O presente trabalho tem como objetivo estudar a eletropolimerização de polímeros baseados em polianilinas e suas propriedades para a proteção contra a corrosão. Assim, foi utilizada a seguinte divisão: (i) estudo das sínteses eletroquímicas monitoradas espectrofotometria de UV-vis, utilizando perturbações potenciodinâmicas e potenciostáticas em diferentes concentrações monoméricas, sobre um eletrodo de ITO (óxido de titânio dopado com índio). Os resultados mostraram que durante as sínteses a polianilina (PAni) apresenta uma baixa formação de oligômeros e degradação. As sínteses de poli-o-metoxianilina apresentam uma maior quantidade de oligômeros, apresentando uma alta sinal de absorbância em 560 mn. Assim, os espectrociclovoltamogramas e espectropotenciogramas mostraram para todas as sínteses os potenciais onde ocorrem os processos formação de: bipolarons, radicais, oligômeros e a conversão de PAni entre as forma leucoesmeraldina e sal esmeraldina. Portanto, o monitoramento UV-vis foi considerado uma ferramenta muito útil e interessante para o entendimento de reações de polimerizações. (ii) A proteção contra a corrosão do aço 304 foi feita recobrindo o mesmo com polímero por via eletroquímica (voltametria cíclica, VC e potenciostáticas, Pot), com otimizações de potencial, tempo de perturbação e número de ciclos, em soluções de elevadas concentrações monoméricas. Na primeira parte foi utilizado somente Ani; por VC foram observadas dois tipos de morfologia diferente. Na primeira, um filme e nanofibras, enquanto que para Pot, uma morfologia granular foi encontrada. As analises de corrosão mostraram que as melhores proteções foram obtidas para as seguintes condiciones: 0,05 - 1,15 V, por 15 ciclos, e 1,15 V, por 300 segundos. Esses filmes apresentaram deslocamento no potencial de corrosão, aumento na resistência de transferência de carga e potencial de circuito aberto elevado. Além disso, mantiveram uma superfície de aço livre de produto de corrosão. Assim, essas condições de sínteses foram reproduzidas para ometoxianilina (OMA) e Poli(anilina-co-o-metoxianilina). A OMA sintetizada por VC apresentou a melhor proteção, deslocando o potencial de corrosão para valores anódicos e mantendo um potencial mantendo um potencial de circuito aberto elevado, devido à morfologia fechada de microfibras, não ocorrendo corrosão na superfície do aço. / The goal of the present work is to study the electropolymerization polymers of based on polianilines and their corrosion protection properties. So, the following division was applied: (i) study of the electrochemical synthesis coupled to a spectrophotometer of UVvis. Using potenciostatic and potentiodynamic perturbations with different monomeric concentrations, on a ITO electrode (titanium oxide doped with Indium). The results show that polianiline (PAni) during the synthesis process present a low generation of oligomers and a null polymeric degradation. Whereas the synthesis of poli-o-metoxianilina presents an important concentration of oligomers, showing a high absorption signal in 560 nm. In this way, the spectrociclovoltammograms and the spectropotenciograms showed for all the synthesis the potential were occur formation processes of: bi-polaron, radicals, oligomers and the transformation of PAni of the form leucoesmeraldina and esmealdina salt. Thats why the UV-vis monitoring process interesting for the understanding of polymerization reactions. (ii) the validations of corrosion protection of steel-304 were performed covering with polymer in a electrochemical way; ciclic voltammetric (VC) and potenciostatic (Pot), with variations of the potential, time and cycle numbers, in solution with high monomeric concentrations. The first part was just Ani. By VC two different types of growth morphology were observed; a granular film and nano fibers, while for Pot, the morphology were granular. The analysis of corrosion show that the best protections were achieved for: 0,05-1,15 V by 15 cycles of 1,15 V during 300 seconds. Those films present a shift on the corrosion potential, increasing the transfer resistance of charge in high open circuit potential, moreover, keeping the steel surface corrosion-free. Those conditions were reproduced for o-metoxianiline (OMA) e Poli (aniline-co-o-metoxianiline). The synthesized OMA by VC present a better protection, shifting to anodic values the corrosion potential and keeping a high open circuit potential, due to the morphology of the microfibers, not happening corrosion on the steel surface.

Os aços inoxidáveis duplex (AID) caracterizam-se pela sua microestrutura composta por austenita numa matriz ferrítica, com fração volumétrica média de 50% para cada fase. A combinação destas características confere-lhes excelente resistência mecânica e à corrosão. A soldagem/junção destes aços é frequentemente uma operação crítica, já que, ao sofrer ciclos térmicos, estes aços têm suas propriedades alteradas. Portanto, processos de junção com ausência de gradientes de temperatura, como a brasagem, mostram-se uma solução prática para a junção destes aços. No entanto, o adequado desenvolvimento do processo de brasagem em AID envolve considerações importantes a respeito da escolha dos parâmetros de processamento e metal de adição em conjunto com os ciclos térmicos de aquecimento e resfriamento. O presente estudo pretende avaliar a brasabilidade dos AID UNS S32101(baixa liga), UNS S32304 (baixa liga), UNS S32507 (superduplex) e UNS S32707(hiperduplex), mediante a caracterização da junta brasada. Estes aços foram brasados em forno continuo com metal de adição BNi-7 (Ni-Cr-P), na temperatura de 1100oC, por tempos de 32 min e 12 min, seguidos de resfriamento em forno, utilizando-se folgas de 0,5, 0,3 e 0,0 mm. A junta brasada foi caracterizada utilizando-se microscopia ótica e microscopia eletrônica de varredura (MEV). A identificação microestrutural foi realizada via Microanálise Química de Energia Dispersiva de Raios-X (EDS) e difração de Raios-X. Foi identificada na junta brasada dos diferentes AID a fase rica em níquel, assim como fases prejudiciais compostas por fosfetos de níquel e cromo. A fase rica em níquel, que usualmente é denominada de -Ni, apresenta-se preferencialmente em toda a região da junta, sem a presença de fase intermetálica contínua no centro da junta. No caso dos aços inoxidáveis super e hiperduplex esses apresentaram a formação de fase sigma na região da interface da junta, do lado do metal de base, devido aos ciclos térmicos de brasagem / The duplex stainless steels (DSS) are characterized by its microstructure consisting of austenite in a ferritic matrix with mean volumetric fraction of 50% for each phase. The combination of these features gives them excellent mechanical strength and corrosion resistance. The welding / joining of these steels are often considered as a critical operation, since, subjected to thermal cycles, they have their microstructures changed and, consequently, their properties. Therefore, joining processes without temperature gradients, like brazing, are shown as a practical solution for joining these steels. However, the proper development of brazing process of DSS involves important issues concerning the choice of processing parameters and the brazing filler metal together with heating and cooling brazing thermal cycles. This study aims at evaluating the brazeability of DSS UNS S32101 (lean duplex), UNS S32304 (lean duplex), UNS S32507 (superduplex) and UNS S32707 (hyperduplex) by characterizing the brazed joint. These steels were brazed in a furnace with filler metal BNi-7 (Ni-Cr-P) at 1100°C for times of 32 min and 12 min, followed by cooling in a continuous brazing furnace, with joint gaps of 0.5 , 0.3 and 0.0 mm. The brazed joint was characterized using optical microscopy and scanning electron microscopy (SEM). The phase identifications were performed by microanalysis using energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction. Results showed, for non-ideal joint gaps, in all duplex used in this work, the Ni rich solid solution, as well as deleterious phases composed of nickel and chromium phosphides. The ideal gap presented Ni rich solid solution, usually called -Ni, was found continuously without a continuous intermetallic region in the joint center. In the case of super duplex and hyperduplex brazing, the brazing thermal cycles produced the formation of sigma phase in the region of the joint interface, in the base metal.

Stainless steel profiled walls have increasingly been used in the process and other industries to protect people and personnel against hydrocarbon or chemical explosions. The existence of various uncertainties, in particular the ones associated with explosion loading and parameters, make the current design and assessment which are based on single degree of freedom (SDOF) and deterministic approach, very complicated and in many cases leading to unreliable design assessment. Therefore, developing an appropriate reliability approach for assessing and designing blast wall structures would greatly assist in improving the safety of personnel and plant facilities. The objective of this research study is to develop a practical framework for performance based design of stainless steel profiled barrier blast walls, with specific focus on reliability assessment by implementing stochastic finite element analysis (SFEA). Initially, the current traditional SDOF method is reviewed to identify the related issues and weaknesses and accordingly an appropriate method for structural assessments of the blast walls is proposed. Furthermore, a comprehensive investigation on various available methods is carried out to identify a suitable probabilistic approach for the reliability assessments. The corresponding reliability of these structures is evaluated with a MCS method, implementing the Latin Hypercube Sampling (LHS) approach. A programming package is developed using Ansys Parametric Design Language (APDL), to generate parametric finite element models and to perform automated reliability assessments. The significant uncertainties are combined with an advanced analysis model to investigate the influence of loading, material and geometric uncertainties on the response of these structures under realistic boundary conditions and connection configuration. Effective implementation of the framework is achieved by the development of a combined programming package to deal with both finite element and reliability analyses. A further development for this research study is associated with the development of performance based design approach, using the results of the probabilistic and finite element assessments. This can be utilised for optimum and appropriate design of the blast wall structures, based on the defined performance levels. Application and practicality of the developed approach and associated programming package is demonstrated through a number of case studies of realistic stainless steel profiled barriers subject to explosion loading. The results of the preliminary probabilistic case studies confirm that the explosion loading is the main influential input parameter and also nonlinearities are more critical than dynamic effects for unstiffened profiled barrier blast walls. An appropriate dynamic load factor (DLF) is proposed for the preliminary stage of the design and assessments. It is observed that using the probabilistic approach can help identify the important variables and parameters to optimize the design of profiled blast walls, and to perform risk assessments for these structures. The study is expanded to develop a performance based design methodology, linking the probabilistic results with various performance levels and associated parameters (e.g., damage levels). The results and discussions of the case studies associated with performance based design assessments confirm the suitability of the proposed framework, and also highlight the complications in defining intermediate levels, without preliminary investigations. This shows that QRA approach and involvement of professionals can play an important role to develop performance levels and the associated objectives. The developed programming package and associated framework are expected to provide valuable guidance to professional design engineers and researchers, by obviating the need for complex computational requirements.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE / Includes bibliographical references. / by Paul Alan Gault. / M.S.

Thesis. 1978. M.S.--Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / M.S.

A corrosão localizada em aços inoxidáveis pode se manifestar de várias formas, tais como, a corrosão por pite, em fresta e corrosão sob tensão. Estes tipos de corrosão ocorrem quando o metal é exposto em meios agressivos como o cloreto, entre outros. O objetivo deste trabalho é estudar o comportamento dos aços inoxidáveis austeníticos e ferríticos em meios agressivos de cloreto, brometo e suas misturas. Para testar a resistência à corrosão por pite foi usado o método de polarização potenciodinâmica em eletrólitos de concentração iônica total de 0,6M. Os materiais estudados foram os aços inoxidáveis: 298 (aço inoxidável Cr-Mn, especificação da ArcelorMittal Inox Brasil) e os aços padronizados segundo a UNS: S30400, S31603, S43000 e S44400; todos, na condição tal como recebida da usina. Os resultados mostraram que, em meio de 0,6M(NaCl+NaBr), para concentrações de 0M a 0,45M NaCl, o desempenho quanto a resistência à corrosão por pite obedece a seguinte ordem decrescente: 444, 316L, 304, 298 e 430. Por sua vez, para a concentração de 0,6M NaCl, ou seja, ausência total de brometo, ocorre a alteração do desempenho dos aços inoxidáveis, colocando a seqüência da seguinte ordem: 316L, 444, 304, 298 e 430. Nota-se, portanto, que o melhor aço para ambientes contendo íon brometo seria o aço 444, já para aplicações em meio de cloreto puro, a melhor seleção é o aço 316L. Foram encontrados sítios de nucleação nos diferentes aços testados nos eletrólitos de 0,6M NaCl e 0,6M NaBr,sempre relacionados a inclusões: em alguns casos a nucleação ocorreu na interface matriz/inclusões insolúveis e, em outros, foram encontrados sinais de dissolução de inclusões, provavelmente de sulfeto. As diferenças de resistência à corrosão por pite entre os diferentes aços, nos diferentes eletrólitos, foram discutidas em função das diferenças de composição química. / Localized corrosion of stainless steels can be manifested in various forms, such as: pitting, crevice and stress corrosion. These types of corrosion occur due to exposition of metal in aggressive environments such as: chloride and bromide. The mean goal of this work is to study the pitting corrosion resistance of both austenitic and ferritic stainless steels in aggressive environments containing chloride, bromide or their mixtures. The potentiodynamic polarization method was used to test the pitting corrosion resistance in media containing a total of ion concentration of 0,6M. The studied materials in this work were stainless steel: 298 (Cr-Mn steel, specification of ArcelorMittal Inox Brazil) and standardized steels according to the UNS: S30400, S31603, S43000 and S44400. The results have shown that maintaining a constant concentration of 0.6M (NaCl+NaBr) into the electrolyte by varying the NaCl concentration between 0M and 0.45M, the performance in terms of pitting corrosion obeys to the following decreasing order: 444, 316L, 304, 298 and finally 430. In turn, for a concentration of 0.6M NaCl, so without any bromide, there is a variation from the performance of stainless steels, putting the sequence as following: 316L, 444, 304, 298 and 430. Nucleation sites were always found related to non-metallic inclusions in all tested stainless steels for the electrolytes of 0,6M NaCl or 0,6M NaBr. Sometimes, pits nucleation occurred at the matrix/inclusion interface, but others times, pits nucleated in water soluble inclusions. Difference of the pitting corrosion resistance between tested steel in the different electrolytes have been discussed as a function of the chemical composition.

Materiais com gradiente funcional (MGF), a base de aço inoxidável e cerâmica têm despertado interesse em diversas áreas tecnológicas: estrutural, térmica, elétrica, biomédica e militar, e têm inspirado pesquisadores a combinar propriedades e características que não estão presentes em peças convencionais. Têm sido também considerados como uma alternativa na preparação de partes de motores de alta eficiência, ferramentas de corte e revestimentos estruturais para reatores químicos. A incorporação de metal e cerâmica em uma estrutura graduada permite a integração de muitas propriedades desejáveis que combinam ambas vantagens do metal e a cerâmica. Os componentes cerâmicos são capazes de suportar altas temperaturas e possuem alta resistência à corrosão, enquanto os componentes metálicos apresentam uma alta resistência à tração e alta ductilidade, e portanto são menos susceptíveis a fratura catastrófica. Neste trabalho, compósitos com níveis variáveis de aço inoxidável 316L e zircônia estabilizada com ítria, obtidos pelo processo de moagem de alta energia, foram preparados e caracterizados para determinar o comportamento térmico de cada composição, com o objetivo de planejar a sinterização dos MGFs com gradação de composição química. Difração de raios-x (DRX), análises de dilatometria e calorimetria exploratória diferencial (DSC) foram realizadas para os materiais compósitos com proporções diferentes de aço inoxidável e de zircônia, com o objetivo de analisar a influência da composição, como da taxa de aquecimento no comportamento dos compósitos selecionados durante a sinterização. Além disso, foram construídos por metalurgia do pó e caracterizados três peças de MGF. As peças de MGFs foram caracterizadas no microscópio óptico e microscópio eletrônico de varredura (MEV). Microanálise química foi feito pela técnica de espectroscopia de energia dispersiva (EDS) para o MGF1 e EDS - Line scan analysis das peças MGF2 e MGF3. Finalmente, as fases presentes nas peças foram medidas pela técnica de penetração Vickers. Os resultados dos ensaios dilatométricos para compósitos com teores de zircônia superiores a 50% e com taxas de aquecimento de 5ºC/min e 10ºC/min até 1200ºC, apresentaram uma contração linear maior em torno a 900ºC, e para composições com taxa de aquecimento de 15ºC/min em torno a 1000ºC, indicando que o processo de densificação se inicio a temperaturas inferiores que as outras composições observadas nas curvas dilatométricas para essas mesmas taxas de aquecimento. Os DSC dos compósitos apresentaram uma mudança correspondente à precipitação dos carbetos de cromo próprios do aço inox austenítico. A adição de zircônia ao aço inoxidável inibiu a precipitação dos carbetos, indicado pelo aparecimento de um pico nas amostras composta somente pelo aço inoxidável. / Functionally graded materials (FGM) based on stainless steel and ceramics has aroused interest in many technological areas: structural, thermal, electrical, biomedical and military, and has inspired researchers to combine properties and features which are not present in conventional samples, and is considered to be an alternative in the preparation of high efficient motors parts, cutting tools and structural coatings for chemical reactors. The incorporation of metal and ceramic in a graduated structure allows the integration of many desirable properties that combine advantages of metallic and ceramic materials. Ceramic components are capable of withstanding high temperatures and have high corrosion resistance, while the metallic components provide a higher mechanical resistance, in particular ultimate tensile strength and ductility, and therefore less susceptible to catastrophic fracture. In this work, composites with variable levels of 316L Stainless Steel and Yttria Stabilized Zirconia, obtained by high-energy milling process, were prepared and characterized, in order to determine the thermal behavior of each composition, with the aim of planning the sintering of a FGM with gradation of chemical composition. X-rays diffractometry (XRD), dilatometric analyses and differential scanning calorimetry (DSC) were performed for composites materials with distinct proportions of Stainless Steel and Zirconia, with the objective of analyzing the influence of the composition, as the heating rate the behavior of Stainless Steel/Zirconia layers during sintering. Additionally, were built by powder metallurgy and characterized three samples of FGM. The samples of MGFs were characterized in the optical microscope and scanning electron microscope (SEM). Chemical microanalysis was done by the technique of energy dispersive spectroscopy (EDS) of FGM1 and EDS-Line Scan Analysis of samples and FGM2 and FGM3. Finally, the phases present in the samples were measured by Vickers penetration technique. The results of dilatometric tests for composites with levels higher than zirconia to 50% and heating rates of 5°C/min and 10ºC/min up to 1200°C showed a greater linear shrinkage around 900ºC, and compositions at a heating rate of 15°C/min to about 1000°C, indicating that the densification process is starting at temperatures below that observed in other compositions dilatometric curves for these same heating rates. The DSC of the composites showed a change corresponding to the chrome carbides precipitation own austenitic stainless steel. The zirconia addition to stainless steel inhibited the carbides precipitation, indicated by the appearance of a peak in the samples composed only of stainless steel.

Nuclear plant stainless steel can become contaminated by radionuclides during normal operation whereby the final disposition of these materials then becomes a major decommissioning challenge to address. Characterisation of the chemical and metallurgical processes that underpin contamination is essential in consideration of developing cost effective decontamination and prevention methods, as are in situ measurement techniques that allow assessment of contamination. To address these issues, contamination experiments to simulate the nitric acid-based reprocessing streams of the PUREX (Plutonium Uranium Redox Extraction) process, and alkaline spent fuel storage ponds were investigated. Solution and surface spectroscopic measurements were performed to characterise the sorption behaviour of stable analogues of two high yield fission products, Sr-90 and Cs-137, on as received and 30 % cold rolled AISI Type 304 stainless steel, respectively. In addition Laser Induced Breakdown Spectroscopy (LIBS) was also investigated as a standoff contamination assessment technique. Fission product accumulation was modelled to a second order kinetic fit that considers chemisorption, typically to a hydrous metal oxide surface, as rate controlling. This process is observed to be independent of solution composition and strain processing regime. This behaviour reflects complexation to the passivating surface chromium oxide film, and as determined by depth elemental analysis, effectively inhibits contaminant migration into the bulk material. Environment chemistry and microstructural variables that destabilise the Cr-rich passive film however reduces the passive layer capabilities to effectively inhibit fission product bulk diffusion. The importance of corrosion phenomena towards radionuclide sorption processes necessitates the consideration of metallurgical and chemical factors during the implementation of decontamination approaches to treat affected plant material at nuclear licenced sites. LIBS was found to be a satisfactory technique for measurement of Sr sorbed to steel but Cs could not be detected at the concentrations used in this experimentation. Furthermore, EDX and TOF-SIMS elemental mapping indicated ablated material may be redistributed into the crater profile during elemental analysis. This process has clear implications for the deployment of LIBS for in situ characterisation of nuclear materials as the uncontrolled redistribution of radioactive material certainly violates decommissioning principles.

There is great interest in understanding the contamination of stainless steel by radionuclides across the nuclear fuel cycle. Through study of uptake mechanisms, contaminant localisation and process conditions that affect uptake, decontamination strategies can be tailored to remove built-up radioactive species. This study focusses on understanding stainless steel contamination by inactive lanthanides and radioactive actinide species (U, Np, Pu and Am) in acidic media. Through depth profiling, contamination has been seen to localise on the interface of the oxide layer and the bulk metal (at depths of up to 100 nm) indicating a potentially tenacious contamination mechanism. Furthermore, contaminant was observed at greater depths within the material (up to ~300 nm), suggesting penetration beyond the passive layer in to the bulk of the material. Long term immersion studies (up to 9 months) in 12 M HNO3 have also been undertaken to investigate the effect of surface corrosion on contaminant uptake. After 3 months the surface had undergone intergranular corrosion and grain droppage was observed. Further surface analysis revealed localisation of contaminants within the steel grain boundaries and vacancies. Once again, this may necessitate a more aggressive decontamination strategy. Conditions have been identified that enhance uptake of transuranic contaminants. Highest levels of uptake were seen in polished steel samples immersed in 4 M HNO3. The Np-237, Pu-239 and Am-241 contaminated samples showed surface concentrations of up to 1.2x107, 9.4x105 and 1x109 Bq/m2, respectively. In the case of Np contamination of stainless steel, microfocus X-ray absorption spectroscopy has shown the surface-mediated reduction of Np(V) leading to Np(IV) adsorption.

No description available.