The electroplating industries use soluble nickel salts in numerous applications. Over the past few years this has become problematic due to the reclassification of these salts from a harmful substance to now a toxic substance. The introduction of the legislation REACH (Registration, Evaluation, Authorisation & restriction of CHemicals) has meant the electroplating industry has had to use less harmful chemicals where possible, thus meaning companies are investing in research to find an alternative to the nickel deposit. In this study, alternative deposits under investigation as a potential replacement to the nickel deposit under the decorative chromium deposit has been characterised in terms of the appearance, surface topography and corrosion resistance by using spectrophotometry, scanning electron microscopy (SEM), atomic force microscopy (AFM), linear polarisation, electrochemical impedance spectroscopy (EIS) and accelerated corrosion salt spray methods. Spectrophotometry identified that a white Cu-Sn alloy gave a bluer appearance in comparison to the nickel deposit, when the chromium deposit was plated on top this modified the colour slightly giving the white Cu-Sn alloy with chromium a similar appearance to the nickel and chromium deposit. The yellow Cu-Sn alloy was yellow in colour with a visibly dull appearance, but when chromium was plated on top of the yellow Cu-Sn alloy the colour was improved but still remained dull. The SEM and AFM results identified that the white Cu-Sn alloy deposit had similar nodulated topography to the nickel deposit and when the chromium was plated on top the topography changed only slightly. While the yellow Cu-Sn alloy deposits showed a more crystalline structure and increased roughness in comparison to the nickel deposit, the chromium deposit plated on top did not change the structure of the underlying deposit but it did reduce the roughness slightly. Electrochemical corrosion tests showed the white Cu-Sn alloy to have a higher polarisation resistance compared to the nickel deposit, thus suggesting it would provide similar corrosion protection to the nickel deposit. The yellow Cu-Sn alloy proved to have a faster corrosion rate in comparison to the nickel deposit. Accelerated corrosion tests proved the white Cu-Sn alloy to be more corrosive than the nickel despite the electrochemical test results, it was concluded that the white Cu-Sn alloy deposit was porous and therefore provided less corrosion protection to the substrate in comparison to the nickel deposit. The yellow Cu-Sn alloy had a lower corrosion protection than the nickel deposit and when combined as a duplex Cu-Sn alloy with the white Cu-Sn alloy deposit there was no improvement in corrosion performance. The plated chromium deposit did improve the corrosion protection for most deposits but none of the alternatives could match the corrosion protection offered by the standard nickel with chromium deposit. This study concluded that the white Cu-Sn alloy with chromium deposit was found to be a potential alternative to the nickel with chromium deposit for applications where appearance is primary, no alternative could be found to match the corrosion protection provided by the standard nickel and chromium process.

Understanding the characteristics of special nuclear materials in LiCl-KCl eutectic salt is extremely important in terms of effective system operation and material accountability for safeguarding pyroprocessing technology. By considering that uranium (U) is the most abundant and important element in the used nuclear fuel, measurements and analyses of U properties were performed in LiCl-KCl eutectic salt. Therefore, the electrochemical techniques such as cyclic voltammetry (CV), open circuit potential (OCP), Tafel, linear polarization (LP), and electrochemical impedance spectroscopy (EIS) were conducted under different experimental conditions to explore the electrochemical, thermodynamic, and kinetic properties of U in LiCl-KCl eutectic. The ultimate goal of this study was to develop proper methodologies for measuring and analyzing the exchange current density (i0) of U3+/U reaction, which has not been fully studied and understood in literature. In the preliminary study, cerium (Ce) was selected as a surrogate material for uranium and its behavior was being explored with the developments of experimental methods. CV was performed to evaluate Ce properties such as the diffusion coefficients (D), apparent standard reduction potential (E0*), Gibbs free energy (DG), and activity coefficient (g). In addition, EIS methods were adapted and specific experimental procedures were established for the proper i0 measurements providing repeatable and reproducible data sets. The i0 values for Ce3+/Ce pair were ranging from 0.0076 A cm-2 to 0.016 A cm-2, depending on the experimental conditions. These preliminary results give insight in developing the experimental setups and methods to evaluate the properties of U in LiCl-KCl. Plus, Ce is one of the lanthanide (Ln) fission products in electrorefiner (ER) system; therefore, the resulting data values yield useful information of the fundamental behaviors of Ln elements in the system. Based on these developed methodologies, the experimental designs and routines were established to explore the main properties (e.g., D, E0*, etc.) of UCl3 in LiCl-KCl eutectic salt under different concentrations (0.5 wt% to 4 wt% UCl3) and temperatures (723 K to 798 K). Specially, the i0 values of U3+/U were evaluated via EIS, LP, Tafel, and CV methods. All i0 values had linear trends with the change of concentration and temperature; however, these values measured by LP, Tafel, and CV methods were greatly influenced by the change in electrode surface area. Overall, the i0 values agreed within 33% relative error range with the EIS method being the most consistent and accurate in comparison to reported literature values. The measured values of i0 were ranging from 0.0054 A cm-2 to 0.102 A cm-2. Therefore, an extremely reliable database for i0 was provided and it is feasible to anticipate the i0 kinetics in other experimental conditions by using the provided equation models. Furthermore, GdCl3 was added to the LiCl-KCl-UCl3 system to explore the effects of other elements on the U properties such as the diffusion coefficients, thermodynamic properties, and i0 kinetics. The diffusion coefficient was generally decreased by 12 ~ 35% with addition of GdCl3 in LiCl-KCl-UCl3; however, the apparent standard potentials and exchange current density follow the same trends with data obtained without GdCl3 additions. Hence, the results indicate that the thermodynamic and kinetic values for U3+/U reaction in LiCl-KCl eutectic salt are not greatly influenced by the presence of GdCl3.

L'utilisation de revêtements sol-gel pour la protection contre la corrosion des métaux est une alternative aux traitements à base de chromates, proscrits du fait de leur forte toxicité. Ces travaux de thèse ont porté sur la caractérisation de revêtements sol-gel hybrides organique-inorganique contenant des pigments inhibiteurs de corrosion non toxiques, pour la protection contre la corrosion de l'alliage d'aluminium 2024. Tout d'abord, la caractérisation par spectroscopie d'impédance électrochimique de différents revêtements relativement poreux a permis d'analyser l'influence de l'épaisseur, de la température de séchage, de l'hydrolyse de la partie silane et du ratio silane/amine sur les performances du revêtement, en particulier des propriétés barrière. Puis, l'ajout d'un époxy dans la formulation a permis d'augmenter de façon significative les propriétés barrière du film. Les diagrammes d'impédance présentent une dispersion en fréquence, exprimée en termes de « constant phase element (CPE) », en haute et basse fréquence. En haute fréquence, ce comportement a été analysé à l'aide d'un modèle qui permet d'obtenir des profils de résistivité dans l'épaisseur du revêtement et au cours du temps d'immersion. Ce modèle est appliqué pour la première fois à l'étude de revêtements. Différents pigments inhibiteurs de corrosion ont ensuite été incorporés dans des revêtements de porosité différente. L'action des inhibiteurs est exacerbée lorsqu'ils sont incorporés dans un revêtement poreux. Néanmoins, lorsqu'ils sont incorporés dans un film dense, les performances vis-à-vis de la résistance à la corrosion sont élevées. / The use of sol-gel coatings for the protection against the corrosion of metals is an alternative to chrome-based treatments, banned for the industry for their high toxicity. This work is based on the characterisation of hybrid organic-inorganic coatings, filled with non-toxic corrosion inhibitors, for the protection against the corrosion of aluminium alloy 2024. First, the characterisation by electrochemical impedance spectroscopy of different, relatively porous coatings, allowed the investigation of the influence of thickness, drying temperature, silane hydrolysis, and the silane/amine ratio on the coating performances, in particular the barrier properties. Then, the addition of an epoxy compound in the formulation allowed a significant increase in the film barrier properties. The impedance diagrams show a frequency dispersion, expressed in terms of a constant phase element (CPE), both in the high and low frequency range. In the high frequency range, this behaviour was analyzed using a model that allows obtaining resistivity profiles in the thickness of the coating and with immersion time. This model is applied for the first time to study coatings. Different corrosion inhibitors were then incorporated in coatings of different porosity. The action of the inhibitors was heightened when they are incorporated in a porous coating. Nevertheless, in a dense coating, the performances towards corrosion are high.

Lithium-ion batteries are today finding use in automobiles aiming at reducing fuel consumption and emissions within transportation. The requirements on batteries used in vehicles are high regarding performance and lifetime, and a better understanding of the interior processes that dictate energy and power capabilities is a key to strategic development. This thesis concerns aging in lithium-ion cells using electrochemical tools to characterize electrode and electrolyte properties that affect performance and performance loss in the cells.   A central difficulty regarding battery aging is to manage the coupled effects of temperature and cycling conditions on the various degradation processes that determine the lifetime of a cell. In this thesis, post-mortem analyses on harvested electrode samples from small pouch cells and larger cylindrical cells aged under different conditions form the basis of aging evaluation. The characterization is focused on electrochemical impedance spectroscopy (EIS) measurements and physics-based EIS modeling supported by several material characterization techniques to investigate degradation in terms of properties that directly affect performance. The results suggest that increased temperature alter electrode degradation and limitations relate in several cases to electrolyte transport. Variations in electrode properties sampled from different locations in the cylindrical cells show that temperature and current distributions from cycling cause uneven material utilization and aging, in several dimensions. The correlation between cell performance and localized utilization/degradation is an important aspect in meeting the challenges of battery aging in vehicle applications.   The use of in-situ nuclear magnetic resonance (NMR) imaging to directly capture the development of concentration gradients in a battery electrolyte during operation is successfully demonstrated. The salt diffusion coefficient and transport number for a sample electrolyte are obtained from Li+ concentration profiles using a physics-based mass-transport model. The method allows visualization of performance limitations and can be a useful tool in the study of electrochemical systems. / <p>QC 20140512</p>

Bei der Errichtung von Windenergieanlagen in Mittelgebirgsregionen ist darauf zu achten, daß an windexponierten Standorten die Gefahr einer Vereisung der Rotorblätter besteht. Es wurden klimatologische Daten im Bereich der Mittelgebirge ausgewertet und daraus eine Karte erarbeitet, in der die jährliche mittlere Häufigkeit der Tage mit Eisablagerungen dargestellt ist. / With the installation of wind turbines in low mountain areas the hazard of ice accretions on rotor blades at windy places must be considered. Interpreting climatological datas of the low mountain areas of S. E. Germany a map has been produced which shows the annual frequencies of days ice accretions on structures occurs.

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.

Esta escrita t ranscorre por linhas que t rabalham um currículo e uma didát ica da t radução. Esse ato de escrever alia-se à imagem poét ica para pensar deslocamentos dos sete elementos que const ituem os blocos de pensamento de um currículo (EIS) e de uma didát ica (AICE). A escrita vem do corpo do pensamento e da linguagem, que se violentam ao encont ro de pensar como criação, sob os conceitos filosóficos de Deleuze e da filosofia da diferença. Os significados das palavras t ranspassam o sent ido literal, ao serem usadas como imagens poét icas e t ranscriadas num Dançário de EIS AICE. Produz poét ica na tentat iva de pôr, em movimentos, textos das imagens eisaiceanas ao serem operacionalizados com materiais desenvolvidos no Projeto Escrileit uras: um modo de ler e escrever em meio à vida, Obeduc/CAPES/INEP (2011-2014) problemat izando a ação docente nos espaços t radutórios do currículo e da didát ica ao most rar suas experimentações em t rês blocos de escrita. De modo que as palavras movam-se por um devir dançante buscando um vazio de fala, de um autor e de uma escrileitura por vir. Propõem dispor, diante dos arquivos operatórios, diferentes formas de pensar sobre o bloco de pensamento de EIS AICE. / This writ ing works with a curriculum and didact ics of the t ranslat ion. This act of writ ing join the poet ic image to think about displacement s of the seven element s that const itute the blocks of thought about a curriculum (EIS) and didact ics (AICE). The writ ing comes from the body of the thought and the language that they clash at t ime to think of creat ion, under the philosophical concept s of Deleuze and the philosophy of difference. The meanings of the words t ranscend the literal meaning, when they are get using as poet ic images and recreated in an Dancing of EIS AICE. I t produces poet ics in the at tempt to put , agoing, text s of the eisaiceanas images when they are operat ionalized with materials developed in the Escrileituras Project : um modo de ler e escrever em meio à vida, Obeduc / CAPES / INEP (2011-2014), problemat izing the teaching act ivity in spaces of the curriculum and didact ics by showing their experiment s in three writ ing blocks. So that the words move through a dancing becoming, seeking a void of speech, of an author and of a writ reading to come. The writ ing proposes to provide, before the operat ive archives, different ways of thinking about the block of thought of EIS AICE.

Made available in DSpace on 2014-06-12T17:38:11Z (GMT). No. of bitstreams: 2 arquivo3828_1.pdf: 4684455 bytes, checksum: 46054e6422517113c139a624d80d96ab (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2008 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O custo global ocasionado pela corrosão representa uma elevada perda econômica. Várias são as tentativas de retardar o processo de corrosão, destacando-se o uso de revestimentos metálicos e orgânicos. Neste trabalho, avaliaram-se as propriedades anticorrosivas de revestimentos aplicados sobre aço carbono utilizados nas áreas industriais como alternativas de proteção anticorrosiva, sendo eles: esquemas de pintura, galvanização a quente e sistema duplex, que consiste na associação da galvanização e pintura. Os ensaios foram realizados em sistema estático de imersão e em sistema dinâmico do tipo looping, contendo água do mar da região do Complexo Portuário e Industrial de SUAPE (Ipojuca PE), onde se encontra instalada a empresa Termoelétrica de Pernambuco (TERMOPE). Para avaliação da influência biocorrosiva no processo de deterioração do metal base e dos revestimentos, os ensaios de imersão em sistema estático foram conduzidos em duas condições: meio estéril (com biocida) e meio não estéril (sem biocida), sendo monitorados ao longo do tempo os parâmetros microbiológicos do meio. Para avaliação do desempenho anticorrosivo dos revestimentos, utilizou-se o monitoramento eletroquímico através da medida de potencial de circuito aberto e da técnica de Espectroscopia de Impedância Eletroquímica (EIS). A técnica de EIS apresentou-se bastante sensível à presença de defeitos nos revestimentos e também apresentou respostas diferenciadas para o comportamento dos revestimentos em meio estéril e meio não estéril. O ensaio em looping mostrou-se mais severo do que o ensaio em sistema estático, sendo a corrosividade obtida em cada sistema, respectivamente classificada como, alta e moderada. O processo biocorrosivo para o meio estático teve uma contribuição aproximada 15,27% para a corrosão observada no metal não revestido, após 75 dias de exposição. O processo de formação de biofilme ao longo do tempo foi mais acentuado no sistema dinâmico do tipo looping, onde, devido ao processo de recirculação da água observou-se um aumento significativo da quantidade de microrganismos presentes no meio

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.

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.