In this study, a two-bed electrically-heated regenerative thermal oxidizer (RTO) was used to test NOx formation characteristics from burning air-laden N, N-dimethyl formamide (DMF) and air-laden DMF mixed with methyl ethyl ketone (MEK). The RTO contained two 0.152 m ¡Ñ 0.14 m ¡Ñ 1.0 m (L ¡Ñ W ¡Ñ H) beds both packed with gravel particles of around 1.11 cm in average diameter to a height of 1.0 m, and the packed section had a void fraction of 0.416. Performances on the thermal destructions of DMF and MEK, the thermal recovery efficiency, as well as the gas pressure drop over the regenerative beds were investigated. Experimental results indicate that, with a valve shifting time (ts) of 1.5 min, gas superficial velocities (Ug) of 0.39-0.78 m/s (evaluated at an influent air temperature of around 30oC), and set maximum destruction temperatures (Tset) of 750-950 oC, there was no NOx in the effluent gas from the RTO with no DMF in the influent air. With only DMF in the influent gas, its destruction efficiencies were 96.3 (750oC), 97.4 (850oC) and 97.9 % (950oC), and increased with increasing influent DMF concentration from 100-250 ppm. Mole ratios of ¡§NOx-N formation/DMF destruction¡¨ were found to be in the range of 0.84-1.20, and the ratio decreased with increasing influent DMF concentration within the experimental range. With both DMF and MEK in the influent gas, no significant influence was found in the NOx formation ratio and the DMF destruction efficiency with influent MEK/DMF ratios of 50/100 - 1500/100 (ppm/ppm) and the set temperatures. The NOx formation ratios were in the range of 0.85-1.07. The Ergun equation was adequate for the estimation of the pressure drop for the gas flowing over the packed regenerative beds in the Ug range of 37-0.74 m/s. It was also found that the thermal recovery efficiency was decreasing with the increasing Ug and invariant with Tset.

A novel method of synthesizing and controlling the size of germanium nanocrystals was developed. A tri-layer structure comprising of a thin (~5nm) SiO₂ layer grown using rapid thermal oxidation (RTO), followed by a layer of Ge+SiO₂ of varying thickness (6 - 20 nm) deposited using the radio frequency (r.f.) co-sputtering technique and a SiO₂ cap layer (50nm) deposited using r.f. sputtering, was investigated. It was verified using TEM that germanium nanocrystals of sizes ranging from 6 – 20 nm were successfully fabricated after thermal annealing of the tri-layer structure under suitable conditions. The nanocrystals were found to be well confined by the RTO SiO₂ and the cap SiO₂ under specific annealing conditions. The electrical properties of the tri-layer structure have been characterized using MOS capacitor test devices. A significant hysteresis can be observed from the C-V measurements and this suggests the charge storage capability of the nanocrystals. The proposed technique has the potential for fabricating memory devices with controllable nanocrystals sizes. / Singapore-MIT Alliance (SMA)

No description available.

No description available.

Les géomembranes (GMB) en polyéthylène haute densité (PEHD) sont utilisées comme barrière d'étanchéité dans les installations de stockage de déchets non dangereux (ISDND). Malgré les bonnes propriétés initiales du PEHD, face aux agressions chimiques et biologiques d'un lixiviat de déchets et aux contraintes thermiques et mécaniques générées par le massif de déchets, sa durabilité reste une question ouverte. L'objectif de cette thèse est de contribuer au développement d'un modèle cinétique non empirique de prédiction de la durée de vie des GMB en PEHD, qui prend simultanément en compte les effets du vieillissement chimique et biologique. Pour cela, nous cherchons à déterminer d'une part les paramètres d'extraction des antioxydants constitutifs des GMB, première étape du vieillissement des GMB, et d'autre part les paramètres cinétiques de vieillissement oxydatif des PE, deuxième étape de vieillissement. Ceci nécessite de connaître et de comprendre les mécanismes physico-chimiques impliqués dans le vieillissement des PE dans les conditions particulières des ISDND. A partir d'une approche multi-échelle (macro- micro) et à l'aide de différentes techniques (IRTF, GPC HT, AED, essais de traction,…), nous évaluons l'impact du vieillissement accéléré sur la composition chimique, les structures macromoléculaire et cristalline ainsi que les propriétés d'usage des GMB et des films en PEHD. Cette étude a permis de déterminer un critère de fin de vie pertinent pour évaluer la durée de vie de la GMB : la fragilisation qui correspond à une masse molaire critique M'C d'environ 100 kg.mol-1. Un couplage de la modélisation chimique de la dégradation oxydante du polymère et biologique de la cinétique de croissance du biofilm est proposé. Enfin, dans une dernière partie, la même approche multi-échelle a été utilisée pour caractériser la dégradation de GMB vieillies 18 ans en bassin de stockage d'eau pour ainsi déterminer les mécanismes impliqués dans le vieillissement sur site / High Density PolyEthylene (HDPE) geomembranes (GMB) are used as basal liners in municipal solid waste (MSW) landfills. In spite of the good initial properties of the HDPE, his durability remains poorly known face to the chemical and biological strains of the MSW landfill leachate and the thermal and mechanical strains generated by the solid waste. The objective of this thesis is to contribute to the development of a non-empirical kinetic model for predicting HDPE GMB life cycle, that simultaneously takes into accounts the chemical and biological aging effects. For this purpose, we seek to determine on the one hand the extraction process parameters of the antioxidants present in the GMB, first step of the GMB aging, and on the other hand the kinetic parameters of the PE thermo-oxidation, second step of the GMB aging. This requires knowing and understanding the physico-chemical mechanisms involved in the PE aging in the particular conditions of MSW landfills. Using a multi-scale methodology (macro-micro) and multi-technique approach (FTIR; GPC-HT, DSC, tensile tests, …), we assess the impact of the accelerated aging on the chemical composition, on the macromolecular and crystalline structures and on the used properties of HDPE GMB and films. This study identified a relevant endlife criterion for assessing the GMB service lifetime: the embrittlement which corresponds to a critical molecular mass M'C of about 100 kg.mol-1. Coupling chemical oxidative degradation modelling of the polymer and biofilm growth kinetic modelling is proposed. In the last part, the same type of multi-scale approach has been applied to characterize the degradation of HDPE GMB aged 18 years in water storage basin in order to determine the mechanisms involved in natural aging

Ti-6Al-4V anterior cervical plates (ACP) are used in spinal fusion surgeries to fixate cervical vertebrae during graft adhesion. However, documented cases of implant failure and the potential for ACP corrosion raise concerns regarding any degradation of material resulting from extended implantation. In addition, abrasion during implantation may damage a section of the protective oxide layer, potentially exposing surrounding tissues to the harmful effects of bare titanium, aluminum, and vanadium. Thermal oxidation has been shown to improve corrosion-resistance and wear-resistance, depending on temperature and time. To quantify the attributes of the thermally grown oxide layer, Ti-6Al-4V coupons underwent thermal oxidation treatments in an atmosphere environment at 600 and 675 ˚C for 1, 4, 8, and 16 hours. Two sample types were produced: non-abraded and abraded. Non-abraded samples underwent potentiodynamic polarization according to ASTM F2129, which included open circuit potential tests. Open circuit potentials (EOC) increased with increasing treatment time, indicating that longer treatment time resulted in thicker oxides. All samples treated at 675˚C displayed higher EOC than samples treated at 600˚C, indicating an increase in oxide thickness with higher temperature. During the first hour of treatment at 675˚C, the rate of oxide growth was greater than the rate of oxide growth of all samples treated at 600˚C. Samples treated at 600˚C for 4 and 8 hours displayed pitting during potentiodynamic polarization, but all other samples withstood the applied potentials and surfaces were further passivated. To simulate damage during surgery, a single abrasion was made across samples in the abraded group with a diamond-tip indenter under a load of 471g at 4.4 mm/s. Abraded samples were subjected to potential-step tests to assess repassivation ability after abrasion. All samples displayed repassivation ability, except for the sample treated at 600˚C for 4 hours. Surface roughness was measured with atomic force microscopy before and after thermal oxidation treatments. Lower surface roughness was desired to discourage osseointegration, or the growth of bone cells. No isothermal surface roughness trends were observed, as high surface roughness outliers were seen in samples treated at 675˚C for 8 hours and 600˚C for 4 hours. Rockwell hardness and Vickers microhardness were also measured to assess bulk changes in mechanical properties and hardness of the oxidized surfaces. No statistical change was seen in Rockwell hardness. Vickers hardness increased with increasing temperature and time, with the exception of the sample treated at 600˚C for 4 hours. Metallography of the thermally oxidized samples was analyzed to determine if a change in microstructure had occurred due to thermal processing. No major change in grain size or the amount of alpha and beta grains was seen in samples treated at 600˚C, but samples treated for extended times at 675˚C showed equiaxed enlarged alpha grains and a reduction in beta grains. The breakdown of samples treated at 600˚C exemplified possible differences in the alpha-beta oxide behavior during thermal oxidation and corrosion. Outlying surface roughness and microhardness values related to the thermal oxidation treatments and resulting oxide structure. Due to delamination of oxides grown at 675˚C for 4, 8, and 16 hours, the treatment parameters would not be effective in the ACP application. Therefore, through corrosion resistance, repassivation ability, low surface roughness, increased microhardness, and no microstructural change, thermal oxidation treatments at 600˚C for more than 16 hours, and 675˚C for 1 hour or less would be suitable treatments for anterior cervical plates.

No description available.

La réduction continue des dimensions des transistors depuis les années 60 est à l’origine de l’explosion des usages de l’électronique. Toutefois, la réduction des dimensions à l’échelle nanométrique s’accompagne de nouvelles difficultés qui tendent à limiter les gains des transistors en termes de performances et de consommation.Afin de surmonter ces obstacles et maintenir cette dynamique, des canaux à base de nouveaux matériaux à forte mobilité et de nouvelles architectures de transistors sont désormais utilisées ou à l’étude. L’intérêt de films SiGe contraint en compression sur isolant (SGOI: SiGe-On-Insulator) ultra-minces est double : ils bénéficient de la forte mobilité des trous du SiGe contraint en compression ainsi que du meilleur contrôle électrostatique des structures dites « sur isolant ». Des films SGOI présentant une forte concentration en Ge et une importante contrainte peuvent être fabriqués par une technique industrielle appelée condensation. Cette technique repose sur deux processus simultanés : l’oxydation thermique et sélective du SiGe (seul le Si est oxydé) et l’inter-diffusion du SiGe entre l’oxyde thermique et l’oxyde enterré qui se comporte comme une barrière à la diffusion.L’utilisation de cette technique dans un environnement industriel nécessite de relever deux défis : maîtriser les mécanismes et la cinétique d’oxydation, et atteindre les plus fortes contraintes et qualités cristallines pour lesfilms SGOI.La cinétique de plusieurs procédés d’oxydation industriels et pertinents au regard des besoins technologiques actuels est étudiée à l’aide d’une nouvelle méthodologie d’analyse quantitative. Nous établissons une corrélationentre le coefficient de diffusion de l’espèce oxydante, qui détermine la cinétique d’oxydation, la concentration en Ge à l’interface d’oxydation, et la densité de l’oxyde mesurée par réflectivité de rayons X sur une ligne desynchrotron.Puis, nous avons fabriqué des films SGOI présentant des concentrations en Ge jusqu’à 80%. Nous discutons l’évolution de la contrainte de ces films en fonction des paramètres du procédé et des niveaux de contrainte. Enfin,nous mettons en évidence les effets du procédé de condensation sur la qualité cristalline du film SiGe aux interfaces avec les oxydes grâce à l’effet de canalisation d’une technique de rétrodiffusion d’ions à moyenne énergie (MEIS : Medium Energy Ion Scattering) / The tremendous spread of electronic devices and networks into our day-to-day life has been enabled by the constant downscaling of transistors since the 60’s. However, downsizing transistors has become increasingly difficult in the past few years and going to the nanometer scale brings new detrimental effects that have put power consumption and performances on quasi-plateaux for a few years. To overcome these limitations, high mobility channels based on new materials and new transistor architectures are being introduced. Ultrathin compressivelystrained SiGe-On-Insulator (SGOI) films benefit from the advantages of both the higher hole mobility of compressively strained SiGe as well as of the better electrostatic control of On-Insulator structures. The condensation techniqueis a CMOS-compatible technique that allows fabrication of such films with possibly high Ge content and high strain levels. The technique is based on Si-selective thermal oxidation of SiGe and concurrent SiGe diffusion between the thermal oxide and the buried oxide layer that acts as a diffusion barrier.Two main challenges still need to be taken up for an efficient and optimized use of the condensation technique in an industrial environment: oxidation mechanisms and kinetics must be well controlled, and strain and crystal quality of the SGOI film must be as high as possible.Firstly, this work bridges the gap between previous studies by covering various oxidation processes relevant to today’s technological needs with a new and quantitative analysis methodology of oxidation kinetics. A correlation is established between the diffusivity of the oxidizing species that governs oxidation kinetics, the Ge concentration at the oxidation interface, and the oxide density measured by X-Ray Reflectivity on a synchrotron beamline.Secondly, SGOI films with Ge concentrations up to 80% were fabricated by the condensation technique. The evolution of strain of SGOI films is discussed as a function of process parameters and strain energy levels. How the condensation technique alters the crystal quality, both at interfaces with oxides and in the bulk of the SiGe crystal, is evaluated by the Medium Energy Ion Scattering (MEIS) technique by using the channeling effect.

L'oxydation thermique est souvent étudiée par les méthodes classiques : mesure thermogravimétrie et observations MEB. L'utilisation de l'EA n'a pas encore été largement développée dans le domaine de l'oxydation thermique. Le présent travail vise à utiliser l'EA pour suivre in-situ l'oxydation et détecter les phénomènes physiques se produisant à haute température. Il porte sur deux groupes de matériaux : sensibles à l'oxydation catastrophique (Ti, Zy-4) et passifs (Cr, Ni). Ce travail présente tout d'abord l'oxydation du Ti pur à 900°C sous 150 mbar d'O2, en tant que matériau modèle. Il aborde également l'influence de la température, de l'atmosphère et de l'état de surface sur le comportement d'EA. L'oxydation du Zy-4, du Cr pur et du Ni pur sous oxygène et/ou sous vapeur d'eau est ensuite étudiée. Les ondes élastiques issues de l'oxydation sont converties en signaux d'EA via un capteur, lequel est collé au côté froid d'un guide d'onde en alumine. Une corrélation entre les mesures d'EA et les résultats classiques a été mise en évidence. La technique d'EA est capable de détecter l'oxydation catastrophique et d'identifier le mode de rupture de l'oxyde. Au-delà des paramètres discriminants d'EA, nous observons deux populations distinctes : la population dite normale est attribuée au bruit de fond et aux relaxations des contraintes dans l'oxyde associées à des phénomènes de fluage micro-mécanique, probablement situé aux joints de grains. La vitesse d'EA peut alors dépendre du niveau de ces contraintes et/ou de leurs relaxations. La population post-transitoire est associée à l'endommagement de l'oxyde conduisant à l'oxydation catastrophique. Selon le niveau d'énergie de transition, le mode de rupture de l'oxyde pourra être identifié. En revanche, l'EA n'a pas donné de résultats probants sur les matériaux passifs. Des signaux enregistrés ont pour principale origine le bruit de fond. / Thermal oxidation was often studied by conventional methods: thermogravimetric measurement and SEM observations. The use of AE has not yet been widely developed in the field of thermal oxidation. The present work aims to use AE to monitor on-line oxidation and detect physical phenomena occurring at high temperature. It focuses on two groups of materials: susceptible to catastrophic oxidation (Ti, Zy-4) and passive (Cr, Ni). This work first presents the oxidation of pure Ti at 900°C under 150 mbar of O2, as a model material. It also discusses the influence of temperature, atmosphere and surface condition on acoustic behaviour. Oxidation of Zy-4, pure Cr and Ni in pure oxygen and/or under water vapour is then studied. Elastic waves from oxidation are converted into AE signals via a sensor, which is placed outside the furnace by an alumina wave guide. A correlation between AE measures and classical results was highlighted. AE technique was able to detect catastrophic oxidation and identify failure modes of the oxide. Beyond the AE discriminated parameters, we observed two distinct populations: the so-called normal population is attributed to background noise and relaxation of stresses in the oxide associated with micro-mechanic creep, probably located at grain boundaries. AE velocity may then depend on stress level and/or their relaxation. Post-transition population is associated to oxide failure leading to breakaway oxidation. According to the transition energy level, the oxide failure modes could be identified. However, AE did not give conclusive results on passive materials. Recorded signals are mainly caused by background noise.

Esta dissertação, investiga o comportamento em fadiga da liga Ti-6Al-4V após o tratamento superficial denominado oxidação térmica, para aplicação em pinos fusíveis mecânicos. A oxidação térmica controlada do titânio e suas ligas apresenta propriedades interessantes na resistência à corrosão-desgaste, devido a sua alta estabilidade e dureza, contudo, há lacunas na literatura se esse benefício é recíproco nas propriedades da vida em fadiga. Corpos-de-prova foram tratados termicamente em atmosfera de ar ambiente e após foram submetidos a ensaios de rugosidade, metalografia, dureza, tração, fadiga e análise fractográfica. Os resultados obtidos em fadiga foram comparados com a mesma liga não oxidada, mostrando que as propriedades em fadiga não são recíprocas às propriedades de corrosão-desgaste da liga Ti- 6Al-4V, após o tratamento superficial de oxidação térmica. Enquanto para uma determinada condição de tratamento superficial, houve melhora de até 30x na resistência à corrosãodesgaste (redução de 97% na taxa de desgaste), nas propriedades mecânicas houve redução de 18% no limite de resistência à fadiga. / This dissertation investigates the fatigue behavior of thermally oxidized Ti-6Al-4V alloy, applied to break bolts. The controlled thermal oxidation of titanium and its alloys presents interesting properties in fretting-corrosion resistance, especially to the high stability and hardness. However, there are gaps in the literature regarding the effect of this oxide layer on fatigue properties. Thermally Oxidized specimens were tested for roughness, metallography, hardness, tensile strength, fatigue and fractographic analysis. The results were compared with the fatigue results of the same alloy when untreated, showing that the fatigue properties and the fretting-corrosion properties of thermally oxidized Ti-6Al-4V are not reciprocal. While with a given condition for the thermal oxidation, an improvement up to 30x occurred on fretting-corrosion resistance (97% reduction in the rate of wear), the endurance decreased 18%.