Current simulations of atmospheric entry into both Mars and Earth atmospheres for the design of thermal protections systems (TPS) typically invoke conservative assumptions regarding surface-catalyzed recombination and the amount of energy deposited on the surface. The need to invoke such assumptions derives in part from lack of adequate experimental data on gas-surface interactions at trajectory relevant conditions. Addressing this issue, the University of Vermont's Plasma Test and Diagnostics Laboratory has done extensive work to measure atomic specie consumption by measuring the concentration gradient over various material surfaces. This thesis extends this work by attempting to directly diagnose molecular species production in air plasmas. A series of spectral models for the A-X and B-X systems of nitric oxide (NO), and the B-X system of boron monoxide (BO) have been developed. These models aim to predict line positions and strengths for the respective molecules in a way that is best suited for the diagnostic needs of the UVM facility. From the NO models, laser induced fluorescence strategies have been adapted with the intent of characterizing the relative quantity and thermodynamic state of NO produced bysurface-catalyzed recombination, while the BO model adds a diagnostic tool for the testing of diboride-based TPS materials. Boundary layer surveys of atomic nitrogen and NO have been carried out over water-cooled copper and nickel surfaces in air/argon plasmas. Translation temperatures and relative number densities throughout the boundary layer are reported. Additional tests were also conducted over a water-cooled copper surface to detect evidence of highly non-equilibrium effects in the form of excess population in elevated vibrational levels of the A-X system of NO. The tests showed that near the sample surface there is a much greater population in the v'' = 1ground state than is predicted by a Boltzmann distribution.

Silicone rubber based on polydimethylsiloxane is used ashigh voltage outdoor insulation, due to its ability to preservethe hydrophobic surface properties during service and evenregain hydrophobicity after exposure to electrical discharges.The underlying processes for the hydrophobic recovery arediffusion of low molar mass siloxanes from the bulk to thesurface and reorientation by conformational changes ofmolecules in the surface region. Only little is known of whichfactors are responsible for the long-term stability of thishydrophobic recovery. It is therefore important to increase theknowledge about the fundamental mechanisms for the loss andrecovery of hydrophobicity of silicone rubbers, exposed toelectrical discharges. Addition-cured polydimethylsiloxanenetworks, with known crosslink densities, were exposed tocorona discharges and air/oxygen-plasma and the loss andrecovery of hydrophobicity was characterised by contact anglemeasurements. The degree of surface oxidation increased withincreasing exposure time with a limiting depth of 100- 150 nm,as assessed by neutron reflectivity measurements. The oxidationrate increased with increasing crosslink density of the polymernetwork, according to X-ray photoelectron spectroscopy. Withinthe oxidised layer, a brittle, silica-like layer was graduallydeveloped with increasing exposure time. The hydrophobicrecovery following the corona or air/oxygen- plasma exposuresoccurred at a slow pace by diffusion of cyclic oligomericdimethylsiloxanes through the micro-porous but uncrackedsilica-like surface layer or at a much higher pace by transportof the oligomers through cracks in the silica-like layer. Theoligomers were present in the bulk, but additional amounts wereformed during exposure to corona discharges. High-temperaturevulcanised silicone rubber specimens were aged in a coastalenvironment under high electrical stress levels (100 V/mm). Thechanges in surface structure and properties were compared tothe data obtained from specimens exposed to coronadischarges/plasma. The dominating degradation mechanism wasthermal depolymerisation, initiated by hot discharges. Thisresulted in the formation of mobile siloxanes, of which the lowmolar mass fraction consisted of cyclic oligomericdimethylsiloxanes. Oxidative crosslinking resulting insilica-like surface layers was not observed during theseconditions. <b>Keywords:</b>silicone rubber, polydimethylsiloxane,hydrophobicity, corona, air-plasma, oxygen-plasma, surfacecharacterisation, degradation products, crosslink density.

<p>Silicone rubber based on polydimethylsiloxane is used ashigh voltage outdoor insulation, due to its ability to preservethe hydrophobic surface properties during service and evenregain hydrophobicity after exposure to electrical discharges.The underlying processes for the hydrophobic recovery arediffusion of low molar mass siloxanes from the bulk to thesurface and reorientation by conformational changes ofmolecules in the surface region. Only little is known of whichfactors are responsible for the long-term stability of thishydrophobic recovery. It is therefore important to increase theknowledge about the fundamental mechanisms for the loss andrecovery of hydrophobicity of silicone rubbers, exposed toelectrical discharges. Addition-cured polydimethylsiloxanenetworks, with known crosslink densities, were exposed tocorona discharges and air/oxygen-plasma and the loss andrecovery of hydrophobicity was characterised by contact anglemeasurements. The degree of surface oxidation increased withincreasing exposure time with a limiting depth of 100- 150 nm,as assessed by neutron reflectivity measurements. The oxidationrate increased with increasing crosslink density of the polymernetwork, according to X-ray photoelectron spectroscopy. Withinthe oxidised layer, a brittle, silica-like layer was graduallydeveloped with increasing exposure time. The hydrophobicrecovery following the corona or air/oxygen- plasma exposuresoccurred at a slow pace by diffusion of cyclic oligomericdimethylsiloxanes through the micro-porous but uncrackedsilica-like surface layer or at a much higher pace by transportof the oligomers through cracks in the silica-like layer. Theoligomers were present in the bulk, but additional amounts wereformed during exposure to corona discharges. High-temperaturevulcanised silicone rubber specimens were aged in a coastalenvironment under high electrical stress levels (100 V/mm). Thechanges in surface structure and properties were compared tothe data obtained from specimens exposed to coronadischarges/plasma. The dominating degradation mechanism wasthermal depolymerisation, initiated by hot discharges. Thisresulted in the formation of mobile siloxanes, of which the lowmolar mass fraction consisted of cyclic oligomericdimethylsiloxanes. Oxidative crosslinking resulting insilica-like surface layers was not observed during theseconditions.</p><p><b>Keywords:</b>silicone rubber, polydimethylsiloxane,hydrophobicity, corona, air-plasma, oxygen-plasma, surfacecharacterisation, degradation products, crosslink density.</p>

Le dimensionnement des protections thermiques des véhicules spatiaux nécessite la connaissance des flux de chaleur à la surface de l'engin. Pour le type de rentrée atmosphérique étudié dans ces travaux (rentrée terrestre à 10-12 km/s ou plus), le rayonnement contribue de manière significative à l'échauffement pariétal. Nous présentons dans cette étude, le développement et la mise en œuvre de modèles et d'outils numériques permettant de prédire les transferts radiatifs dans les couches de choc de rentrée terrestre hors d'équilibre en géométrie multi-dimensionnelle. Nous avons d'abord formulé dans une approche raie par raie l'expression des propriétés radiatives relatives à des plasmas de N2-O2 hors d'équilibre. Cette formulation est adaptée à une modélisation multi-température et/ou une modélisation par niveau électronique du déséquilibre thermique. Les expressions obtenues ont été mises en œuvre sur le cas d'épreuve FIRE II afin de déterminer les luminances au point d'arrêt pour quatre points de trajectoire. Les résultats montrent un bon accord global avec les données en vol dans les différents intervalles de mesure allant de l'IR à l'UV, hormis pour le point de rentrée le plus hors d'équilibre. Les calculs montrent également que la partie VUV du spectre contribue de manière très importante à la luminance à la paroi et que la prise en compte du déséquilibre chimique est primordiale. Un modèle approché de propriétés radiatives a ensuite été développé sur la base d'un modèle statistique à bandes étroites (MSBE) pour les systèmes électroniques moléculaires optiquement non minces (dans notre application), d'un modèle à coefficients d'émission et d'absorption moyennés par bande étroite pour les systèmes électroniques optiquement minces et les continua, et d'une approche raie par raie pour les transitions lié-lié atomiques. La mise en œuvre de cette modélisation hybride a nécessité une formulation adaptée de l'ETR pour tenir compte du déséquilibre et des corrélations spectrales. Des validations systématiques du MSBE, contribution par contribution, ont été réalisées. Le modèle hybride a ensuite été validé sur le cas d'épreuve FIRE II par rapport à des calculs raie par raie. Le modèle hybride a été implémenté dans le solveur radiatif ASTRE, code basé sur une approche de Monte Carlo. L'implémentation a été validée par rapport à une méthode de lancer de rayons sur une con_figuration plans tangents. Des calculs 3D de rayonnement ont ensuite été réalisés sur le cas d'épreuve FIRE II. Les résultats montrent des écarts de l'ordre de 10-15 % sur les flux au point d'arrêt par rapport aux résultats obtenus dans l'approximation des plans tangents habituellement utilisée dans la littérature. Les outils développés permettent d'obtenir des résultats relativement bien convergés (5 %) en géométrie tri-dimensionnelle (100000 cellules) en un temps CPU raisonnable permettant d'envisager des calculs couplés à terme. / Thermal protection design of spacecraft requires the knowledge of heat fluxes at the vehicle surface. For the kind of atmospheric entry considered in this work (earth reentry at 10-12 km/s or more), radiation significantly contributes to the surface heating. We present in this study, the development and the use of models and numerical tools to predict radiative transfers in the shock layers encountered in earth re-entry in nonequilibrium conditions and multi-dimensionnal geometry. First of all, we have formulated, in a line by line approach, the expressions of radiative properties of N2-O2 plasmas in nonequilibrium conditions. This formulation is suitable for a multi-temperature and/or a electronic state to state description of the thermal nonequilibrium. It has been used to simulate the test case FIRE II in order to determine radiative intensity at the stagnation point for four trajectory points. Results show a good agreement with flight data for different spectral measurement ranges form IR to UV, except for the trajectory point in strong nonequilibrium conditions. Calculations show moreover that VUV spectral range contributes significantly to the intensity at the wall and that taking into account chemical nonequilibrium is crucial. An approximate model of radiative properties has been developed on the basis of a statistical narrow band (SNB) model for optically thick (in our application) electronic molecular systems, of a box model for optically thin electronic molecular systems and continua, and of a line by line approach for atomic lines. The use of the hybrid model has required a suitable RTE formulation to take into account nonequilibrium and spectral correlations. Systematic validations of the SNB model for each contribution have been carried out. The hybrid model has then been validated on the test case FIRE II against line by line calculations. The hybrid model has been implemented in the ASTRE radiative solver, which is based on a Monte Carlo approach. The implementation has been validated in comparison with a ray tracing method on a tangent slab configuration. 3D radiative calculations have been then carried out on the test case FIRE II. Results show discrepancy of 10-15 % on the fluxes at the stagnation point with results obtained in the tangent slab approximation which is usually used in the litterature. The developed tools allow to obtain relatively well converged (5 %) results in tri-dimensional geometry (100000 cells) with a reasonable CPU time enabling to consider coupled calculations in futur works.

This work is devoted to the computational modeling of a lightning strike electric arc discharge induced air plasma and the material response under the lightning strike impact. The simulation of the lightning arc plasma has been performed with Finite element analysis in COMSOL Multiphysics. The plasma is regarded as a continuous medium of a thermally and electrically conductive fluid. The electrode mediums, namely the cathode and anode, have also been included in the simulation in a unified manner, meaning that the plasma and electrode domains are simulated concurrently in one numerical model. The aim is to predict the lightning current density, and the heat flux impinged into the anode's material surface, as well as the lightning arc expansion and pressure and velocity of the plasma flow. Our predictions have been validated by the existing experimental data and other numerical predictions reported by former authors.

Indiana University-Purdue University Indianapolis (IUPUI) / Thermal barrier coatings (TBCs) have been extensively employed as thermal protection in hot sections of gas turbines in aerospace and power generation applications. However, the fabrication of TBCs still needs to improve for better coating quality, such as achieving coating thickness' uniformity. However, several previous studies on the coating thickness prediction and a systematic understanding of the thickness evolution during the deposition process are still missing. This study aims to develop high-fidelity computational models to predict the coating thickness on complex-shaped components. In this work, two types of models, i.e., ray-tracing based and heat transfer based, are developed. For the ray-tracing model, assuming a line-of-sight coating process and considering the shadow effect, validation studies of coating thickness predictions on different shapes, including plate, disc, cylinder, and three-pin components. For the heat transfer model, a heat source following the Gaussian distribution is applied. It has the analogy of the governing equations of the ray-tracing method, thus generating a temperature distribution similar to the ray intensity distribution in the ray-tracing method, with the advantages of high computational efficiency. Then, using a calibrated conversion process, the ray intensity or the temperature profile are converted to the corresponding coating thickness. After validation studies, both models are applied to simulate the coating thickness in a rotary turbine blade. The results show that the simulated validation cases are in good agreement with either the experimental, analytical, or modeling results in the literature. The turbine blade case shows the coating thickness distributions based on rotating speed and deposition time. In summary, the models can simulate the coating thickness in rotary complex-shaped parts, which can be used to design and optimize the coating deposition process.

Les traitements plasma sont devenus des moyens incontournables et puissants pour modifier les propriétés de surface de nombreux matériaux sans intervenir sur les propriétés massiques et ceci en étant respectueux de l’environnement. Si ces traitements ont été appliqués à de nombreuses reprises aux élastomères réticulés pour améliorer leurs propriétés d’adhérence, ils n’ont quasiment jamais été appliqués à des élastomères non réticulés. Les expositions plasma ont été réalisées à basse pression, en décharge radiofréquence dans un environnement d’air. Pour limiter la complexité de l’étude et pour obtenir une meilleure compréhension des mécanismes d’interaction plasma-surface, un SBR et un polybutadiène (BR) non chargés et non réticulés ont été utilisé comme élastomères modèles. Le rôle d’un d’antioxydant (6PPD) classiquement utilisé a également été étudié. L’influence de la configuration du réacteur plasma sur les modifications surface a été suivie par mouillabilité et spectroscopie XPS. La cartographie des espèces plasmagènes a été obtenue par spectroscopie d’émission optique.L’augmentation du caractère hydrophile des surfaces avec l’énergie du plasma jusqu’à un seuil énergétique a pu être mise en évidence. Au-delà les phénomènes d’ablation et de réticulation de surface deviennent prépondérants. Les modifications de surface et leur cinétique de réorganisation de surface des chaînes polymère dépendent essentiellement de la température, l’environnement est un paramètre secondaire. L’influence de ces modifications physico-chimiques de surface induite sur les propriétés de tack est clairement mise en évidence. L’augmentation du caractère hydrophile conduit à une augmentation importante des performances adhésives instantanées (temps courts de contact 100s) au contact du verre. Par contre, la réticulation superficielle consécutive à des expositions plasma trop énergétiques diminue de façon drastique l’autohésion, ie le contact entre deux surfaces élastomères traitées. Le rôle de l’antioxydant sur la recombinaison des radicaux macromoléculaires formés lors du traitement a été montré. Le succès de la mise en œuvre d’un traitement de surface par plasma repose sur le contrôle du seuil énergétique à ne pas dépasser de sorte à minimiser les phénomènes de réticulation superficielle. / Plasma treatment has become a powerful candidate to modify surface properties without any change in bulk properties. It combines high chemical reactivity with low operational costs, in environmentally friendly processes. Plasma treatment has been intensively applied for surface modification of vulcanized rubbers. Almost no studies have been dedicated to plasma treatment of unvulcanized rubbers. The role of each additive during plasma exposure is poorly understood. It is also admitted that surface crosslinking occurs easily on rubber surfaces exposed to plasmas. This impacts the adhesive properties of the rubbers because it mimics chain interdiffusion. In this context, determining the key plasma parameters that have a significant effect on the surface properties is a prerequisite for further process control. To limit the complexity of the study, we concentrated our efforts on unvulcanized filler-free styrene butadiene rubber (SBR) and polybutadiene rubber (BR) which has been used for the first time as rubber models. The effect of three main parameters that directly impact the amount of energy and the nature of the excited species in the plasma phase (i.e. the RF source power, the exposure time and the distance between the rubber samples and the plasma) was analyzed. Optical Emission Spectroscopy was used to characterize the plasma phase. Surface modifications were investigated by wettability measurements and X-Ray Photoelectron Spectroscopy. Surface aging was investigated under ambiant and inert atmosphere at different temperatures and finally tack properties were measured and connected to surface properties determined with optical emission spectroscopy.

The laser beam interaction with matter and the plasma generation have been studied for many years. In some applications what is really important is to understand the composition and the temporal evolution of the species in the interested medium. In this thesis, time resolved optical spectroscopy was employed to understand the evolution of the plasma which is produced by interaction of Infrared (1.064 &micro / m) laser beam with air. In this thesis, a new technique is suggested to analyze the time evolution of laser induced breakdown spectroscopy. The suggested method and the instrumentation of the setup are tested with a single gas (He). After the tests, we analyzed time sequence spectra of Laser Induced Air Breakdown. The suggested method is based on triggering the laser and the spectrometer at different time and applying the spectrometer trigger time by adding the time delay (&amp / #916 / t) between them by using the pulse generator. The results show that the decay rates are slowing down microseconds after the excitation of the plasma. The results of the time-resolved measurements of the line spectra show that different component of the air has different decay rate, and lifetime. The lifetime of helium is 20 &micro / s, and the decay start 5 &micro / s after the initiation of plasma. Air has 12 &micro / s lifetime, and the decay start 3 &micro / s after the initiation of the plasma. Also, the decay rate and the lifetime depend on the state. We also calculate Doppler velocity for different component and different emission states. Doppler velocities show that the component which has great mass has small velocity, the component which has small mass has high velocity.

This diploma thesis deals with a plasmochemical treatment of photoanodes with an active layer containing TiO2 deposited on two different substrates by material printing. The plasmochemical treatment was performed by a low-temperature ambient-air plasma using a diffuse coplanar surface barrier discharge (DCSBD). The experimental part is focused on the investigation of DCSBD influence on the fabricated photoanodes photoelectrochemical properties, and the influence of plasma treatment time. Process optimization was achieved by height adjustment of the electrode. The processed coatings were electrochemically investigated by linear sweep voltammetry and chronoamperometry.

Cette étude porte sur l’application de différents procédés d’oxydation avancée, POA (plasma d'air humide, électro-Fenton, photo-Fenton et oxydation anodique avec BDD) pour le traitement des colorants de textile. La particularité de ces procédés tient à la génération dans le milieu d’entités très réactives et très oxydantes, les radicaux hydroxyles •OH qui sont capables d’oxyder n’importe quelle molécule organique jusqu’au stade ultime d'oxydation, c'est-à-dire la minéralisation (transformation en CO2 et H2O). Le plasma d'air humide a été appliqué pour l'oxydation d'un colorant azoïque, l'OD 61. Différents catalyseurs (Fe2+, Fe3+ et TiO2) ont été ajoutés dans leurs conditions optimisées afin d'améliorer les performances du système Glidarc. La combinaison des deux catalyseurs: Fe2+ et TiO2 a permis de décolorer 91% de l'OD 61 au bout de 3 heures et d'atteindre un taux d'abattement du COT de l'ordre de 52% après 10 heures de traitement. La méthodologie de la recherche expérimentale a été appliquée dans ce mémoire afin d'étudier l'influence de: l'intensité du courant, la concentration du colorant et le temps d'électrolyse sur la vitesse de disparition de l'OD 61 et afin de déterminer les conditions optimales de sa minéralisation. Dans les conditions optimales obtenues ([colorant] = 0,53.10-3 mol.L-1, I = 250 mA), le procédé électro-Fenton (EF) permet d'atteindre des taux de minéralisation de l'ordre de 98% dans le cas de l'OD 61 et l'AO 7 et de 88% dans le cas de l'indigo carmine. L’identification des produits intermédiaires au cours de l’électrolyse a permis de proposer un mécanisme de minéralisation de l'AO7. Les constantes cinétiques apparentes et absolues ont été déterminées. La dégradation de l'indigo a été étudiée par oxydation anodique avec BDD (OA-BDD) et par procédé photo-Fenton (PF). Cette étude a montré que l'électrolyse de l'indigo suit une cinétique de pseudo premier ordre et que le taux d'abattement du COT était de l'ordre de 97% et 63% respectivement avec OA-BDD et PF. Une étude comparative pour l'oxydation de l'AO 7 a été menée par trois procédés d'oxydation avancée: PF, OA- BDD et EF-Pt et EF-BDD. Cette étude a montré que le procédé photo-Fenton permet d'atteindre des taux d'abattement supérieurs à 90% après seulement 2 heures de traitement. Toutefois, le PF s'est révélé le plus coûteux suite à l'utilisation de la lumière artificielle UV et l'ajout des réactifs. Par ailleurs, le traitement d'un effluent réel issu de l'industrie de textile par le procédé électro-Fenton avec une anode de platine a permis la minéralisation presque totale du rejet initial (94% du COT initial ont été éliminés) / This study concerns the application of various advanced oxidation processes, AOP (humid air plasma, electro-Fenton, photo-Fenton and anodic oxidation with BDD) to treatment of wastewater containing the persistent organic pollutants such as textile dyes. The characteristic of these processes is due to the generation of very reactive and very oxidizing species, hydroxyl radicals •OH which are able to oxidize any organic molecule until the ultimate oxidation stage, i.e. mineralization (transformation into CO2 and H2O). The humid air plasma was applied for DO 61degradation. Various catalysts (Fe2+, Fe3+ and TiO2) were added under their optimized conditions in order to improve the performances of Glidarc system. The combination of Fe2+and TiO2 lead to reach 91% of DO 61 degradation after 3 hours and 52% of TOC abatement after 10 H of treatment. The experimental design methodology was applied in this work in order to investigate the influence of experimental parameters (current intensity, dye concentration and electrolysis time) on the degradation rate of DO 61 dye and then for determining the optimal mineralization conditions. Under the optimal obtained conditions ([dye] = 0.53 10-3 mol.L-1, I = 250 mA), electro-Fenton process can lead to a complete mineralization of dyes: 98% of TOC abatement are obtained in the case of the DO 61 and the AO 7 and 88% in the case of indigo carmine. The identification of the intermediates during electrolysis permitted to propose a mineralization of AO 7 dye under examination. The apparent and absolute kinetic constants were determined. The degradation of indigo dye was studied by anodic oxidation with BDD (AO-BDD) and photo-Fenton process (PF). This study shows a pseudo first order reaction kinetics for indigo degradation. The mineralization efficiency is about 97% and 63% of TOC abatement, respectively with OA-BDD and PF A comparative study of the mineralization efficiency of AO 7 dye was been investigated by different advanced oxidation processes (PF, AO-BDD, EF-Pt, EF-BDD). This study shows that PF process lead to reach more than 95% of TOC abatement after only 2 hours. Nevertheless, this process is the most expensive due to the use artificial UV light and the addition of reagents. The treatment of an industrial textile effluent by electro-Fenton process lead to a complete mineralization (94% of initial TOC were eliminated)