Banca: Luis Antônio Borelli Barros
Mestre

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15

Swaroop, N. R. Sathya. "Processing And High Temperature Deformation Of Pure And Magnesia Doped Alumina." Thesis, Indian Institute of Science, 2000. https://etd.iisc.ac.in/handle/2005/180.

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Creep resistance is an important design criterion at high temperatures especially when continuous attempts are made to increase the efficiencies by increasing the operating temperatures. Alumina is an important high temperature material and in addition to that it is used in wide variety of applications such as substrates for electronic packaging, spark plugs, envelopes for sodium vapour lamps, cutting tools (when reinforced with silicon carbide) and in artificial joint prostheses. Studies on creep in alumina. have started as early as 1961. There are differing mechanisms proposed to explain the creep behaviour of alumina in the literature, but until now there is no any unanimous decision as to what the rate controlling mechanism is. Magnesia doped at ppm levels can produce significant changes in the microstructure of alumina, the most important consequence of that being the grain growth inhibition, which renders alumina superplastic. However, in a stoichiometric oxide like alumina, small impurities can create extrinsic defects which would change the diffusivities and creep rates. Therefore the background impurities in alumina should be kept to a minimum, if small dopant effects have to be studied. The present study was undertaken making use of high purity alumina powder and comparing the grain growth and creep properties of pure and magnesia doped alumina, especially since no such investigation was carried out in the recent past with high purity alumina. Pure alumina was processed by cold compaction followed by cold isostatic pressing (CIP) and pressureless sintering in air at 1773 K for 1 hour. Magnesia doped alumina was prepared by calcining a mixture of alumina and magnesium nitrate at 973 K for 2 hours followed by cold compaction, CIPing and pressureless sintering in air at 1773 K. Both pure and magnesia doped alumina were further annealed at 1873 K for various times to get grain sizes in the ranges of 1-5 μm. Grain growth kinetics of pure and magnesia doped alumina were studied at 1823 and 1873 K. The parameter Kg which quantifies the mobility of the grain boundary was got. It was found that Kg had decreased in the magnesia doped alumina (in comparison with pure alumina) by a factor of about 3 to 4 which was marginal and insignificant. The grain sizes followed a log normal distribution in both the cases, indicative of normal grain growth. Creep studies were conducted on pure and magnesia doped alumina in three modes, namely, constant stress, temperature jump and stress jump test. The temperature range used was 1673 to 1773 K and the stress range used was 10 to 100 MPa. The creep parameters were found to be n~1.6, p~3.7 and Q-545 kJ mol"1 for pure alumina and n~l .3, p~3.0 and Q~460 kJ mol-1 for magnesia doped alumina. The creep rates in the case of magnesia doped alumina were found to have increased by a factor of 2 to 3, in comparison with pure alumina. The increase in creep rates were found to be insignificant. The creep data were analyzed and the possibility of the dislocation and interface reaction controlled creep mechanisms were ruled out since they were inconsistent with the data. It was found, from creep parameters and the comparison of theoretical Coble and Nabarro-Herring creep rates with the experimental rates, that Coble creep might be rate controlling. The activation energy values suggested that aluminium ion diffusing along grain boundary might be the rate controlling species. However, when the theoretical creep rates considering various species were compared, the rate controlling species turned out to be oxygen ion diffusing along the grain boundary.

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16

Swaroop, N. R. Sathya. "Processing And High Temperature Deformation Of Pure And Magnesia Doped Alumina." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/180.

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Creep resistance is an important design criterion at high temperatures especially when continuous attempts are made to increase the efficiencies by increasing the operating temperatures. Alumina is an important high temperature material and in addition to that it is used in wide variety of applications such as substrates for electronic packaging, spark plugs, envelopes for sodium vapour lamps, cutting tools (when reinforced with silicon carbide) and in artificial joint prostheses. Studies on creep in alumina. have started as early as 1961. There are differing mechanisms proposed to explain the creep behaviour of alumina in the literature, but until now there is no any unanimous decision as to what the rate controlling mechanism is. Magnesia doped at ppm levels can produce significant changes in the microstructure of alumina, the most important consequence of that being the grain growth inhibition, which renders alumina superplastic. However, in a stoichiometric oxide like alumina, small impurities can create extrinsic defects which would change the diffusivities and creep rates. Therefore the background impurities in alumina should be kept to a minimum, if small dopant effects have to be studied. The present study was undertaken making use of high purity alumina powder and comparing the grain growth and creep properties of pure and magnesia doped alumina, especially since no such investigation was carried out in the recent past with high purity alumina. Pure alumina was processed by cold compaction followed by cold isostatic pressing (CIP) and pressureless sintering in air at 1773 K for 1 hour. Magnesia doped alumina was prepared by calcining a mixture of alumina and magnesium nitrate at 973 K for 2 hours followed by cold compaction, CIPing and pressureless sintering in air at 1773 K. Both pure and magnesia doped alumina were further annealed at 1873 K for various times to get grain sizes in the ranges of 1-5 μm. Grain growth kinetics of pure and magnesia doped alumina were studied at 1823 and 1873 K. The parameter Kg which quantifies the mobility of the grain boundary was got. It was found that Kg had decreased in the magnesia doped alumina (in comparison with pure alumina) by a factor of about 3 to 4 which was marginal and insignificant. The grain sizes followed a log normal distribution in both the cases, indicative of normal grain growth. Creep studies were conducted on pure and magnesia doped alumina in three modes, namely, constant stress, temperature jump and stress jump test. The temperature range used was 1673 to 1773 K and the stress range used was 10 to 100 MPa. The creep parameters were found to be n~1.6, p~3.7 and Q-545 kJ mol"1 for pure alumina and n~l .3, p~3.0 and Q~460 kJ mol-1 for magnesia doped alumina. The creep rates in the case of magnesia doped alumina were found to have increased by a factor of 2 to 3, in comparison with pure alumina. The increase in creep rates were found to be insignificant. The creep data were analyzed and the possibility of the dislocation and interface reaction controlled creep mechanisms were ruled out since they were inconsistent with the data. It was found, from creep parameters and the comparison of theoretical Coble and Nabarro-Herring creep rates with the experimental rates, that Coble creep might be rate controlling. The activation energy values suggested that aluminium ion diffusing along grain boundary might be the rate controlling species. However, when the theoretical creep rates considering various species were compared, the rate controlling species turned out to be oxygen ion diffusing along the grain boundary.

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17

Landázuri, del Barrio Ricardo Andrés [UNESP]. "Efeito da dieta com deficiência de magnésio sobre a manutenção da osseointegração de implantes de titânio: análise radiográfica, densitométrica e de torque reverso." Universidade Estadual Paulista (UNESP), 2008. http://hdl.handle.net/11449/96175.

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A deficiência de magnésio (Mg) na dieta pode ser considerada um fator de risco para o desenvolvimento de osteoporose. A diminuição de Mg na dieta está relacionada à perda de massa óssea em humanos; e em animais, estudos têm demonstrado osteopenia, crescimento ósseo anormal e fragilidade esqueletal. Este estudo avaliou a influência da deficiência de Mg na dieta em ratos jovens e adultos sobre o torque de remoção de implantes e sobre a densidade óssea e radiográfica ao redor de implantes osseointegrados instalados na tíbia dos ratos. Noventa ratos Holtzman foram separados em 2 grupos (n=45; 180 gr - animais jovens/ n=45; 360 gr - animais adultos); cada animal recebeu um implante em cada metáfise tibial. Após a osseointegração dos implantes (60 dias), os dois grupos de animais foram sub-divididos em três grupos: grupo Controle (CTRL, n=15), grupo de deficiência de Mg de 75% (Mg1; n=15) e grupo de deficiência de Mg de 90% (Mg2; n=15). Após 150 dias da instalação dos implantes, todos os animais foram sacrificados. Foram coletadas amostras de sangue e urina, realizada a densitometria óssea das vértebras lombares (L2, L3 e L4) e do fêmur, realizada a densidade óssea radiográfica e mensuração da espessura da cortical óssea, além do teste biomecânico de torque de remoção dos implantes. A análise densitométrica (vértebras lombares e fêmur) e os valores da concentração plasmática e urinária de Mg confirmaram o comprometimento sistêmico dos animais, mostrando valores menores de densidade óssea para os grupos Mg1 e Mg2. A análise da densidade radiográfica demonstrou alterações no osso cortical e medular dos grupos Mg1 e Mg2. A análise da espessura da cortical óssea demonstrou alterações na espessura do osso cortical, apresentando valores menores nos grupos Mg1 e Mg2.
Low dietary magnesium (Mg) may be a risk factor for osteoporosis. Mg intake has been associated with bone mass loss in humans. Mg deficiency in animal models has showed osteopenia, impaired bone growth and skeletal fragility. This study evaluated the influence of magnesium deficiency on diet in young and adult rats on the removal torque of osseointegrated titanium implants. Ninety male Holtzman rats (n=45; 180 gr - young rats / n=45; 360 gr - adult rats) were divided in two groups and received a titanium implant in the tibia metaphysis. After the healing period of 60 days, the animals were randomly divided in three sub-groups: control group (CTRL, n=15 animals), 75% magnesium deficiency group (Mg1, n=15 animals) and 90% magnesium deficiency group (Mg2, n=15 animals). The dietary magnesium deficiency was induced in two groups (Mg1 and Mg2) for 90 days. After 150 days postimplant placement, all animals were sacrificed and collected samples of blood and urine. Densitometry of femur and lumbar vertebrae was performed by dual-energy x-ray absorptiometry (DXA), bone density was measured by digital radiographs at 6 points on sides of the implant and was performed the measurement of the thickness of the cortical bone. All implants were subjected to removal torque. Densitometric analysis (femur and lumbar vertebrae) and serum and urinary magnesium concentration confirmed a systemic impairment of the animals, showing lower bone mineral density for Mg1 and Mg2 in young and adult rats. The analysis of radiographic bone density revealed a negative impact of the Mg deficiency in the cancellous and cortical bone. Analysis of the thickness of cortical bone showed alterations on cortical bone in Mg1 and Mg2 groups. Analysis of the removal torque of the implants in young rats showed a decrease of the removal torque for the Mg1 and Mg2 groups (P <0.05) with a statistical difference in relation to the CTRL group.

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18

Formosa, Mitjans Joan. "Formulaciones de nuevos morteros y cementos especiales basadas en suproductos de magnesio." Doctoral thesis, Universitat de Barcelona, 2012. http://hdl.handle.net/10803/97207.

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En la presente tesis doctoral se evalúa el potencial de algunos subproductos de magnesio empleados para la formulación de diferentes materiales de construcción y su utilización en diferentes soluciones constructivas. En este sentido, el uso de subproductos industriales para el desarrollo de materiales de construcción potencia criterios de sostenibilidad y beneficios medioambientales asociados a la reutilización de materiales secundarios y a la disminución de actividades extractivas de recursos naturales. La memoria de la presente tesis doctoral se ha estructurado siguiendo el mismo eje conductor desarrollado en la parte experimental del trabajo. Así, ésta incluye una primera parte en la que se detalla el estado del arte referente a los materiales de construcción, así como las soluciones constructivas propuestas. Estas soluciones son, por un lado, el desarrollo de morteros destinados a la protección pasiva frente al fuego (PPF) y, por otro, la formulación de cementos químicos de fosfato (CBPC) de magnesio como material reparador de estructuras de hormigón. Como primer punto del trabajo experimental se ha estudiado y caracterizado exhaustivamente los diferentes subproductos empleados, tanto físico-química como morfológicamente. Esta caracterización preliminar es de gran importancia en el desarrollo de la investigación, dado que, al tratarse de subproductos industriales, no se conocen de antemano las características y las propiedades que éstos presentan, siendo su conocimiento de vital importancia para la correcta consecución de los objetivos establecidos. En el desarrollo experimental de la primera de las soluciones constructivas propuestas, se ha empleado dos subproductos de magnesio [Low-Grade Magnesium Hydroxide (LG-MH) y Low-Grade Magnesium Carbonate (LG-MC)] en la formulación de morteros PPF, utilizando en este caso el cemento Portland convencional como material aglomerante. Ambos subproductos industriales descomponen térmicamente mediante procesos endotérmicos que cubren un amplio rango de temperaturas, retardando así el tiempo necesario para alcanzar una determinada temperatura. En este caso, se han formulado morteros empleando como áridos distintos porcentajes de ambos subproductos, dando lugar a un material con buenas propiedades térmicas y mecánicas, factible de ser utilizado como un mortero PPF. Sin embargo, su utilización como mortero revoco puede verse limitada por la elevada densidad de los áridos utilizados. En este supuesto, puede mejorarse su aplicabilidad añadiendo a los morteros formulados con subproductos de magnesio un árido ligero, como la vermiculita, sin que ello perjudique al resto de propiedades evaluadas. En la consecución de la segunda solución constructiva propuesta, se evalúa la viabilidad del uso como materia prima de otro subproducto de magnesio [Low-Grade Magnesium Oxide (LG-MgO)], en este caso para el desarrollo de cementos químicos de fosfato (CBPC) de magnesio. A tal efecto, se han determinado las propiedades mecánicas de distintas dosificaciones, así como el efecto de un aditivo retardante del fraguado, el ácido bórico (HB), descrito en la bibliografía como retardante de fraguado que permite mejorar la trabajabilidad de los CBPC. Este estudio se ha realizado empleando una herramienta estadística, el diseño de experimentos (DoE), con la finalidad de obtener modelos matemáticos que justifiquen las interacciones entre los distintos componentes de la mezcla y su efecto sobre las propiedades mecánicas y el tiempo de fraguado. Asimismo, el uso del DoE ha de permitir reducir el número de experimentos y establecer el mejor rango de dosificaciones en función de las características deseadas, dando lugar a una formulación adecuada para su utilización en las soluciones constructivas objeto de estudio. Destacar que el uso de LG-MgO en la formulación de CBPC introduce fases inertes no-reactivas contenidas en el propio subproducto, lo que implica que los CBPC desarrollados puedan considerarse como morteros. A partir de los resultados obtenidos se ha seleccionado un pequeño grupo de formulaciones con porcentajes adecuados para evaluar su potencial empleo en el desarrollo de morteros reparadores de estructuras de hormigón. Con este propósito, se han realizado ensayos de adhesión sobre distintos sustratos (hormigón o terrazo) y se ha determinado algunas propiedades requeridas para su uso en la solución constructiva propuesta. La presente tesis doctoral pretende confirmar la viabilidad tecnológica para los distintos campos de aplicación que se han postulado. Sin embargo, no es un objetivo de este estudio el desarrollar un producto final que pueda ser comercializado, sino demostrar su viabilidad gracias al know-how adquirido durante los años de esta investigación, y sentar así las bases para futuros estudios en el desarrollo de materiales de construcción empleando estos subproductos.
The present thesis is focused in the assessment of some magnesium by-products and their potential reutilization for the formulation of different materials for several construction applications. Therefore, the use of industrial by-products for the development of construction materials highlights the sustainability criteria along with the environmental benefits associated with the reutilization of secondary materials whilst diminishing the extractive activities of natural resources. This thesis has been structured following the same pattern for the experimental work. Thus, the first part details the state of the art in what construction materials concerns as well as some of the construction solutions suggested. These solutions are, on the one hand, included in the development of mortars for passive fire protection (PFP) and, on the other hand, in the formulation of chemical bonded phosphate ceramics (CBPC) as a repairing material for concrete structures. The first part presents an exhaustive chemical, physical and morphological characterization of the by-products used. This preliminary characterization is of great importance in the development of the research because of the industrial origin of these by-products. In the first part of the experimental section, the first of the solutions proposed used two types of magnesium by-products [Low-Grade Magnesium Hydroxide (LG-MH) and Low-Grade Magnesium Carbonate (LG-MC)] in the formulation of PFP mortars, using conventional Portland cement as a binder. Both industrial by-products thermally decompose through endothermic processes in a wide range of temperatures, delaying the time needed to achieve a selected temperature. In this case, the mortars were formulated by using different percentages of both by-products as aggregates, obtaining a material with good thermal and mechanical properties and therefore feasible to be used as a PFP mortar. However, its utilization as a sprayed mortar can be limited because of the high density of the aggregates used. In this sense, the practical applicability can be improved by adding a lightweight aggregate such as vermiculite, without diminishing the rest of the assessed properties. Subsequently, in the second part of the experimental section, the viability of another magnesium by-product [Low-Grade Magnesium Oxide (LG-MgO)] is evaluated. In this case, for the development of chemical bonded phosphate ceramics (CBPC). The assessment was made by determining the mechanical properties of different dosages as well as by measuring the effect of a setting-time retarder additive, boric acid (HB), described in the literature as a good additive for this purpose while improving workability as well. This study has been realized by means of a statistical method, the design of experiments (DoE), with the purpose of obtain mathematical models that justify the interactions between different components in the mix and their effect in the mechanical properties and the setting-time. Moreover, the use of DoE enables the reduction in the number of experiments and establishes the best range of dosages as a function of the desired characteristics, giving an optimized formulation to be used in the construction solutions that are object of study. It has to be emphasize that the use of LG-MgO in the formulation of CBPC introduces inert phases that are contained in the by-product itself and that are non-reactive, which implies that the CBPC obtained could be considered as mortars. From the results obtained, a small group of formulations with different percentages was selected to be studied with respect their potential as repairing mortars in concrete structures. Following this objective, adhesion tests were performed over different substrates (concrete or terrazzo) and some of the properties required for their use were determined. The main objective of this thesis is to confirm the technological viability for the different fields of application postulated. However, it is not the main purpose to develop a final product able to be commercialized but to prove the viability by means of the know-how acquired during the years of this research and setting up the base for future studies in the development of construction materials using these by-products.

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19

Reis, Bárbara Araújo dos. "Avaliação das propriedades de superfície de ligas de titânio anodizadas com elementos bioativos /." Araraquara, 2018. http://hdl.handle.net/11449/153482.

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Orientador: Luis Geraldo Vaz
Resumo: O titânio comercialmente puro e suas ligas vêm sendo amplamente utilizados para confecção de implantes dentários e ortopédicos devido à adequada resistência mecânica, resistência à corrosão e biocompatibilidade. Entretanto, para aprimorar o tratamento com o uso de implantes, novas ligas e novos tratamentos de superfície vêm sendo pesquisados. A técnica de funcionalização de superfície, baseada em processos úmidos, é amplamente utilizada para desenvolver superfícies a base de óxido de titânio que induza e aumente a osseocondução. Assim, o objetivo deste estudo foi caracterizar a superfície de discos de Ti-6Al-4V e Ti-35Nb-7Zr-Ta após anodização para funcionalização com íons cálcio (Ca) e fósforo (P) ou fluoreto e dopagem com magnésio (Mg++) em diferentes condições experimentais, sendo a liga Ti-6Al-4V utilizada como controle. As ligas foram analisadas antes e após a realização dos tratamentos (anodização e dopagem), para avaliação das propriedades de superfície- composição química, energia livre de superfície (ELS), morfologia/ topografia e rugosidade média (Ra). Para interpretação dos resultados referentes a ELS e Ra foi aplicado teste estatístico por um operador cego, de acordo com o tipo de distribuição e nível de significância de 5%. As micrografias obtidas demonstraram que a anodização com Ca e P propiciou a formação de superfícies com poros interconectados e a anodização com ácido fluorídrico (HF) resultou em superfícies com formação de nanotubos. Todos íons adicionados ... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Commercially pure titanium and its alloys have been widely used in the manufacture of dental and orthopedic implants due to adequate mechanical strength, corrosion resistance and biocompatibility. However, to improve the treatment with the use of implants to optimize osseointegration, new alloys and new surface treatments have been researched. The surface functionalization technique, based on wet processes, is widely used to develop titanium oxide based surfaces that induce and increase osseoconduction. The aim of this study was to characterize the surface of Ti-6Al-4V and Ti-35Nb-7Zr-Ta discs after anodization for functionalization with calcium ions (Ca) and phosphorus (P) or fluoride and doping with magnesium (Mg ++) in different experimental conditions. The Ti-6Al-4V alloy was used as a control. The alloys were analyzed before and after the treatments (anodization and doping), to evaluate the surface properties - chemical composition, surface free energy (ELS), morphology / topography and medium roughness (Ra). For the interpretation of the ELS and Ra results, a statistical test was applied according to the type of distribution and level of significance of 5%. The obtained micrographs showed that the anodization with Ca and P allowed the formation of surfaces with interconnected pores and the anodization with hydrofluoric acid resulted in surfaces with formation of nanotubes. All ions added to the electrolytes were incorporated into the samples, detected by ELS. The roughn... (Complete abstract click electronic access below)
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20

Bedoya, Escobar Juliana. "Recubrimientos micro-nano estructurados de grandes espesores por proyección fría para la reparación y protección de componentes industriales de altro valor añadido." Doctoral thesis, Universitat de Barcelona, 2017. http://hdl.handle.net/10803/462825.

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La proyección fría es una técnica de proyección térmica que permite la obtención de recubrimientos metálicos y metal/cerámicos con estructuras densas (porosidad inferior a 0,1%) y libres de óxidos. De manera general, ésta técnica se caracteriza por la alta velocidad que pueden alcanzar las partículas y la baja temperatura empleada en el proceso. Los recubrimientos son formados en estado sólido, las partículas con alta energía cinética, impactan la superficie a recubrir, se deforman y se adhieren al sustrato y a otras partículas. Por lo tanto, para lograr microestructuras densas se requiere un alto nivel de deformación plástica así como la combinación de parámetros como las características y composición del polvo de partida, los parámetros del proceso y los tratamientos posteriores que puedan afectar la formación y las propiedades del recubrimiento. Este trabajo se enfoca en la optimización de los parámetros de proyección, basados en la relación de las propiedades microestructurales (microestructura, deformación de partículas), propiedades mecánicas (microdureza, adherencia y resistencia la desgaste) y resistencia a la corrosión (celda electroquímica y niebla salina). El objetivo se basa en encontrar la relación entre las propiedades microscópicas y las propiedades macroscópicas, así como los factores que pueden influir en el proceso para la obtención de recubrimientos de grandes espesores (recargues) mediante la tecnología de proyección fría para la reparación y restauración de componentes de alto valor añadido fabricados en aleaciones ligeras. Los materiales empleados para la evaluación de recubrimientos fueron Al puro, Al-12Si, Al-7,5Mg nanoestructurado y metal-cerámicos Al/Al2O3 sobre sustratos de aleación de aluminio AA5083 y aleación de magnesio AZ91D. Las propiedades microestructurales fueron evaluadas mediante diferentes técnicas de microscopía (MO, SEB, TEM); la resistencia al desgaste fué determinada empleando un medio abrasivo (ensayo de Rubber-Wheel) y por fricción (Ball-on-disk) y la resistencia a la corrosión fué determinada mediante medidas en celda electroquímica (Potencial en circuito abierto y curvas de polarización) así como en cámara de niebla salina. Las aplicaciones que se han dado a la proyección fría, han sido para la obtención de recubrimientos en grandes espesores desde 500 μm hasta recargues de más de 15 mm de espesor totalmente densos. Este tipo de recargues ha sido proyectado sobre un componente fabricado en aleación ligera a modo de estudiar la viabilidad industrial de esta aplicación.
Cold spray technique is presented as a new way for component repair; this is a solid state process in which spray particles are deposited via supersonic velocity impact at a temperature much below the melting point of the spray material. It presents outstanding characteristics such as high density coatings (porosity less than 0.1%) and absence of thermal degradation (no oxidation or particles dissolution). In addition, this technique is as a viable alternative for obtained very thick coatings (overlays) for dimensional restoration of damaged components. The objective is to find the relationship between the microscopic properties and the macroscopic properties, as well as the factors that can influence the process for the obtaining for obtained very thick coatings (overlays) by cold spray. Commercially available gas-atomised powders of Aluminum and Al-12Si were used as feedstock in the present study, as well as a nano-structured Al-7,5Mg powder obtained by cryomilling. Aluminum alloy AA5083 and magnesium alloy AZ91D were used as substrates. Dense and well bonded Al based coatings of up to 15 mm of thickness have been obtained. The microstructure, mechanical performance and corrosion resistance properties were investigated and discussed. These coatings offer an alternative protection against corrosion and increased wear resistance in a relatively economic process that can simplify the maintenance and repair tasks and to extend the shelf life of some light alloys An industrial part (as-cast automotive wheel) has been satisfactorily repaired by Cold Spray, this technique will provide new opportunities for maintenance, repair and protection of light alloys.

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21

Landázuri, del Barrio Ricardo Andrés. "Efeito da dieta com deficiência de magnésio sobre a manutenção da osseointegração de implantes de titânio : análise radiográfica, densitométrica e de torque reverso /." Araraquara : [s.n.], 2008. http://hdl.handle.net/11449/96175.

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Resumo: A deficiência de magnésio (Mg) na dieta pode ser considerada um fator de risco para o desenvolvimento de osteoporose. A diminuição de Mg na dieta está relacionada à perda de massa óssea em humanos; e em animais, estudos têm demonstrado osteopenia, crescimento ósseo anormal e fragilidade esqueletal. Este estudo avaliou a influência da deficiência de Mg na dieta em ratos jovens e adultos sobre o torque de remoção de implantes e sobre a densidade óssea e radiográfica ao redor de implantes osseointegrados instalados na tíbia dos ratos. Noventa ratos Holtzman foram separados em 2 grupos (n=45; 180 gr - animais jovens/ n=45; 360 gr - animais adultos); cada animal recebeu um implante em cada metáfise tibial. Após a osseointegração dos implantes (60 dias), os dois grupos de animais foram sub-divididos em três grupos: grupo Controle (CTRL, n=15), grupo de deficiência de Mg de 75% (Mg1; n=15) e grupo de deficiência de Mg de 90% (Mg2; n=15). Após 150 dias da instalação dos implantes, todos os animais foram sacrificados. Foram coletadas amostras de sangue e urina, realizada a densitometria óssea das vértebras lombares (L2, L3 e L4) e do fêmur, realizada a densidade óssea radiográfica e mensuração da espessura da cortical óssea, além do teste biomecânico de torque de remoção dos implantes. A análise densitométrica (vértebras lombares e fêmur) e os valores da concentração plasmática e urinária de Mg confirmaram o comprometimento sistêmico dos animais, mostrando valores menores de densidade óssea para os grupos Mg1 e Mg2. A análise da densidade radiográfica demonstrou alterações no osso cortical e medular dos grupos Mg1 e Mg2. A análise da espessura da cortical óssea demonstrou alterações na espessura do osso cortical, apresentando valores menores nos grupos Mg1 e Mg2.
Abstract: Low dietary magnesium (Mg) may be a risk factor for osteoporosis. Mg intake has been associated with bone mass loss in humans. Mg deficiency in animal models has showed osteopenia, impaired bone growth and skeletal fragility. This study evaluated the influence of magnesium deficiency on diet in young and adult rats on the removal torque of osseointegrated titanium implants. Ninety male Holtzman rats (n=45; 180 gr - young rats / n=45; 360 gr - adult rats) were divided in two groups and received a titanium implant in the tibia metaphysis. After the healing period of 60 days, the animals were randomly divided in three sub-groups: control group (CTRL, n=15 animals), 75% magnesium deficiency group (Mg1, n=15 animals) and 90% magnesium deficiency group (Mg2, n=15 animals). The dietary magnesium deficiency was induced in two groups (Mg1 and Mg2) for 90 days. After 150 days postimplant placement, all animals were sacrificed and collected samples of blood and urine. Densitometry of femur and lumbar vertebrae was performed by dual-energy x-ray absorptiometry (DXA), bone density was measured by digital radiographs at 6 points on sides of the implant and was performed the measurement of the thickness of the cortical bone. All implants were subjected to removal torque. Densitometric analysis (femur and lumbar vertebrae) and serum and urinary magnesium concentration confirmed a systemic impairment of the animals, showing lower bone mineral density for Mg1 and Mg2 in young and adult rats. The analysis of radiographic bone density revealed a negative impact of the Mg deficiency in the cancellous and cortical bone. Analysis of the thickness of cortical bone showed alterations on cortical bone in Mg1 and Mg2 groups. Analysis of the removal torque of the implants in young rats showed a decrease of the removal torque for the Mg1 and Mg2 groups (P <0.05) with a statistical difference in relation to the CTRL group.
Orientador: Elaine Maria Sgavioli Massucato
Coorientador: Silvana Regina Perez Orrico
Banca: Rodolfo Jorge Boeck Neto
Banca: Alvaro José Bosco
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22

Santos, Emanuel Ernesto Fernandes 1966. "Acúmulo de nutrientes e relação Ca:Mg no cultivo da cebola, no submédio São Francisco /." Botucatu : [s.n.], 2007. http://hdl.handle.net/11449/103219.

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Resumo: A cebola apesar de ser a hortaliça de maior expressão econômica no Submédio São Francisco, seu cultivo apresenta baixo nível tecnológico, tomando como exemplo seu sistema de fertilização. Foram instalados dois experimentos no Submédio São Francisco com o objetivo de avaliar o acúmulo de nutrientes pela cultura da cebola, assim como a influência de diferentes relações Ca:Mg no seu desenvolvimento. No primeiro experimento foram avaliados o acúmulo e o teor de nutrientes em duas cultivares de cebola - Alfa São Francisco e Franciscana IPA - 10. Para tanto foram coletadas plantas transplantadas, em áreas de produtores em duas ordens de solo: Vertissolo no município de Juazeiro - BA e um Argissolo no município de Casa Nova - BA. Para essa situação, os tratamentos correspondentes a datas de coleta de material vegetal, foram dispostos em blocos ao acaso com três repetições, sendo colhidas oito plantas competitivas, por repetição. No Vertissolo, o material vegetal foi colhido aos 20, 40, 60, 80 e 94 dias após o transplante - DAT e no Argissolo aos 20, 40, 60 e 80 DAT. As plantas foram separadas em folhas e bulbos para determinação da matéria seca e posterior determinação do teor e acúmulo de nutrientes. No segundo experimento foi avaliada a influência da relação Ca:Mg em amostras de um Argissolo Amarelo Eutrófico, em vasos com capacidade de 13 dm3, sem controle das condições ambientais. Os tratamentos foram dispostos em delineamento inteiramente casualizado, com quatro repetições, constaram das seguintes relações Ca:Mg, dados em percentual: 95:5, 80:20, 50:50, 20:80, 5:95 e um tratamento sem correção do solo. Para essa situação foram coletadas amostras de solo para análises químicas após o processo de incubação e por ocasião da colheita. Nesse experimento as plantas foram mantidas até a colheita... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Despite being the vegetable crop of highest economical value in the middle lower São Francisco river basin the onion crop has a low technological asset, as it can be seen in the fertilizing system. Two experiments were set in the middle lower São Francisco river basin to evaluate nutrient accumulation by the onion crop and the influence of different rations Ca: Mg for the onion development. In the first experiment the nutrient content of two different onion cultivars were evaluated (Alfa São Francisco and Franciscana IPA - 10). Then transplanted plants were collected from farmers with two orders of soils in their farms: Vertisol in the town of Juazeiro-BA and Argisol in the town of Casa Nova-BA. For the first experiment the treatments, regarding the vegetal material collecting date, were done in randomized blocks with three replications, where eight plants were collected per replication. In the Vertisol the vegetal material was collected 20, 40, 60, 80 and 94 days after transplanting - DAT, and in the Argisol 20, 40, 60 and 80 DAT. The plants were sorted in leaves and bulbs to determine dry matter weight as well as accumulation and nutrient content. In the second experiment the influence of the Ca: Mg ration was evaluated in Yellow Eutrophic Argisol, in 13 dm3 vases, with no control of environmental conditions. The treatments were set in a completely randomized design, with four replications, with the following Ca: Mg relations in percentages: 95:5, 80:20, 50:50, 20:80, 5:95 and one treatment was the check. For this experiment soil samples were collected for chemical analyses after the incubation process e during the harvest. In this experiment the plants were kept until harvest and the nutrient content was evaluated in the bulbs and leaves and the productivity was also evaluated. The highest macronutrient accumulation in the Vertisol was for N followed by... (Complete abstract click electronic access below)
Orientador: Dirceu Maximino Fernandes
Coorientador: Leonardo Theodoro Büll
Coorientador: Davi José Silva
Banca: Roberto Lyra Villas Bôas
Banca: Rumy Goto
Banca: Paulo Augusto da Costa Pinto
Banca: Alessandra Monteiro S. Mendes
Doutor

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23

Carter, Ellen Angharad. "High Current Anodization of Magnesium and Magnesium Alloys." Thesis, University of Auckland, 1996. http://hdl.handle.net/2292/2289.

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High current anodization of magnesium and magnesium alloys Ellen Angharad Carter Pure magnesium and three magnesium alloys containing different amounts of aluminium (2-9%) plus zinc and manganese were anodized with constant current density in sodium hydroxide solution with and without fluoride or phosphate ions. Electric field strengths of resultant anodic films were calculated from galvanostatic transients. These transients showed three characteristic features: linear voltage increase, noisy high voltage signals accompanied by sparking, and sawtooth-like events characterized by instantaneous voltage drops followed by slower voltage increases. Each feature was linked to certain physical processes occurring in the metal/film/solution system. Oxidation of magnesium and magnesium alloys formed anodic films with bilayer structures: a passive barrier layer adhering to the metal electrode, topped by a porous secondary layer. Cation injection into the barrier film across the metal/oxide interface was the rate determining step for film growth. Interstitial cations migrated through the film under the influence of the electric field. At the film/solution interface they reacted with electrolyte species and either thickened the film or dissolved in solution. Electric field strength was constant for particular metal/solution combinations and was independent of applied current density. Changing the electrode material altered the resultant electric field strength: pure magnesium produced oxides with lower electric field strengths than films formed on the three magnesium alloys. Changing the electrolyte had no discernable effect on the electric field strength. Charge efficiency of the film growth process was investigated by oxygen gas evolution; efficiency decreased during sparking. Ion beam analysis (Rutherford backscattering, fluorine depth profiling and nuclear reaction analysis) coupled with X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction studies and Raman spectroscopy gave information about the anodic film surface. These techniques showed that oxides formed on magnesium-aluminium alloys were thinner than those formed on pure magnesium caused by aluminium dissolution. Fluorine depth profiling revealed that concentration profiles for fluorine in anodic oxides formed in fluoride-containing solution altered depending on the aluminium content of the electrode material.

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24

Tye, Andrew. "The preparation and characterisation of magnesia-stabilised zirconia and alumina/magnesia-stabilised zirconia composites." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305440.

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25

Sato, Takanori. "Power-law creep behaviour in magnesium and its alloys." Thesis, University of Canterbury. Mechanical Engineering, 2008. http://hdl.handle.net/10092/1576.

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Creep is a time-dependent deformation of materials under stress at elevated temperatures. The phenomenon of creep allows materials to plastically deform gradually over time, even at stress levels below its yield point or below its transformation temperature. The issues involving creep are especially significant for magnesium alloys, since they are susceptible to creep deformation from temperatures as low as 100 ºC, which inhibits their potential application in areas such as automotive engines. The University of Canterbury has developed a significant level of experience and infrastructure in the field of Electron Backscatter Diffraction (EBSD). EBSD allows microstructures to be characterized by imaging the crystal structure and its crystallographic orientation at a given point on a specimen surface, whereby the process can be automated to construct a crystallographic “orientation map” of a specimen surface. In light of this, the creep of magnesium and its alloys was studied using a novel technique, in which a conventional tensile creep test was interrupted at periodic intervals, and the EBSD was used to acquire the crystallographic orientation maps repeatedly on a same surface location at each interruption stages. This technique allows simultaneous measurement of the rate of creep deformation and the evolution of the specimen microstructure at various stages of creep, bringing further insight into the deformation mechanisms involved. This thesis summarizes the study of the microstructural and crystallographic texture evolution during creep of pure magnesium and a creep resistant magnesium alloy Mg- 8.5Al-1Ca-0.3Sr. Pure magnesium exhibit a conventional “power-law” type creep, and although its creep properties are well established in the past literatures, there has been little in terms of reconciliation between the observed creep rates and the underlying deformation mechanisms. The alloy Mg-8.5Al-1Ca-0.3Sr, on the other hand, is a modern die casting alloy used in the automotive industry for engine and gearbox applications, and despite its superior creep resistance, little is known about the microstructural contributions to its creep properties. This research was conducted to provide a link between the creep properties, observed microstructures, and theories of creep deformation by the use of advanced microscopy techniques. For the first time, the detailed, sequential microstructural development of magnesium and its alloys during creep has been revealed.

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26

Murray, Mary Josephine. "Interstellar magnesium studies." Thesis, Queen's University Belfast, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.254246.

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27

Weetman, Catherine. "Magnesium hydride reductions." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669043.

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Initial developments within group 2 chemistry led to the chemistry being described as ‘lanthanide mimetic’ however, over the last 10 years group 2 catalysis has emerged in its own right, making these comparisons unjustified. Development of this catalytic chemistry has, until now, largely focussed upon the use of protic reagents in order to achieve turnover. Reported in this thesis is the development of magnesium hydride chemistry for both stoichiometric and catalytic purposes. Reported in chapter 2 of this thesis, is the use of the pharmaceutically relevant magnesium dihydropyridide complexes and explores their use as hydride transfer reagents with respect to a representative ketone, benzophenone, whilst further study with various different isocyanate reagents with differing electronic and steric demands provides divergent reactivity. Extension of this chemistry with respect to carbodiimides provides a series of N-heterocyclic guanidinates in all but one case. The chemistry described in chapters 3-6 investigates the use of magnesium hydrides in catalysis. Using the commercially available hydridic pinacol borane (HBpin) reagent a series of catalytic reactions with respect to pyridines (chapter 3), nitriles (chapter 4), iso-nitriles (chapter 5) and heterocumulenes (chapter 6) are investigated. In each case, studies have sought to underpin the catalytic reactivity by examining the single steps of the proposed catalytic cycle via a series of stoichiometric reactions which has allowed for the isolation and characterisation of numerous potential catalytic intermediates. Monitoring of these catalytic reactions in situ with NMR spectroscopy, combined with kinetic analysis, has allowed for further information to be obtained with regards to the mechanism and calculation of the activation energy parameters associated with each reaction.

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28

RAAS, ISABELLE. "Diuretiques et magnesium." Strasbourg 1, 1992. http://www.theses.fr/1992STR15054.

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29

Romero, Güiza Maycoll Stiven. "Nutrient recovery and improvement of anaerobic digestion process by low grade magnesium oxide application." Doctoral thesis, Universitat de Barcelona, 2015. http://hdl.handle.net/10803/348261.

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Anaerobic digestion is a worldwide technology to treat organic waste streams, primarily due to its capacity to produce methane as renewable energy. However, there is an increasing interest on nutrient recovery (N and P), which from both environmental and economic reasons have been identified as key feature in anaerobic digestion plants. Controlled struvite formation has been attracting increasing attention as a near mature technology to recover nutrients from anaerobic digestion. However, struvite feasibility is generally limited by the high cost of chemical reagents. Because the economic feasibility of struvite is heavily influenced by reagent cost, several authors have trialled lower-cost magnesium sources. Studies to date on struvite precipitation with MgO have largely focused on the aqueous phase, with little attention given to the preceeding MgO dissolution. However, the observations noted above suggest that there may be opportunity to better understand, intervene and improve dissolution and access to MgO. The present study uses experiments and chemistry modelling to evaluate and better understand TAN removal from pig manure using MgO. Tests were performed with four industrial magnesium oxide (MgO) from natural magnesite calcination: a commercial high grade MgO (HGMgO) as well as a number of low-grade MgO (LGMgOs) by-products. All these MgO reagents were also pre-treated with phosphoric acid and tested separately after pre-treatment. The study focussed on the underlying chemistry to show how reactivity and dissolution of the various magnesium by-products influenced struvite precipitation and TAN removal performance. Moreover, another option to minimise struvite precipitation cost is to combine struvite precipitation and AD in the same reactor. Several authors have studied the addition of magnesium reagents (MgCl2 and Mg(OH)2) to precipitate struvite during anaerobic digestion, causing in some cases inhibition by pH or cation toxicity. However, to our knowledge, no references bave been found evaluating the utilization of magnesium by- products within the reactor to precipitate struvite during anaerobic digestion. In this study struvite precipitation and pig manure anaerobic digestion were coupled in the same reactor in order to mitigate the inhibitory effect of free ammonia and avoid precipitator costs. The stabilizing agent used to facilitate struvite precipitation was formulated with low-grade magnesium oxide by-product; an approach that would notably reduce struvite processing costs. Therefore, the feasibility of coupling anaerobic digestion and struvite precipitation in the same reactor was evaluated to enhance manure anaerobic digestion methane yields through ammonia inhibition mitigation. Five different magnesium sources were tested as struvite (ammonia sequestration agent) precursor, i.e. MgCl2, Mg(OH)2, two industrial by-products rich in MgO but with different reactivity, and a stabilizing agent. The latter was formulated in advance with the low reactivity industrial by-product and phosphoric acid. The effect of each magnesium source on anaerobic digestion as well as its struvite precipitation capacity was evaluated through a series biomethane potential test. However, a long term anaerobic digester operation was required to assess the feasibility of the process and to ensure that the stabilizing agent does not introduce any harmful compound for the anaerobic biomass. In this vein, the -3 addition of 5 and 30 kg m of the stabilizing agent in a pig manure continuous digester 3 -1 3 -1 resulted in a 25% (0.17 m kg ) and a 40% (0.19 m kg ) increase in methane production per mass of volatile solid, respectively, when compared with the reference digester (0.13 3 -1 m kg ). Moreover, the stability of the process during four hydraulic retention times guarantees that the stabilizing agent did not exert a negative effect on the consortium of microorganisms.
Diferentes esfuerzos han sido desarrollados para reducir la inhibición por nitrógeno amoniacal en la DA. Entre ellos, la adición de materiales con capacidad de intercambio catiónico (por ejemplo: bentonita, glauconita, fosforita y zeolitas) o materias con capacidad de adsorción (ej. arena, óxidos de magnesio, sepiolitas y zeolitas) han mostrado buenos resultados. Igualmente, en años recientes la posibilidad de acoplar la DA y la precipitación de estruvita (MgNH4PO4·6H2O) en el mismo reactor han llamado la atención. La precipitación de estruvita ocurre de manera natural cuando la concentración de 2+ + 3- Mg , NH4 y PO4 excede el producto de solubilidad de la estruvita. Con lo cual, la precipitación de estruvita en muchos sistemas de DA requiere la adición de compuestos 2+ 3- + químicos, ya que la concentración de Mg y PO4 es típicamente inferior a la del NH4 . El objetivo de este estudio es comparar el desempeño de cinco diferentes fuentes de magnesio (ej. MgCl2, Mg(OH)2, HG-MgO, LG-MgO y SA) en reactores, simultaneando los procesos de la DA y la precipitación de estruvita dentro del mismo reactor. La adición de agente estabilizante al purín de cerdo presento una máxima eficiencia de remoción de nitrógeno amoniacal total del 80%. La operación de los -1 digestores mostró que la adición de agente estabilizante de 5 y 30 g L al digestor resulta en un incremento del 25 y 40% en la producción de metano, respectivamente, comparado con el reactor de referencia. Este resultado puede estar relacionado con la reducción de la concentración de amonio y el incremento de la concentración de magnesio y concentración de partículas en el medio de digestión. Adicionalmente, los resultados de alcalinidad y ácidos grasos volátiles muestran que la adición de agente estabilizante no presenta un efecto negativo en los microorganismos anaeróbicos.

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30

Moulin, Silva Wagner. "Microsilica-bonded magnesia-based refractory castables." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2011. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-77492.

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Among the most impressive developments observed in the last 20 years, the improvement of the installation methods of monolithic refractories is certainly to be taken into account. However, this evolution, from vibratable castables to shotcrete and drycrete was not applied to materials based on magnesia, which are still mostly commercialized as ramming mixes, or as pouring castables with poor properties due to excessive water use. The major issues associated to this lack of technology is the scarcity of submicrometric powders compatible to magnesian systems, and the expansion followed by hydration of the magnesia, which is a disruptive reaction. By a thorough research on the literature, some potential additives were identified to be tested as anti-hydration additives. Hydration tests of powders in autoclave, complemented by pH and rheological measurements on magnesia pastes have identified five possible additives which can be used to inhibit the hydration: tartaric acid, citric acid, boric acid, magnesium fluoride and microsilica. Salts from the organic acids can also be successfully used. Of these, microsilica also presented the advantage of providing the submicrometric particles necessary to improve the flow of the castable, and to improve the bond of the castable. The three acids are very effective in inhibiting the formation of magnesium hydroxide, but affect negatively flow properties and mechanical resistance after cure. Microsilica prevented hydration cracks due to the reaction between the silicic acid generated under basic environment with the newly formed brucite, leading to the precipitation of a magnesium-silica-hydrated phase of poor crystallinity between the magnesia grains. This phase does not promote volumetric change, and also enable water release at a wider temperature range. Due to its nature close to serpentine minerals, it forms forsterite and enstatite at low temperatures, thus generating suitable strength between room temperature and at least 1400 °C. Magnesium fluoride changed the nature of this magnesium-silica-hydrated phase, by being incorporated to it and forming a phase more similar to the humite minerals. These minerals present higher MgO:SiO2 molar ratio than serpentine, and their formation requires a lower content of microsilica for a same effect against hydration, which is beneficial for the overall properties of the castable. The properties of the castable, as well as the influence of a number of other variables (for instance, refractoriness under load, creep, cold crushing strength, cold modulus of rupture, bulk density and apparent porosity) were also studied and hereby reported. It is believed that this technology can be further developed for industrial use, provided that some issues regarding the properties at high temperatures are solved. Not only had the study and comprehension of the nature of the bond between microsilica and magnesia, and the role of magnesium fluoride been pioneered by this work, but also the methodology used to evaluate the hydration after the drying process of castings, which was close to real refractory components.

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31

Abdelrazig, Baha Eldin Ismail. "The hydration of magnesia-phosphate cements." Thesis, University of Sheffield, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277605.

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32

Genin, Clément. "Cathodic Protection of carbon steel in the tidal zone : involved mechanisms." Electronic Thesis or Diss., La Rochelle, 2023. http://www.theses.fr/2023LAROS028.

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Ces travaux s’intéressent aux mécanismes mis en jeu dans la protection cathodique (PC) en zone de marnage (ZdM, zone verticale balayée par les marées). En effet, une étude de 2015 menée par Ph. Refait et coll. a mis en exergue une persistance de la PC même pendant les périodes émergées, a priori impossible à cause du retrait de l’eau de mer. Comprendre les mécanismes intervenant dans cette protection étendue pourrait, à terme, permettre de réduire l’impact environnemental de la conception et la maintenance de structures telles que les éoliennes offshores. Une première étude, sur toute la hauteur de la ZdM du port de commerce de La Rochelle, a permis de mettre en évidence que la PC pourrait être considérée efficace jusqu’à 45% de taux d’immersion (soit 74% de la hauteur de la ZdM). En parallèle, une étude menée au LaSIE visait à s’interroger de façon plus fondamentale sur le comportement de l’acier à marée descendante. Pour cela, des échantillons disposés à l’horizontal, sous de fines couches d’électrolyte (1 mm ou 5 mm) ont été placés en condition de protection satisfaisante (-950 mV/Ag/AgCl3M) et en condition de sous-protection (-750 mV/Ag/AgCl3M). Il apparaît alors qu’une protection insuffisante conduit à la formation d’une épaisse couche d’aragonite recouvrant une fine couche de produits de corrosion résiduels. De plus, une fine couche d’eau de mer augmente le caractère protecteur du dépôt formé sous PC suffisante (-950 mV/Ag/AgCl3M). Enfin, à mi-chemin entre les deux études précédentes, le dernier axe de recherche évoqué ici a permis de suivre l’évolution des paramètres de PC au cours des marées pendant 16 mois. Aux temps courts (8 j), la PC était efficace jusqu’à 40% d’immersion alors que toute la colonne était protégée pour des temps plus longs (180 j). Finalement, la persistance de la PC en ZdM est multifactorielle. Elle dépend de l’amplitude des marées, du temps d’exposition ainsi que du taux d’immersion. Son efficacité a été démontrée valable jusqu’à 45% d’immersion, pour des ZdM étendues
This PhD work focuses on understanding the mechanisms involved in cathodic protection (CP) in tidal zones (vertical zone between high tide and low tide levels). In 2015 a study by led by Ph. Refait et al. highlighted the unexpected persistence of CP even during emerged periods, which theoretically should not occur because of seawater withdrawal. Understanding the mechanisms involved in this spread-out CP could ultimately contribute to diminish the environmental impact of production and maintenance of structures such as offshore wind turbines. An initial study, covering the entire height of the La Rochelle commercial port tidal zone, showed that CP could be considered effective up to 45% of immersion rate (i.e. 74% of the tidal zone height). On the other hand, a study carried out at LaSIE laboratory aimed to investigate the behavior of steel during ebb tides in a more fundamental way. To this purpose, samples were set horizontally under thin layers of seawater (1 mm or 5 mm) and polarised under conditions of sufficient protection (-950 mV/Ag/AgCl3M) and insufficient protection (-750 mV/Ag/AgCl3M). Insufficient protection led to the formation of a thick layer of aragonite overlying a thin residual corrosion products layer. In addition, a thin layer of seawater enhances the protective character of the deposit formed under sufficient CP (-950 mV/Ag/AgCl3M). Furthermore, in the last research axis mentioned here, the evolution of CP parameters was monitored for 16 months of tidal cycles. For short periods (8 days), CP remained effective up to 40 % of immersion rate, while the entire column was protected for longer times (180 days). Finally, the persistence of CP in tidal zone is multifactorial. It depends on tidal amplitude, exposure time and immersion rate. Its effectiveness has been demonstrated to be valid up to 45% immersion, for extended tidal zones

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33

Hennig, Martin. "Laser-assisted friction stir welding of magnesium and magnesium/aluminium dissimilar joints." Master's thesis, Pontificia Universidad Católica del Perú, 2013. http://tesis.pucp.edu.pe/repositorio/handle/123456789/6241.

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The present master thesis is dealing with the influence of workpiece temperature in the process loads, generated during the FSW process. The investigation is focused on welding of the magnesium alloy AZ31. To affect the initial temperature of the joining members, two different methods are investigated. by using a laser, the material is heated and soften local direct in front of the welding tool. In contrast, a heating element, located beneath the workpieces, enable the heating of a laser area. The consequences of both methods are regarded and compared in the investigation. In addition, the comparison to the conventional welding process is made. Thereby, main aspects are the rached load levels as well as surface appearance and tensile properties. the successfully reduction of process forces is obtained for both procedures; however, the tensile properties got worse.
Das Anliegen dieser Arbeit ist es, den Einfluss der Ausgangstemperatur der zu fügenden Teile auf die für den Rührreibprozess charakteristischen Belastungen zu erarbeiten. Fokus der Untersuchungen lag dabei auf dem Fügen der Magnesiumbasislegierung AZ31. Die Erhöhung der Grundtemperatur der Werkstoffe wurde dabei auf zwei unterschiedliche Weisen erzeugt. Zum einen das lokale aufwärmen und Erweichen der Fügepartner, welches durch den Einsatz eines Lasers erreicht wurde, der direkt vor dem Schweißwerkzeug angebracht war. Die andere Methode beinhaltete das Einsetzen eines Heizelementes unter den Werkstoffen. Dadurch wurde eine gleichmäßige Erwärmung über die gesamte Fläche erreicht. Im Verlauf der Untersuchung wurden die Ergebnisse beider Methoden betrachtet und hinsichtlich der Prozesskräfte sowie Oberflächenbeschaffenheit und Festigkeitseigenschaften verglichen. Dazu wurden auch Schweißungen des konventionellen Rührreibschweißverfahrens herangezogen. Als Ergebnis konnte eine deutliche Verringerung der Prozesskräfte für beide Verfahren festgestellt werden. Allerdings war eine Verschlechterung der Festigkeitswerte zu beobachten.
Tesis

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34

Bohn, Torsten. "Magnesium absorption in humans /." [S.l.] : [s.n.], 2003. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=14930.

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35

Johnson, Kristien Paul. "Variability of ionic magnesium." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ60850.pdf.

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36

Willcocks, James Peter. "Magnesium in cellular energetics." Thesis, University of Oxford, 2002. http://ora.ox.ac.uk/objects/uuid:f4f5de76-8c72-4b42-8bd4-eb151485d47e.

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Most cellular magnesium is bound, yet it is the concentration of free magnesium, [Mg²⁺]_free, in red blood cells that is vital in the regulation of enzyme activity and ion transport. It is unknown how changes in total blood magnesium affect the [Mg²⁺]_free within red blood cells or in tissue, because the presence of other cations, especially H⁺ and potassium, K⁺ , affects the degree to which Mg²⁺ is bound. Consequently, this Thesis presents a new ³¹P NMR spectroscopic method to measure [Mg²⁺]_free in blood, which analyses the changes in the phosphorus chemical shifts of ATP and 2,3-DPG using theoretical equations expressing the observed chemical shift as a function of pH, K⁺ and [Mg²⁺]_free, over the pH range of 5.75 to 8.5 and [Mg²⁺]_free range 0 to 5 mM. The equations were adjusted for the binding of haemoglobin to ATP and DPG, which required knowledge of the intracellular concentrations of ATP, DPG, K⁺ and Hb. These equations enabled, for the first time, the simultaneous analyses of the chemical shifts of 3P-DPG and β-ATP to measure both intracellular 04- pH and [Mg²⁺]_free in normal and sickle blood. To simulate in vivo 100% oxygenated blood, samples were prepared for analysis by equilibration with a mixture of O₂ and CO₂, adjusted to give a pCO₂ of 40 mmHg and pO₂ > 150 mmHg. Under these conditions, normal whole blood had an intracellular pH of 7.20 ± 0.02 and a [Mg²⁺]_free of 0.41 ± 0.03 mM (n = 33). Further work determined blood pH and [Mg²⁺]_free for several clinical conditions including sickle cell anaemia, pre-eclampsia, hypoxia, patients with sub-arachnoid haemorrhage and chronic fatigue syndrome. This Thesis has demonstrated the potential of this new technique to evaluate the importance of [Mg²⁺]_free in the regulation of metabolite concentration and metabolic function, and to elucidate some of the properties of magnesium transport across the erythrocyte cell membrane.

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37

Lee, Young. "Grain refinement of magnesium /." St. Lucia, Qld, 2002. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16885.pdf.

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38

Zargar, Hamidreza. "Sintering studies of magnesia-chromite refractory composites." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46175.

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The magnesia-chromite refractory composites are the best candidates for the lining of non-ferrous metal smelting and refining furnaces, due to their high melting temperature, chemical inertness, and excellent thermal shock resistance. However, their high sintering temperatures (>1700°C) increase the processing complexity and costs. In this investigation, the primary goal was to study the sintering of these composites, with the long-term engineering goal to reduce their sintering temperature to <1500°C in air. The materials were synthesized via chemical methods using nitrates to assure chemical homogeneity. Al₂O₃, Fe₂O₃, and SnO₂ affected the kinetics of the MgCr₂O₄ formation and increased the density of MgCr₂O₄ in the order Fe₂O₃>Al₂O₃>SnO₂. The enhanced MgCr₂O₄ densification was attributed to the cation distribution in spinel structure (inversion phenomenon), caused by the inherent affinity of Fe⁺³ and Al⁺³ to tetrahedral sites. Fe₂O₃ and Al₂O₃ showed to form inverted spinel, while SnO₂ resulted in the formation of normal spinel solid solutions. Twelve magnesia-chromite composites were synthesized to study the effects of Al₂O₃, Fe₂O₃ and Cr₂O₃ on their sintering conditions; Cr₂O₃ decreased the density, while Fe₂O₃ and Al₂O₃ enhanced the densification of composites. The microstructural studies revealed that Fe₂O₃ and Al₂O₃ reduced the dihedral angle between MgO and spinel, while Cr₂O₃ increased it. The increased densification by Fe₂O₃ and Al₂O₃ was attributed to the decreased dihedral angle and formation of inverted solid solutions. The optimized composition [MgO6.9Cr₂O₃6.9Al₂O₃2.7Fe₂O₃]mol% (MK) reached nearly full density in air at 1475°C for 70minutes; 1700°C is currently used for magnesia-chromite refractories. In order to study the effects of the particle size on densification, magnesia-chromite composites (NMK) with average particle size of ~20 nm were synthesized via Pechini's method. Reducing the particle size from 1.2 um for MK to 20 nm for NMK reduced the onset sintering temperature by 200°C to 1000°C. The densification results were evaluated using master sintering curve theory for the first time for this kind of composites. The sintering activation energy was 443.7 and 302.6 kJ/mol for MK and NMK respectively. It was hypothesized that the oxygen diffusion through lattice and grain boundaries was rate controlling mechanism for MK and NMK respectively.

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39

Smith, Roger. "A Mossbauer study of chromite-magnesia refractories." Thesis, Sheffield Hallam University, 1994. http://shura.shu.ac.uk/20372/.

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A range of natural chrome ores, containing iron in two valence states, have been investigated using the technique of Mossbauer spectroscopy. The instrumentation required to cry out the technique was studied and an additional item of equipment was designed and constructed to extend the temperature range over which the effect could be observed. All the chrome ores yielded a complex spectra which could be attributed to a combination of octahedrally and tetrahedrally co-ordinated Fe2+ and Fe3+ quadrupole doublets. A model for fitting the spectra was devised assuming the presence of octahedrally co-ordinated Fe3+ and tetrahedrally co-ordinated Fe2+. The inhomogeneous nature of the samples caused a broadening of the tetrahedral Fe2+ contribution which was fitted as a distribution of three doublets. The Mossbauer parameters obtained were compared with those of pure compounds of a similar structure. Spectra recorded from 12K to 600K enabled effective Debye temperatures to be calculated. Second order Doppler shift (S.O.D.S.) calculations gave values for theta[D] of 385K and 658K for the Fe2+ and Fe3+ contributions respectively. Absorption area data gave similar values. An examination of the temperature dependence of the quadrupole splitting of the Fe2+ contributions appeared to confirm the validity of the proposed fitting model. Estimations of the Fe2+ / Fe3+ ratio were made using the data obtained and yielded values of 1.6 - 3.6.

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40

Shepherd, Mark. "Characterisation of magnesium chelatase and magnesium protoporphyrin IX methyltransferase from Synechocystis sp. PCC6803." Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274959.

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41

Grace, Richard William. "Corrosion mechanisms and corrosion inhibition of commercial purity magnesium and advanced magnesium alloys." Thesis, Swansea University, 2012. https://cronfa.swan.ac.uk/Record/cronfa43082.

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42

Sadjady, Seyed Kazem. "A study of tablet lubricant behaviour." Thesis, Liverpool John Moores University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262273.

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43

Eisheh, Jens-Tarek. "Untersuchungen zur Thermodynamik, Konstitution und Diffusion an den Systemen Magnesium-Platin und Magnesium-Palladium." [S.l.] : [s.n.], 2006. http://e-diss.uni-kiel.de/diss_1798/d1798.pdf.

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44

Yang, Zhiqiang. "Preparation of palladium, palladium sulfide, cadmium selenide nanoparticles and magnesium oxychloride, magnesium hydroxide nanorods." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/891.

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45

Barnackas, Irmantas. "Investigation of hydrogenation kinetics of magnesium and magnesium alloys in the ionized reactive atmosphere." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2008. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2008~D_20080919_140633-22213.

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In the present work Mg and MgAl thin films were fabricated using physical vapour deposition (PVD) technologies as non-traditional and new nanotechnology methods for designing high performance hydrogen storage materials. The physical vapour deposition technologies allow the formation of metastable metal, alloy and chemical compounds with strictly controlled composition, microstructure and stoichiometry at low temperatures. The synthesis of MgH2, MgAl and Mg(AlH4)2 films has been conducted in two steps: (i) fabrication of thin films employing magnetron sputtering in Ar gas, and (ii) hydrogenation of thin films employing plasma immersion ion implantation technologies. For the first time, chemical compound Mg(AlH4)2 has been synthesized using the deposition of Mg and Al atoms from gas phase in hydrogen plasma (reactive deposition with simultaneously hydrogen implantation). The transformation of Mg thin film to MgH2 takes place at 400 K temperature during hydrogenation in hydrogen plasma. Experimental results showed that hydriding kinetics of Ti-doped Mg film increases and desorption temperature decreases by 60-80 K and the maximum H2-effusion from the Ti-undoped Mg-Al takes place at temperature 475 K, and for the Ti-doped Mg-Al film – at temperature 410 K; the release time of accommodated hydrogen is shorted for the Ti-doped Mg-Al film. The mathematical model of hydrogenation shows that during the process of material irradiation in plasma the concentration of incident ions in... [to full text]
Šiame darbe, panaudojant jonines-plazmines technologijas, sintezuotos Mg, MgH2, Mg-Al ir Mg(AlH4)2 plonos nanokristalinės dangos. Ištirta jų struktūros, paviršiaus morfologijos ir sudėties priklausomybė nuo nusodinimo ir hidrinimo plazmoje technologinių parametrų. Darbe panaudoti plėvelių formavimo metodai: (i) magnetroninis-joninis garinimas Ar dujų aplinkoje; (ii) plonų dangų prisotinimas vandeniliu, panaudojant vandenilio jonų implantacijos iš plazmos technologijas. Šio darbo originalumas susijęs su nepusiausvyrinių plazminių technologijų panaudojimu nanokristalinių medžiagų hidrinimui. Pirmą kartą atlikta metalų hidridų sintezė ir ištirta vandenilio kaupimosi kinetika nanostruktūrinėse medžiagose panaudojant plazminės vandenilio implantacijos technologiją. Gauti rezultatai patvirtina joninių-plazminių technologijų pranašumus, iš kurių svarbiausias - formuojamų plėvelių mikrostruktūros valdymas nanometriniame lygyje. Tyrimo metu, panaudojant vandenilio jonų implantaciją į Mg-Al dangas, pirmą kartą susintezuotas Mg(AlH4)2 hidridas. 5 storio Mg dangų transformacija į MgH2, hidrinimo procesą atliekant vandenilio plazmoje, įvyksta esant 400 K temperatūrai. Eksperimentiniai rezultatai atskleidė, kad Ti priemaišomis legiruotose Mg dangose paspartėja hidridų formavimosi kinetika, o vandenilio desorbcijos temperatūra sumažėja 60-80 K. Vandenilio desorbcijos kinetika Ti priemaišomis legiruotose Mg-Al dangose taip pat yra spartesnė, o jų desorbcijos temperatūra sumažėja 65 K... [toliau žr. visą tekstą]

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46

Lubaba, Nicholas C. H. "Microstructure and strength of magnesia-graphite refractory composites." Thesis, University of Sheffield, 1986. http://etheses.whiterose.ac.uk/10254/.

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The relationships between fabrication variables, microstructure and selected properties of carbon bonded magnesia-graphite refractory composite materials have been investigated. A novel optical microscope method of characterizing the morphology of flake graphites was developed and used to determine distributions of length and thickness and average aspect ratios for the four graphite samples used in the study. The compaction behaviour of magnesia alone and in combination with the flake graphites has been studied in some detail and the microstructures of the products elucidated. It is shown that the amount of magnesia of small particle size plays a significant role in determining the graphite-graphite contact area in the structure. An irreversible volume expansion is observed on firing composites, the magnitude of which can be related to the microstructure and the graphite content. A phenolic resin binder restricts this expansion. It is shown that the carbon binder does not bond to the graphite phase and only weakly, if at all, to the magnesia. Consequently the strengths and moduli are low and show only a small variation with graphite type. The effect of adding graphite to carbon-bonded magnesia is to lower the strength slightly, but increasing the graphite content from 20-30% causes a small increase in strength. Increasing the amount of carbon bond from pitch has little effect on strength at levels of 5-15% whereas over the range 5-13% the resin binder has a more pronounced effect. The most significant factor affecting the strength and modulus of fired composites is the amount of silicon or aluminium, added as oxidation inhibitors, which react to form carbide and nitride phases. Finally, a brief study of slag penetration shows that this can be reduced by decreasing the amount of oxide fines in the composite because of the changes in microstructure that, result.

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47

Aarstad, Kari. "Protective films on molten magnesium." Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-901.

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Molten magnesium will oxidize uncontrollably in an atmosphere of air. To inhibit this, a protective gas is used to cover the melt. The gas most commonly used today is SF₆. Fluorine is known to be the active component of the gas. There is a major problem with SF₆, and that is that it has a strong Global Warming Potential (GWP). The GWP of SF₆ is 23 900 times that of CO₂.

The aim of the present work is to understand the mechanism of the protection of molten magnesium. Hopefully, this allows us to find less problematic alternatives to the use of SF₆ gas.

The present work was performed with three different experimental units:

- A furnace was especially built to expose molten magnesium to various atmospheres.

- A hot stage made it possible to study the surface of the molten or solid sample under the microscope at high temperature with SF₆ or with other gases in the atmosphere.

- Finally, the solubility of fluorine in magnesium was measured at temperatures from 700°C to 950°C.

To obtain a basic knowledge of magnesium melt protection, molten magnesium was exposed to various combinations of gases. Both SF₆ and SO₂ in air protects molten magnesium well from oxidation. It is also known that pure CO₂ has a protective effect. In these experiments, it was tested whether SF₆ and SO₂in other carrier gases than air will be protective. Nitrogen, argon and CO₂ were used as carrier gases. Also, air was added to CO₂ to see how much air the CO₂ can contain and still be protective. An important conclusion for SF6 and SO₂ is that air is necessary to build a protective film on the melt surface. Inert gases like nitrogen and argon will obviously not oxidize the metal, but since no film forms on the melt, the metal will keep on evaporating. A CO₂atmosphere can contain at least 20% air, and still be protective. Problems employing CO₂, are that the metal surface gets discolored, which is at least a cosmetic problem, and that C may be introduced into the metal, which may give corrosion problems.

The hot stage placed under an optical microscope made it possible to observe the magnesium sample as it was heated under an atmosphere of SF6 in air, pure CO₂and 1% SO₂ in air. The samples were held at temperatures from 635°C to 705°C for varying holding times. The partial pressure of SF6 was varied between 0.5 and 5%. The samples produced were excellent for further studies with Transmission

Electron Microscope (TEM), Field Emission Scanning Electron Microscope (FESEM), microprobe and Focused Ion Beam Milling (FIB). The examinations showed that a thin, dense film was formed. Magnesium fluoride particles formed on the interface between the metal and the oxide film in some cases. It is suggested that then the magnesium oxide is saturated with fluorine. The fluorine diffuses through the oxide layer and forms magnesium fluoride at the interface between MgO and Mg. In other cases, it is seen that a matrix rich in fluorine forms in between larger oxide grains. Combinations of these two situations are also seen.

Proposed explanations for the protective behavior of SF₆ are:

-the formation of a second phase, that is magnesium fluoride, which helps to give a Pilling-Bedworth ratio close to one.

-the formation of a MgO matrix containing F.

The thickness of the films formed with SF₆ is found to be proportional to the square root of time. The proportionality constant depends on temperature and the partial pressure of SF₆ in the gas.

Samples in CO₂ heated above the melting point did not keep their initial shape. The films formed with CO₂ are probably therefore not as strong as the films formed in SF₆since these samples managed to keep their initial shape even after they had melted. The surfaces after exposure to CO₂ were black and uneven. Formation of MgCO₃ has not been confirmed in this work. Also thermodynamic calculations indicated that MgCO₃ does not form.

It was not possible to tell experimentally whether the sulphur found in the samples exposed to SO₂ is bound as magnesium sulphide or magnesium sulphate or even dissolved in MgO, although it may look like two different phases are present with a slightly different sulphur content. Thermodynamic calculations do not indicate that MgSO₄should form.

It was considered to introduce fluorine directly into the melt as an alternative to the use of SF₆. In this case formation of MgF₂ would limit the content of fluorine in the molten magnesium. Therefore, the solubility of fluorine in molten magnesium has been studied by melting magnesium in a magnesium fluoride crucible. Samples were taken at various temperatures from 700°C up to 950°C. Three different analytical methods were employed to measure the fluorine content: The Sintalyzer method, Glow Discharge Mass Spectrometry (GD-MS) and Secondary Ion Mass Spectrometry (SIMS). The various analytical methods did not all give the same results. However, it is suggested that the SIMS results are the most reliable. The value for the dissolution of fluorine, 1/2 F₂ (g) = F (in mass%) is then:

ΔG°3/2 = (- 329 000 + 65 000) - (83+64)T

ΔGo for the equilibrium between magnesium and magnesium fluoride,

MgF2 = Mg (l) + 2F is found to be:

ΔGo = (471 000 ± 131 000) - (350±130) T

Iron is found to have no effect on the solubility of fluorine in molten magnesium.

The solubility of fluorine does not seem to be sufficiently high for direct dissolution of fluorine into the melt to be an alternative to SF6.

Iron is found to have no effect on the solubility of fluorine in molten magnesium.

The solubility of fluorine does not seem to be sufficiently high for direct dissolution of fluorine into the melt to be an alternative to SF6.

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48

Mwembela, Aaron Absalom. "Hot workability of magnesium alloys." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0003/NQ39793.pdf.

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49

Cadman, M. L. F. "Magnesium chelation and organic reactions." Thesis, University of Nottingham, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384304.

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50

Mistry, Jayshree. "Oat phytoalexins and magnesium chelates." Thesis, University of Nottingham, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.276204.

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