State of the art thermal barrier coatings (TBCs) for gas turbine applications comprise (7 wt.%) yttria partially stabilized zirconia (7YSZ). 7YSZ offers a range of attractive functional properties – low thermal conductivity, high thermal expansion coefficient and high in-plane strain tolerance. However, as turbine entry temperatures are raised, the performance of 7YSZ coatings will be increasingly affected by sintering and environmental contamination, by calcia-magnesia-alumina-silica (CMAS) deposits. The effect of sintering-induced stiffening on the driving force for spallation of plasma-sprayed (PS) TBCs was investigated. Spallation lifetimes of TBC specimens sprayed onto alumina substrates were measured. A simple fracture mechanics approach was employed in order to deduce a value for the strain energy release rate. The critical strain energy release rate was found to be constant, and if this value had been known beforehand, then the rationale presented here could be used for prediction of coating lifetime. The effect of vermiculite (VM) and volcanic ash (VA) contamination on the sintering-induced spallation lifetime of PS TBCs was also investigated. The presence of both VM and VA was found to accelerate the rise in their Young’s modulus with sintering. Spallation results show that coating lifetime may be significantly reduced, even at relative low addition levels, due to the loss of strain tolerance caused by the penetration of glassy deposits. This result gives a clear insight into the role CMAS plays in destabilizing TBCs. Finally, the adhesion characteristics of ingested volcanic ash were studied using a small jet engine. The effects of engine speed and particle size were investigated. Deposition on turbine surfaces was assessed using a borescope. Deposition mainly occurred on the nozzle guide vane and blade platform. A numerical model was used to predict particle acceleration and heating in flight. It was observed that larger particles are more likely to adhere because they have greater inertia, and thus are more likely to impact surfaces. The temperature of the larger particles at the end of its flight was predicted to be below its softening point. However, since the component surface temperatures are expected to be hotter, adhesion of such particles is probable, by softening/melting straight after impact.

Thermal barrier coatings (TBCs) have been widely used in gas turbine engines to protect the underlying metal from high operating temperature so as to improve the durability of the components and enhance the engine efficiency. However, since the TBCs always operate in a demanding high-temperature environment of aircraft and industrial gas-turbine engines, a better understanding of this complex system is required to improve the durability and reliability. The objective of this study is to investigate the effects of surface modification for the NiCoCrAlY bond coats on the thermal cycling lifetime and failure characteristics of TBCs. Parameters of modification for the bond coats included as-sprayed, barrel-finished, hand-polished and pre-oxidation heat treatment at 1100[degrees]C in P=10O2-8 atm up to 4 hours, carried out prior to the electron beam physical vapor deposition (EB-PVD) of ZrO2-7wt% Y2O3 (7YSZ) ceramic topcoat. The resulting characteristics of the bond coat and the thermally grown oxide (TGO) scale were initially documented by surface roughness, phase constituents of the TGO scale, and residual stress of the TGO scale. The thermal cycling test consisted of 10-minute heat-up to 1121°C, 40-minute hold at 1121°C, and 10-minute forced air-quench. As-coated and thermally-cycled TBCs were characterized by optical profilometry (OPM), photo-stimulated luminescence spectroscopy (PSLS), optical microscopy, scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and scanning/transmission electron microscopy (TEM/STEM) equipped with high angle annular dark field (HAADF) and X-ray energy dispersive spectroscopy (XEDS). TBC specimens for TEM/STEM analysis were prepared by focused ion beam (FIB) in-situ lift-out (INLO) technique. Superior thermal cycling lifetime was observed for TBCs with as-sprayed bond coats regardless of pre-oxidation heat treatment, and TBCs with hand-polished bond coats only after pre-oxidation heat treatment. With pre-oxidation heat treatment, relative photostimulated luminescence intensity of the equilibrium α-Al2O3 increased. Thus, the improvement in TBC lifetime can be correlated with an increase in the amount of α-Al2O3 in the TGO scale, given a specific surface modification/roughness. The lifetime improvement due to pre-oxidation was particularly significant to TBCs with smooth hand-polished bond coats and negligible for TBCs with rough as-sprayed bond coats. Spallation-fracture paths depended on the lifetime of TBCs. Premature spallation of TBCs occurred at the interface between the YSZ and TGO. Longer durability can be achieved by restricting the fracture paths to the TGO/bond coat interface. Small particulate phase observed through the TGO scale was identified as Y2O3 (cubic) by diffraction analysis on TEM. While small addition of Y in the NiCoCrAlY bond coat helps the adhesion of the TGO scale, excessive alloying can lead to deleterious effects.

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Lead enters drinking water by a process of corrosion, dissolution or particle detachment from lead bearing plumbing materials. Preventing contamination of water from lead-tin solder corrosion and achieving effective removal of particulate lead by point-of-use (POU) filters are important public health goals. These topics are especially timely given forthcoming revisions to the Lead and Copper Rule and ongoing efforts to reduce lead levels at the tap. Recently a switch from non-corrosive groundwater to a surface water source at a utility in Illinois caused unusual drinking water contamination from the release of large lead solder chunks from plumbing to water. Point-of-use (POU) filters distributed to remove the lead at this utility and elsewhere were not always completely effective. Here, we elucidate the mechanism of lead solder release in two chapters, followed by two more chapters examining lead removal by POU filters. The lead solder contamination arose after the water utility switched sources from high sulfate and low nitrate groundwater to a surface water with lower sulfate and high nitrate during runoff events. Such problems were unexpected because the surface water with high nitrate was not considered corrosive according to current theory. A chapter entitled A Novel Mechanism of Lead-Tin Solder Spallation in the Presence of Nitrate describes how 1) nitrate is extremely corrosive to lead:tin solder galvanically connected to copper, 2) nitrate corrosion can sometimes cause detachment of solder chunks to water, and 3) nitrate corroded the metal by reduction to ammonia and other reaction products. Another Chapter reports a follow up study, that reproduced the essence of nitrate induced spallation corrosion as observed in homes, using copper pipe with beads of lead-tin solder attached. During a 4-month experiment, the non-corrosive groundwater with high sulfate caused no solder beads to detach and only about 1% of the total lead was released to water. But in the surface water with high nitrate believed to cause the lead problem, 100% of the solder beads detached after just two months, and 80% of the total lead in the solder was released to water after 4 months. In the same surface water that had lower nitrate, with or without zinc orthophosphate or polyphosphate inhibitors, only 8 to 17% of the solder beads detached. Electrochemical studies also found that equimolar concentrations of chloride did not cause the disintegration of tin solder or as much weight loss as nitrate. Moreover, sulfate concentrations as low as 0.75 mM could effectively inhibit tin corrosion caused by 10 mg/L NO3-N. Studies focused on efficacy of POU filters have indicated that soluble lead in water is reliably removed, but sometimes particulate lead can escape capture and contaminate the treated water. To better understand this issue and practical limitations of filter use, field studies were performed in occupied and unoccupied homes in Enterprise, LA and New Orleans under both normal and extreme conditions of water lead contamination. For severe lead contamination present after lead pipes were disturbed or when a very long lead service line was present, and filters were tested to 200% of their rated capacity, the treated water occasionally had more than 15 ppb lead even when a very high percentage of the lead was removed. In Enterprise and New Orleans water with more typical levels of influent lead, the treated water was always below 1 ppb lead. But in Enterprise water with high iron and manganese the filters clogged quickly, causing higher costs for filtered water and consumer dissatisfaction. The occasional problems in removing particulate lead observed in this and prior research gave impetus to a series of bench-scale experiments elucidating particulate lead removal mechanisms by conventional ion-exchange media in sodium (Na+), strong acid (H+), chloride (Cl-) or strong base (OH-) form. Suspensions of lead phosphate particles of varying sizes and age revealed marked differences in dissolution rates under acidic, circa neutral and basic pHs that are caused by treatment with H+, Na +, OH -, Cl- form resin. Fresh nanoparticle lead phosphate particles were very labile, and immediately dissolved at pH 4 to form soluble Pb+2 ions which were quickly removed by strong acid media. High pHs > 10 and phosphate removal by OH– form resin could also dissolve the particles, and then remove the anionic soluble lead formed at high pHs. Na+ and Cl- resin caused little or no dissolution at the circa neutral pHs associated with their use and had lower rates of lead removal from water as a result. Older lead phosphate particles acquired from a New York City harvested lead pipe loop rig or purposefully synthesized in the laboratory, did not dissolve as readily as fresh nanoparticles which profoundly affected their relative removal efficiency by the different media. Overall, dissolution of lead phosphate particles in the ion-exchange media can sometimes have a range of important effects that can enhance or hinder lead removal dependent on circumstance. This thesis enhances our understanding of water lead contamination mechanisms by spallation of lead-tin solder and factors affecting lead removal by some POU filters. These novel insights can be helpful in preventing and mitigating future water lead contamination events. / Master of Science / Lead enters drinking water by a process of corrosion, dissolution or particle detachment from lead bearing plumbing materials. Preventing contamination of water from lead-tin solder corrosion and achieving effective removal of particulate lead by point-of-use (POU) filters are important public health goals. These topics are especially timely given forthcoming revisions to the Lead and Copper Rule and ongoing efforts to reduce lead levels at the tap. Recent studies have revealed that high nitrate sometimes causes severe lead contamination of water in homes with lead soldered copper pipe. This thesis elucidates a novel mechanism of lead solder corrosion from nitrate attack in two chapters, followed by two more chapters examining problems associated with lead removal from water by point-of-use (POU) filters. In a recent water lead contamination event, nitrate somehow caused large chunks of metallic lead solder to fall off pipes into the drinking water, a novel process that we term "spallation" corrosion. This observation inspired experiments to recreate this problem in the laboratory which found 1) nitrate and its reduced reaction products create a very low pH at the lead or tin anode during the nitrate-accelerated corrosion 2) the corrosion eats at the bond between the lead-tin solder and the copper pipe, cracking the lead:tin solder, causing chunks of metal to completely detach into water, and 3) corrosion of metal via nitrate reduction to ammonia at the tin anode. Follow-up electrochemical studies reproduced the essence of field nitrate induced spallation corrosion as seen in homes using copper pipe with beads of lead-tin solder attached. These beads detached to water during a 4-month experiment in some water chemistries and not others. No solder beads detached, and only about 1% of the total lead in the solder was released to water, during exposure to a non-corrosive groundwater with high sulfate. But all the solder beads detached in just two months, and 80% of the total lead was released to the water in 4 months, in a surface water with high nitrate. Electrochemical studies found that sulfate concentrations as low as 0.75 mM effectively inhibited the extreme tin corrosion caused by 10 mg/L NO3-N. Testing of lead certified POU filtration performance under varying conditions offers insight into challenges facing consumers. Field filtration studies were conducted in occupied homes for typical water lead challenges, or in unoccupied homes for testing of potentially dangerous water lead hazards, in Enterprise and New Orleans, LA. Results illustrate the difficulty of always achieving effective lead removal in cases where 1) the lead service line is very long, or 2) there is high erratic particulate lead after a lead service line is disturbed. Although effective lead removal occurred in other situations, the presence of very high levels of iron caused premature filter clogging and associated consumer frustration. Problems observed in removing particulate lead informed a series of bench-scale studies evaluating the role of particle age and size on filtration effectiveness by cation and anion form exchange resins (H+, Na +, OH -, Cl-). Batch tests demonstrated that fresh lead phosphate particles less than 1 micron in size are quickly dissolved at pH less than 4 caused by H+ form ion-exchange resin and were dissolved moderately fast at pH higher than 10 caused by OH- form ion-exchange resin. But the particles hardly dissolved at all at the moderate pHs present when Na+ and Cl- form resins are used. Dissolved lead was readily removed by H+, OH - and Na+ form resins at the pH range they created during treatment, but not by Cl- form resins. Lead phosphate particles from New York City did not dissolve as quickly as fresh nanoparticles, which sometimes enhanced or hindered their relative removal efficiency in the range of media tested. Overall, dissolution of lead phosphate particles within the media had important effects on the overall lead removal and could even cause previously removed lead to be released in some cases. This thesis enhances our understanding of water lead contamination mechanisms by spallation of lead-tin solder and lead removal by some POU filters. These novel insights can be helpful in preventing and mitigating future water lead contamination events.

The spallation of aluminum, chromium, and iron oxide scales is a chronic problem that critically impacts technological applications like aerospace, power plant operation, catalysis, petrochemical industry, and the fabrication of composite materials. The presence of interfacial impurities, mainly sulfur, has been reported to accelerate spallation, thereby promoting the high-temperature corrosion of metals and alloys. The precise mechanism for sulfur-induced destruction of oxides, however, is ambiguous. The objective of the present research is to elucidate the microscopic mechanism for the high-temperature corrosion of aluminum alloys in the presence of sulfur. Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM) studies were conducted under ultrahigh vacuum (UHV) conditions on oxidized sulfur-free and sulfur-modified Al/Fe and Ni3Al(111). Evaporative deposition of aluminum onto a sulfur-covered iron surface results in the insertion of aluminum between the sulfur adlayer and the substrate, producing an Fe-Al-S interface. Aluminum oxidation at 300 K is retarded in the presence of sulfur. Oxide destabilization, and the formation of metallic aluminum are observed at temperatures > 600 K when sulfur is located at the Al2O3-Fe interface, while the sulfur-free interface is stable up to 900 K. In contrast, the thermal stability (up to at least 1100 K) of the Al2O3 formed on an Ni3Al(111) surface is unaffected by sulfur. Sulfur remains at the oxide-Ni3Al(111) interface after oxidation at 300 K. During annealing, aluminum segregation to the g ¢ -Al2O3-Ni3Al(111) interface occurs, coincident with the removal of sulfur from the interfacial region. A comparison of the results observed for the Al2O3/Fe and Al2O3/Ni3Al systems indicates that the high-temperature stability of Al2O3 films on aluminum alloys is connected with the concentration of aluminum in the alloy.

Space vehicles, while entering the planetary atmosphere, experience high loads of heat. Ablative materials are commonly used for a thermal protection system, which undergo mass removal mechanisms to counter the heat rates. Spallation is one of the ablative processes, which is characterized by the ejection of solid particles from the material into the flow. Numerical codes that are used in designing the heat shields ignore this phenomenon. Hence, to evaluate the effectiveness of spallation phenomenon, a numerical model is developed to compute the dynamics and chemistry of the particles. The code is one-way coupled to a CFD code that models high enthalpy flow field around a lightweight ablative material. A parametric study is carried out to examine the variations in trajectories with respect to ejection parameters. Numerical results are presented for argon and air flow fields, and their effect on the particle behavior is studied. The spallation code is loosely coupled with the CFD code to evaluate the impact of a particle on the flow field, and a numerical study is conducted.

Les mécanismes de la réaction de spallation ne sont pas encore parfaitement compris, parce qu'il est difficile de séparer expérimentalement les effets respectifs des différentes étapes de la réaction. Afin de comprendre ces mécanismes, nous avons mis au point un dispositif expérimental permettant d'effectuer des mesures exclusives. Le système de détection des particules légères chargées est plus spécialement détaillé. <br /> Afin de valider notre dispositif expérimental, nous avons comparé nos résultats préliminaires sur le système 56Fe+p à 1 GeV/u avec des mesures inclusives obtenues auparavant sur le spectromètre FRS du GSI. La comparaison des sections efficaces différentielles en charge montre un accord raisonnable. Cependant, notre dispositif a permis d'étendre les mesures précédentes aux charges Z=1 et Z=2, importantes pour les études relatives aux dommages des matériaux. Compte tenu des barres d'erreurs que nous avons obtenues, l'évolution des vitesses moyennes longitudinales avec la masse du résidu de spallation est comparable à celle observée au FRS. Ces premiers résultats, même s'ils restent préliminaires, permettent de valider notre dispositif expérimental. Il est maintenant possible d'envisager d'exploiter les points forts des mesures exclusives réalisées, à savoir les corrélations entre les différents observables mesurées. Enfin, les problèmes expérimentaux soulevés lors de l'analyse effectuée pourront être pris en compte lors des expériences, afin notamment de mieux définir les programmes de mesure nécessaires aux étalonnages des détecteurs.

Le travail de thèse s'articule autour de deux études : étude de la réaction de spallation p+Au à 2.5 GeV et étude de la production neutronique en cibles épaisses. Ces deux études s'inscrivent dans un programme de recherche initié dans le cadre du projet de Source Européenne de Spallation (ESS) et du projet français de traitement des déchets radioactifs (GEDEON). A l'aide d'un dispositif expérimental très complet alliant un détecteur de neutrons à des détecteurs de particules chargées, tous deux d'efficacité supérieure à 80\%, nous avons pu étudier l'évolution du processus élémentaire de spallation en fonction de l'énergie déposée par le proton incident dans le noyau (énergie d'excitation). Nous avons ainsi montré le réalisme d'une description du processus en deux étapes et validé l'utilisation du code de cascade intra-nucléaire de J. Cugnon (INCL2.0) couplé à un code de désexcitation statistique (GEMINI). Les sections efficaces de production des particules chargées légères ont été mesurées et la contribution de l'émission de prééquilibre évaluée. La formation des particules composites ``directes'' a été ajoutée au code INCL2.0 à l'aide d'un modèle de coalescence. La production neutronique (multiplicités moyennes et distributions) a été étudiée en fonction de l'énergie du faisceau, de la géométrie de la cible et de la nature de la cible. Nous avons montré que le gain en neutrons, lorsque l'épaisseur de cible augmente, est dominé par la probabilité de réaction (pour des épaisseurs de cibles inférieures à 2 ou 3 longueurs d'interaction) et d'une façon moindre par le développement des réactions secondaires. Ces deux paramètres ont été étudiés séparément. Les données expérimentales ont été comparées aux résultats du code de transport HERMES, validant celui-ci pour l'émission de neutrons.

This document describes work performed related to the determination of how elemental additions affect the interfacial fracture toughness of thermal barrier coatings at the bond coat/thermally grown oxide interface in gas turbines. These turbines are exposed to cyclical thermal loading, therefore a simulation was designed to model this interface in a temperature cycle between 200 K and 1000 K that included oxide growth between 2 μm and 27 μm. The fracture toughness of this interface was then determined to elucidate the function of elemental additions. It was shown that minimal concentrations of atomic species, such as hafnium and yttrium cause notable increases in the toughness of the bond coat/thermally grown oxide interface, while other species, such as sulphur, can dramatically reduce the toughness. Furthermore, it was shown that, contrary to some empirical results, the addition of platinum has a negligible effect on the fracture toughness of this interface.

Les réacteurs hybrides, bases sur le couplage entre un accélérateur de particules et un coeur sous-critique via une cible<br />de spallation, présentent des possibilités de réduction de la radiotoxicité des déchets de haute activité et a vie<br />longue promis au stockage. Les différents concepts proposes ces dernières années dans la communauté scientifique montrent<br />la nécessite de réaliser un démonstrateur.<br />Ce travail de thèse a porte sur l'optimisation par simulation Monte Carlo a l'aide du code MCNPX, de la neutronique d'un tel<br />système dans le but de réaliser un réacteur pilote.<br />Tout d'abord, nous avons indique les principales caractéristiques neutroniques d'un réacteur hybride avant de présenter le<br />concept de démonstrateur refroidi au gaz base sur le remontage effectue par la société Framatome ANP. Nous avons<br />caractérise puis optimise la neutronique a travers la géométrie et les matériaux utilises pour ce démonstrateur.<br />Dans le cadre de l'incinération des actinides mineurs, nous avons calcule l'évolution des combustibles envisageables suivant<br />les phases de démonstration prévues. Les grandeurs liées a l'incinération des actinides mineurs sont rapportées. En vue<br />de la transmutation du 99Tc et de l'129I, nous avons calcule les temps caractéristiques et les taux de transmutation<br />a l'équilibre.<br />D'autre part, nous avons analyse le passage du démonstrateur vers un réacteur incinérateur de puissance a partir de<br />critères physiques tels que les facteurs de forme et les niveaux de flux. A partir de cette analyse, des solutions innovantes sont<br />proposées pour améliorer les facteurs de forme d'un incinérateur de puissance.<br />Enfin, dans des perspectives a plus long terme, l'utilisation des réacteurs hybrides dans le cadre de la génération<br />d'233U pour accélérer le démarrage d'une filière de réacteurs a sels fondus basée sur le cycle<br />232Th/233U a été explorée et s'avère particulièrement efficace.