Aços de alta resistência e baixa liga (ARBL) têm sido bastante utilizados na fabricação de tubulações para o transporte de petróleo e gás. Entretanto, o uso destes materiais em meios com elevadas concentrações de H2S, denominados sour, tem resultado em falhas frequentes, devido à suscetibilidade destes materiais ao desenvolvimento do fenômeno de trincamento induzido pelo hidrogênio (Hydrogen Induced Cracking - HIC), assim como devido a problemas de corrosão. O desenvolvimento de diferentes processos tecnológicos para a produção de tubos de aços ARBL, tais como a laminação controlada e resfriamento acelerado, a adição de microligantes, assim como a diminuição do teor de enxofre, fósforo, carbono e manganês, tem levado à elaboração de materiais com propriedades mecânicas otimizadas, permitindo também um melhor controle da microestrutura. As perdas de dureza e resistência mecânica devidas à redução do teor de manganês, são compensadas pela adição de elementos como cromo e nióbio. Neste trabalho estão sendo comparadas a resistência à corrosão e os parâmetros de permeabilidade do hidrogênio de dois tubos de aço API 5L X65 e uma chapa API 5L X65, todos do tipo ARBL e com baixo manganês (0,27%) e alto nióbio (0,083% a 0,090%), na solução B da norma NACE, TM-0284 (2011). Para isto, foram realizados ensaios de potencial de circuito aberto (Open Circuit Potential - OCP), espectroscopia de impedância eletroquímica (Electrochemical Impedance Spectroscopy - EIS) e curvas de polarização potenciodinâmicas no eletrólito naturalmente aerado, desaerado e saturado com H2S. Os testes de permeabilidade do hidrogênio foram realizados com base na norma ASTM INTERNATIONAL G148 - 97, porém usando a célula modificada de DEVANATHAN e STACHURSKY (1962) e com H2S como veneno catódico. Os materiais foram caracterizados por microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva de Raios-X (X-Ray Energy Dispersive Spectroscopy - EDS) antes e depois de testes de imersão nos diferentes eletrólitos. Caracterização dos produtos de corrosão por difração de raios-X (DRX) também foi realizada após imersão em meio saturado com H2S (sour). As análises por MO e MEV mostraram matrizes ferríticas para os três aços, com a presença de baixos teores do microconstituinte martensita/austenita (M/A), de perlita e com baixo nível de inclusões uniformemente distribuídas e com composições químicas semelhantes. Os resultados dos ensaios de corrosão mostraram que, para todos os meios investigados, o aço denominado como B apresentou a melhor resistência à corrosão, enquanto aquele denominado como C se mostrou o mais suscetível em todas as condições estudadas. Para os três aços, a resistência à corrosão apresentou a seguinte ordem crescente de acordo com o meio de exposição: meio saturado com H2S < meio naturalmente aerado < meios desaerados. Ensaios de OCP e EIS no meio saturado com H2S em um período de 24h mostraram que a resistência à corrosão aumenta com o tempo em razão da formação de uma camada de sulfeto de ferro, que, no entanto, se apresentou pouco aderente. Os resultados dos ensaios de permeação de hidrogênio mostraram que o aço denominado B, que apresentou maior resistência à corrosão em todos os meios e que não apresenta perlita em sua microestrutura, teve o maior valor de difusividade efetiva de hidrogênio, menor concentração de hidrogênio atômico na sub-superfície e menor quantidade de traps por unidade de volume. Quanto aos outros dois materiais, os resultados dos testes de permeabilidade ficaram em desacordo com os resultados da caracterização microestrutural e dos testes de resistência à corrosão, indicando que fatores diferentes dos detectados neste estudo são importantes para governar essas propriedades. / High strength low alloy (HSLA) steels have been widely used in the manufacture of pipelines for the transport of oil and gas. However, the application of these steels in media with high H2S concentrations, denominated sour, has resulted in frequent failures due to the susceptibility of these materials to the development of Hydrogen Induced Cracking (HIC) phenomena, as well as due to corrosion problems. The development of different technological processes for HSLA piping production, like controlled rolling and accelerated cooling, the addition of microalloying elements, as well as the reduction of the amounts of sulphur, phosphorus, carbon and manganese, has led to the development of materials with optimized mechanical properties, also allowing a better microstructural control. Hardness and mechanical resistance reduction due to the lowering of Mn content are compensated by niobium and chromium addition. In this work, the corrosion resistance and the hydrogen permeability parameters of two API 5L X65 steel tubes and an API 5L X65 plate, all HSLA type and with low manganese (0.27%) and high niobium (0.083% to 0.090%) contents, are compared in solution B of NACE standard TM-0284 (2011). For this, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves were carried out in the naturally aerated, deaerated and H2S saturated electrolyte. Hydrogen permeability tests were performed based on ASTM INTERNATIONAL G148-97, but using a modified DEVANATHAN and STACHURSKY (1962) cell and with H2S as cathodic poison. The materials were characterized by means of optical microscopy (OM), scanning electron microscopy (SEM) and X-Ray Energy Dispersive Spectroscopy (EDS) prior and after immersion tests in the different electrolytes. Characterization of the corrosion products by X-ray diffraction (XRD) was also performed after immersion in the H2S-saturated (sour) medium. The OM and SEM characterization showed ferritic matrices for the three steels, with the presence of low levels of the martensite/austenite (M/A) microconstituent, perlite and with a low level of inclusions evenly distributed and with similar chemical compositions. The results of the corrosion tests showed that, for all investigated media, the steel denominated as B presented the best resistance to corrosion, whereas the one denominated as C showed to be the most susceptible in all the conditions studied. For the three steels, the corrosion resistance showed the following ascending order according to the exposure medium: H2S saturated < naturally aerated medium < deaerated media. OCP and EIS tests in the H2S-saturated medium in a period of 24 hours showed that the corrosion resistance increases over time due to the formation of an iron sulphide layer, which, however, presented little adhesion. The results of the hydrogen permeation tests showed that the steel denominated B, that presented greater corrosion resistance in all media and that does not present perlite in its microstructure, had the highest values of effective hydrogen diffusivity, the lowest concentration of atomic hydrogen in the subsurface and the smallest amount of traps per unit volume. Concerning the other two materials, the results of the permeability tests were at variance with the results of the microstructural characterization and corrosion resistance tests, indicating that factors other than those detected in this study are important to govern such properties.

A crescente preocupação com o desenvolvimento sustentável, aliada com uma maior conscientização com relação à preservação do meio ambiente, tem incentivado pesquisas com a finalidade de encontrar substitutos ambientalmente amigáveis para os eficientes sistemas à base de cromo hexavalente (Cr6+), que são empregados como pré-tratamento em ligas de alumínio de alta resistência utilizadas na indústria aeronáutica. Neste trabalho, o desempenho do silano BTSE (Bis-1,2-(trietoxisilil) etano) como método de proteção contra a corrosão da liga de alumínio 2024-T3 foi investigado utilizando técnicas de caracterização eletroquímicas, microestruturais e químicas. Para melhorar as propriedades anticorrosivas do sistema, a camada de silano foi modificada pela introdução de aditivos, tendo sido estudados também sistemas em bi-camada. Efeitos das condições de cura (tempo e temperatura) do BTSE e da quantidade de modificantes sobre as propriedades dos substratos revestidos também foram avaliados. Para os estudos eletroquímicos, realizados em solução de NaCl 0,1 M, foram empregadas a espectroscopia de impedância eletroquímica (EIS) e curvas de polarização potenciodinâmica anódica e catódica. As técnicas de caracterização morfológica e microestrutural foram microscopia de força atômica (AFM), microscopia eletrônica de varredura (SEM) e medidas de ângulo de contato. A caracterização da composição e do estado químico da camada foi realizada usando as espectroscopias por energia dispersiva de Raios-X (EDS), de infravermelho (IR) e de fotoelétrons excitados (XPS). Os resultados dos ensaios de corrosão mostraram que a adição dos modificantes à camada de BTSE melhora o desempenho anticorrosivo do sistema, o qual também teve seu comportamento melhorado quando utilizado em forma de bi-camada. Verificou-se que um excesso de aditivos tende a deteriorar as propriedades protetoras do silano, e que o aumento do tempo e da temperatura de cura é benéfico para as propriedades anticorrosivas dos diferentes sistemas. Os resultados dos ensaios de caracterização química e microestrutural também detectaram que os modificantes contribuem para uma melhor cobertura do substrato pela camada de silano, assim como para uma maior reticulação da mesma, sem, no entanto, modificar sua estrutura química e física. / The increasing concern with sustainable development, allied with a stronger awareness with environmental preservation, has stimulated researches in order to find environmentally friendly substitutes to replace the efficient hexavalent chromium-based pre-treatment systems (Cr6+) used to protect high-strength aluminium alloys employed in the aircraft industry. In this work, the performance of BTSE (bis-1, 2-(triethoxysilyl) ethane) as a protection method against corrosion of aluminium alloy 2024-T3 was investigated using electrochemical, microstructural and chemical characterization techniques. In order to improve the system anticorrosion properties, modifiers were added to the silane layer, and bi-layers systems were also tested. The effects of the silane curing conditions (time and temperature) and of the modifiers amounts on the properties of the layers were also evaluated. Electrochemical impedance spectroscopy (EIS) and anodic and cathodic potentiodynamic polarization curves were employed for the electrochemical studies, which were performed in 0.1 M NaCl solution. For microstructural and morphological characterization, atomic force microscopy (AFM), scanning electron microscopy (SEM) and contact angle measurements were used. The chemical state and the composition of the different layers were evaluated using X-ray photoelectrons (XPS), infrared (IR) and X-ray dispersive energy (EDS) spectroscopy. The results of the corrosion studies have shown that the addition of modifiers to the BTSE layer improves its anticorrosion performance, which was also improved in the bi-layers systems. It was also verified that addition of modifiers excess hinders the performance of the layers, as well as that increasing curing time and temperature are beneficial to the anticorrosion properties of the systems. The results of the different chemical and microstructural analyses showed that the modifiers contribute to better substrate coverage by the silane layer, as well as to a more complete reticulation. However, this does not imply in modifications of the chemical and physical structure of the layer.

Aluminium alloys are widely used in the aerospace industry due to their lightweight and high specific strength. However, these alloys are particularly sensitive to localized corrosion in chloride environments and need to be protected by a robust system. One of the protection methodologies consists in anodizing. The produced layer increases the corrosion resistance and also serves as anchoring site for organic coatings application. Chromium-based anodizing has been usually employed, nevertheless, as chromate compounds are toxic for health and the environment, chromium-based surface treatments will be prohibited in the aerospace industry in a near future. Tartaric-sulphuric acid (TSA) anodizing is a promising environment compliant alternative, which is already being used at industrial level with appropriate corrosion protection and paint adhesion properties. This study aims at proposing a hybrid sol-gel treatment after TSA anodizing of AA2524 specimens in order to improve the corrosion resistance of the anodized layer while maintaining its compatibility with organic coatings. For this, anodic aluminium oxides (AAO) were produced at different anodizing voltages and protected by dip-coating with a hybrid sol-gel layer obtained from a tetraethoxysilane (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) hydrolysis solution with high water content. Corrosion resistance evaluation was carried out by means of electrochemical impedance spectroscopy (EIS) in NaCl 0.1 mol L-1 and salt-spray chamber exposure (ASTM B117-11 standard). The morphology of the anodic porous layer was investigated by means of FE-SEM, whereas glow discharge optical emission spectroscopy (GDOES) was employed to evaluate the distribution of the sol-gel layer within the porous AAO. FE-SEM characterization confirmed that the layer properties (pore distribution, porosity and thickness) were strongly dependent on the anodizing conditions, whereas GDOES depth profile showed penetration of the hybrid coating within the pores of the anodized layer. The two characterization techniques showed inefficient surface sol-gel coverage for the samples anodized at higher voltage, likely due to insufficient sol-gel deposition. The results of the EIS characterization tests up to 1008 h (42 days) showed that, irrespectively to the anodizing voltage, the hybrid sol-gel protected AAO was stable with only slight evolution of the diagrams with immersion time. Moreover, the hybrid coating protected samples presented higher low frequency impedance modulus than hydrothermally sealed (HTSed) reference TSA anodized samples, which was confirmed by electrical equivalent circuit (EEC) fitting of the EIS data. EEC fitting also revealed that the resistance of the pores to electrolyte penetration was increased by the application of the sol-gel coating when compared to the resistance of the HTSed reference samples and indicated better anticorrosion performance for the sample anodized at 16 V. These results were confirmed by the salt-spray tests. Investigation on the ageing of the hybrid sol-gel hydrolysis solution showed that its viscosity hardly changed up to two weeks of test and that hybrid coatings applied from these solutions were stable and afforded good corrosion protection to the TSA anodized substrate, an improvement of the anticorrosion properties of the hybrid coating was verified for an ageing time of 168 h. Preliminary tests performed with a solvent-free organic coating (epoxy) indicated good compatibility with the hybrid TEOS-GPTMS coating characterized by very high impedance and good stability upon exposure to the salt-spray chamber. / Ligas de alumínio são muito utilizadas na indústria aeronáutica por serem materiais leves e altamente resistentes. Porém, essas ligas são particularmente sensíveis à corrosão localizada em meios que contêm cloretos, e precisam de sistemas robustos de proteção. Uma das metodologias de proteção consiste em anodização. A camada produzida aumenta a resistência à corrosão e também serve como sítio de ancoragem para aplicação de revestimentos orgânicos. A anodização crômica tem sido usualmente empregada na indústria aeronáutica. No entanto, como compostos contendo íons cromato são tóxicos para a saúde e para o meio-ambiente, tratamentos de superfície à base de cromo serão proibidos na indústria espacial em um futuro próximo. Anodização em banho de ácido sulfúrico-tartárico (TSA) é uma alternativa promissora e ambientalmente compatível, a qual já está sendo usada industrialmente com apropriada proteção à corrosão e adesão para pintura. Este estudo tem como objetivo propor um tratamento utilizando um revestimento híbrido sol-gel para melhorar a resistência à corrosão da liga AA2524 anodizada em TSA e que mantenha sua compatibilidade com revestimentos orgânicos. Para isso, camadas anodizadas de alumínio (CAA) foram produzidas em diferentes voltagens e protegidas por camada de híbrido sol-gel obtida pela hidrólise de tetraetilortosilano (TEOS) e glicidóxipropiltrimetóxisilano (GPTMS) em solução com alto teor de água e aplicada pela técnica de dip-coating. A avaliação da resistência à corrosão foi realizada através de espectroscopia de impedância eletroquímica (EIS) em NaCl 0,1 mol.L-1 e por exposição à câmara de névoa salina (norma ASTM B117-11). A morfologia da camada porosa foi investigada por MEV e a espectroscopia de emissão óptica por descarga luminescente (GDOES) foi empregada para avaliar a distribuição do híbrido sol-gel no interior dos poros da camada porosa. As caracterizações por MEV confirmaram que as propriedades da camada (distribuição dos poros, porosidade e espessura) são fortemente dependentes das condições de anodização, e a composição em profundidade obtida por GDOES mostrou que o revestimento híbrido penetrou nos poros da camada anodizada. As duas técnicas de caracterização mostraram uma cobertura ineficiente da camada sol-gel para as amostras anodizadas nas voltagens mais elevadas, provavelmente devido à deposição insuficiente do híbrido. Os testes de EIS com duração de até 1008 h (42 dias) mostraram que, independentemente da voltagem de anodização empregada, a camada anódica coberta com sol-gel ficou estável ocorrendo apenas pequenas evoluções dos diagramas com o tempo de imersão. Além do mais, as amostras protegidas com o revestimento híbrido apresentaram maiores valores de módulo de impedância em baixa frequência do que as amostras anodizadas em TSA e hidrotermicamente seladas (HTsed) usadas como referências. Essa tendência foi confirmada pelo ajuste com circuitos elétricos equivalentes (EEC) dos resultados de EIS que também mostrou que a aplicação do sol-gel híbrido torna mais difícil a penetração do eletrólito agressivo nos poros da camada anodizada quando comparada com as amostras HTSed, e indicou melhor desempenho anticorrosivo para a amostra anodizada em 16 V. Esses resultados foram confirmados pelos testes de névoa salina. A investigação do envelhecimento da solução de sol-gel mostrou pouca mudança na viscosidade da solução de hidrólise em duas semanas de testes e que os revestimentos híbridos aplicados a partir dessas soluções foram estáveis e promoveram boa proteção à corrosão para as amostras anodizadas em TSA, com melhora das propriedades anticorrosivas após 168 h de envelhecimento. Testes preliminares realizados com revestimento orgânico livre de solvente (epóxi) indicaram boa compatibilidade deste com o revestimento híbrido TEOS-GPTMS. O revestimento epóxi propiciou valores de módulo de impedância elevados e estáveis e também boa estabilidade após exposição à câmara de névoa salina quando aplicado sobre o revestimento híbrido aplicado sobre a liga 2524.

Cette thèse, réalisée en étroite collaboration avec le partenaire industriel RSE S.p.A (Italie), s’inscrit dans le cadre du projet européen BIOCOR ITN. Les alliages de cuivre habituellement utilisés dans les circuits de refroidissement de centrales électriques peuvent être affectés par la biocorrosion induite par la formation d’un biofilm. L’objectif de ce travail était d’étudier the comportement à la corrosion de l’alliage 70Cu-30Ni et d’un laiton contenant 2% d’aluminium en milieu marin, dans des conditions industrielles réelles (expériences sur le terrain) et en laboratoire. L’influence de différents paramètres, tels que la solution (eau de mer naturelle filtrée (FNSW) vs eau de mer artificielle (ASW)), la concentration en biomolécules (biomolécules naturellement présentes dans l’eau de mer vs une protéine modèle, l’albumine de sérum bovin (BSA)), l’hydrodynamique (conditions statiques, sous circulation et agitation, électrode à anneau tournant) et le pH (8,0 ; 6,0 et 3,7), a été évaluée. Sur le terrain, le comportement global à la corrosion et les traitements antifouling ont été suivis en utilisant des techniques électrochimiques (potentiel de corrosion Ecorr vs temps, LPR), gravimétriques (pertes de masse) et génétiques. En laboratoire, des mesures électrochimiques (Ecorr vs temps, courbes de polarisation, spectroscopie d’impédance électrochimique), réalisées pendant les toutes premières étapes de formation des couches d’oxydes (1 h d’immersion), ont été combinées à des analyses de surface par XPS et ToF-SIMS. A partir des expériences sur le terrain, l’analyse microbiologique et moléculaire des biofilms formés sur les deux alliages de cuivre dans l’eau de mer naturelle montre la présence des espèces bactériennes Marinobacter, Alteromonas et Pseudomonas. In the case of Al brass, the single experimental loop illustrates both anodic charge transfer and anodic mass transport. A partir des expériences en laboratoire, des modèles sont proposés pour analyser les données d’impédance obtenues à Ecorr. Dans le cas de 70Cu-30Ni, la boucle HF illustre principalement le transfert de charge anodique (diamètre égal à Rta) ; alors que la boucle BF est liée au transport de matière anodique et au blocage partiel de la surface par CuCl. Dans le cas du laiton, la seule boucle expérimentale illustre à la fois le transfert de charge anodique et le transport de matière anodique. Le comportement électrochimique et la composition chimique de surface de l’alliage 70Cu-30Ni sont similaires dans ASW et dans FNSW statiques, du fait de la faible concentration en biomolécules dans FNSW. En comparaison de l’alliage 70Cu-30Ni dans ASW statique sans biomolécules, pour lequel une couche duplex épaisse (couche externe de Cu2O redéposé et couche interne de nickel oxydé) est montrée, la présence de BSA conduit à une couche mixte d’oxydes de Cu et de Ni d’épaisseur plus faible ; les résultats montrent aussi un ralentissement de la réaction anodique et un faible effet d’inhibition de la corrosion en présence de BSA. Sous circulation et agitation, une couche mixte d’oxydes de Cu et de Ni, de très faible épaisseur, est obtenue. Pour les deux alliages dans FNSW, le courant de corrosion icorr estimé à partir de Rta est indépendant de la vitesse de rotation de l’électrode tournante, du fait de la compensation des effets du potentiel et du transport de matière. Pour 70Cu-30Ni dans FNSW statique, la réaction anodique est ralentie à pH acide (effet cinétique). Pour le laiton, un effet d’inhibition de la corrosion est montré à pH acide, et plus le pH est acide, plus la réaction anodique est lente. Pour 70Cu-30Ni, l’épaisseur de la couche d'oxyde augmente avec la diminution du pH, dans le cas du laiton il est indépendante du pH. La composition chimique de la couche d'oxyde semble avoir un effet sur la quantité de protéines adsorbées et l'épaisseur équivalente calculée de la couche organique est très faible (quelques Å pour 70Cu-30Ni et 1 Å pour laiton). / This thesis was carried out in the frame of the BIOCOR ITN European project, in close collaboration with the industrial partner RSE S.p.A. (Italy). Copper alloys commonly used in cooling systems of power plants may be affected by biocorrosion induced by biofilm formation. The main objective of this work was to study the corrosion behavior of 70Cu-30Ni alloy and aluminum brass in seawater environments, under real industrial conditions (field experiments) and in laboratory. The influence of different parameters, such as the solution (filtered natural seawater (FNSW) vs artificial seawater (ASW)), the concentration of biomolecules (biomolecules naturally present in seawater vs a model protein, the bovine serum albumin (BSA)), hydrodynamics (static conditions, under flow and stirring, rotating ring electrode (RRE)) and pH (8.0, 6.0 and 3.7), was evaluated. In field, the overall corrosion behavior and antifouling treatments were monitored using electrochemical (corrosion potential Ecorr vs time, LPR), gravimetric (weight losses) and genetic techniques. In lab, electrochemical measurements (Ecorr vs time, polarization curves, EIS), performed during the very first steps of oxide layers formation (1 h immersion time), were combined to surface analysis by XPS and ToF-SIMS. From field experiments, microbiological and molecular analysis of biofilms formed on both copper alloys in natural seawater indicates the presence of Marinobacter, Alteromonas and Pseudomonas bacterial species. From lab experiments, models are proposed to analyze impedance data obtained at Ecorr. In the case of 70Cu-30Ni, the HF loop illustrates mainly the anodic charge transfer (diameter equal to Rta); whereas the LF loop is related to the anodic mass transport and partial blocking effect by CuCl. In the case of Al brass, the single experimental loop illustrates both anodic charge transfer and anodic mass transport. Similar electrochemical behavior and surface chemical composition of 70Cu-30Ni alloy are obtained in static ASW and FNSW, due to the low biomolecule concentration in FNSW. Compared to 70Cu-30Ni in static ASW without biomolecules, for which a thick duplex oxide layer (outer redeposited Cu2O layer and inner oxidized nickel layer) is shown, the presence of BSA leads to a mixed Cu and Ni oxide layer with a lower thickness; the results also show a slow-down of the anodic reaction and a small corrosion inhibition effect in the presence of BSA. Under flow and stirring, a very thin mixed Cu and Ni oxide layer is obtained. For both alloys in FNSW, the corrosion current icorr estimated from Rta is independent of the rotation speed of the RRE, due to compensated potential and mass transport effects. For 70Cu-30Ni in static FNSW, the anodic reaction is slown down at acidic pH (kinetic effect). For Al brass, there is a corrosion inhibition effect at acidic pH, and the more acidic the pH, the slower the anodic reaction. In the case of 70Cu-30Ni alloy, the oxide layer thickness increases with decreasing pH, whereas for Al brass it is independent of the pH. The chemical composition of the oxide layer seems to have an effect on the amount of adsorbed proteins and the calculated organic layer equivalent thickness is very low (few Å for 70Cu-30Ni and 1 Å for Al brass).

The choice of corrosion protection system depends on the environment and needed lifetime for the product. The right corrosion protection should be selected in a sustainable point of view, since a well-selected coating system can reduce the environmental and economical impact, by using less and better material. The systems used for classifying corrosion protection often give a passed/not passed result for the number of years it is expected to last in a specific corrosive environment. In the last decades, Electrochemical Impedance Spectroscopy (EIS) has become a popular method for evaluating corrosion protection for organic coatings. EIS can collect quantitative data by monitoring the coatings electrochemical behavior over time, which can be used for optimizing the coating system. The purpose of this thesis was to try to predict how different combinations of coating layers and substrates will perform as a corrosion protection, which could provide information that can optimize the coating process. In this thesis, EIS has been used as a test method to evaluate organic coating systems for corrosion protection, by looking at barrier properties and adhesion for powder coatings on aluminum substrates. The main part of the coatings were applied in the coating plant at Fagerhult AB, but an external supplier has been used as a reference. The powders used in the coating process were based on polyester resins and the substrates were different aluminum alloys. The EIS measurements were performed in the chemistry lab at the School of Engineering at Jönköping University and depending on the sample setup was each sample evaluated for two or four weeks of testing. Two groups of samples had intact coatings and a third group had samples with an applied defect in the coating. The analysis of sample setups with intact coatings showed that the topcoat absorbed water faster than the primer. The samples showed no significant degradation in corrosion protection for the evaluated period and could thereby not provide enough information to be able to conclude which setup give the best corrosion protection over time. The samples with a defect in the coating indicated that two of the substrates provided similar adhesion in the coating-substrate interface. The coating from the external supplier was also included in the test and it showed the best adhesion of the tested samples. The main conclusion is that the coating system used at Fagerhult AB provides a very good corrosion protection. Longer testing time with EIS measurements on intact coatings is needed to be able to rank the different sample setups by failure of corrosion protection.

The design of new engineering materials resistant to both wear damage and corrosion degradation becomes increasingly demanding in complex service conditions. Unfortunately, there is typically a tradeoff between wear and corrosion resistance, even for important passive metals such as Al alloys. This is because the presence of precipitates hardens the material but at the same time lead to unfavorable galvanic coupling between the precipitates and the matrix, resulting in accelerated corrosion. This work showed that Al (or Mg) supersaturated solid solution formed using non-equilibrium methods exhibited enhanced corrosion resistance without compromising strength. For Al, alloying with Mn up to ~ 20.at.% simultaneously increased the wear resistance of Al as well as the protectiveness of the passive layer, thus improving the overall tribocorrosion resistance. For Mg, alloying with Y (4.67 wt.%), Zr (0.45 wt%), and Nd (1.79 wt%) in solid solution led to ~ 8 fold increment in corrosion resistance in physiological environment. Magnetron-sputtered aluminum (Al) and aluminum–manganese (Al-Mn) films with structures ranging from nanocrystalline to amorphous were obtained by tuning the Mn% up to 20.5 at.%. Corrosion behavior of the films was investigated in 0.6 M and 0.01 M NaCl aqueous solutions by potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS). Pitting corrosion was found to be strongly affected by alloy composition. The amorphous Al–20.5 at.% Mn exhibited the best pitting resistance during short term exposure. However, over longer immersion in 0.01 M NaCl up to 108 hrs, nanocrystalline Al–5.2 at.% Mn showed the highest corrosion resistance. The dual-phase Al-11.5 at % Mn alloy was found to have higher nominal corrosion rate compared to its nanocrystalline or amorphous counterparts. The effects of Mn alloying on the tribocorrosion behavior of magnetron-sputtered Al-Mn thin films with 5.2 at.% and 20.5 at.% Mn were investigated in 0.6 M NaCl aqueous solution. Tribocorrosion resistance of Al-Mn was found to be strongly affected by the alloying composition and applied potential. Higher Mn content increased H/E ratio and promoted the formation of denser and more compact passive film, hence improving tribocorrosion resistance of Al. In particular, alloying with 20.5 at.% Mn led to an increase of the corrosion resistance by ~ 10 times and the hardness ~ 8 times compared to pure Al. The total material loss during tribocorrosion was found to increase with applied potential. When the applied potential was increased from cathodic to anodic, simultaneous contribution of the mechanical and the electrochemical wear leads to accelerated material loss. A galvanic cell model was used to investigate the depassivation-repassivation kinetics during tribocorrosion. It was found that alloying with 5.2 at.% Mn led to more than 10-fold reduction in the current density required to re-passivate similar worn areas compared to pure Al. The origin of wear-corrosion synergy was discussed based on these observations. Magnesium alloys such as WE43 are considered for biomedical applications including cardiovascular stents and bone implants due to their biocompatibility, good cell adhesion, and mechanical properties close to that of bones. Unfortunately, their high degradation rate and subsequent loss of structural integrity in physiological environments hinders such applications. To improve the corrosion resistance of WE43 magnesium alloy, its microstructure was optimized to prevent micro-galvanic coupling between Mg matrix and precipitates. Chemically homogeneous WE43 with nanoscale surface roughness was obtained by magnetron sputtering with high effective quench rate. The effect of chemical heterogeneity on the corrosion resistance of biodegradable WE43 magnesium alloy was studied by performing corrosion tests in blood bank buffered saline using samples from two metallurgical states, cast and deposited. The microstructure of all samples was investigated by grazing incidence X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The deposited samples, prepared by magnetron sputtering using targets with the same global composition as cast WE43, exhibited chemically homogeneous microstructure without the formation of secondary phases typically observed in the cast alloy. The corrosion behavior was studied by PD and EIS tests. It was found that the deposited alloy showed enhanced corrosion resistance, ~8-fold reduction in corrosion rate compared to the cast alloy, owing to the elimination of micro-galvanic coupling between the Mg matrix and the precipitates. In-situ monitoring of hydrogen bubble evolution during corrosion indicated significantly reduced cathodic reaction kinetics in the deposited alloy. Post-corrosion surface and cross-sectional SEM studies showed that the high corrosion rate in the cast alloy was associated with the formation of severely cracked corrosion products preferably around Zr- and Y-containing precipitates.

No description available.

The thesis deals with liquid aprotic electrolytes based on mixtures of ionic liquid and solvent. EmimBF4, namely 1-ethyl-3-ethylimidazolium tetrafluoroborate, was used as the starting ionic liquid. A mixture of propylene carbonate, ethylene carbonate and dimethyl carbonate was used as solvents. Electrolytes were enriched with two electrolyte salts LiBF4 and NaBF4 from the resulting mixtures selected the most suitable electrolytes for Li-ion and Na-ion accumulators. Electrolytes were selected taking into account the required properties: the width of the potential window, the measured electrical conductivity and, last but not least, the safety.

The main aim of this paper are models of Li-Ion storage batteries made and simulated in ANSYS Fluent software. Various ways of simulations are discussed with main aim on ECM method and how its numerical model is computed. A process of getting information and required data from real battery to be compared with simulation results by EIS method is also discussed. These results are then compared with results from ANSYS Fluent.

.Tato diplomová práce se zabývá elektrochemickými procesy v lítium-iontových bateriích. Pro charakterizaci různých elektrochemických procesů se používá metoda nazývaná elektrochemická impedanční spektroskopie (EIS). V prvních kapitolách jsou popsány různé typy baterií a jejich rozdíly. Práce také obsahuje popis experimentálního zařízení používaného pro EIS. Součástí práce je také porovnání experimentálního zařízení a zařízení od společnosti BioLogic Science Instruments.