With the advancement and accessibility of local probing techniques that can operate at the submicron scale it has become possible to analyse the local corrosion properties of industrially important metallic materials and relate these properties to microstructure characteristics of the same materials. In this doctoral study the focus has been on copper-zinc samples, both as industrial brass alloys and as micro-patterned copper-zinc samples. They have been exposed to dilute chloride solutions and to an atmosphere that mimics indoor conditions that cause corrosion. The main goal has been to investigate micro-galvanic effects caused by surface heterogeneities in the copper-zinc samples, and the corrosion inhibition ability of a self-assembled octadecanethiol (ODT, CH3(CH2)17SH) monolayer when applied to these heterogeneous samples. The local chemistry, local electrochemistry, and local surface chemistry in the presence of the copper-zinc galvanic couplings have been elucidated, and their importance has been investigated for corrosion initiation, propagation, termination, and inhibition. A broad spectrum of local probe techniques has been utilised. They include optical microscopy (ex situ and in situ), electrochemical techniques, scanning electron microscopy with energy dispersive spectroscopy, atomic force microscopy, scanning Kelvin probe force microscopy and confocal Raman spectroscopy. In addition, infrared reflection absorption spectroscopy (in situ) and vibrational sum frequency spectroscopy have been employed to analyse the formation of corrosion products and monitor the corrosion kinetics.    A characteristic selective zinc dissolution process was triggered in non-metallic inclusions when a brass alloy was exposed to 1 mM NaCl. Disc-like corrosion areas spread radially outwards from the inclusions, the shape and termination of which was attributed to accessibility to chloride ions. An ODT-layer deposited on brass retarded access to chloride ions at the brass surface and slowed down the radial corrosion process. Instead a delayed formation of filiform-like corrosion was observed.    Upon exposure of the copper-zinc patterned sample to humidified air containing formic acid, micro-galvanic effects were induced by the copper patches on zinc that accelerated the zinc dissolution in the thin aqueous adlayer with concomitant precipitation of zinc formate. The micro-galvanic effects not only resulted in accelerated corrosion rates for zinc, but also in broadening of shapes and atomic structures for the corrosion products formed. Crystalline zinc oxide and zinc formate were observed on the copper-zinc patterned samples, whereas amorphous zinc oxide and zinc formate were formed on the bare zinc surface. Micro-galvanic effects occurred in the two-phase Cu40Zn (Cu with 40 wt% Zn) brass alloy as well, induced by more zinc-rich beta-phase grains surrounded by an alpha matrix with lower zinc-content.    The application of a self-assembled monolayer of ODT for corrosion inhibition of pure zinc and the patterned copper-zinc samples was also explored. In situ infrared reflection absorption spectroscopy analyses showed that ODT initially reduced the rate of zinc formate formation on pure zinc and on the copper-zinc micro-patterned sample. However, the inhibition efficiency was slightly reduced with exposure time due to local removal of ODT on pure zinc and on the micro-patterned samples. This caused micro-galvanic effects that resulted in increased rates of zinc formate formation on the ODT-covered samples – even higher than on the uncovered samples. When applied to the single-phase Cu20Zn alloy, ODT resulted in a corrosion inhibition that was comparable to that of pure copper, a metal for which ODT has shown very good corrosion inhibition. On double-phase Cu40Zn local galvanic effects resulted in less efficient corrosion inhibition and more abundant corrosion products than on Cu20Zn. Based on vibrational sum frequency spectroscopy, the ODT-layer retained its well-ordered molecular structure throughout the exposure to both Cu20Zn and Cu40Zn.    In all, the inhibiting action of the ODT-layer was attributed to the transport hindrance of corrosion promoters (O2, H2O, and HCOOH) to the brass surface. This result suggests that ODT can function as a temporary corrosion inhibitor for brass exposed to benign indoor environments. / Med utvecklingen av och tillgången till lokala analysmetoder som kan ge information med en lateral upplösning på mindre än en mikrometer har det blivit möjligt att analysera lokala korrosionsegenskaper hos industriellt viktiga metalliska material och relatera dessa egenskaper till mikrostrukturen hos samma material. I doktorsavhandlingen har denna möjlighet utnyttjats för koppar-zinkprover, dels som industriella mässingslegeringar dels som mikro-mönstrade koppar-zinkprover, som exponerats för utspädda kloridlösningar samt för en atmosfär som kan efterlikna den atmosfäriska korrosionen inomhus. Det huvudsakliga målet har varit att undersöka dels mikro-galvaniska korrosionseffekter som orsakas av heterogeniteter på koppar-zinkytorna dels korrosionsförmågan hos självorganiserande monolager av oktadekantiol (ODT, CH3(CH2)17SH) vid adsorption på dessa heterogena ytor. På så vis har den lokala kemin, ytkemin och elektrokemin kunnat klarläggas i närvaro av galvaniska effekter, och dess betydelse har undersökts för korrosionsprocessens initiering, propagering, terminering och inhibering. Ett brett spektrum av lokala analysmetoder har utnyttjats. De innefattar ljusoptisk mikroskopi (ex situ och in situ), elektrokemiska metoder, svepelektronmikroskopi med energidispersiv röntgen-spektroskopi, atomkraftsmikroskopi för mikro-kartering och Voltapotentialmätningar samt konfokal Raman-spektroskopi. Dessutom har infrarödreflektions absorptionsspektroskopi (in situ) och vibrationssummafrekvens spektroskopi (engelska: vibrational sum frequency generation) använts.    När en mässingslegering exponerades för 1 mM NaCl observerades en selektiv utlösning av zink med karakteristiskt utseende som växte radiellt från icke-metalliska inneslutningar för att bilda cirkulärt formade korrosionsområden. Formen och termineringen av denna korrosionsprocess bestäms av tillgången på kloridjoner. När ett monolager av ODT adsorberades på mässingslegeringen hämmades tillgången av kloridjoner på mässingsytan och den radiella korrosionsprocessen stannade upp. Istället iakttogs en fördröjd bildning av s.k. filiform korrosion.    Vid exponering av mikro-mönstrade koppar-zinkprover för befuktad luft med låga tillsatser av myrsyra inducerades mikro-galvaniska effekter i gränsen mellan koppar och zink som accelererade utlösningen av zink i den adsorberade fuktfilmen på provet, under samtidig utfällning av zinkformat. De mikro-galvaniska effekterna resulterade inte bara i förhöjda korrosionshastigheter jämfört med de på ren zink, utan även i andra faser hos bildade korrosionsprodukter. På de mikro-mönstrade koppar-zinkproverna bildades kristallint zinkoxid och zinkformat, under det att amorft zinkoxid och zinkhydroxyformat bildades på ren zink. Mikrogalvaniska effekter observerades även i den tvåfasiga mässingslegeringen Cu40Zn (Cu med 40 vikt-% Zn) orsakade av kontakten mellan den mer zinkrika beta-fasen och den omgivande alfa-fasen med lägre zinkhalt.    Appliceringen av ett självorganiserat monolager av ODT för korrosionsinhibering av ren zink och koppar-zinkprover har också undersöks. In situ infrarödreflektions absorptionsspektroskopi visade att adsorberat ODT initialt hämmade bildningen av zinkformat på ren zink och på de mikro-mönstrade koppar-zinkproverna. Med tiden minskade ODTs korrosionsinhiberings-förmåga på grund av att ODTs vidhäftning lokalt försvann. De mikro-galvaniska effekter som därigenom uppstod resulterade i bildandet av zinkformat som med tiden blev snabbare på de ODT-belagda proverna än på motsvarande prover utan ODT. När ODT applicerades på den enfasiga mässingslegeringen Cu20Zn resulterade detta i en korrosionsinhibering som var jämförbar med den på ren koppar, en metall på vilken ODT tidigare visat mycket bra korrosionsskydd. På den tvåfasiga mässingslegeringen Cu40Zn ledde lokala galvaniska effekter till en mindre effektiv korrosions-inhibering och en rikligare mängd korrosionsprodukter än på Cu20Zn. Baserat på vibrationssummafrekvens spektroskopi behöll ODT-lagret dess välordnade struktur under hela exponeringen på både Cu20Zn och Cu40Zn.    ODTs korrosionsinhibering tillskrivs främst transport-hämningen av korrosionsstimulatorer (O2, H2O och HCOOH) till mässingsytan och antyder att ODT kan fungera som en temporär korrosionsinhibitor för mässing i milda inomhusmiljöer. / <p>QC 20140915</p>

This work deals with the influence of atmospheric corrosion on high-cycle fatigue properties of a weathering steel ATMOFIX B. New experimental data on fatigue strength of a steel exposed for 20 years to an atmospheric corrosion were compared to those characterizing the base material. Reduction of the fatigue lifetime of the exposed material compared with the base material was predicted on the basic of fractographic examination of fracture surfaces and the influence of surface notches on fatigue strength. The predicted results agree well with the experimental results.

La thèse porte sur l'étude de la compréhension des mécanismes de corrosion atmosphérique à long terme des alliages ferreux. Les applications sont doubles : d'une part, l'entreposage multi-barrières des déchets nucléaires en surface pendant plusieurs centaines d'années, et d'autre part, la préservation et conservation des objets du patrimoine. Dans un premier axe d'étude, une caractérisation fine du système de produits de corrosion est nécessaire afin de déterminer les phases en présence, leur localisation et leur rôle dans les mécanismes. Cela a nécessité de travailler sur des objets issus des sites archéologiques de référence afin de prélever des échantillons d'études. Dans un second axe d'étude, la réactivité de ces phases et leur comportement électrochimique dans les conditions de corrosion doit être déterminée précisément. Il est alors nécessaire de combiner des études sur phases de référence et sur les objets archéologiques eux-mêmes. La localisation des sites de réduction de l'oxygène dans les objets archéologiques doit être déterminée, après les avoir remis quelques mois en corrosion dans des milieux contenant des traceurs judicieux (l'oxygène 18O2), à l'aide des méthodes nucléaires adhoc. En dernier axe, l'identification de ces processus moteur devrait permettre de proposer de nouvelles méthodes d'inhibition de la corrosion à long terme. Cela concerne uniquement le patrimoine / The present report relates to the understanding of long term atmospheric corrosion mechanisms of low alloy steels which are necessary for various applications such as the interim storage of nuclear waste, and the conservation of cultural heritage artefacts. At a first stage, it may be necessary to characterize ancient corrosion system in order to identify the reactive phases in the rust layers, their localisation and their role in the mechanism. In that purpose, the work on objects reference archaeological sites (analogues) can help to take sample of studies. At a second stage, the electrochemical behaviour and their reactive of the phases constitutive of the corrosion layer must be determined precisely. In that field, it is necessary to combine the study of the pure phases and the powders taken on the analogues. The localisation of oxygen reduction sites in the rust layer is a very pertinent tool. To that end, specific experiments have been set up to re-corrode the ancient samples in marked medium (using 18O2), were investigated by nuclear reaction analysis. Finally, the identification of these newly-formed phases give precious information to develop new methods of inhibition of long term corrosion. It concerns only the heritage

This work deals with the influence of atmospheric corrosion on high-cycle fatigue properties of a weathering steel ATMOFIX B. New experimental data on fatigue strength of a steel exposed for 20 years to an atmospheric corrosion were compared to those characterizing the base material. Reduction of the fatigue lifetime of the exposed material compared with the base material was predicted on the basic of fractographic examination of fracture surfaces and the influence of surface notches on fatigue strength. The predicted results agree well with the experimental results.

Effects of sodium sulfate (Na2SO4) particle deposition on the atmospheric corrosion of copper (Cu) metal and a Cu-based alloy (Cu5Al5Zn) used in architectural applications were investigated at laboratory conditions compared with effects induced by sodium chloride (NaCl) and to some extent ammonium sulfate (NH4)2SO4 induced corrosion. Pre-deposited surfaces were exposed to repeated wet/dry conditions in a climatic chamber and the formation of corrosion products were assessed using light optical microscopy (LOM), scanning electron microscopy with elemental analysis (SEM/EDS), Fourier transform infrared techniques (FTIR microscopy) and cathodic reduction (CR). Na2SO4 induced corrosion resulted in corrosion cells locally over the surface on both Cu and Cu5Al5Zn, of increased oxygen content in the anodic area of the cells (center of pre-deposited area). The main corrosion products formed on Cu metal are basic copper sulfates and cuprite (Cu2O), while basic sulfates (copper and/or zinc) and Cu2O were the main corrosion products formed on Cu5Al5Zn. A combined deposition of Na2SO4 + NaCl was carried out on the Cu5Al5Zn alloy using two different deposition methods to investigate the possible interplay from a corrosion initiation perspective between the two salt particles. For short time exposed Cu5Al5Zn (1 cycle), two different corrosion cells formed, mainly induced by Na2SO4 and NaCl. Corrosion products formed in anodic areas of a Na2SO4 induced corrosion cell were similar to findings observed for Cu5Al5Zn pre-deposited with Na2SO4 only, whereas peripheral cathodic areas primarily were affected by NaCl dissolution and predominantly composed of Cu2O that was the main corrosion product with small amount of hydroxides and carbonates of the NaCl induced corrosion cells. After relatively longer exposure periods (2 and 6 wet/dry cycles), NaCl dominated the corrosion of the entire surface with the formation of more Cu2O, hydroxides and carbonates. Cathodic reduction findings revealed a negative interplay on corrosion for the mixed salt after short time exposures (1 and 2 cycles), whereas a slight synergistic effect was evident after a longer exposure period (6 cycles), compared with corrosion induced by single salts.

This licentiate study was initiated by copper, zinc and galvanized steel producers in Europe, who felt a need to assess runoff rates of copper and zinc from the pure metals and commercial products at marine exposure conditions. Their motive was the increasing concern in various European countries and the on-going risk assessments of copper and zinc within the European commission. Also the circumstance that available runoff rates so far, had been reported for mainly urban exposure conditions, rather than marine. A collaboration was therefore established with the French Corrosion Institute, which runs a marine test site in Brest, and a set of vital questions were formulated. Their answers are the essence of this licentiate study. Based on the ISO corrosivity classification and one-year exposures, the marine atmosphere of Brest is fairly corrosive for zinc (class C3) and highly corrosive for copper (C4). Despite higher corrosivity classifications for both metals in Brest compared to the urban site of Stockholm, used as a reference site, nearly all runoff rates assessed for copper, zinc and their commercial products were lower in Brest compared to Stockholm. This was attributed to a higher surface wetting in Brest and concomitant higher removal rate of deposited chloride and sulphate species from the marine-exposed surfaces. The comparison shows that measured corrosion rates cannot be used to predict runoff rates, since different physicochemical processes govern corrosion and runoff respectively. For copper, the runoff rate in Brest was approximately 1.1 g m-2 yr-1 with cuprite (Cu2O) as main patina constituent. During periods of very high chloride and sulphate deposition, paratacamite (Cu2Cl(OH)3) formed which increased the runoff rate to 1.5 g m-2 yr-1. For zinc, with hydrozincite (Zn5(CO3)2(OH)6) as the main patina constituent, the runoff rate was relatively stable at 2.6 g m-2 yr-1 throughout the year, despite episodes of heavy chloride and sulphate deposition. The application of organic coatings of varying thickness on artificially patinated copper or on different zinc-based products resulted in improved barrier properties and reduced runoff rates that seem highly dependent on thickness. The thickest organic coating (150 µm thick), applied on hot dipped galvanized steel, reduced the runoff rate by a factor of 100. No deterioration of organic coatings was observed during the one-year exposures. Alloying zinc-based products with aluminium resulted in surface areas enriched in aluminium and concomitant reduced zinc runoff rates. The release rate and bioavailability of copper from different anti-fouling paints into artificial seawater was also investigated. It turned out that the release rate not only depends on the copper concentration in the paint, but also on paint matrix properties and other released metal constituents detected. Far from all copper was bioavailabe at the immediate release situation. In all, the results suggest the importance of assessing the ecotoxic response of anti-fouling paints not only by regarding the copper release, but rather through an integrated effect of all matrix constituents. / QC 20101126

No description available.

No description available.

Cette étude a pour objet d’apporter des éléments de compréhension quant à l’amélioration de la résistance à la corrosion des alliages de ZnMg(Al), en comparaison du Zn, en milieu atmosphérique chloré. Le cheminement de réflexion part de considérations fondamentales et tend vers des conditions réelles d’utilisation. La première étape a consisté à synthétiser et caractériser des films de ZnO dopé Mg et notamment l’évolution de la structure cristalline, la structure électronique, la résistivité, (…) avec le dopage. La pertinence de ces paramètres a ensuite été évaluée et discutée au regard de la stabilité de ces films en solution. Dans un second temps, les produits de corrosion formés, en laboratoire, en présence ou non de chlorures, sur des phases pures de Zn et ZnMg, ont été caractérisés. Les processus physico-chimiques liés à la formation de ces produits ont ensuite été discutés, afin de mettre en lumière le rôle du Mg dans l’amélioration de la résistance à la corrosion. La dernière étape, s’est attachée à caractériser des produits de corrosion formés après 6 mois en milieu naturel, en atmosphère marine, sur des phases pures de Zn et ZnMg, et des revêtements industriel de type ZnMgAl. Les résultats obtenus ont permis de mettre en évidence une meilleure stabilité en solution des films de Zn0.84Mg0.16O en comparaison du ZnO, en corrélation avec une présence accrue de liaisons hydroxyles, une augmentation de la résistivité et de la fonction de travail. Ces trois paramètres sont apparus également pertinents, sur les produits de corrosion formés en laboratoire et naturellement en présence de Mg et de Mg, Al, et corrélés à l’amélioration de la résistance à la corrosion. / The aim of this study was to provide some understanding about the improvement of the corrosion resistance of ZnMg and ZnMgAl alloys in comparison to Zn, in chloride content atmospheric environment, from fundamental considerations gradually towards the actual use of these materials. The first approach consisted in the synthesis and physicochemical characterization of films of magnesium doped zinc oxide and particularly the evolution of parameters such as the crystal structure, the electronic structure (band gap), the resistivity, (…) with doping. The relevance of these parameters was then evaluated and discussed regarding to the stability of these films in a solution of pH 8.4. The second stage focused on the characterization of corrosion products formed in the laboratory with or without chloride, on pure Zn and ZnMg. The physico-chemical processes related to the formation of these products were then discussed to highlight the role of Mg in the improvement of the corrosion resistance of ZnMg alloys in comparison with the Zn. The third and final stage consisted in the characterization of corrosion products formed in marine atmosphere on pure Zn and ZnMg, as well as on industrial coating-type ZnMgAl, after 6 months of exposure. The results obtained in this study showed a better stability in solution of solid solution films of Zn0.84Mg0.16O in comparison with the ZnO, correlated with the increase of hydroxyl bonds, associated with an increase of resistivity and work function. These three parameters appeared also relevant regarding the corrosion products formed naturally in the laboratory and in the presence of Mg and Mg-Al, and correlated with improvement of the corrosion resistance.

Orientador: Eduardo Norberto Codaro / Resumo: O presente trabalho tem por objetivo avaliar o efeito da corrosão atmosférica marinha sobre os aços ASTM Grau 80, Grau 100 e Grau 120, que são utilizados na montagem de lingas de corrente destinadas à movimentação de cargas. Os problemas atribuídos à deterioração desses materiais são comuns e frequentes, pois basicamente em todos os ramos da atividade econômica há materiais que necessitam ser transportados. E para analisar o comportamento destes aços frente à corrosão, foram realizados ensaios eletroquímicos e ensaios de imersão por perda de massa utilizando uma solução contendo NaCl a 3,56% (em massa) que simula a atmosfera marinha em ambientes laboratoriais. Os resultados dos ensaios de OCP (Potencial em Circuito Aberto) e de Polarização de Tafel revelaram que o processo de corrosão é controlado pela difusão de O2 dissolvido neste meio. Pode-se concluir que os valores de OCP e de Ecorr (potencial de corrosão) obtidos foram muito similares entre si para todas as regiões do elo analisadas (solda, corpo e deformação). A região do corpo demonstrou maior resistência à corrosão, obtendo os maiores valores médios de resistência de polarização (Grau 80: 10,14 kΩ; Grau 100: 12,61 kΩ; e Grau 120: 11,74 kΩ). As densidades de corrente de corrosão (Icorr) observadas são baixas e da mesma ordem de magnitude (abaixo de 7µA/cm2). Nos ensaios de imersão, observou-se que a perda de massa relativa das amostras, após os 10 dias de permanência na solução, foi mínima (entre 0,05 e 0,08 %/cm2), i... (Resumo completo, clicar acesso eletrônico abaixo) / Mestre