Dissertations / Theses on the topic 'Aluminium corrosion inhibitors'

Les composés à base de chrome hexavalent sont industriellement utilisés pour inhiber la corrosion des alliages d'aluminium. Ils sont reconnus comme étant des inhibiteurs de corrosion très efficaces et permettent de renforcer les propriétés inhibitrices de la couche d'oxyde formée naturellement sur la surface en présence d'oxygène dans un environnement favorable. Cependant ces composés sont toxiques et cancérigènes. Ils doivent être éliminés (directives européennes) et remplacés par de nouveaux inhibiteurs de corrosion aussi efficaces mais respectueux de l'environnement. Certaines molécules organiques, biodégradables et non toxiques, pourraient jouer ce rôle. De nombreux travaux expérimentaux ont notamment démontré l'efficacité de la molécule de 8-hydroxyquinoléine (8HQ) pour améliorer la résistance à la corrosion de l'aluminium pur et de l'alliage 2024. Néanmoins, le mécanisme de l'inhibition de la corrosion à l'échelle atomique par cette molécule restait inconnu. Dans ces travaux de thèse, nous avons cherché, à l'aide de calculs de physico-chimie quantique, à identifier des facteurs favorables aux processus d'inhibition. Les propriétés d'inhibition de la corrosion sont directement liées au mécanisme d'interaction et aux phénomènes d'adsorption de ces molécules sur la surface du substrat. Nous avons ainsi étudié l'interaction de la molécule 8HQ et ses dérivés sur une surface Al(111). Les taux de recouvrement choisis ont permis de simuler divers cas, de l'adsorption d'une molécule isolée sur la surface à la formation de couches compactes sur le substrat. Outre la détermination des topologies d'adsorption et des énergies associées, nous avons réussi à déterminer la nature et la force des interactions molécules/substrat, notamment par l'étude de la structure électronique à l'interface hybride inhibiteur/métal. Quelle que soit la forme chimique de la 8-HQ (forme native, tautomère, espèces hydrogénée ou déshydrogénée) nous avons démontré que la couche organique adsorbée sur le métal est stable et fortement chimisorbée. Elle peut former une barrière à la pénétration d'agents agressifs sur la surface du substrat et limiter la réaction cathodique de réduction de l'oxygène. Les résultats obtenus contribuent à une meilleure connaissance des mécanismes d'inhibition de la corrosion de l'aluminium pur et aident à la recherche de nouvelles molécules qui pourraient assurer une protection avec une efficacité optimale
Chromates are currently used in the aeronautic industry to inhibit corrosion of aluminum alloys. They are known as very effective. However, these compounds are toxic and carcinogenic. They must be replaced by new efficient environmentally friendly corrosion inhibitors. Organic species that are biodegradable and non-toxic molecules could play this role. Several experimental studies demonstrated the efficiency of the 8-hydroxyquinoline molecule (8-HQ) to improve the corrosion resistance of pure aluminum and of 2024 aluminum alloy. However, the inhibition mechanism by the 8-HQ molecule is not totally understood, particularly at the atomic scale. In this PhD work, we tried, thank to DFT calculations, to identify factors that could be favorable to the inhibition processes. From a general point of view, the corrosion inhibition is directly related to the interaction mechanism and adsorption process of the molecules on the substrate surface. We studied the interaction of the 8-HQ molecule and its derivatives on the Al (111) surface. Various adsorption concentrations on the Al surface, from a single molecule to the formation of compact monolayer were modeled. Besides the determination of adsorption topologies and energies, we have identified the nature and strength of the molecules/substrate interactions by analyzing the electronic structure modification at the inhibitor/metal interface. Whatever the chemical form of the 8-HQ (native form, tautomer, hydrogenated or dehydrogenated species), it was demonstrated that the organic layer adsorbed on the metal is stable and strongly chemisorbed. This layer forms a barrier which could prevent the aggressive species to reach the Al surface and limit the oxygen cathodic reduction. The results contribute to a better understanding of the pure Al inhibition mechanisms and help the search for more efficient inhibitive “green” molecules

Mestrado em Engenharia de Materiais
The goal of this work was to systematically seek and study the corrosion and corrosion protection of metallic materials and alloys. Aluminium alloys were the materials in scope due to their specific properties (low density and good mechanical properties) and practical applications, especially in aeronautical industries. The systematic screening and development of corrosion inhibition strategies for extensive localised corrosion conditions at selected Al alloy surfaces has been done. To study these concepts the combination of well-known integral techniques such as EIS with sophisticated localized scanning vibrating probe technique (SVET) was systematically applied. The advantages of combining different techniques and approaches are critically analysed and evaluated from the point of view of corrosion behaviour estimation on different aluminium alloy surfaces in chloride containing electrolytic environments.
O objectivo deste trabalho foi procurar/pesquisar de forma sistemática os efeitos da corrosão em estruturas metálicas e ligas, bem como a protecção das mesmas a este fenómeno. Devido às suas propriedades específicas (baixa densidade e boa resistência mecânica) e aplicações práticas em áreas como a aeronáutica, as ligas de alumínio foram os materiais estudados. Este estudo foi feito através do enquadramento e desenvolvimento de estratégias de inibição da corrosão, à superfície das ligas de alumínio seleccionadas, em condições de extensiva corrosão localizada. A combinação e sistemática aplicação de técnicas de análise electroquímica - desde técnicas bem conhecidas de análise integral (EIS) a técnicas sofisticadas para análise localizada (SVET) - foram as ferramentas usadas para levar a cabo este estudo. As vantagens desta abordagem e da combinação de diferentes técnicas serão criticamente analisadas e avaliadas do ponto de vista da estimativa do comportamento corrosivo nas superfícies das diferentes ligas de alumínio quando em contacto com ambientes electrolíticos que contêm iões cloreto.

The present work provides an insight in the development of silica films prepared by water-based sol-gel process. The weaknesses of the coating technology are identified, also solutions are discussed. The silica film is applied on aluminium alloy 6082-T6 and magnesium alloy AZ31. The development of the coating properties such as cost-efficiency, crack-free, self-healing and long-term corrosion protection is the main topic of this work. Cracking is the major drawback of silica films; the cracks are generated due to shrinkage of the film during the heat treatment, nanoparticles-doped silica film is successfully reduced the shrinkage which leads to crack-free silica films. The self-healing of the coated aluminium and magnesium samples is generated by corrosion inhibitors-doped silica film. When a defect appears in the film, the corrosion inhibitors leach out of the silica film to the defect area to heal the corroded surface. The long-term corrosion protection is realized by means of a mixture of corrosion inhibitors-doped silica film
Die vorliegende Arbeit liefert einen Einblick in die Entwicklung von Silikafilmen, die mittels Sol-Gel-Prozess auf Wasserbasis hergestellt wurden. Die Schwächen der Beschichtungstechnologie werden dargestellt und Lösungen diskutiert. Der Silikafilm wird auf Aluminiumlegierung 6082-T6 und Magnesium-legierung AZ31 aufgebracht. Schwerpunkt dieser Arbeit ist die Entwicklung der Schichteigenschaften, wie Kosteneffizienz, Rissfreiheit, Selbstheilung so wie langfristiger Korrosionsschutz. Rissbildung ist ein wesentlicher Nachteil von Silikafilmen; rissfreie Filme wurden mittels nanopartikeldotierter Silikafilme hergestellt. Die Selbstheilung von Aluminium-und Magnesiumsubstraten mit Silikafilm wird durch den Effekt der wasserlöslichen Korrosionsinhibitoren generiert. Die Experimente haben gezeigt, dass die Proben mit inhibitordotierter Beschichtung selbst gegen Korrosion geschützt sind. Ein langfristiger Korrosionsschutz wird durch eine Mischung aus Korrosionsinhibitor-dotierten Silika-Film realisiert

L’alliage d’aluminium 2024 est très répandu dans l’industrie aéronautique et automobile. Le processus de corrosion peut entrainer des dommages irréversibles pouvant engendrer des issues fatales dans le domaine aéronautique. Ainsi plusieurs couches de revêtements sont déposées à la surface du métal à protéger pour prévenir le processus de corrosion. Depuis le début du 20ième siècle, le chrome hexavalent (CrVI) a été largement utilisé comme inhibiteur de corrosion dans les différentes couches du revêtement (prétraitement, primer et top-coat). La toxicité de ce composé envers l’homme et l’environnement a entrainé son interdiction et donc son remplacement comme agent de protection. Le confinement d’agent anticorrosif dans des nano-conteneurs a ainsi été reporté puisqu’un effet auto-réparant, en relargant sur demande, peut-être apporté : l’inhibiteur de corrosion agit quand le dommage apparait. Cette étude est focalisée sur l’utilisation de matériaux de type Hydroxydes Doubles Lamellaires (HDL) comme réservoir d’inhibiteurs de corrosion en raison leur propriété d’échange. Dans ce travail, plusieurs molécules ont été étudiées comme potentiel inhibiteur de corrosion. Celles-ci ont été tout d’abord caractérisées par DC-polarisation afin de déterminer la nature de leur comportement inhibiteur (anodique, cathodique ou les deux). Ensuite, ces agents anticorrosifs ont été intercalés dans des matrices HDL et leur capacité de relargage ainsi que leur comportement face au processus de corrosion ont été étudiés. Les particules HDL ainsi obtenues ont été dispersées dans la formulation d’un revêtement primaire et déposé directement sur l’alliage aluminium 2024. La résistance à la corrosion a été suivie par spectroscopie d’impédance complexe. Les propriétés d’auto-protection de notre revêtement (relargage d’agent anticorrosive encas de dommage) et leur propriété barrière, apportée par la morphologie lamellaire des nano-conteneurs, entrainant une diminution de la perméabilité aux espèces agressives (ex. eau, O2, électrolyte) responsable de l’apparition de cloques sur les revêtements, ont ainsi été caractérisées
Aluminum alloy 2024 is widely used in aircraft and automotive industry. Corrosion processes can provide irreversible damage on the metal substrate which could have a tragic issue in the aircraft domain. Thus, several coating layers have been applied on the metal substrate to prevent corrosion process. Since the beginning of the 20th century, hexavalent chromate compounds have been extensively used as corrosion inhibitor agents for paint, primer and conversion coating. The toxicity for human health and environment has led to replace such compounds. The literature has reported different possibilities to replace such unfriendly compounds. Moreover, the entrapment of corrosion inhibitors in nanocontainer provides a self-healing effect by releasing, on demand, the active species when damage occurs. This study focuses on Layered Double Hydroxide (LDH) material as reservoir due to its exchange properties. This study has characterized several potential corrosion inhibitor molecules by DC-Polarization to determine the nature of the inhibitor compound (i.e. anodic, cathodic or both of them). Further, active anticorrosive species have been intercalated into LDH framework. Then, the release of inhibitor agents and their subsequent behaviour toward corrosion inhibition have been evaluated. Modified LDH materials have been further dispersed in the primer coating formulation and applied on aluminum alloys 2024 substrate. Corrosion inhibition has been followed by electrochemical impedance spectroscopy experiments on scratched and unscratched panel which have permitted to evaluate the self-healing property of these modified LDH materials when damage occurs and the barrier property provided by the lamellar morphology of the inorganic reservoir that is found to decrease the permeation by enhancing the tortuosity of the coating layer towards aggressive species (i.e. water, O2, electrolyte) responsible of the blistering phenomenon

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

Thèse de doctorat : Électrochimie : Paris 12 : 2006.
Version électronique uniquement consultable au sein de l'Université Paris 12 (Intranet). Titre provenant de l'écran-titre. Bibliogr. : 110 réf.

Thèse doctorat : Génie des Matériaux : Villeurbanne, INSA : 2005. Thèse doctorat : Génie des Matériaux : Université de Pitesti (Roumanie) : 2005.
Thèse soutenue en co-tutelle. Titre provenant de l'écran-titre. Bibliogr. , 6 p.

La protection contre la corrosion du matériau constituant le radiateur de chauffage dans les moteurs automobiles est habituellement assurée par une formulation adaptée du liquide de refroidissement. Les mécanismes de corrosion et de protection sont complexes. Ils dépendent des conditions physico-chimiques de service (nature de l'inhibiteur, température de fonctionnement, cyclages thermiques, agitation du milieu) et des caractéristiques du matériau (nature de l'alliage, état de surface). Ces dernières années, l'entreprise automobile roumaine (Dacia – Renault) a connu de sérieux problèmes de corrosion interne lors du remplacement de l'acier par l'alliage d'aluminium AlMn1. L'étude entreprise a consisté en une caractérisation physico-chimique, par méthodes électrochimiques stationnaires et non stationnaires et par métallographie, de l'efficacité protectrice de deux types de liquides de refroidissement se différenciant principalement par la nature de l'inhibiteur. L'influence de la température et des cyclages thermiques (simulant les périodes de fonctionnement et d'arrêt) a été déterminée, ainsi que celle des conditions de dilution (eau permutée ou eau de distribution) du produit commercial concentré. Le mode de corrosion (par piqûres) et les zones d'amorçage ont été identifiés. Le mécanisme d'interaction de ces inhibiteurs a été déterminé par Spectroscopie d'Impédance Electrochimique et les circuits électriques équivalents au comportement des interfaces métal – milieu ont été proposés. Cette modélisation a permis de déterminer les paramètres principaux relatifs aux couches passives formées par l'action de ces inhibiteurs filmogènes. L'intérêt du manganèse comme élément d'addition a été confirmé par des essais conduits avec de l'aluminium pur
The radiators associated to car engines are usually protected against corrosion by well adapted cooling liquids. Corrosion and protection mechanisms are complex, and linked to the physico-chemical conditions (nature of the inhibitor, temperature, thermal cyclings, stirring conditions…), as well as to the characteristics of the material (its nature and surface state). Several years ago, the Romanian car manufacturer Dacia – Renault has encountered some severe problems of corrosion, when it has been decided to replace iron by the AlMn1 alloy. The present work consists in characterising, by stationary and transitory electrochemical methods coupled with metallography, the protective efficiency of two cooling liquids, differentiated by the nature of their inhibitor. Influence of temperature, thermal cycling (simulating the actual operating of the radiator), and inhibitor's concentration has been determined. The type of attack has been also characterized (pitting especially) and the initiation sites have been identified. A model of interaction between the metallic surface and the inhibitor has been proposed, by considering the impedance results. This model allows then to discriminate the key-parameters linked to the formed passive protective film. The beneficial effect of manganese additions has been moreover confirmed by measurements carried out with pure aluminium

Dans les systèmes collés ou peints époxy-amine / aluminium, la mise en contact du liquide polymérique sur le substrat métallique, provoque, par dissolution de l'oxyde de surface par les groupements amine du durcisseur aminé, la formation d'une zone modifiée appelée interphase. Les propriétés finales de ces systèmes dépendent fortement des caractéristiques de cette interphase. Pourtant les molécules aminées sont reconnues et utilisées comme inhibiteurs dans les problèmes de corrosion. L'étude de l'interaction d'une molécule aminée simple (le 1,2-diaminoéthane) avec un substrat d'aluminium a permis de mettre en évidence un double effet sur le substrat. En effet la molécule peut former un complexe de sphère interne bidentate mononucléaire instable (adsorption des deux pôles amines sur le même cation métallique) provoquant la dissolution du substrat et permettant d'expliquer le phénomène de formation de l'interphase dans les systèmes époxy-amine / aluminium. Par ailleurs, cette molécule peut former des complexes stables de sphère externe (monodentate ou bidentate) qui permet, dans certaines conditions, la protection du substrat
When they are applied onto aluminium substrates, epoxy-amine liquid monomers react with the oxide-covered metal to form an interphase by dissolution of the oxide layer by amine hardener. This interphase is of particular interest to determine the physical and chemical properties of the bondary (practical adhesion, corrosion resistance and durability). On the other hand diamine molecules are often used as inhibitors of corrosion. The study of the interaction of 1,2-diaminoethane (molecule used as amine curing agent and inhibitor) with aluminium susbstrate has displayed different effects of the molecule on the substrate. The diamine molecule can form a mononuclear inner-sphere complex (bidentate). This complex is not stable and leads to the dissolution of the substrate thus explaining the formation of the interphase. On the other hand the diamine molecule can form a binuclear outer-sphere complex (monodentate or bidentate). This complex is very stable and can protect the substrate

Les alliages à base d’aluminium sont largement utilisés dans les industries automobiles et aéronautiques. Des problèmes de corrosion localisée (piqûration notamment) sont rencontrés. L’interdiction des traitements utilisant des chromates nécessite la recherche d’inhibiteurs respectueux de l’environnement. L’objectif des travaux présentés est l’étude de l’acide gallique en tant qu’inhibiteur de corrosion de l’aluminium respectueux de l’environnement. Une approche théorique de cette étude est d’abord proposée. Celle-ci consiste en l’élaboration, la caractérisation et l’étude de la réactivité vis-à-vis de O2 de modèles de couches minces d’alumine hydroxylée sur aluminium métallique en la présence ou l’absence d’une monocouche d’acide gallique en surface. Une étude expérimentale de ces systèmes est ensuite proposée, consistant en la caractérisation par XPS et ToF-SIMS de la couche d’acide gallique adsorbée à la surface d’échantillons d’aluminium. L’influence de la présence de la couche d’acide gallique en surface de l’échantillon sur la corrosion en milieu chloruré de l’aluminium est finalement étudiée, par spectroscopie XPS et électrochimie classique
Aluminium alloys are widely used in the automotive and aeronautic industries. Localized corrosion (such as pitting) stills an issue for these materials. The prohibition of chromate-based treatments requires the research for new environment-friendly corrosion inhibitors. The objective of the work presented herein is the study of gallic acid as an environment-friendly corrosion inhibitor for aluminium. First, a theoretical approach is proposed. This one consists in the elaboration, the characterisation and the study of the reactivity toward O2 of thin hydroxylated alumina on metallic aluminium models, with or without a gallic acid monolayer on top of it. An experimental study of these systems, which consists in the XPS and ToF-SIMS characterisation of the gallic acid layer adsorbed on aluminium samples, is proposed. The influence of this layer presence on top of aluminium on its corrosion behaviour in a chloride medium is then studied, using XPS spectroscopy end classical electrochemistry tools

Etude de l'interface metal-inhibiteur, du comportement de l'inhibiteur en fonction du temps et de la temperature et evaluation de sa stabilite. Mise au point d'une methode de mesure de la concentration des inhibiteurs de corrosion introduits dans les circuits de chauffage ou de refroidissement

Tratamentos de metais contra a corrosão usando formulações contendo derivados de cromo hexavalente (Cr6+) tem sido padrão na indústria de tratamento de superfície durante muitas décadas. Esses tratamentos oferecem excelente proteção contra a corrosão, fornecem boa base para pinturas, são baratos e relativamente fáceis de aplicar. Além do mais oferecem proteção ativa ao substrato devido à capacidade de autorregeneração. Porém, restrições ambientais e de saúde, tornadas mais severas a partir das últimas décadas, requerem a substituição destes tratamentos por processos que sejam ambientalmente corretos e não agressivos à saúde humana. Neste contexto, a indústria aeroespacial, amplamente dependente de ligas de alumínio com elevada resistência mecânica para a construção das aeronaves, é uma das mais atingidas, visto que várias das etapas do tratamento superficial e dos processos de proteção contra a corrosão destas ligas utilizam compostos de Cr6+. Dentro dessa nova realidade, a utilização de revestimentos híbridos derivados de silanos, obtidos pelo processo sol-gel, tem se apresentado como uma das alternativas mais investigadas para a substituição dos pré-tratamentos à base de cromato. Estes revestimentos formam uma cadeia polimérica compacta sobre a superfície do metal constituindo uma barreira efetiva contra espécies agressivas, podendo também ser funcionalizados para apresentarem compatibilidade com revestimentos orgânicos. Entretanto os mesmos não exibem proteção ativa contra a corrosão. Nesse trabalho o comportamento anticorrosivo, em solução de NaCl 0,1 M, de um revestimento híbrido produzido pela hidrólise e condensação do 3-glicidóxipropiltrimetóxisilano (GPTMS) e do tetraetil ortosilicato (TEOS) aplicado sobre a liga AA2024-T3 foi investigado por espectroscopia de impedância eletroquímica (EIS) e analisado por SEM/EDX. Com a finalidade de melhorar o desempenho dos revestimentos, as soluções de hidrólise foram modificadas pela introdução de 0,005 M de inibidores de corrosão derivados de triazol (benzotriazol (BTAH) e toliltriazol (TTA)) ou de organofosfonatos (ácido trimetileno fosfônico (ATMP) e ácido 1-hidróxietileno 1,1-difosfônico (HEDP)). Os resultados dos ensaios eletroquímicos mostraram que, apesar de eficientes para a proteção contra a corrosão da liga, o BTAH e o TTA interferem negativamente nas propriedades anticorrosivas do revestimento híbrido. Por sua vez, a modificação do híbrido com o ATMP ou HEDP melhorou a resposta de impedância do revestimento e aumentou sua estabilidade, se mostrando como um enfoque promissor para aumentar o desempenho do revestimento. A espectroscopia por emissão de fotoelétrons (XPS) e a espectroscopia Raman foram utilizadas para caracterizar o híbrido modificado com os organofosfonatos. Através da primeira técnica foi possível evidenciar a interação das moléculas de inibidor com a superfície metálica. Já os resultados de espectroscopia Raman indicaram a incorporação dos inibidores no revestimento, tendo sido mais eficaz para esta finalidade que as análises por XPS. Entretanto, para evidenciar esse processo, foi necessário aumentar a concentração dos inibidores em 10 vezes com relação à quantidade empregada nos ensaios eletroquímicos.
Anticorrosion metals treatments using formulations containing derivatives of hexavalent chromium (Cr6+) have been standard in the surface treatment industry for many decades. These treatments afford excellent corrosion protection, offer good base for paintings, are inexpensive and relatively easy to apply. Besides, they provide active protection to the substrate due to their selfhealing abilities. However, environmental and health restrictions, made more severe from the end of the eighties, require replacement of these treatments by processes that are environmentally friendly and not aggressive to human health. In this context, the aerospace industry, which is strongly dependent on high strength aluminium alloys, is one of the most heavily affected, as (Cr6+) compounds are used in several steps of the surface treatment and corrosion protection processes. Within this new reality, the use of hybrid coatings derived from silanes and obtained by the sol-gel process, has emerged as one of the most investigated alternatives to replace the chromate based pre-treatments. These coatings form a compact polymer network on the metal surface providing an effective barrier against aggressive species, they may also be tailored to present compatibility with organic coatings. However they do not exhibit active corrosion protection. In this study the corrosion behavior, in 0.1 M NaCl, of a hybrid coating produced by hydrolysis and condensation of 3glycidoxypropyltrimethoxysilane (GPTMS) and tetraethyl orthosilicate (TEOS) applied on AA2024-T3 alloy was investigated by means of electrochemical impedance spectroscopy (EIS) and analysed by SEM/EDX. Aiming to improve the coatings performances, the hydrolysis solutions were modified by the addition of 0.005 M of triazoles (benzotriazole (BTAH) and tolyltriazole (TTA)) or organophosphates (trimethylene phosphonic acid (ATMP) and 1hydroxyethylidene-1 1-diphosphonic acid (HEDP)) based corrosion inhibitors. The results of the electrochemical tests showed that, although effective for corrosion protection of the alloy, BTAH and TTA adversely impacted the anticorrosive properties of the hybrid coating. In turn, the modification of the hybrid with ATMP or HEDP improved the impedance response of the coating and increased its stability, proving to be a promising approach to enhance the coating performance. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to characterize the hybrid modified with organophosphates. With the first technique it was possible to demonstrate the interaction of the inhibitor molecules with the metal surface. Raman spectroscopy results indicated the incorporation of the inhibitors in the coating, being more effective for this purpose than the XPS analysis. However, to demonstrate this process, it was necessary use the concentration of the inhibitors 10 times more than the amount employed in the electrochemical tests.

Cette etude porte sur la recherche d'une solution de remplacement des chromates, reconnus toxiques, dans les peintures pour la protection contre la corrosion d'un alliage d'aluminium 2024 (aluminium - 4% cuivre) utilise dans l'industrie aeronautique. Dans un premier temps, une recherche bibliographique a permis d'identifier differents composes inhibiteurs de la corrosion de l'aluminium et du cuivre. En effet, l'intervention des precipites riches en cuivre al 2cu joue un role important dans la degradation de l'alliage. L'efficacite des produits a ete evaluee par des mesures electrochimiques, releve des courbes courant-tension et trace des diagrammes d'impedance. La combinaison de deux produits (8-hydroxyquinoleine et benzotriazole) permet d'atteindre une protection proche de celle apportee par le chromate. Le trace des diagrammes d'impedance et les analyses de surface (esca) ont montre d'une part, que la 8 hydroxyquinoleine favorise le renforcement de l'effet de film de la couche d'alumine et, d'autre part, que l'action du benzotriazole est essentiellement localisee au niveau des precipites. L'effet de synergie observe a ete explique par le mode d'action different mais complementaire de ces deux composes. La derniere partie de cette etude est consacree a l'evaluation de la protection contre la corrosion par des peintures polyurethanne et epoxydique qui contiennent ces inhibiteurs en utilisant les tests de corrosion definis par le cahier des charges de l'industrie aeronautique et les mesures d'impedance electrochimique. Les revetements etudies presentent des performances comparables a celles des primaires chromates. Neanmoins, l'emploi de ces substituants a montre le role fondamental des proprietes de film, du traitement de surface et de l'adherence pour la protection contre la corrosion.

Processos corrosivos geram perdas incalculáveis para a sociedade. Existe, portanto, uma incessante busca por métodos cada vez mais econômicos, eficientes e que não gerem impacto ao meio-ambiente. Polímeros heterocíclicos são macromoléculas de elevada performance que vêm sendo estudados como inibidores de corrosão por atenderem as premissas citadas acima. Neste trabalho realizou-se a modificação química da poliacrilonitrila com a incorporação de grupos 2-vinil-2-oxazolina no teor teórico de 20%. O copolímero obtido e a poliacrilonitrila não modificada foram caracterizados por espectroscopia na região do infravermelho e avaliados como inibidores de corrosão para alumínio e aço carbono em meio salino em temperatura de 60C. As concentrações utilizadas foram de 20, 50, 100 e 200 ppm e os períodos de checagem: 1, 2, 3 e 4 semanas. Os polímeros estudados apresentaram atividade inibitória de corrosão apenas para o aço carbono. Para o alumínio, o ensaio em branco apresentou a menor taxa de corrosão dentre todos os ensaios realizados
Corrosive processes, still generate unmeasurable losses to society. There is therefore a constant search for methods that are more economical, efficient and that does not generate impact to the environment. High performance heterocyclic polymers are macromolecules which have been studied as corrosion inhibitors for meeting the premises mentioned above. In this work, a chemical modification of polyacrylonitrile with the incorporation of 2-vinyl-2-oxazoline groups at the theoretical rate of 20% is proposed. The obtained copolymer and not modified polyacrylonitrile were characterized qualitatively by infrared spectroscopy and evaluated as corrosion inhibitors for aluminum and carbon steel in saline medium at 60 C. The concentrations used were 20, 50, 100 and 200ppm and checking timeline of: 1, 2, 3 and 4 weeks. The results indicate that the studied polymers showed corrosion inhibiting activity only for carbon steel. For aluminum, blank test showed the lowest rate of corrosion of all tests performed

En motorisation, les problèmes liés à la compatibilité ‘matériaux-liquides de refroidissement’ sont complexes du fait de leur nature et de leur fonction, mais ils peuvent être résolus en modifiant la forme des pièces pour contrôler l’écoulement ou par l’addition d’inhibiteurs de corrosion efficaces. Ceux-ci sont très utilisés dans l’industrie automobile et doivent sans cesse être optimisés et adaptés à l’évolution des matériaux. Et, pour répondre aux contraintes actuelles de consommation et d’environnement, de plus en plus de motoristes optent pour l’aluminium ou ses alliages. Dans ce travail nous avons caractérisé le comportement en corrosion d’un alliage Al-Mn et d’un nouveau matériau, dit ’’matériau sandwich’’ constitué d’un cœur en alliage Al-Mn recouvert par placage sur chaque face d’une mince plaque d’alliage Al-Si et donc de structure Al-Si/Al-Mn/Al-Si en contact avec un liquide de refroidissement commercial dénommé Glaceol D. Celui-ci contient dans sa formulation un inhibiteur de corrosion, le tolytriazole. Cette étude de caractérisation comportementale de ces matériaux a été menée à partir de tests électrochimiques stationnaires classiques (suivi de potentiel en temps, tracés de courbes potentiodynamiques, détermination de résistances de polarisation), couplés à des observations métallographiques. Les principaux paramètres retenus ont été d’une part l’influence d’un prétraitement de surface du métal, et les conditions physicochimiques du milieu d’étude comme la teneur en produits actifs (en choisissant la dilution du Glaceol D, on fixe la teneur en inhibiteur), la nature de l’eau de dilution (permutée ou enrichie en NaCl) et la température : soit maintenue constante (entre la température ambiante et 80°C) soit en cyclage thermique. D’autre part, et ceci a permis d’établir la supériorité de comportement du matériau sandwich, nous avons, pour comparaison, testé aussi dans nos conditions de concentration et de température, l’aluminium pur 99,99%. Outre cet inhibiteur classique et industriellement utilisé, contenu dans la formulation du produit commercial recommandé par l’entreprise automobile franco-roumaine ’’Dacia-Renault’’, nous avons tenté une nouvelle approche originale en testant l’efficacité d’un inhibiteur vert – extrait de plantes : l’Allium Sativum (ou ail), dont le principal composant actif est l’allicine. Par son groupement fonctionnel de type thiosulfinate R-S(=O)-SR, et les atomes électrodonneurs que sont le soufre et l’oxygène disposant de doublets non liants, ce composé possède les caractéristiques d’un produit filmogène et entre dans la catégorie des nouveaux types d’inhibiteurs verts investigués depuis quelques années
For motorization, problems related to the compatibility ‘materials cooling liquids’ are complex because of their nature and function. They can be solved either by changing the shape of some parts of engine in order to obtain a better flow, or by introduction of effective corrosion inhibitors. And these later that are very used in the automotive industry, must be always optimized and adapted to the evolution of the materials. Today, the demands connected with carburant consummation and environment lead more and more operators to opt for aluminum and its alloys. In this work, we have characterized the corrosion behavior of Al-Mn alloy and of a new material, namely ''sandwich material'' consisting in a core of Al-Mn alloy veneered on both sides by a thin layer of Al-Si alloy and therefore with a structure Al-Si/Al-Mn/Al-Si in contact with commercially coolant, namely Glaceol D. The later one contains in its composition tolytriazole, as a corrosion inhibitor. This study of behavioral characterization of these materials was carried on using conventional stationary electrochemical techniques as the open circuit potential measurements, the potentiodynamic recordings, the determination of polarization resistance, coupled with metallographic observations. The main parameters considered were the influence of a pretreatment of metal surface and physic–chemical conditions of environmental study as the content of active compounds (by choosing the dilution of Glaceol D, the content of inhibitor is fixed), the nature of the dilution water (deionized or added of NaCl) and temperature: this latter one was chosen either stationary (between room temperature and 80°C) or as a thermal cycling. On the other hand, and that has allowed to establish the better behavior of the sandwich material, we tested the 99.99% pure aluminum, in the same conditions of concentration and temperature. In addition to this traditional and industrially used inhibitor, which is in the composition of the commercial product recommended by the French – Romanian company “Dacia-Renault”, we tried a new original approach by testing the effectiveness of a “green inhibitor” - a plant extract: Allium Sativum (or garlic), where the main active ingredient is allicine. By its functional group type thiosulfinate RS(= O)-SR, and the sulfur and oxygen atoms with non-binding electronic doublets, this compound has the characteristics of a film-forming product and can be put into the category of new types of “green” inhibitors investigated during the last few years

Au cours des dernieres annees, le generateur aluminium - air a ete etudie, particulierement pour son application a la propulsion de vehicules electriques. L'aluminium presente en effet une energie theorique importante (8 kw. H/kg) et son utilisation en pile pourrait permettre d'augmenter l'autonomie d'un vehicule. La premiere partie du travail concerne l'etude technologique de ces generateurs utilisant l'electrolyte naoh. Elle a ete realisee sur une cellule aluminium - air pilote (1 v / 70 a), et a permis de degager les parametres essentiels (concentration en soude, temperature, concentration en inhibiteurs de corrosion. . . ) du fonctionnement de l'anode. Le rapport cout de l'alliage/performances en decharge a ete optimise en utilisant la methodologie experimentale des plans d'experiences. Il s'avere que le materiau d'anode habituellement utilise (aluminium 5n) peut etre avantageusement remplace par une nuance 3n5 moins chere, tout en garantissant des caracteristiques en puissance sensiblement equivalentes. Le maintien des performances, en cours de decharge prolongee, exige toutefois d'associer un volume important d'electrolyte au module electrochimique. La masse du systeme parait alors exclure une integration sur vehicule electrique ; le generateur reste adapte a une utilisation sur site fixe. La seconde partie du travail presente une analyse a caractere plus fondamental des mecanismes de dissolution - corrosion de l'aluminium en milieu concentre en soude. Un montage experimental original a permis de determiner, par mesure en continu du degagement d'hydrogene, la contribution du courant de corrosion au courant total de dissolution de l'anode. L'obtention de courbes de polarisation decorrelees permet d'analyser separement les cinetiques des deux reactions partielles qui ont lieu a la surface de l'aluminium. Le caractere passif de l'aluminium en milieu sodique tres concentre est mis en evidence. Les resultats obtenus dans des conditions experimentales, mettant en jeu les differents parametres de fonctionnement de la pile, permettent de rendre compte de l'effet de la temperature, des conditions hydrodynamiques, des impuretes et de la presence d'ions aluminate et stannate en solution, sur les cinetiques des deux reactions d'oxydation de l'aluminium et de degagement d'hydrogene.

En aéronautique, les structures en alliage d’aluminium 2024 sont protégées par un primaire anticorrosion fonctionnalisé par des pigments inhibiteurs permettant une cicatrisation rapide de la surface de l’alliage exposée à l’environnement extérieur lors d’un endommagement mécanique superficiel. Compte tenu de la perte de fonctionnalité des primaires par lessivage, il semble nécessaire d’évaluer les risques d’amorçage de la corrosion. En pratique, il a été envisagé de mettre en place des capteurs dits de « corrosion ».L’objectif de ce travail était de comprendre le fonctionnement d’un capteur censé représenter l’endommagement d’une peinture, dont le concept repose sur la compétition entre l’amorçage de la corrosion d’une surface d’un alliage d’aluminium mis à nu et le relâchement d’inhibiteurs (provenant de la peinture). Le comportement de l’alliage 2024 et de solutions solides (constituant le capteur) a été étudié en milieu chloruré en présence ou non d’inhibiteurs à différentes concentrations. En variant la taille d’électrodes peintes exposées sur leur tranche, on a pu quantifier l’efficacité des inhibiteurs sur ces deux types de matériaux, en détectant l’amorçage de la corrosion ou son inhibition, par mesure de pH de surface. Cette analyse chimique couplée à des observations in situ, a permis de déterminer les étapes limitantes qui définissent la compétition entre corrosion et passivation dans le cas de l’alliage 2024. Ces différentes analyses ont montré que, pour quantifier cette compétition, la cinétique d’amorçage de la corrosion microstructurale constitue un élément clé qui ne peut pas être représenté par la réponse des électrodes du capteur constituées d’une solution solide. L’existence d’une distance maximale entre la source d’inhibiteurs et la zone pouvant être passivée a pu être confirmée par la simulation du transport des espèces inhibitrices qui dépend principalement du régime de lessivage du primaire
The conventional aircraft paint scheme for corrosion protection of aluminum structures is partly based on application of a primer containing inhibitors. In such coatings, release of the inhibiting species enables fast healing of a bare metal surface after a mechanical damage of the protective layers. Nevertheless, considering possible depletion of inhibitors by uncontrolled leaching, it appears important to estimate the corrosion risk integrating “corrosion” sensors in the structure. The objective of this work was to understand the operating mode of a sensor simulating a damaged paint coating whose concept is based on the competition between the triggering of localized corrosion and the passivation of a bare 2024 alloy. The behavior of this massive alloy and Al-Cu solid solutions (the active metallic slots of the sensor) was studied in chloride solution in presence or not of inhibitor ions at different concentrations.Varying the size of a cut-edge electrode coated on both sides, the effectiveness of these inhibitors was demonstrated detecting the microstructural corrosion triggering or its inhibition, by mapping surface pH. Combining these chemical probing with in situ observations it was possible to confirm the nature of the limiting steps controlling the competition between corrosion and passivation. These analyzes highlighted that to quantify this competition, the triggering of the microstructural corrosion represents a key factor which is not possible to mimic by the response of the solid solutions.The existence of a threshold value for the distance between the inhibitor source and the area to be passivated has been confirmed by simulating the mass transport of inhibiting species which appear to be dependent of the release rate of inhibitors

Des poudres Mg-xZn-yAl (x = 1, 3 et y = 8, 15 ou 20% at) de 50 à 100 micromètres ont été élaborées par pulvérisation centrifuge et consolidées par extrusion à chaud. Il y a recristallisation dynamique dans la filière: on passe d'une structure dendritique biphasée (matrice alpha et précipité béta Mg₁₇Al₁₂) à gros grains (10 micromètres) à une structure biphasée à grains submicroniques ( 0. 7 micromètre). La répartition des éléments zinc et aluminium entre matrice et précipités, et donc la fraction volumique fv, ont été déterminées par mesure des paramètres en DRX. On observe une augmentation linéaire du module d'Young et de la microdureté des alliages avec fv. La texture de déformation développée initialement dans la filière n'est pas complètement effacée par la recristallisation dynamique: ceci conduit à des comportements différents en traction et en compression, et cela malgré la finesse du grain. À 20°C on mesure des limites d'élasticité de l'ordre de 500MPa pour quelques % de ductilité. Au dessus de 150°C le matériau se déforme de façon superplastique. Les courants de corrosions mesurés sont de l'ordre de 20 microampères par centimètre carré. La perte de masse en milieu NaCl 3% est dix fois plus faible pour les alliages solidifiés rapidement. La corrosion est de type galvanique, et son amplitude est diminuée par l'affinement de la microstructure. L’ajout d'aluminium augmente la passivité, celle de zinc le potentiel de corrosion, ces effets sont bénéfiques. Le pouvoir inhibiteur des carboxylates de sodium est étudié en fonction de la longueur de la chaine. Le taux d'inhibition augmente avec celle-ci et peut atteindre 96%. La meilleure formulation est susceptible d'être substituée aux chromates en milieu faiblement agressif

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Um processo corrosivo em embalagens metálicas para alimentos pode ser iniciado durante a fabricação destas, bem como em todo o período no qual o alimento está em contato com a mesma. O uso de extratos de plantas como inibidores naturais em recobrimentos protetores para o alumínio podem auxiliar na redução da corrosão, além de diminuir a preocupação com o risco de toxicidade causada por inibidores sintéticos industrialmente utilizados. Extratos da espécie Solidago chilensis, conhecida como arnica-brasileira, abundante em todo o Brasil e em maior concentração na região Sul do país, ainda não foram relatados na literatura no uso como inibidores naturais de corrosão, porém, possuem propriedades e compostos que já foram apresentados que indicam capacidade anticorrosiva. O presente estudo busca desenvolver um recobrimento contendo Solidado chilensis como inibidor natural de corrosão para aplicação em embalagens de ligas de alumínio para alimentos. Para avaliar estes recobrimentos foram realizados ensaios de Polarização Potenciodinamica (PP), Espectroscopia de Impedância Eletroquímica (EIE), Microscopia de Força Atômica (MFA), Espectroscopia na região do Infravermelho com Transformada de Fourier (FT-IR) e Difração de Raios-X (DRX). Considerando a possibilidade de alteração da resistência à corrosão devido a algum dano mecânico foi avaliada a adesão do recobrimento através de ensaios de resistência mecânica por Análise Mecânico-Dinâmica (AMD). Para o desenvolvimento da superfície foram realizadas: anodizações, com objetivo de proteção contra a corrosão e aderência do inibidor e do recobrimento; e aplicados o inibidor natural (Solidago chilensis) e o recobrimento de verniz, com o objetivo de proteção contra a corrosão. As anodizações foram realizadas em três diferentes tempos 15, 20 e 30 minutos, após as amostras foram imersas em solução inibidora contendo três diferentes concentrações de inibidor (2,5, 5 e 15 g/L de metanol) e por fim foram recobertas com verniz. A resistência à corrosão e a eficiência do inibidor foram avaliadas através de ensaios eletroquímicos. O módulo de elasticidade das amostras foram avaliadas através do AMD. A morfologia das amostras foram determinadas através de MFA. A composição do inibidor e a interação entre as ligações químicas de compostos do inibidor, do verniz, da anodização e do alumínio foram determinadas por FT-IR. A estrutura cristalina das amostras foram determinadas por DRX. Os resultados apontaram que o melhor tempo de anodização quanto a resistência à corrosão e a resistência mecânica do sistema foi de 15 min. As amostras anodizadas nesse tempo foram escolhidas para serem imersas em solução contendo o inibidor natural. Os resultados eletroquímicos indicaram que a maior concentração de inibidor de corrosão (15 g de extrato de Solidago chilensis por L de solvente) obteve maior eficiência à corrosão, 92,5 %. O uso do inibidor de corrosão natural junto a anodização e ao recobrimento de verniz diminuiu a degradação da amostra ao longo do tempo, aumentou o potencial de corrosão e a resistência de polarização. A rigidez do sistema diminuiu com a aplicação do verniz mas não foi influenciada significativamente, p≤0,05 pela anodização. Estes resultados indicaram que o Al anodizado contendo extrato de Solidago chilensis como inibidor de corrosão recoberto com verniz pode ser uma alternativa interessante na industria de alimentos na utilização em embalagens metálicas.
A corrosion process in metallic food packing can be started during the manufacturing of these, as well as throughout the period in which the food is in contact with it. The use of plant extracts as green inhibitors in protective coatings for aluminum can help reduce corrosion, and reduce concern about the risk of toxicity caused by synthetic inhibitors used industrially. Extracts of the species Solidago chilensis, known as arnica-Brazilian, abundant in Brazil and in greater concentration in the southern region of the country, have not yet been reported in the literature used as natural corrosion inhibitors, however, have properties and compounds that have been presented indicating corrosion efficiency. This study aims to develop a coating containing solidated chilensis as green corrosion inhibitor for use in packaging of aluminum alloys for food. To evaluate these coatings were conducted Potentiostatic Polarization tests (PP), Electrochemical Impedance Spectroscopy (EIS), Atomic Force Microscopy (AFM), Infrared Spectroscopy in the region Fourier Transform (FT-IR) and X-Ray Diffraction (XRD). Considering the possibility of change in resistance to corrosion due to some mechanical damage was assessed the adhesion of coating by mechanical strength tests for Dynamic-Mechanical Analysis (DMA). For the development of the surface were carried out anodizing, in order to corrosion protection and adhesion inhibitor and coating; and applied the natural inhibitor (Solidago chilensis) and the varnish coating, in order to protect against corrosion. The anodizing was performed in three different times 15, 20 and 30 minutes after the samples were immersed in inhibitor solution containing three different inhibitor concentrations (2.5, 5 and 15 g/L methanol) and finally were coated with varnish. The corrosion resistance and the efficiency of the inhibitor were evaluated by electrochemical tests. The modulus of elasticity of the samples were evaluated by DMA. The morphology of the samples were determined by AFM. The inhibitor composition and interaction between the chemical bonding inhibitor compounds, varnish, and anodization of aluminum are determined by FT-IR. The crystal structure of the samples were determined by XRD. The results showed that the best time of anodization as the corrosion resistance and the mechanical strength of the system was 15 min. The anodized samples at this time were chosen to be immersed in a solution containing the natural inhibitor. The electrochemical results indicated that the highest concentration of corrosion inhibitor (15 g of Solidago chilensis extract per L of solvent) had higher efficiency corrosion, 92.5%. The use of natural corrosion inhibitor with anodization and varnish coating reduced the degradation of the sample over time, potential increased corrosion resistance and polarization. The system stiffness decreased with the application of varnish but was not significantly influenced by p≤0,05 anodizing. These results indicated that the anodized Al containing Solidago chilensis extract as a corrosion inhibitor coated with varnish can be an interesting alternative in the food industry in use in metal packaging.

The corrosion inhibition behaviour of seven macrocyclic compounds (including phthalocyanines and naphthalocyanines) namely 1,4,8,11,15,18,22,25 -Octabutoxy-29H,31 Hphthalocyanine( Pc 1), 2,3,9,10,16,17,23 ,24-Octakis(octyloxy)-29H,3 1 H-phthalocyanine(Pc2), 2,9,1 6,23-Tetra-tert-butyl-29H,3 1 H-phthalocyanine 29H,3 I H-phthalocyanine(Pc3), 5,9,14,18,23,27,32,3 6-Octabutoxy-2,3-naphthalocyanine(nPc 1), 2,11 ,20,29-Tetra-tert-butyl- 2,3-naphthalocyanine(nPc2) and 2,3-naphthalocyanine(nPc3) on the corrosion of aluminium in 1M HC1 was studied by means of weight loss, electrochemical, quantum chemical and quantitative structure activity relationship(QSAR) techniques. The inhibition efficiencies and corrosion rates were evaluated at temperatures ranging from 30°C - 70°C. The results suggest that inhibition efficiencies are relatively low but increased on the addition of potassium iodide (KI) due to synergistic effect. Langmuir isotherm agrees well with the experimental data. The individual quantum chemical parameters and combined ones (in a QSAR study) suggest strong interactions between the inhibitor and the metal surface. The results also point to the fact that 1,4,8,11,15,1 8,22,25-Octabutoxy-29H,31 H-phthalocyanine and 5,9,14,18,23,27,32,3 6-Octabutoxy-2,3-naphthalocyanine have the highest tendency to donate electrons to an electron poor species. The results are indicative of the possible role of macrocyclic compounds as corrosion inhibitors for Al surface.
Thesis (M.Sc. (Physical Chemistry) North-West University, Mafikeng Campus, 2014

Aluminum and its alloys are widely used as constructional materials in the aerospace sector. Since aircrafts are often exposed to hostile environments and their alloying additions usually make aluminum alloys more susceptible to corrosion, several strategies have been applied to protect these materials against corrosion-caused degradation. The most common measure for prevention of corrosion in aluminum alloys 2024-T3 is based on the application of three-layered paint schemes, which include chromium(VI)-based pretreatments. Cr(VI)-based conversion films have been widely used to promote the adhesion of subsequent organic layers and confer active protection to the underlying substrate. Despite being the most efficient inhibitors for AA2024-T3, chromates are considered environmentally unsafe and can also affect human health. For this reason, the use of such compounds has been restricted under EU legislation. The need to replace hazardous chromate conversion coatings has prompted intense research toward the development of “greener”, equally efficient technologies. Layered double hydroxide (LDH)-based conversion coatings have been found amidst the most promising alternatives. Their low-toxicity, biocompatibility and low-cost preparation make them potential substitutes for Cr(VI)-based pretreatments. Besides, these dual-function anion-exchanger structures can be used both for releasing anionic corrosion inhibitors and entrapping aggressive anionic species, such as chlorides. However, in order for these systems to meet the performance and reliability specifications required by the aerospace industry, some aspects still require further improvement. In addition to cost effectiveness and low environmental reactivity, it is important to ensure that LDH films exhibit a uniform coverage, proper adhesion to the substrate and good anti-corrosion performance. The industrial implementation of LDH layers as pretreatments for aluminum alloys entails the optimization of the conditions involved in their preparation, which requires the analysis and comparison of different synthesis routes. The present work aimed at developing Zn/Al LDH-based conversion films on AA2024-T3 substrates, with active protection functionality and enhanced adhesion and coverage characteristics. Two synthesis methodologies were employed, namely the hydrothermal growth and the electrochemical deposition, in order to optimize the involved parameters and compare the quality of the obtained conversion films in terms of their coverage, adhesion to the substrate and anti-corrosion performance through appropriate characterization techniques
As ligas de alumínio são materiais amplamente utilizados para fabrico de elementos estruturais no setor aeroespacial. Dada a constante exposição das aeronaves a ambientes hostis e a suscetibilidade das ligas de alumínio à corrosão, várias estratégias têm sido implementadas de forma a proteger estes materiais da degradação causada por fenómenos corrosivos. A medida mais comum de prevenção da corrosão em ligas de alumínio 2024-T3 consiste na aplicação de um esquema de pintura multicamada, que inclui um pré-tratamento com crómio(VI) na sua composição. Os filmes de conversão à base de crómio hexavalente têm sido bastante utilizados para promover a adesão de camadas orgânicas posteriores e conferir proteção ativa ao substrato subjacente. Apesar de serem reconhecidos como os inibidores mais eficientes para as ligas de alumínio 2024, os cromatos não são considerados seguros do ponto de vista ambiental e saúde humana. Por essa razão, a sua utilização foi rigorosamente restringida na União Europeia. A necessidade de substituir os filmes de conversão baseados nestes compostos perigosos promoveu um intenso trabalho de investigação com o objetivo de desenvolver tecnologias mais ecológicas, que igualem os revestimentos à base de Cr(VI) em termos de eficácia. Os filmes de conversão baseados em hidróxidos duplos lamelares (HDLs) encontram-se entre as alternativas mais promissoras. A sua toxicidade reduzida, biocompatibilidade e preparação económica tornam-nos potenciais substitutos dos pré-tratamentos com cromatos. Além disso, estas estruturas com capacidade de permuta aniónica podem ser utilizadas não só para libertar de forma controlada inibidores de corrosão, como também para capturar espécies aniónicas agressivas, como por exemplo iões cloreto. No entanto, para que estes sistemas possam ser implementados na indústria aeroespacial, alguns aspetos carecem de melhoria. Além da relação custo-eficácia e reduzido impacto ambiental, os filmes de LDHs devem apresentar uma cobertura uniforme do substrato, uma adesão adequada ao mesmo e propriedades inibidoras de corrosão. A implementação de camadas de HDLs como pré-tratamentos para ligas de alumínio implica a otimização das condições envolvidas na sua preparação, o que requere a análise e comparação de diferentes métodos de síntese. O principal objetivo deste trabalho consistiu no desenvolvimento de filmes de conversão baseados em Zn/Al-HDLs em ligas de alumínio 2024-T3, com funcionalidade de proteção ativa e propriedades de adesão e cobertura melhoradas. Duas metodologias foram utilizadas para a sua síntese, nomeadamente o crescimento hidrotermal e a deposição eletroquímica, de forma a otimizar os parâmetros envolvidos e comparar a qualidade dos filmes obtidos em termos de cobertura, adesão ao substrato e propriedades anti corrosão através de técnicas de caracterização apropriadas
Mestrado em Engenharia de Materiais