Pollution from hydrofluorocarbons (HFC) poses a serious challenge to the environmental community. Released from industrial operations, they have contaminated both the atmosphere and groundwater and are considered persistent in both media.1 For over the past 20 years, the practice of synthesizing hydrofluorocarbons as alternatives to chlorofluorocarbons (CFC) has been conducted in an effort to reverse the effects of stratospheric ozone layer depletion. 2,3 However, in doing so these new fluorinated compounds exhibited an unexpected property as a potent global warming greenhouse gas (GHG) with radiative forcing potentials in the range of 100 to 10,000 equivalents greater than carbon dioxide.4 Conversely, HFCs exhibit desirable properties as precision cleaning solvents due to their low surface energy but that use has lead to releases contaminating groundwater resulting in recalcitrant pollution in the form of dense nonaqueous phase liquids (DNAPL).5 The Environmental Protection Agency (EPA) has recently requested studies on the environmental impact of HFCs with respect to a number of petitions received from various environmental action groups imploring the use of the Montreal Protocol as the vehicle by which to achieve elimination of the compounds from industrial operations.6,7 Additionally, results from studies requested by the international community have shown HFCs to exhibit developmental and neurological damage in animal life along with their impact to humans remaining not completely understood.8,9,10 Therefore, the potential hazards of HFCs to human health and the environment necessitates the development of an effective and environmentally responsible technology for their remediation from groundwater. The National Aeronautics and Space Administration (NASA) has employed the use of various halogenated solvents in its spacecraft cleaning operations at its facilities for many years iv and in that time experienced accidental releases which eventually resulted in environmental contamination.11,12,13 Many of the organic solvents employed in these operations consisted of halogenated compounds with most being partially chlorinated and fluorinated hydrocarbons. Through normal use and operation, releases of these materials found their way into the environs of atmosphere, soil and groundwater. Remediation of fluorinated compounds has not followed the successful path laid by clean-up technologies developed for their chlorinated counterparts.14,15,16,17 Fluorinated compounds are resistant however to those methods due to their unreactive nature stemming from the properties of the strong carbon-fluorine bond. 18 This unique bonding property also ensures that their environmental persistence endures. 19 One particular fluorinated groundwater contaminant, the HFC 1,1,1,2,2,3,4,5,5,5-decafluoropentane (DFP), which serves as an excellent cleaning agent and has been used by NASA since the late 1990’s and still remains in use today, was selected as the focus of this study. 20 For this study, various reductive metal systems were evaluated for their capability towards effective degradation of DFP. These included the metals: iron, magnesium, aluminum and zinc and several bimetallic alloys as well as attempts employing some on carbon support. Variations in protic solvent reaction media and acidic metal activation were also explored. The bimetallic reductive catalytic alloy, magnesium with palladium on carbon support Mg(Pd/C) in aqueous media, proved to be the successful candidate with 100% conversion to simple hydrocarbons. Mechanistic evaluation for degradation is proposed via a series of stepwise catalytic reduction reactions. Kinetic studies revealed degradation to obey second order reaction kinetics. Further study should be conducted optimizing an in situ groundwater delivery method for field application. Additionally, the developed technology should be assessed against other v groundwater fluorocarbon pollutants; either as a method for remediating multiple fluorinated polluted sites or as a polishing agent where all other non-fluorinated halogen pollutants have been abated.

This study aims to experimentally explore the possibility to join the two pieces of low-carbon steel and Cu-Ni alloy as the cladding material into a thick clad steel plate during a Friction Stir Lap Welding¡]FSLW¡^process without a probe. Two methods are employed to enhance the welding strength. Firstly, a layer of nickel is coated on the low-carbon steel to prevent it from oxidizing during the welding process. Secondly, the surface of the low-carbon steel is knurled to increase the contact area between the welding surfaces. Experimental results show that Ni-coating can effectively prevent the generation of oxidation and improve the welding strength. According to the tensile test using a plate of Cu-Ni alloy with a thickness of 4 mm, the welding strength of the clad steel plate with Ni-coating is about 2.3 times greater than that without Ni-coating. Moreover, according to the impact test, the clad steel plate with Ni-coating can absorb more impact energy than that without Ni-coating. This difference increases with increasing thickness of the plate. It is also found that the welding strength at the center of joints using the Ni-coating is greater than that at the substrate of copper-nickel alloy. For the clad steel plate with knurling, since it is difficult to fill the gap between the patterns of knurling, the increase in the contact area between the welding surfaces has been offset. Hence, the welding strength of the clad steel plate with knurling is less than that with Ni-coating.

Dry reforming of methane (DRM) is an attractive and promising process for the conversion of methane and carbon dioxide which are the most abundant carbon sources into valuable syngas. The produced syngas, which is a mixture of hydrogen and carbon monoxide, can be used as intermediates in the manufacture of numerous chemicals. To achieve high conversion, DRM reaction is operated at high temperatures (700-900 °C) that can cause major drawbacks of catalyst deactivation by carbon deposition, metal sintering or metal oxidation. Therefore, the primary goal is to develop a metal based catalyst for DRM that can completely suppress carbon formation by designing the catalyst composition. The strategy of this work was to synthesize Ni-based catalysts all of which prepared by homogeneous deposition precipitation method (HDP) to produce nanoparticles with narrow size distribution. In addition, control the reactivity of the metal by finely tuning the bimetallic composition and the reaction conditions in terms of reaction temperature and pressure. The highly endothermic dry reforming of methane proceeds via CH4 decomposition to leave surface carbon species, followed by removal of C with CO2-derived species to give CO. Tuning the reactivity of the active metal towards these reactions during DRM allows in principle the catalyst surface to remain active and clean without carbon deposition for a long-term. The initial attempt was to improve the resistance of Ni catalyst towards carbon deposition, therefore, a series of 5 wt.% bimetallic Ni9Pt1 were supported on various metal oxides (Al2O3, CeO2, and ZrO2). The addition of small amount of noble metal improved the stability of the catalyst compared to their monometallic Ni and Pt catalysts, but still high amount of carbon (> 0.1 wt.%) was formed after 24 h of the reaction. The obtained results showed that the catalytic performance, particle size and amount of deposited carbon depends on the nature of support. Among the tested catalysts, Ni9Pt1/ZrO2 showed high stability with the least carbon amount (0.55 wt.%). On the other hand, mono- and bimetallic Co-Ni/ZrO2 were then prepared following the same synthesis protocol. The ZrO2 support was chosen because of its high thermal stability and absence of mixed oxide formation with the active metals. It was demonstrated that on monometallic Co catalyst, the kinetic analysis showed first-order in CH4 and negative-order in CO2 on the DRM rate. The Co catalyst deactivated without forming carbon deposits. On contrary, on monometallic Ni catalyst, the DRM rate was proportional to CH4 pressure but insensitive to CO2 pressure. The Ni surface provides comparatively higher rates of CH4 decomposition and the resultant DRM than the Co catalyst but leaves some deposited carbon on the catalyst surface. In contrast, the bimetallic CoNi catalyst showed kinetics resembling the Co catalyst, i.e., the first-order with respect to CH4 pressure and the negative-order with respect to CO2 pressure on the DRM rate. Noticeably, the stability of CoNi catalyst was drastically improved over the monometallic counterparts and no deposited carbon was detected after the DRM reaction. The results suggest that for an appropriate Co/Ni ratio, the bimetallic CoNi/ZrO2 catalyst exhibits intermediate reactivity towards CH4 and CO2 between Co and Ni producing negligible carbon deposition by balancing CH4 and CO2 activation.

This master‘s thesis deals with the thermal overload trip unit in automatically operated electrical switching devices. The first part of this thesis serves as a basis for a design of thermostatic bimetal element in electrical switching device. The thesis presents important parameters and calculation principles needed for the design of bimetal element. The thesis further describes the operating principle of thermal trip unit and its possible design solutions. The main part is devoted to analytical calculation and measurement of specific thermostatic bimetal type contained in thermal trip unit of molded case circuit breaker. It is measurement of force and deflection, depending on temperature change. In the next part a numerical model of the bimetallic strip was created and its deflection was simulated. The analytical results are compared with the measured and simulated results at the end of the thesis.

The objective of this Ph.D. study is to explore an important and fertile research topic on the methods for synthesis of nanomaterials by homogeneous nonaqueous solution phase reaction. Research in this work focuses on synthesizing several kinds of nanomaterials in different environments and structure, including spherical nanoparticles, nanowires and core-shell structure composites We first synthesized metallic nanomaterials in this system, such as ~10 nm Fe nanoparticles, ~6 nm Au nanoparticles, and ~100 nm Bi nanoparticles, this system are the preparation for the following studies. Secondly, we synthesized bimetallic nanomaterials in this system, such as Fe50Co50 alloy and Bi doped with Mn. For FeCo alloy, after annealing at 500 °C, a pure phase of Fe50Co50 was obtained. And we first synthesized the nanowires of bismuth doped with manganese. By studying intermediates at different temperatures during the growth process of nanowires, the evolution of the crystallization of metallic products and the mechanism of the formation of the nanowires are investigated. Thirdly, we synthesized core-shell structure nanocomposites, including either gold as the shell or polymer as the shell. Au-coated magnetic Fe nanoparticles have been successfully synthesized by partial replacement reaction in a polar aprotic solvent with about 11 nm core of Fe and about 2.5 nm shell of Au. HRTEM images show clear core-shell structure with different crystal lattices from Fe and Au. SQUID magnetometry reveals that particle magnetic properties are not significantly affected by the overlayer of a moderately thick Au shell. The Aucoated particles exhibit a surface plasmon resonance peak that red-shifts from 520 to 680 nm. And Poly (Vinyl Pyrolidone) (PVP) coated iron nanoparticles also have been successfully synthesized in a polar aprotic solvent, which shows the welldefined core-shell structures. In this approach, Poly (Vinyl Pyrolidone) (PVP) was employed as the coating polymer directly coated on metallic core (iron) nanoparticles. In this work, a combination of TEM (transmission electron microscopy), EDS (Energy disperse X-ray spectroscopy), XRD (X-ray powder diffractometry), ICP (inductively-coupled plasma spectrometer), TGA (Thermogravimetric analysis), UV-visible absorption spectroscopy, IR (infrared) spectroscopy and SQUID magnetometry (Superconducting Quantum Interference Device) were employed to characterize the morphology, structure, composition and magnetic properties of the products. In summary, this Ph.D. study successfully and systematically synthesized several kinds of nanocomposites in a system. The synthetic procedure is simple, economic and easily scaled-up for further applications. And many techniques were employed to characterize the products.

Le présent travail est une contribution au domaine de la récupération de l’énergie. La conversion mise en place est faite à échelle centimétrique, les puissances électriques produites étant suffisantes pour alimenter des dispositifs à basse consommation, comme par exemple les capteurs sans fil. Une technologie innovante pour la récupération de l’énergie thermique est proposée, l’objectif étant de fabriquer des dispositifs fins, flexibles et bas coût pour une utilisation sans radiateur. Le fonctionnement choisi repose sur une conversion de la chaleur en électricité en deux étapes : thermomécanique (réalisée avec des bilames thermiques) et mécano-électrique (réalisée avec des piézoélectriques). Plusieurs prototypes ont été élaborés, aboutissant à des dispositifs matriciels flexibles, d’une épaisseur de quelques millimètres et fonctionnant sans radiateur avec refroidissement par convection naturelle. Les signaux générés sont des pics de tension qui dépassent les 10 V, pour une puissance mécanique disponible autour de 200 µW à 75°C. Plusieurs études ont été réalisées pour l'optimisation des dispositifs et la caractérisation de leurs composants. Leurs lois d’échelle ont été déduites, prédisant un gain en puissance avec la miniaturisation. Des modèles ont été proposés pour le comportement du piézoélectrique et pour le comportement thermique d’un dispositif. Les premiers cas d’usage ont été identifiés et les premiers tests ont été faits dans les environnements proposés par des potentiels utilisateurs. / The present work is a contribution to the domain of energy harvesting. The developed conversion is made at centimeter scale, and the generated electrical power is sufficient for low power devices, as for example wireless sensor nodes. An innovative technology for heat energy harvesting is proposed, with the goal to fabricate thin, flexible, and low cost devices for a use without a heat sink. Their working principle relies on a two-step conversion of heat into electricity: thermo-mechanical (with thermal bimetals) and mechanoelectrical (with piezoelectrics). Several prototypes have been built, resulting in flexible matrix devices that are a few millimeters thick and work without a heat sink with natural convection. The generated signals are voltage peaks above 10 V, for an available mechanical power in the order of 200 µW around 75°C. Several studies have been done for the optimization of the devices and the characterization of their components. Scale laws have been established, and predict significant power gain with miniaturization. Analytical models have been elaborated for the behavior of the piezoelectric and for the thermal behavior of a device. The first use cases have been identified, and the first tests have been performed in environments proposed by potential end users.

Le développement des systèmes de récupération d'énergie est liée à l'émergence des applications de type Internet des objets (IoT) plus spécifiquement à la prolifération des réseaux de capteurs autonomes. Les progrès réalisés ces dernières années dans le domaine des technologies de l’information et de la communication ont permis de lever certains verrous technologiques au développement de ces réseaux de capteurs intelligents et autonomes, notamment grâce à l’amélioration des performances intrinsèques des composants microélectroniques (vitesse, consommation), la conception de circuits plus économes en énergie, ou bien la mise en place de standards de communications radio adaptés à ces contraintes énergétiques. Etant donné l’ubiquité des sources d’énergie, la fabrication de générateurs permettant d’alimenter directement ces capteurs et les rendre autonomes en énergie à partir de ces sources représente une alternative viable à l’utilisation de batteries pour prolonger la durée de vie de ces capteurs communicants. Diverses technologies de générateurs ont ainsi été proposées pour s’adapter aux différentes formes que peut prendre l’énergie, qu’elle soit d’origine thermique, mécanique ou solaire. Le présent travail est une contribution à l'élaboration d’un récupérateur d’énergie thermique à base de bilames thermiques et de matériaux piézoélectriques. Ce type de générateurs, proposé et développé au sein de STMicroelectronics à Crolles, se veut être une alternative fiable et bas coût à l’utilisation de matériaux thermoélectriques exploitant l’effet Seebeck pour générer de l’énergie électrique. Des preuves de concept de tels systèmes ont déjà été développées aussi bien à macro-échelle qu’a micro-échelle. Ce travail s’inscrit dans la continuité du développement d’un récupérateur d’énergie macroscopique reposant sur ce principe-là. L’objectif de cette thèse est dans un premier temps d’optimiser cette structure pour atteindre des niveaux de puissances plus élevés que la première preuve de concept puis dans un second temps, de réaliser son intégration afin d’effectuer des démonstrations de capteur autonome et confirmer la viabilité de la technologie développée pour de telles applications. / The development of energy harvesting systems is linked to the emergence of the Internet of Things (IoT) more specifically to the proliferation of Wireless Sensor Networks that should respond to the growing needs for monitoring data in domains as diverse as the industry, the urban environments, the home or even the human body. Recent progress in the CMOS technology have enabled to remove some of the technical obstacles to the deployment of these smart and autonomous devices, specifically thanks to the improvements of the performances of microelectronic components, the design of ultra-low-power circuits and even the creation of wireless communication standards well adapted to the needs of wireless sensors. Given the availability of ambient energy sources like mechanical, thermal, light etc., energy harvesters are becoming reliable alternatives to batteries in order to extend the autonomy of these sensors. Consequently, various technologies of generators have been developed to harvest different kind of energies in function of their availability. The present work is a contribution to the development of a thermal energy harvester based on bimetallic strips heat engine and piezoelectric membranes. This type of technology developed by STMicroelectronics is intended to be a low cost alternative to thermoelectric generators exploiting the seebeck effect to convert heat into electricity. Based on this working principle, many harvesters both at the micro and macro scale have been fabricated. This thesis deals with the development of macroscopic energy harvesters whose first proofs of concept were established in a previous thesis. An important part of this manuscript deals with the thermal optimization of this energy harvester both in static and dynamic modes. Once the thermal properties improved, various piezoelectric materials were tested and compared to find the most adapted ones to our application and the same work is realized to choose the best device’s architecture. The integration of the energy harvester is then realized and wireless sensor node applications are demonstrated using various communication protocols and sensors. SPICE modeling of the system is also made and coupled with simulations of power management circuits developed by CEA’s design team. Finally, alternative ways to exploit wasted heat and vibrations are proposed through the development of piezoelectric bimetals and dual energy harvesters able to harvest thermal energy and mechanical energy at the same time: piezoelectric bimetals are realized either by direct deposition of piezoelectric composites or piezoelectric thin films onto bimetals. In the case of the dual energy harvester, piezoelectric cantilever beams were designed and simulated to vibrate at low frequencies (between 50Hz and 125Hz).

Dans le contexte de la valorisation de la biomasse par catalyse hétérogène, la chimie théorique est essentielle pour guider la détermination de la nature des sites actifs en combinaison avec des caractérisations expérimentales. Ensuite, le mécanisme de réaction peut être étudié pour déterminer l’état de transition et intermédiaire déterminant la vitesse et ensuite concevoir de meilleurs catalyseurs in silico. Nous avons mis en œuvre cette approche dans plusieurs réactions impliquant des alcools qui jouent un rôle clé dans le passage du pétrole à la biomasse comme source de matière première pour les produits chimiques de commodités ou spécialités. Tout d'abord, nous nous sommes concentrés sur l'oxydation des alcools en phase liquide par l'oxygène, une réaction qui nécessite généralement un environnement alcalin, ce qui nuit à l'économie d’atomes du processus car il génère le sel carboxylate au lieu de l'acide carboxylique. Nous avons proposé un modèle d'interface métal / eau basique incluant l'adsorption d'anion hydroxyde. Cet anion charge la surface métallique et modifie son activité catalytique. Ce modèle a tout d’abord été validé en comparant l’activité prédite de Au et de Pt en présence et en l’absence de base, puis a été utilisé pour étudier l’oxydation d’éthoxylates d’alcool par des bimétalliques. Ensuite, nous sommes passés à la déshydratation en phase gazeuse d’alcools en C3 et C4 en utilisant des catalyseurs à base de phosphate. La modélisation des surfaces s’est basée sur des caractérisations expérimentales. La couverture moléculaire de l'eau à la surface en fonction de la pression et de la température a été établie à l'aide de la thermodynamique ab initio. Les simulations de spectres infrarouges d'adsorption de CO, NH3 et C2H2 nous ont permis d'identifier les sites acido-basiques qui jouent un rôle important dans l'investigation du mécanisme de réaction qui a suivi. / In the context of biomass valorization by heterogeneous catalysis, computational chemistry is key to provide guidance to establish the nature of the active sites in combination with experimental characterizations. Then, the reaction mechanism can be studied to determine the rate determining transition state and intermediate and further design in silico better catalysts. We implemented this approach in several reactions involving alcohols that are key in the shift from a petroleum chemical feedstock to a biomass-based feedstock. Firstly, we focused on liquid phase alcohol oxidation by oxygen, a reaction that generally requires an alkaline environment, which is detrimental to the atom economy of the process since it generates the carboxylate salt instead of the carboxylic acid. We proposed a model of metal/basic water interface that includes the adsorption of hydroxide anion. It charges the metallic surface and modifies its catalytic activity. This model was first validated comparing the predicted activity of Au and Pt in presence and in absence of a base, and then used oxidation of alcohol ethoxylates by bimetals. Then, we switched to gas phase dehydration of C3 and C4 alcohols using phosphate-based catalysts. The modeling of the surfaces was based on experimental characterizations. The molecular coverage of water on the surface in function of the pressure and temperature was established using ab initio thermodynamic. The simulations of infrared spectra of CO, NH3 and C2H2 adsorption allowed us to identify the acido-basic sites which play an important role in the reaction mechanism investigation that followed.

Catalytic combustion is a promising combustion technology for gas turbines, which results in ultra low emission levels of nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (UHC). Due to the low temperature achieved in catalytic combustion almost no thermal NOx is formed. This thesis is concentrated on the first stage in a catalytic combustion chamber, i.e. the ignition catalyst. The catalyst used for this application is often a supported palladium based catalyst due to its excellent activity for methane combustion. However, this type of catalyst has a serious drawback; the methane conversion decreases severely with time during operation. The unstable activity will result in increasing difficulties to ignite the fuel. The parameters that govern the poor stability and other features of the palladium catalysts are discussed in the thesis. The objective of the work is to improve the catalytic performance of supported palladium catalysts, with focus on stabilising the methane conversion. A large number of different bimetallic palladium catalysts have been evaluated, where the influence of co-metals, molar ratio and support material is addressed. Results from the activity tests of methane combustion showed that it is possible to stabilise the activity by adding certain co-metals into the palladium catalyst. An extensive characterisation study has been carried out on the various bimetallic catalysts in order to gain a better understanding of how their morphology and physicochemical properties determine the various patterns of combustion behaviour. The environment inside a gas turbine combustor is very harsh for a catalyst. Since the stability of the catalyst is of great importance for ignition catalysts, it is essential to evaluate the risk of deactivation. In this work special emphasis has been given to thermal deactivation, water inhibition and sulphur poisoning. It was found that a bimetallic Pd Pt catalyst is significantly more tolerant to the various deactivation processes investigated than the monometallic palladium catalyst. Finally, the influence of pressure on the catalytic performance has been investigated. The catalysts were assessed at more realistic conditions for gas turbines, in a high-pressure test facility with 100 kW fuel power. / QC 20100916

<p>Catalytic combustion is a promising combustion technique in gas turbines, which results in ultra low levels of NO_x, CO and unburned hydrocarbons. Due to the low combustion temperature achieved in catalytic combustion almost no thermal NOx is formed. The focus in this thesis will be on the first stage in a catalytic combustion chamber, i.e. the ignition catalyst. The catalyst used for this application is often a supported palladium-based catalyst due to its excellent activity for methane combustion. However, this type of catalyst has a serious drawback; the methane conversion decreases with time during operation. The unstable activity will result in increasing difficulties to ignite the fuel. The objective of the work presented in this thesis has been to improve the catalytic performance of supported palladium catalysts, with focus on stabilizing the methane conversion.</p><p>The first part gives a general background to gas turbines and catalytic combustion.</p><p>The second part concerns the monometallic palladium catalysts; their behaviour during methane combustion is addressed.</p><p>The third part describes different bimetallic catalysts, which all have palladium as one of the active components. Results from the activity tests of methane combustion showed that it is possible to stabilize the activity by adding certain co-metals into the palladium catalyst. The morphology of the various bimetallic catalysts has been studied to gain a better understanding of the various combustion behaviours.</p><p>Finally, the influence of pressure on the catalytic performance is evaluated. The catalysts were tested under more realistic conditions for gas turbines, with elevated pressure, in a high-pressure test facility with a 100 kW fuel power.</p>