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Forthun, Kari. "Alternating Current Corrosion of Aluminium Sacrificial Anodes." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22387.
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Direct Electric Heating (DEH) is applied to subsea oil production and transmission pipelines to prevent freezing of hydrates as wax during productions shut downs. To prevent clogging, the pipes are heated by application of alternating current (AC) voltage. As a result, a risk for AC corrosion is introduced, which is the motivation and subject of this thesis. The steel pipes are coated and applied conventional cathodic protection (CP) by use of AlZnIn sacrificial anodes. The present work focused on the risk of increased rates of AC influenced corrosion of the AlZnIn anodes. Anode samples coupled to steel samples were investigated under applied AC by use of laboratory scale test cells in synthetic seawater at room temperature. In these experiments, which lasted for one week, the applied AC was varied in the range 0.5 to 150 A m-2, and the anode-steel area ratio (AR) was set to either 10:1 or 100:1. Corrosion rates were assessed by weight loss measurements and properties of surface deposits and corroded surfaces were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. For better assessment of anode-steel coupling in practice and the significance of anode-steel area, similar tests were performed by using a connection of two identical pairs of parallel-coupled anode-steel, with area ratio of 100:1. Equipment and methodology for investigation of AC corrosion were developed and evaluated. Results show that the anode corrosion rate increased with increasing applied AC level, while steel is sufficiently protected under the experimental conditions specified above. Anode corrosion rate was influenced both by current provided for the protection of the steel and self-corrosion and the attack was characterized by pit formation and coalescence of these at higher AC levels. High self-corrosion rates were attributed to successive alkalization, explained by hydrogen evolution, and acidification of the anode surface at each AC cycle, which destabilized the protective oxide layer. Corrosion was limited at high AC levels, explained by hydrogen blanketing of the anode surface and by hydrogen trapped within pores of the hydroxide surface film. AC corrosion of the anodes depended strongly on the anode-steel area ratio. In experiments with electrode pair configuration as described above, the significance of the steel samples vanished by increasing the anode-steel area ratio to 100:1. The system functioned as an anode?anode galvanic couple, which caused a significant decrease in the potential of the anodes, giving rise to runaway self-corrosion rates. In experiments with one anode-steel couple, the couple potential also decreased once AC was applied, increasingly in extent with applied AC potential. This further increased the current requirement by increasingly cathodic steel, thereby resulting in extreme anode corrosion at high AC levels in experiments with AR of 10:1. A subsequent positive shift in the couple potential to a stable level lower than the DC operation potential (-1.05 VSCE) of the AlZnIn anode was observed within 20 hours, caused by hydrogen evolution on steel. The time until the positive shift increased with applied AC level and decreased AR. Formation of calcareous deposits on the steel surface under DC conditions is an important aspect of CP in seawater because the deposits reduce the current requirement significantly. Such deposits did not appear to have a similar significance in the presence of applied AC. Increased water reduction by AC, causing pH increase on the steel surface higher than the DC case, reduced the protectiveness of the deposits by inhibition of electrically insulating CaCO3 formation. Preconditioning of the steel surface by CP under usual DC conditions to form the desired deposits did not have a clear influence on the AC corrosion of anodes. The decrease of both the AC and DC components of the cell current as a function of time under moderate applied AC levels, however, indicated the formation of calcareous deposits on steel. No calcareous scales were found to deposit on the anode surface. The decrease of cell current with time can also be attributed to the development of corrosion products on the anode surface. Decrease in the cell current was not appreciable for high AC levels (> 2 V RMS) with an AR of 10:1, explained by the destruction and instability of the calcareous deposits due to vigorous gas evolution. In conclusion, these results suggest that the lifetime of the CP system at high levels of applied AC (V(AC) > 2 V AC or iAC > 30 A m-2) may become significantly reduced in relation to the expected lifetime under DC conditions.
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Baker, Devon Scott. "Understanding the Corrosion of Low-Voltage Al-Ga Anodes." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/53835.
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Aluminum is an attractive metal for use as an anode in the cathodic protection of steels in seawater due to its low cost and high current capacity. Zinc is often used for its ability to readily corrode, but it has a low current capacity and it operates at very negative voltages, leading to hydrogen generation at the steel cathode, which may cause hydrogen embrittlement. Aluminum can operate at less-negative voltages, therefore reducing hydrogen generation, but it forms a passive oxide film, preventing the anode from corroding. Ga is added to aluminum in small amounts (0.1 wt%) to destabilize this oxide film and allow for active corrosion. The mechanism of how Ga activates Al is still not well-known, though there are prevailing proposals. A previous study noted a difference in behavior between Al-Ga master heats and the alloys that were later produced by re-melting them. This study is focused on characterizing the corrosion behavior of Al-0.1 wt% Ga in synthetic seawater, with samples from a master heat and two subsequent remelts. Galvanostatic, potentiostatic, and open-circuit tests were run, as well as galvanic coupling with 1123 steel. It was found that the remelted anodes behaved more consistently and maintained stable corrosion behavior for longer times than the master heat. X-ray Photoelectron Spectroscopy analysis showed elevated concentrations of Ga inside the oxide layer. The findings support the mechanism in the literature of discrete particles of Ga forming under the oxide film but do not support the mechanism of an amalgam layer formation. This project was funded by NACE International, Virginia Tech project number 457789.Master of Science
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Tunnicliffe, Matthew. "Corrosion of lead anodes in metallic electrowinning environments." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/37789.
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The corrosion of anodes in electrowinning is costly because of their relatively short lifespan, material cost, and their impact on cathodic deposit quality. The objective of this thesis was to understand the corrosion behavior of Pb anodes in electrolyte simulating Zn and Ni electrowinning conditions. Pb-based alloys have been used because they are cheap, conductive and stable at high potential and low pH. Experiments in this thesis included open circuit potential (OCP), potentiodynamic, and potentiostatic polarizations. The parameters studied include; icorr, Ecorr, slope of the oxygen evolution region and O₂ potential.
For Zn electrowinning, variables changes included modifying H₂SO₄, Mn²⁺, Cl⁻, Zn²⁺ concentrations and increasing temperature. The best corrosion resistance in Zn electrowinning was achieved by increasing H₂SO₄ concentration, using 15 g/L Mn²⁺, 0 g/L Cl⁻, and increasing both Zn²⁺ temperature. Corrosion products were studied using SEM and EDX and the relationship between surface morphology of the working electrode and operating potential. Deaerating the cell reduced the dissolved oxygen in the cell and generally increased icorr, oxygen evolution region slope and OER overpotential. For Ni electrowinning applications, three materials were used as cast PbAg, rolled PbAg, and as cast PbCaSn. The effects of H₂SO₄ and Cl- on corrosion behavior were studied using both potentiodynamic and galvanostatic polarizations. Corrosion rates were determined by measuring the length of the discharge peak after 24 hours galvanostatic polarization and SEM and XRD were used to determine the surface morphology and phase composition of the anodes.
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Dinh, Thi Mai Thanh. "Stabilité et performances de matériaux d'électrode à base de titane en milieu acide." Paris 6, 2003. http://www.theses.fr/2003PA066095.
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Dugarte, Margareth. "Polarization of Galvanic Point Anodes for Corrosion Prevention in Reinforced Concrete." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3466.
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The polarization performance of two types of commercial galvanic point anodes for protection of reinforced steel around patch repairs was investigated. Experiments included measurement of the polarization history of the anode under constant current impressed by galvanostatic circuits and in reinforced concrete slabs. The tests revealed, for both types of anodes, a potential-current function (PF) indicating relatively little anodic polarization from an open circuit potential at low current levels, followed by an abrupt increase in potential as the current approached an apparent terminal value. Aging of the anodes was manifested by a continually decreasing current output in the concrete tests, and by increasingly more positive potentials in the galvanostatic tests. Those changes reflected an evolution of the PF generally toward more positive open circuit potentials and, more importantly, to the onset of elevated polarized potentials at increasingly lower current levels. There was considerable variability among the performance of replicate units of a given anode type. Modest to poor steel polarization levels were achieved in the test yard slabs. Modeling of a generic patch configuration was implemented with a one-dimensional approximation. The model calculated the throwing distance that could be achieved by a given number of anodes per unit perimeter of the patch, concrete thickness, concrete resistivity, amount of steel and amount of polarization needed for cathodic prevention. The model projections and aging information suggest that anode performance in likely application scenarios may seriously degrade after only a few years of operation, even if a relatively optimistic 100 mV corrosion prevention criterion were assumed. Less conservative criteria have been proposed in the literature but are yet to be substantiated. Other investigations suggest a significantly more conservative corrosion prevention may apply instead. The latter case would question the ability of the point anodes to provide adequate corrosion prevention.
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Christodoulou, Christian. "Repair and corrosion management of reinforced concrete structures." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13577.
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The durability of concrete structures is affected by a number of factors such as environmental exposure, electrochemical reactions, mechanical loading, impact damage and others. Of all of these, corrosion of the reinforcement is probably the main cause for the deterioration of steel reinforced concrete (RC) structures. Corrosion management is becoming increasingly necessary as a result of the growing number of ageing infrastructure assets (e.g. bridges, tunnels etc.) and the increased requirement for unplanned maintenance in order to keep these structures operational throughout their design life (and commonly, beyond). The main RC repair, refurbishment and rehabilitation approaches generally employed can be broadly categorised under a) conventional, b) surface treatments, c) electrochemical treatments and d) design solutions. The overarching aim of this research was to identify the key corrosion management techniques and undertake empirical investigations focused on full-scale RC structures to investigate their long-term performance. To achieve this, individual research packages were identified from the above broad five approaches for repair, replacement and rehabilitation. These were 1) Patch repairs and incipient anodes, 2) Impressed Current Cathodic Protection, 3) Galvanic Cathodic Protection and 4) Hydrophobic treatments. The selection of the above research packages was based on past and present use by the construction industry to repair, refurbish and rehabilitate RC structures. Their contributions may be broadly categorised as i) Investigations on how specific treatments and materials perform, ii) Investigations on the effectiveness of existing methods of measurements and developing alternatives, iii) Changes to the existing theory of corrosion initiation and arrest and iv) Changes to management framework strategies. The key findings from each research package can be summarised as follows: Macrocell activity appears to be a consequence rather than a cause of incipient anode formation in repaired concrete structures, as has previously been presented; ICCP has persistent protective effects even after interruption of the protective current; Discrete galvanic anodes installed in the parent concrete surrounding the patch repair are a feasible alternative to galvanic anodes embedded within the patch repairs of RC structures; Silanes may have a residual hydrophobic effect even after 20 years of service.
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Mohammadi, Maysam. "Development of Pb-MnO₂ composite anodes for electrowinning application : electrochemical and corrosion evaluations." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/57299.
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Electrowinning is the last step of the extraction of zinc in which aqueous zinc ions are electrodeposited to produce highly pure zinc metal. This process operates in highly acidic solutions and at high current densities. Conventional lead-based anodes used in the zinc electrowinning are associated with high corrosion rates and oxygen evolution overpotential in the electrowinning process. These result in some problems such as Pb contaminating the zinc cathode, shortened anode lifetime, and high energy consumption in the process.
Lead-based composite anodes have been introduced to address these issues by using electroactive oxide particles dispersed in the Pb anode. Manganese ions, which typically exist in the zinc electrowinning electrolyte, can influence the anode performance, depending on their concentration and the anode material. The main aim of this work was to develop a new composite anode using MnO₂ particles in a Pb matrix to improve the anode performance in the zinc electrowinning operating conditions in Mn-free and Mn-containing electrolytes.
A combination of electrochemical and analytical methods was used to understand the oxidation, electrocatalytic activity, and corrosion performance of the Pb-MnO₂ composite anodes compared to the conventional PbAg anode. Potentiometric titration was utilized to measure the oxidation rate of manganese ions. The anodic corrosion layers and the MnO₂ deposited layers were characterized by Scanning Electron Microscopy and X-Ray Diffraction. A new electrochemical method was also developed for an on-site investigation of the deposited MnO₂ layer on the anodes.
The Pb-MnO₂ composite anodes showed higher catalytic activity and better corrosion resistance than the PbAg anode under the zinc electrowinning operating conditions. The Pb–MnO₂ anode can decrease the energy consumption in the electrowinning process in the Mn-free electrolyte by up to 5%. The composite particles were not effective in decreasing the anode potential in the Mn-containing electrolyte. The MnO₂ particles catalyzed Mn(III) disproportionation, contributing to the deposition of a uniform, adherent, and protective MnO₂ layer. Formation of this layer decreased the lead dissolution and manganese consumption rates. The Pb-MnO₂ composite anode can be put into service without any pre-treatment since it quickly develops a stable MnO₂ layer and generates very low MnO₂ mud.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Alhamalawi, Mazen. "Offshore Wind Power Foundations' Corrosion Protection Strategy : Anlysis remotely controlled corrosion protection system and comparison to traditional corrosion protection of offshore wind foundation." Thesis, Linnéuniversitetet, Sjöfartshögskolan (SJÖ), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-103460.
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När en metall är omgärdad av en elektrolyt, så som havsvatten, kommer det att byggas upp en naturlig potential. Det sker en elektronvandring mellan materialet och havsvattnet och ju större potentialskillnad desto större sannolikhet att metallen kommer korrodera. Korrosion är en stor och viktig fråga för offshorekonstruktioner och byggnader. För att uppnå en konstruktions designade livslängd kan åtgärder vidtas med hänsyn till kapitalkostnader och drift- och underhållskostnader. Denna studie syftar till att jämföra ekonomiska för- och nackdelar hos de två korrosionsskyddssystemen Galvanic Anode Corrosion Protection (GACP) och Impressed Current Cathodic Protection (ICCP) på havsbaserade vindkraftsfundament. Det förstnämnda systemet använder offeranoder och det sistnämnda är ett katodiskt korrosionsskydd med hjälp av påtryckt ström. Studien bestod av flera steg av litteraturstudier där teori om korrosion och korrosionssystem användes för att till slut kunna jämföra valda korrosionsskyddssystem. Resultatet visar att GACP har fler fördelar och färre nackdelar än ICCP och skulle därmed vara mer ekonomiskt fördelaktig i marina miljöer. GACP ger också önskad effekt direkt vid installation och behöver inte någon strömkälla, ICCP är mer komplicerat och är inte effektivt förrän hela systemet är monterat och i drift. Dessutom behöver ICCP extra strömkälla samt kablage.When a metal is surrounded by an electrolyte, such as seawater, a natural potential will be built up. An electron migration between the material and the seawater will happen and the greater the potential difference, the greater the probability that the metal will corrode. Corrosion is an important issue when it comes to offshore structures. In order to achieve a structure designed lifetime, measures can then be taken with regard to capital costs and operating and maintenance costs. This study aims to compare the economic advantages and disadvantages of the two, Galvanic Anode Corrosion Protection (GACP) and Impressed Current Cathodic Protection (ICCP), corrosion protection systems on offshore wind power foundations. The first mentioned system uses sacrificial anodes and the second is a cathodic corrosion protection by an applied current. The study consisted of several stages of literature studies where theory of corrosion and corrosion systems was used to finally be able to make a comparison between selected corrosion protection systems. The result shows that GACP has more advantages and fewer disadvantages than ICCP and would thus be more economical. GACP, for example, is efficient during installation and does not need an additional power source, but ICCP is more complicated and not efficient until complete assembly of the entire system and requires additional power source and cables. Right now, there is no design standard available with detailed requirements and advice has been given as for galvanic anodes systems.
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Kidd, Jr Michael Scott. "Al-Ga Sacrificial Anodes: Understanding Performance via Simulation and Modification of Alloy Segregation." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89066.
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Marine structures must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum satisfies these conditions, and would be a good choice for a sacrificial anode to protect steel structures if it did not passivate. However, various elements can be added to aluminum to prevent this passivation. Currently, Al-Ga alloys are used commercially as sacrificial anodes but their performance is not consistent. In this research, Thermo-Calc software was used to simulate various aspects of the Al-Ga system in an attempt to understand and potentially correct this reliability issue. Simulations showed that gallium segregates to the grain boundaries during solidification and then diffuses back into the grains during cooling to room temperature. Simulations also suggest that faster cooling rates and larger grains cause the potential segregation of gallium at the grain boundaries to remain after cooling. A set of aluminum plus 0.1% weight percent gallium alloy plates were produced with varying cooling rates, along with a control set (cooled slowly in a sand mold). Some samples were later homogenized via annealing. Samples were subjected to a 168 hour long galvanostatic test to assess voltage response. The corrosion performance of samples was found to have both consistent and optimal voltage range when subjected to quick cooling rates followed by annealing. Testing samples at near freezing temperature seems to completely remove optimal corrosion behavior, suggesting that there are multiple causes for the voltage behavior.Master of Science
Ships must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum has properties which could allow a plate of it to rust instead of a ship it is attached to, thus protecting the ships from rusting. However, because aluminum usually does not rust, gallium can be added to aluminum to allow it to rust. Currently, aluminum-gallium alloys are used commercially to protect ships, but their performance is not consistent. In this research, various aspects of the aluminum-gallium system were simulated in an attempt to understand and potentially correct this reliability issue. Simulations showed that the gallium concentration may not be uniform in the alloy, and various conditions can cause the gallium concentration to be inconsistent. A set of aluminum-gallium alloy plates were cast in molds from liquid aluminum. Some of the plates were cooled quickly, and some cooled slowly. Some samples were later heated in an oven at high temperatures in an attempt to even out the gallium concentration. Samples were subjected to tests to observe corrosion behavior. The corrosion performance of samples was found to be best when subjected to quick cooling rates followed by the oven heating. Testing the samples in cold temperatures seemed to remove the desired corrosion behavior, suggesting that there are multiple reasons for the inconsistent corrosion behavior of aluminum gallium.
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Kidd, Michael Scott Jr. "Al-Ga Sacrificial Anodes: Understanding Performance via Simulation and Modification of Alloy Segregation." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/89066.
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Marine structures must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum satisfies these conditions, and would be a good choice for a sacrificial anode to protect steel structures if it did not passivate. However, various elements can be added to aluminum to prevent this passivation. Currently, Al-Ga alloys are used commercially as sacrificial anodes but their performance is not consistent. In this research, Thermo-Calc software was used to simulate various aspects of the Al-Ga system in an attempt to understand and potentially correct this reliability issue. Simulations showed that gallium segregates to the grain boundaries during solidification and then diffuses back into the grains during cooling to room temperature. Simulations also suggest that faster cooling rates and larger grains cause the potential segregation of gallium at the grain boundaries to remain after cooling. A set of aluminum plus 0.1% weight percent gallium alloy plates were produced with varying cooling rates, along with a control set (cooled slowly in a sand mold). Some samples were later homogenized via annealing. Samples were subjected to a 168 hour long galvanostatic test to assess voltage response. The corrosion performance of samples was found to have both consistent and optimal voltage range when subjected to quick cooling rates followed by annealing. Testing samples at near freezing temperature seems to completely remove optimal corrosion behavior, suggesting that there are multiple causes for the voltage behavior.Master of Science
Ships must withstand the corrosive effects of salt water in a way that is low cost, reliable, and environmentally friendly. Aluminum has properties which could allow a plate of it to rust instead of a ship it is attached to, thus protecting the ships from rusting. However, because aluminum usually does not rust, gallium can be added to aluminum to allow it to rust. Currently, aluminum-gallium alloys are used commercially to protect ships, but their performance is not consistent. In this research, various aspects of the aluminum-gallium system were simulated in an attempt to understand and potentially correct this reliability issue. Simulations showed that the gallium concentration may not be uniform in the alloy, and various conditions can cause the gallium concentration to be inconsistent. A set of aluminum-gallium alloy plates were cast in molds from liquid aluminum. Some of the plates were cooled quickly, and some cooled slowly. Some samples were later heated in an oven at high temperatures in an attempt to even out the gallium concentration. Samples were subjected to tests to observe corrosion behavior. The corrosion performance of samples was found to be best when subjected to quick cooling rates followed by the oven heating. Testing the samples in cold temperatures seemed to remove the desired corrosion behavior, suggesting that there are multiple reasons for the inconsistent corrosion behavior of aluminum gallium.
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Guessoum, Khadoudj. "Nouveaux alliages zinc-terres rares pour des applications anticorrosion : élaboration, propriétés et traitements de surfaces." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0071/document.
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De nouveaux alliages Zn-TR1-5 %mass.(TR = Ce, La et Mischmetal : Ce 75%/La25%) ont été synthétisés par fusion sous atmosphère contrôlée et coulés sous forme de plaques. Dans ces nouveaux matériaux, les terre rare sont localisées exclusivement dans des phases intermétalliques dispersées de manière homogène dans la matrice de zinc : Zn11Ce, Zn13La ou Zn11Ce1-xLax and Zn13CeyLa1-y. Le comportement électrochimique de ces nouveaux alliages a été étudié dans un milieu corrosif de référence simulant les conditions atmosphériques. En parallèle, les phases intermétalliques pures Zn11Ce and Zn13La ont été synthétisées et leur influence électrochimique a été évaluée par voltamétrie et couplage galvanique. Les résultats montrent que les deux phases intermétalliques sont des sites cathodiques préférentiels de la réduction du dioxygène et induisent une inhibition cathodique de la corrosion des alliages Zn-TR par rapport au zinc pur. Ce phénomène est plus marqué dans le cas des alliages au lanthane. Dans le cas spécifique des alliages au cérium, une inhibition anodique a également été observée et corrélée avec une modification chimique des produits de corrosion (composés majoritairement d'hydrozincite). En fait, une faible quantitéhomogène de cérium a pu être mise en évidence dans la couche de corrosion par spectrométrie dispersive en longueur d'onde. D'après les résultats d'expériences de précipitation contrôlée de sels de cérium et zinc en milieu carbonaté, la présence de cérium dans la couche de corrosion et son caractère protecteur pourraient être attribués à la formation d'un composé mixte double lamellaire zinc-cérium. L'addition de moins de 2%mass. de cérium ou lanthane permet d'améliorer la résistance à la corrosion du zinc. Cependant, lorsque la teneur en terre-rare augmente, l'effet de couplage galvanique devient plus important et rend les alliages moins résistants que le zinc purNew Zn-RE1-5 wt.% alloys (RE=Ce, La and Mischmetal: Ce 75%/ La 25%) were synthesized by melting under controlled atmosphere and cast in plates. In these materials, rare earth metal are exclusively present in intermetallic phases homogeneously dispersed in the zinc matrix: Zn11Ce, Zn13La or Zn11Ce1-xLax and Zn13CeyLa1-y. The electrochemical behavior of these new alloys was investigated in a reference corrosivemedium. In parallel, the pure intermetallic phases Zn11Ce and Zn13La were synthesized and their electrochemical influence was studied by voltametry and galvanic coupling. Results show that both intermetallic phases act as preferential cathodic sites of dioxygen reduction and induce a cathodic inhibition of the corrosion of the Zn-RE alloys by comparison with pure zinc. This phenomenon is much more significant in the case of lanthanum containing alloys. In the specific case of cerium addition to zinc, an anodic inhibition was also observed and correlated with a chemical modification of the corrosion products (mainly made of hydrozincite). Actually, low quantities of cerium (less than 1 at.%) have been detected homogeneously in the corrosion layer by wave-length dispersive spectrometry. From results of controlled precipitation experiments of cerium and zinc salts performed in carbonated medium, the presence of cerium in the corrosionlayer and its protective character could be attributed to the formation of a mixed double lamellar zinc-cerium product. Therefore, addition to zinc of less than 2 wt.% of cerium or lanthanum allow to improve the corrosion resistance of zinc. However, by increasing the rare earth content in the alloys, the galvanic coupling phenomenon becomes more important and makes the alloys less resistant than pure zinc
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Zhang, Wei. "Performance of lead anodes used for zinc electrowinning and their effects on energy consumption and cathode impurities." Thesis, Université Laval, 2010. http://www.theses.ulaval.ca/2010/27021/27021.pdf.
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Chénard, Benoit. "Contribution à l'étude de méthodes de mitigation de la corrosion de l'acier d'armature dans les ouvrages en béton armé." Master's thesis, Université Laval, 2020. http://hdl.handle.net/20.500.11794/66593.
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Plusieurs pays nordiques qui utilisent des sels de déglaçage et les régions côtières bordées par les eaux salines sont confrontés à d’importants problèmes de corrosion affectant leurs infrastructures en béton armé. Afin de prolonger la durée de vie de ces ouvrages, les produits de mitigation de la corrosion présentent un réel intérêt. Dans le cadre de ce projet de recherche, deux traitements directs de mitigation de la corrosion ont été étudiés, soit les inhibiteurs de corrosion migrateurs et la protection cathodique par anode sacrificielle noyée, ainsi qu’un traitement à incidence indirecte sur la corrosion, soit le chemisage par tissu de fibres de carbone. L’objectif de cette recherche était de déterminer l’influence de ces approches sur la cinétique de corrosion mesurée dans des corps d’épreuve en béton armé préalablement corrodés. Pour ce faire, des mesures du suivi de l’activité électrochimique ont été réalisées sur les corps d’épreuve en béton armé, ayant fait l’objet d’un conditionnement préalable pour favoriser l’initiation de la corrosion, et comparées aux résultats de simulations numériques. Ni les mesures électrochimiques, ni les résultats générés dans les simulations n’ont révélé de réduction significative de l’activité de corrosion dans les corps d’épreuve. Pour les inhibiteurs de corrosion migrateurs testés, il est présumé que les produits n’ont pas été en mesure de pénétrer jusqu’à l’armature. Il semble toutefois que son efficacité repose sur une fonction secondaire qui est l’imperméabilisation du béton. En ce qui concerne les anodes sacrificielles, la résistivité électrique du béton empêche la formation efficace d’une pile galvanique entre celles-ci et la barre d’armature corrodée. Le modèle numérique a permis d’évaluer une diminution maximale du 63 % du courant de corrosion lorsqu’une anode sacrificielle est directement apposée contre la surface de corrosion active. Le chemisage avec tissu de fibres de carbone s’est quant à lui montré inefficace dans une perspective de mitigation de la corrosion à court terme. En effet, le taux de consommation de l’oxygène par l’activité électrochimique dans la dalle ne permet pas de diminuer significativement les courants de corrosion.It is well known that corrosion of steel rebar is the most important degradation mechanism in reinforced concrete structures. Coastal regions bordered with saline water and northern countries using de-icing salts are faced with tremendous corrosion problems of their reinforced concrete structures. To enhance the lifespan of corroded concrete structures, corrosion mitigation products become more essential. In this research project, two direct mitigation treatments were studied, migrating corrosion inhibitors and cathodic protection with sacrificial anodes, as well as a secondary perspective treatment that is carbon fibre-reinforced polymers wrapping. The objective was to study the influence of mitigation products on corrosion rate in pre-corroded reinforced concrete specimens. The program is conducted throughout experimental phase that requires electrochemical monitoring on concrete specimens, preliminary corroded in a controlled environment, and a modeling phase for validation. In spite of the widespread use of these treatments, the experimental and numerical based results have shown no significant reduction of corrosion rates in the various specimens. For the tested migrating corrosion inhibitors, it is suggested that the products have not been able to reach the reinforcement. Nevertheless, their efficiency seems to be promoted by a secondary function that is the concrete waterproofing. Concerning the sacrificial anodes, the electrical resistivity of concrete hinders the formation of an efficient galvanic cell between the zinc pellet and the corroded rebar. The numerical model evaluated a maximum decrease of 63 % of the corrosion current in case the zinc pellet is place directly under the corrosion zone. Finally, wrapped polymer has not exhibited any significant short-term corrosion-mitigation effect in concrete. In fact, the rate of oxygen consumption associated with the electrochemical activity inside the test slabs is not enough to cause a significant decrease in the currents of corrosion.
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Mottin, Elmina. "Incidence de la dégradation des anodes sacrificielles en zinc chez deux mollusques, l’huître creuse Crassostrea gigas et l’ormeau Haliotis tuberculata : approches in vivo et in vitro." Caen, 2010. http://www.theses.fr/2010CAEN2024.
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Afin de réduire la corrosion de l’acier, des anodes sacrificielles sont fréquemment utilisées en milieu marin. Leur dégradation libère du zinc, ce qui peut représenter un risque pour l’environnement marin. Ainsi, ce travail de thèse vise à étudier la bioaccumulation et l’impact de ce métal chez l’huître creuse Crassostrea gigas. Les analyses in situ ont montré que les huîtres bas-normandes présentaient une concentration de Zn plus faible que celles d’autres régions de France. En laboratoire, un dispositif expérimental, reproduisant la libération de Zn dans le milieu, à partir d’une anode sacrificielle, a été réalisé. Deux expositions y sont effectuées : une dite « chronique » (0,5 mg Zn/L, 10 semaines) et une dite « aiguë » (10 mg Zn/L, 1 semaine). Le suivi de la bioaccumulation montre une forte capacité d’accumulation du Zn par les huîtres, notamment dans la glande digestive. Aucune mortalité n’est observée lors de l’exposition chronique, alors que des mortalités importantes sont enregistrées lors de l’exposition aiguë (81,8 % après une semaine). Les marqueurs moléculaires de stress (MT, SOD, MXR) et les paramètres immunitaires mesurés par cytométrie en flux (phagocytose, production de ROS, activité estérases non spécifiques, présence de lysosomes) ont été modifiés en fonction de la concentration en Zn. Enfin, des études in vitro ont montré une sensibilité au zinc des hémocytes d’ormeau Haliotis tuberculata en culture primaire. En effet, une mortalité hémocytaire importante, ainsi que des modifications morphologiques de ces cellules ont été observées. D’autre part, des variations de paramètres immunitaires et enzymatiques (PO, AcP, ALP) ont été mesuréesApplication of Zinc sacrificial anodes to mitigate marine corrosion is currently used in marine environment. But, the anode degradation by oxidation process conducts to release to significative soluble zinc concentrations in seawater which can conduct to exceed ecotoxicological limits. The aim of this work was to study zinc bioconcentration in oyster Crassostrea gigas by two in-vivo tests performed at different time scales and zinc concentrations due to an electrochemical device providing controlled release of zinc from sacrificial anode degradation as met in in-situ condition. A first test was achieved during 10 weeks and the zinc concentration released from the anode was imposed at 0. 53 ± 0. 04 mg L-1 to simulate a chronic exposure. A second test was conditioned by one week period of 10. 2 ± 1. 2 mg Zinc L-1 and reproduce an acute exposure. Results show zinc bioconcentration in organs of oysters, especially in digestive gland (target organ). No mortality was observed in chronic assay but 81. 8% of oysters died at the end of the acute assay. Moreover, stress molecular markers (MT, SOD, MXR) and immune parameters analysed by flow cytometry (phagocytosis activity, ROS production, nonspecific esterase activity, lysosome content) were modulated by zinc concentration. Moreover, a model based on primary cultured hemocytes from the gastropod mollusc Haliotis tuberculata was established to investigate the effects of zinc in vitro. Immunotoxicity was reflected by a significant decrease in the number of viable hemocytes and dramatic morphological changes of the cells. On the other hand, some modulation of immune and enzymatic (PO, AcP, ALP) parameters were recorded
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Silva, Rodrigo Sanchotene. "Binder a base de polianilina para proteção anódica de aço carbono." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/31388.
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A proteção anódica de metais se caracteriza pela formação de um filme de óxidos protetores na sua superfície, promovendo assim a passivação e a desaceleração do processo corrosivo. O uso de polímeros intrinsecamente condutores (PIC), como a polianilina (PAni) utilizada neste trabalho, tem-se apresentado como alternativa de revestimento ou componente de revestimentos protetores, devido às suas características peculiares que podem proporcionar e induzir o efeito de proteção anódica em metais passiváveis. Devido à dificuldade de dissolução e de coesão de filmes a base de PAni, foi investigada a possibilidade da obtenção de seus filmes pela mistura de PAni no estado oxidado e desdopada, conhecida como PAni esmeraldina base (PAni EB), com o plastificante não dopante 4-cloro-3-metilfenol (CMF) e solvente conveniente. Os filmes produzidos foram caracterizados química e morfologicamente, apresentando-se como um revestimento coeso e auto-suportado com a preservação das funções e das características desejáveis da PAni para aplicação como revestimento anticorrosivo. Os ensaios eletroquímicos realizados em filme de PAni EB aplicado sobre aço carbono AISI 1006, em diferentes concentrações de H2SO4 aquoso, ofereceram respostas que indicam a formação de par redox polímero-metal na faixa de potencial em que é possível a passivação ou manutenção da passivação do substrato metálico, o que resulta na elevação do potencial de corrosão, fazendo com que o metal se comporte de forma mais nobre. Com isso viabiliza-se a utilização do binder de PAni EB como filme anticorrosivo ou/e resina de tintas que promovam a proteção anódica e o efeito de barreira na proteção do aço carbono AISI 1006 contra a corrosão.The anodic protection of metals is characterized by the formation of a protective oxide film on its surface, thus promoting the passivation and the slowdown of the corrosion process. The use of intrinsically conductive polymers (PCI) such as polyaniline (PAni) used in this work, has been presented as an alternative coating or component of protective coatings, due to their peculiar characteristics that may induce and provide the protective anodic effect on oxidizable metals. Due to the difficulty of dissolution and cohesion of films based the polyaniline, was investigated the possibility of obtaining of their films by mixing PAni in the oxidized state and undoped, known as PAni base emeraldine (PAni EB), with plasticizer no dopant 4 -chloro-3-methylphenol (CMF) and convenient solvent. The films produced were characterized chemically and morphologically, presenting itself as a coating cohesive and self-supported, with the preservation of the functions and desirable characteristics of the PAni to application as anticorrosive coating. The electrochemical tests performed on PAni EB film applied over carbon steel AISI 1006, at different concentrations of aqueous H2SO4, offer answers that indicate the formation of redox pair polymer-metal in the potential range in which is possible the passivation or maintenance of the passivation of metallic substrate, resulting in the increase potential of corrosion, doing with that metal to behave of more noble form. With that enables the use of binder of PAni EB as film anticorrosive or/and resin of paints that promote the anodic protection and the effect of barrier in the protection the carbon steel AISI 1006 against corrosion.
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Lewin, R. G. "Positive pillar corrosion in the lead acid battery." Thesis, University of Salford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292911.
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Banjade, Dila Ram. "Galvanic Corrosion of Magnesium Coupled to Steel at High Cathode-to-Anode Area Ratios." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/5623.
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In this study, the impact of galvanic coupling of magnesium to steel on the corrosion rate, surface morphology, and surface film formation was investigated. In particular, the role of self-corrosion was quantified as previous studies showed discrepancies between model predictions and experimental results that were likely due to significant self-corrosion. This experimental study examined the corrosion of Mg coupled to steel in 5 wt% NaCl at cathode-to-anode area ratios that ranged from 5 to 27. Results showed that self-corrosion was significant and accounted for, on average, one-third of total corrosion. Moreover, self-corrosion varied with time and cathode size, and was accelerated by the high dissolution rate. Film formation was observed on the magnesium surface that inhibited the corrosion rates. This film contained approximately 30% of the Mg lost to corrosion. The morphology of the coupled Mg showed the rapid formation of pits with considerable depth, and was quite distinct from previously studied filiform and disk corrosion for uncoupled Mg. This study demonstrates the important role of self-corrosion during galvanic corrosion of Mg and the need to account for such corrosion when predicting corrosion rates. This study also provides important insight into the processes that control Mg corrosion under several conditions.
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Monzel, William Jacob. "Investigation of New, Low-Voltage, Aluminum, Sacrificial Anode Chemistries." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/77501.
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The ultimate goal of this research was to gain a more fundamental understanding of the effects of “active"? alloying elements on the performance of low voltage, aluminum, sacrificial anodes. We have developed an overview of elemental trends and a comparison with literature, in support of a larger program on predicting anode behavior. The broader impact of this work was to enhance the ability to control corrosion and reduce the likelihood of hydrogen embrittlement induced by cathodic protection on ships and marine structures.
As compared to high voltage anodes, low voltage, aluminum, sacrificial anodes reduce the likelihood of causing hydrogen embrittlement or stress corrosion cracking when used to protect high strength steels. In this study, open circuit potential, potentiostatic, galvanostatic and Tafel tests were performed on eleven high-purity aluminum-based binary and ternary alloys containing Bi, Ga, In and Zn in an effort to understand the individual effects of each element and the interactions between these elements. The microstructures of the as-cast alloys and the corrosion surfaces after testing were characterized using electron microscopy. Current capacities and current capacity efficiencies were calculated from potentiostatic and galvanostatic data. Galvanic coupling data from Druschitz et al was plotted with average values from potentiostatic and galvanostatic tests on Tafel curves for all alloys. [1] Variance of weight loss, average galvanostatic current, and average potentiostatic potential of the Al-0.57 wt% Zn-0.55 wt% Bi alloy was evaluated.
Indium and gallium had the most significant effect on corrosion behavior (per wt% added), followed by zinc and bismuth. Bismuth had only a small effect on the weight loss, galvanostatic current and potentiostatic potential. However during potentiostatic testing Al-Bi alloys showed a steady increase in current with time, indicating that larger effects may be seen at longer periods of time. In Al-Zn alloys preferential dissolution of the zinc-rich interdendritic regions was observed. The Al-5.3 wt% Zn alloy showed high current values, but also exhibited high weight loss and more adherent corrosion products. Interdendritic corrosion also occurred with the Al-5.3 Zn-0.011 In alloy. Also, non-uniform dissolution of the remaining primary aluminum dendrites by the formation of small holes was observed, possibly due to indium precipitates. Grain boundary attack and severe intra-granular pitting was observed in Al-In alloys. Small holes were also evident on the surface of pits, similar to those seen on dendrites with the Al-5.3 Zn-0.011 In alloy. The addition of Indium greatly shifted voltages to more negative values (-0.802 to -0.858 VSCE at 9 A/m²) and significantly increased the observed currents (42-83 A/m² at -0.730 VSCE). High potentiostatic current capacities were exhibited by Al-In alloys, Al-0.1 wt% Ga, Al-5.3 wt% Zn-0.011 wt% In, and Al-0.57 wt% Zn-0.55 wt% Bi. However some calculated current capacity values were actually above the theoretical values, possibly due to corrosion products affecting the weight loss measurements.Master of Science
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Lauxen, Flávia. "Eletrossíntese de filmes poliméricos condutores em meio alcalino na proteção contra a corrosão." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/96405.
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A utilização de filmes de polímeros intrinsecamente condutores (PIC) na proteção contra a corrosão tem se mostrado uma alternativa atraente como prérevestimento, pois estes materiais possuem a característica de proporcionar ou induzir o efeito de proteção anódica em metais passiváveis, de modo a desacelerar o processo corrosivo. Neste trabalho foi estudada a possibilidade de obtenção de filmes de PIC sobre aço carbono SAE1006 por eletrossíntese, utilizando os monômeros anilina e 5-amino-1-naftol em meio aquoso KNO3 alcalino. Através da caracterização dos filmes poliméricos, observou-se que os filmes são compactos, homogêneos, uniformes e delgados. Ensaios de eletroatividade mostraram que ambos os filmes possuem pares redox polímero-metal na faixa de potencial em que o substrato metálico é passivável, logo, os filmes são eletroativos. Este comportamento ficou evidente quando as amostras com filmes de PIC foram expostas a soluções ácidas de HCl e H2SO4. O estudo do comportamento eletroquímico via polarização potenciodinâmica mostrou a elevação do potencial de corrosão do aço, confirmando os resultados da eletroatividade. Após caracterização dos filmes de PIC, os corpos de prova foram revestidos com tintas nitrocelulósica, poliuretânica e epoxídica. Os ensaios de aderência mostraram que os filmes de polianilina e poli(5-amino-1-naftol) tem excelente aderência com o substrato metálico e com a tinta. A partir dos ensaios de polarização potenciodinâmica e espectroscopia de impedância eletroquímica em solução de NaCl, observou-se que os filmes PIC apresentaram bom desempenho quando comparados às amostras somente desengraxadas e fosfatizadas.The use of intrinsically conducting polymers films (ICP) for corrosion protection have proved to be an attractive alternative as pre-coating, because these materials have the characteristic of providing or inducing the effect of anodic protection in passivable metals aimed at slowing down the corrosion process. This scientific research investigated the possibility of achieving ICP films on SAE1006 carbon steel surface through electrochemical synthesis using the aniline and 5-amino-1-naphthol monomers in alkaline medium, KNO3. Through the characterization of the polymeric films it was found were observed that the primers are compact, homogeneous, uniform and somewhat thick. Electroactivity trials have shown that both films have redox polymer-metal pairs in the potential range where the steel substrate is passivable, therefore the films have conductivity. This behavior was evident when samples with ICP films were exposed to HCl and H2SO4 acid solutions. The study of the electrochemical behavior through potentialdynamic polarization has shown an increase in steel potential corrosion, thus corroborating the electroactivity results. After the characterization of ICP films, samples were coated with nitrocellulose, polyurethane and epoxy paints. The adherence trials have shown that the polyaniline and poly(5-amino-1-naphfthol) films have an excellent adherence to paint as well as to steel substrate. From the polarization potentialdynamics testings and electrochemical impedance spectroscopy in NaCl solution, it was found that the ICP films have positive results when compared with without films samples and phosphatized samples.
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Curioni, Michele. "Graded anodic film morphologies for corrosion protection of aerospace aluminium alloys." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498976.
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Ready, William Judson IV. "Factors Which Enhance Conductive Anodic Filament Formation." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/5905.
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Oliveira, Leandro Antonio de. "Desenvolvimento de filmes anódicos sobre o aço API 5l X80 e caracterização de seu comportamento eletroquímico e morfológico." reponame:Repositório Institucional da UFABC, 2016.
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Orientador: Prof. Dr. Renato Altobelli AntunesDissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2016.
O fenômeno da corrosão é uma das maiores ameaças à integridadedos aços de alta resistência e baixa liga (ARBL) utilizados para transporte de petróleo e gás.No presente trabalho, investigou-sea estabilidade de filmes anódicos formados sobre o aço API 5L X80 em eletrólitos utilizados para testes de inibidores de corrosão, variando o pH da solução, o potencial de formação na técnica de voltametria cíclica, e a formação espontânea dos filmes por ensaios de imersão. Explorando outro objetivo, foram produzidos filmes anódicos por polarização potenciostática com o intuito de formar uma camada de proteção contra a corrosão do aço API 5L X80. Estes experimentos foram conduzidos em solução de metassilicato de sódio.Neste caso otempo de exposição da amostra aumpotencial fixode formaçãofoi variadoe, como forma de estabelecer um comparativo, foram formados filmes espontaneamente sobre o eletrodo por ensaios de imersão.A caracterização do comportamento eletroquímico foi investigadausando espectroscopia de impedância eletroquímica(EIE)epolarização potenciodinâmica. As propriedades eletrônicas dos filmes anódicos foram analisadas pela abordagem de Mott-Schottky. A morfologia dos produtos de corrosão foi observada com auxílio de microscopia confocal a laser e microscopia eletrônica de varredura (MEV). A composição das camadas de óxido foi identificada com auxílio de espectroscopia Raman. Os resultadosmostraramque os filmesformados em solução alcalina foram mais resistentes àdissolução,menos defeituosos e mais estáveis do que aqueles formados em solução ácida.O produto de corrosão formado por voltametria cíclica tanto emeletrólitode caráter ácido quanto em eletrólitode caráter básico foi identificado como sendo hematita,enquanto a composição doproduto de corrosão formadopor imersãoem eletrólito de caráter básico indicouumadiversidade de compostos, especialmente quando o tempo de imersão foi maior, sendo possível identificar outros compostos além de hematita.A caracterização do comportamento eletroquímico dos filmes obtidos em solução de metassilicato de sódiomostrou que tanto apolarização potenciostáticaquanto a produçãoespontâneados filmes(ensaios de imersão)apresentaram poucos defeitos,alta estabilidade superficiale um aumentosignificativoda resistência à corrosão.A respeito da sua composição química, os filmes formados por cronoamperometria em solução de metassilicato de sódio apresentaram compostos à base de óxidos e oxihidróxidosde ferro, embora a análise de EDS sugerisse a presença de silíciona composição dosfilmes. Por sua vez, a composição dos filmes formados por imersão, em especial o espectro do filme imerso pelo maior período detempo, não foi possível deser identificada com precisão por espectroscopia Raman.
Corrosion is a major threat to the integrity ofhigh strength low alloy (HSLA) steels usedaspipelinesfor oil and gas transportation. In this study, we investigated the stability of the formed anodic films on API 5L X80 steel in electrolytes used for testing corrosion inhibitors, varying the pH of the solution, the formation potential in cyclic voltammetry technique and the spontaneous formation of films by immersion tests. Exploring another objective,anodic films were produced by potentiostatic polarization in order to form a protective layer against corrosion of the API 5L X80 steel. These experiments were conducted in a sodium metasilicate solution. In this case,the exposure time of the sample at a fixed formation potential was varied and, in order to establish a comparison, films were formed spontaneously on the electrode by immersion tests. The characterization of the electrochemical behavior was carried outusing electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The electronic properties of anodic films were assessedbytheMott-Schottky approach. The morphology of corrosion products was observed with the aid of confocal laser scanning microscopy and scanning electron microscopy (SEM). The composition of the oxide layers was identified with the aid of Raman spectroscopy. The results showed that the films formed in alkaline solutions were more resistant to dissolution, less defective and more stable than those formed in acidicsolution. The corrosion product formed by cyclic voltammetry in both the acidic and alkaline solutionswas identified as hematite, while the corrosion product composition formed by immersion in the alkaline solutionindicated a diversity of compounds.Especially whenthe immersiontime was longer, it waspossible to identify other compounds in addition to hematite. The characterization of the electrochemical behavior of the films obtained in the sodium metasilicate solution showed that both the potentiostatic polarizationandthe spontaneous production of films (immersion test) produced layers withfew defects, high surface stability and significantlyincreased corrosion resistance. Regarding its chemical composition, the films formed by chronoamperometry insodium metasilicate solution presented iron oxides and oxyhydroxides, althoughEDS analysis suggested the presence of silicon in the composition of the films. In turn, the composition of thefilms formed upon immersion, in particular the spectrum of the film immersed forthe longest time, could not be reliably determined using Raman spectroscopy.
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Oudot, Magaly. "Mécanismes de formation, dégradation et régénération de couches d'oxydes à la surface d'électrodes métalliques sous polarisation en milieu cryolithique." Toulouse 3, 2014. http://www.theses.fr/2014TOU30148.
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Ce travail s'inscrit dans le cadre d'un projet de recherche visant à élaborer une anode permettant de dégager de l'oxygène dans un électrolyte de cryolithe fondue à environ 960°C, et dont l'utilisation supprimerait les émissions de dioxyde de carbone du procédé de production d'aluminium par électrolyse. L'objectif a été de comprendre les mécanismes de formation, dégradation et régénération de couches d'oxydes à la surface d'anodes métalliques en milieu cryolithique fondu. Le type d'anode étudié est un alliage ternaire Ni-Fe-Cu recouvert d'une couche d'oxyde protectrice. Les réactions se produisant dans les alliages ternaires étant complexes, la démarche a consisté à étudier dans un premier temps les mécanismes d'oxydation impliqués pour les métaux purs, avant d'étendre l'étude aux alliages binaires et ternaires. Les techniques électrochimiques in situ (voltammétrie linéaire, électrolyse intentiostatique/relaxation de potentiel en circuit ouvert, électrolyse potentiostatique) associées à des caractérisations physico-chimiques ex situ ont permis d'identifier les produits de corrosion. Des diagrammes d'équilibre ont également été déterminés pour aider à la compréhension des réactions impliquées, en calculant l'état d'équilibre du système anode/électrolyte en fonction du potentiel électrochimique et de la teneur en alumine de l'électrolyte. Parmi les conditions d'oxydation testées, la pré-oxydation sous CO2 à 900 °C des électrodes métalliques s'est révélée la plus adaptée pour former des couches d'oxydes denses et adhérentes à la surface des anodes. L'étude électrochimique des anodes pré-oxydées a mis en évidence d'importants phénomènes de transport intermétallique dans l'alliage et une réaction entre couches d'oxydes et milieu cryolithique. Ces phénomènes entraînent une dégradation rapide de l'anode, conduisant, selon la composition de l'alliage, à une perte d'adhérence des couches d'oxydes ou à une dissolution sélective du fer contenu dans l'alliage. Ces phénomènes tendent à prouver que les conditions qui permettraient de former une couche protectrice à la surface d'une anode métallique sont, si elles existent, très restreintes. Plusieurs axes d'étude sont proposés pour la suite du projet, parmi lesquels l'élaboration d'une anode sur laquelle une couche de ferrite de nickel est pré-déposée, l'ajout dans l'alliage d'un élément permettant de réguler le transport intermétallique, ou l'utilisation d'un électrolyte basse température pour diminuer la solubilité des couches d'oxydes ainsi que les phénomènes de diffusion dans les phases solidesThe present work is part of a project aiming at the development of an inert metallic Ni-Fe-Cu anode with a protective oxide layer. The use of such an anode would replace CO2 emissions, produced in the current aluminum electrolysis process, by O2 emissions. The purpose is to understand oxide layers growth, degradation and regeneration mechanisms on metallic electrodes in a cryolite-alumina melt at about 960 °C. Because reactions involved in Ni-Fe-Cu alloys are complex, the work was first carried on pure metals. Then, binary and ternary alloys were studied. Corrosion products were identified by the mean of in situ electrochemical techniques (linear voltammetry, intentiostatic electrolysis/open-circuit potential decay, potentiostatic electrolysis) combined with ex situ physicochemical characterizations. To help understanding the oxidation mechanisms, equilibrium diagrams were computed: the equilibrium of the anode/molten salt system was determined versus the electrochemical potential and the alumina concentration. Among tested oxidation conditions, pre-oxidation of metallic electrodes under CO2 atmosphere at 900 °C is the most efficient to form dense and adherent oxide layers on the anode surface. Electrochemical study of pre-oxidized anodes revealed the existence of intermetallic transport phenomena in the alloy and a reaction between the oxide layer and the molten salt. This provokes the anode degradation, leading either to the loss of oxide layer adhesion or to a selective dissolution of iron from the alloy, depending on the alloy composition. It is thus concluded that the conditions required to form a protective oxide layer on a metallic anode are, if they exist, very narrow. Some recommendations are proposed for future work on this project: the elaboration of an anode with a pre-deposited nickel ferrite layer, the addition of an alloying element that could balance intermetallic transport phenomena, or the use of low temperature electrolyte in order to decrease oxide layer solubility as well as solid-state diffusion phenomena
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Agarwal, Arun Sureshchandra. "Characterization of Cathodic and Anodic Processes Associated with Crevice Corrosion under Thin Electrolyte Films." Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1244036563.
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Thesis (Ph.D.)--Case Western Reserve University, 2009Title from PDF (viewed on 19 August 2009) Department of Chemical Engineering Includes abstract Includes bibliographical references Available online via the OhioLINK ETD Center
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Hamada, A. S. (Atef Saad). "Manufacturing, mechanical properties and corrosion behaviour of high-Mn TWIP steels." Doctoral thesis, University of Oulu, 2007. http://urn.fi/urn:isbn:9789514285844.
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Abstract
Austenitic high-Mn (15–30 wt.%) based twinning-induced plasticity (TWIP) steels provide great potential in applications for structural components in the automotive industry, owing to their excellent tensile strength-ductility property combination. In certain cases, these steels might also substitute austenitic Cr-Ni stainless steels. The aim of this present work is to investigate the high-temperature flow resistance, recrystallisation and the evolution of microstructure of high-Mn steels by compression testing on a Gleeble simulator. The influence of Al alloying (0–8 wt.%) in the hot rolling temperature range (800°C–1100°C) is studied in particular, but also some observations are made regarding the influence of Cr alloying. Microstructures are examined in optical and electron microscopes. The results are compared with corresponding properties of carbon and austenitic stainless steels. In addition, the mechanical properties are studied briefly, using tension tests over the temperature range from -80°C to 200°C. Finally, a preliminary study is conducted on the corrosion behaviour of TWIP steels in two media, using the potentiodynamic polarization technique.
The results show that the flow stress level of high-Mn TWIP steels is considerably higher than that of low-carbon steels and depends on the Al concentration up to 6 wt.%, while the structure is fully austenitic at hot rolling temperatures. At higher Al contents, the flow stress level is reduced, due to the presence of ferrite. The static recrystallisation kinetics is slower compared to that of carbon steels, but it is faster than is typical of Nb-microalloyed or austenitic stainless steels. The high Mn content is one reason for high flow stress as well as for slow softening. Al plays a minor role only; but in the case of austenitic-ferritic structure, the softening of the ferrite phase occurs very rapidly, contributing to overall faster softening. The high Mn content also retards considerably the onset of dynamic recrystallisation, but the influence of Al is minor. Similarly, the contribution of Cr to the hot deformation resistance and static and dynamic recrystallisation, is insignificant. The grain size effectively becomes refined by the dynamic and static recrystallisation processes.
The tensile testing of TWIP steels revealed that the Al alloying and temperature have drastic effects on the yield strength, tensile strength and elongation. The higher Al raises the yield strength because of the solid solution strengthening. However, Al tends to increase the stacking fault energy that affects strongly the deformation mechanism. In small concentrations, Al suppresses martensite formation and enhances deformation twinning, leading to high tensile strength and good ductility. However, with an increasing temperature, SFE increases, and consequently, the density of deformation twins decreases and mechanical properties are impaired.
Corrosion testing indicated that Al alloying improves the corrosion resistance of high-Mn TWIP steels. The addition of Cr is a further benefit for the passivation of these steels. The passive film that formed on 8wt.% Al-6wt.%Cr steel was found to be even more stable than that on Type 304 steel in 5–50% HNO3 solutions. A prolonged pre-treatment of the steel in the anodic passive regime created a thick, protective and stable passive film that enhanced the corrosion resistance also in 3.5% NaCl solution.
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Gostin, Petre Flaviu. "Corrosion Behaviour of Advanced Fe-Based Bulk Metallic Glasses." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-68080.
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Early developed non-bulk Fe-based glasses, e.g. Fe-Cr(-Mo)-metalloid(s), exhibit extraordinary corrosion resistance, but low glass formation ability (GFA). Newly developed bulk glass-forming Fe-based alloys have on the contrary high GFA, but also very different compositions and therefore their corrosion behaviour is expectedly not similar. Fundamental investigations regarding corrosion behaviour were performed for one of the most prominent bulk glassy alloy, namely (Fe44.3Cr5Co5Mo12.8Mn11.2C15.8B5.9)98.5Y1.5. Particularly, the free corrosion and the anodic polarization behaviour, the passivation ability and the pitting susceptibility have been assessed in electrolytes with varying pH values and anion species concentrations. Due to its monolithic single phase microstructure this alloy has a much lower corrosion rate in acids than a two-phase conventional steel (DIN X210Cr12) with much higher content of passivating Cr, i.e. 11.4 at. %. However, the high concentration of electrochemically active Mn and B as well as the unfavourably high Mo to Cr concentration ratio determine a higher corrosion rate of this bulk glassy alloy in strong alkalis and also a very poor passivation ability in acids. On the contrary, the high content of Mo has a positive influence on the pitting resistance by inhibiting very effectively the propagation of pits occurring at Y2O3 inclusions. Detailed microscopic analysis investigations by HRSEM and in-situ AFM revealed the formation of characteristic morphological features at the micro- and nanometre scale on the surface of samples exposed to acidic solutions. These were explained by selective dissolution of active elements, e.g. Mn, B. This study demonstrated the necessity to investigate the corrosion properties of newly developed bulk glass-forming Fe-based alloys – they are not per-se highly corrosion resistant, but their corrosion behaviour depends on their particular chemical compositionFrüh entwickelte, nicht-massive amorphe Eisenbasislegierungen, z.B. Fe-Cr(-Mo)-Metalloid(e), zeigen bemerkenswerte Korrosionsbeständigkeit, aber niedrige Glasbildungsfähigkeit (englisch: glass-forming ability, GFA). Neu entwickelte massiv-glasbildende Eisenbasislegierungen haben im Gegenteil eine höhere GFA, aber auch sehr unterschiedliche Zusammensetzungen und deshalb ist ihr Korrosionverhalten ist wie zu erwarten nicht änlich. Grundlegende Untersuchungen des Korrosionsverhaltens einer der bekanntesten massiven amophen Legierung, nämlich (Fe44.3Cr5Co5Mo12.8Mn11.2C15.8B5.9)98.5Y1.5, wurden vorgenommen. Insbesondere wurde das Augenmerk auf das freie Korrosions- und das anodische Polarisationsverhalten, die Passivierungseigenschaften und die Anfälligkeit gegenüber Lochfraß in Elektrolyten mit verschiedenen pH-Werten und Anionenkonzentrationen gerichtet. Aufgrund ihres einphasig monolitischen Gefüges zeigt diese Legierung in Säuren eine viel niedrigere Korrosionsgeschwindigkeit als die eines zweiphasigen herkömmlichen Stahls (DIN X210Cr12) mit viel höherem Gehalt an passivierendem Cr, d.h. 11.4 at.%. Der höhere Gehalt an electrochemisch aktivem Mn und B sowie das nachteilige Verhältnis von Mo zu Cr Konzentration sind für eine höhere Korrosionsgeschwindigkeit dieser massiven amorphen Legierung in konzentrierten Alkalien sowie eine geringere Passivierungsfähigkeit in Säuren verantwortlich. Der hohe Gehalt an Mo hat jedoch einen positiven Einfluss auf die Lochfraßbeständigkeit – er hindert sehr wirksam das Wachstum der an Y2O3-Einschlüssen gebildeten Löcher. Detaillierte mikroskopische Untersuchungen durch HRSEM und in-situ AFM zeigten die Bildung charakteristischer Morphologien im Mikrometer- und Nanometerbereich auf der Oberfläche von Proben, die starken Säure ausgesetzt waren. Dieses wurde durch selektive Auflösung aktiver Elemente, z.B. Mn, B, erklärt. Diese Arbeit unterstreicht die Notwendigkeit, die Korrosionseigenschaften der neu entwickelten, massivglasbildenden Eisenbasislegierungen zu untersuchen – diese sind nicht per-se „hochkorrosionsbeständig“, stattdessen hängt ihr Korrosionsverhalten vielmehr von ihrer besonderen chemischen Zusammensetzung ab
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Padgett, Barbara Nicole. "Investigation into the stress corrosion cracking properties of AA2099, an Al-Li-Cu alloy." Columbus, Ohio : Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1204515486.
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Ready, William Judson IV. "Reliability investigation of printed wiring boards processed with water soluble flux constituents." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/5907.
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The purpose of this research was to investigate the factors that enhance conductive anodic filament (CAF) formation in printed wiring boards. The variables studied were (1) flux formulation, (2) conductor spacing, (3) operating voltage, and (4) temperature.
A Weibull distribution of failure times due to CAF was observed. A novel test circuit was designed and implemented that allowed the mean time to failure to be determined for boards processed with three different fluxes, at 0.5 mm and 0.75 mm conductor spacings and at 150V and 200V. The boards were aged at 85%RH and a
temperature of 75°C, 85°C or 95°C.
It was found that the flux formulation affected the rate of CAF formation. A modified linear aliphatic polyether flux with a chloride activator had a significantly different activation energy than control printed wiring boards or those boards processed with a poly(ethylene/propylene) glycol flux or a poly(ethylene/propylene) glycol flux with a bromide activator.
The addition of bromine to a poly(ethylene/propylene) glycol flux decreased the rate of CAF formation as compared to poly(ethylene/propylene) glycol without a halide
activator. The inter-relation between voltage and conductor spacing was quantified as a L4/V2 relationship for the plated through hole test pattern used in this study. 325V/mm was found to be a critical voltage gradient for the formation of CAF. The maximum temperature of the reflow profile also greatly enhances CAF formation and decreases the mean time to failure.
Microscopic analysis showed distinct differences in CAF morphology between the various processed boards. Control boards had small halo-like CAF formations around a separated fiber / epoxy interface. CAF that formed on boards processed with poly(ethylene/propylene) glycol or poly(ethylene/propylene) glycol with a bromine activator had a stratified appearance that penetrated well into the epoxy. Boards that were processed with the modified linear aliphatic polyether with chlorine activator had a striated morphology that also penetrated into the epoxy. All CAFs were consistently copper and chlorine containing despite the use of a bromine containing flux. Electron diffraction revealed that a CAF observed in this study was synthetic atacamite. Stainless steel (i.e., iron, nickel, and chromium) residues were also observed as a result of drill bit breakage during PTH formation.
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Das, S. C. "Zinc rich paint as anode system for cathodic protection (CP) of reinforced concrete structures and development of corrosion/CP monitoring probes." Thesis, Coventry University, 2012. http://curve.coventry.ac.uk/open/items/5f6b4228-1557-4cf8-bebd-97b5b70bb594/1.
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Since mid-80‟s cathodic protection (CP) has been recognised as the „‟only technique known to stop corrosion regardless of the levels of chloride contamination in concrete‟‟ (FHWA, 1982) and is proved to be the most cost effective means to extend the useful life of the structure. Cathodic protection is an electrochemical technique to stop/mitigate corrosion by supplying „current‟ from an external source in order to suppress the „internally generated‟ current flow due to corrosion processes. The „external‟ current source could be obtained simply by coupling the steel to another electrochemically more active metal, e.g. zinc; alternatively the „external‟ current may be derived from a mains operated low voltage DC power source, viz. transformer/rectifier unit. These two different approaches to supply „external‟ current to stop corrosion are generically termed as: „Sacrificial Anode Cathodic Protection (SACP)‟ system and „Impressed Current Cathodic Protection (ICCP)‟ system, respectively. Both approaches have proved to be feasible, but the impressed current CP system offers greater flexibility with regard to its ability to provide the necessary current in situations where concrete resistivity is relatively high and variable. The sacrificial anode system is most effective if the concrete resistivity is very low or the anode is placed in a very low resistivity environment such as soil with low resistivity, as the inherent driving voltage is low e.g. the potential difference between zinc and corroding steel in concrete is limited to approximately 0.7 volts. Other contra-distinction between the two approaches are that the design life of the sacrificial anode systems are usually range between 10 -15 years; on the other hand the design life of the ICCP systems could be well in excess of 60+ years ( depending on the type of anode system). Page 2 Following the successful application of first CP system, based on impressed current CP (ICCP), on a bridge deck in California, USA 1973, the technology has advanced significantly, particularly the anode systems (which is the main arbiter of a CP system) to deliver the protection current efficiently providing adequate protection (i.e. meeting the criteria recommended in BS EN ISO 12696: 2012 and other International Standards). Most of the CP installations worldwide are operating in ICCP mode. However, due to the escalating cost of anode systems and associated external power supply as well as monitoring/control units for ICCP installation has led researchers to actively pursue different means of developing low cost anode systems. Researchers have mainly focused on sacrificial anode CP (SACP) systems, as SACP does not require an external power supply and control units, but the drawback to this anode system is that it has a shorter life span (usually 10 -15 years compared to 60+ years for ICCP anodes). This work describes the development of an ICCP anode system design utilising commercially available zinc rich paint (ZRP) as a primary anode material offering an innovative but considerably low cost alternative to currently used materials for ICCP anode systems. It also describes the development of a simple and low cost „multifunctional‟ probe for monitoring the performance of the installed CP system, among other functions, such as LPR measurements, macrocell corrosion current measurement, E-log I tests for assessing the current requirements for CP design. For these functions both laboratory investigations and field trial on real life structure were employed.
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Poot, Thirza. "Tuned sustainable anodic coatings for reduced ice adhesion." Thesis, Linköpings universitet, Molekylär ytfysik och nanovetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-158214.
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Aluminum alloys are widely used materials in the aircraft industry due to their high specific strength and durability. The natural corrosion resistance of aluminum can be improved through an electrochemical anodizing process. Due to recent restrictions in the use of chromic acid with toxic hexavalent chromium as electrolyte, the industry has shifted towards the use of the functional comparable tartaric sulfuric acid (TSA). TSA anodizing provides a porous alumina layer with good corrosion resistance, yet there is a desire to tune the process to fit other purposes. For instance, ice accretion to aircraft surfaces implies a safety risk and reduced energy efficiency. Due to insufficient active anti-icing systems, aircraft manufacturers are in the search for passive anti-acing materials. The ice adhesion properties of a material are thought to be affected by wettability. In turn, the wettability is affected by the morphology of the alumina influenced by the anodizing conditions. Herein, the effects of the anodizing voltage, electrolyte temperature and anodizing time on the morphology and wettability of TSA-anodized aluminum alloy 2024-T3 were studied by scanning electron microscopy (SEM) and contact angle (CA) measurements. The morphology in relation to wettability and ice adhesion strength as well as the use of posttreatments such as hydrothermal sealing and silanization was investigated. SEM images show a clear influence by the anodizing conditions on the porosity, interpore distance and pore diameter of the porous alumina. The morphology has influence on the wettability although the relationship needs further investigation. A superhydrophobic surface obtained by silanization of a surface anodized at high voltage characterized by a rod-like morphology has potential as a passive anti-icing surface. Future work may include additional polishing pretreatments, testing of additional parameters, investigating the CA hysteresis and roll-off angle as well as measuring the adhesion strength of high-impact ice. By tuning the morphology of sustainable anodic coatings, the research area is one step closer to implementing passive anti-icing materials in aircrafts.
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Rios, Giancarlo. "Effect of chlorides on the electrochemical behaviour of thermally sprayed aluminium protective coatings." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/effect-of-chlorides-on-the-electrochemicalbehaviour-of-thermally-sprayed-aluminiumprotective-coatings(2ab6cac3-d935-40d1-948a-02e968199217).html.
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Sacrificial metallic coatings have been used in the past, for protecting steel in industrial and urban developments. It has been suggested that thermally sprayed aluminium coatings, immersed in marine environments, are also capable of protecting steel by providing galvanic protection. Researchers have also speculated that the growth of inert oxide products, on top of the coating as well as inside pores and cracks, could enhance even further its protective “shielding” properties. In addition, the self-healing abilities of the coatings, in case of mechanically induce damage, are still a matter of debate. This research project takes a critical look at these assumptions, focusing on the electrochemical response of aluminium metal sprayed (AMS) coatings immersed in 0.6 M NaCl and 0.6 M Na2SO4 solutions, in order to investigate how the presence of chlorides can alter the corrosion behaviour of these coatings. For such, a thin aluminium protective coating was deposited over two different panels (aluminium 1050 and low carbon steel), by the steel making company Fairfield-Mabey, using electric arc thermal spraying (TS). Subsequently, the coated panels were sectioned into smaller specimens, and with the aid of a SEM/EDS, and XRD, observations and analysis were conducted in their surfaces and cross sections, in order to determine the morphology, quality of deposition, and chemical composition of the coatings. Internal porosity/oxide growth after immersion, was studied using 3-D X-ray tomography scanning. Furthermore, the electrochemical behaviour of the coatings (intact and scribed) was also investigated, initially by analyzing the evolution of the open circuit potential in time, when immersed in chloride rich and chloride free environments. Additionally, the anodic polarization behaviour of the substrate and coatings were simultaneously analyzed, by connecting a zero resistance ammeter (ZRA) with the W.E. terminal of a potentiostat. To conclude, EIS and Rp vs. time plots were made in order to corroborate the data obtained from other tests. Results show that although the coating can generate superficial and internal corrosion products, these oxides are not isolating in nature nor will enhance its protective properties. On the other hand, the corrosion potential behaviour of the coatings revealed that AMS coatings have a more active than the substrate; regardless of the environment in which they were immersed or their substrate. Nevertheless, it was also observed that AMS coatings deposited onto steel will corrode faster than their substrates, and for that matter capable of offering corrosion protection, exclusively if chlorides are present in the solution.
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Cé, Nataly Araújo. "Measuring the effect of cathodic protection on the performance of thermally sprayed aluminium coatings at elevated temperature." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/173316.
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Alumínio Pulverizado Termicamente (TSA) é amplamente utilizado em instalações offshore como revestimento de ânodo de sacrifício em tubulações de aço carbono. O transporte e a instalação desses componentes podem levar a pequenos danos no revestimento, o que pode expor a superfície do aço à água do mar. Sabe-se que o depósito calcário é formado na superfície do aço polarizado catodicamente. Assim, esta pesquisa avaliou o TSA aplicado por sistema de pulverização de arco duplo (TWAS) no aço ao carbono S355J2 + N quando ocorrem danos (holidays) para estudar a formação de depósitos calcários no aço e adquirir dados sobre o desempenho do TSA sob altas temperaturas. A aplicação de diferentes condições também foi considerada: presença de selantes; liga do revestimento (99,5% de Al e Al-5% de Mg) e condições enterradas/não enterradas. Dois tipos de experimentos foram realizados: i) testes em potencial livre sob temperaturas constantes (30, 60 e 90°C) e diferentes tamanhos de holidays (expondo 5, 10 e 20% da superfície do aço) e ii) testes sob gradient térmico onde óleo a ~125°C foi adicionado em uma torre polimérica e água externa a ~10°C ficou em contato com a superfície das amostras (tanto potencial livre como polarização de -950 mVAg/AgCl foram aplicados). Análises incluíram inspeção visual, microscópio eletrônico de varredura e difração de Raio-X. A partir dos testes em temperaturas constante, o TSA atingiu um bom potencial de proteção (-800 a -900 mVAg/AgCl) e pouca diferença nos resultados devido à diferença na composição doTSA e no tamanho do holiday foi observada. As taxas de corrosão foram mantidas entre 0,02 e 0,01 mm/ano. No ensaio sob gradiente térmico e potencial livre, a perda de revestimento e as taxas de corrosão foram de 0,4 a 0,002 mm/ano. Além disso, o potencial alcançado foi de uma faixa menor do que a obtida anteriormente (-745 a -835 mVAg/AgCl). No entanto, quando o TSA foi combinado com proteção catódica externa e gradiente térmico, a espessura do TSA foi satisfatório e as taxas de corrosão obtidas foram inferiores a 0,076 mm/ano. O depósito calcário formado no holiday protegeu o aço contra a corrosão e seu mecanismo de crescimento baseado nesta pesquisa foi construído.Thermally Sprayed Aluminium (TSA) is widely used in offshore facilities as sacrificial anode coating for carbon-steel risers and pipelines. Transportation and installation of those components can lead to small damages in the coating, which can expose the steel surface to the seawater. It is known that calcareous deposit is formed on the cathodically polarised steel surface. Thus, this research evaluated the TSA applied by twin wire arc spray system (TWAS) on S355J2+N carbon-steel when damage (holidays) is present in order to study the calcareous deposit formation on steel and acquire data regarding the TSA performance at high temperatures. Application of different conditions was also considered: presence of sealing; coating alloy (99.5%Al and Al-5%Mg) and buried/unburied conditions. Generally, two types of experiment were conducted – i) tests at free potential at steady temperatures (30, 60 and 90°C) and different holiday sizes (exposing 5, 10 and 20% of the steel surface) and ii) tests under thermal gradient where oil at ~125°C was added in polymeric tower and external water at ~10°C was in contact with the samples surface (both free potential and polarisation of -950 mVAg/AgCl were applied). Methodology of analyses included visual inspection, scanning electron microscope and X-ray Diffraction. From the tests at steady temperatures, the TSA reached a very good protective potential (-800 to -900 mVAg/AgCl) and little difference in results due to difference in TSA composition and holiday size was observed. Corrosion rates were kept between 0.02 and 0.01 mm/year. From the thermal gradient test under free potential, the coating loss and corrosion rates were 0.4 to 0.002 mm/year. Also, the potential achieved was in a lower range than previously obtained (-745 to -835 mVAg/AgCl). However, when TSA was combined with external cathodic protection and thermal gradient, the thickness of the TSA was satisfactory and corrosion rates obtained were below 0.076 mm/year. The calcareous deposit formed within the holiday protected the steel substrate against corrosion and its growth mechanism based in this research was built.
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Vu, Anh Quang. "Etude des mécanismes de corrosion - cicatrisation d'aciers revêtus par des alliages d'aluminium : sur tranche et en zone confinée : approche expérimentale et numérique." Thesis, Dijon, 2012. http://www.theses.fr/2012DIJOS062/document.
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L’objectif de ce travail était d’étudier les mécanismes de corrosion-cicatrisation d’aciers revêtus par des alliages d’aluminium, sur tranche et en zone confinée. Sur la tranche, les techniques de mesures locales ont été utilisées pour étudier le comportement de deux types de revêtements sacrificiels : l’un étant constitué d’un alliage d’aluminium à 55% en masse et de Zn (Aluzinc) et d’un alliage d’aluminium contenant environ 11% silicium (Alusi). L’ensemble des résultats montre que les revêtements à base alliages d’aluminium ont un comportement sacrificiel qui dépend fortement de leur composition selon le type d’environnement concerné. Si le milieu corrosif contient des chlorures il est plus facile d’amorcer et/ou de stabiliser le comportement sacrificiel. Cela est par exemple parfaitement illustré par le comportement du revêtement Alusi qui reste passif dans le milieu sulfate et donc ne permet aucune protection à l’acier. Par contre pour les revêtements 55%Al-Zn, on a pu constater un effet sacrificiel très stable en milieu chloruré (l’acier est protégé cathodiquement) qui se confirme en milieu sulfate mais seulement pour de courtes périodes d'immersion (t < 1 h). L’étude du comportement de ces mêmes traitements de surface en situation de corrosion perforante a permis de proposer un dispositif d’étude représentatif ayant une géométrie assez proche de celles des éprouvettes qui ont fait l’objet d’une normalisation. On a mis l’accent sur la possibilité de mesurer l’évolution du pH en positionnant de manière précise une microélectrode de pH à membrane liquide sélective dans une cavité modèle. Par des simulations numériques basées sur des modèles de transport et de réaction on a montré que l’on pouvait calculer les gradients chimiques et électriques dans la cavité testée en utilisant la résolution des équations de transport (Nernst-Planck) par la méthode des éléments finisThe objective of this work was to study the self healing mechanisms of aluminium based alloy coated steels on cut-edge specimens in confined condition. In situ chemical and electrochemical probe techniques have been used to study the behaviour of two types of sacrificial coatings: one is consisting on an Al alloy containing 55% of Zn (Aluzinc) and the other one contains about 11% of Silicon (Alusi). The results showed that the aluminium based coatings have a sacrificial behaviour which depends strongly on their composition and on the environment concerned. In a corrosive environment containing chlorides it is easier to initiate and / or stabilize the sacrificial behaviour. This is clearly illustrated by the behaviour of the Alusi coating which remains passive in a neutral sulphate solution and therefore does not protect the steel. On the opposite, for 55% Al-Zn coatings, a very stable sacrificial effect has been demonstrated in chloride medium (steel is cathodically protected) which is confirmed in sulphate medium but only for short periods of immersion (t <1 h). An experimental setup allowing pH measurements inside a confined volume representing a lapped joint was designed. The pH evolution over steel and galvanized steel surfaces in confined conditions was monitored. This experimental pH was compared with that calculated using a two-dimensional transport-reaction model only in the case of a confined iron surface. The difference between the experimental and calculated pH in the steady state was attributed to the limitation of the modelling approach, more especially concerning solid phases precipitation inside the cavity
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Holmes, Steven. "An investigation into the practical and theoretical aspects of hybrid cathodic protection." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/12280.
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Galvanic anode technology has in recent years come to the fore as a cost-effective method of successfully mitigating the corrosion of reinforcing steel in concrete structures. Developments in the field of cathodic protection have included the introduction of a novel Hybrid anode system, which uses the same sacrificial anode to pass a short-term impressed current before being connected to the steel directly to provide a long-term galvanic current. Galvanic and hybrid technologies are often seen as less powerful solutions in the treatment of reinforcement corrosion, and the test methodologies which determine the efficacy of cathodic protection systems favour impressed current technologies. The work completed has investigated the application of traditional and novel corrosion assessment techniques to laboratory samples to assess the protection offered by the hybrid treatment methodology in both treatment phases. In addition, the response of both galvanic and hybrid anodes to environmental conditions has been recorded and assessed before being discussed in the context of steel protection criteria. Finally, an investigation is presented into the on-site deterioration of commercially pure titanium feeder wire installed as part of the hybrid anode system and potential solutions to the problem have been documented. The research undertaken found that the hybrid anode system is capable of protecting steel in challenging, aggressive environments. This was confirmed by steel corrosion rate and indicative steel potential measurements. The responsive behaviour investigation showed that the current output of galvanic and hybrid anodes responds rapidly to changes in the corrosion risk posed to the steel and that this has a direct effect on anode system lifetimes. An assessment of the polarisation-based protection criteria applied to steel in concrete has found that the standard inhibits the use of responsive behaviour, and that revisions which consider the present risk of steel corrosion by considering the corrosion current resulting from the relative aggressivity of the concrete environment would be more valid in their application. A cathodic protection system based on the concepts of pit re-alkalisation and pH maintenance can fully utilise galvanic anode responsive behaviour. It was discovered that the deterioration of commercially pure titanium feeder wire seen on site installations was due to anodising in the presence of chloride media which had the potential to lead to pitting corrosion. The pitting risk varied depending on the duration of the treatment and proximity to the installed anode. An anodically grown oxide delayed the onset of corrosion in aqueous KBr solution, but did not significantly increase the pitting potential.
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Paoliello, Flávio Abelha. "Corrosão de digestores contínuos: influência dos processos de cozimento e análise das tecnologias protetoras." Universidade Federal de Viçosa, 2010. http://locus.ufv.br/handle/123456789/5895.
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Previous issue date: 2010-06-14Most of the Kraft pulp produced in the world come from continuous digesters. Digester corrosion has become a significant topic for the pulp and paper industry since it brought about the need for high expenditures with repairs, replacement of components and upgrade of materials, as well as losses in connection with unplanned outages. Risks to life and property are also significant, as catastrophic failure of pressure bearing equipment may also result. From the Eighties to present days, corrosion problems in many pulp and paper mills around the world have been increasing, for reasons ranging from materials and design aspects of the digesters themselves, to process modifications introduced ever since. The present work examines this scenario, studies the corrosive behavior of continuous digesters in its several forms, and seeks to indicate the main causes. Actual corrosion cases are presented and the main current protective technologies are discussed. Electrochemical testing, metallurgical analyses, corrosivity testing and field inspections are used to support the discussions and conclusions. Highlight is given to the field experience with a type 316 stainless-clad digester, the only known continuous cooker built in such material in the industry, whose prospective corrosion hazards prompted the execution of studies and protective measures that are unique for stainless cooking vessels. The risks to carbon or austenitic stainless steel digesters running on modern cooking processes are demonstrated to be significant. The effectiveness of the main protective technologies, as well as the compatibility among them, was proved. The need to include these technologies in cooking plant retrofit projects was established.
A maior parte da celulose Kraft produzida no mundo provém de digestores contínuos. A corrosão destes digestores tornou-se uma questão relevante para a indústria de celulose, na medida em que trouxe a necessidade de elevados gastos com reparos, substituições de componentes e melhoria de materiais, bem como prejuízos por paralisações imprevistas e prolongadas da produção. O risco ao patrimônio e à vida humana é também considerável, já que há possibilidade real de falhas catastróficas em equipamentos pressurizados. Desde a década de 80 até os dias atuais, os problemas de corrosão em digestores de muitas fábricas de celulose Kraft vêm se acentuando, por razões que vão desde materiais e aspectos construtivos dos próprios digestores até mudanças nos processos desde então introduzidas. O presente trabalho examina este cenário, estuda o comportamento corrosivo dos digestores contínuos em suas diversas formas e procura evidenciar as principais causas. Casos reais de corrosão e proteção são apresentados e as principais tecnologias protetoras atualmente disponíveis são discutidas. Testes eletroquímicos, análises metalúrgicas, testes de corrosividade e inspeções de campo são utilizados para suportar as discussões e conclusões. Destaca-se a experiência com um digestor revestido em aço inoxidável tipo 316,sem similar conhecido, cujos riscos potenciais de corrosão instaram a execução de estudos e a adoção de providências inéditas para digestores em material inoxidável. Os riscos de corrosão dos digestores em aço carbono ou inoxidável austenítico operando com processos atuais são evidenciados como sendo significativos. A eficácia das principais tecnologias protetoras, bem como a compatibilidade entre elas, foi comprovada. A necessidade de inclusão destas tecnologias em projetos de retrofit de cozimento foi estabelecida.
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Bustamante, Rina Huamanrayme. "Fabricação de nanoestruturas de alumina anódica porosa e suas aplicações na síntese de nanomateriais." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-13062013-162134/.
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Nanoestructuras de alumina anódica porosa (AAP) têm sido tradicionalmente fabricadas por duas etapas de anodização a temperaturas relativamente baixas (de 0 até 5°C), e usadas como máscaras ideais para formação de vários materiais nanoestruturados. Neste sentido, o objetivo do trabalho foi estudar sistematicamente a formação e a fabricação de nanoestruturas de AAP autoorganizadas por uma só etapa de anodização e posterior aplicação na síntese de nanopartículas e nanofios metálicos. As nanoestruturas auto-organizadas de AAP foram obtidas por apenas uma etapa de anodização em ácido oxálico (H2C2O4) a temperatura ambiente; diferentemente dos processos convencionais onde são utilizados duas ou mais etapas de anodização. As características estruturais dos filmes de AAP foram moduladas através do controle dos parâmetros da concentração da solução, temperatura e potencial de polarização. O procedimento principal, para a obtenção de AAP auto-organizadas apenas por uma etapa de anodização, foi o pós-processamento de abertura dos poros através de um processo de corrosão química. Os resultados obtidos neste trabalho mostraram que o diâmetro médio dos poros apresentou uma dependência linear com a temperatura, potencial e tempo de corrosão química e foi constante em relação à concentração da solução eletrolítica. No entanto, a análise estrutural via microscopia eletrônica de varredura (MEV), mostrou que a circularidade e a ordem dos nanoporos sobre a superfície anodizada melhoraram com o aumento da concentração do eletrólito. A estrutura de AAP com um arranjo hexagonal de poros regularmente distribuídos foi obtida quando a anodização foi realizada em 0,3M de H2C2O4, a 45V e 20°C de temperatura seguido de uma corrosão química a temperatura de 17°C por 102 minutos. Adicionalmente foram obtidos nanopartículas e nanofios metálicos utilizando-se as nanoestruturas de AAP como moldes. Como os filmes de AAP são isolantes a obtenção das nanopartículas e nanofios foi realizado através de um processo de eletrodeposição de corrente alternada (CA). Os resultados deste trabalho mostraram que nanoestruturas de AAP autoorganizadas podem ser fabricadas por uma etapa de anodização controlando o tempo de corrosão química. Os resultados apresentados neste trabalho mostram-se vantajosos em relação aos reportados na literatura, já que normalmente as nanoestruturas de AAP são obtidas mediante processos de anodização em duas etapas e tempos longos de anodização.Nanostructures of porous anodic alumina (PAA) have been traditionally manufactured by two steps anodization at relatively low temperatures (0 to 5°C) and used as templates suitable for the formation of various nanostructured materials. In this sense, the goal of this work was the fabrication of self-organized porous Anodic alumina nanostructures (AAP) by a one anodization step and subsequent application in the synthesis of metal nanowires and nanoparticles. The self-organized nanostructures of PAA were obtained by just one anodization step in oxalic acid (H2C2O4) at ambient temperature unlike to conventional processes where they are used two or more anodization steps. The structural characteristics of PAA films were modulated through control of the solution concentration, temperature and potential of polarization. The key procedure to obtain the periodic organized PAA by only one step anodization was the post-processing of pore opening through a process of corrosion chemistry. The results of this work showed that the average diameter of pores presented a linear dependence with temperature, time of chemical corrosion, polarization potential and it was constant relative to the concentration of the electrolyte solution. However, the structural analysis via scanning electron microscopy (SEM) showed that the roundness and the order of nanoporos over the anodized surface improved with the electrolyte concentration increasing. The PAA structure with a hexagonal arrangement of pores was obtained when the anodization was held in 0.3 M of H2C2O4, 45V, and 20°C of temperature followed by a chemical corrosion at 17°C of temperature for 102 minutes. Additionally it was obtained nano particles and nano metal wires using the PAA structures as molds. Since the PAA films are insulating, the nanoparticles and nanowire were obtained through an electrodeposition process using alternating current. The results of this work have shown that self-organized PAA nanostructures can be fabricated by one anodization step controlling the time of chemical etching process. The results presented in this work are advantageous in relation to reported in the literature, since normally the structures of PAA are obtained by two step anodization and for long anodization time.
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Salero, Paul. "Elaboration et caractérisation d'alliages Mg-Ca pour un procédé de minéralisation de l'eau par attaque électrochimique." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0045.
Full textAbstract:
Les alliages Mg-Ca sont des alliages biocompatibles et biodégradables largement utilisés pour des applications biomédicales comme prothèses bio-résorbables. Ils sont très utilisés car leurs taux de corrosion et de dégradation dans l'organisme peuvent être contrôlés par le taux de calcium et par l'influence du milieu d'implantation. Ces solutions ont inspirées le Groupe SEB qui cherche à mettre au point un procédé fiable de minéralisation d'une eau par dissolution d'alliages Mg-Ca. L'objectif de ce travail de thèse est double, à savoir, la conception des alliages Mg-Ca pour ce procédé, en choisissant les techniques de production adaptées et les paramètres d'élaborations optimisés, puis, la mise en œuvre d'un processus de dissolution assisté par un courant et la maîtrise des paramètres de dissolution. Le magnésium et le calcium étant des métaux très réactifs au contact de l'atmosphère, l'élaboration d'alliages Mg-Ca se fait sous atmosphère neutre. Il est possible d'obtenir une microstructure stable avec des teneurs en calcium comprises entre 0% et 33% atomique, lorsque le calcium et le magnésium forment l'intermétallique Mg2Ca. Lors du refroidissement du mélange métallique à fusion, il se forme une microstructure d'équilibre constituée de dendrites (de Mg si 0 at.% < Ca < 10 at.% et de Mg2Ca si 10 at.% < Ca < 33 at.%) et d'un agrégat eutectique lamellaire composé de Mg et de Mg2Ca. La dissolution anodique d'alliages Mg-Ca s'effectue par l'application d'une différence de potentiel entre une électrode constituée de l'alliage à dissoudre et une contre électrode constituée d'un métal plus noble. Il a été mis en évidence que les relargages d'ions Mg2+ et Ca2+ en solution peuvent être augmentés en diminuant la chute ohmique entre les électrodes (distance minimale, tension appliquée maximale) et en augmentant la réactivité du processus (alliages riches en calcium, conductivité et minéralité de la solution, durée de dissolution et surfaces exposées importantes). Cependant, les forts relargages d'ions Mg2+ et Ca2+, qui alcalinisent fortement la solution, favorisent la formation de précipités limitant la dissolution tels que le tartre, les oxydes et hydroxydes de magnésium et de calcium. Plusieurs solutions pour réguler le pH de la solution et optimiser les relargages de cations Mg2+ et Ca2+ ont été envisagéesThe Mg-Ca alloys are biocompatible and biodegradable alloys widely used for biomedical applications such as bioresorbable implants because of their corrosion rate and degradation behaviour into human body. These solutions have inspired the SEB Group to develop a new process for the mineralization of water by dissolving Mg-Ca alloys. The objective of this thesis is to design new Mg-Ca alloys choosing the appropriate production techniques and optimizing elaborations settings and then, to work on the dissolution process assisted by a current controling of dissolution parameters. Magnesium and calcium being very reactive metal in contact with the atmosphere, the development Mg-Ca alloys was done in a neutral atmosphere. It is possible to obtain a stable microstructure with calcium contents between 0% and 33 atomic% through the intermetallic form Mg2Ca. It's possible to obtain equilibrium microstructures consisting of dendrites (Mg if 0 at.%
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Silva, Anderson Rodrigo da. "Corrosão em armaduras de espera enterradas com 60 anos - estudo de caso das fundações da ala zero do ITA." Instituto Tecnológico de Aeronáutica, 2011. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=1566.
Full textAbstract:
A corrosão das armaduras de espera na condição enterrada é um dos fatores de redução da vida útil do concreto armado devido à interação com diversos parâmetros dos materiais, solos e condições ambientais adversas. No presente trabalho buscou-se analisar o estado e evolução da corrosão em armaduras de espera em contato com o solo, presentes em blocos de fundações com idade média de 60 anos. A área de estudo está localizada dentro do complexo do CTA - Centro Tecnológico de Aeronáutica, em São José dos Campos - SP - Brasil, próximos aos edifícios da Reitoria, Aeronáutica e Mecânica, onde havia uma estrutura em concreto armado com a finalidade de servir de fundações para a construção do futuro Prédio da Ala Zero do ITA, concentrando as salas administrativas e salas de aula da Aeronáutica e Mecânica. Como material de análise dispôs-se de um conjunto de 42 blocos de fundações e 211 barras de espera com idade média de 60 anos, cuja eficiência do sistema concreto/aço encontrava-se bastante comprometida a fim de poder utilizá-la na continuidade das obras, no ano de 2008. Para tanto, como resultado das análises dos parâmetros de pH, acidez, sulfetos, óxidos de cálcio, magnésio e resistividade, observou-se que o solo não apresentava agressividade do meio aquoso ao sistema concreto/aço. Pela análise de reconstituição do traço de concreto retiradas das amostras de blocos de fundações e estacas, observou-se que a resistência característica do concreto apresentava-se em torno de 12 a 14 MPa, e por fim a análise das barras de espera apresentou uma velocidade de corrosão caracterizada como moderada a alta. As conclusões a respeito do assunto destacam-se sobre o processo de corrosão desencadeado nas barras de espera, uma vez que o solo não era caracterizado como agressivo. A aplicação do teste estatístico da ANOVA mostrou que as amostras estudadas eram equivalentes, independentes da situação de enclausuramento e em relação aos prédios existentes. Os resultados das velocidades de corrosão confirmaram a análise expedita do Comando da Aeronáutica, da impossibilidade da reutilização das fundações para o término da construção do Prédio da Ala Zero do ITA, uma vez que a estrutura encontrava-se com a vida útil comprometida. Por fim, algumas recomendações a respeito da atual normatização brasileira e do processo de dobras nas barras de espera adotado para enclausuramento das barras de espera são abordadas no presente trabalho, a fim de evitar a chamada corrosão por deformações excessivas das armaduras.
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Nguyen, Vinh. "Determining localized anode condition to maintain effective corrosion protection /." 2009. http://hdl.handle.net/1957/12744.
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Li, Ching, and 李情. "The Influence of Sacrificial Anode And Electrolytes on Corrosion Control." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/78729734689852328099.
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Graham, Fiona Jane. "Electrochemical investigation of the growth of anodic films on iron and ferrous alloys." Thesis, 1994. http://hdl.handle.net/10413/4875.
Full textAbstract:
An electrochemical investigation of the corrosion of iron and Fe18Cr based stainless steel alloys was
undertaken with particular emphasis on the nucleation and growth of surface films.
Chronoamperometry was shown to be a sensitive technique to investigate the initial stages of film
formation and growth. In a variety of acidic (pH < 7), alkaline and alkaline cyanide electrolytes,
providing dissolution of the substrate metal could occur rising current transients, similar to those
reported in electrocrystallisation studies, were observed when the electrode was stepped to the
appropriate potential. This indicated that at these potentials the surface film formed via the nucleation and growth of discrete nuclei. A significant aspect of this study was visual evidence of this nucleation
and subsequent growth of the film provided by scanning electron microscopy which supported the
electrochemical data and interpretation thereof.
Existing electrocrystallisation models were used to evaluate the experimental rising current transients.
While these models gave an indication as to the prevailing nucleation and growth mechanism, they were
found to be inadequate in describing anodic oxide formation on an oxidising substrate. A qualitative
model was proposed.
In acidic electrolytes, rising chronoamperometric transients were observed for Fe, Cr and Fe18Cr at
passive potentials and for FexCr (x = 16,18, 20,23% Cr) and alloys 444, 4732, 4733, 304L and 316L at
transpassive potentials. The transients were shown to be sensitive to variations of potential,
temperature, electrolyte and alloy composition.
A systematic investigation of the influence of temperature (20 0 C - 1200 C) on the chronoamperometric,
cyclic voltammetric and rotating ring - disc electrode behaviour of Fe in O.5M and 1.0M NaOH was also
undertaken. In alkaline electrolytes, the formation of a duplex surface film was proposed, with x-ray
photoelectron spectroscopy indicating that the protective base layer consisted of FeO while Fez03 and
FeOOH constituted the upper layer. Base layer formation was favoured with increasing temperature
and increasing hydroxide ion concentration of the electrolyte. Addition of OAM NaCN to O.5M and
1.0M NaOH had a marked effect on the electrochemistry of the system, with CN- inhibiting surface film
formation, particularly of the upper layer. A mechanism for the oxidation of Fe in alkaline and alkaline
cyanide electrolytes was proposed.Thesis (Ph.D.)-University of Natal, 1994.
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Ni, Chung-Chuan, and 倪忠川. "A Study on Corrosion Resistance of 6066 Anodic Film with Taguchi Method." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/88676391759633575003.
Full textAbstract:
碩士國立臺灣大學
材料科學與工程學研究所
101
6XXX series aluminum alloys have excellent formability. For examples, the commonly used 6061-T6 alloy has maximum elongation of 17 %, and 6066-T6 alloy has maximum elongation of 12 % at room temperature. Although 6XXX alloys have lower strength than 2XXX and 7XXX alloys in as-wrought state, the strength of 6066-T6 alloy can be inceresed to near 400MPa after T6 treatment. Compared to 6061-T6, 6066-T6 has 100 MPa more increment in strength due to higher fraction of alloy elements, while these two alloys cost about the same. Therefore, it would be a good selection for aluminum plants. For this reason, we chose 6066 aluminum, and coated a protective film with anodic treatment. At first, we purchased 4 in. billet in order to solve problems directly during experiment. Experiments were proceeded in sequence with hot rolling, process annealing, cold rolling, and T6 treatment. Then, we prepared specimens identically for the following anodic treatment. For anodic treatment, we selected four important process parameters that influence the product quality (corrosion resistance) very much as four control factors in Taguchi''s method. These four parameters are Al2O3‧14 ~ 18H2O(s) addition, H2SO4(aq) concentration, current density, and working time. Furthermore, by selecting three appropriate levels for each factor, we can construct the L9 (34) matrix experiment. Then we proceeded two parts experiment and analysis of surface properties of anodic films. Eventually, we obtained an optimum condition of 6066-T6 aluminum anodic film for corrosion resistance at 9 g/l Al2O3‧14 ~ 18H2O(s) addition, 17 wt% H2SO4(aq), 1.2 A/dm2 current density, and 10 min working time. Results from polarization curve and 1392-hour neutral salt spray test show that corrosion current density can reach 10-10 scale (3 ~ 4 order increased compared to raw material) and has just 2.7 % corrosion area. It can provide excellent corrosion resistance certainty and hardness of 554 Hv. On our results, the anodic films should have excellent corrosion resistance, but they were still corroded. Thus, if we would like to obtain better anodic film, we should also consider physical defects except for an optimum condition in practice. We should reduce the content of impurities in our specimens before anodic treatment, For example, lower content limit of impurities is required for better control of charge during anodic process. Hence we can obtain excellent anodic film with less cracks. Keywords：6066 aluminum, anodic treatment, corrosion resistance, Taguchi method
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Wang, Yan-Jie, and 王彥捷. "Improvement of Corrosion Properties on Aluminum-Sputtered AZ91D Magnesium Alloy by Anodic Aluminum Oxidation." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/21780333622489526446.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
104
Magnesium and its alloy have been used widely for the living facilities and military defense owing to their excellent physical and mechanical properties, such as low density, high strength, good cast-ability and weld-ability, excellent electrical and thermal conductivity, high dimensional stability, good electromagnetic shielding and high recyclability. However, the poor corrosion resistance of magnesium alloys have limited their engineering applications, especially in acidic environment and salt-water conditions. Two processes were used to improve the corrosion resistance of the magnesium alloys, including sputtering and anodized. Since the aluminum film is more stable than magnesium substrate, the aluminum film can be oxidized to aluminum oxide film, to further improve the corrosion resistance. In this study, the sputtering + anodized were carried out on an AZ91D Mg alloy, and the effects on the corrosion resistance were evaluated. The cross-sectional configuration of film was analyzed by Dual Beam Field Emission Focused Ion Beam (DB-FIB), indicated thickness of anodized oxide films increased with the oxide time. The film surface is characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) which indicated that the anodized oxide layer was amorphous structure and composed by Al2O3. The results of potentiodynamic polarization show that the sputtering Al film and the anodized oxide layer on the AZ91D alloys performed more positive corrosion potential and lower corrosion current density than the AZ91D substrate, by adopting an anodizing treatment 15 minutes specimen have higher corrosion potential value of -1.359 V and lower corrosion current density value of 0.262 μA/cm2. Similar, according to EIS results, the charge transfer resistance of the anodized specimens were larger than the AZ91D substrate. These results proved that the sputtering Al film with anodizing treatment coated on the AZ91D alloys significantly improved the corrosion resistance property of the AZ91D alloys.
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Chen, Cheng-Yi, and 陳正義. "Influence of corrosion resistance of different processing parameters of AA1050 and AA5052 anodic films." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/26525062232601659570.
Full textAbstract:
碩士國立中央大學
機械工程研究所
98
Magnesium added in aluminum can increase the strength of aluminum alloy. But it also brings about inclusions in the matrix of aluminum alloy to decrease the corrosion resistance. This study used the materials of AA1050H16 and AA5052H32 as base metals to carry out anodization with different anodizing conditions and sealing processes. Pre-treatment of electro-chemical polish (ECP) is also concerned and treated as variable to compare its effect on the amorphous anodization film (AAO) quality and corrosion resistance. After salt water spraying test, we found that AAO film formed on AA5052H32 surface has a lower corrosion resistance than AA1050H16 that mainly affected by (1) forming MgO in AAO film and (2) high amount of inclusion particle existed in matrix. Experimental results also point out that sealing AAO film by using nickel acetate can improve sample’s corrosion resistance due to the existence of nickel hydroxide on AAO film. Pre-treatment of ECP process smoothed the sample’surface and improved the regularity of anodized pore arrangement. The residues on surface tended to interact with oxygen to form complex products during anodization deteriorating the AAO film’s corrosion resistance. Anodized samples (AA1050H16) sealed by hot water show a higher color difference than those sealed by nickel acetate solution. Contrarily, anodized samples (AA5052H32) show less degree of color difference after hot water sealing was used.
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Gostin, Petre Flaviu. "Corrosion Behaviour of Advanced Fe-Based Bulk Metallic Glasses." Doctoral thesis, 2010. https://tud.qucosa.de/id/qucosa%3A25566.
Full textAbstract:
Early developed non-bulk Fe-based glasses, e.g. Fe-Cr(-Mo)-metalloid(s), exhibit extraordinary corrosion resistance, but low glass formation ability (GFA). Newly developed bulk glass-forming Fe-based alloys have on the contrary high GFA, but also very different compositions and therefore their corrosion behaviour is expectedly not similar. Fundamental investigations regarding corrosion behaviour were performed for one of the most prominent bulk glassy alloy, namely (Fe44.3Cr5Co5Mo12.8Mn11.2C15.8B5.9)98.5Y1.5. Particularly, the free corrosion and the anodic polarization behaviour, the passivation ability and the pitting susceptibility have been assessed in electrolytes with varying pH values and anion species concentrations. Due to its monolithic single phase microstructure this alloy has a much lower corrosion rate in acids than a two-phase conventional steel (DIN X210Cr12) with much higher content of passivating Cr, i.e. 11.4 at. %. However, the high concentration of electrochemically active Mn and B as well as the unfavourably high Mo to Cr concentration ratio determine a higher corrosion rate of this bulk glassy alloy in strong alkalis and also a very poor passivation ability in acids. On the contrary, the high content of Mo has a positive influence on the pitting resistance by inhibiting very effectively the propagation of pits occurring at Y2O3 inclusions. Detailed microscopic analysis investigations by HRSEM and in-situ AFM revealed the formation of characteristic morphological features at the micro- and nanometre scale on the surface of samples exposed to acidic solutions. These were explained by selective dissolution of active elements, e.g. Mn, B. This study demonstrated the necessity to investigate the corrosion properties of newly developed bulk glass-forming Fe-based alloys – they are not per-se highly corrosion resistant, but their corrosion behaviour depends on their particular chemical composition.Früh entwickelte, nicht-massive amorphe Eisenbasislegierungen, z.B. Fe-Cr(-Mo)-Metalloid(e), zeigen bemerkenswerte Korrosionsbeständigkeit, aber niedrige Glasbildungsfähigkeit (englisch: glass-forming ability, GFA). Neu entwickelte massiv-glasbildende Eisenbasislegierungen haben im Gegenteil eine höhere GFA, aber auch sehr unterschiedliche Zusammensetzungen und deshalb ist ihr Korrosionverhalten ist wie zu erwarten nicht änlich. Grundlegende Untersuchungen des Korrosionsverhaltens einer der bekanntesten massiven amophen Legierung, nämlich (Fe44.3Cr5Co5Mo12.8Mn11.2C15.8B5.9)98.5Y1.5, wurden vorgenommen. Insbesondere wurde das Augenmerk auf das freie Korrosions- und das anodische Polarisationsverhalten, die Passivierungseigenschaften und die Anfälligkeit gegenüber Lochfraß in Elektrolyten mit verschiedenen pH-Werten und Anionenkonzentrationen gerichtet. Aufgrund ihres einphasig monolitischen Gefüges zeigt diese Legierung in Säuren eine viel niedrigere Korrosionsgeschwindigkeit als die eines zweiphasigen herkömmlichen Stahls (DIN X210Cr12) mit viel höherem Gehalt an passivierendem Cr, d.h. 11.4 at.%. Der höhere Gehalt an electrochemisch aktivem Mn und B sowie das nachteilige Verhältnis von Mo zu Cr Konzentration sind für eine höhere Korrosionsgeschwindigkeit dieser massiven amorphen Legierung in konzentrierten Alkalien sowie eine geringere Passivierungsfähigkeit in Säuren verantwortlich. Der hohe Gehalt an Mo hat jedoch einen positiven Einfluss auf die Lochfraßbeständigkeit – er hindert sehr wirksam das Wachstum der an Y2O3-Einschlüssen gebildeten Löcher. Detaillierte mikroskopische Untersuchungen durch HRSEM und in-situ AFM zeigten die Bildung charakteristischer Morphologien im Mikrometer- und Nanometerbereich auf der Oberfläche von Proben, die starken Säure ausgesetzt waren. Dieses wurde durch selektive Auflösung aktiver Elemente, z.B. Mn, B, erklärt. Diese Arbeit unterstreicht die Notwendigkeit, die Korrosionseigenschaften der neu entwickelten, massivglasbildenden Eisenbasislegierungen zu untersuchen – diese sind nicht per-se „hochkorrosionsbeständig“, stattdessen hängt ihr Korrosionsverhalten vielmehr von ihrer besonderen chemischen Zusammensetzung ab.
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Cheng, Jyh Shyan, and 陳志賢. "The Influence of Anodic Treatment on The Corrosion Behavior of 304 and 430 Stainless Steels." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/86399608469251055972.
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Chen, Wei-ting, and 陳威廷. "The preparation of the superhydrophobic anodic aluminum film and the study of its anti-corrosion property." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/64217626810396771658.
Full textAbstract:
碩士大同大學
化學工程學系(所)
99
Using the two methods of anodic oxidation and chemical etching to make a rough surface structure on aluminum, then the super-hydrophobic self-cleaning surfaces are obtained through the procedure of self-assembled surface from the siloxane. The roughness of aluminum film is between 316nm and 364nm, the contact angle is above to 150 °, it is required to make a super-hydrophobic surface. And the best operating conditions to obtain the super-hydrophobic surface are: 3M sulfuric acid in the anodizing step and 20min etching time, the contact angle with water droplets will up to 157.58°, and the wetting area will be 10.94%, and the remaining area of 89.06% is the 343nm rough structure on which the gas is contacted, that resulting in the highest corrosion resistance . After the different microstructure and hydrophobicity of the surface were studied, the effects of film thickness and roughness on the hydrophobic properties were analyzed. The structure of the coating surface and the super-hydrophobic properties were also investigated. It indicates that the surface roughness and low surface energy material are the two key points of the super-hydrophobic effect.
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Chou, Fang-Wei, and 周芳蔚. "The Effects of Pulse Duration of Anodic Coating of AZ31 Magnesium Alloy on the Corrosion Resistance." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/23041803827195128840.
Full textAbstract:
碩士大同大學
材料工程學系(所)
96
Magnesium alloys have many advantages, but the poor corrosion resistance restricts the development and application of magnesium alloys. The electrochemical anodic treatment is one of the effective surface modification methods, and the pulse voltage anodic method of micro-arc oxidation process is used in this paper. The main parameters of pulse anodic process used in this work include voltage, frequency, and duty ratio. The electrolytic solution of anodic process contains fluorine and silicon ions. From SEM observation, the pore size of anodic coating surface prepared at higher frequency and lower duty ratio is smaller and the more narrow pore size distribution. The diameter of the pore is approximately 0.5 μm. From electrochemical polarization analysis in 3.5wt% NaCl, the corrosion resistance of anodic coating prepared at higher frequency and lower duty ratio is better than the corrosion resistance of anodic coating prepared at lower frequency and higher duty ratio. For the best result in this study, say anodic coating prepared at higher frequency and lower duty, the corrosion potential can shift toward noble potential by 0.25V, and corrosion current density is decreased by 4 orders, and passive region can reach as high as 1V. From salt spray test, the time of spray salt test for the sample of anodic coating can be reached over than 200 hours.
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林青嫺. "The Study of Anodic Oxidation Film of Al and Co-Cr Alloy and its Corrosion Resistance Properties." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/11732336103799006768.
Full textAbstract:
碩士清雲科技大學
機械工程研究所
92
Anodic aluminum film can be applied to increase the corrosion resistance properties of Al-alloy. In industry, aluminum acid anodizing was usually processed in acidic solution in the past. This study tries to use the solution of alkaline NaOH and add the Na2SiO3 modifization to it. After changing various forming voltages (50V~350V) and processing the materials by anodizing, all of them are put in 0.05M H2SO4 solution, using electrochemical measurement to probe into the electrochemical corrosion resistance behavior of anodic oxidation film caused by different forming voltages. The result shows that during the process of anodizing, when the forming voltage rises to 250V, a clear and obvious plasma arc will appear. After aluminum is processed by anodizing, it has noble potential, higher Rp and lower icorr. In the test of Electrochemical Impedance Spectroscopy(EIS), in addition to Rp increasing with the rise of forming voltage, the Rp of the anodic aluminum film forming when the forming voltage is above 250V can increase to tenfold compared with Al-alloy (e.g. from 2000Ω to 20000Ω) due to the action of plasma arc. Thus it forms more delicate correction to protect the anodic oxidation film. Co-Cr alloy is one of the common-used metals and biomaterials. This study tries to use the electrochemical processes, deposit thin films of Co-Fe-O in Co-Cr alloy, and then put it in 3.5wt％ NaCl solution and de-aerated Hank’s solution(pH 7.4, 37℃), using electrochemical measurement to explore the electrochemical corrosion resistance behavior of different films and to use the Scanning Electron Microscopy(SEM) to carry out the observation of its surface and the electrochemical measurement, including DC linear polarization, potentidynamic, cyclic polarization, and EIS. The result shows that although Co-Cr alloy has the noble potential, higher Rp and lower icorr in 3.5wt％ NaCl solution, the material of thin films of Co-Fe-O in Co-Cr alloy deposition has negative hysteresis according to the curve diagram of cyclic polarization. And it has the highest Epp and widest passive region, which implies that the protection ability after the passivation film breaks is the strongest.
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Chuang, Che-Hao, and 莊哲豪. "The Study on Corrosion Behaviors of Hot-Dip Aluminized Coating Formed on Low Carbon Steel by Anodic Treatment in the Sodium Chloride Aqueous Solution and High-Temperature Oxidation." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/53667859144585051307.
Full textAbstract:
碩士國立臺灣科技大學
機械工程系
97
AISI 1005 steel was coated by hot-dipping into a molten pure aluminum, and then underwent an anodizing treatment to form an anodic oxide layer on the coating surface. The corrosion behavior of the modified aluminide steel was analyzed by immersion and electrochemical tests in NaCl aqueous solution and high-temperature oxidation and hot corrosion tests. The results showed that the anodized aluminide steel can not used in high-temperature oxidation and hot corrosion environment due to the spallation of the anodic alumina oxide layer caused by the thermal stress. On the other hand, the immersion and electrochemical tests in NaCl aqueous solution revealed that corrosion resistance of the aluminide steel after anodizing treatment of 60 minutes is better than the mild steel and aluminide steel, indicating that the aluminide mild steel after anodizing treatment can enhance its corrosion resistance in NaCl aqueous solution.