66 research outputs found
Le contrôle de réactivité d'aluminium en peinture anti-corrosion résistant à la haute température
No full textThe aim of this work is to understand Al reactivity at a fundamental level and to use this knowledge for the development of Cr(VI)-free sacrificial paints for high temperature aeronautic applications.Pure Al, Al intermetallics and alloys are studied. The atomic emission spectroelectrochemistry is used to isolate the individual phenomena during paint degradation. A linear relationship between cathodic current and Al dissolution is shown and interpreted with a simple model where OH- generation, Al(OH)3 formation/dissolution and Al(OH)4− diffusion are kinetically coupled. For early formulations significant binder dissolution is measured under cathodic polarization, while Al reactivity is suppressed. Similar Al behavior is observed for Al-Mg intermetallics. In terms of the cathodically generated hydroxide mechanism these results are interpreted as the reaction of either Si or Mg with OH-. These results confirm the cathodic Al reactivity model. The loss of anodic activity is explained by the loss of electrical contact at the metal/oxide/polymer/substrate interfaces and the oxide layer modifications are studied to circumvent this problem. It is found that Mg2+ ions retard Al passivation and improve conductivity due to the formation of semiconducting spinel. Finally, two major factors are found to be critical for the Al reactivity control: solution pH and oxide properties. Using additives to control them, the new coating formulation stable up to 550°C and protective more than 1000H in salt spray test is developedL'objectif de ce travail est de comprendre le mécanisme fondamentales de la réactivité de l'Al et d'utiliser ces connaissances pour développer une peinture sacrificielle sans Cr(VI). L'Al pur, ses alliages et ses intermétalliques sont étudiés. La spectroélectrochimie atomique à émission de plasma est utilisée pour isoler les phénomènes individuels au cours de la dégradation. La relation linéaire entre le courent cathodique et la vitesse de dissolution de l'Al est démontrée et interprétée par un modèle dans lequel la génération d'OH-, la formation/dissolution d'Al(OH)3 et la diffusion d'Al(OH)4- sont cinétiquement couplées. La dissolution significative du liant de première formulation a été accompagnée de la passivation d'Al pendant la polarisation cathodique. Un comportement similaire est observé pour des intermétalliques Al-Mg. Ceci est interprété comme la réaction des composants (du Mg ou du Si) avec OH-. Ces résultats confirment le modèle de réactivité cathodique de l'Al. La perte d'activité anodique est expliquée par la perte de contact électrique au niveau des interfaces métal/oxyde/polymère/substrat. Les modes de transformation de la couche d'oxyde sont étudiées. Les ions de Mg2+ retardent la passivation d'Al par la formation de spinelle semi-conducteur qui est responsable de l'amélioration de la conductivité.Finalement, deux facteurs principaux sont jugés essentiels pour la réactivité de l'Al: le pH de la solution et la conductivité de l'oxyde. En utilisant des additifs pour contrôler ces facteurs, on a proposé la formulation d'une nouvelle peinture, stable jusqu'à 550°C et sacrificielle plus de 1000 H au test de brouillard salin
Le contrôle de réactivité d'aluminium en peinture anti-corrosion résistant à la haute température
No full textThe aim of this work is to understand Al reactivity at a fundamental level and to use this knowledge for the development of Cr(VI)-free sacrificial paints for high temperature aeronautic applications.Pure Al, Al intermetallics and alloys are studied. The atomic emission spectroelectrochemistry is used to isolate the individual phenomena during paint degradation. A linear relationship between cathodic current and Al dissolution is shown and interpreted with a simple model where OH- generation, Al(OH)3 formation/dissolution and Al(OH)4− diffusion are kinetically coupled. For early formulations significant binder dissolution is measured under cathodic polarization, while Al reactivity is suppressed. Similar Al behavior is observed for Al-Mg intermetallics. In terms of the cathodically generated hydroxide mechanism these results are interpreted as the reaction of either Si or Mg with OH-. These results confirm the cathodic Al reactivity model. The loss of anodic activity is explained by the loss of electrical contact at the metal/oxide/polymer/substrate interfaces and the oxide layer modifications are studied to circumvent this problem. It is found that Mg2+ ions retard Al passivation and improve conductivity due to the formation of semiconducting spinel. Finally, two major factors are found to be critical for the Al reactivity control: solution pH and oxide properties. Using additives to control them, the new coating formulation stable up to 550°C and protective more than 1000H in salt spray test is developedL'objectif de ce travail est de comprendre le mécanisme fondamentales de la réactivité de l'Al et d'utiliser ces connaissances pour développer une peinture sacrificielle sans Cr(VI). L'Al pur, ses alliages et ses intermétalliques sont étudiés. La spectroélectrochimie atomique à émission de plasma est utilisée pour isoler les phénomènes individuels au cours de la dégradation. La relation linéaire entre le courent cathodique et la vitesse de dissolution de l'Al est démontrée et interprétée par un modèle dans lequel la génération d'OH-, la formation/dissolution d'Al(OH)3 et la diffusion d'Al(OH)4- sont cinétiquement couplées. La dissolution significative du liant de première formulation a été accompagnée de la passivation d'Al pendant la polarisation cathodique. Un comportement similaire est observé pour des intermétalliques Al-Mg. Ceci est interprété comme la réaction des composants (du Mg ou du Si) avec OH-. Ces résultats confirment le modèle de réactivité cathodique de l'Al. La perte d'activité anodique est expliquée par la perte de contact électrique au niveau des interfaces métal/oxyde/polymère/substrat. Les modes de transformation de la couche d'oxyde sont étudiées. Les ions de Mg2+ retardent la passivation d'Al par la formation de spinelle semi-conducteur qui est responsable de l'amélioration de la conductivité.Finalement, deux facteurs principaux sont jugés essentiels pour la réactivité de l'Al: le pH de la solution et la conductivité de l'oxyde. En utilisant des additifs pour contrôler ces facteurs, on a proposé la formulation d'une nouvelle peinture, stable jusqu'à 550°C et sacrificielle plus de 1000 H au test de brouillard salin
Le contrôle de réactivité d'aluminium en peinture anti-corrosion résistant à la haute température
No full textThe aim of this work is to understand Al reactivity at a fundamental level and to use this knowledge for the development of Cr(VI)-free sacrificial paints for high temperature aeronautic applications.Pure Al, Al intermetallics and alloys are studied. The atomic emission spectroelectrochemistry is used to isolate the individual phenomena during paint degradation. A linear relationship between cathodic current and Al dissolution is shown and interpreted with a simple model where OH- generation, Al(OH)3 formation/dissolution and Al(OH)4− diffusion are kinetically coupled. For early formulations significant binder dissolution is measured under cathodic polarization, while Al reactivity is suppressed. Similar Al behavior is observed for Al-Mg intermetallics. In terms of the cathodically generated hydroxide mechanism these results are interpreted as the reaction of either Si or Mg with OH-. These results confirm the cathodic Al reactivity model. The loss of anodic activity is explained by the loss of electrical contact at the metal/oxide/polymer/substrate interfaces and the oxide layer modifications are studied to circumvent this problem. It is found that Mg2+ ions retard Al passivation and improve conductivity due to the formation of semiconducting spinel. Finally, two major factors are found to be critical for the Al reactivity control: solution pH and oxide properties. Using additives to control them, the new coating formulation stable up to 550°C and protective more than 1000H in salt spray test is developedL'objectif de ce travail est de comprendre le mécanisme fondamentales de la réactivité de l'Al et d'utiliser ces connaissances pour développer une peinture sacrificielle sans Cr(VI). L'Al pur, ses alliages et ses intermétalliques sont étudiés. La spectroélectrochimie atomique à émission de plasma est utilisée pour isoler les phénomènes individuels au cours de la dégradation. La relation linéaire entre le courent cathodique et la vitesse de dissolution de l'Al est démontrée et interprétée par un modèle dans lequel la génération d'OH-, la formation/dissolution d'Al(OH)3 et la diffusion d'Al(OH)4- sont cinétiquement couplées. La dissolution significative du liant de première formulation a été accompagnée de la passivation d'Al pendant la polarisation cathodique. Un comportement similaire est observé pour des intermétalliques Al-Mg. Ceci est interprété comme la réaction des composants (du Mg ou du Si) avec OH-. Ces résultats confirment le modèle de réactivité cathodique de l'Al. La perte d'activité anodique est expliquée par la perte de contact électrique au niveau des interfaces métal/oxyde/polymère/substrat. Les modes de transformation de la couche d'oxyde sont étudiées. Les ions de Mg2+ retardent la passivation d'Al par la formation de spinelle semi-conducteur qui est responsable de l'amélioration de la conductivité.Finalement, deux facteurs principaux sont jugés essentiels pour la réactivité de l'Al: le pH de la solution et la conductivité de l'oxyde. En utilisant des additifs pour contrôler ces facteurs, on a proposé la formulation d'une nouvelle peinture, stable jusqu'à 550°C et sacrificielle plus de 1000 H au test de brouillard salin
Selagem com proteção ativa de ligas de magnésio tratadas por PEO
No full textThis work pretends to test active sealants for the porosity of plasma electrolytic oxidation (PEO) coatings applied in AM50 magnesium alloy. Layered double hydroxides (LDH) were chosen as active nanocontainers and were synthesized by two different methods, so called “in situ 1” and “in situ 2” on the surface of AM50 alloy. For the in situ 1 method, the alloy substrate is used as source of cations (Mg2+) to form the LDH structure, while in situ 2 is based in co-precipitation method, with the surface acting as a nucleation point for the LDH growth. The LDH nanocontainers were intercalated with 2–Mercaptobenzothiazole. PEO was used to grow a ceramic layer on AM50 surface. In situ 2 synthesis was used to grow LDH on the surface of the ceramic PEO layer to seal the porosity of the PEO coating and add “smart” self-healing ability to this layer.
The LDH and PEO coatings were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD).
Electrochemical impedance spectroscopy (EIS) was performed in both LDH on the surface of bare AM50 and LDH on the PEO surface in order to evaluate their corrosion behaviorNeste trabalho pretende-se selar a porosidade de revestimentos aplicados na liga de magnésio AM50 através de oxidação por plasma eletrolítico (PEO). Nanocontentores constituídos por Hidróxidos duplos lamelares (LDHs - Layered Double Hydroxides) foram testados como selantes. Procedeu-se à síntese de LDH’s para intercalação de inibidores de corrosão. Os LDH foram sintetizados na superfície de uma liga de magnésio AM50, através de dois métodos diferentes, aqui denominados por “in situ 1 e “in situ 2”. No método in situ 1 os catiões de magnésio (Mg2+) necessários à formação da estrutura dos LDH provêm exclusivamente da liga metálica, enquanto que no método in situ 2 é realizada uma síntese pelo método de co-precipitação, em que a nucleação para o crescimento dos LDHs pode ser feita diretamente na superficie da liga de magnésio ou sobre um revestimento intermédio. Os nanocontentores foram intercalados com o inibidor de corrosão 2 – Mercaptobenzothiazole. Por forma a crescer um revestimento cerâmico na superfície da liga AM50 utilizou-se o método de PEO. O método in situ 2 foi então utilizado para crescer LDH na superfície tratada com PEO de modo a selar a porosidade do filme e atribuir-lhe propriedades de auto-reparação “inteligente”.
A caracterização microestrutural e química dos LDH e dos filmes cerâmicos foi efectuada por microscopia eletrónica de varrimento (SEM – Scanning Electron Microscopy) e por difração de raios X (XRD – X-Ray Diffraction).
A avaliação do desempenho anticorrosivo dos nano-contentores aplicados diretamente na superfície metálica e na liga pré-tratada com PEO foi efectuada através de espectroscopia de impedância eletroquímica (EIS – Electrochemical Impedance Spectroscopy)In dieser Studie wurden sogenannte layered double hydroxides(LDH) mittels zweier unterschiedliche Methoden (in Folge "in situ1" und "in situ2" genannt), auf der Oberfläche der Magnesiumlegierung -AM50 synthetisiert. LDH's dienen typischerweise als Nanocontainer für Korrosionsinhibitoren.Innerhalb der ersten Methode "in situ1" wurde die Substratlegierung selbst als (Mg2+) -Kationenquelle genutzt, um die Strukturbildung und das Wachstum der LDH 's zu gewährleisten. Die Methode "in situ2" hingegen sah vor, die AM50 Oberfläche selbst, lediglich als Keimbildungsort für das LDH-Wachstum zu nutzen.Im nächsten Schritt wurden die LDH Nanocontainer mit dem Inhibitorsystem 2–Mercaptobenzothiazolebeladen, mit dem Ziel, sie in einer Keramikschicht auf der AM50 Oberfläche einzulagern. Die Schicht selbst wurde mittels PEO hergestellt.Die "in situ2" Synthesemethode wurde genutzt, um LDH's auf der Oberfläche einer PEO-Keramikschicht wachsen zu lassen. Ziel war das absenken der Porösität (versiegeln) der PEO-Schicht. Komplementär wurde der Schicht so ebenfalls (durch die beladenen Nanocontainer) die Fähigkeit zur aktiven "intelligenten" Selbstheilung vermittelt.Die LDH/PEO Schichtsysteme wurden systematisch mit einem Rasterelektronenmikroskop (REM) und mittels Röntgendiffraktometrie (XRD) untersucht. Um den Einfluss der LDH's auf das Korrosionsverhalten der AM50-bzw. Der PEO-Oberfläche zu beurteilen, wurde elektrochemischeImpedanzspektroskopie durchgeführt. Der experimentellen Ergebnisse wurden zur abschließenden Bewertung des Ansatzes verwendet.Mestrado em Engenharia de Materiai
Active protective treatments for galvanically coupled AA2024 and CFRP
No full textMestrado em Engenharia de MateriaisVII
Abstract
In the present work “smart” nanocontainers were synthesized in order to incorporate them into an organic coating and protect against corrosion of the aluminum alloy (AA2024) galvanically coupled with carbon fiber reinforced plastic (CFRP). The containers were loaded with organic (2-mercaptobenzothiazole and 1,2,3 – benzotriazole) and inorganic (metavanadate, tungstate and molybdate) inhibitors in the case of Mg/Al and Zn/Al LDH nanoreservoirs. In the case of the bentonite nanocontainers, the containers were loaded with Ce(NO3)3. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were performed in order to characterize the obtained nanocontainers.
The nanocontainers were enbeded into epoxy coating on the surface of model multi-material system (AA2024 galvanically coupled with CFRP). The LDHs loaded with different inhibitors and combined with bentonite loaded with Ce3+, increase the anticorrosion protection properties of the coating. The analyses of the anticorrosion properties of the coatings were performed using zero resistance ammetry (ZRA), electrochemical impedance spectroscopy (EIS), optical microscopy, salt spray test (SST) and scanning vibrating electrode technique (SVET) measurements.
The laboratory work was realized in University of Aveiro in collaboration with industrial environment of Airbus group.No presente trabalho revestimentos "inteligentes" foram sintetizados com a finalidade de proteger contra a corrosão a liga de alumínio AA2024 acoplada galvanicamente com a fibra de carbono reforçado com plástico (CFRP). Os nanocontentores LDH Mg/Al LDH e Zn/Al LDH foram carregados com os inibidores orgânicos 2-mercaptobenzotiazole e 1,2,3-benzotriazole, e com inibidores inorgânicos metavanadato, tungstato e molibdato. No caso dos nanocontentores de bentonite o inibidor incorporado foi o Ce(NO3)3.
A análise por difração de raios-X (DRX) e microscopia eletrónica de varrimento (MEV) foram realizadas a fim de caracterizar os nanocontentores obtidos.
Os nanocontentores foram aplicados em revestimento epóxi na superfície do sistema modelo (AA2024 galvanicamente acoplado com CFRP), os LDH’s preenchidos com inibidores em mistura com Ce3+ carregado na bentonite foram usados com o objetivo de aumentar as propriedades de proteção do revestimento contra a corrosão. As análises das propriedades anticorrosivas dos revestimentos foram realizadas utilizando o ZRA (Zero resistance ammeter), espectroscopia de impedância eletroquímica (EIS), microscopia ótica, teste de nevoeiro salino (SST) e SVET (scanning vibrating electrode technique).
O trabalho foi realizado em ambiente laboratorial e posteriormente em ambiente industrial (Airbus group)
Filmes de conversão baseados em hidróxidos duplos lamelares (HDLs) para proteção de ligas de alumínio para aplicações aeroespaciais
No full textAluminum 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 techniquesAs 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 apropriadasMestrado em Engenharia de Materiai
The control of Al reactivity for high temperature anticorrosion paint formulation
No full textThe aim of this work is to understand Al reactivity at a fundamental level and to use this knowledge for the development of Cr(VI)-free sacrificial paints for high temperature aeronautic applications.Pure Al, Al intermetallics and alloys are studied. The atomic emission spectroelectrochemistry is used to isolate the individual phenomena during paint degradation. A linear relationship between cathodic current and Al dissolution is shown and interpreted with a simple model where OH- generation, Al(OH)3 formation/dissolution and Al(OH)4 diffusion are kinetically coupled. For early formulations significant binder dissolution is measured under cathodic polarization, while Al reactivity is suppressed. Similar Al behavior is observed for Al-Mg intermetallics. In terms of the cathodically generated hydroxide mechanism these results are interpreted as the reaction of either Si or Mg with OH-. These results confirm the cathodic Al reactivity model. The loss of anodic activity is explained by the loss of electrical contact at the metal/oxide/polymer/substrate interfaces and the oxide layer modifications are studied to circumvent this problem. It is found that Mg2+ ions retard Al passivation and improve conductivity due to the formation of semiconducting spinel. Finally, two major factors are found to be critical for the Al reactivity control: solution pH and oxide properties. Using additives to control them, the new coating formulation stable up to 550C and protective more than 1000H in salt spray test is developedL objectif de ce travail est de comprendre le mécanisme fondamentales de la réactivité de l Al et d utiliser ces connaissances pour développer une peinture sacrificielle sans Cr(VI). L Al pur, ses alliages et ses intermétalliques sont étudiés. La spectroélectrochimie atomique à émission de plasma est utilisée pour isoler les phénomènes individuels au cours de la dégradation. La relation linéaire entre le courent cathodique et la vitesse de dissolution de l Al est démontrée et interprétée par un modèle dans lequel la génération d OH-, la formation/dissolution d Al(OH)3 et la diffusion d Al(OH)4- sont cinétiquement couplées. La dissolution significative du liant de première formulation a été accompagnée de la passivation d Al pendant la polarisation cathodique. Un comportement similaire est observé pour des intermétalliques Al-Mg. Ceci est interprété comme la réaction des composants (du Mg ou du Si) avec OH-. Ces résultats confirment le modèle de réactivité cathodique de l Al. La perte d'activité anodique est expliquée par la perte de contact électrique au niveau des interfaces métal/oxyde/polymère/substrat. Les modes de transformation de la couche d'oxyde sont étudiées. Les ions de Mg2+ retardent la passivation d Al par la formation de spinelle semi-conducteur qui est responsable de l'amélioration de la conductivité.Finalement, deux facteurs principaux sont jugés essentiels pour la réactivité de l Al: le pH de la solution et la conductivité de l oxyde. En utilisant des additifs pour contrôler ces facteurs, on a proposé la formulation d une nouvelle peinture, stable jusqu'à 550C et sacrificielle plus de 1000 H au test de brouillard salin.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF
Atomic emission spectroelectrochemistry study of the degradation mechanism of model high-temperature paint containing sacrificial aluminum particles
No full text
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