Dissertations / Theses on the topic 'Corrosion'

En general, un material tenderá a corroerse espontáneamente en un determinado medio si los productos de corrosión son más estables que el material de partida, o si bajo las condiciones de exposición la corrosión resulta favorecida. En la práctica, lo que se busca es extender la vida útil de estructuras, equipos o dispositivos, es decir, mejorar su durabilidad.
In general, a material will tend to corrode in a specific environment when the corrosion products are more stable than the starting material or, when exposed to certain conditions, a corrosion process results favored. In general practice, the goal is to extend the service life of structures, equipment or devices, that is, to improve their durability.

Nenhuma
A liga 800GN (grau nuclear) é um material utilizado na fabricação de geradores de vapor para reatores de água pressurizada (PWR) de usinas nucleares devido à sua elevada resistência à corrosão. A resistência à corrosão da liga 800GN é devida ao caráter protetor da película de óxido formada na superfície do tubo em contato com a água pressurizada à alta temperatura. No entanto, a corrosão tem sido a principal causa de falhas nos tubos dos geradores de vapor de usinas nucleares. Os problemas gerados pela corrosão têm sido atribuídos a condições e excursões da química da água do circuito secundário, muitos dos quais resultantes da entrada de água de refrigeração do condensador no circuito secundário. A experiência adquirida em diferentes centrais nucleares mostra que a composição química da água tem um papel importante na manutenção da integridade da película protetora de óxido formada na superfície do tubo. Neste trabalho foi avaliada a resistência à corrosão por pites de tubos da liga 800GN, em meio similar ao do circuito secundário de um reator PWR contendo teores de contaminação por íons cloreto de 250 ppb, 1 ppm, 5 ppm, 10 ppm e 50 ppm. A susceptibilidade dos tubos de liga 800GN ao processo de corrosão por pites foi avaliada em célula eletroquímica à temperatura de 80 C e em autoclave à temperatura de 250 oC, empregando-se a técnica eletroquímica de polarização anódica potenciodinâmica cíclica. A observação da morfologia da superfície das amostras após os ensaios eletroquímicos foi realizada por meio de microscopia ótica e microscopia eletrônica por varredura e microanálise por EDS (Energy Dispersive Spectrometry). A 80 C, a liga 800GN apresentou resistência à corrosão por pites, mesmo quando concentrações 5 ppm de Cl- foram adicionadas ao meio similar ao do ambiente secundário de um reator PWR. Corrosão por pites foi observada somente com a adição de 10 e 50 ppm de Cl-. Os ensaios eletroquímicos a 250 C mostraram que na condição normal de operação de um reator PWR e com a adição de 250 ppb de íons cloreto a liga 800GN exibiu elevada resistência à corrosão por pites, não ocorrendo nenhuma modificação na superfície do material. No entanto, ficou evidenciado que com a adição de 1 ppm de cloreto ao meio PWR iniciou-se uma modificação no filme passivo formado na superfície da liga 800GN.

This study investigated the corrosion of an aluminum alloy with and without coatings under simulated corrosive environments. Coatings were selected and applied from commercial materials and techniques, consisting of microceramic, epoxy primer, and topcoat. The experiments for coated specimens were carried out under various corrosive conditions, specifically, hydrodynamic flow, immersion in salt water and DI water, varying temperatures, and simulated sun light. The hydrodynamic conditions were simulated using a rotating cylinder electrode (RCE) with rotational speeds of 200, 400, 600, 800, and 1000 rpm. The immersion in saltwater and sunlight illumination tests were applied for 8 hours, and the simulated exterior temperature variation were cycled for 7 days. Polarization techniques were used to study the corrosion mechanism and calculate the corrosion rate of coated specimens under simulated salt water. Microstructure of coated specimens were identified by using atomic force microscopy (AFM) and optical microscope (OM) analysis. Results indicated that corrosions in the simulated salt water were generally more serious than those in the distilled water. This was especially true for bare aluminum alloys, that its corrosion rates in the salt water exhibited two orders of magnitude higher than those in the DI water. The combination of an environmentally friendly electrodeposited ceramic coating with a primer and topcoat, which results in a chromium-free coating, exhibited a higher polarization resistance and a lower corrosion rate than the traditional chromate conversion coating combination. In addition, for all coated Al alloys, the corrosion rate increased with increasing rotation speed. For immersion portion, immersion in salt water accelerated the pitting corrosion process and increased the corrosion rate of the aluminum alloy five times higher as compared to the samples without immersion. For the varying temperature portion, the rates of corrosion nearly doubled for bare and ceramic coated Al alloy, under varying temperature conditions for 7 days. Besides, addition of ionic liquid inhibitors, such as BMIMBR and BEIMCl, exhibited great improvement of corrosion resistances of aluminum alloy in the salt water. The corrosion rates of aluminum in the presence of inhibitors were almost one order of magnitude lower than that in the absence of inhibitors.

O presente trabalho teve como objetivos determinar a resistência à corrosão e as propriedades mecânicas da liga Cu10Ni-3Al-1,3Fe, nas condições solubilizada e envelhecida a 550°C. Foi também objetivo do trabalho identificar a microestrutura nestas condições de tratamento térmico. As propriedades mecânicas foram avaliadas a partir de ensaios de tração e medidas de microdureza. Para caracterizar a resistência à corrosão e corrosão-erosão, foram realizados ensaios de polarização potenciodinâmica na condição estagnada e associada à erosão em 0,01M NaCl, 0,01M Na2SO4 e 0,0001M Na2S.9H2O. Para tanto, foi necessário elaborar a liga Cu10Ni-3Al-1,3Fe, por fundição em forno do tipo mufla. O lingote obtido foi solubilizado a 900ºC e laminado a frio. Posteriormente a chapa obtida foi novamente tratada a 900ºC por 1 h para garantir uma microestrutura homogênea de fase a. A partir desta chapa foram retiradas amostras para os tratamentos térmicos de envelhecimento por até 1.032 h a 550ºC. Os exames metalográficos mostraram intensa precipitação nas condições envelhecidas. Através dos ensaios de tração e medidas de microdureza, verificou-se que a presença dos precipitados melhora significativamente as propriedades mecânicas, sendo que os valores máximos de dureza, limite de escoamento e de resistência ocorrem para o tempo de 16 h de envelhecimento. Este efeito é decorrente de duas parcelas, uma dos precipitados intergranulares que se formam num processo de precipitação celular e a outra das partículas finamente dispersas (precipitados intragranulares). Em relação a resistência à corrosão, constatou-se que a liga, em todas as condições de tratamento térmico, apresenta um potencial de quebra (Eq) quando polarizada em eletrólitos que contém cloreto, sulfato ou sulfeto. Em 0,01M NaCl, o potencial Eq está relacionado com o processo de corrosão seletiva do níquel (desniquelação). Observou-se ainda que o envelhecimento provocou um aumento nos valores de Eq, sendo mais evidente para as amostras envelhecidas por 2 e 1.032 h. Nos ensaios de corrosão-erosão (realizados apenas nas condições solubilizada e envelhecida por 16 h), também ocorre o potencial Eq, mas os valores são mais baixos. Nestes casos foram observadas cavidades, que não estão relacionadas com o processo de corrosão seletiva, mas sim com o processo de erosão. Nos eletrólitos de 0,01M Na2SO4 e 0,0001M Na2S.9H2O o potencial Eq está relacionado com a formação de cavidades (pites), e não com o processo de corrosão seletiva. Nestes eletrólitos, não foi observada qualquer dependência entre Eq e o envelhecimento da liga, diferentemente do verificado em 0,01M NaCl, onde o envelhecimento proporcionou um efeito benéfico. Igualmente, não houve diferenças significativas nos valores de Eq quando o material foi submetido à corrosão-erosão.
The present work evaluated the corrosion resistance and mechanical properties of Cu10Ni-3Al-1.3Fe cupronickel alloy, in the solution-treated and 550°C aged conditions. It was also objective of the work to identify the microstructural changes in these conditions of aging treatment. Mechanical properties were evaluated through microhardness and tension tests; to evaluate the corrosion and corrosion-erosion resistance, potenciodynamic polarization tests were done in the stagnated condition and polarization associated to erosion in 0.01M NaCl, 0.01M Na2SO4 or 0.0001M Na2S.9H2O. The alloy had been casting and solution treated at 900°C, and after that cold rolled. From cold rolled sheet, specimens were solution treated at 900°C for 1 h, and aged at 550°C until 1,032 hours. The microstructural exams showed precipitation in the aged samples. The microhardness and tension tests showed that the presence of precipitates improve the mechanical properties, and the maximum value of hardness was obtained after 16 h of aging at 550°C. This effect is related to two microstructural aspects, one regarding intergranular precipitates that were formed by cellular precipitation and other related to the presence of finely dispersed intragranular precipitation. Concerning corrosion resistance, it was verified that the alloy, in all conditions, presented a break potential (Eq) when polarized in the tested solutions. In 0.01M NaCl, Eq is related with the process of selective corrosion of the nickel (denickelification). It was observed although that aging increased the values of Eq, being more evident for the aged samples for 2 and 1,032 h. The corrosion-erosion tests (just accomplished in the conditions solution-treated and aged by 16 h), also presented Eq, but the values were lower. In these cases cavities were observed, however not related to the process of selective corrosion, but to the erosion process. The tests in 0.01M Na2SO4 or 0.0001M Na2S.9H2O showed that Eq is related with the formation of cavities (pits), and not with the process of selective corrosion. In these solutions was not observed dependence between Eq and the aging time, differently of the verified in 0.01M NaCl, where the aging provided a beneficial effect. There were not significant differences in the values of Eq when the material was submitted to the corrosion-erosion in the solutions (0.01M Na2SO4 and 0.0001M Na2S.9H2O).

In a previous project, mobile exposures in road environments have been performed in various areas of the world. A number of materials and coatings have been attached under trailers which travels long distances in different types of road environments. One of the materials, zinc, demonstrated various corrosion rates in different parts of the world. In this investigation two various accelerated corrosion tests have been performed at the laboratory of Swerea Kimab in order to realize parameter influence on zinc. Even though the corrosion rates are known, the relation to formed corrosion products has not been investigated earlier. In the present study, corrosion products on zinc have been analyzed using XRD and FTIR. The results from analyses of formed corrosion products have been evaluated together with measured corrosion rates, both from the mobile exposure and the accelerated tests, in order to try to understand under what conditions certain corrosion products are formed and how it affects the corrosion rate. A cold humid climate was found to be the most corrosive. In these environments, de ‐icing salts are used which promotes formation of Simonkolleite and in a subsequent step; Gordaite (if there is a not negligible deposition rate of SO2/SO42‐) which is often observed as the end product in marine environments.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
O cromato à amplamente utilizado como inibidor de corrosÃo. No entanto, à altamente tÃxico e carcinogÃnico, o que tem levado pesquisadores a buscarem alternativas ecologicamente amigÃveis a este inibidor. Dentre estes, molibdato, tungstato, silicato e fosfato surgem como potenciais candidatos por apresentarem propriedades inibidoras e serem atÃxicos. Assim, este trabalho tem por objetivo desenvolver um estudo sistemÃtico dos Ãons como inibidores da corrosÃo do Zn. Foram utilizadas soluÃÃes aquosas de NaCl 10-1 mol dm-3 com concentraÃÃes dos inibidores variando de 10-4 a 10-1 mol dm-3 . A eficiÃncia destes com relaÃÃo à corrosÃo do Zn foi avaliada empregando-se medidas do potencial a circuito aberto, curvas de polarizaÃÃo potenciodinÃmica e espectroscopia de impedÃncia eletroquÃmica. As tÃcnicas de Microscopia EletrÃnica de Varredura (MEV), Energia Dispersiva de Raios-X (EDX), DifraÃÃo de Raios-X (DRX) e Espectroscopia FotoeletrÃnica de Raios-X (XPS) foram usadas para caracterizar o Zn apÃs os ensaios de corrosÃo. Todos os Ãnions estudados inibiram a corrosÃo do Zn. Com as tÃcnicas de caracterizaÃÃo foi possÃvel identificar a presenÃa de filmes superficiais de silicato, tungstato, molibdato e fosfato na superfÃcie do Zn apÃs os ensaios de corrosÃo nas respectivas soluÃÃes contendo os inibidores
The chromate is widely used as a corrosion inhibitor. However, it is highly toxic and carcinogenic, which has done researchers to study environmentally friendly alternatives to this inhibitor. Among these, molybdate, tungstate, silicate and phosphate anions appear as potential candidates because they are non toxic. Thus, this work aims to develop a systematic study to investigate molybdate, tungstate, silicate and phosphate as corrosion inhibitors of zinc. Aqueous solutions of 10-1 mol dm-3 NaCl were used and the concentrations of the inhibitors ranging from 10-4 to 10-1 mol dm-3. The corrosion studies were carried out by open circuit potential measurements, potentiodynamic linear polarization and electrochemical impedance spectroscopy. The Scanning Electron Microscopy (SEM), X-Ray Dispersive Energy (XDE), X-Ray diffraction (XRD) and X-Ray Photoelectronic Spectroscopy (XPS) techniques were used to characterize the Zn after the corrosion tests. All the studied anions inhibited the zinc corrosion. The characterization techniques made possible to detect the presence of molybdate, silicate, tungstate and phosphate on the zn surface after the corrosion tests in the solution containing the corresponding inhibitors

Nous avons étudié la corrosion de l'alliage de magnésium AM60 d'un point de vue microstructural et à l'aide de méthodes électrochimiques, dans une solution saturée de magnésie, et en milieu chlorure de sodium. Pour limiter la corrosion de l'alliage AM60 ou pour améliorer l'adhérence des revêtements rganiques, nous avons étudié deux traitements de surface. Le premier, à base de fluorure de irconium ou de titane entraîne la formation d'un film par réaction acide-base à l'interface métal-électrolyte. La structure et la composition du film obtenu ont été analysées par Microscopie Electronique à Balayage (MEB) ainsi que par Spectroscopie de Photo-électrons X (XPS). Ce traitement de surface ne protège pas l'alliage AM60 de la corrosion. Un second traitement de surface par anodisation plasma a été développé. Nous avons étudié a formation du film ainsi que sa structure et sa composition (MEB, Diffraction des rayons X). La résistance à la corrosion est faiblement améliorée par ce traitement.

Since the introduction of medical implants into human bodies, corrosion and wear have been regarded as key issues for their long-term durability. There has been a recent renewed interest in the use of large diameter metal-on-metal (MoM) hips, primarily because of the reduced volumetric wear compared with the wellestablished polyethylene-on-metal joints. Long term durability of MoM joints relies on control of both their corrosion resistance (relating to ion release) and wear behaviour (relating to creation of nanometre-scale wear debris). Concerns about the potential risk of released metal ions to the biological environment (patient) are of great importance. In this respect tribocorrosion is a serious consideration in joint performance. An integrated electrochemical cell on a reciprocating tribo-meter was employed to evaluate the corrosion and tribocorrosion behaviour in a protein rich solution (Bovine Serum), a cell culture solution (DMEM) and a saline solution (NaCI) with the attempt to isolate the organic species effects. Three commonly used orthopaedic materials were involved in this study. A High Carbon Cobalt-Chromium-Molybdenum alloy, a Low Carbon Cobalt-Chromium-Molybdenum and UNS S31603 Stainless Steel (316L). A range of electrochemical methods were used in the assessment of materials under biotribocorrosion systems and results were supported by surface analysis and bulk solution analysis techniques. The material degradation rate is strongly dependent upon the charge transfer (corrosion), the mechanical damage (tribology) and also their interactions (tribocorrosion) in these simulated biological environments.

The overall aims of this thesis were to conduct a broad survey of possible organic corrosion inhibitors in near-neutral chloride solutions and to elucidate the mechanisms of such action. Altogether, 130 organic compounds were studied as possible corrosion inhibitors for pure iron, mild steel, copper and aluminium in aerated near-neutral (pH = 8.4) solutions containing 500 ppm NaCl and 100 ppm NaHCO, conditions often encountered in water-based automotive engine coolants. Inhibitor behaviour was investigated using steady-state electrochemical techniques including polarisation curves, Stern-Geary and corrosion potential (Em,) measurements. The organic compounds examined were found to be highly specific in their inhibitive action toward the metals studied. Typical examples of highly effective corrosion inhibitors were: sebacate and octanoate for pure iron; oleate and sebacate for mild steel; benzotriazole and 2-mercaptobenzothiazole for copper; and laurate and oleate for aluminium. E, was found to provide a rapid and convenient screening test for evaluating the inhibitor performance of organic compounds toward pure iron, mild steel and aluminium but was less useful for copper. Good organic inhibitors were found to act as anodic inhibitors toward pure iron and mild steel but as anodic or mixed-type inhibitors toward copper. For aluminium, the majority of the compounds studied were found to act as anodic inhibitors. However,However, it was also found that only pit initiation was inhibited, i.e. existing pits were not prevented from developing. Optical microscopy of pitted aluminium surfaces indicated their nature varied considerably with inhibition efficiency. The role of complex formation in organic corrosion inhibitors was found to vary with the metal. Complexation of either iron(I1) or iron(II1) ions was found to have an insignificant effect on mild steel. The corrosion rate of copper was found to increase with the copper(LI) complex stability, thus indicating complex formation to be the rate-determining step. For aluminium, the observed effects were found to depend on complex stability. For weak to moderate complexants, inhibitor efficiency (measured as E,,) increased with increasing complexation. However, very strong complexing agents were sufficiently stable to dissolve the aluminium oxide surface, leading to poor inhibition. Aluminium pit morphology was found, using scanning electron microscopy, to change from hemispherical in the uninhibited solution to irregular in the presence of complexing inhibitors. No simple relationships between inhibitor efficiency and molecular structure were found. However, carbon chain length, the nature of functional group(s) and their location in the molecule were found to be important but varied according to the metal. The inhibiting ability of sebacate (a straight chain C, dicarboxylate) was found not to be compromised by water movement (stirring) or pre-existing corrosion product layers. Immersion tests showed that passive film formation on mild steel in sebacate solution involved two stages and was complete only after -100 h immersion. The ion selective properties of several iron(II1) carboxylates and hydrated iron(II1) oxide films were studied by membrane potential measurements in neutral sodium chloride solutions. Some specimens were also studied by Mossbauer spectroscopy. These results show that dicarboxylates are good inhibitors toward mild steel because they form impermeable films. Poor inhibitor performance is associated with the anion selectivity of the film which in turn appears to be related to the film purity. A model is suggested for the inhibition mechanism of mild steel corrosion by dicarboxylates in aerated near-neutral chloride solutions.

The overall aims of this thesis were to conduct a broad survey of possible organic corrosion inhibitors in near-neutral chloride solutions and to elucidate the mechanisms of such action. Altogether, 130 organic compounds were studied as possible corrosion inhibitors for pure iron, mild steel, copper and aluminium in aerated near-neutral (pH = 8.4) solutions containing 500 ppm NaCl and 100 ppm NaHCO,, conditions often encountered in water-based automotive engine coolants. Inhibitor behaviour was investigated using steady-state electrochemical techniques including polarisation curves, Stern-Geary and corrosion potential (Em,) measurements. The organic compounds examined were found to be highly specific in their inhibitive action toward the metals studied. Typical examples of highly effective corrosion inhibitors were: sebacate and octanoate for pure iron; oleate and sebacate for mild steel; benzotriazole and 2-mercaptobenzothiazole for copper; and laurate and oleate for aluminium. E, was found to provide a rapid and convenient screening test for evaluating the inhibitor performance of organic compounds toward pure iron, mild steel and aluminium but was less useful for copper. Good organic inhibitors were found to act as anodic inhibitors toward pure iron and mild steel but as anodic or mixed-type inhibitors toward copper. For aluminium, the majority of the compounds studied were found to act as anodic inhibitors. However,However, it was also found that only pit initiation was inhibited, i.e. existing pits were not prevented from developing. Optical microscopy of pitted aluminium surfaces indicated their nature varied considerably with inhibition efficiency. The role of complex formation in organic corrosion inhibitors was found to vary with the metal. Complexation of either iron(I1) or iron(II1) ions was found to have an insignificant effect on mild steel. The corrosion rate of copper was found to increase with the copper(LI) complex stability, thus indicating complex formation to be the rate-determining step. For aluminium, the observed effects were found to depend on complex stability. For weak to moderate complexants, inhibitor efficiency (measured as E,,) increased with increasing complexation. However, very strong complexing agents were sufficiently stable to dissolve the aluminium oxide surface, leading to poor inhibition. Aluminium pit morphology was found, using scanning electron microscopy, to change from hemispherical in the uninhibited solution to irregular in the presence of complexing inhibitors. No simple relationships between inhibitor efficiency and molecular structure were found. However, carbon chain length, the nature of functional group(s) and their location in the molecule were found to be important but varied according to the metal. The inhibiting ability of sebacate (a straight chain C, dicarboxylate) was found not to be compromised by water movement (stirring) or pre-existing corrosion product layers. Immersion tests showed that passive film formation on mild steel in sebacate solution involved two stages and was complete only after -100 h immersion. The ion selective properties of several iron(II1) carboxylates and hydrated iron(II1) oxide films were studied by membrane potential measurements in neutral sodium chloride solutions. Some specimens were also studied by Mossbauer spectroscopy. These results show that dicarboxylates are good inhibitors toward mild steel because they form impermeable films. Poor inhibitor performance is associated with the anion selectivity of the film which in turn appears to be related to the film purity. A model is suggested for the inhibition mechanism of mild steel corrosion by dicarboxylates in aerated near-neutral chloride solutions.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Neste trabalho foi realizado o estudo da fragilização pelo hidrogênio em um tubo de aço API 5L X65 de alto grau de limpidez para uso em dutos de condução para aplicação em ambientes que contém gás sulfídrico. Ensaios normalizados foram realizados com o objetivo de caracterizar as propriedades do material em estudo, através de análise química, análise microestrutural, ensaios mecânicos - dureza, tração, impacto e drop weight (DWTT), ensaios de corrosão - ensaios de HIC e SSC - e ensaios eletroquímicos - curvas de polarização potenciodinâmica, voltametria cíclica e medições de corrente de permeação de hidrogênio. Os resultados apresentaram: a) microestrutura refinada predominante de ferrita acicular, b) caracterização mecânica com resultados dentro do especificado pela norma de fabricação, c) análise química e ensaios de corrosão com resultados superando os requisitos da norma de fabricação e d) nos ensaios eletroquímicos foi evidenciado que o aço em estudo apresentou uma baixa corrente de permeação e uma maior resistência à corrosão em meio de NaCl 3,5% em relação a um aço padrão. Os resultados indicam que o material em estudo atende os critérios da norma de fabricação do tubo (API 5L), sendo evidenciado que o mesmo é adequado para utilização ao ambiente que lhe é proposto
In this paper, it was carried out a study of a hydrogen embrittlement in a pipe API 5L X65 with high level of cleanness for linepipe used in sour service environment.. It was performed standardized testing in order to perform an assessment of the material properties, through the chemical analysis and microstructural analysis, mechanical tests – hardness, tensile, impact and drop weight tear test (DWTT), corrosion tests - HIC and SSC tests - and electrochemical tests - potentiodynamic polarization curves, cyclic voltammetry and hydrogen permeation current measurements. The results presented: a) refined microstructure predominant of acicular ferrite, b) mechanical characterization with results that fulfilled with the pipe fabrication standard, c) chemical analysis and corrosion tests with results exceeding the requirements of the standard and d) electrochemical tests showing the studied steel presenting a low permeation current and a higher corrosion resistance in a environment of NaCl 3,5% in relation of standard steel. The results indicate that the studied material complies with the acceptance criteria of the pipe fabrication standard (API 5L), and it was evidenced that the material is suitable for use in sour service environment

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)
Este trabalho consistiu de um estudo da resistência à corrosão relativa de um amálgama dentário comercial e de suas principais fases constituintes, pelo uso de técnicas eletroquímicas, em meio salino e aerado que simula a agressividade do ambiente bucal. Os amálgamas dentários são formados pela reação do mercúrio com uma liga original em pó que contém predominantemente Ag, Sn e Cu, podendo também conter Zn ou outros elementos em menores proporções, resultando numa estrutura metalúrgica complexa e multifásica, com a presença das seguintes fases: γ1-Ag2Hg3 - matriz; γ-Ag3Sn - a segunda fase mais proeminente na microestrutura dos amálgamas dentários; γ2-Sn7-8Hg - a mais suscetível à corrosão dentre todas aquelas que compõem a microestrutura dos amálgamas dentários, de acordo com a literatura especializada; a composição eutética Ag-Cu (72%Ag, 28%Cu) - um componente adicionado às ligas mais modernas com o objetivo de reduzir a quantidade de γ2-Sn7Hg formada durante a reação de amalgamação e, neste sentido, aumentar a resistência à corrosão no meio bucal; e as fases do sistema Cu-Sn, ε-Cu3Sn e η'-Cu6Sn5 presentes em menor quantidade. Dada a natureza multifásica da microestrutura de amálgamas dentários, para este estudo foram elaboradas ligas metálicas binárias com composições químicas correspondentes às fases presentes em sua microestrutura. As ligas que contêem mercúrio, γ1-Ag2Hg3 e γ2- Sn7Hg, foram preparadas de acordo com as normas contidas na Especificação n. 1 para amálgamas dentários, da Associação Dentária Americana (ADA). As demais, correspondentes aos sistemas Ag-Cu, Ag-Sn e Cu-Sn foram preparadas pelos processos metalúrgicos convencionais de fundição, com o propósito de se reproduzir as principais fases que podem estar presentes na estrutura metalúrgica dos amálgamas...
Dental amalgams are formed by the reaction of mercury with a powder alloy containing mainly Ag, Sn, Cu and Zn, and have a complex metallurgical structure which can contain up to six phases. Their observed corrosion is thus a complex process, which involves contributions from each of the phases present as well as intergranular corrosion. It is thus of interest to investigate the corrosion of individual phases present in dental amalgams. Some of the products of the reaction are particles of the original alloy which did not react during the amalgamation process such as, γ-Ag3Sn and the Ag-Cu eutectic. Other products are the γ- phase of the silver-mercury system, designated γ1-Ag2Hg3, the γ-phase of the tin-mercury system, designated γ2-Sn7-8Hg, and intermetallic compounds of the tin-copper system, ε-Cu3Sn and η'-Cu6Sn5. The purpose of this work was to evaluate the corrosion resistance of the phase components of dental amalgams: the matrix phase of the microstructure, γ1-Ag2Hg3; the second more prominent, γ-Ag3Sn; the phase most susceptible to corrosion in the oral cavity, according to the literature, γ2-Sn7Hg; and spherical particles of the Ag-Cu eutectic (72% Ag, 28% Cu), a component of the more modern powder alloys, the objective being to reduce the quantity of γ2-Sn7Hg formed during the amalgam reaction and in this way increase its corrosion resistance. The Ag-Hg and Sn-Hg alloys were made in the correct stoichiometric proportions, taking into account the phase diagrams, by mechanical amalgamation and moulding under high pressure following the criteria adopted by the American Dental Association, Specification No. 1. The commercial dental amalgam employed in this study was Dispersalloy, a copper enriched alloy, type blended. The Ag-Sn, Ag-Cu and Cu-Sn alloys were prepared by heating the components until they were completely melted, and then the melt was poured into a mould...(Complete abstract click electronic access below)

The work in this thesis concerns the behaviour of cutting fluids used for drilling aluminium. A cutting fluid which is useful must neither corrode nor stain aluminum unduly. The compositional factors which lead to a successful cutting fluid have been investigated using electrochenucal techniques. Linear sweep and impedance measurements were used to assess the corrosion of pure alummium and aluminium alloys in contact with aqueous solutions in the pH range 8-11 , in the presence and absence of oxygen. It was found that a low corrosion rate required that the solution pH was kept lower than 9.5. Clear and stable cutting fluids were formulated with and without the use of amines and the corrosion of aluminium in contact with these cutting fluid emulsions was studied. The corrosion rate of aluminium was found to be a factor of ten times lower when in contact with a typical emulsion compared to contact with an aqueous borax solution of the same pH. The most important factor in respect of corrosion control was the pH. The presence/absence of amines did not significantly affect the corrosion rates. In order to simulate the drilling process,a glass cell was designed with a glass frit situated at the base onto which an aluminium rotating disc electrode was lowered, and electrochemical measurements were made, in situ in this way. Abrasion of the electrode caused the anodic process on the metal to be affected to a greater extent than the cathodic process. The electrochemical techniques used in this work have readily allowed us to assess the suitability of different cutting fluid formulations.

Includes bibliographical references.
Reinforcement corrosion in concrete has presented engineers with the challenge of finding ways of prolonging the service life of structures built in aggressive environments. One method of increasing the durability of concrete in aggressive environments is the use of corrosion inhibitors. In this work, two organic corrosion inhibitors were tested to observe their effectiveness in decreasing the rate of corrosion or delaying the onset of corrosion. One of the inhibitors was a migrating corrosion inhibitor while the other was an admixed inhibitor. The corrosion rate of reinforcement in concrete specimens used in this evaluation, was measured using the Linear Polarisation Resistance method. The performance of the admixed inhibitor was also measured in aqueous phase tests. Results of the tests conducted indicate that the admixed inhibitor does delay the onset of corrosion. The Mel caused short to medium term inhibition when the chloride concentration was less than 1.5%.

[ES] En los últimos años, se han desarrollado numerosos tipos de recubrimientos superficiales frente a la corrosión basados especialmente en aleaciones de cinc-aluminio-magnesio (conocidas como aleaciones "ZM"), como alternativas a los recubrimientos tradicionales basados en cinc (conocidos como "Z"), con el fin de mejorar sus características técnicas y reducir su coste. Los fabricantes de estos nuevos tratamientos reivindican una mayor resistencia a la corrosión, basándose en ensayos de corrosión acelerada y ensayos de campo, estos últimos de muy pocos años de duración. La presente tesis, tiene como principal objetivo la estructuración y análisis de toda la información existente en el actual estado de la técnica, y en particular, el estudio de los ensayos de campo existentes para corroborar su resistencia a la corrosión en distintos tipos de ambientes y a partir de ello, proponer un modelo matemático que facilite su cálculo a largo plazo. Se presenta una revisión del estado de la técnica de recubrimientos metálicos basados en aleaciones ZM, que cubre su evolución en el tiempo, las diferentes calidades y designaciones existentes en el mercado, su estructura y composición, normas internacionales que los regulan y una detallada investigación sobre ensayos de campo en localizaciones de todo el mundo, habiéndose encontrado ensayos de una duración máxima de 6 años. A partir del análisis de estos ensayos de campo, se propone una Metodología para verificar el rendimiento y la evolución de la función corrosión-tiempo, en los diferentes ambientes de exposición, categorizados a través de la norma internacional ISO 9223 (ISO, 2012), que los denomina "categorías de corrosividad", y que abarcan desde C1 (muy bajo) hasta CX (extremo). Este análisis ha clasificado todos los resultados de los ensayos por material, categoría de corrosividad y evolución a lo largo del tiempo. De esta forma, cada categoría de corrosividad ha sido investigada en profundidad, mediante un análisis estadístico, poniendo especial énfasis en la corrosión anual, medida como pérdida de masa (µm / año), la función corrosión-tiempo y su ajuste a un determinado comportamiento. Se han analizado asimismo los recubrimientos Z con el fin de poder comparar ambas alternativas y corroborar la hipótesis de partida, cuyo supuesto principal es la mayor resistencia a la corrosión de las aleaciones ZM frente a los recubrimientos Z. Este análisis ha sido el punto de entrada, para establecer un modelo matemático que determine el rendimiento de la corrosión a largo plazo, con el fin de proporcionar a los profesionales de proyectos en la ingeniería, una herramienta que permita estimar la resistencia a la corrosión y la optimización del coste de una instalación cuando se utilizan diferentes tipos de materiales. El compendio de todo este análisis se ha reflejado en el apartado de Resultados y comentarios. La referida metodología, se ha aplicado a un caso de estudio para mostrar cómo seleccionar la calidad del recubrimiento y su espesor óptimo, así como un cálculo de costes, con el objetivo de garantizar los requisitos de un determinado proyecto, en términos de resistencia a la corrosión y coste. Las conclusiones finales ponen de manifiesto que existen algunas ventajas de las aleaciones ZM frente a recubrimientos Z, principalmente en lo que respecta a la resistencia a la corrosión, al haber encontrado relaciones que pueden duplicar y triplicar su rendimiento, en los períodos para los que hay datos disponibles. Del mismo modo, se han encontrado algunas desventajas, que deben investigarse más a fondo en futuros trabajos de investigación, para dar continuidad a esta tesis. Por ejemplo, la limitación de estos recubrimientos para lograr grandes espesores, la limitada duración de los ensayos de campo, el rendimiento en partes específicas de los componentes (cortes, embuticiones, doblados, soldaduras...), etc.
[CA] En els últims anys, s'han desenvolupat nombrosos tipus de recobriments superficials enfront de la corrosió basats especialment en aliatges de zinc-alumini-magnesi (conegudes com a aliatges "ZM"), com a alternatives als recobriments tradicionals basats en zinc (coneguts com a "Z"), amb la finalitat de millorar les seues característiques tècniques i reduir el seu cost. Els fabricants d'aquests nous tractaments reivindiquen una major resistència a la corrosió, basant-se en assajos de corrosió accelerada i assajos de camp, aquests últims de molt pocs anys de duració. La present tesi, té com a principal objectiu l'estructuració i anàlisi de tota la informació existent en l'actual estat de la tècnica, i en particular, l'estudi dels assajos de camp existents per a corroborar la seua resistència a la corrosió en diferents tipus d'ambients i a partir d'això, proposar un model matemàtic que facilite el seu càlcul a llarg termini. Es presenta una revisió de l'estat de la tècnica de recobriments metàl·lics basats en aliatges ZM, que cobreix la seua evolució en el temps, les diferents qualitats i designacions existents en el mercat, la seua estructura i composició, normes internacionals que els regulen i una detallada investigació sobre assajos de camp en localitzacions de tot el món, havent-se trobat assajos d'una duració màxima de 6 anys. A partir de l'anàlisi d'aquests assajos de camp, es proposa una metodologia per a verificar el rendiment i l'evolució de la funció corrosió-temps, en els diferents ambients d'exposició, categoritzats a través de la norma internacional ISO 9223 (ISO, 2012), que els denomina "categories de corrosivitat", i que abasten des de C1 (molt baix) fins a CX (extrem). Aquesta anàlisi ha classificat tots els resultats dels assajos per material, categoria de corrosivitat i evolució al llarg del temps. D'aquesta manera, cada categoria de corrosivitat ha sigut investigada en profunditat, mitjançant una anàlisi estadística, posant especial èmfasi en la corrosió anual, mesura com a pèrdua de massa (µm / any), la funció corrosió-temps i el seu ajust a un determinat comportament. S'han analitzat així mateix els recobriments Z amb la finalitat de poder comparar totes dues alternatives i corroborar la hipòtesi de partida, el supòsit principal de la qual és la major resistència a la corrosió dels aliatges ZM enfront dels recobriments Z. Aquesta anàlisi ha sigut el punt d'entrada, per a establir un model matemàtic que determine el rendiment de la corrosió a llarg termini, amb la finalitat de proporcionar als professionals de projectes en l'enginyeria, una eina que permeta estimar la resistència a la corrosió i l'optimització del cost d'una instal·lació quan s'utilitzen diferents tipus de materials. El compendi de tota aquesta anàlisi s'ha reflectit en l'apartat de Resultats i comentaris. La referida metodologia, s'ha aplicat a un cas d'estudi per a mostrar com seleccionar la qualitat del recobriment i la seua grossària òptima, així com un càlcul de costos, amb l'objectiu de garantir els requisits d'un determinat projecte, en termes de resistència a la corrosió i cost. Les conclusions finals posen de manifest que existeixen alguns avantatges dels aliatges ZM enfront de recobriments Z, principalment pel que fa a la resistència a la corrosió, en haver trobat relacions que poden duplicar i triplicar el seu rendiment, en els períodes per als quals hi ha dades disponibles. De la mateixa manera, s'han trobat alguns desavantatges, que han d'investigar-se més a fons en futurs treballs de recerca, per a donar continuïtat a aquesta tesi. Per exemple, la limitació d'aquests recobriments per a aconseguir grans grossàries, la limitada duració dels assajos de camp, el rendiment en parts específiques dels components (talls, embuticions, doblegats, soldadures...), etc.
[EN] In recent years, numerous types of surface corrosion coatings, based especially on zinc-aluminium-magnesium alloys (known as "ZM" alloys), have been developed as alternatives to traditional zinc-based coatings (known as "Z"), to improve its technical characteristics and reduce its cost. The manufacturers of these new treatments claim greater resistance to corrosion, based on accelerated corrosion tests and field tests, the latter lasting only a few years. The main objective of this thesis is the structuring and analysis of all the existing information in the current state of the art, and in particular, the study of the existing field tests to corroborate their resistance to corrosion in different types of environments and based on this, propose a mathematical model that facilitates its long-term calculation. A review of the state of the art of metal coatings based on ZM alloys is presented, which covers their evolution over time, the different qualities and designations existing in the market, their structure and composition, international standards that regulate them and a detailed research on field tests in different locations around the world, having found tests of a maximum duration of 6 years. From the analysis of these field tests, a methodology is proposed to verify the performance and evolution of the corrosion-time function in the different exposure environments, categorized through the international standard ISO 9223 (ISO, 2012), which calls them "corrosivity classes", and which range is from C1 (very low) to CX (extreme). This analysis has classified all the test results by material, corrosivity class and evolution over time. In this way, each corrosivity class has been investigated in depth, through statistical analysis, with special emphasis on annual corrosion, measured as mass loss (µm / year), the corrosion-time function and its adjustment to a certain behaviour. The Z coatings have also been analysed to be able to compare both alternatives and corroborate the main hypothesis, whose main assumption is the greater resistance to corrosion of ZM alloys compared to Z coatings. This analysis has been the entry point to establish a mathematical model that determines the long-term corrosion performance, to provide project engineering professionals, with a tool to estimate the corrosion resistance and optimize the cost of an installation when different types of materials are used. The summary of all this analysis has been reflected in the Results and discussion section. The referred methodology has been applied to a case study to show how to select the quality of the coating and its optimal thickness, as well as a cost calculation, in order to guarantee the requirements of a specific project, in terms of resistance to corrosion and cost. The final conclusions show that there are some advantages of ZM alloys over Z coatings, mainly with regard to corrosion resistance, having found relationships that can double and triple their performance, in the periods for which there are data available. In the same way, some disadvantages have been found, which must be investigated further in future research works, to give continuity to this thesis. For example, the limitation of these coatings to achieve large thicknesses, the limited duration of field tests, the performance of specific parts of the components (cuts, embossments, bends, welds ...), etc.
Chenoll Mora, E. (2021). Analysis of metallic coatings based in zinc-aluminium-magnesium alloys, in terms of performance and long-term corrosion. Case study: Electrical cable trays selection in project design [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/167418
TESIS

Doutoramento em Ciência e Engenharia de Materiais
A indústria aeronáutica utiliza ligas de alumínio de alta resistência para o fabrico dos elementos estruturais dos aviões. As ligas usadas possuem excelentes propriedades mecânicas mas apresentam simultaneamente uma grande tendência para a corrosão. Por esta razão essas ligas necessitam de protecção anticorrosiva eficaz para poderem ser utilizadas com segurança. Até à data, os sistemas anticorrosivos mais eficazes para ligas de alumínio contêm crómio hexavalente na sua composição, sejam pré-tratamentos, camadas de conversão ou pigmentos anticorrosivos. O reconhecimento dos efeitos carcinogénicos do crómio hexavalente levou ao aparecimento de legislação banindo o uso desta forma de crómio pela indústria. Esta decisão trouxe a necessidade de encontrar alternativas ambientalmente inócuas mas igualmente eficazes. O principal objectivo do presente trabalho é o desenvolvimento de prétratamentos anticorrosivos activos para a liga de alumínio 2024, baseados em revestimentos híbridos produzidos pelo método sol-gel. Estes revestimentos deverão possuir boa aderência ao substrato metálico, boas propriedades barreira e capacidade anticorrosiva activa. A protecção activa pode ser alcançada através da incorporação de inibidores anticorrosivos no prétratamento. O objectivo foi atingido através de uma sucessão de etapas. Primeiro investigou-se em detalhe a corrosão localizada (por picada) da liga de alumínio 2024. Os resultados obtidos permitiram uma melhor compreensão da susceptibilidade desta liga a processos de corrosão localizada. Estudaram-se também vários possíveis inibidores de corrosão usando técnicas electroquímicas e microestruturais. Numa segunda etapa desenvolveram-se revestimentos anticorrosivos híbridos orgânico-inorgânico baseados no método sol-gel. Compostos derivados de titania e zirconia foram combinados com siloxanos organofuncionais a fim de obter-se boa aderência entre o revestimento e o substrato metálico assim como boas propriedades barreira. Testes industriais mostraram que estes novos revestimentos são compatíveis com os esquemas de pintura convencionais actualmente em uso. A estabilidade e o prazo de validade das formulações foram optimizados modificando a temperatura de armazenamento e a quantidade de água usada durante a síntese. As formulações sol-gel foram dopadas com os inibidores seleccionados durante a primeira etapa e as propriedades anticorrosivas passivas e activas dos revestimentos obtidos foram estudadas numa terceira etapa do trabalho. Os resultados comprovam a influência dos inibidores nas propriedades anticorrosivas dos revestimentos sol-gel. Em alguns casos a acção activa dos inibidores combinou-se com a protecção passiva dada pelo revestimento mas noutros casos terá ocorrido interacção química entre o inibidor e a matriz de sol-gel, de onde resultou a perda de propriedades protectoras do sistema combinado. Atendendo aos problemas provocados pela adição directa dos inibidores na formulação sol-gel procurou-se, numa quarta etapa, formas alternativas de incorporação. Na primeira, produziu-se uma camada de titania nanoporosa na superfície da liga metálica que serviu de reservatório para os inibidores. O revestimento sol-gel foi aplicado por cima da camada nanoporosa. Os inibidores armazenados nos poros actuam quando o substrato fica exposto ao ambiente agressivo. Numa segunda, os inibidores foram armazenados em nano-reservatórios de sílica ou em nanoargilas (halloysite), os quais foram revestidos por polielectrólitos montados camada a camada. A terceira alternativa consistiu no uso de nano-fios de molibdato de cério amorfo como inibidores anticorrosivos nanoparticulados. Os nano-reservatórios foram incorporados durante a síntese do sol-gel. Qualquer das abordagens permitiu eliminar o efeito negativo do inibidor sobre a estabilidade da matriz do sol-gel. Os revestimentos sol-gel desenvolvidos neste trabalho apresentaram protecção anticorrosiva activa e capacidade de auto-reparação. Os resultados obtidos mostraram o elevado potencial destes revestimentos para a protecção anticorrosiva da liga de alumínio 2024.
The aerospace industry employs high strength aluminum alloys as a constructional material for aircrafts. Aluminum alloys possess advanced mechanical requirements, though suffer from corrosion. Therefore, corrosion protection is always used for aluminum alloys. Up to now the most effective corrosion protection systems include chromium (VI) as the main constituent of pretreatments and corrosion inhibitive pigments. However, the chromates are strongly carcinogenic and the present health regulations banned the use of Cr (VI) containing materials in industry. Consequently, there is a need for environmentally safe corrosion protection systems. The main objective of the present work is the development of active anticorrosion pre-treatments for 2024 aluminum alloy on the basis of hybrid sol-gel layers. The effective corrosion pre-treatment should confer adequate adhesion together with good barrier properties and active corrosion protection ability. The active corrosion protection can be achieved by introducing the corrosion inhibitors in the pre-treatment. Successful fulfilment of the main objective required accomplishing of different stages of the work. At first the localized corrosion of AA2024 was investigated in detail. The obtained results provide better understanding of the intimate aspects of the corrosion susceptibility of AA2024. Different prospective corrosion inhibitors were investigated using electrochemical and microstructural methods. At the second stage the development of hybrid sol-gel coatings was performed. Titania and zirconia based derivatives were combined with organofunctional silanes in order to provide the enhanced adhesion between the metal and the coating and to confer good barrier properties. Industrial tests show that the developed sol-gel coatings are compatible with common organic protection systems. The stability and life time of the sol-gel formulations were also optimized by changing the storage temperature and the amount of water during the synthesis. Sol-gel systems were doped with the selected corrosion inhibitors and studied from the point of view of passive and active corrosion protective properties at the third stage of the work. The results demonstrate the influence of the inhibitive additives on the corrosion performance of the sol-gel coatings. Some inhibitors can provide active corrosion protection in combination with the sol-gel coating, but some chemically interact with the sol-gel matrix resulting in failure of the protective properties of coatings. New approaches of inhibitor incorporation and delivery were used in the fourth stage of the work due to problems associated with the direct introduction of inhibitors in the sol-gels. A nanoporous titania-based pre-layer applied directly to the alloy was employed for storage and release of inhibitors. Nanocontainers of corrosion inhibitors based on silica and halloysite nanoclay with Layer-by- Layer assembled polyelectrolyte shells were used in the second approach. Amorphous cerium molybdate nanowires have been used as corrosion inhibitor nanoparticles in the third approach. During the sol-gel synthesis these nanocontainers were added to impart active corrosion protective properties of the sol-gel coatings. Using these approaches the negative effect of inhibitor on the sol-gel matrix stability was eliminated. The developed sol-gel pretreatments demonstrate important active corrosion protection and self-healing ability. The obtained results show high potential of the developed hybrid sol-gel pretreatment doped with corrosion inhibitors for the corrosion protection of AA2024.
FCT; FSE - SFRH/BD/25469/2005

As the UH-1 aircraft continue to age, there is growing concern for their structural integrity. With corrosion damage becoming a bigger part of the sustainment picture with increasing maintenance burden and cost, it is becoming increasingly important for corrosion management to be updated with more advanced techniques. The current find-and-fix technique for handling corrosion has many shortfalls, spurring the recent interest in early detection through structural health monitoring. This condition based technique is becoming more prevalent and is recognized for the potential to greatly reduce maintenance cost. Through corrosion monitoring, structural and environmental conditions can be closely observed, preventing excessive maintenance action and saving cost. Searches for corrosion monitoring system designs revealed several commercial companies with prototype systems installed on commercial aircraft, however, details on system design and data analysis were scarce. This study attempted to bridge the gap in literature by providing insight into the development of a corrosion damage prediction model and the design of a corrosion monitoring system. This study attempted to use aircraft maintenance data to make prediction models for determining what corrosion damage an aircraft can expect, given varying operating conditions. Although a reliable prediction model could not be created, trends observed in the data were still valuable for identifying problematic areas of the aircraft. In order to create reliable models, more accurate corrosion data is needed. This can be accomplished through the implementation of a corrosion monitoring system. A custom corrosion monitoring system was designed for the UH-1 aircraft. Commercial off-the-shelf products were fit to the design and a benefits-to-cost analysis was performed for the monitoring system, evaluating the system based on criteria developed from user requirements. The system proved to meet and exceed expectation, making it an ideal choice for the UH-1 aircraft.

There is a need to enhance our understanding of the corrosion mechanisms and their effect on the level and loss of prestressing forces. This research program consisted of accelerated corrosion tests on eight prestressed concrete prisms, measuring 127 x 127 x 2,060 mm, with three different levels of prestress (0, 30, and 60% of the ultimate strength of prestressing strand). The aim of the investigation was to simulate and monitor the corrosion of prestressing strands in prestressed systems. The specimens were submerged in a saline solution and subjected to an impressed constant voltage, aimed at accelerating the corrosion of the strands.
During the corrosion period, various electrochemical tests were performed to monitor the corrosion activity as a function of elapsed time. Strains at selected locations were measured regularly to check the instantaneous level of prestress. At the end of the experiment, the prestressing strands were removed from the concrete, visually inspected, and weighed. They were also tested in tension to determine their residual tensile strength and their mode of failure.
An assessment of the electrochemical results did not point to any relationship between the initial levels of prestress and the corrosion activity. A similar observation was made in verifying the effect of the initial level of prestress on the corrosion activity as manifested in the residual tensile strength of the strands or their final measured weights.
This research program was therefore valuable to the practicing engineer in the design and maintenance of durable prestressed concrete structures. The findings confirmed that the risk and extent of corrosion in all prestressing strands in corrosive environments are roughly similar, regardless of the initial prestressing level.

Novel electrochemical techniques, Scanning Vibrating Electrode (SVET) and Scanning Kelvin Probe (SKP), have been used to characterise pitting and filiform corrosion characteristics of aerospace alloy 2024-T3/T351. They have also been used to semi-quantify the inhibition efficiencies of chromate and trivalent Rare Earth Metal (REM) salts (cerium, lanthanum, and yttrium), both in solution and in coatings. It is shown that after long periods (hours) of immersion in 3.5% aqueous NaCl stable pitting occurs, these pits are believed to be in the form of interconnected tunnels, emerging at various points on the surface. It is also shown that chromate is the most effective inhibitor of those tested, both in solution and in coatings. The role of S phase intermetallic particles on the pitting corrosion of the alloy has also been investigated using SVET, and secondary and back-scatter electron microscopy. It is shown that the pitting corrosion rate exhibited by the alloy increases with the increase of fractional surface area occupied by precipitate. It is also shown that, when a non-uniform distribution of intermetallic particles is present, the maximum density of stable corrosion pits coincides with the minimum surface density of intermetallic particles.

The objective of this thesis is to improve understanding of the development of corrosion products (scales) that form on the inner walls of carbon steel pipelines in CO2-rich (sweet) oilfield environments. If well adherent to the carbon steel surface, such scales can significantly reduce the metal’s rate of corrosion. Typically, the open literature labels sweet corrosion scale as ferrous (II) carbonate (FeCO3) or siderite, although this may not always be the case. For example, Fe2(OH)2CO3 (chukanovite) and Fe3O4 (magnetite) are known to modify the protective character of a sweet corrosion product scale. Practical electrochemical methods for the assessment of substrate corrosion, and electron/photon-based characterisation techniques for investigating scale structure and composition, have revealed interesting aspects of the nature of sweet corrosion scale development on model high purity Fe and real-world pipeline steel surfaces. Concerning scale development on model Fe substrates immersed in CO2-saturated deionised water (buffered to pH = 6.8, T = 80°C, Ptotal = 1 bar), electrochemical data supplemented by grazing incidence x-ray diffraction (GIXRD) and scanning electron microscopy (SEM) show that a semi-protective mixed corrosion scale comprising siderite and chukanovite becomes a highly protective siderite scale with longer exposure time. The introduction of sodium chloride to the CO2-saturated solution (T = 80°C, pH = 6.8, Ptotal = 1 bar) impedes the rate of scale formation. Increasing [NaCl] from the start of experiment is suspected to limit the precipitation kinetics of sweet corrosion scale crystals, since chukanovite is no longer observed, and siderite formation is somewhat slowed as well. SEM imaging, using an electronic workfunction-sensitive detector (in lens), reveals nanoscale deposits on the corroded Fe surface in regions that are devoid of µm-scale crystals. With the Raman spectra from these regions considered, it is interpreted that the nanoscale deposits are likely amorphous iron carbonate, albeit oxidised to a significant extent. Moving to real-world carbon steel immersion in sweet solutions, a scale comprising predominantly chukanovite is observed (using GIXRD and SEM) on the 1% Ni weld zone (WZ) surface of a pipeline weld-joint, but not on adjacent, distinct regions (heat affected zones (HAZ) and base metal (BM)). This selective scaling is suggested to be due to some initial corrosion of the weld-joint, which generates sufficient [Fe2+(aq)], and a macro-galvanic effect across the weld, i.e. WZ is cathodic to HAZ and BM. Further, to gain mechanistic insight into compositional changes during sweet corrosion scale growth, an electrochemical cell for in situ GIXRD (named E-cell) has been developed and commissioned. Diffraction patterns acquired using synchrotron radiation, from a pipeline steel surface, reveal the formation and temporal evolution of a multicomponent corrosion scale. Accompanying electrochemical data suggest that the scale is quite protective.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Um grande problema metalúrgico encontrado na fabricação de equipamentos e componentes industriais com materiais inoxidáveis austeníticos, é a susceptibilidade à corrosão intergranular causada pela precipitação de carbonetos de cromo, devido à exposição destes materiais às altas temperaturas oriundas dos serviços de corte e soldagem. A norma de soldagem Petrobrás N-133 Rev. J restringe, preventivamente, a utilização do método de goivagem ao arco elétrico com eletrodo de grafite, processo este muito produtivo e econômico principalmente na remoção de soldas e execução de reparos em juntas soldadas. Os resultados dos testes realizados não demonstram que as alterações microestruturais relacionem a goivagem com a susceptibilidade à corrosão intergranular, principalmente quando aplicada em aços inoxidáveis austeníticos da série ASTM A-240-Tp 304L. A conclusão foi baseada: a) no levantamento de curvas de polarização anódica e catódica segundo técnica eletroquímica de reativação potenciodinâmica, que não apresentaram desvios substanciais entre suas relações de correntes de pico, b) no estudo comparativo do metal de base, zona de fusão, zona termicamente afetada e metal de solda através de ensaios metalográficos, que mostraram apenas uma descaracterização da estrutura original próxima à área goivada e linha de fusão, c) nas poucas alterações de análises químicas, microdureza e teores de ferrita nas áreas adjacentes à goivagem, e d) na confirmação da ausência de sinais de susceptibilidade a corrosão intergranular conforme análise microestrutural através da prática A do ASTM A 262.
A great metallurgic problem found in the manufacture of equipment and industrial components with austenitic stainless materials, is the susceptibility to intergranular corrosion caused by the precipitation of chromium carbides, due to exposition of these materials to high temperatures after services of cutting and welding. The standard welding Petrobras N-133 Rev. J restricts, preventively, the use of the method of arc gouging with graphite electrode, process very productive and economical especially in the removal of welds and carrying out repairs in welded joints. The results of the carried through tests do not demonstrate that the microstructural alterations relate the arc gouging with susceptibility to intergranular corrosion, especially when applied to the austenitic stainless steel ASTM A-240-Tp 304L series. The conclusion was based: a) on a survey curves of anodic and cathodic polarization second of Electrochemical Potentiodynamic Reactivation Technique, which showed no substantial deviations of relationships between its current peak, b) in the comparative study of base metal, fusion zone, heat affected zone and welding metal through metallography tests, which showed only a adulteration of the original structure and gouged area near the line of fusion, c) on the few alterations of chemical analysis, microhardness and ferrite content in the adjacent arc gouging areas, and d) in confirming the absence of signs of susceptibility to intergranular corrosion according to microstructural analysis by ASTM A 262, practice A.

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Universidade Estadual Paulista (UNESP)
As ligas de alumínio desempenham papel fundamental na indústria aeronáutica. A liga Al 7050 é usada em diversas partes da estrutura dos aviões e, em particular, na fabricação de componentes do trem-de-pouso. As condições operacionais fazem com que estes componentes trabalhem sob condições ambientais agressivas, tornando necessário aumentar sua resistência à corrosão através de tratamentos superficiais. Para o alumínio e suas ligas, a anodização é um dos tratamentos mais utilizados para esta finalidade. Os processos de anodização melhoram a resistência à corrosão das ligas de alumínio, mas reduzem a resistência à fadiga. Para minimizar ou eliminar os efeitos negativos das anodizações foram realizados estudos com o processo mecânico de shot peening sobre o material base antes das anodizações. Foram realizados ensaios de fadiga por flexão rotativa e por flexão alternada para as condições sem e com shot peening e fadiga axial, sem shot peening para as direções longitudinal e transversal à direção de laminação. Os resultados somente com anodização mostram que, para todos os processos de anodização, há redução na resistência à fadiga do material e que a anodização crômica é a que apresenta os melhores resultados, seguidos da anodização sulfúrica e dura. Os dados com shot peening seguido de anodização mostram que este tratamento neutraliza os efeitos negativos da anodização e promove um aumento na resistência à fadiga, sobre o material-base para a maioria das condições analisadas. Nos ensaios de fadiga por flexão rotativa e flexão alternada não foram observadas tendências de melhor comportamento em fadiga em relação à direção dos corpos-de-prova. Na fadiga axial os melhores resultados foram obtidos para a direção transversal a laminação.
Aluminum alloys play a fundamental role in the it elaborates aeronautics. The 7050 aluminum alloy is used in several parts of the structure of the airplanes and in the production of landing year components. The operational conditions like aggressive environment, made necessary to increase corrosion resistance through superficial treatments. For the aluminum alloys, the anodization is one of the treatments used for this purpose. The anodization processes improve the resistance to corrosion of the aluminum alloy, but reduce the resistance to fatigue. To minimize or to eliminate the negative effects of the anodization, studies they were performed with the mechanical process of shot peening on the base material before the anodization. Rotating and reverse bending for the conditions without and with shot peening, for the longitudinal and traverse directions were performed. The results only with anodizing they show that for all processes was reduction in the fatigue strength of the material occurred among them the anodizing chromic was the one that presented the best results, followed by the sulfuric and hard anodizing. The results with shot peening followed by anodizing show that the shot peening neutralized the negative effects of the anodizing and promoted an increase in the fatigue resistance, for most of the analyzed conditions. In the results for rotating and reverse bending tendencies of better behavior were not observed in fatigue with relation to the direction of the samples and in the axial fatigue the best results were obtained for the traverse direction.

Orientador: Inez Valeria Pagotto Yoshida
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Mestrado
Quimica Inorganica
Mestre em Química

Orientador: Antonio Carlos Guastaldi
Resumo: Este trabalho consistiu de um estudo da resistência à corrosão relativa de um amálgama dentário comercial e de suas principais fases constituintes, pelo uso de técnicas eletroquímicas, em meio salino e aerado que simula a agressividade do ambiente bucal. Os amálgamas dentários são formados pela reação do mercúrio com uma liga original em pó que contém predominantemente Ag, Sn e Cu, podendo também conter Zn ou outros elementos em menores proporções, resultando numa estrutura metalúrgica complexa e multifásica, com a presença das seguintes fases: γ1-Ag2Hg3 - matriz; γ-Ag3Sn - a segunda fase mais proeminente na microestrutura dos amálgamas dentários; γ2-Sn7-8Hg - a mais suscetível à corrosão dentre todas aquelas que compõem a microestrutura dos amálgamas dentários, de acordo com a literatura especializada; a composição eutética Ag-Cu (72%Ag, 28%Cu) - um componente adicionado às ligas mais modernas com o objetivo de reduzir a quantidade de γ2-Sn7Hg formada durante a reação de amalgamação e, neste sentido, aumentar a resistência à corrosão no meio bucal; e as fases do sistema Cu-Sn, ε-Cu3Sn e η'-Cu6Sn5 presentes em menor quantidade. Dada a natureza multifásica da microestrutura de amálgamas dentários, para este estudo foram elaboradas ligas metálicas binárias com composições químicas correspondentes às fases presentes em sua microestrutura. As ligas que contêem mercúrio, γ1-Ag2Hg3 e γ2- Sn7Hg, foram preparadas de acordo com as normas contidas na Especificação n. 1 para amálgamas dentários, da Associação Dentária Americana (ADA). As demais, correspondentes aos sistemas Ag-Cu, Ag-Sn e Cu-Sn foram preparadas pelos processos metalúrgicos convencionais de fundição, com o propósito de se reproduzir as principais fases que podem estar presentes na estrutura metalúrgica dos amálgamas...(Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Dental amalgams are formed by the reaction of mercury with a powder alloy containing mainly Ag, Sn, Cu and Zn, and have a complex metallurgical structure which can contain up to six phases. Their observed corrosion is thus a complex process, which involves contributions from each of the phases present as well as intergranular corrosion. It is thus of interest to investigate the corrosion of individual phases present in dental amalgams. Some of the products of the reaction are particles of the original alloy which did not react during the amalgamation process such as, γ-Ag3Sn and the Ag-Cu eutectic. Other products are the γ- phase of the silver-mercury system, designated γ1-Ag2Hg3, the γ-phase of the tin-mercury system, designated γ2-Sn7-8Hg, and intermetallic compounds of the tin-copper system, ε-Cu3Sn and η'-Cu6Sn5. The purpose of this work was to evaluate the corrosion resistance of the phase components of dental amalgams: the matrix phase of the microstructure, γ1-Ag2Hg3; the second more prominent, γ-Ag3Sn; the phase most susceptible to corrosion in the oral cavity, according to the literature, γ2-Sn7Hg; and spherical particles of the Ag-Cu eutectic (72% Ag, 28% Cu), a component of the more modern powder alloys, the objective being to reduce the quantity of γ2-Sn7Hg formed during the amalgam reaction and in this way increase its corrosion resistance. The Ag-Hg and Sn-Hg alloys were made in the correct stoichiometric proportions, taking into account the phase diagrams, by mechanical amalgamation and moulding under high pressure following the criteria adopted by the American Dental Association, Specification No. 1. The commercial dental amalgam employed in this study was Dispersalloy, a copper enriched alloy, type blended. The Ag-Sn, Ag-Cu and Cu-Sn alloys were prepared by heating the components until they were completely melted, and then the melt was poured into a mould...(Complete abstract click electronic access below)
Doutor

Today, ethanol, as well as other biofuels, has been increasingly gaining popularity as a major alternative liquid fuel to replace conventional gasoline for road transportation. One of the key challenges for the future use of bioethanol is to increase its availability in the market via an efficient and economic way. However, one major concern in using the existing gas-pipelines to transport fuel-grade ethanol or blended fuel is the potential corrosion and stress corrosion cracking (SCC) susceptibility of carbon steel pipelines in these environments. Both phenomenological and mechanistic investigations have been carried out in order to address the possible degradation phenomena of X-65 pipeline carbon steel in simulated fuel-grade ethanol (SFGE). Firstly, the susceptibilities of stress corrosion cracking of this steel in SFGE were studied. Ethanol chemistry of SFGE was shown to have great impact on the stress corrosion crack initiation/propagation and the corrosion mode transition. Inclusions in the steel can increase local plastic strain and act as crack initiation sites. Secondly, the anodic behavior of carbon steel electrode was investigated in detail under different ethanol chemistry conditions. General corrosion and pitting susceptibility under unstressed condition were found to be sensitive to the ethanol chemistry. Low tendency to passivate and the sensitivity to ethanol chemistry are the major reasons which drive corrosion process in this system. Oxygen plays a critical role in controlling the passivity of carbon steel in ethanol. Thirdly, the detailed study was carried out to understand the SCC mechanism of carbon steel in SFGE. A film related anodic dissolution process was identified to be a major driving force during the crack propagation. Fourthly, more detailed electrochemical impedance spectroscopy (EIS) studies using phase angle analysis and transmission line simulation reveal a clearer physical picture of the stress corrosion cracking process in this environment. Fifthly, the cathodic reactions of carbon steel in SFGE were also investigated to understand the oxygen and hydrogen reactions. Hydrogen uptake into the pipeline steel and the conditions of the fractures related to hydrogen embrittlement were identified and studied.

Carbon steel (CS) is the most commonly used material for equipment and pipes in the oil production processes. However, presence of water/salts and carbon dioxide, among other gases, in the oil is a serious problem due to increased corrosion rate of the material. The most common way of mitigating this problem is by using corrosion inhibitors. However, many common corrosion inhibitors that are in use today are health hazards. Therefore, there is a need to develop more environmentally compatible and biodegradable corrosion inhibitors. Bioorganic and naturally occurring molecules, such as amino acids, are the most obvious candidates. This work was aimed at studying the influence of some amino acids, 11-aminoundecanoic acid (11AA) and 12-aminododecanoic acid (12AA), as corrosion inhibitors for carbon steel (CS) in hydrochloric acid and some other electrolytes that might be used in certain industries.In this study the inhibiting effect of 12AA on corrosion of CS in CO2-free and CO2-saturated 0.5 HCl was investigated as a function of various parameters: inhibitor concentration, electrolyte pH, temperature, treatment time, CS surface roughness, electrolyte flow rate and pattern, effect of electrolyte type. In addition, the interaction of 11AA with the CS surface under selected experimental conditions was also investigated. It was found that 12AA inhibits both partial corrosion reactions, with a slightly stronger inhibition of the anodic corrosion reaction which indicated that 12AA acts as a mixed-type inhibitor. The corrosion protection mechanism is by formation of a surface-adsorbed 12AA monolayer that offers a hydrophobic barrier to transport of solvated corrosive ions to the surface yielding a maximum inhibition efficiency of ~98%. The adsorption of 12AA onto the CS surface was described by the Langmuir adsorption isotherm. The corresponding Gibbs energy of adsorption was calculated to be −26 and −28 kJ mol−1 in the CO2-free and CO2-saturated 0.5 M HCl, respectively. This indicated that the self assembled monolayers (SAM) formation process is spontaneous and reversible. PM-IRRAS measurements revealed that the SAM is amorphous, which could be attributed to the repulsion between the neighboring positively charged amine groups and also to a high heterogeneity of the CS surface. The study showed also that the 12AA can be used as an effective inhibitor of CS general corrosion in several other electrolytes including; acetic acid, perchloric acid and sodium chloride, but its application in nitric and sulfuric acid should be avoided. The corrosion inhibition of the CS surface by 12AA is also effective at higher pH values, although the corresponding corrosion inhibition efficiency decreased due to a decrease in 12AA solubility. 12AA was also confirmed to be an efficient corrosion inhibitor of a CS surface of different roughness.The effect of flow and flow pattern of CO2-saturated HCl on the corrosion inhibition of CS by 12AA was also investigated in a square duct, rotating disk electrode (RDE) and jet impingement cell configuration. 3 mM 12AA provided high corrosion inhibition efficiency in the square duct and RDE configuration. However, in 1 mM 12AA solution, the inhibition efficiency decreased with an increase in Reynolds number (Re), due to desorption of 12AA from the CS surface. 12AA was found to poorly protect CS in the impingement-jet configuration at low Re, while at high Re, acceleration of CS corrosion was recorded.Similar results were also obtained for inhibition of CS corrosion by 11AA. In fact, this molecule was found to better protect CS from corrosion than 12AA. This was attributed to the higher surface coverage of 11AA on the CS surface, i.e. the formation of a more compact 11AA monolayer.
L'acier au carbone est le matériel le plus couramment utilisé pour les équipements et les pipelines reliés aux processus de production pétrolière. Toutefois, la présence de certains éléments comme l'eau, les sels and le dioxyde de carbone dans l'huile pose plusieurs problèmes reliés à l'augmentation du taux de corrosion du matériel. La façon la plus répandue d'éliminer ce problème est l'utilisation d'inhibiteurs de corrosion. Il est cependant important de mentionner que la majorité de ces inhibiteurs sont nocifs pour l'être humain. Il est donc nécessaire de développer des composés compatibles avec l'environnement et biodégradables et ceci peut être fait avec l'utilisation d'acides aminés.Ce projet a pour but d'étudier l'influence des acides aminés "11-aminoundecanoic acid" (11AA) et "12-aminododecanoic acid" (12AA) en tant que qu'inhibiteurs pour l'acier carbone dans l'acide chlorhydrique et plusieurs autres électrolytes utilisés dans certaines industries.Dans cette étude, l'effet inhibiteur du 12AA sur la corrosion de l'acier carbone dans une solution sans ou saturée en dioxyde de carbone et avec 0.5 M d'acide chlorhydrique a été étudié. Différents paramètres tels que la concentration des inhibiteurs, la concentration des électrolytes, le pH, la température, le temps de traitement, la rugosité de surface, le taux de flux et les différents types d'électrolytes furent analysés pour mieux comprendre le mécanisme de fonctionnement. De plus, l'interaction du 11AA avec la surface de l'acier à certaines conditions fut également prise en considération.Il fut démontré que le 12AA inhibait les corrosions partielles et démontrait une corrosion anodique légèrement plus inhibée. Ceci nous a donc indiqué que cet inhibiteur était de type mixte. Le mécanisme de protection de la corrosion se faisait par adsorption de l'inhibiteur 12AA et cela procurait une protection hydrophobique contre les ions corrosifs avec une efficacité de 98%. L'adsorption de 12AA à la surface de l'acier suit le modèle de l'isotherme de Langmuir. L'énergie de Gibbs correspondante de cette adsorption a été calculée comme étant environ −26 (sans CO2) et −28 kJ mol−1 (saturée en CO2 et 0.5 M HCl). Ceci a indiqué que la formation de la couche (composée d'une épaisseur) est amorphe et que cela est causé par la répulsion engendrée avec les groupes voisins de même charge positive et par le caractère très hétérogène de la surface. L'étude a aussi démontré que le 12AA peut être très efficace contre la corrosion de l'acier carbone et ce avec une grande variété d'électrolytes et d'acides. Il est important de mentionner que l'inhibiteur est inefficace contre l'acide nitrique et sulfurique. L'inhibiteur peut aussi réduire la corrosion lorsque le pH est élevé, mais voit son efficacité réduite dans ces conditions en raison de l'augmentation de sa solubilité. Finalement, le 12AA semble aussi performant avec toutes les rugosités. L'effet et le type de flux d'une solution de HCl saturée en dioxyde de carbone fut aussi étudié avec l'aide d'une électrode à disque rotatif. L'inhibiteur 12AA (3mM) se démontra très performant à contrer la corrosion dans un espace carré et avec un électrode à disque rotatif. Cependant, lorsque la concentration fut réduite à 1mM la performance de l'inhibiteur diminua et son nombre de Reynolds fut augmenté. Ceci fut causé par désorption de 12AA de la surface de l'acier. Cet inhibiteur ne fut donc pas efficace à protéger l'acier carbone dans ces conditions.L'étude de l'inhibiteur 11AA donna des résultats similaires. Cependant, la protection de l'acier carbone fut plus efficace qu'avec le 12AA à cause que le 11AA est capable de couvrir une surface plus importante tout en faisant une couche plus compacte.

Modeling of chloride-induced deterioration of bridge decks by using Fickâ s Second Law of diffusion was performed. The objective of this study is to select suitable input parameters for the model to estimate the service life of bridge decks. Five bridge decks, one in each of the following states, Virginia, Florida, New Jersey, New York, and Minnesota were evaluated. Data collection process involved visual inspections, damage surveys, corrosion testing including continuity, one-point resistivity, four-point resistivity, half-cell potentials, and three-electrode linear polarization, reinforcement cover depths, chloride samples. The Virginia bridge deck was built with epoxy-coated reinforcement as top reinforcement mat and black bar as the bottom mat. The Florida bridge is a segmental prestressed box girder structure built with black bar. The New Jersey bridge deck was overlaid with latex modified concrete. The New York bridge deck, which was built in 1990, is six inch concrete topping over prestressed adjacent box beams structure with epoxy-coated bar in the negative moment area. The Minnesota bridge was rebuilt in 1984. The deck was rebuilt with epoxy coated reinforcing steel in the top and bottom mats. The probabilistic Fickian model requires reinforcement cover depths, surface chloride concentration, chloride initiation concentration, and diffusion coefficients as input parameters. The chloride initiation concentration was input via parametric bootstrapping, while the other parameters were input as simple bootstrapping. Chloride initiation concentration was determined from the chloride concentration at the reinforcement bar depths. The modeling results showed that the deterioration of the Virginia bridge deck was corrosion controlled and the bridge will undergo increasingly severe damage in the future. Florida bridge deck is not undergoing corrosion and will not experience corrosion damage within 100 years. New Jersey bridge deckâ s service life has been most likely extended by the overlay. Deterioration of the New York bridge was not corrosion controlled, but was related to longitudinal cracking of the topping at match lines of adjacent box beams. Minnesota bridge deck is delaminated and contained a large number of cracks that should be included in service life modeling; otherwise the service life estimate is underestimated. In addition to service life corrosion performance modeling, analyses were conducted on the relationships and interrelations of resistivity, corrosion potential, corrosion current and chloride at the reinforcing bar depth.
Ph. D.