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<p dir="ltr">Metal speciation and structure can be influenced by the deposition method used during synthesis, interactions with the support, and by post-deposition treatments and reaction conditions experienced during its lifetime of carrying out a catalytic reaction. Supported metal particles of different size contain different surface structures and coordination environments, which may not only influence reaction rates but also the interconversion between agglomerated metallic domains and dispersed metal atom or ion sites. Here, we address the influence of post-deposition treatments and support properties on the structural interconversion of Pd and Cu on aluminosilicate chabazite (CHA) zeolites, Pt on gamma-alumina (γ-Al2O3), and Pd on amorphous oxides (γ-Al2O3, La-doped Al2O3, ΘΔ-Al2O3). The fundamental insights from these studies can be used to design catalysts used widely in automotive exhaust aftertreatment systems, including Pd-exchanged zeolites for passive NOx (x = 1,2) adsorbers (PNA), Cu-exchanged zeolites for NOx (x = 1,2) selective catalytic reduction (SCR), Pt/Al2O3 for NH3 oxidation, and Pd/oxides for three-way catalysts (TWC). Incipient wetness impregnation (IWI) and colloidal methods were used to prepare Pd nanoparticles deposited on CHA zeolites with distinct Pd nanoparticle sizes and distributions. These Pd-CHA samples were used to investigate the effects of Pd particle size distribution on structural interconversion between ion-exchanged Pd and agglomerated Pd domains under realistic operating conditions. Smaller Pd nanoparticles had larger fractions of agglomerated Pd that converted to ion-exchanged Pd2+ sites at fixed air treatment temperatures (598–973 K) and H2O pressures (2–6 kPa H2O), consistent with thermodynamic predictions from DFT calculations. Furthermore, the addition of H2O during air treatment of different Pd nanoparticles (2–14 nm) inhibited the formation of ion-exchanged Pd2+ (thermodynamics), but not the rate of redispersion (kinetics). This demonstrates that, regardless of Pd nanoparticle size, water vapor in automotive exhaust streams facilitate metal sintering in PNA applications. Aqueous-phase exchange of Cu on CHA zeolites with varying support properties (i.e., number of paired Al sites in the 6 membered ring) were used to prepare materials with distinct types and numbers of extraframework Cu species (Cu2+, CuOH+). These Cu-CHA materials were used to analyze Cu structural changes before and after exposure to hydrothermal aging conditions. In the absence of H2O, some Cu2+ sites condense to form binuclear Ox-bridged Cu species that can be reduced with H2 to form Cu-hydride sites and reject H2O, leading to a sub-stoichiometric H2 consumption (H2/Cu < 0.5). In the presence of H2O, all nominally isolated Cu2+ species convert to [CuOH]+ structures, which can subsequently be reduced by H2 to form a Cu-hydride and reject H2O, leading to stoichiometric H2 consumption (H2/Cu ~ 0.5). Furthermore, the presence of H2O led to reduction features in H2 temperature programmed reduction (TPR) profiles that were similar among Cu-CHA materials, regardless of the initial Cu2+ speciation, further supporting the proposal that all nominally isolated Cu2+ sites convert to a similar [CuOH]+ motif. This demonstrates how water influences Cu speciation on CHA materials of varying origin or treatment history, aiding in quantifying SCR-active isolated Cu ions and SCR-inactive Cu species (e.g., CuO, CuAl2O4). Pt supported on γ-Al2O3 were prepared with different average Pt particle sizes (2–13 nm) by increasing the temperature of post-deposition air treatment (523–873 K). This suite of materials was interrogated to isolate the effects of Pt particle size on NH3 oxidation rates and selectivities during conditions relevant to NH3 slip applications in diesel exhaust aftertreatment. For all Pt particle sizes, NH3 oxidation rates displayed a hysteresis with temperature, with high rates measured during temperature decreases than during temperature increases. Smaller Pt particles (2 nm) had lower rates (per surface Pt, quantified by CO chemisorption) than larger Pt particles (13 nm), signifying that NH3 oxidation is a structure-sensitive reaction. Furthermore, surfaces of Pt particles restructure under NH3 oxidation reaction conditions, influencing effective Pt oxidation states, surface structures (numbers and types of exposed Pt sites), and surface coverages of intermediates leading to the observed hysteresis in rate. These findings demonstrate that Pt particles undergo dynamic structural changes during reaction, influencing their ability to convert NH3 to environmentally benign products in NH3 slip applications. The influence of treatment conditions, support properties, and initial Pd particle size and distribution on the kinetics of nanoparticle sintering were investigated to identify which material properties allow maintaining high dispersion to maximize metal utilization for three way catalysts (TWC) during the conversion of regulated pollutants (CO, hydrocarbons, NOx). Pd was deposited by IWI methods to generate polydiserse particle size distributions, and using colloidal Pd nanoparticle solutions to generate monodisperse size distributions, onto various supports (γ-Al2O3, La-doped Al2O3, ΘΔ-Al2O3) and subjected to aging under oxidative and reductive conditions relevant for TWC operation. The average Pd particle size for all materials increased with treatment time under both reductive and oxidative environments. For samples prepared with IWI (i.e., log normal distribution of Pd particle sizes), reductive aging treatments led to higher sintering rates than oxidative treatments. In contrast, for samples prepared using colloidal Pd solutions (i.e., normal distribution of Pd particle sizes), oxidative aging treatments led to higher sintering rates than reduction treatments. Furthermore, after the same treatment condition and time, samples prepared with IWI resulted in higher average Pd particle sizes. These results indicate that more monodisperse initial Pd particle size distributions lead to lower sintering rates, providing guidance to design of supported metal TWCs with improved metal utilization during their lifetimes. Here, the combination of synthesis approaches to prepare a suite of model (e.g., powder) supported metal catalysts of varying structure and composition, interrogated using site and structural characterizations and steady-state and transient kinetic measurements, along with predictions from theoretical calculations, enabled unraveling the influence of material properties and gas environments that affect metal speciation, structure, and oxidation state in real-world aftertreatment systems that use more complex catalytic architectures (e.g., layered washcoats) and reactor designs (e.g., monoliths). This approach provides insights into the fundamental thermodynamic and kinetic factors influencing metal restructuring and interconversion under realistic conditions encountered in automotive exhaust aftertreatment applications, and the kinetic and mechanistic factors that underlie complex phenomena (e.g., reaction rate hysteresis) from data measured in the absence of hydrodynamic artifacts. The overall approach used in this work enabled development of synthesis-structure-function relationships on various metal supported catalysts for automotive exhaust aftertreatment applications, which can provide guidance for material design and treatment strategies to form and retain desired metal structures throughout the material lifetime, including synthesis, reaction, and regeneration treatments.</p>

An experimental evaluation of the mixed-mode fracture behavior of bonded composite joints is presented. Commonly used experimental techniques for characterizing the mode I, mixed-mode I/II, mode II, and mode III fracture behavior have been employed for the purpose of developing a fracture envelope to be utilized in the automotive design process. These techniques make use of such test geometries as the double cantilever beam (DCB), asymmetric double cantilever beam (ADCB), single-leg bend (SLB), end-loaded split (ELS), and split cantilever beam (SCB) specimens. Symmetric versions of the DCB, SLB, and ELS specimens produced mode mixities of 0°, 41°, and 90° respectively, while the testing of ADCB specimens allowed for mode mixities of 18°, 31°. Pronounced stick-slip behavior was observed for all specimen test geometries under both quasi-static and dynamic loading conditions. Due to the nature of the adhesive studied, a limited number of data points were obtained under mode I loading conditions. A significant increase in the number of measurable crack initiation events was observed for mixed-mode I/II loading conditions, where stick slip behavior was less pronounced. Additionally, a comparison of the measured fracture energies obtained under mixed-mode I/II loading conditions reveals that the addition of a small mode II component results in a decrease in the mode I fracture energy by roughly 50%, as the crack was driven to the interface between the adhesive layer and composite adherends. Furthermore, the propensity of debonds to propagate into the woven composite laminate adherends under mode II loading conditions limited the number of crack initiation points that could be obtained to one or two usable data points per specimen. A limited number of experimental tests using the SCB specimen for mode III fracture characterization, combined with a numerical analysis via finite element analysis, revealed a significant mode II contribution toward the specimen edges. Similarly, FE analyses on full bond width and half bond width SCB specimens was conducted, and results indicate that by inducing a bond width reduction of 50%, the mode II contribution is greatly decreased across the entire width of the specified crack front. To provide a means for comparison to results obtained using the standard DCB specimen, an alternative driven wedge test specimen geometry was analyzed, as this geometry provided a significant increase in the number of measurable data points under mode I loading conditions. A three-dimensional finite element analysis was conducted to establish ratios of simple beam theory results to those obtained via FEA, GSBT/GFEA, were of particular interest, as these ratios were used to establish correction factors corresponding to specific crack lengths to be used in correcting results obtained from an experimental study utilizing a driven wedge technique. Corrected results show good agreement with results obtained from traditional mode I double cantilever beam tests. Finally, bulk adhesive experiments were conducted on compact tension specimens to establish a correlation between adhesively bonded composite joint and bulk adhesive fracture behavior under mode I loading conditions. Measured fracture energy values were shown to gradually drop across a range of applied loading rates, similar to the rate-dependent behavior observed with both the DCB and driven wedge specimens. Application of the time-temperature superposition principle was explored to determine whether or not such techniques were suitable for predicting the fracture behavior of the adhesive studied herein. Good correlation was established between the fracture energy values measured and the value of tan d obtained from dynamic mechanical analysis tests conducted at corresponding reduced test rates. / Master of Science

lavare lente | a place for slow washing | alexandria, virginia the proposal is for a slow laundering facility for alexandria, virginia. the building is intended to be slow and deliberate in its construction and inhabitation. without conventional machines, the architecture and the individual must take on increased roles in the process of washing. ideas about how slowness relates to memory, drawing and construction, and about how we might ground ourselves in a manageably paced lifestyle are at the root of the thesis. / Master of Architecture

The purpose of this study is to make a survey of the liability of municipal corporations in Texas for the construction, repair, and maintenance of their streets and sidewalks, and for injuries sustained by the traveling public through defects in same.

L’optimisation du dimensionnement des structures passe par une meilleure connaissance de leur mode d’endommagement. Cette étude se focalise donc sur la caractérisation de l’endommagement du contact aube/disque des moteurs aéronautique. Cet assemblage mécanique est soumis a une combinaison d’un effort normal (force centrifuge) et tangentiel (dynamique de l’aube). La portée du disque en Ti-6Al-4V subi donc un chargement complexe de type fretting fatigue. Ce type de sollicitation entraine, entre autre dégradation, de la fissuration dont la modélisation expérimentale et numérique est rendue difficile par les limitations des moyens et des connaissances actuelles. Le premier objectif de ce travail de thèse est de développer un moyen d’essai et une instrumentation associée afin d’étudier de façon qualitative et quantitative la fissuration d’un contact Ti-6Al-4V/Ti-6Al-4V. Le second but est d’utiliser les données issues de ce moyen expérimental afin de proposer un modèle de prédiction des durées de vie de cet assemblage. Un montage inédit de fretting fatigue double vérin mono-contact a été mis en place avec une instrumentation nouvelle pour ce type d’essai : suivi de fissuration par suivi de potentiel et par émission acoustique. Une attention particulière a été apportée aux calibrations et aux méthodologies expérimentales. Ce banc d’essai permet notamment de simuler des efforts de fretting applique en phase ou alors de telle manière a simuler un vrai cycle de vol. Cet outil a permis de décrire quantitativement les premières courbes de Wohler en fretting à amorçage (Effort de fretting vs Nombre de cycles à amorçage) pour deux configurations de contact (cylindre/plan et plan/plan). Les impacts des différents paramètres de fretting sur l’amorcage ont pu être quantifies. Les paramètres influant sont : la configuration du contact, les niveaux des efforts appliques et leur mode de combinaison (cycles en phase ou cycles de type vol). De plus des courbes de cinétique de propagation des fissures ont pu être extraites des différents essais, montrant un fort impact du fretting sur les vitesses de propagation des fissures. Une analyse qualitative via l’émission acoustique a montré un mécanisme d’amorçage et de propagation en 3 étapes suivant la perte d’influence du contact. Un modèle de prédiction de l’amorçage et de simulation de la propagation des fissures a été mis en place. Bien que limite dans la prise en compte des effets gradients (approches non locales), ce modèle se montre très performant surtout dans sa capacité à utiliser les données expérimentales dans l’identification des lois d’amorçage ou de propagation. Ce travail a donc permis d’importantes avancées dans la compréhension des mécanismes de fissuration et dans leur modélisation ouvrant ainsi la porte vers une prédiction fiable de l’endommagement des contacts aube/disque. / Optimization of structures design requires a better understanding of their damage process. This study focuses on the characterisation of the blade/disk contact damaging process on aircraft engines. That mechanical structure is subjected to a normal load (centrifugal forces) combined with a tangential force (blade dynamic). Thus the Ti-6Al-4V disk seat sees a complex fretting fatigue loading. This type of solicitation can generate a series of degradations like cracking. Experimental and numerical simulation of this damaging is very difficult considering the present state of arts. The first aim of this work is to develop a new experimental set-up with the appropriate instrumentation in order to conduct a qualitative and a quantitative analysis of the cracking in a Ti-6Al-4V/Ti6-Al-4V contact. The second goal is to build a life prediction numerical model that would be able to use the data obtain with the new experimental tests. The new dual-actuator fretting-fatigue set-up is now operational. It allows to run single contact test under different loading combinations: fretting and fatigue loads can be applied in phase or in a way to simulate the real ‘in flight’ conditions. New instrumentations have been added in order to follow the crack initiation and propagation: potential-drop technique and acoustic emission. Thanks to this new test procedure, the first fretting Wöhler curve to crack nucleation have been described (fretting load vs number of cycles to crack nucleation) for two contact geometries (cylinder on flat and flat on flat). The separate influences of fatigue and fretting parameters have been determined. The mains parameters are: the contact characteristics, the stress level and the force combination modes (‘in phase’ cycles or ‘in-flight’ cycles). Moreover, the very first crack propagation kinetics have been drowned. Also, a major influence of the fretting on the crack propagation has been exposed. The qualitative analysis conducted with the acoustic emission has revealed a three steps crack propagation process. The crack propagation process evolves with the decrease of the contact influence. A model has been developed in order to predict crack initiation and propagation lives. Even if the model suffers from a major limitation due to the difficult considerations of the stress gradient effects, it has shown very good results through its ability to directly include experimental data. This work has led to major breakthroughs in the understanding of the cracking mechanisms and their simulation. This forms solid foundations for future predictions of the blade/disk interface durability.

L’industrie produit de grandes quantités d’effluents aqueux qu’il convient de traiter. Des traitements alternatifs aux procédés biologiques doivent être développés pour certains effluents toxiques et/ou non biodégradables. L’oxydation en voie humide catalytique repose sur l’action de l’oxygène sur les polluants en phase aqueuse à haute température et haute pression. Préalablement à cette étude, des catalyseurs au Ru ou Pt supportés sur ZrO2 ou TiO2très actifs et très stables pour l’OVHC de polluants modèles et de quelques effluents réels ont été développés. Ce travail a examiné ces catalyseurs sur d’autres effluents réels : un effluent provenant d’une unité de production de membranes contenant du glycérol et du DMF, uneffluent de sauce de couchage provenant de l’industrie papetière et un concentrât de lixiviatde décharge. Les catalyseurs se sont révélés très actifs et stables pour la minéralisation du glycérol, mais une forte lixiviation a été observée lors de l’OVHC du DMF du fait de la présence d’amines. L’oxydation de l’effluent de sauce de couchage permet de minéraliser la charge organique, facilitant le recyclage de la charge minérale, avec une amélioration accrue de la biodégradabilité du surnageant en présence des catalyseurs. Enfin, l’ajout de catalyseurs lors de l’OVH du concentrât de lixiviat de décharge permet d’améliorer sa minéralisation et d’éliminer totalement les ions ammonium / Industries produce huge volumes of effluents which need to be treated before disposal.Alternative treatments to the more classical biological techniques are required in the case oftoxic and/or non biodegradable effluents. The wet air oxidation (WAO) and catalytic wet airoxidation (CWAO) are based on the reaction of an oxidant (oxygen) with the pollutants in aqueous phase at high temperature and pressure. Ru or Pt catalysts supported on zirconium and titanium oxides were previously shown to be highly active and stable in the CWAO of awide range of model compounds and real complex effluents. These catalysts were evaluated in the CWAO of problematic effluents: one containing glycerol and DMF, one paper coatingslip effluent and one concentrated landfill leachate. The catalysts showed high activity and stability in the CWAO of glycerol, while the metal leached upon DMF CWAO due to the presence of amines. WAO leads to the partial mineralization of the organic load in paper coating slip, allowing an easy separation recycling of mineral pigments, with an improved biodegradability of the supernatant with the use of a catalyst. The use of a catalyst upon landfill leachate WAO leads higher COT conversion and complete ammonia elimination

La spectroscopie électronique basée sur l'effet tunnel donne accès à la densité d'états des électrons (DoS) dans les matériaux conducteurs, et renseigne ainsi en détail sur leurs propriétés électroniques. <br />Au cours de cette thèse, nous avons développé un microscope permettant d'effectuer la spectroscopie tunnel résolue spatialement (10 nm) de nanocircuits individuels, avec une résolution en énergie inégalée (10 µeV). Cet appareil combine les fonctions de Microscopie par Force Atomique (mode AFM) et de spectroscopie Tunnel locale (mode STM), et fonctionne à 30 mK. Dans le mode AFM, la topographie de l'échantillon est imagée grâce à un diapason en quartz piézoélectrique, ce qui permet de repérer les circuits. La spectroscopie tunnel peut ensuite être faite sur les zones conductrices. <br />Avec ce microscope, nous avons mesuré la DoS locale dans une structure hybride Supraconducteur-métal Normal-Supraconducteur (S-N-S). Dans un tel circuit, les propriétés électroniques de N et de S sont modifiées par l'effet de proximité supraconducteur. Notamment, pour des fils N courts, nous avons pu observer -comme prédit- la présence d'un gap dans sa DoS, indépendant de la position dans la structure : le “minigap”. De plus, en modulant la phase supraconductrice entre les deux S, nous avons mesuré la modification de ce gap, et sa disparition lorsque la différence de phase vaut π. <br />Nos résultats expérimentaux pour la DoS, ainsi que ses dépendances en phase, en position, et en longueur de N sont en accord quantitatif avec les prédictions de la théorie quasiclassique de la supraconductivité. Certaines de ces prédictions sont observées pour la première fois.

In the present work, deformation behavior, texture and microstructure evolution of commercially pure titanium (CP Ti) are investigated by electron backscattered diffraction (EBSD) after compression tests at elevated temperatures. By analysing work hardening rate vs. flow stress, the deformation behaviour can be divided into three groups, viz. three-stage work hardening, two-stage work hardening and flow softening. A new deformation condition map is presented, dividing the deformation behavior of CP Ti into three distinct zones which can be separated by two distinct values of the Zener-Hollomon parameter. The deformed microstructures reveal that dynamic recovery is the dominant deformation mechanism for CP Ti during hot working. It is the first time that the Schmid factor and pole figures are used to analyse how the individual slip systems activate and how their activities evolve under various deformation conditions. Two constitutive equations are proposed in this work, one is for single peak dynamic recrystallization (DRX), the other is specially for CP Ti deformed during hot working. After the hot compression tests, some stress-strain curves show a single peak, leading to the motivation of setting up a DRX model. However, the examinations of EBSD maps and metallography evidently show that the deformation mechanism is dynamic recovery rather than DRX. Then, the second model is set up. The influence of the deformation conditions on grain size, texture and deformation twinning is systematically investigated. The results show that {10-12} twinning only occurs at the early stage of deformation. As the strain increases, the {10-12} twinning is suppressed while {10- 11} twinning appears. Three peaks are found in the misorientation frequency-distribution corresponding to basal fiber texture, {10-11} and {10-12} twinning, respectively. A logZ-value of 13 is found to be critical for both the onset of {10-11} compressive twinning and the break point for the subgrain size. The presence of {10-11} twinning is the key factor for effectively reducing the deformed grain size. The percentage of low angle grain boundaries decreases with increasing Z-parameter, falling into a region separated by two parallel lines with a common slope and 10% displacement. After deformation, three texture components can be found, one close to the compression direction, CD, one 10~30° to CD and another 45° to CD. / QC 20100819