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Treeman, Nicole M. "Electrochemical study of corrosion phenomena in zirconium alloys." Thesis, Cambridge, Massachusetts, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/10945/37785.
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CIVINSShadow corrosion of zirconium alloy fuel cladding in BWR environments, the phenomenon in which accelerated corrosion is experienced when the cladding surface is in close proximity to other metals, has become a potential life-limiting issue for BWR fuel. Recent results from experimentation at MIT, Halden and Studvik suggest that a galvanic coupling drives the phenomenon between the cladding and the adjacent material. However, the actual processes involved are not understood. One key parameter that would help in the understanding of the phenonenon would be a measurement of the actual corrosion current between fuel cladding and adjacent materials in the actual in-reactor environment. The limitations placed on the burn-up of uranium oxide fuel corelates to the amount of corrosion seen through a directly measurable oxide thickness on the waterside of the zirconium alloy cladding. This oxide corrosion product directly correlates to distance from structure components, leading the effect commonly referred to as shadow corrosion. In recent experiments, Studvik determined that there are large ECP differences associated with Inconel and zirconium alloys that correlate to increased galvanic current density when the materials are coupled. In this thesis research, four electrode pairs wre used to measure galvanic cirrent densities in the irradiation environment:Pt-Pt, Zircalloy (Zr-2), Inconel (X-750)-Pt, and Zr-2-X-750. To determine the changes in the coolant water conductivity dus to the presence of radiolysis products, electrochemical potential mesurements of Pt-Pt coupled electrodes were analyzed. Finally, attempts to characterize the observed oxide behavior using measurement from Electrochemical Impedance Spectroscopy (EIS), also known as Alternating Current Impedance, were conducted. Through the measurements taken, analysis of the mechanisms potentially causing the shadow corrosion phenomenon was conducted. The results of the observations included: Measurement of increased conductivity of coolant water correlating to increases in reactor power, measurement of increased galvanic current measurements correlating to increases in reactor power.
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Setiadinata, Sylvester Brian. "Corrosion and hydrogen pickup mechanisms of zirconium alloys." Thesis, University of Oxford, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.728802.
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Zhang, Yue. "Corrosion of titanium, zirconium and their alloys for biomedical applications." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8033/.
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in vivo degradation of Ti implants has remained as a concern despite its perceived excellent corrosion resistance. Elevated levels of metal have been detected both locally and systemically, often leading to unfavourable biological responses. Corrosion of Ti, Zr and their alloys (Ti6Al4V and TiZr) were studied in simulated physiological solutions. It was found that albumin, the most prevalent tissue fluid protein, induced a time dependent dissolution of Ti6Al4V in the presence of H2O2, an inflammatory biomolecule commonly found in peri implant sites, in 0.9% NaCl. However, the corrosion of Zr was observed to be unaffected by the presence of H2O2 and/or albumin in 0.9% NaCl. Furthermore, TiZr alloys have been shown to possess enhanced passivity in comparison to CP Ti in the various exposure conditions including highly acidic (HCl), oxidative environments (H2O2 in 0.9% NaCl) and cell cultures (macrophage). Corrosion products of Zr were characterised in situ by synchrotron X ray methods, which were found to be ZrOCl2 ∙ 8H2O, tetragonal ZrO2, and Zr metal fragments in 0.9% NaCl regardless of the presence or absence of H2O2 and/or albumin. The presence of Zr metal fragments as a result of a corrosion process indicates the generation of metal species in the absence of wear.
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Wei, Jianfei. "Effect of hydrogen on the corrosion performance of zirconium alloys." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/abstracteffect-of-hydrogen-on-the-corrosion-performance-of-zirconium-alloys(b6683f8b-9286-4ebd-bf8a-d240c62b7a79).html.
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This study is part of the multidisciplinary research program funded by the EPSRC aimed at further understanding the mechanisms behind the oxidation, transition and breakaway of zirconium alloys. The current study concentrates on the effect of artificially introduced hydride rich rim region upon the corrosion performance of zirconium alloys. The methodology of cathodic hydrogen charging of zirconium specimen has been described. The intention is to create a hydride rich rim similar to observation made in end-of-life fuel claddings from nuclear reactor. The overall hydrogen levels in the samples were determined via inert gas fusion and the local hydride volume fractions via laboratory x-ray diffraction. The residual stress state in the rim was investigated by synchrotron x-ray diffraction. The rim was determined to have local hydrogen levels about 11,000 wt.ppm and predominantly δ-hydrides. Hydrided samples and their references were tested in autoclaves simulating primary water environment. Reference samples exhibited typical corrosion kinetics with a change from pre- to post-1st transition. The duration before 1st transition varies with alloy chemistry and heat treatment conditions. Hydrided samples generally experienced accelerated corrosion while the extent to which the material was affected depends on alloy chemistry. Parabolic rather than cubic oxide growth with a very slow early corrosion rate was recorded in hydrided alloys. Both hydrided and reference samples of three Zr-Sn-Nb alloys, ZIRLOTM, low tin ZIRLO and X2 with tin concentration ranging from 0.14 to 0.92 wt.% became the gravity of further characterisations since they exhibited improved corrosion performance with decreasing tin content. The microstructure of the oxide was investigated via cross-sectional Scanning Electron Microscope (SEM). The residual stress state in tetragonal and monoclinic phases as well as tetragonal phase fraction were studied via synchrotron x-ray diffraction, showing high in-plane compressive stresses in the oxide of different levels depending on the phase and alloy. The presence of a hydride rim lowered the residual stress. White oxide in hydrided samples displays lower residual stress level, smaller tetragonal phase fraction and higher degree of oxide grain misorientation when compared to black oxide regions of reference and hydrided samples. It was also found that the hydride rim region undergoes local depletion of hydrides in alloy with low Sn content during the early stage of aqueous corrosion. Finally a model was given to describe the different roles played by individual oxide and hydride phases during the oxidation of zirconium alloys.
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Feltham, Andrew Martin Charles. "The corrosion and passivity of some engineering alloys in acidic solution." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359526.
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Garner, Alistair John. "Investigating the effect of oxide texture on the corrosion performance of zirconium alloys." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/investigating-the-effect-of-oxide-texture-on-the-corrosion-performance-of-zirconium-alloys(c98f3395-4ee7-42c5-b9f3-2a55e7923c14).html.
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This work was performed as part of the MUZIC-2 (Mechanical Understanding of Zirconium Corrosion) collaboration, established with the goal of understanding the mechanism of hydrogen pickup in zirconium alloys. Hydrogen pickup is one of the least understood and most significant degradation mechanisms affecting zirconium alloys in nuclear reactors. These alloys are used as cladding and structural materials in the reactor core, mainly due to their low thermal neutron absorption cross section and excellent corrosion resistance. This project aims to investigate the effect of oxide texture (i.e. the degree of preferred orientation) on the corrosion performance of zirconium alloys. The texture of the oxide is expected to affect the microstructural development of the oxide, the grain boundary distribution and the stress state. It is therefore considered to be one of the most important factors in determining how the corrosion process occurs, and why different alloys exhibit significantly different corrosion performance. It is hoped that this project will add to the current knowledge of the corrosion process, and in particular hydrogen pickup, so that the route of hydrogen through the protective oxide can be identified. This will lead to the development of a new generation of alloys that provide improved oxidation and hydrogen pickup performance, whilst maintaining the required mechanical properties. This work focuses on four zirconium alloys; Zircaloy-4, ZIRLO™, low-Sn ZIRLO™ and Zr-1.0Nb-0.1Fe. The alloys all have different chemical compositions and therefore exhibit different corrosion performance. The macrotexture of the oxide formed on different alloys was measured by glancing angle X-ray diffraction (XRD) and Electron Backscatter Diffraction (EBSD). A fibre texture was formed in all cases, with the (10-3) to (10-5) planes oriented parallel to the metal-oxide interface for the monoclinic phase. The major orientation was found to be independent of alloy chemistry, substrate orientation and oxidation conditions. The monoclinic texture strength was found to be weakened with increasing oxidation temperature, The major orientation of the tetragonal phase was also found to be a fibre texture, with the (001) planes oriented approximately parallel with the interface. Although significant variation from this texture component was observed. It is suggested that the main driving force for oxide texture development is the transformation stress induced by the Zr-ZrO2 transformation. The microtexture of the oxides was measured using two novel techniques, Transmission Kikuchi Diffraction (TKD) and automated crystal orientation mapping with transmission electron microscopy (TEM). The techniques revealed an oxide microstructure consisting of an outer layer of equiaxed grains with a large range of orientations and an inner layer consisting of well-aligned columnar monoclinic grains. This layer of equiaxed grains was observed to form again after the transition in corrosion kinetics. A large fraction of transformation twin boundaries were observed throughout the oxides. Some of these boundaries were observed to surround large monoclinic grains, providing evidence that the tetragonal grains from which they transformed had grown considerably larger than the critical grain size for stabilisation. Without the presence of Sn, larger monoclinic grains were observed to form with a greater degree of preferred orientation, and with a lower fraction of transformation twin boundaries than Sn-containing alloys. In addition, an increased number of well-oriented tetragonal grains was correlated with the presence of Sn. It is therefore concluded that a reduction in Sn will lead to the formation of an oxide microstructure that is more resistant to both oxidation and hydrogen pickup. An analysis of the crystallography and morphology of a ZrO phase present at the metal-oxide interface was also performed. Finally, the observations have been used to construct a model of the corrosion process.
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Châtelain, Anthony R. (Anthony Roger) 1972. "Enhanced corrosion of zirconium-based alloys in proximity to other metals : the "shadow effect"." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8871.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2000.Includes bibliographical references.
Fuel cladding for water-cooled power reactors must meet certain requirements for optimal performance. To function in the extreme conditions typical of a nuclear reactor core the material used must be corrosion resistant, have low thermal neutron cross section, and high strength. Corrosion resistance is one of the most important parameters for reactor materials. From the beginning of the use of reactors, engineers have been faced with the problem of excessive corrosion in several different forms. In recent years, a peculiar corrosion phenomenon has increased in significance. Several occurrences of local corrosion enhancement of zirconium-base alloys in proximity to other components have been observed. This corrosion enhancement talcs the form of a "shadow" of a metal component in proximity, hence its name, "shadow effect." Although much recent attention has been given to the shadow effect, it has been known since the sixties, but has only lately been considered a possible threat to material integrity. Today the interest in local corrosion enhancement due to the shadow effect and its implications for in-core performance of cladding and structural material is increasing worldwide. International experience has shown that the phenomenon has occasionally resulted in serious corrosion problems threatening material integrity. In order to prevent future obstruction from the phenomenon an understanding of the shadow effect needs to be developed. This becomes important in today's rapid expansion of aggressive reactor environments with higher burn-up and the need for longer fuel residence times for more economical runs. This project was conducted at MIT, funded by ABB Atom, which had the goal of identifying the basic mechanisms of the shadow effect. The MIT research reactor MITR-11 was used to simulate BWR core coolant conditions. The sample train included Zr-2- alloy with various surface treatments. Different counter electrodes surrounded each cladding piece. They were high and low beta emitters, inert material and Zircaloy-2 in contact and non-contact at various separation distances. Post-irradiation examination of the cladding pieces showed: * Beta-radiation is not the main mechanism for the shadow effect. * Shadow corrosion is partly dominated by an electrochemical mechanism. * Radiolysis plays an important role for the formation of shadow corrosion.
by Anthony R. Châtelain.
S.M.
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Wang, Peng. "Corrosion behaviour of zirconium alloys in high temperature aqueous environment by electrochemical impedance spectroscopy." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/corrosion-behaviour-of-zirconium-alloys-in-high-temperature-aqueous-environment-by-electrochemical-impedance-spectroscopy(e1bf6a9f-c8ca-45db-8e05-14ee723886d9).html.
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The corrosion behaviour of zirconium based alloys has been primarily investigated by electrochemical impedance spectroscopy (EIS). In-situ autoclave EIS experiments were performed in simulated primary coolant conditions in order to study the high temperature water corrosion of zirconium alloys in PWRs. In-situ impedance response of the corroding material was recorded throughout first kinetic transition. A physical model of the zirconium oxide was proposed in accordance with the microstructural observation' made by SEM analysis. Electrical properties of the oxide was evaluated with equivalent circuit model (ECM) which was constructed according to the physical oxide model. Evolution of various oxide parameters obtained from ECM was analysed in accordance with the microstructure observation made by SEM. A two layer structure consists of a outer porous oxide and an inner barrier oxide, was found to be the most accurate description for the autoclave formed oxide. Supporting evidence from the SEM cross-section and surface analysis of the oxide had shown cracks and pores that were linked and connected with the environment. This observation is also confirmed by the in-situ EIS measurement which has shown porous electrode behaviour throughout the course of oxidation. The porous oxide behaviour was also confirmed by the ex-situ soaking experiment on samples with incremental exposure time. Evolution of inner barrier layer oxide thickness was found to be correlated with kinetic transition which was determined from weight gain measurement. This indicated that barrier layer maybe the oxidation rate controlling layer and its thickness maybe reduced during transition. Thus, a thinner barrier layer would resulted in a rapid corrosion of zirconium alloys. Furthermore, maintaining the barrier layer thickness maybe the possible route to improve zirconium alloy corrosion resistance.
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Lalgudi, Srinivas Bhadrinarayanan. "Experimental evalution of oxide growth in binary zirconium alloys along with pure zirconium and Zircaloy-2 by steam corrosion testing." Thesis, KTH, Fysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95310.
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Proff, Christian. "Aspects microstructuraux de l'oxydation d'alliages de Zirconium." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00609232.
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Cette thèse est axée sur la caractérisation microstructurale des précipités dans les oxydes des alliages binaires de zirconium (1 wt.% Fe, Cr , Ni ou 0.6 wt.% Nb). La température d'oxydation est fixée au 415°C. Les échantillons sont oxydés dans l'air et dans l'autoclave sous des pressions différentes et dans un microscope électronique à balayages environnemental sous vapeur d'eau. Les résultats des recherches peuvent être résumés ci-dessous : -Deux types d'oxydation (retardée et non retardée) ont été observés pour les précipités. -Le facteur de Pilling-Bedworth des précipités est plus élevé par rapport à celui de zirconium. -Les précipités contenant du fer entrainent une formation des cristaux de l'oxyde de fer pur à la surface du matériau, quand les précipités sont à la surface ou à la proximité. Ces observations mènent à la conclusion que le comportement d'oxydation des précipités peut être corrélé à leurs compositions et à la tendance d'oxydation de leurs éléments constituants.
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Ni, Na. "Study of oxidation mechanisms of zirconium alloys by electron microscopy." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:c60cdca2-e576-414a-8a10-eb3a60264998.
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The current work is part of the EPSRC MUZIC project, which established the collaboration among several universities to carry out a multidiscipline study on the breakaway oxidation of zirconium alloys. The overall goal of the project is to further understand the mechanisms of the oxidation and breakaway process of zirconium alloys. This thesis describes the nano/micro-structural study and nano-analysis of the corroded zirconium alloys using up-to-date TEM and 3D focused ion beam (FIB) slicing and reconstruction techniques. The work mainly focused on the characterization of ZIRLO. The oxide morphology in general comprises an inner columnar layer and an outer equiaxed layer, except for a post-second transition oxide grown on a Zr-Nb-Ti test alloy with a very poor corrosion resistance, which exhibits generally only equiaxed grains throughout the whole oxide scale. Detailed investigation reveals oxides in a slower oxidation stage exhibit better developed columnar grain structure. All the oxides, independent of different corrosion stages and alloy types, contain predominantly monoclinic oxide and a small amount of tetragonal oxide. Defects at different length scales were examined. In stead of a sudden burst of crack nucleation at the kinetic transition, a gradual introduction of cracks parallel to the metal/oxide interface throughout the pre-transition stage is found, suggesting no direction correlation between the formation of cracks and the transition. Besides cracks, the oxide also contains different forms of nano-porosity: isolated pores of 1-3 nm or interconnected pores at grain boundaries. The density of interconnected porosity, especially those along the oxide growth direction, increases towards the oxide surface, evolving over time. It is suggested that the kinetic transition is related to the development of an interconnected porosity down to the metal/oxide interface, providing easy pathways for the transportation of oxidation species. The metal-oxide interface has a wavy morphology both in the micrometer and nanometer scale. The roughness develops to a maximum just before the first kinetic transition. An intermediate suboxide layer with complex 3D morphology between the bulk oxide and the metal substrate is found. Quantitative EELS analysis shows the composition of this layer to be 40-50 at. % oxygen. The suboxide appears to develop in thickness with increasing oxidation time for the pre-transition oxides, while is very thin or absent in the post-, and post-second transition oxides. In the suboxide region, multiple phases including α-Zr, ω-Zr, tetragonal oxide and a phase with an unidentified structure were found, suggesting different structures can coexist in the suboxide layer. Second-phase particles (SSPs) of β-Nb and hexagonal Zr(Fe,Nb)2 types were found in ZIRLO samples and FCC Zr(Fe,Cr)2 was the predominant type in Zircaloy-4. The SPPs showed delayed oxidation compared to surrounding Zr. In ZIRLO, those containing high Fe contents were found to be oxidized and transform into an amorphous state much earlier than β-Nb. Hydrides of different types (γ, σ and ε) were observed in the metal and metal/oxide region for both Zircaloy-4 and ZIRLO samples. A higher density of hydrides was seen in post-transition oxides of ZIRLO than in pre-transition oxides.
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Youssef, Mostafa Youssef Mahmoud. "Predicting the equilibria of point defects in zirconium oxide : a route to understand the corrosion and hydrogen pickup of zirconium alloys." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87492.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 172-178).
The performance of zirconium alloys in nuclear reactors is compromised by corrosion and hydrogen pickup. The thermodynamics and kinetics of these two processes are governed by the behavior of point defects in the ZrO₂ layer that grows natively on these alloys. In this thesis, we developed a general, broadly applicable framework to predict the equilibria of point defects in a metal oxide. The framework is informed by density functional theory and relies on notions of statistical mechanics. Validation was performed on the tetragonal and monoclinic phases of ZrO₂ by comparison with prior conductivity experiments. The framework was applied to four fundamental problems for understanding the corrosion and hydrogen pickup of zirconium alloys. First, by coupling the predicted concentrations of oxygen defects in tetragonal ZrO₂ with their calculated migration barriers, we determined oxygen self-diffusivity in a wide range of thermodynamic conditions spanning from the metal-oxide interface to the oxide-water interface. This facilitates future macro-scale modeling of the oxide layer growth kinetics on zirconium alloys. Second, using the computed defect equilibria of the tetragonal and monoclinic phases, we constructed a temperature-oxygen partial pressure phase diagram for ZrO₂. The diagram showed that the tetragonal phase can be stabilized below its atmospheric transition-temperature by lowering the oxygen chemical potential. This work adds a new explanation to the stabilization of the tetragonal phase at the metal-oxide interface where the oxygen partial pressure is low. Third, using the developed framework, we modeled co-doping of monoclinic ZrO₂ with hydrogen and a transition metal. Our modeling predicted a volcano-like dependence of hydrogen (proton) solubility on the first-row transition metals, which is consistent with a set of systematic experiments from the nuclear industry. We discovered that the reason behind this behavior is the ability of the transition metal to p-type-dope ZrO₂ and hence lower the chemical potential of electron. Therefore, the peak of the hydrogen solubility in monoclinic ZrO₂ also corresponds to an increased barrier for hydrogen gas evolution on the surface. This explanation opens the door to physics-based design of resistant zirconium alloys, and qualitatively consistent with the monoclinic ZrO₂. Finally, we uncovered the interplay between certain hydrogen defects and planar compressive stress which tetragonal ZrO₂ experiences on zirconium alloys. The stress enhances the abundance of these defects, while these same defects tend to relax the stress. This interplay was used to propose an oxide fracture mechanism by which hydrogen is picked up.
by Mostafa Youssef Mahmoud Youssef.
Ph. D.
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Pecheur, Dominique. "Evolution des précipités à base de zirconium lors de l'oxydation et de l'irradiation d'alliages de zirconium : impact sur la cinétique d'oxydation d'alliages de zirconium." Grenoble INPG, 1993. http://www.theses.fr/1993INPG0013.
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Le zircaloy-4, materiau de gainage des crayons combustibles utilise dans les rep francais, presente une vitesse d'oxydation plus elevee en reacteur qu'en autoclave. Il est par ailleurs etabli que la vitesse d'oxydation depend de la nature et de la repartition des precipites dans l'alliage. Or, ces conditions evoluent justement sous irradiation: en particulier les precipites s'amorphisent. Dans ce travail, nous etudions le role des precipites sur le processus d'oxydation des alliages de zirconium et l'impact de l'irradiation, notamment celui de l'amorphisation des precipites, sur cette oxydation. Le mode d'incorporation dans la couche d'oxyde, des precipites de reference et des precipites amorphises par irradiation ionique, est caracterise par microscopie electronique a transmission et par analyse edx. Les evolutions de composition chimique et de structure, qu'ils subissent au cours de leur oxydation, sont analysees et leurs consequences sur la cinetique d'oxydation sont discutees. A quelques centaines de nanometres de l'interface metal-oxyde, la remise en solution partielle du fer dans la zircone formee et l'augmentation de volume des precipites, dues a leur oxydation, pourraient retarder la destabilisation de la zircone quadratique et prolonger la formation d'une couche d'oxyde dense protectrice au-dela des premiers stades de l'oxydation. Ainsi, la transition cinetique des alliages de zirconium serait retardee et leur vitesse d'oxydation ralentie. Par ailleurs, les precipites amorphises par irradiation ionique et ceux de reference presentent dans la couche d'oxyde des evolutions semblables. L'amorphisation des precipites ne semble donc pas etre en mesure de modifier la cinetique de croissance de l'oxyde. Cependant, on constate experimentalement que la vitesse d'oxydation des materiaux irradies aux ions est plus elevee que celle des materiaux de reference. L'origine d'un tel effet reste toutefois mal comprise. Enfin, les premiers resultats des tests d'oxydation realises en autoclave blinde, sur des troncons de gaine de crayons combustibles irradies aux neutrons, sont presentes et commentes
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Skocic, Milan. "Etude (photo)-électrochimique en réacteur simulé du phénomène de shadow corrosion des alliages de zirconium." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI015/document.
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Des méthodes électrochimiques classiques, et des caractérisations photoélectrochimiques (PEC), utiliséesex-situ et in-situ, ont permis d’étudier le phénomène de Shadow Corrosion, considéré ici comme une corrosion galvanique entre des alliages de zirconium et de nickel, corrosion influencée par l’environnement chimique et l’irradiation de ces alliages. Une cellule électrochimique simulant les conditions d’un réacteur à eau bouillante (REB), permettant l’illumination UV--Visible des échantillons et le contrôle de la chimie de l’eau, a été conçue, développée et validée. Cette cellule a permis de mesurer pour la première fois des spectres en énergie de photocourant d’un alliage de zirconium, in-situ en milieu REB simulé. Par ailleurs, les résultats expérimentaux obtenus tendent à montrer que les impuretés de type cations métalliques jouent un rôle important dans le mécanisme d’activation du couplage galvanique, donc potentiellement dans le mécanisme d’activation du phénomène de Shadow Corrosion, alors que la présence d’oxygène et/ou de peroxyde d’hydrogène n’induit pas de différences significatives du comportement électrochimique des échantillons. Il est montré également que l’illumination UV--Visible des échantillons, qui amplifie notablement les courants de couplage, est un paramètre important du phénomène de Shadow CorrosionConventional electrochemical methods as well as photoelectrochemical characterisations (PEC), performedex-situ et in-situ, were used to study the Shadow corrosion phenomenon, considered as a galvanic corrosion between Zr-based and Ni-based alloys. The Shadow corrosion is influenced by the chemical environment and the irradiation of these alloys. An electrochemical cell , simulating the conditions of a boiling water reactor (BWR), allowing the illumination of the samples with UV--Visible as well as monitoring the water chemistry was designed, developed and validated. The cell allowed, for the first time, recording of emph{in-situ} photocurrent energy spectra on a Zr-based alloy in simulated BWR environment. Furthermore, the obtained experimental results pointed out that the metallic cation impurities played an important role in the activation mechanism of the galvanic coupling, thus potentially in the activation mechanism of the Shadow corrosion phenomenon, whereas the presence oxygen and/or hydrogen peroxide did not induce significant differences in terms of electrochemical behavior of the samples. It was also shown that the illumination of the sample with UV--visible light, which significantly amplified the galvanic current, is an important parameter of the Shadow corrosion phenomenon
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ASSIS, SERGIO L. de. "Investigação da resistência a corrosão da liga Ti-13Nb-13Zr por meio de técnicas eletroquímicas e de análise de superfície." reponame:Repositório Institucional do IPEN, 2006. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11398.
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Made available in DSpace on 2014-10-09T12:51:29Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:00:10Z (GMT). No. of bitstreams: 1 11326.pdf: 1707325 bytes, checksum: f4b793f522e5d69e25de853d166b1c79 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Tanprayoon, Dhritti [Verfasser]. "Investigation of the precipitation hardening behaviour and the corrosion properties of novel aluminium : manganese alloys containing scandium and zirconium / Dhritti Tanprayoon." Clausthal-Zellerfeld : Universitätsbibliothek Clausthal, 2015. http://d-nb.info/1079106235/34.
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Oskarsson, Magnus. "Study on the Mechanisms for Corrosion and Hydriding of Zircaloy." Doctoral thesis, Stockholm : Tekniska högsk, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3045.
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Lelievre, Gwenn. "Etude du rôle des précipités intermétalliques dans l'absorption d'hydrogène lors de la corrosion aqueuse d'alliages de zirconium." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10174.
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Le phenomene d'absorption de l'hydrogene lors de la corrosion aqueuse par les gaines en alliages de zirconium peut devenir l'un des facteurs limitant la duree de sejour des crayons combustibles dans les reacteurs a eau pressurisee. L'objectif de ce travail vise a mieux comprendre le role joue par la composition chimique et la microstructure de l'alliage, en particulier le role des precipites intermetalliques zr(fe,cr)#2 et zr#2(fe,ni) (presents dans les zircaloys2 et 4), dans le transport de l'hydrogene a travers la couche d'oxyde superficielle formee par corrosion aqueuse. Trois methodes ex situ de caracterisation des isotopes de l'hydrogene et des precipites intermetalliques ont ete developpees ou adaptees : il s'agit de l'imagerie ionique (sims), de l'autoradiographie du tritium et de la microanalyse nucleaire. La diffraction de neutrons in situ a egalement ete utilisee pour caracteriser les evolutions structurales des phases minoritaires (precipites intermetalliques, zircone quadratique et monoclinique, hydrures de zirconium) durant des premiers stades de l'oxydation. Les resultats obtenus ont permis de montrer qu'une couche d'oxyde formee sur les zircaloys peut toujours etre scindee en une sous-couche externe poreuse et une sous-couche interne dense, jouant a elle seule un role barriere vis a vis de l'absorption de l'hydrogene. La complementarite de ces resultats et leur confrontation avec les resultats de la litterature ont egalement permis de confirmer l'implication des precipites dans le processus d'absorption de l'hydrogene : ils constitueraient des sites de reduction des protons de l'eau ainsi que des chemins privilegies de l'hydrogene dans l'oxyde dense protecteur. Des elements tels que le fer et le nickel presents dans ces precipites pourraient egalement favoriser l'absorption d'hydrogene en inhibant sa reaction de recombinaison. Le cas de l'alliage zr-1nb qui ne contient pas de precipites intermetalliques, est egalement apprehende.
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Daniel, Geoffrey Morrall. "Evaluation of material properties of mechanically alloyed SUS304L with Zr addition." Kyoto University, 2019. http://hdl.handle.net/2433/242327.
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Françon, Virginie. "Corrosion sous contrainte par l’iode des alliages de zirconium : étude des paramètres critiques pour l’amorçage intergranulaire et la transition inter/transgranulaire." Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0046.
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La corrosion sous contrainte par l’iode (CSC-I) est l’un des mécanismes de rupture potentiels des crayons combustibles en alliage de zirconium, pouvant intervenir au cours des transitoires de puissance des réacteurs nucléaires. La fissuration par CSC-I comporte trois étapes : amorçage de la fissure, développement intergranulaire puis propagation transgranulaire. Le but du travail est d’identifier des paramètres critiques gouvernant les transitions entre ces différentes étapes. En premier lieu, des essais sur des éprouvettes en Zircaloy présentant des finitions de surface et des états métallurgiques variés permettent de discriminer l’influence de différents paramètres sur l’amorçage des fissures. Nous mettons en évidence le rôle critique du niveau des contraintes résiduelles, de leur répartition en surface ainsi que de leur profil au sein du matériau. La sensibilité des alliages à l’amorçage des fissures n’est pas directement corrélée à la rugosité de la surface. Cependant, la dispersion des paramètres de rugosité traduit l’irrégularité du profil, l’hétérogénéité du niveau des contraintes résiduelles, et donc l’existence de zones où les contraintes résiduelles sont localement moins protectrices. Dans un second temps, des éprouvettes de Zircaloy-4 possédant différents états d’écrouissage sont sollicitées sous charge constante, en présence de méthanol iodé. Les modifications microstructurales induites par l’écrouissage favorisent l’apparition de la propagation transgranulaire des fissures de CSC-I. Des observations des faciès de rupture en MET révèlent que la transition inter/transgranulaire intervient dans des zones où les grains sont fortement désorientés les uns par rapport aux autres, suite à l’augmentation des contraintes locales résultant des incompatibilités de déformation grain à grainIodine-induced stress corrosion cracking (I-SCC) is one of the potential failure modes of zirconium alloy fuel claddings during power transients in nuclear reactors. I-SCC failures are usually described in three steps: initiation of cracks, intergranular development and transgranular propagation. The objective of this work is to identify critical parameters controlling transitions between crack propagation modes. First of all, experiments conducted on Zircaloy samples with various surface conditions and metallurgical states lead to discriminate the influence of several parameters responsible for cracks initiation. The critical role of residual stresses level, their distribution at the subsurface and their evolution in the bulk of the material is evidenced. Sensitivity to I-SSC is not directly correlated to surface roughness. However, dispersion in roughness parameters indicates the presence of surface irregularities, heterogeneities of residual stresses and the existence of surface areas where residual stresses are less protective. In a second step, Zircaloy-4 samples with various strain-hardening pre-treatments are submitted to constant load tests in an iodine methanol solution. Microstructural modifications induced by a strain-hardening pre-treatment enhance transgranular propagation of I-SCC cracks. TEM observations of fracture surfaces show that the intergranular to transgranular crack transition takes place preferentially where the relative crystallographic orientation is large between two adjacent grains, because of local stress concentrations resulting from strain incompatibilities between neighbouring grains
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Fayeulle, Dominique. "Elaboration et étude de révêtements céramiques à sous-couche d'accrochage cellulaire pour la protection chimique et thermique de composants de turbomachines." Paris, ENMP, 1989. http://www.theses.fr/1989ENMP0149.
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Etude d'un nouveau procédé de fabrication des barrières thermiques fondé sur le dépôt électrophorétique d'une couche métallique (nicraly+ta) pour obtenir des sous-couches d'accrochage par aluminisation en phase vapeur avant la réalisation des barrières thermiques par projection plasma de zircone partiellement stabilisée. On analyse les propriétés des produits réalisés par ce procédé et leur potentiel d'application pour la protection des composants de turbomachines
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Reitz, W. (Wayne). "Influence of laser processing on the corrosion and microstructure of zirconium based material." Thesis, 1990. http://hdl.handle.net/1957/37438.
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Silva, Marcelo Jose Gomes da. "Influence of oxide microstructure on corrosion behavior of zirconium-based model alloys." 2007. http://www.etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2267/index.html.
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Lepule, Masego Liberty. "Tribo-corrosion characteristics of laser deposited titanium-based smart coatings." 2013. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001018.
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M. Tech. Department of Chemical and Metallurgical Engineering.Aims to understand and study the tribology and tribocorrosion behaviour of the adaptive titanium-nickel-zirconia composite coatings deposited on AISI 316 stainless steel using laser surface deposition technique under various laser processing speeds. The research aim is meant to be achieved through the following objectives: 1. Determine appropriate procedure for laser feedstock deposition ; 2. Investigate tribological performance of laser composites under various loads ; 3. Evaluate the corrosion of the laser composites coatings. and 4. Assess tribocorrosion behavior of the composite coatings
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Molele, Tebogo Amelia. "Tribocorrosion behaviour of copper and zirconia reinforced nickel-titanium shape memory composites." 2013. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000990.
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M. Tech. Metallurgical Engineering.StudIes the tribocorrosion behaviour of copper-nickel-titanium shape memory composite reinforced by zirconia,synthesized through powder metallurgy process. The research aims to achieve the following objectives: 1. Study the tribocorrosion mechanisms of the composites in NaCl solution (typical human body fluid). 2. Investigate the tribocorrosion mechanisms of the composites in other environments typical of some engineering applications.The proposed study on incorporating zirconia into the matrix NiTiCu through powder metallurgical process and investigations of the phenomenon of joint wear-corrosion synergism occurring in sodium chloride considered typical of human body system and sulphuric acid environment typical of wide range engineering applications is therefore very novel. It is therefore aimed that information on the tribocorrosion behaviour of NiTiCu as well as with zirconia incorporation will form basis for typical compositional formulation approaches for improved bio-tribocorrosion improvement in biomedical applications and actuators used in other engineering applications.
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Chang, Chu-Ting, and 張筑婷. "Corrosion behavior and charge ratio of zirconia coating on magnesium alloys using micro-arc discharge oxidation." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/43828085067682810505.
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碩士國立臺灣科技大學
機械工程系
103
In this study, the characteristics of the zirconia coating on magnesium alloys were discussed on different charge ratio using micro-arc discharge oxidation (MDO) process in zirconate-based electrolyte. The element content and phase distribution of zirconia coating from charge ratio plasma have been investigated. The morphologies and phase components of the coating were examined by SEM and XRD. In order to understand the corrosion behavior of the zirconia coatings with different phase composition distribution, the zirconia coatings were immersed in chloride environments with varying pH value. In the first part, it was found that the content of aluminum in the Mg17Al12 (β-phase) magnesium alloys substrate precipitation has a very important effect during the initial deposition process. The formation of an initial oxide film in the early stage is caused by Mg matrix (α-phase) and Mg17Al12 (β-phase) which have different oxidation potential. Therefore, the electric charge can’t reach the breakdown potential. The addition of the fluoride ion concentration can help the initial oxide film formation. As a result, the β-phase substrate can emit arc. If the electrolytes have partial precipitation, the particles can help the film densification using electrophoretic adsorption. The second part of the experiment discusses about the effect of positive and negative charge ratio. There is some evidence that negative charge significantly affects coatings density, growth direction, and phase distribution of zirconia coatings. Increasing the negative charge can help cation adsorption to anode electrode which can produce high zirconia content on the coating surface. Simultaneously, the negative charge can affect the phase distribution of the zirconia coatings. The cross-sectional morphologies of charge ratio coating BEI image have different type layer. The coating is relatively dense and composed of MgO in the inner layer and ZrO2- Mg2Zr5O12-MgO in the outer layer. With the increase in negative charge, the thickness of the MgO inner layer starts evolving. Inner layer thickness is related to the degree of oxygen diffusion. And the degree of oxygen diffusion is related to charge ratio. The final part of this research discusses about the two types of zirconia coating component immersed in NaCl solution with pH of 3, 7 and 11, respectively. The experiment results show that rapid chemical dissolution happened in the oxide coating and lost its protection capability very quickly in acidic NaCl solution. In the alkaline NaCl solution, the coating underwent only a slight degradation. On the other hand, the results show that the deterioration of MDO coating was influenced by its density and composition distribution. It can be found that the coatings formed in small charge ratio have dense inner layer and mainly composed of MgO which can provide good corrosion protection for a long period of time. The coating produced in large charge ratio was mainly composed of zirconia, but pores in the coating suffered from rapid chemical dissolution.
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Chiu, Hsin-Yao, and 邱信堯. "Microstructural and Corrosion Characteristics of Zirconium Carbides Containing Alloyed Layer on Spheroidal Graphite Cast Iron by Electrical Discharge Alloying Processing." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/63rnv5.
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碩士遠東科技大學
機械工程研究所在職專班
101
In the study, surface modification of SG cast iron by electrical discharge alloying is used to examine the effect of machining parameters (discharge current, pulse duration and duty factor) on the thickness and surface roughness of the surface modified layer on ferric spheroidal graphite (SG) cast iron while the electrode polarity (anode) and the electrode composition (Zr) are fixed. EPMA composition analysis reveals that the zirconium element in the electrode effectively dissolves and passes into the substrate of SG cast iron, forming an alloyed layer, and the amount of dissolved zirconium element decreases as the distance from the surface increases. X-ray diffraction results of the zirconium alloyed layer show that α-Fe, ZrC and FeSiC are the main constituent phases. According to the results of an experiment that explores the effect of changes in conditions for single-stage electrical discharge alloying on the characteristics of the alloyed layer, the thickness and hardness of the layer generated by discharge alloying using the pure Zr electrode as well as the corrosion potential of the ZrC alloyed layer increase together with the discharge current. To examine the changes in conditions for two-stage discharge alloying, particularly pulse duration and duty factor, on the characteristics of the ZrC alloyed layer, the first-stage process continued for 10 minutes in the fixed conditions of 50A discharge current, 500 s pulse duration and 50% duty factor. The experimental results show that individual specimens subjected to two-stage discharge alloying process using varying parameters (changes in pulse duration and duty factor) have better surface states (including number of defects and roughness) than their counterparts subjected to single-stage discharge alloying. The thickness of ZrC alloyed layers tend to increase with pulse duration with the maximum thickness of about 55m when DF = 33%, but tends to decreases when DF > 33%. During two-stage discharge alloying, each alloyed layer resulted from each variance in pulse duration has higher corrosion potential than the substrate of SG cast iron and the maximum corrosion potential is achieved when pulse duration = 750 s. Also, each alloyed layers resulted from each variance in duty factor has higher corrosion potential than the substrate of SG cast iron although changes in duty factor have no significant effect on the corrosion potential of the alloyed layers.
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Lin, Yen-Jun, and 林延潤. "Electrolytic deposition of hydroxyapatite/zirconia composite coatings on AZ31 magnesium alloy to enhance corrosion resistance for biomedical applications." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/7u4wmn.
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碩士國立中興大學
材料科學與工程學系所
106
Magnesium alloy materials have been approved and widely used in the global medical market nowadays. Although magnesium alloy has poor corrosion resistance, it is the biodegradable metal in biomedical applications. The main objective of this study was to improve the corrosion resistance of AZ31 magnesium alloy. Using electrolytic deposition HAp/ZrO2 composite coating on this alloy, the optimum process was searched by tuning different deposition parameters. In the experiment, the magnesium alloy AZ31 specimen was immersed in the solution of sodium hydroxide (NaOH) for forming the passivation film. Consequently, the electrochemical deposition of zirconia (ZrO2) is carried out in ZrO(NO3)2 aqueous solution, finally forming the composite coating of HAp/ZrO2 in a mixed solution of Ca(NO3)2·4H2O and NH4H2PO4 also by the electrochemical method. Through sintering, the composite coating can form a more stable bond with the alloy specimen. The prepared specimens were characterized by scanning electronmicroscope (SEM), X-ray diffraction (XRD) and dynamic polarization tests to analyze and discuss the coating structure and corrosion resistance. The results show that the corrosion resistance of HAp/ZrO2 composite coated specimen in better than that of single-layer HAp coated one by the immersion method or the and uncoated one in 3.5wt% NaCl, leading to the current density of Icorr decreased from 136.51 to 20.162 μA/cm2. It is concluded that magnesium alloy AZ31 could be a biodegradable material used in impants after the improved corrosion resistance.
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Chen, Yung-lu, and 陳永錄. "Corrosion behavior and properties of silicate and zirconia composite coatings on AZ91D magnesium alloy using micro-arc discharge oxidation." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/29983425743123390119.
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碩士國立臺灣科技大學
機械工程系
102
In this study, the characteristics of the oxide film coated on magnesium alloy AZ91D are discussed using silicate-based and zirconate-based electrolyte system. The microstructure, phase composition, oxide hardness and corrosion resistance of the MDO coatings were discussed by adjusting duty ratio and working time under constant frequency (500 Hz) and working voltage(400 V/-50 V). In the silicate-based electrolyte system, the higher duty ratio results in the high working current. Besides, the working current is proportional to the oxide growth rate. When the duty ratio is larger than 20%, greater oxide growth rate leads to the increasing surface roughness and enlarges the size of micro-pores. Exaggeration energy leads to partially ablation around the substrate surface, hence the phase structures of the oxide coating transform from MgO and Mg2SiO4 to SiO2, Mg2SiO4 and MgSiO3 alternatively in the silicate-based electrolyte system. From the formation of SiO2 revealed that the local micro-arc temperature was almost up to 1650℃, and so did the existence of MgSiO3.It is also found that the severe level of electric charge accumulation deteriorated the coatings during a long anodic working time. Due to release of thermal stress, the cracks form on the coating surface which has a great influence on mechanical properties and corrosion behavior. In summary, the best parameters for the oxide with optimum mechanical properties are 30% and 30 minutes(431 HV), and the most anti-corrosive one is 10% and 10 minutes (4.18 x106 Ω‧cm2) in the silicate-based electrolyte system. On the other hand, the zirconate-based electrolyte system seldom exhibit linear regular relationship between duty ratio and working current. The growth rate of oxide coating is much slower compared to that in silicate-based electrolyte system. However, the operation range for MDO process using zirconate-based electrolyte is wide (5%~70%). Larger duty ratio results in cracks and roughness on surface. When the duty ratio is up to 70%, the coating can’t accumulate densely owing to the vigorous arc, but the oxide doesn’t strip from substrate. According to XRD pattern, the main phases in the coating are Mg2Zr5O12 and t-ZrO2 for MDO specimens in the zirconate-based electrolyte system. The intensity of t-ZrO2 and MgF2 becomes obvious at larger duty ratio(70%). Besides, the existence of Mg2Zr5O12 represents that MgO solutes into ZrO2 and stabilizes it. To sum up, the best parameters for the oxide with optimum mechanical properties are 70% and 30 minutes(708 HV), and the most anti-corrosive one is 10% and 30 minutes (1.02 x106 Ω‧cm2) in the zirconate-based electrolyte system. Electrochemical corrosion tests indicate that the phase contents of MDO coating has a significant effect on the degradation process of coated magnesium alloy in the 3.5 wt% NaCl corrosive environment. The MDO coating in the silicate-based electrolyte system composed of MgO suffered from pitting corrosion in the twenty hours immersion test, whereas the MDO coating with ZrO2 compounds shows a much superior stability during the corrosion tests and provides an efficient corrosion protection for long period of time.
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森永, 正彦, 純教 村田, 尚和 江崎, and 恵美子 東中川. "分子軌道法による原子炉用ジルコニウム合金の耐食機能設計." 1997. http://hdl.handle.net/2237/13033.
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