Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xiv, 78 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 64-66).

O refratário dolomítico é amplamente utilizado como revestimento de trabalho para panelas no processo de Aciaria, por sua excelente refratariedade em condições de serviço, principalmente em usinas que produzem aços acalmados ao silício. O emprego deste refratário é em virtude de uma formação natural de uma capa protetora, a qual potencializa a vida do refratário, acarretando em um aumento da vida útil do equipamento. O trabalho baseia-se em um estudo comparativo entre dois tijolos dolomíticos nomeados aqui como tijolos A e B. Os testes em escala industrial foram dados pela montagem de seis revestimentos, de cada tijolo, colocados sob as mesmas condições, monitorando-se a temperatura e o grau de oxidação do banho metálico. Ao final da campanha da panela se realizou alguns testes POST MORTEM, onde se destaca as medidas dos residuais. Além disso, para completar este estudo comparativo, separaram-se tijolos novos de cada marca, os quais foram submetidos às análises microestruturais via MEV, análises termogravimétricas, análises químicas por EDS e DRX, entre outros ensaios. Os resultados mostraram que o tijolo A teve um desempenho 20% superior ao tijolo B. O tijolo A tem maior pureza, microestrutura com agregados arredondados, com maior homogeneidade, uma ótima distribuição entre partículas finas e médias, favorecendo o empacotamento o que justifica sua maior tenacidade à fratura e resistência à corrosão. Também foi evidenciada de forma clara a presença de carbono grafite no tijolo A, conferindo-lhe uma maior resistência ao choque térmico e à corrosão. / The refractory dolomite is widely used as coating for ladles work in steelmaking process for its excellent refractoriness in terms of service. The use of this refractory is due to a natural formation of a protective layer, which enhances the life of the refractory, resulting in increased equipment life. This work is based on a comparative study between two bricks dolomite named here as A and B. Tests were given on an industrial scale by assembling six coatings of each brick placed in the same conditions by monitoring the temperature and the degree of oxidation of the metal bath. At the end of the campaign applied some tests POST MORTEM, how measurements of residual stresses. Moreover, to complete this comparative study, separated from each brand new bricks, which were subjected to microstructural analyzes via MEV, thermogravimetric analysis, chemical analysis by EDS and XRD, among other tests. The results showed that the performance of brick A was 20% higher than brick B. The Brick A has a higher purity, microstructure with rounded aggregates with greater homogeneity, optimal distribution between fine and medium particles, favoring the packaging which justifies a higher fracture toughness and corrosion resistance. It was also clearly evidenced the presence of graphitic carbon in the brick A, giving it a higher resistance to thermal shock and corrosion.

O refratário dolomítico é amplamente utilizado como revestimento de trabalho para panelas no processo de Aciaria, por sua excelente refratariedade em condições de serviço, principalmente em usinas que produzem aços acalmados ao silício. O emprego deste refratário é em virtude de uma formação natural de uma capa protetora, a qual potencializa a vida do refratário, acarretando em um aumento da vida útil do equipamento. O trabalho baseia-se em um estudo comparativo entre dois tijolos dolomíticos nomeados aqui como tijolos A e B. Os testes em escala industrial foram dados pela montagem de seis revestimentos, de cada tijolo, colocados sob as mesmas condições, monitorando-se a temperatura e o grau de oxidação do banho metálico. Ao final da campanha da panela se realizou alguns testes POST MORTEM, onde se destaca as medidas dos residuais. Além disso, para completar este estudo comparativo, separaram-se tijolos novos de cada marca, os quais foram submetidos às análises microestruturais via MEV, análises termogravimétricas, análises químicas por EDS e DRX, entre outros ensaios. Os resultados mostraram que o tijolo A teve um desempenho 20% superior ao tijolo B. O tijolo A tem maior pureza, microestrutura com agregados arredondados, com maior homogeneidade, uma ótima distribuição entre partículas finas e médias, favorecendo o empacotamento o que justifica sua maior tenacidade à fratura e resistência à corrosão. Também foi evidenciada de forma clara a presença de carbono grafite no tijolo A, conferindo-lhe uma maior resistência ao choque térmico e à corrosão. / The refractory dolomite is widely used as coating for ladles work in steelmaking process for its excellent refractoriness in terms of service. The use of this refractory is due to a natural formation of a protective layer, which enhances the life of the refractory, resulting in increased equipment life. This work is based on a comparative study between two bricks dolomite named here as A and B. Tests were given on an industrial scale by assembling six coatings of each brick placed in the same conditions by monitoring the temperature and the degree of oxidation of the metal bath. At the end of the campaign applied some tests POST MORTEM, how measurements of residual stresses. Moreover, to complete this comparative study, separated from each brand new bricks, which were subjected to microstructural analyzes via MEV, thermogravimetric analysis, chemical analysis by EDS and XRD, among other tests. The results showed that the performance of brick A was 20% higher than brick B. The Brick A has a higher purity, microstructure with rounded aggregates with greater homogeneity, optimal distribution between fine and medium particles, favoring the packaging which justifies a higher fracture toughness and corrosion resistance. It was also clearly evidenced the presence of graphitic carbon in the brick A, giving it a higher resistance to thermal shock and corrosion.

O refratário dolomítico é amplamente utilizado como revestimento de trabalho para panelas no processo de Aciaria, por sua excelente refratariedade em condições de serviço, principalmente em usinas que produzem aços acalmados ao silício. O emprego deste refratário é em virtude de uma formação natural de uma capa protetora, a qual potencializa a vida do refratário, acarretando em um aumento da vida útil do equipamento. O trabalho baseia-se em um estudo comparativo entre dois tijolos dolomíticos nomeados aqui como tijolos A e B. Os testes em escala industrial foram dados pela montagem de seis revestimentos, de cada tijolo, colocados sob as mesmas condições, monitorando-se a temperatura e o grau de oxidação do banho metálico. Ao final da campanha da panela se realizou alguns testes POST MORTEM, onde se destaca as medidas dos residuais. Além disso, para completar este estudo comparativo, separaram-se tijolos novos de cada marca, os quais foram submetidos às análises microestruturais via MEV, análises termogravimétricas, análises químicas por EDS e DRX, entre outros ensaios. Os resultados mostraram que o tijolo A teve um desempenho 20% superior ao tijolo B. O tijolo A tem maior pureza, microestrutura com agregados arredondados, com maior homogeneidade, uma ótima distribuição entre partículas finas e médias, favorecendo o empacotamento o que justifica sua maior tenacidade à fratura e resistência à corrosão. Também foi evidenciada de forma clara a presença de carbono grafite no tijolo A, conferindo-lhe uma maior resistência ao choque térmico e à corrosão. / The refractory dolomite is widely used as coating for ladles work in steelmaking process for its excellent refractoriness in terms of service. The use of this refractory is due to a natural formation of a protective layer, which enhances the life of the refractory, resulting in increased equipment life. This work is based on a comparative study between two bricks dolomite named here as A and B. Tests were given on an industrial scale by assembling six coatings of each brick placed in the same conditions by monitoring the temperature and the degree of oxidation of the metal bath. At the end of the campaign applied some tests POST MORTEM, how measurements of residual stresses. Moreover, to complete this comparative study, separated from each brand new bricks, which were subjected to microstructural analyzes via MEV, thermogravimetric analysis, chemical analysis by EDS and XRD, among other tests. The results showed that the performance of brick A was 20% higher than brick B. The Brick A has a higher purity, microstructure with rounded aggregates with greater homogeneity, optimal distribution between fine and medium particles, favoring the packaging which justifies a higher fracture toughness and corrosion resistance. It was also clearly evidenced the presence of graphitic carbon in the brick A, giving it a higher resistance to thermal shock and corrosion.

Primary angiitis of the central nervous system (PACNS) is a rare form of vasculitis. It is a diagnosis of exclusion and often diagnosed post mortem on pathologic evaluation. Cerebral angiography can be suggestive, but biopsy is required. Symptoms can vary from headache to focal cranial nerve deficits. On the more severe spectrum, patients can present with ischemic and vary rarely hemorrhagic stroke. We present in this case report key clinical pearls regarding suspected diagnosis. Younger patients with cortical hemorrhages may have PACNS instead of the more common cerebral amyloid angiopathy. Early suspicion may aid in initiating effective treatment as we highlight in the discussion.

<p dir="ltr">Ceramic/metal composites are being explored as potential replacements for conventional metal alloys in high-temperature components used in aerospace and power generation applications. Co-continuous ceramic/metal composites can offer attractive combinations of properties, such as improved mechanical toughness and thermal conductivity (relative to monolithic ceramics) and enhanced stiffness and corrosion/erosion resistance (relative to monolithic metals). However, development of cost-effective and scalable manufacturing routes to dense, complex-shaped ceramic/metal composites is a non-trivial challenge.</p><p dir="ltr">Chapter 1 of this dissertation is focused on the fabrication of WC/Cu composites using pressureless Cu liquid infiltration. The microstructure, density, porosity, phase content and properties of the resulting WC/Cu composites have been investigated. Mechanical properties, such as flexural strength and Vickers hardness have been evaluated, and the thermal cycling behavior of the WC/Cu composites have been examined. This study successfully demonstrates the fabrication of near-net-shape WC/Cu composites and provides insights into potential applications for such composites.</p><p dir="ltr">In Chapter 2, the limitations of metal alloy-based heat exchangers are discussed, leading to the exploration of alternative materials such as composite of zirconium carbide (ZrC) and tungsten (W). The favorable properties of ZrC/W composites, such as chemical compatibility, low vapor pressure, high thermal conductivity, stiffness, and thermal cyclability are highlighted. The fabrication of ZrC/W composites using reactive infiltration processes, emphasizing the importance of scalable fabrication methods, is also demonstrated.</p><p dir="ltr">Chapter 3 is focused on the fabrication and characterization of functionally graded ZrC/W – WC/Cu composites. These composites have been prepared by immersing WC/Cu preforms in Zr – Cu liquid at different temperatures, and the microstructures and phase distributions have been evaluated. It is observed with the same immersion time, the thickness of the ZrC/W reaction zone decreases with increasing immersion temperature due to the rapid reaction between WC and Zr at higher temperatures. Additionally, a model has been developed to describe the thermal conductivity of the composites as a function of the distance from the external surface. These findings provide insights into the fabrication and properties of functionally-graded composites for potential heat dissipation applications.</p><p dir="ltr">In Chapter 4, the development of a Ti-bearing, Ni-based active metal braze for joining Al₂O₃/Cr composites to Ni-based alloys is discussed. Joining ceramic components to metal parts poses challenges due to material property mismatches and ceramic brittleness. Conventional brazing materials often suffer from oxidation at high temperatures in air which compromises joint integrity. The focus of this chapter is the evaluation of the oxidation behavior of the developed brazing material to assess the suitability of this braze for reliable joining of ceramic-based composites to Ni-based alloys for use in air at high temperatures. Differential scanning calorimetry (DSC) has also been used to evaluate the solidus and liquidus temperatures of the Ni-19Cr-10Si and Ni-18Cr-10Si-4Ti alloys.</p><p><br></p>

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<p>The local corrosion of refractories at the slag/gas interface is a serious problem that limits the life of the refractories.Although, there have been several studies focused on understanding the Marangoni effect on the refractory dissolution process, there is little quantifiable analysis available. The aim of this study is to establish a better fundamental understanding of refractory dissolution mechanisms, and develop appropriate models for predicting the extent and rate of slag-line dissolution.</p> <p>In the first part of this research, experimental studies using a high temperature dip technique were performed: MgO refractory in SiO₂-CaO-FeO_x-MgO slag and Al₂O₃- SiO₂-CaO-FeO_x-MgO. The experiments were conducted at varies temperature. There was significant evidence of a spinel phase formed at the slag/refractory interface for slags containing 20wt.% Al₂O₃. This existence of the spinel seems to have retarded the dissolution of the refractory. The decrease in erosion rate in the presence of spinel is in proportion to the decrease in the equilibrium MgO concentration at the slag/solid interface. The activation energy is calculated from the relationship of effective mass transfer coefficient vs. temperature and found in the range of mass transfer activation energy.</p> <p>The second part of this search is developing a numerical model to predict the slag-line dissolution. An effective algorithm for analysis of unsteady Marangoni convection in refractory slag line dissolution has been developed. The results show that the Marangoni effect plays a very important role in slag-line erosion at this condition; both the moving boundary condition and curved surface condition have significant effects on the slag-line erosion rate. The comparison of experimental and numerical results shows that the model can predict the refractory maximum corrosion distance caused by Marangoni flow at the slag line. However, the eroded material volume was predicted within 20~30% deviation</p> / Doctor of Philosophy (PhD)