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Rozprawy doktorskie na temat "Revêtements protecteurs – Environnement"
Cheminet, Hélèna. "Élaboration de nouveaux revêtements de contrôle thermique pour applications spatiales". Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14330.
Pełny tekst źródłaThis work presents the formulation and the study of polysiloxane resins and hybrid sol-gel materials to develop new protective coatings resistant to space environment. Spacecraft thermal control and polymer protection towards atomic oxygen are required in Low Earth Orbit applications. Besides the stability in the space environment and the process requirements, the coatings have to exhibit innovative properties (such as a low curing temperature) and be composed of raw materials with easy supply in order to avoid any risk of obsolescence
Chahboun, Najat. "Compréhension des mécanismes de colmatage des couches anodisées sur alliages d’aluminium aéronautiques et développement de nouvelles formulations de colmatage". Electronic Thesis or Diss., Université de Lorraine, 2015. http://www.theses.fr/2015LORR0318.
Pełny tekst źródłaAluminium alloys are very used in the aircraft industry as structural materials because of their low density and their good mechanical properties. They have a polyphase microstructure that is causing electrochemical discontinuities and increasing sensitivity to corrosion. A system of protective coatings containing chromate Cr(+VI) is traditionally formed at the surface of these alloys. However, the REACH environmental guidelines impose Cr(+VI) surface treatments replacement because of chromate carcinogenicity. The aim of the thesis work has been the development of a new surface treatment constituted of a sulfuric acid anodizing (SAA) and a sulfate chromium and fluorozirconate salts sealing (Cr3+/ ZrF62-). The study of the SAA electrochemical process linked the alloys microstructure and the anodic layer porous morphology developed at their surface. The Cr3+ / ZrF62- sealing treatment is realized by a simple immersion of the anodized alloy in the solution. It is demonstrated that the sealing is caused by a local alkalinization of the anodized coating surface that leads to the precipitation of the Cr3+ and ZrF62- salts. These ones are forming a sealing film of about 300 nm thick, very covering of the nanometric pores. The anodic layers sealing greatly improves the corrosion resistance of the anodized alloys by forming an additional barrier against corrosive agents and by healing the corrosion initiation. The developed treatment allows both to achieve Cr(+VI) treatments performance over a wide range of alloys and to satisfy the environmental requirements
Merlatti, Céline. "Etude de la dégradation de matrices organiques et des interfaces dans des systèmes de peinture : contribution à la maîtrise de leur durabilité en environnement humain". Toulon, 2006. http://www.theses.fr/2006TOUL0011.
Pełny tekst źródłaIn the French Navy, organic coating systems are used to protect ships from corrosion. The service life requirements for protection are a long-term durability of 15 years. Today, the protection is insufficiently durable to meet the requirements, involving important maintenance cost. Thus, coating weatherability testing must be carried out to predict coating failures. The goal of this work is to, first, evaluate whether artificial test is reliable and representative of weathering, secondly, define a new reliable artificial test and finally, understand and identify loss of protection controlling factor. Three anticorrosive systems are studied. Each system presents three layers: topcoat – basecoat – primer. The total width is comprised between 200 and 250 μm. All samples are exposed to four different standard artificial weathering tests: a neutral salt spray test (NSS ISO 9227) and three cycles (QUV ASTM G53, ASTM D5894 and ISO 20340. Besides, the same samples are exposed to a natural weathering during four years in three different locations: Bandol, (83, France) classified as a C3 site, Pipady (83, France) and Kure Beach (North Caroline, USA), classified as C5M sites. Both Kure Beach and Pipady permit to expose coatings to high intensity sunlight in a marine atmosphere. After ageing, the rate of chemical and physico-chemical changes in each layer is followed using different characterisation methods (FTIR Microscopy, Pyrolysis – GC/MS, Dynamical Mechanical Analysis, Vickers Microhardness and SEM). Substrate/primer interface properties are studied by destructive method (the corroded area measurement in the scribing area beneath the coating) and non –destructive methods (Electrochemical Impedance Spectroscopy (EIS), Local EIS, surface potential measure). By comparing the kinds of chemical and physico-chemical changes in the different tests, it is possible to assess the validity of the accelerated tests. QUV ASTM G53, ASTM D5894 and ISO 20340 artificial cycles involve chemical processes which differ from those obtained after natural exposure. Here, the temperature is believed to be a key factor to explain such differences. On the bases of these results, a new cycle has been defined, more reliable. The variety of different weathering conditions permits to determine the more severe conditions in terms of degradation. Coating durability is not directly linked to physicochemical evolution that occurs in the coating. In fact, internal stresses developed during both temperature and moisture cycles control the coating performance
Michau, Alexandre. "Dépôts chimiques en phase vapeur de revêtements à base de chrome sur surfaces complexes pour environnements extrêmes : expérimental et simulation". Thesis, Toulouse, INPT, 2016. http://www.theses.fr/2016INPT0088/document.
Pełny tekst źródłaNuclear fuel cladding tubes resistance against high temperature oxidation during accident conditions is crucial because it means protecting the first containment barrier. This can be done by coating the inner wall of the cladding tube with CVD processes, which are most likely to do so. More specifically, we used DLI-MOCVD to grow chromium based (Cr(S), metallic crystalline chromium) and chromium carbides based (amorphous chromium carbides CrxCy, recycled CrxCy, silicon doped CrxSizCy) coatings, known for their good oxidation resistance. The coating process was optimized using numerical modelling to improve coatings performance. A reaction kinetics model of the deposition process of amorphous CrxCy coatings was adjusted and validated after the identification of the chemical mechanism. It was also shown that the liquid solution containing organometallic precursor (bis(arene)chromium) and solvent (toluene) could be directly recycled, thereby increasing the industrialization potential of such process. Physical, chemical and structural properties of coatings deposited with this process were characterized. A study of the coatings mechanical properties has also been undertaken. It shows that compared to related coatings grown with other processes, those deposited by DLI-MOCVD exhibit a particularly high hardness (up to 30 GPa), compressive residual stresses, good adhesion with the substrate and finally a different abrasive wear resistance depending on the temperature. The assessment of their oxidation resistance at 1200 °C revealed excellent performances of amorphous chromium carbides coatings, which can delay catastrophic oxidation up to two hours with only a 10 µm thickness. All the other coatings only increase the thermal resistance of zircaloy substrates
Boulesteix, Claire. "Synthesis, environmental degradation and repairability of slurry aluminium coatings elaborated on steels employed in power plants". Thesis, La Rochelle, 2017. http://www.theses.fr/2017LAROS022/document.
Pełny tekst źródłaHigher energy efficiencies can be achieved by the increase of temperatures and pressures in power plant, thus allowing the reduction of the polluting emissions. Therefore, more efficient materials, compared to those currently employed, have to be used in order to resist to harsh environmental conditions (high temperatures, steam, pressure…). Despite of the good mechanical properties of many steels, the elaboration of a protective coating able to form a dense, protective and stable oxide layer at high temperature, is necessary. Thus, in the framework of the “POEMA” European project, the mechanisms of the formation of aluminium diffusion coatings were studied on ferritic-martensitic and austenitic stainless steels that are currently employed in power plants. The sealing of cracks eventually created during the aluminisation of steels was also studied. The degradation mechanisms of the B2-(Fe (Ni))Al coatings were then studied in steam and in air at 650 and 700°C up to 10000 hours and under different pressures (1 and 300 bar). We have demonstrated that the pre-oxidation induced during the elaboration of coatings grew a thin protective oxide scale composed of α-Al2O3 which developed further upon oxidation. Nevertheless, the long exposures under high steam pressures promoted the cationic diffusion of Fe, thus allowing the formation of small surface oxide nodules. Finally, the dissolution mechanisms of coatings with a diluted acid have been studied in order to demonstrate the possibility of strip and realuminise the materials initially coated
Chahboun, Najat. "Compréhension des mécanismes de colmatage des couches anodisées sur alliages d’aluminium aéronautiques et développement de nouvelles formulations de colmatage". Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0318.
Pełny tekst źródłaAluminium alloys are very used in the aircraft industry as structural materials because of their low density and their good mechanical properties. They have a polyphase microstructure that is causing electrochemical discontinuities and increasing sensitivity to corrosion. A system of protective coatings containing chromate Cr(+VI) is traditionally formed at the surface of these alloys. However, the REACH environmental guidelines impose Cr(+VI) surface treatments replacement because of chromate carcinogenicity. The aim of the thesis work has been the development of a new surface treatment constituted of a sulfuric acid anodizing (SAA) and a sulfate chromium and fluorozirconate salts sealing (Cr3+/ ZrF62-). The study of the SAA electrochemical process linked the alloys microstructure and the anodic layer porous morphology developed at their surface. The Cr3+ / ZrF62- sealing treatment is realized by a simple immersion of the anodized alloy in the solution. It is demonstrated that the sealing is caused by a local alkalinization of the anodized coating surface that leads to the precipitation of the Cr3+ and ZrF62- salts. These ones are forming a sealing film of about 300 nm thick, very covering of the nanometric pores. The anodic layers sealing greatly improves the corrosion resistance of the anodized alloys by forming an additional barrier against corrosive agents and by healing the corrosion initiation. The developed treatment allows both to achieve Cr(+VI) treatments performance over a wide range of alloys and to satisfy the environmental requirements
Bonnal, Justine. "Étude des mécanismes d'attaque des sables fondus (CMAS) vis-à-vis des barrières environnementales (EBC) et développement de protections anti-CMAS". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0366.
Pełny tekst źródłaLowering the environmental impact of aeronautical engines is made possible due to higher operating temperatures. This temperature increase (from 1200°C to 1400°C) requires the use of ceramic matrix composites (CMC) protected by an Environmental Barrier Coating (EBC). Rare earth silicates are relevant materials for EBC, as rare earth disilicates (RE₂Si₂O₇, RE = rare earth) or rare earth monosilicates (RE₂SiO₅). The EBC is submitted to corrosion by molten sands ingested by the engine. These sands are mainly constituted of oxides as CaO, MgO, Al₂O₃ and SiO₂ and are called « CMAS ». At operating temperature, liquid CMAS infiltrates the porosity and the grain boundaries of EBC, thus notably leading to thermochemical degradation through dissolution and precipitation phenomena. The ternary system CaO-SiO₂-REO₁.₅ contains elements from the liquid medium (CaO), from the material (REO₁.₅), or from both (SiO₂), and is well documented in the literature for RE = yttrium. Two precipitated phases of interest appear in this phase diagram: apatite Ca₂RE₈(SiO₄)₆O₂ and cyclosilicate Ca₃RE₂(Si₃O₉)₂. This work proposes first to consider the thermodynamic aspects of the CaO-SiO₂-REO₁.₅-Al₂O₃ quaternary system in order to show the influence of the alumina content on the liquid field and on the nature of the phases at equilibrium. Then, the EBC/CMAS interaction is studied by using a simplified system, chosen as a reference, constituted of yttrium disilicate and a CAS type liquid (constituted of only three oxides CaO, Al₂O₃ and SiO₂). This model system allows the establishment of reaction mechanisms through (i) the identification of the precipitated phases, (ii) the evolution of the composition of the liquid during the reaction, and (iii) the determination of thermodynamic data as the solubility limits in the liquid. The influence of the EBC/CMAS proportion on the thermodynamic equilibria is emphasized. The influence of the rare earth element and of the liquid composition are then studied in more complex systems. Thus, ytterbium disilicate is used as EBC material, and liquids are enriched in MgO to study both influences of magnesia content and of basicity of the melt. Ytterbium favors equilibrium between liquid and cyclosilicate phase, whereas MgO inhibits cyclosilicate precipitation. The last part of this work confirms the consistence between the experimental results arising from model systems and those obtained from bulk coatings. Different methods are discussed to evaluate the lifetime of EBC in situation of CMAS corrosion: (i) through the calculation of consumed EBC thickness in assuming a limitation by the amount of CaO brought by the liquid, or (ii) through the measurement of data influencing the corrosion rate, as for example the diffusion coefficient of rare earth in the liquid. Lastly, the behavior and efficiency of a new coating proposed as anti-CMAS solution is evaluated