Nos últimos anos, a utilização de nanotubos (Nts) de dióxido de titânio (TiO2) têm atraído interesse tecnológico e científico de forma significativa devido às suas propriedades únicas, tais como grande área de superfície específica, alta capacidade de absorção e apresentam excelentes atividades fotoeletroquímicas e um meio para melhorar essas propriedades está relacionada ao controle da morfologia dos Nts durante a sua sintetização no processo de anodização. O objetivo desse estudo é avaliar a influência do potencial aplicado durante o processo de anodização para obtenção de Nts de TiO2, tendo em vista a utilização desses nanotubos como catalisador fotoeletroquímico. Para que houvesse a cristalização do óxido, realizou-se tratamento térmico a 400 °C ao ar, durante 3 h com taxa de aquecimento de 10 °C / min. Analisou-se a relação do potencial aplicado durante o processo de anodização com a morfologia dos nanotubos e a sua resposta fotoeletroquímica. As caracterizações foram realizadas através das técnicas de microscopia eletrônica de varredura com emissão de campo (MEV-FEG), difração de raios X (DRX), espectrofotometria no ultravioleta visível (UV-VÍS), voltametria linear e espectroscopia de impedância eletroquímica (EIE).Observou-se que o potencial de anodização exerce influência na geometria do nanotubo, isto é, no comprimento, na espessura da parede e no diâmetro, alterando a absorção de luz e, consequentemente, o desempenho fotoeletroquímico das amostras. Os resultados obtidos por espectroscopia de impedância eletroquímica mostraram pouca diferença na resistividade das amostras estudas. Contudo, as correntes desenvolvidas no ensaio de voltametria linear, indicaram que a amostra Nt30 é um fotoeletrodo promissor para formar heteroestruturas baseado em nanotubos de dióxido de titânio. / In recent years, the use of TiO2 nanotubes (Nts) has attracted technological and scientific interests in a significant way due to its unique properties, such as large specific surface area, high absorption capacity and excellent photoelectrochemical activities. One way to improve these properties is to control the nanotubular morphology during its synthesis through the anodizing process. The objective of this study is to evaluate the influence of the applied potential during the anodization process to obtain titanium dioxide (TiO2) nanotubes and applying these nanotubes as a photoelectrochemical catalyst. In order to crystallize the Nts, heat treatment was carried out at 400 ° C in air for 3 h at a heating rate of 10 ° C / min. The effect of the applied potential during the anodizing process on the morphology of the nanotubes and their photoelectrochemical response were analyzed. The characterization was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), visible ultraviolet spectrophotometry (UV-VIS) and electrochemical impedance spectroscopy (EIS). It was observed that the anodization potential influences the geometry of the nanotubes, that is, their length, wall thickness and diameter, altering their light absorption properties; consequently, influencing the photoelectrochemical performance of the samples. The results obtained from the electrochemical impedance spectroscopy showed a slightly small difference in the charge transportation resistance of the studied samples. However, the currents developed in the linear voltammetry tests indicated that the Nt30 sample is a promising photoelectrode to apply for other applications such as heterostructures and cationic/anionic doped structures based on titanium dioxide nanotubes.

Laser surface melting (LSM) of aluminium alloys with high power continuous wave (CW) CO2 and Nd:YAG lasers has been shown to produce dendritic/cellular microstructures with refined second-phase particles distributed along the dendritic boundaries. Although refinement of the microstructure and extension of the solute solubility in the matrix can be achieved, the refined second-phase particles still act as preferential sites to initiate localized corrosion. In contrast to a CW laser, an excimer laser with a UV wavelength and pulses width in the range of nanoseconds, resulting in extremely high cooling rate up to 1011 K/s, is expected to generate a further refining of the near-surface microstructure and hence, improved corrosion performance. In this project, a Lumonics IPEX 848 KrF excimer laser, with a wavelength of 248 nm and pulse width of 13 ns, has been used for surface melting of an AA2024-T351 alloy. The aim is to investigate the microstructure and the resultant corrosion behaviour of the laser treated surface, and its contribution to alloy performance. The laser fluence was fixed at 7 J/cm2 and the number of pulses per unit area was varied as 10, 25 and 50 pulses respectively. Microstructural characterisation and compositional analysis have been performed by SEM/EDX, TEM/EDX and XRD to disclose solidification phenomena and phase transformations. The results show that the melted layers, with a melt depth from 3 to 7 µm, have been achieved, that is far more chemically uniform than the bulk alloy. In particular, the relatively fine precipitates and dispersoids in the matrix have been dissolved, while large constituent intermetallic particles at the melted layer/matrix interface have been partially melted. In addition, solute-rich bands, containing particularly copper, were formed within the melted layers, especially at the melted layer/matrix interface. SKPFM also reveals that the laser-melted layers exhibit a uniform surface potential distribution. The corrosion performance of AA2024-T351 alloy before and after LSM has been evaluated by anodic polarisation in deaerated and aerated 0.1 M NaCl solution, and immersion tests in 0.1 NaCl solutions. Exfoliation corrosion immersion test ASTM G34- 01 (EXCO test) was also carried out to evaluate the intergranular corrosion (IGC)/exfoliation resistance of the alloy. The results show that the untreated alloy exhibits severe pitting corrosion and IGC. After LSM, significant improvement of corrosion resistance has been achieved. However, delamination of the laser melted layer from the matrix was evident after an EXCO test for 6 hours. The absence of significant corrosion product may suggest a stress-related mechanism. In order to investigate the effect of LSM on anodising of AA2024-T351 alloy and its influence on the corrosion resistance, excimer LSM has been applied as a pre-treatment method prior to anodising in 0.46 M H2SO4 solution. The results show that LSM significantly improved the corrosion performance following anodising compared with the alloy anodised without LSM and LSM alone.

Anodic films have been produced on zirconium and zirconium alloys potentiostatically (at either 20 or 40 V) in 0.35 M ammonium fluoride in glycerol, with interest in the addition of small amounts of water (up to 5 vol.%) to the electrolyte on their growth, morphologies and compositions. Scanning and transmission electron microscopies have been employed to analyse morphologies of the films, which appeared to be porous under all the investigated conditions.Rutherford backscattering spectroscopy and nuclear reaction analysis, used as techniques to investigate film compositions, disclosed the presence of zirconium, oxygen, fluorine, carbon and nitrogen in the films. The contents of fluorine and oxygen in the films were found to increase and decrease respectively by decreasing the amount of water added to the electrolyte from 5 to 0 vol.%. Moreover, the content of fluorine increased by decreasing the applied formation voltage, from 40 to 20 V, for films formed in electrolytes containing similar amounts of added water.In order to get information on the distribution of the species in the films, cross-sections of selected specimens were produced by focused ion beam and analysed by analytical transmission electron microscopy. Oxide-rich nanotubes were revealed embedded in a fluoride-rich matrix, suggesting that the mechanism of growth of the anodic films is governed by different migration rates of the anionic species in the film base, with F- ions, being the fastest anions. The relative amounts of the oxide-rich and fluoride-rich materials were related to the composition of the electrolyte, with the fluoride regions being less extensive and the oxide-rich nanotubes being thicker-walled by adding small amounts of water. Moreover, nanotubes are constituted of two shells (an outer one surrounding the pores and an inner one located between the outer shell and the matrix), suggesting differences in the composition in these two regions, presumed to be due to the incorporation of carbon species, being the slowest migrating species, in the outer shell. The fluoride-rich matrix chemically dissolved following 1 h immersion of the specimens in the formation electrolytes, promoting the transition from porous to nanotubular morphologies. Ageing of the specimens in deionized water for similar times did not significantly influence the morphologies and compositions of the anodic films.

The present study investigates the effect of fluorine species during anodizing of aluminium and AA2024-T3 alloy in sulphuric acid and tartaric-sulphuric acid (TSA) electrolytes. The investigation comprises four main parts; (i) Effects of fluoride on barrier film formation on aluminium. (ii) Effects of fluoride and fluorozirconic acid (FZ) on porous film growth on aluminium in sulphuric acid. (iii) Effects of FZ on porous film growth on aluminium and AA 2024-T3 alloy in sulphuric acid and TSA. (iv) Effects on anodizing of other fluoroacids (fluoroboric (FB), fluorosilicic (FS) and fluorotitanic acid (FT)). The anodic films were examined by analytical scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, Rutherford backscattering spectroscopy, nuclear reaction analysis and glow discharge optical emission spectroscopy. The behaviour of fluoride ions during the growth of barrier-type films on aluminium was investigated in ammonium pentaborate solution with added sodium fluoride. Additions of up to 3.5 x 10-3 M sodium fluoride had a negligible influence on the film growth. In contrast, 3.5 x 10-2 M sodium fluoride reduced the efficiency to 60% as fluoride ions promoted field-assisted ejection of Al3+ ions from the film. Incorporated fluoride ions migrated inwards at a rate about twice that of O2- ions, forming a fluoride-rich layer at the film base. The study of the influence of FZ on formation of porous anodic films in sulphuric acid and TSA employed a range of anodizing voltages, electrolyte temperatures and anodizing times. Fluoroacid increased the growth rate, with a reducing influence as the temperature increased. The films contained fluoride and sulphate ions, zirconium was not detected. The fluoride concentration decreased with increasing temperature, whereas the sulphate concentration was unaffected. Anodizing aluminium and AA 2024-T3 alloy in other fluoroacids resulted in similar influences on the anodizing behaviour as FZ. The differences in growth rate, film composition and film morphology were comparatively small and did not show a systematic dependence on the type of fluoroacid employed. Boron, silicon and titanium were not detected in the films.

In this work, the nucleation and growth of pores in anodic films formed on aluminium in chromic acid and the effect of low levels of sulphate impurity in the anodizing bath on the formation of the films on aluminium and AA 2024 alloy are investigated. The sulphate concentrations considered include levels within specified limits for industrial processing. The anodizing is carried out either potentiostatically or by stepping the voltage. The films are examined by scanning electron microscopy, transmission electron microscopy and atomic force microscopy to determine the pore spacing, pore population densities, pore diameters and film thicknesses. Film compositions were determined using energy-dispersive X-ray spectroscopy, Rutherford backscattered microscopy and nuclear reaction analysis. In order to investigate the mechanism of pore formation, two tracer methods are employed. In one method, anodic films are formed first in an arsenate electrolyte in the second method, a tungsten tracer band deposited by magnetron sputtering. The behaviours of arsenic and the tungsten are investigated during the subsequent anodizing in chromic acid. The results suggest that the initiation and growth of pores in occurred as a result of electric field assisted chemical dissolution. The effect of sulphate impurity in the chromic acid is investigated using electrolytes with different sulphate content. In the initial stages of anodizing aluminium at 100 V, sulphate impurity at a level of 38 ppm in the chromic acid is shown to lead to significant incorporation of sulphate ions into the anodic film, a lower current density, a smaller cell size and less feathering of the pore walls. In addition, the efficiency of film formation is increased. In later stages of anodizing, the growth of larger pores and cells, leads to a duplex film morphology, with finer pores in the outer region. The change in pore size correlates with a reduction in the incorporation of sulphate into the film. From the results of sequential anodizing experiments, it is suggested that incorporated sulphate ions generate a space charge layer, which has an important role in determining the current density. The effects of higher sulphate concentrations up to 3000 ppm are investigated, which are shown to significantly affect the current density and the pore diameter. Anodizing of aluminium and AA 2024 alloy was also carried out according to industrial practice. The results show that there is significant effect of sulphur impurity on the film thickness. Corrosion tests in 3.5 % NaCl solution for the alloy after anodizing in low (smaller or equal to 1.5 ppm) and high (~38 ppm) sulphate-containing chromic acid electrolytes demonstrate a better corrosion resistance with films formed in the latter electrolyte.

Neste trabalho é estudada a influência de Friction Stir Welding (FSW) em um processo subsequente de anodização porosa, avaliando-se o impacto da microestrutura produzida por FSW na espessura, na estrutura e na resistência à corrosão de óxidos anódicos. Um perfil da liga AA7050 foi soldado por FSW a um chapa da liga AA2024, simulando a junta sobreposta entre reforçadores e revestimento na fuselagem de um avião. Como uma primeira aproximação, a superfície da liga AA7050 em contato com a ferramenta de soldagem foi selecionada para a anodização, por ser o lado que sofre maior modificação microestrutural. A solda foi caracterizada por técnicas de microscopia ótica e eletrônica, distinguindo-se três zonas: zona afetada pelo calor (ZAC), zona termomecanicamente afetada (ZTMA) e nugget (onde ocorre recristalização dinâmica). Medições de dureza Vickers revelaram uma menor dureza na fronteira entre ZTMA e ZAC, provavelmente devido à dissolução de precipitados. Amostras da solda foram anodizadas galvanostaticamente em eletrólito sulfúrico, sendo algumas seladas em água deionizada fervente. A camada de óxido produzida sobre a ZTMA é ainda mais espessa do que sobre o material base e apresenta uma interface plana com o substrato, enquanto no nugget a camada de óxido é mais fina e tem interface rugosa. Infere-se que a presença de precipitados endurecedores (como MgZn2) afeta a espessura dos filmes de óxido. Defeitos relacionados à dissolução de precipitados ricos em Cu são encontrados nos filmes de óxido em todas as zonas. A técnica de varredura com eletrodo vibratório (SVET) foi utilizada para testar a resistência à corrosão dos filmes de óxido em eletrólito contendo NaCl, com polarização simultânea acima do potencial de pite. Ocorre corrosão por pite preferencialmente no nugget e em sua fronteitra com a ZTMA. Por fim, transientes de corrente são calculados para cada pite a partir dos mapas de SVET. Conclui-se que as soldas FSW anodizadas apresentam região localizada de menor resistência à corrosão pelo crescimento heterogêneo da camada anódica, mas alta resistência à corrosão é atingida após selagem. / In this work, the influence of Friction Stir Welding (FSW) on a posterior porous anodizing process is studied, with emphasis on how the friction stir weld’s microstructure affects thickness, structure and corrosion resistance of anodic oxide films. An AA7050 profile was friction stir welded to an AA2024 sheet in order to simulate the assembly of airplane stringers and skin. As a first approach, the AA7050 surface facing the welding tool was selected for anodizing, for it is the side that is most modified. The weld was characterized by optical and electron microscopy techniques, and 3 different zones were distinguished: heat affected zone, thermomecanically affected zone (TMAZ), and the nugget (where dynamic recrystallization occurs). Vickers hardness measurements revealed a lower hardness at the frontier between thermomecanically and heat affected zones, possibly due to dissolution of precipitates. Welded samples were galvanostatically anodized in sulfuric electrolyte and some of them were sealed in boiling deionized water. Micrographs showed that on the TMAZ the anodic oxide is thicker than on the base material and the metal/oxide interface is flat. On the nugget zone, however, the anodic oxide is thinner and more defective, and the metal/oxide interface is rougher. It is inferred that the presence of hardening precipitates (such as MgZn2) affects the thickness of oxide films. Defects related to the dissolution of Cu-rich precipitates were found in the oxide layers on all zones and inferences about how they affect anodization kinetics are drawn. The Scanning Vibrating Electrode Technique (SVET) was used to test the corrosion resistance of anodic oxide layers in NaCl electrolyte. The samples were scanned simultaneously to anodic polarization at a potential higher than the AA7050 alloy’s pitting potential. Results showed that pitting happened preferentially on the nugget zone and its frontier with the TMAZ. Finally, pit current transients were calculated from SVET maps. It can be concluded that anodized friction stir welds present a region of diminished corrosion resistance caused by heterogeneous anodic oxide growth, but high corrosion resistance can be achieved after sealing.

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.

Anodisation has been studied for almost eighty years, primary in the field of corrosion science, as a simple and efficient way of producing thick protective oxide coatings on Al, Ti or Zr alloys. Anodisation is an electrochemical oxidation process which relies on the migration of ions across solid films under the action of a large electric field. From the fundamental point of view, many aspects regarding the growth of anodic films have been studied extensively. However, so far, little interest has been devoted to the mechanical aspects involved in the growth process, despite their considerable importance both from an applied as well as from a fundamental point of view. A solid understanding of internal stresses development is indeed crucial in order to guarantee the durability of anodic coatings, their structural and functional properties. In addition, the stress evolution directly reflects the motion of the ions in the film and therefore provides a unique means to investigate in situ the growth mechanisms of anodic films. In this thesis, we have studied the evolution of the internal stresses in anodic TiO2 films in situ during their growth. The stresses have been obtained from changes in the curvature of cantilevered anode samples, measured using a high-resolution multi-beam optical sensor. We demonstrate, for the first time, the capability of this type of curvature sensor for monitoring processes in liquid environments. Experimental data on the internal stresses developing in anodic TiO2 films is provided, and trends regarding the influence of the experimental conditions on the stress evolution are identified. In particular, the evolution of the internal stresses is shown to be strongly correlated with the evolution of the electrochemical variables, which directly demonstrates the interest of curvature measurements as a fundamental technique for investigating the details of the growth process of anodic oxide films. The reversible and irreversible stress contributions associated, respectively, with electrostriction and with growth-related ionic transport have been separated from one another and quantified. A novel constitutive model for the electrostriction stress has been proposed which explicitly takes into account the effect of dielectrostriction.

La faible masse volumique et les bonnes propriétés mécaniques des alliages d’aluminium en font des matériaux de structure de choix dans l’industrie aéronautique. Ils présentent une microstructure polyphasée qui crée des discontinuités électrochimiques et une sensibilité accrue à la corrosion. Un système de revêtements protecteurs composé de chromate Cr(+VI) est traditionnellement formé à la surface de ces alliages. Néanmoins, les directives environnementales REACH imposent leur remplacement en raison de la cancérogénicité des chromates. L'objectif des travaux a été le développement d'un nouveau traitement constitué d’une Oxydation Anodique Sulfurique (OAS) et d’un colmatage aux sels de sulfate de chrome et de fluorozirconate (Cr3+ / ZrF62-). L’étude du procédé électrochimique d’OAS a permis de faire le lien entre la microstructure des alliages et la morphologie poreuse de la couche anodique développée à leur surface. Le traitement de colmatage Cr3+ / ZrF62- est réalisé par simple immersion dans la solution. Il est démontré que le colmatage est le fait d’une alcalinisation locale de la surface de la couche anodique qui mène à la précipitation des sels de Cr3+ et ZrF62-. Ces derniers forment un film de colmatage de 300 nm d’épaisseur très recouvrant des pores nanométriques. Le colmatage des couches anodiques permet d’améliorer considérablement la tenue à la corrosion des alliages anodisés en formant une barrière supplémentaire contre les agents corrosifs et en cicatrisant les départs de corrosion. Le traitement développé permet à la fois d’atteindre les performances des traitements aux Cr(+VI) sur une large gamme d’alliages et de satisfaire aux exigences environnementales / Aluminium alloys are very used in the aircraft industry as structural materials because of their low density and their good mechanical properties. They have a polyphase microstructure that is causing electrochemical discontinuities and increasing sensitivity to corrosion. A system of protective coatings containing chromate Cr(+VI) is traditionally formed at the surface of these alloys. However, the REACH environmental guidelines impose Cr(+VI) surface treatments replacement because of chromate carcinogenicity. The aim of the thesis work has been the development of a new surface treatment constituted of a sulfuric acid anodizing (SAA) and a sulfate chromium and fluorozirconate salts sealing (Cr3+/ ZrF62-). The study of the SAA electrochemical process linked the alloys microstructure and the anodic layer porous morphology developed at their surface. The Cr3+ / ZrF62- sealing treatment is realized by a simple immersion of the anodized alloy in the solution. It is demonstrated that the sealing is caused by a local alkalinization of the anodized coating surface that leads to the precipitation of the Cr3+ and ZrF62- salts. These ones are forming a sealing film of about 300 nm thick, very covering of the nanometric pores. The anodic layers sealing greatly improves the corrosion resistance of the anodized alloys by forming an additional barrier against corrosive agents and by healing the corrosion initiation. The developed treatment allows both to achieve Cr(+VI) treatments performance over a wide range of alloys and to satisfy the environmental requirements.

Embora o uso do cimento Portland com altos teores da fase alita [silicato tricálcico - C3S – (CaO)3.(SiO2)] seja difundido mundialmente, argumentos ambientais indicam a fabricação de cimentos com baixos teores desta fase e altos teores da fase belita [silicato dicálcico - C2S, (CaO)2.(SiO2)] justamente ao contrário do que é produzido atualmente. A alita tendo mais cálcio que a belita, libera mais CO2 para a atmosfera quando ocorre a decomposição do calcário (CaCO3 CaO + CO2 ) durante sua fabricação. Além disso, o C2S é formado a uma temperatura mais baixa (800 a 900ºC) que a temperatura em que o C3S (1350 a 1450ºC) é formado, necessitando desta forma, menos combustível e produzindo um cimento de moagem mais facilitada, tornando-o mais eco-eficiente. Um aspecto negativo dos cimentos belíticos é que os mesmos atingem seu nível máximo de resistência em idades mais avançadas, e este comportamento não é considerado adequado na indústria da construção civil atual, que busca alta produtividade em um curto espaço de tempo. Uma maneira de eliminar este problema seria acelerando as reações iniciais de hidratação e endurecimento. Uma alternativa à esta questão é combinar estes clínqueres belíticos com agentes expansivos de base sulfoaluminato ou em uma produção simultânea no clínquer, tais como os sulfoaluminato de cálcio belítico (CSAB), sendo estes ligantes considerados de baixo impacto ambiental. No entanto, o cimento CSAB requer uma maior quantidade de alumina, que geralmente é provinda da bauxita na sua fabricação. Devido ao elevado custo da bauxita para a produção deste cimento, a utilização de resíduos ricos em alumina é uma opção que pode agregar valor ao resíduo e aumentar a disponibilidade de ligantes de reduzido impacto ambiental. Desta forma, este trabalho apresenta uma alternativa para utilização do resíduo na produção do cimento CSAB. Foi realizada a caracterização físico-química do resíduo estudado, e são apresentados os resultados da produção de clínqueres CSAB formados a partir de três misturas, com variações no teor deste resíduo. As propriedades físico-mecânicas destes clínqueres foram avaliadas e comparadas com um clínquer referência e um cimento Portland comercial, da mesma forma, técnicas de difração de raio X, calorimetria e termogravimetria foram utilizadas para verificar a formação dos produtos de hidratação de pastas. Desta maneira, foi demonstrado que o aproveitamento do resíduo de anodização do alumínio para a produção do cimento CSAB é viável tecnicamente. O produto gerado possui características especiais, apresentando elevado desenvolvimento da resistência mecânica nas primeiras horas de hidratação. / Although currently Portland cement with high alite [(CaO)3.(SiO2)] content is the most used globally, environmental advices call for changes on the production for cements with lower alite and higher belite [(CaO)2.(SiO2)] contents. Alite, having more calcium than belite, releases more CO2 to the atmosphere in the course of cement manufacture, due to limestone decomposition (CaCO3 CaO + CO2 ). Besides, belite is formed at lower temperatures (800- 900ºC) than alite (1350-1450ºC), and for this reason less fuel is necessary for the process. Additionally, clinker is easier to grind, resulting in a less energy demanding and more sustainable process. However, belite cements reach the maximum strength level at later ages, drawing back the fast and active civil construction industry, which aims high productivity in a short time spam. In order to minimize this problem it is possible to accelerate the initial hydration reactions and hardening by combining the belite clinkers with expansive sulfoaluminate base agents, or in a simultaneous clinker production, such as calcium sulfoaluminate belite cements (CSAB). These binders have lower environmental impact. However, CSAB cement requires a higher amount of alumina, which comes from bauxite. As this material is costly, the use of alumina-rich residues comes as an option to aggregate value to the residue and to increase the availability of low environmental impact binders. This work presents an alternative use for alumina-rich residues in CSAB cement production. Physicochemical characterization of the aluminium anodizing sludge is presented together with results of the production of CSAB clinkers from 3 mixtures, with different residue content. Properties of the produced clinkers were evaluated and compared to a control clinker and to an ordinary Portland cement. X-ray diffraction, calorimetry and thermogravimetry analysis track the formation of hydration products in the cement pastes. The use of aluminium anodizing sludge to produce CSAB cement was proved to be technically viable, as the generated product has special characteristics, presenting high mechanical strength development at the first hours of hydration.