L’utilisation d’un composite Carbone/Carbone 2D est envisagée pour des pièces de structure, travaillant entre 150 et 400°C, dans l’aéronautique civile. Dans ce domaine de température, la durabilité de ces matériaux n’est pas connue car ils n’ont jamais été développés pour de telles applications. Une première approche a permis de corréler la réactivité chimique des constituants élémentaires (fibres et matrices) à leur état d’organisation structurale. Les vieillissements réalisés sur matériau composite ont ensuite mis en évidence qu’un faible taux d’oxydation pouvait conduire à un abaissement significatif des propriétés mécaniques résiduelles. Les fissures et les décohésions consécutives au procédé d’élaboration conduisent à une oxydation préférentielle du composé le plus réactif et à la ruine prématurée du composite par délaminage. L'évolution des propriétés de ce matériau sur de longues durées est finalement discutée afin d’évaluer sa capacité à remplacer les matériaux métalliques dans des pièces aéronautiques. / A 2D Carbon/Carbon composite is envisaged for structural parts, operating between 150 and 400°C, in civil aircraft. In this temperature range, the durability of these materials remains unknown because they have never been developed for this kind of applications. A first approach allowed us to correlate the chemical reactivity of the elemental constituents (fiber and matrix) to their structural organization. Then, thermal ageing tests performed on the composite material have demonstrated that a low rate of oxidation could be responsible to a significant reduction of residual mechanical properties. Cracks and fiber/matrix debonding resulting to the elaboration process create an extended pathway to a preferential oxidation of the most reactive compound. This latter is followed by a premature failure by delamination. The reduction of the material properties over long periods is finally discussed in order to evaluate its ability to replace metallic materials in aircraft structural parts.

To improve the understanding of aerosol composition, sources, and spatial and temporal variations, atmospheric aerosols were characterized in three locations. Ambient aerosols were characterized using 24-hour samples collected from Kathmandu, Nepal (urban), New Hampshire (semi-rural) and Houston (urban). Results are reported in the main chapters. Chamber studies of secondary organic aerosols (SOA) formation from polycyclic aromatic hydrocarbons (PAHs) and the effects of in-situ SOA formation on atmospheric mercury oxidation are described in the appendices. Carbonaceous, ionic, and isotopic species in aerosols from Kathmandu identified local primary emissions, most likely vehicular exhaust as the most important aerosol sources. Carbonaceous aerosols collected in Kathmandu (24.5 μg C m -3 ) were much larger than those in New Hampshire (3.74 μg C m -3 ) during winter. Stable carbon isotope in aerosols of Kathmandu and New Hampshire were similar (Δδ 13 C ∠ 0.5[per thousand]) while stable nitrogen isotope were much lower in aerosols of Kathmandu (Δδ 15 N = 8.3[per thousand]). Aerosols in New Hampshire exhibited a large seasonal variation for carbonaceous aerosols, stable nitrogen isotope, and the aromatic fraction of water-soluble organic carbon (WSOC). Pure aliphatics (H-C) were the dominant functional group in WSOC. Results illustrate the importance of secondary aerosol sources throughout the year, with enhanced importance of primary sources during winter. Stable carbon isotope values suggest a consistent isotopic signature of carbonaceous aerosol sources, while the nitrogen isotope values indicate the variable nitrogenous sources and the strong influence of meteorological parameters (temperature and relative humidity) on nitrogen isotope fractionation. Characteristics of methoxyphenols (lignin macropolymers) in the ambient aerosols are reported for the first time using CuO oxidation method. The study illustrates the use of lignin oxidation products (LOPs) in aerosols as potential tracers of primary biological aerosol particles (PBAP). The methoxyphenols identified soil organic matter and altered woody angiosperms, with minor influence from soft tissues and gymnosperms as the important PBAP sources in mainly coarse particles in Houston atmosphere. Solvent-extracted methoxyphenols (lignin monomers) and anhydrosugars (levoglucosan, mannosan, and galactosan) in aerosols were either absent or very small, suggesting very limited biomass burning influence with any trace-level presence originating from long-range transport.

Des complexes à base de palladium (II) ont été appliqués comme catalyseurs pour la réaction d’hydroestérification de l’isosorbide, matériau biosourcé, avec le 1-octène. Dans un premier temps, l’utilisation de liquides ioniques standards a permis l’immobilisation du catalyseur (palladium + phosphine) et la conversion du 1-octène. L’activité catalytique est dépendante de la nature du liquide ionique. Le liquide ionique sulfoné bSmimAPTS a permis l’obtention de conversions élevées, avec des rendements en diesters importants sur trois cycles catalytiques tout en s’affranchissant de l’emploi d’acide paratoluènesulfonique. Le catalyseur (palladium + phosphine sulfonée) est immobilisé dans la phase liquide ionique. La régiosélectivité de la réaction peut être modifiée (85/15 contre 75/25 dans les conditions classiques) avec le remplacement de la TPPTS par une phosphine bidentate sulfonée (XANTPHOS sulfonée). Un système constitué de Pd(OAc)2/APTS/NBu4Br s’est également montré très efficace dans la conversion du 1-octène en diester d’isosorbide mais n’est pas très stable dans le temps (recyclé à deux reprises). Dans un second temps, l’utilisation de charbons actifs commerciaux a permis d’immobiliser le métal (après filtration à froid) tout en conservant une activité catalytique élevée. Il est possible de convertir le 1-octène en substituant l’APTS par un matériau carboné sulfoné (obtenu par voie hydrothermale en une étape entre le saccharose et l’acide sulfurique). Les synthèses, caractérisations et applications d’un matériau carboné nanorépliqué sulfoné de type CMK-3 ont été considérées. Le matériau carboné sulfoné (MC-NR-saccharose-500-SO3H) a permis l’obtention de conversions et de rendements en diesters élevés, avec une sélectivité en large faveur de l’isomère linéaire (rapport l/b=92/8). Une extension à été étudiée avec la synthèse d’un matériau hybride sulfoné (MCSi 10.4-SO3H) et a également conduit à une activité catalytique élevée avec une sélectivité importante en isomère linéaire (rapport l/b=92/8). Des tests avec des matériaux acides contrôles (résine commerciale sulfonée et silice sulfonée) ont été réalisés. / Complex based on palladium salt (II) were applied as catalysts for the hydroesterification of isosorbide, a biobased molecule, with 1-octen. First, the use of standard ionic liquids permits the immobilization of the catalyst (palladium + phosphine) and the conversion of 1-octen. The catalytic activity is dependent on the nature of the ionic liquid. The sulfonated ionic liquid bSmimAPTS permit the obtention of high conversions, with important yield in diester during three catalytic cycles, and avoid the use of paratoluenesulfonic acid. The catalyst (palladium + sulfonated phopshine) is immobilized in the ionic liquid phase. The regioselctivity of the reaction can be changed with the replacement of the TPPTS by a sulfonated bidentate phosphine (XANTPHOS, l/b ratio= 85/15 against 75/25 in classical condition). A system containing Pd(OAc)2/APTS/NBu4Br proved also highly effective in the conversion of 1-octen but it was not very stable over time (recycled just two times). Secondly, the use of commercial activated carbons has immobilized the palladium after cold filtration while maintaining high catalytic activity. It’s possible to convert the 1-octen using a sulfonted carbonaceous material (obtained by hydrothermally condition in one step between sucrose en sulfuric acid). Synthesis, characterization and applications of a sulfonated nanoreplicated carbonaceous material, as CMK-3, were considered. This one (MC-NR-saccharose-500(SO3H) permit the obtention of high conversions and high yields of diesters, with a selectivity in favor of the linear isomer (l/b ratio= 92/8). An extension was studied with the synthesis of a sulfonated hybrid material (MCSi 10.4-SO3H) and also results in high conversion and high selectivity in linear isomer (l/b ratio= 92/8). Tests with acidics materials controls (sulfonated commercial resin and sulfonated silica) were performed.

Les serpentines riches en fer sont des composants majeurs des chondrites CM. Formées au cours d'épisodes d'altération hydrothermale sur leur corps parent astéroïdal, à une étape précoce de la formation du Système Solaire, elles peuvent constituer un proxy des conditions d'altération de ces roches et permettre de mieux comprendre l'évolution à long terme des colis de stockage des déchets nucléaires, car ces processus sont considérés comme un bon analogue des interactions fer-argiles-eau. Pendant cette thèse, nous nous sommes intéressés aux conditions de formation et d'équilibre des ces minéraux, en prêtant une attention particulière à l'évolution de la valence du fer pendant l'altération. Trois approches sont présentées : la synthèse de Fe-serpentines, l'altération expérimentale d'assemblages chondritiques à basse température, en milieu anoxique, et l'affinement d'un modèle thermodynamique incluant des serpentines de composition Fe2+-Fe3+-Mg-Al-Si-O-H. Le modèle thermodynamique, basé sur des données expérimentales, devrait permettre de mieux prédire les assemblages à l'équilibre dans les chondrites altérées. Nos expériences de synthèses suggèrent que la précipitation de phases de composition proche du pôle pur cronstedtite est contrôlée cinétiquement. Aux premiers stades de l'altération expérimentale de minéraux primaires anhydres, nous avons observé la formation de phases peu cristallines avec une proportion relativement faible de fer ferrique. Nos résultats suggèrent que le rapport Fe/Si et la teneur en Fe3+ favorisent la précipitation des serpentines. Ils apportent un éclairage intéressant aux premiers stades d'altération dans les chondrites carbonées. / Iron-rich serpentines are major components of CM carbonaceous chondrites. They formed during early alteration events on their asteroidal parent bodies at an early stage of formation of the Solar System. The study of these minerals aims at better understanding the conditions in which they altered, but it would also help understanding the long term evolution of nuclear waste storage. Indeed, aqueous alteration in chondrites is considered as a good analog for iron-clay-water interactions. During this thesis, we studied the conditions of formation and stability of Fe-rich serpentines, and we paid particular attention to the evolution of the Fe valence state during alteration. Three approaches have been adopted : the synthesis of Fe-rich serpentines, the experimental alteration of chondritic assemblages at low temperature and under anoxygenic conditions, and the refinement of a themodynamic model of serpentines in the Fe2+-Fe3+-Mg-Al-Si-O-H system. This model, mostly refined using data from iron-clay experiments, gave encouraging results, and should allow to better predict equilibrium assemblages in altered chondrites. Out of equilibium processes were also experimentally explored, and our results suggest that there is a kinetic control of the precipitation of Fe-rich serpentines close to the ideal end-member. At the first stages of alteration of primary minerals under anoxic conditions, we observed poorly crystalline phases with a relatively low ferric iron content. Our result suggest that the Fe/Si ratio and the Fe3+ content favor the precipitation of serpentines. They provide interesting insight into the first stages of alteration in chondrites.

Polymer brush patterns were prepared by a combination of electron beam induced damage in self-assembled monolayers (SAMs), creating a stable carbonaceous deposit, and consecutive self-initiated photografting and photopolymerization (SIPGP). This newly applied technique, reactive writing (RW), is investigated with 1H,1H,2H,2H-perfluorooctyltriethoxysilane SAM (PF-SAM) on silicon oxide, which, when modified by RW, can be selectively functionalized by SIPGP. With the monomer N,N-dimethylaminoethyl methacrylate (DMAEMA), we demonstrate the straightforward formation of polymer brush gradients and single polymer lines of sub-100 nm lateral dimensions, with high contrast to the PF-SAM background. The lithography parameters acceleration voltage, irradiation dose, beam current and dwell time were systematically varied to identify the optimal conditions for the maximum conversion of the SAM into a carbonaceous deposit. The results of this approach were compared to patterns prepared by carbon templating (CT) under analogous conditions, revealing a dwell time dependency, which differs from earlier reports. This new technique expands the range of CT by giving the opportunity to not only vary the chemistry of the created polymer patterns with monomer choice but also vary the chemistry of the surrounding substrate.

<p>Space weathering refers to the gradual spectral, microstructural, and chemical alteration of airless planetary regoliths due to their exposure to the harsh environment of outer space. Solar wind irradiation and micrometeoroid impacts are the primary space weathering processes at work in our solar system. Although the microstructural and compositional effects of space weathering are small, occurring at the sub-micron scale in individual regolith grains, their collective impact on the spectral signature of planetary surfaces is critical. Space weathering is known to change the slope, albedo, and strength of absorption band features of reflectance spectra acquired by ground- and spacecraft-based instrumentation. In this way, space weathering impedes our ability to determine planetary surface compositions from remote sensing data and pair meteorites with their parent bodies. Thanks to decades of research since the Apollo sample return missions, the planetary science community has developed a comprehensive understanding of how space weathering alters the Moon and silicate-rich asteroids. However, the effects of space weathering on primitive, carbon-rich asteroids—which dominate the outer main belt—are more poorly constrained and very complex. This dissertation aims to improve our understanding of how solar wind irradiation and micrometeoroid bombardment modifies the spectral, microstructural, and chemical properties of carbonaceous asteroidal regoliths. To accomplish this goal, this research experimentally simulates constituent space weathering processes in the laboratory on carbon-rich analog materials. A multi-faceted analytical approach including a variety of electron microscopy and spectroscopic techniques is used to probe the spectral, microstructural, and chemical changes induced by experimental space weathering.</p><p>Chapter 1 of this dissertation provides an introduction to space weathering, including a description of the current state of knowledge in the field as well as the motivation for this research. Similarly, chapter 2 provides an overview of the various experimental simulations and coordinated analytical techniques employed in this work. Chapter 3 initiates the discussion of research accomplished during this doctoral program, presenting a detailed characterization of the spectral, microstructural, and chemical effects derived from simulated solar wind irradiation of a carbonaceous asteroid analog material. More specifically, in chapter 1, I perform high flux (~1013 ions/cm2/s), high fluence (1018 ions/cm2) 1 keV H+ and 4 keV He+ irradiation experiments on the Murchison meteorite. Chapter 2 investigates the role of incident ion flux in solar wind space weathering of carbonaceous asteroidal regolith by performing a set of low flux (~1011 ions/cm2/s) and high flux (~1013 ions/cm2/s) H+ and He+ irradiation experiments on Murchison samples. These experiments are the lowest flux solar wind simulations carried out, to date. Finally, chapter 5 presents results from the first <i>combined</i> ion irradiation and heating experiments performed on a carbon-rich analog using in situ transmission electron microscopy (TEM). In situ TEM is a relatively novel technique in the planetary and geological sciences which allows users to observe the physiochemical changes caused by an external stimuli in <i>real time</i>. The experimental approach used in chapter 5 simulates both solar wind irradiation and micrometeoroid impacts, and, thus, probes the cumulative microstructural and compositional modifications induced by these concurrent space weathering processes. In chapters 3 through 5, I compare my results to previous space weathering simulations and observations of lunar and asteroidal returned samples. Findings from this dissertation advance the existing model of space weathering on carbon-rich asteroids, help inform remote sensing observations from the Hayabusa2 and OSIRIS-REx missions which have rendezvoused with C-complex asteroids Bennu and Ryugu, respectively, and provide experimental ground-truth for analyzing returned samples from these missions.</p>

No description available.

<p>The class of meteorites called carbonaceous chondrites are examples of material from the solar system which have been relatively unchanged from the time of their initial formation. We investigate the carbonaceous chondrite subclasses CI, CM, CR, CV, and CO, which contain high levels of water and organic material, including amino acids. These subclasses span petrologic types 1 through 3, indicating the degree of internal chemistry undergone by the meteoritic parent body. The goal of this thesis is two-fold: to obtain a comprehensive view of amino acid abundances and relative frequencies in carbonaceous chondrites, and to recreate these patterns via thermodynamic computational models.</p> <p>We collate available amino acid abundance data for a variety of meteorites to identify patterns in total abundance and relative frequencies. We consider only a set of 20 proteinogenic alpha-amino acids created via a specific chemical pathway called Strecker synthesis. We plot abundances of individual amino acids for each subclass, as well as total abundances across all subclasses. We see a predominance in abundance and variety of amino acids in the CM and CR subclasses, which contain concentrations of amino acids greater by several orders of magnitude than other carbonaceous subclasses. These subclasses correspond to an aqueous alteration temperature range of 200 deg. C to 400 deg. C. Within the CM2 and CR2 meteorites, we identify trends in the relative frequencies of amino acids in preparation for computational modeling.</p> <p>Now having a baseline observed amino acid abundance plot, we recreate both the total amino acid abundance pattern as well as the relative frequency of amino acids within the CM2 chondrite subclass using computational models. We use thermodynamic theory of Gibbs free energies to calculate the output of amino acids in a meteoritic parent body assuming chemical equilibrium and some set of initial concentrations of organic material. Our model recreates abundance patterns in the temperature range 200 deg. C to 400 deg. C, ~10⁵ parts-per billion (ppb), and the temperature range 400 deg. C to 500 deg. C, ~10² ppb. Our model does not fit well between temperatures of 150 deg. C to 200 deg. C. Our current model assumes a uniform composition of initial chemical reactants; likely an inhomogeneous composition would be a more accurate physical representation of a parent body. In addition, we match relative frequencies to observed frequencies for each amino acid in the CM2 subclass to well within an order of magnitude.</p> / Master of Science (MSc)

Ce manuscrit est consacré à l’étude et au développement de microsystèmes capteurs de gaz sélectifs au dioxyde d’azote, destinés au contrôle de la qualité de l’air atmosphérique. La stratégie que nous avons développée consiste à associer une structure sensible à base de matériaux semi-conducteurs partiellement sélectifs aux gaz oxydants et des filtres sélectifs à l’ozone. L’objectif premier est la mise en oeuvre et la caractérisation de matériaux chimiques strictement imperméables à l’ozone (O3) et non-réactifs vis-à-vis du dioxyde d’azote (NO2). Notre choix s’est focalisé sur un matériau moléculaire, l’indigo, connu pour sa réactivité vis-à-vis de O3, et plusieurs nanomatériaux carbonés. Pour ces derniers, la possibilité de conformer leurs textures, leurs morphologies et leurs chimies de surface par traitements thermiques, chimiques et mécaniques, permet d’étendre le panel de matériaux potentiels et d’identifier les facteurs d’influence de leur réactivité avec les espèces gazeuses. La caractérisation de l’ensemble de ces matériaux a nécessité l’utilisation de techniques adaptées et complémentaires (adsorption de N2 à 77 K, spectroscopies Raman, XPS, IR en mode ATR, RPE et NEXAFS). Les filtres chimiques les plus efficaces (hauts rendements de filtration et grande durabilité) ont été sélectionnés d’après des tests de soumission aux gaz selon une méthodologie adaptée. Enfin, l’association de ces meilleurs filtres et de la structure capteur a conduit à l’élaboration de prototypes microsystèmes capteurs de gaz optimisés. De plus, une contribution à la compréhension des mécanismes d’interaction de l’indigo et de certains nanocarbones avec O3 et NO2 a aussi permis d’améliorer le microsystème en développant des méthodologies pertinentes et innovantes mais également en réalisant la synthèse de nouveaux filtres indigo / nanocarbone. / This work is devoted to the study and the development of gas sensors microsystems highly selective to nitrogen dioxide, dedicated to the air quality control. The strategy developed consists in the implementation of a sensitive structure based on semiconductor materials partially selective to oxidizing gases associated to an ozone selective filter. The first objective is the development of chemical filters strictly impervious to ozone (O3) and non-reactive towards the nitrogen dioxide (NO2). We have chosen a molecular material, indigo, well-known for its reactivity towards O3, and several carbonaceous nanomaterials. For these one, the possibility to modify their textures, their morphologies and their surface chemistries by chemical, mechanical and thermic treatments, enables us to extend the range of potential materials and to identify the factors of influence on their reactivity with gaseous species. The characterization of all these materials required the use of appropriate and complementary techniques (N2 adsorption at 77 K, Raman, XPS, IR in ATR mode, EPR and NEXAFS). The more efficient filters (high filtering yield and life-time) have been selected by means of specific tests of gas exposure. Finally, the association of the best filter and the sensitive structure has led to the development of optimized gas sensors microsystems prototypes.

Une nouvelle méthode de haute précision pour analyser les isotopes de Sn à avec double-spike 117Sn-122Sn a été développée. / A new high-precision isotope method for analyzing Sn using the 117Sn-122Sn double-spike technique was developed.