M. Tech. Metallurgical Engineering. / Studies the tribological and electrochemical behaviour of various WC-Co, WC-Co-Cr and CrC-NiCr based thermal sprayed coatings in synthetic mine water environment. The research aims to achieve the following objectives. 1. Characterize commercially available cermet powders used during thermal spray process. 2. Explore and understand the relationship between feedstock powder parameters, the phases and microstructures generated during thermal spray process. Study the interrelationship of feedstock powder chemistry and method of powder synthesis on wear and corrosion behavior of thermally sprayed coatings. Assess the joint actions of wear and corrosion behaviour of the coatings in synthetic mine water environment.

Thesis (Ph.D.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Filmes de benzotriazol (BTAH) formados sobre aços carbono e inoxidável 316L foram estudados em meios de ácido sulfúrico, ácido clorídrico e cloreto de sódio a 25°C. Os seguintes aspectos foram considerados: as condições de formação do filme, sua eficiência, sua resistência em meios não contendo o inibidor,a presença de aditivos e o efeito do transporte de massa sobre o mecanismo da reação. Foram empregadas como técnicas: transitórios de potencial de circuito aberto, ensaios gravimétricos, curvas de polarização potenciostáticas e potenciodinâmicas com eletrodo parado e de disco rotativo, cronoamperometria, espectroscopia de impedância eletroquímica, microscopia ótica, microscopia eletrônica de varredura e análise da superfície por dispersão de energia. O BTAH se mostrou inibidor na grande maioria dos meios para os dois materiais estudados. A resistência dos filmes formados não existe ou é parcial quando as superfícies metálicas revestidas com o filme são imersas nos meios estudados sem inibidor. A adição de Cu(II) aumenta a resistência dos filmes, para determinadas relações [BTAH]/[Cu(II)] que estabilizem o intermediário Cu(I). A presença de íons provenientes da dissolução do aço inoxidável 304 em H2SO4 0,50 mol.L-1 contendo BTAH, eleva significativamente a resistência dos filmes formados, quando estes são expostos aos meios sem inibidor. O cloreto de trimetildodecil amônio exerce sinergismo sobre a ação do BTAH como inibidor de corrosão do aço carbono 1010 em meios ácidos. Superfícies de aço carbono previamente reduzidas são mais eficientes na formação de filmes resistentes aos meios sem inibidor. O transporte de massa do BTAH é uma etapa cinética importante no mecanismo de formação do filme sobre aço inoxidável 316L em meio de HCI 2,0 mol.L-1. O BTAH se mostrou inibidor para a corrosão do aço quando revestido pelo \"primer\" da tinta epóxi, quando adicionado à tinta ou quando o filme é formado antes da aplicação do \"primer\". / Benzotriazole (BTAH) films formed on carbon steel and 316L stainless steel have been studied in sulfuric and chloridric acids and in sodium choride solutionsat 25°C. Different aspects were considered: the film formation conditions, its efficiency, its resistance, the presence of additives and the effect of mass transport on the reaction mechanism. Open circuit potential measurements, weight loss experiments, potenciostatic and potentiadynamic polarization curves using stationary and rotating disc electrode, chronoamperometry, electrochemical impedance spectroscopy, optical and scanning electron microscopies and energy dispersive surface analysis have been used as techniques. BTAH have shown inhibitive effect over the majority of the systems studied. The film resistance depends on the presence of the inhibitor in the solution but the result is different if the film is formed in solution containing additives as copper (II) ions or cations obtained from 304 SS dissolution in H2SO4 media; in this case the films resist to chloridric acid media without BTAH. Dodecyltrimetilammonium chloride presents synergism on the inhibitive BTAH action forcarbon steel in acid solution. The BTAH mass transport represents an important step on the film formation mechanism. BTAH is also an effective inhibitor for carbon steel covered by epoxy primer when it is added to the primer or when the film is formed on the carbon steel surface from a H2SO4 solution containing BTAH.

Engineering : Chemical / M. Tech. (Chemical Engineering)

This work developed a process to provide physical, electrical, and environmental protection to the electrical lead system of an optical switch device. A literature review was conducted to find materials and processes suitable to the stress-sensitive, high voltage characteristics of many optical switch devices. An automatic dispensing dam and fill process, and three candidate materials (two epoxy and one silicone) were selected for investigation. Experimental and analytical techniques were used to evaluate the materials. Methods applied included interferometric die warpage measurements, electrochemical migration resistance tests (ECMT), thermal cycling, and finite element analysis. The silicone dam and fill system was selected based upon the results of die warpage and electrochemical migration resistance tests. A modified, selective dam and fill process was developed and preliminary reliability testing was performed. The paper provides detailed instructions for successful encapsulation of the optical switch's lead system.

D. Tech. Chemical, Metallurgical and Materials Engineering / Discusses the objective of this present study is to manufacture particulate-strengthening Zn-Al-SnO2-TiO2 composite alloy on mild steel from chloride and sulphate baths with the target of improving mechanical and anti-corrosion, wear properties for automotive and decorative applications. Sub-Objectives:To study the effect of Zn-Al-SnO2-TiO2 composite properties on mild steel substrate To investigate the novel multifunctional thin films evolution formed on mild steel and their tribological properties. To investigate thermo-mechanical recrystallization behaviour and its thermal instability.To study the anti-corrosion resistance performance of the electrofabricated quaternary Zn-Al-SnO2-TiO2 coatings.To draw attention to the functional processing parameters of Zn-Al-SnO2-TiO2 produced coatings for high durability.

D. Tech. Chemical, Metallurgical and Materials Engineering. / Aims to produce and improve the tribocorrosion property of Ti6Al4V by means of laser surface cladding with Ni and ZrO2. The results of this study would be useful for the design of high performance components for chemical and oil industry and potential applications in other engineering fields. The aim would be achieved through the following objectives: 1. Synthesize and characterise Ti, Ti-Ni and Ti-Ni-ZrO2 admixed powders. 2. Explore the feasibility of laser surface treatment of Ti6Al4V with Ti, Ti-Ni and Ti-Ni-ZrO2. 3. Investigate possible metallurgical interactions and phenomenon during and after laser surface cladding of the composite. 4. Evaluate the microstructural and mechanical properties of Ti based composites in terms of hardness. 5. Analyze the interaction between wear and corrosion wear as well as tribocorrosion resistance of the alloys and composites after laser surface cladding in 3.5 % NaCl and 1M H2SO4 environments.

The electrochemical corrosion behavior of mild steel in apple, grape, mango, orange and the mixture of these juices was investigated in this study. Open circuit potential and weight loss analytical techniques were employed to establish the comparative corrosion rates of this material in the agro media over the interval of five days for a sixty-day immersion period at an ambient temperature. The chemical compositions of both mild steel and the agro media were determined to ascertain corrosion mechanism for the reaction. Polarization behavior of mild steel in the agro media were determined by Tafel extrapolation curves. The analysis showed that cathodic polarization curves were almost identical irrespective of the concentration of the various media while the anodic polarization curves exhibited varying active and passive corrosion behaviour due to passivating oxide films. The analysis of the results further showed that the corrosion rate of the metallic sample decreased with longer immersion periods which could be attributed to a gradual decline in acidity of these media as revealed by the pH results. Hence, the evolution of hydrogen gas and reduction of dissolved oxygen molecules from the reacting system were presumed to be major factors retarding corrosion of the solution involved. Similarly, the presence of suspended particles on the surface of the test steel sample could have also led to the impediment to corrosion rates from the surrounding atmosphere. Microscopic analysis of the corroded mild steel specimens revealed uniform and localized corrosion with Fe2O3 spotted as the main corrosion product. The result obtained from the electrochemical study showed that the corrosion rate of the mild steel sample was highest in the orange medium (1.53mm/yr), followed by grape medium (1.40mm/yr), mixture of these media (0.67mm/yr), mango medium (0.40mm/yr) while the metal corroded least in the apple medium (0.30mm/yr) over the duration of immersion. / Engineering : Chemical / M. Tech. (Chemical Engineering)

Nesta dissertação, é apresentada uma rotina computacional para modelar a corrosão por pites em aço inoxidável baseada em modelos matemáticos existentes que levam em consideração efeitos determinísticos e estocásticos. Como contribuição, modificações baseadas em resultados experimentais foram inseridas no modelo, com o objetivo de avaliar a influência de inclusões de MnS na matriz metálica, locais típicos de maior nucleação de pites. Foi modelado também o efeito do potencial de aplicado verificando-se assim a sua influência na formação de pites e a determinação da faixa possível para o potencial de pite. A modelagem consiste da avaliação espaço-temporal da nucleação, com a possibilidade de visualização da evolução de pites metaestáveis e estáveis, além do transiente de corrente anódica gerado pelo processo. Os resultados são apresentados em termos da avaliação das variáveis de maior influência na suscetibilidade de formação de pites, tais como concentração de espécies agressivas, dano à camada passiva e queda no potencial ôhmico, o que possibilita estudos futuros para se obter formas mais eficientes de combate à corrosão por pites. / In this work is presented a computational routine to model pitting corrosion of stainless steel based on pre-existing mathematical models that take into account deterministics and stochastic effects. As contribution, modifications based on experimental results were inserted, evaluating the influence of MnS inclusions on metal surface, a typical site of major pitting nucleation. Applied potential effect was modeled, thus, it was possible to verify its influence on pitting formation and the possible range of pitting. The model consists on spatio-temporal evaluating of nucleation process, with visualization of metastable and stable pitting evolution and the anodic current transient. The results are presented in terms of variables with greatest influence on the susceptibility of pitting formation, such as concentration of aggressive species, passivity layer damage and ohmic potential drop, allowing future studies to obtains more efficient ways to combat pitting corrosion

Nesta dissertação, é apresentada uma rotina computacional para modelar a corrosão por pites em aço inoxidável baseada em modelos matemáticos existentes que levam em consideração efeitos determinísticos e estocásticos. Como contribuição, modificações baseadas em resultados experimentais foram inseridas no modelo, com o objetivo de avaliar a influência de inclusões de MnS na matriz metálica, locais típicos de maior nucleação de pites. Foi modelado também o efeito do potencial de aplicado verificando-se assim a sua influência na formação de pites e a determinação da faixa possível para o potencial de pite. A modelagem consiste da avaliação espaço-temporal da nucleação, com a possibilidade de visualização da evolução de pites metaestáveis e estáveis, além do transiente de corrente anódica gerado pelo processo. Os resultados são apresentados em termos da avaliação das variáveis de maior influência na suscetibilidade de formação de pites, tais como concentração de espécies agressivas, dano à camada passiva e queda no potencial ôhmico, o que possibilita estudos futuros para se obter formas mais eficientes de combate à corrosão por pites. / In this work is presented a computational routine to model pitting corrosion of stainless steel based on pre-existing mathematical models that take into account deterministics and stochastic effects. As contribution, modifications based on experimental results were inserted, evaluating the influence of MnS inclusions on metal surface, a typical site of major pitting nucleation. Applied potential effect was modeled, thus, it was possible to verify its influence on pitting formation and the possible range of pitting. The model consists on spatio-temporal evaluating of nucleation process, with visualization of metastable and stable pitting evolution and the anodic current transient. The results are presented in terms of variables with greatest influence on the susceptibility of pitting formation, such as concentration of aggressive species, passivity layer damage and ohmic potential drop, allowing future studies to obtains more efficient ways to combat pitting corrosion