La présente étude porte sur les problématiques d’entreposage de colis de déchets nucléaires. En France, via le projet Cigéo, il est envisagé d’entreposer les déchets radioactifs de moyenne et haute activité à vie longue à 500 mètres de profondeur dans un conteneur en acier API 5L X65 (chemisage) déposé dans des galeries creusées au sein d’une formation argileuse (argilites). Une température maximum de 90°C est attendue à la surface de l’acier en raison de l’intense radioactivité. Finalement, un coulis cimentaire (matériau de remplissage) sera injecté entre le chemisage et les argilites. La synthèse de couches de produits de corrosion susceptibles d’être rencontrées à la surface de l’acier dans les conditions de stockage a constitué le premier objectif de ce travail. Les conditions pour l’obtention de sidérite (FeCO3), de mackinawite (FeS) et de magnétite (Fe3O4) ont été déterminées. Par la suite, des essais de couplage impliquant deux électrodes recouvertes de produits différents ont été réalisés dans le but de simuler le comportement d’une surface d’acier recouverte d’une couche hétérogène de produits de corrosion. Il est apparu que l’acier recouvert d’une couche de mackinawite se comportait dans chaque cas comme une cathode. Ce phénomène est associé au caractère plutôt protecteur de la couche de mackinawite. Parallèlement, les essais de formation de la mackinawite par polarisation anodique ont montré que la formation d’une couche de produits de corrosion composée de magnétite/mackinawite était associée à un phénomène de corrosion localisée. Le comportement de l’acier au contact du matériau de remplissage envisagé pour combler l’espace entre le chemisage et les argilites a ensuite été étudié. Ce deuxième volet de l’étude a montré que la couche de produits de corrosion se formant à la surface de l’acier était principalement composée de magnétite, associée à des sulfures de fer tels que la mackinawite. L’hétérogénéité du matériau de remplissage, la présence de sulfures en son sein et la présence d’oxygène dissous dans les solutions de test sont les principales causes de l’apparition d’un phénomène de corrosion localisée. Ce résultat traduit également le caractère imparfaitement protecteur des couches d’oxyde se formant sur l’acier au contact du matériau cimentaire. Enfin, la dernière partie de ce travail de recherche a porté sur l’étude d’éventuels effets galvaniques entre une zone recouverte d’argilites et une zone recouverte de matériau de remplissage impliquant la présence de magnétite et de mackinawite et pouvant faire office de cathode. De tels effets n’ont pas été mis en évidence, ce qui est attribué à l’absence d’un véritable état passif de l’acier en contact avec le matériau cimentaire. / The present study relates to the problem of long-term disposal of nuclear waste. In France, with the Cigéo project, it is envisaged to store high and intermediate level long lived radioactive waste at a depth of 500m inside a carbon steel (API 5L X65) casing in a deep geological disposal, drilled in a very stiff clay formation. A maximum temperature of 90°C is expected at the carbon steel surface, because of the intense radioactivity. Finally, a specific cement grout will be injected between the carbon steel casing and the argilites. The synthesis of corrosion product layers likely to form on the steel surface was the first objective of this work. The different parameters to obtain siderite (FeCO3), mackinawite (FeS) and magnetite (Fe3O4) have been determined. Subsequently, coupling tests were carried out with two steel electrodes covered with different corrosion products in order to simulate the behaviour of a steel surface covered with a heterogeneous corrosion product layer. It appeared that the steel electrode covered with mackinawite was in each case the cathode. This phenomenon is associated with the somewhat protective properties of the mackinawite layer. Besides, anodic polarization experiments conducted to prepare mackinawite layers showed that the formation of a corrosion product layer composed of magnetite/mackinawite was associated with localized corrosion. The behaviour of carbon steel in contact with cement grout envisaged to fill the gap between casing and argillites was studied next. This second part of the study showed that the corrosion product layer forming on the steel surface was mainly composed of magnetite, associated with iron sulphides such as mackinawite. Heterogeneity of the cement grout, presence of sulphide within it, and presence of dissolved oxygen in the test solutions are the main causes of the appearance of localized corrosion processes. This result also shows that the oxide layers forming on the steel surface in the specific cement grout only provides an imperfect protection. Finally, the last part of this research work focused on the study of possible galvanic effects between a zone covered with argilites, and a zone covered with cement grout implying the presence of magnetite and mackinawite and thus able to act as cathode. Such effects could not be evidenced which is attributed to the absence of a real passive state of the steel in contact with the cement grout.

No description available.

Made available in DSpace on 2014-10-09T12:53:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:32Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:53:30Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:09:32Z (GMT). No. of bitstreams: 0 / Polidutos, tanques de armazenamento de combustíveis e outras estruturas metálicas estão em constante contato com diferentes tipos de solos, diversos horizontes ou camadas, expostos à ação corrosiva nessa interação. Isso possibilita a ocorrência de danos de conseqüências expressivas ao ambiente e à expectativa de trabalho, podendo implicar em contaminações derivadas por vazamento dos produtos de estocagem, derramamento durante transporte, acidentes causados por tubulações sem adequada manutenção além das perdas financeiras associadas. Conhecer a dinâmica de interações entre as superfícies metálicas e o entorno é fundamental a fim de prever comportamentos e desenvolver materiais melhor aplicados. Os aços classe API são utilizados em tubulações de alta e baixa pressão mantendo características de elevada resistência mecânica e à corrosão e, ainda assim, são suscetíveis de ocorrências do processo corrosivo, dado que, estão em contanto com diferentes ambientes desde regiões de mangue até atmosferas industriais. No presente caso, avaliou-se como se comportam aços API 5L X70 em contato com diferentes horizontes de alguns solos no Brasil. O estudo correlacionou a presença de espécies químicas como íons formados em solução, minerais primários e secundários. Além disso, foram avaliadas as características físicas e químicas como pH, condutividade elétrica, sólidos totais dissolvidos, entre outras, com as respostas quanto à resistência e formas de corrosão. Para tanto, foram utilizadas técnicas como difratometria de raios X, microscopia eletrônica de varredura, fluorescência por raios X por reflexão total, análise de injeção de fluxo além de análises de granulometria e gravimetria, dentre outras. Isto foi feito com a finalidade de obter a caracterização dos solos, a identificação dos produtos de corrosão, a análise da solução dos solos, a avaliação dos metais ensaiados e a classificação das formas e tipos de corrosão. Os resultados demonstraram que diferentes horizontes dos solos, assim como os diversos tipos de solos analisados, produzem um ataque diferenciado na estrutura metálica evidenciando essa seletividade. Também, o estudo demonstrou que tais respostas podem ser rapidamente obtidas com o emprego da solução do solo como meio analítico em comparação às avaliações usuais. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

La présente étude porte sur le problème de l'entreposage à long terme des déchets nucléaires. En France, il est prévu que les déchets radioactifs à haute activité et vie longue soient confinés dans un surconteneur en acier au carbone, puis stockés à une profondeur d'environ 450 m dans une formation argileuse (argilite). En raison de l'intense radioactivité, une température proche de 90°C est attendue à la surface de l'acier. Dans un premier temps, il a été nécessaire de synthétiser, par polarisation anodique à courant imposé, des couches de produits de corrosion susceptibles de se former en conditions de stockage. Les électrodes d’acier S235 ont été recouvertes d’une couche d’argilite broyée et immergées en solutions carbonatées. La synthèse a d’abord été effectuée à 25°C afin de déterminer les paramètres influant sur la nature des produits de corrosion, puis à 80°C de façon à se rapprocher des conditions réelles. Les composés obtenus dépendent de la concentration en NaHCO3, de la densité de courant imposée et du temps de polarisation. A 80°C, la magnétite Fe3O4 et la sidérite FeCO3 sont les principaux produits formés. La rouille verte carbonatée FeII4FeIII2(OH)12CO3.2H2O et la chukanovite Fe2(OH)2CO3 n'ont pu être détectées que localement dans certaines conditions. Des sulfures de fer, notamment la mackinawite, se forment en début d’expérience pour des densités de courants anodiques modérées. Dans la deuxième partie de l’étude, nous avons étudié l’influence des espèces sulfures sur un système constitué par l’acier et une couche de produits de corrosion modèle. Les modifications de cette couche préalablement formée, induites par les espèces sulfures, ont été plus particulièrement étudiées. Enfin, la dernière partie de notre travail de recherche a porté sur l’étude des couplages galvaniques pouvant s’établir entre deux zones de la surface de l’acier recouvertes de produits de corrosion différents. Nous avons notamment étudié les couplages impliquant la magnétite Fe3O4, principal composé conducteur susceptible de se former en conditions de stockage. / The present study relates to the problem of the long-term interim storage of nuclear wastes. In France, it is envisaged that high-level radioactive wastes will be confined in a glass matrix, stored in a stainless steel canister, itself placed in a carbon steel overpack. The wastes will then be stored at a depth of ~450 m in a deep geological disposal, drilled in a very stiff (indurated) clay (argillite) formation. A temperature as high as 90°C is expected at the steel surface because of the intense radioactivity. Anodic polarization at applied current density was used to synthetize corrosion product layers likely to be formed in storage conditions. The S235 steel electrodes were covered by a layer of argillite and dipped in carbonated solutions. The synthesis was first achieved at 25°C to determine the parameters controlling the nature of the corrosion products and then at 80°C to be closer to the real conditions. The nature of the obtained compounds proved to be dependent on NaHCO3 concentration, on current density and on polarization time. At 80°C, magnetite Fe3O4 and siderite FeCO3 were the main identified compounds. Carbonate green rust FeII4FeIII2(OH)12CO3.2H2O and chukanovite Fe2(OH)2CO3 were detected locally in some experiments. Iron sulfides, mainly mackinwaite, also formed at the beginning of the experiments with a moderate current density. In the second part of the study, the influence of sulfide species on the steel / model corrosion products layer system was investigated. The modifications of the layers previously formed by anodic polarization induced by sulfide species were more particularly studied. Finally, the last part of our research was focused on the effects of a galvanic coupling that could appear between two areas of the steel coated by different corrosion products. In particular, galvanic couplings involving magnetite Fe3O4, the main conductive compound likely to form under storage conditions, were studied.

In a previous project, mobile exposures in road environments have been performed in various areas of the world. A number of materials and coatings have been attached under trailers which travels long distances in different types of road environments. One of the materials, zinc, demonstrated various corrosion rates in different parts of the world. In this investigation two various accelerated corrosion tests have been performed at the laboratory of Swerea Kimab in order to realize parameter influence on zinc. Even though the corrosion rates are known, the relation to formed corrosion products has not been investigated earlier. In the present study, corrosion products on zinc have been analyzed using XRD and FTIR. The results from analyses of formed corrosion products have been evaluated together with measured corrosion rates, both from the mobile exposure and the accelerated tests, in order to try to understand under what conditions certain corrosion products are formed and how it affects the corrosion rate. A cold humid climate was found to be the most corrosive. In these environments, de ‐icing salts are used which promotes formation of Simonkolleite and in a subsequent step; Gordaite (if there is a not negligible deposition rate of SO2/SO42‐) which is often observed as the end product in marine environments.

Steel corrosion is one of the major distress mechanisms that causes the deterioration of reinforced concrete structures around the world. It is an electrochemical reaction between the reinforcing steel and the surrounding concrete that produces a mass loss of the metal. Through the process of corrosion in reinforced concrete, iron ions get oxidized to form corrosion products (CP). Although multiple experiments and studies have been developed to understand the rheological behavior of corrosion products, this topic stays inconclusive. This work aims to characterize corrosion products at micro-scale in order to trace the progress of the formation of rust, to determine its nature and to analyse its rheological behavior in reinforced concrete. An experimental procedure to produce CP in the laboratory is also presented in this research. In addition, material characterization methods have been used to identify the iron oxide phases present in CP, determine their viscosity and rheological behavior and to study how CP flows in a porous media. In order to identify the different stages in the corrosion process, the CP was analysed at 2, 4, 6 and 8 weeks. The experiments identified four phases of iron oxide for each period. Furthermore, it was found that CP behaves as a shear-thinning slurry and as a result, its viscosity decreases with the applied shear rate. In addition, the damage caused by CP on concrete depends on the w/c ratio of the concrete mix and the exposure time to a corroding environment. The rebar mass loss results show that CP is formed in layers around the rebar, and the flow of each CP layer can differ.

No description available.

The purpose of this study was to examine the effect of partial and total immersion in sodium hypochlorite on nickel-titanium rotary files and to determine whether resistance to fracture was influenced by the immersion time. One hundred K3™ and 100 ProFile® rotary files were either partially or totally immersed in 5.25% sodium hypochlorite for zero, one, five, thirty, or sixty minutes. After immersion, files were subjected to cyclic fatigue testing. Time to fracture was recorded and analyzed by a two-way ANOVA. Tukey's honest significant difference was used to identify any differences in immersion times. Within all ProFile groups and partial immersion K3 groups, there was no significant decrease in time to fracture with increased immersion time in sodium hypochlorite. Only the K3 total immersion groups revealed a significant decrease in time to fracture with increased immersion time in sodium hypochlorite.

Polidutos, tanques de armazenamento de combustíveis e outras estruturas metálicas estão em constante contato com diferentes tipos de solos, diversos horizontes ou camadas, expostos à ação corrosiva nessa interação. Isso possibilita a ocorrência de danos de conseqüências expressivas ao ambiente e à expectativa de trabalho, podendo implicar em contaminações derivadas por vazamento dos produtos de estocagem, derramamento durante transporte, acidentes causados por tubulações sem adequada manutenção além das perdas financeiras associadas. Conhecer a dinâmica de interações entre as superfícies metálicas e o entorno é fundamental a fim de prever comportamentos e desenvolver materiais melhor aplicados. Os aços classe API são utilizados em tubulações de alta e baixa pressão mantendo características de elevada resistência mecânica e à corrosão e, ainda assim, são suscetíveis de ocorrências do processo corrosivo, dado que, estão em contanto com diferentes ambientes desde regiões de mangue até atmosferas industriais. No presente caso, avaliou-se como se comportam aços API 5L X70 em contato com diferentes horizontes de alguns solos no Brasil. O estudo correlacionou a presença de espécies químicas como íons formados em solução, minerais primários e secundários. Além disso, foram avaliadas as características físicas e químicas como pH, condutividade elétrica, sólidos totais dissolvidos, entre outras, com as respostas quanto à resistência e formas de corrosão. Para tanto, foram utilizadas técnicas como difratometria de raios X, microscopia eletrônica de varredura, fluorescência por raios X por reflexão total, análise de injeção de fluxo além de análises de granulometria e gravimetria, dentre outras. Isto foi feito com a finalidade de obter a caracterização dos solos, a identificação dos produtos de corrosão, a análise da solução dos solos, a avaliação dos metais ensaiados e a classificação das formas e tipos de corrosão. Os resultados demonstraram que diferentes horizontes dos solos, assim como os diversos tipos de solos analisados, produzem um ataque diferenciado na estrutura metálica evidenciando essa seletividade. Também, o estudo demonstrou que tais respostas podem ser rapidamente obtidas com o emprego da solução do solo como meio analítico em comparação às avaliações usuais. / Pipelines, fuel storage tanks and other metallic structures are in permanent contact and exposed to different types of soils, of horizons or layers, or of soil aggressiveness. This interaction may cause expressive damages to the environment and to the planned work. Contamination may occur due to leakage of stored products, splitting during transportation, accidents caused by pipelines without extensive maintenance. The result of these accidents could be, among others, some financial losses. In order to recognize the dynamic interactions between metallic surfaces and the environment it is crucial to have preventive actions and to develop better-applied materials. API steel 5L X70 has been used in structures of low and high pressure with high mechanical strength and corrosion and, even so, it is susceptible to etching corrosion since it is in contact with different environments from mangrove regions to industrial environments. The present case evaluated the role of 5L X70 API steel in contact with different soil horizons representative of the Brazilian soil. This investigation correlated chemical species with solute ions in soil solution, secondary and primary phase minerals besides physical and chemical characteristics as pH, electric conductivity, total dissolved solids, among others, to the results of corrosion resistance and ways of corrosion. The evaluation was carried out using x-ray diffractometry, scanning electron microscopy, total reflection x-ray fluorescence, fuel injection flow besides texture and gravimetric analyses to soil characterization and mineralogy, identification of corrosion products, soil solution analyses, evaluation of tested materials and classification of ways and types of corrosion. This was an attempt to integrate the data to a better understanding of the process involving reagents and products. The results showed that different soil horizons such as different types of analyzed soils produce specific etching in metallic structures showing this selectivity. The study also shows that these results can be readily obtained with soil solution as an analytical means in comparison with nowadays evaluations.