Compte tenu de leur bioactivité et de leur ostéoconduction, les revêtements d’hydroxyapatite (HA) favorisent le développement de tissu osseux et contribuent à l’adhérence et à la prolifération des cellules osseuses tout en préservant l’intégrité mécanique du dispositif métallique de l’implant. Toutefois, des signes de résorption de cette couche ont été constatés et l’introduction du procédé de projection plasma pour la réalisation de dépôts d’HA a donné lieu à plusieurs controverses. Certaines études ont montré que les dépôts d’HA par projection plasma présentent une mauvaise adhérence sur le titane, une dégradation et écaillage avec le temps. Ce phénomène est attribuable à la décomposition de l'HA au cours de la projection et à l'existence de phases secondaires cristallisées ou amorphes qui fragilisent le dépôt. A l’heure actuelle, les recherches de nouvelles apatites thermiquement plus stables se développent. Ainsi des dépôts à base de fluorapatite ou de fluorhydroxyapatite fournissent des dépôts plus stables et plus adhérents. Il existe d’autres formes d’apatites comme la chlorapatite (ClA) qui fond sans se décomposer ce qui permettrait d’éviter la formation des phases étrangères qui provoquent l’écaillage du dépôt. Ce travail porte sur la synthèse et la caractérisation de phosphates de calcium apatitiques destinés au recouvrement de prothèses ostéoarticulaires et/ou d’implants dentaires métalliques. L’élaboration des poudres d’apatite a été réalisée par réaction solide-solide, en solution aqueuse ou en sel fondu. Plusieurs apatites ont été étudiées : la fluorapatite, la fluorhydroxyapatite, la chlorapatite et l’apatite calcostrontique. On obtient des poudres pures, bien cristallisées et stoechiométriques. Nous avons ensuite étudié la stabilité thermique des poudres d’apatite par analyse thermogravimétrique. La stabilité thermique de la ClA et sa fusion sans décomposition permettent d’obtenir des dépôts sans phases secondaires avec un taux de cristallinité élevé. Parmi toutes les poudres étudiées, nous avons choisi de sélectionner la chlorapatite pour la suite de l’étude ainsi que l’hydroxyapatite comme référence. La poudre de ClA est déposée sur un substrat en titane via une mini-torche plasma mobile à basse énergie, conçue pour les implants dentaires ou orthopédiques de petites tailles et de géométries complexes. La projection par la mini-torche plasma permet de réaliser des dépôts fins et adhérents. Les propriétés structurales et microstructurales des dépôts de ClA et d’HA effectués dans les mêmes conditions ont été évaluées par diffraction des rayons X, spectroscopies FTIR et Raman. L’analyse des revêtements de ClA et d’HA par diffraction des rayons X atteste de la présence d’une seule phase cristalline. Néanmoins, le rapport de cristallinité des dépôts de ClA est largement supérieur à celui des dépôts d’HA, pour lesquels le rapport de cristallinité est supérieur à la norme requise. Ce résultat est du à la stabilité thermique de la ClA par rapport à l’HA. Les spectroscopies FTIR et Raman montrent la présence d’un faible taux de phase amorphe et d’oxyapatite. Nous avons également développé une nouvelle méthode semi-quantitative par cartographie Raman permettant de déterminer l’homogéneité de composition du dépôt. Enfin, nous avons montré que l’adhérence des dépôts de ClA au substrat déterminée suivant la norme ASTM C633 est équivalente à celle de l’HA. La réponse biologique des dépôts a été étudiée in vitro avec des cellules pré-ostéoblastes humaines sur les deux compositions ClA et HA. Les tests montrent que quelle que soit la composition du dépôt, la prolifération cellulaire augmente au cours du temps d’incubation. Une étude in vivo a été menée sur un modèle animal ovin en site fémur et humérus pour des durées de 2 et 6 mois afin d’évaluer le potentiel ostéoconducteur des dépôts d’HA et de ClA. Aucune réaction inflammatoire n’a été observée et l’interprétation des résultats d’analyses histologiques et physico-chimiques est en cours. / Plasma-sprayed hydroxyapatite (HA) has been shown to enhance bone apposition as compared with uncoated metal implants. In spite of their good clinical performances, implant bio-integration is still limited due to the poor adhesion of HA-coating on the titanium surface and the decomposition of HA into several foreign phases during plasma spray. The plasmaspray process was thus considered not to be optimum for HA coatings. To circumvent these disadvantages, other types of calcium phosphates have been proposed to replace HA, such as tricalcium phosphate or biphasic calcium phosphate with little improvement. Chlorapatite (ClA) however has never been tested despite its ability to melt without decomposition which could be a decisive advantage to avoid apatite decomposition and could increase coating crystallinity. This work concern the synthesis and the characterization of apatitic calcium phosphate as coating for endoprostheses and dental implants. The syntheses of the different apatite powders were performed by solid-solid reaction, in aqueous solution or by molten salt reaction. Several apatites were studied: fluorapatite, fluorhydroxyapatite, chlorapatite and strontium substituted apatite. The as-synthesized powders are pure, well crystallized and stoechiometric. The thermal properties of apatite powders were compared using thermogravimetric analysis. The thermal stability of ClA and its melting without decomposition allows to obtain deposits with no secondary phases and with a degree of crystallinity close to 100 %. We have therefore chosen ClA and HA as feedstock powders to achieve coatings. The as-synthesized ClA powder was deposited on a titanium substrate using a novel low energy plasma mini-gun characterized by a low power range (<13 kW) and portability allowing in-situ coating deposition designed for dental and orthopedic small implants with complex geometry. The plasma spray with the mini-gun gives thin and adherent coatings. It also provides economic benefits such as low energy and a higher yield of feedstock powder than conventional gun. The structural and microstructural properties of ClA and HA coatings performed under the same conditions were evaluated by X-ray diffraction, Raman and infrared spectroscopy. X-ray diffraction analyses on the ClA and HA coatings indicate the presence of crystalline apatite as the only crystalline phase. However, the crystallinity ratio of ClA coatings was much higher than that of HA coatings but superior to the required standard in both cases. This difference is due to the thermal stability of ClA powder. IR and Raman spectroscopy shows the presence of low levels of amorphous phase and oxyapatite. We have also developed a new semiquantitative method by Raman imaging in order to determine coating homogeneity. The mechanical properties of coatings were determined according to the standard test measurements ASTM C633. The adhesion of ClA coatings to the substrate is equivalent to HA coatings. The biological response of the coatings was studied in vitro with human preosteoblast cells on both ClA and HA coatings. Tests show that wathever the composition of coating, cell proliferation increases with time of incubation. The in vivo osteoconductive properties of coatings were studied in femur and humerus sites of an ovine animal model during 2 and 6 months. No inflammatory reaction has been observed and the interpretation of histological and physico-chemical results is in progress.

The aim of this work was to develop a solid knowledge on formulation effects controlling offset ink-paper coating adhesion and to identify key factors of the coating and printing process affecting it. Focus lay on comprehending the impact of pigment dispersant on ink-paper coating adhesion and ultimately on the print quality of offset prints. The work covers laboratory studies, a pilot coating trial designed to produce coated material with a span in surface chemistry and structure, and an industrial offset printing trial. The lab scale studies quantified ink-paper coating adhesion failure during ink setting with a developed laboratory procedure based on the Ink-Surface Interaction Tester (ISIT) and image analysis. Additional polyacrylate dispersant resulted in slower ink setting and reduced ink-paper coating adhesion, with a dependence on its state of salt neutralisation and cation exchange, mainly in the presence of moisture/liquid water. The industrial printing trial on pilot coated papers was designed to study how these laboratory findings affected full scale offset print quality. These trials confirmed the dispersant-sensitive effect on ink-paper coating adhesion, especially at high water feeds. Evaluation of prints from the printing trial resulted in two fundamentally different types of ink adhesion failure being identified. The first type being traditional ink refusal, and the second type being a novel mechanism referred to as ink-lift-off adhesion failure. Ink-lift-off adhesion failure occurs when ink is initially deposited on the paper but then lifted off in a subsequent print unit. In this work, ink adhesion failure by this ink-lift-off mechanism was observed to occur more often than failure due to ink refusal. Print quality evaluation of the industrial prints suggested that water induced mottle was caused by a combination of ink-surface adhesion failure, creating white spots on the print, together with variation in ink layer thickness due to emulsified ink. / <p>QC 20161019</p>

Le vaporeformage du méthane (SMR) est encore aujourd’hui la méthode industrielle de synthèse d’hydrogène la plus rentable. L’efficacité globale de ce procédé est cependant limitée par les contraintes techniques intrinsèques au design des unités de production actuelles. Dans un souci constant d’intensification des procédés, des échangeurs-réacteurs intensifiés sont à l’étude chez AIR LIQUIDE. Les progrès dans le domaine des techniques de fabrication additive métallique ont permis d’envisager des unités de production sous formes d’équipements compacts, présentant des canaux millimétriques, qui optimisent les transferts de masse et de chaleur. Pour atteindre des taux de conversion élevés, et ce malgré des temps de contacts réduits, ces structures obligent à développer de nouvelles architectures de catalyseurs. Des phases actives supportées stables et très actives pour la réaction SMR à base de rhodium ont été préparés à partir de supports MgAl2O4 commerciaux. L’étude de l’impact du taux de métal noble, des propriétés des supports, ainsi que des traitements thermiques a permis de comprendre les interactions existantes entre les phases actives et les supports oxydes. Les propriétés catalytiques en condition de reformage ont pu être reliées aux morphologies des phases actives synthétisées. La fonctionnalisation des canaux des échangeurs-réacteurs millistructurés par une méthode proche du dip-coating est détaillée dans cette thèse. Des formulations de suspensions adaptées, aux comportements rhéologiques maîtrisés, ont permis avec des protocoles de dépôt adéquats, de rendre fonctionnel des échangeurs-réacteurs de taille semi-industrielle qui ont été testés avec succès durant plusieurs centaines d’heures. / The Steam Methane Reforming (SMR) process is still today the most profitable industrial synthesis process of hydrogen. The efficiency of this technique is however facing intrinsically technical limitations due to the design of production units. In order to intensify the global process, exchangers-reactors are under investigation at AIR LIQUIDE. Thanks to recent progresses in metallic additive manufacturing, new compact equipment can be designed. Structures made of millimetric channels allow optimizing heat and mass transfers. New catalyst architecture design needs to be developed to reach high conversion rates despite extreme low contact times in such devices. Stable and highly active rhodium-based catalysts supported on spinel MgAl2O4 have been prepared in this aim. The impact of rhodium loading, properties of supports, as well as thermal treatments have allowed us understanding active phase and support interactions. Catalyst properties under SMR conditions have been linked to active phase morphologies. Functionalization of exchangers-reactors channels through a dip-coating technique has been detailed in this thesis. The formulations of suspensions of washcoat have been optimized thanks to rheological behavior characterizations to achieve very low viscosities. A procedure to deposit homogeneous coatings with controlled thicknesses on the internal channels has been validated on a pilot structure. These new intensified exchangers-reactors have been successfully tested for methane conversion during several hundred of hours.

O demorado tratamento térmico, comum no preparo de fotocatalisadores e sua imobilização em substratos, foi contornado nesta tese, em que se investigaram duas estratégias de modificação de eletrodos de ouro com TiO2 P25. A primeira consiste em promover a formação de uma nanocamada pela simples exposição do metal por 1 min à suspensão aquosa de TiO2 (10 g L-1 em HCl 0,1 mol L-1); na segunda, deposita-se uma pequena alíquota (5 ou 8 &#181;L) da suspensão diretamente no substrato (drop coating) para secá-lo em seguida por irradiação com lâmpada incandescente (60 W a 20 cm), obtendo-se bons resultados de uma a três camadas depositadas. Comprovou-se grande aumento da estabilidade da suspensão aquosa e duplicação da atividade fotocatalítica do nanofilme de TiO2 em decorrência da repulverização de P25 comercial em almofariz, melhoria inalcançável por sonicação da suspensão. O tamanho de partícula médio obtido por DLS para o TiO2 disperso em meio de HCl 0,1 mol L-1 atingiu 103±3 nm, enquanto que o filme depositado na superfície do ouro (observado por MEV e caracterizado por EDS) não ultrapassou 100 nm de espessura, sendo dominado por partículas de diâmetro de 20 (anatase) a 30 nm (rutilo), observadas por MET. A estabilidade da suspensão é susceptível ao ânion do ácido utilizado, sendo que resultados igualmente satisfatórios foram obtidos com HCl e HclO4 0,1 mol L-1, enquanto que para a mesma concentração de H2SO4 o TiO2 sofreu sedimentação rápida e o eletrodo preparado com a suspensão apresentou fotoatividade 10x menor. Filmes de espessuras bastante distintas (100 nm e 2 m) depositados a partir de suspensão 10 g L-1 por contato e drop coating com gota de 5,0 &#181;L, respectivamente, foram comparados em relação à sua capacidade de transporte de elétrons e resposta eletroquímica ao Fe(CN)6 3 1,0 mmol L-1, sendo que a carga líquida formal de oxidação do EDTA 1,0 mmol L-1 é apenas 50 % maior para o filme 20x mais espesso, além de gerar distorções consideráveis nas ondas voltamétricas do sistema-sonda reversível em relação ao filme nanométrico e à superfície polida. Com eletrodos modificados pelo protocolo otimizado de drop coating (8,0 &#181;L de TiO2 2 g L-1), testou-se o efeito da presença de diferentes eletrólitos de suporte (ácidos 0,1 mol L-1) em processos anódicos de fotooxidação em geral. A curva de decaimento da fotocorrente iph com o tempo pode ser descrita por uma equação de decaimento exponencial duplo iph = i0 + A1 exp(k1t) + A2 exp( k21t), permitindo distinguir as contribuições da fotocorrente de oxidação da água (i0) e de termos referentes a dois tipos de sítio superficiais, sendo um de cinética rápida e outro de cinética lenta. A seguinte ordem foi determinada para a fotocorrente total inicial (iph0 total) dos eletrólitos: HNO3 > HClO4 > HCl > H1SO4 > H3PO4 e as explicações propostas para tal se embasam na adsortividade dos ânions no TiO2 e na reatividade dos respectivos traps formados. O mesmo modelo de ajuste matemático foi utilizado para avaliar a fotoatividade do eletrodo modificado pela sua irradiação sucessiva e repetida em HNO3 0,1 mol L-1 (sem EDTA), sendo observada redução significativa principalmente nos parâmetros relativos aos sítios de reação e, assim, sugere-se um impedimento dos mesmos através, p. ex., da formação de peróxidos superficiais. Na presença também de EDTA, a carga líquida total despendida na sua fotooxidação se mantém relativamente constante nas sucessivas irradiações. Por fim, os experimentos de fotooxidação do EDTA sob varredura de potencial revelaram uma região de relação linear entre a fotocorrente e o potencial aplicado ao eletrodo modificado com TiO2 que se estende até a região de saturação de fotocorrente ser atingida, comportamento compatível com filmes nanoparticulados porosos não-dopados. A inclinação da região linear aumenta em função da [EDTA], como se os valores de condutância (di/dE) se elevassem dependendo da reação interfacial. Ajuste de modelo matemático hiperbólico correlacionando a (foto)resistência do filme em função da fotocorrente de saturação R = R0 + kIsph1, fornece resistência ôhmica do filme R0 de 5,0 k&#937; e uma constante atrelada ao fotopotencial de 237 mA &#937;. Já a curva monotônica de fotocorrente de saturação (Isph) com a [EDTA] apresenta comportamento linear até cerca de 0,7 mmol L-1, sugerindo-se que nessa região o controle por transporte de massa é a etapa limitante do processo global. Acima dessa concentração o coeficiente angular diminui gradualmente à medida que a reação de cinética de captura das lacunas passa a ser o determinante até um limite máximo (aparentemente 5,0 mmol L-1 de EDTA, nas condições do experimento) onde a disponibilidade de lacunas fotogeradas passa a governar. / The lengthy thermal treatment is a common step during the preparation and immobilization of photocatalysers on substrates, which by the way, was overcome in this thesis by the investigation of two strategies of modification of gold electrodes with P25 TiO2. The first one consists in promoting the formation of a nanolayer by the simple exposure of the metal surface to an aqueous suspension of TiO2 (10 g L-1 on 0.1 mol L-1 HCl) during 1 min; the second involves the deposition of a small drop (5 or 8 L) of the suspension on the gold substrate (drop coating) and its drying by irradiation with an incandescent lamp (60 W at 20 cm far), with worthy results also for two or three deposited layers. The stability of this aqueous suspension was appreciably improved by the repulverization of commercial P25 in a grinding mortar. As a consequence the photocatalytic activity conferred to the electrode by the formation of the TiO2 nanofilm doubled. Such improvements cannot be attained by bath sonication of the suspension. The average particle size determined by DLS for the TiO2 dispersed in 0.1 mol L-1 HCl was 103±3 nm, while the film deposited on the surface of gold consisted of particles of 20 nmn (anatase) and 30 nm (rutile) characterized by TEM and barely achieved a thickness of 100 nm (characterized by SEM and EDS). The stability of the modifying suspension is susceptible to the type of anion of the electrolyte. Good results were found with 0.1 mol L-1 HCl and HClO4, but not with 0.1 mol L-1 H2SO4. This last medium causes fast sedimentation of TiO2 and generates electrodes with one tenth of the photoactivity achieved with the other acids. The effect of film thickness on the photoactivity was evaluated for films with 100 nm and 2.0 &#181;m prepared from a 10 g L-1 TiO2 suspension by the contact and drop coating (5 &#181;L) strategies, respectively. The electron transport across both films and the electrochemical response for the 1.0 mmol L-1 Fe(CN) 63- probe was compared. The formal net charge for the 1.0 mmol L-1 EDTA oxidation was only 50 % higher for the 20x thicker film that also considerably distorts the voltammetric waves of the aforementioned reversible probe. The effect of different supporting electrolytes (0.1 mol L-1 acids) on the anodic photooxidation processes in general was tested with electrodes modified by an optimized drop coating protocol (8.0 &#181;L of 2 &#181;g L-1 TiO2). The curve describing the photocurrent decay in function of time might be ascribed to an equation of double exponential decay iph = i0 + A1 exp(k1t) + A2 exp (k2t), which allows the distinction of the contribution of water oxidation (i0) from terms of two types of surface sites: a kinetically fast site and a slow one. The total initial photocurrent (iph0 total) of the following electrolytes decays in the order: HNO3 > HClO4 > HCl > H2SO4 > H3PO4; explanations comprise the adsorbability of each respective anion on TiO2 and the reactivity of the corresponding traps formed. Similar curve fitting applied to the data of photoactivity of the gold electrode during successive irradiations of its surface in 0.1 mol L-1 HNO3 (absence of EDTA) revealed that sites reactivities underwent considerable reduction. It is suggested that during repetitive experiments the sites are impaired by the formation of surface peroxides. However, in the presence of 1.0 mmol L-1 of EDTA, the formal net charge of oxidation of the organic species remains almost unaltered. Ultimately, the experiments concerning the photooxidation of EDTA under linear potential scan revealed a region of linear relation between the photocurrent and the potential applied to the electrode modified with a TiO2 film (nanometric or micrometric), which holds until the saturation photocurrent is attained. This behavior is typical for porous non-doped nanoparticulate electrodes. The slope of the linear region increase somewhat with the EDTA concentration, as though the conductance values (di/dE) were raised depending on the interfacial reaction rate. The fitting of a hyperbolic model R = R0 + kIsph-1 for the correlation of the (photo)resistence (R) of the film with the photocurrent of saturation (Isph) allows the estimation of an ohmic resistance of 5.0 k&#937;, and a photopotential related constant of 237 mA &#937;. The curve of correlation between Isph and the [EDTA] is linear fit until 0.7 mmol L-1, suggesting that in this initial region the mass transport to the interface is the limiting step of the global process. Above that concentration, the slope of the curve is gradually reduced as the kinetic of capture of the holes becomes the determining step and from 5.0 mmol L-1 on an asymptotic Isph is reached (under the conditions of the experiments), where the holes photogeneration might start governing.

Le chrome dur, utilisé comme revêtement de tige d’actionneurs hydrauliques linéaires, a été interdit pour risque sanitaire (directive européenne REACH). A cet effet, un revêtement de WS2 a été sélectionné par Safran Landing Systems pour substituer le chrome dur comme revêtement de tige de piston de frein hydraulique. La démarche de sélection utilisée, est limitée par son incapacité à expliquer les performances observées et démontre le besoin d’une démarche de sélection d’autant plus appropriée que la notion d’étanchéité des actionneurs hydrauliques linéaires est « floue ». Comme, la tribologie n’a pas vocation à caractériser les revêtements de surface, parce que son plus petit objet d’étude est un triplet tribologique, cette étude propose l’évaluation de la compatibilité tribologique du revêtement de WS2, avec la fonction d’étanchéité. La démarche utilisée montre que l’étanchéité est régie, par un critère en pression, et par une vérification des caractéristiques tribologiques du système tige/joints requises pour la réalisation de l’étanchéité ; ce qui nécessite un piston hydraulique instrumenté. L’absence de ce piston est compensée par une « caractérisation tribologique approchée » du contact tige/joints, qui associe les expertises tribologiques de pistons hydrauliques d’essais de qualification, appuyées par un modèle éléments finis (EF) du piston hydraulique d’une part, et les résultats d’un essai de frottement piste/joints, conçus à cet effet à l’aide d’un modèle EF d’autre part. Les résultats montrent que le système tige/joints présente de bonnes caractéristiques tribologiques pour le facteur de frottement et l’usure, alors que la localisation de l’accommodation de vitesses dans le cas du contact tige/joint d’étanchéité, accélère le débit source du revêtement et limite sa durée de vie. Enfin, cette thèse comble un vide méthodologique en proposant, une démarche de sélection d’un revêtement pour une application tribologique, et une démarche de triboconception d’un actionneur hydraulique linéaire dans le cas d’un fonctionnement quasi-statique. / Hard chromium used as rod coating in linear hydraulic actuators has been forbidden by the European Directive REACH. In this situation, a WS2 coating has been selected by Safran Landing Systems to replace the hard chromium coating on rod pistons actuators of landing gear braking systems. The selection method was unable to explain the observed performance, and shows the lack of an appropriate methodology for the rod coating selection, mainly because the sealing concept is rather vague. Since tribology is not intended to characterize surface coatings, because its smallest object of study is a tribological triplet, this study proposes the evaluation of the tribological compatibility of the WS2 coating with the sealing function of the hydraulic piston. The adopted approach shows that the sealing performance is governed by a rod/seal contact pressure criterion and by the verification of the tribological characteristics of the rod/seal contact required to achieve a sealing performance. This tribological characterization requires an instrumented hydraulic piston. The absence of this piston is compensated by an "approximate tribological characterization" of the rod/seal contact, which combines the tribological expert analysis of hydraulic pistons of qualification tests, supported by a finite elements model (FE) of the hydraulic piston, and the results of a plate rod/seal friction test, designed for this purpose using another FE model. The results show that the rod/seal contact exhibits good tribological characteristics for the friction factor and wear, whereas the location of the velocity accommodation in the case of the rod/anti-extrusion seal contact accelerates the 3rd body generation of the coating and limits its life expectancy. Finally, this thesis fills a methodological lack by proposing a method of selecting a coating for a tribological application and a triboconception method of a linear hydraulic actuator in the case of quasi-static operating conditions.

Le procédé de projection à froid (cold spray en anglais) est un procédé fondé sur l’accélération de particules qui restent à l’état solide pour former des dépôts. L’un des forts potentiels applicatifs de ce procédé réside dans la réalisation de dépôts composites car l'incorporation des particules céramiques dans des poudres métalliques influence la microstructure et les propriétés des dépôts. Néanmoins, le principe de construction du dépôt composite n’est pas encore parfaitement établi. En conséquence, les recherches menées dans cette étude sur la fabrication de dépôts composites s’articulent autour de plusieurs domaines, à savoir :• La science des matériaux avec des études sur l’effet de la taille et de la teneur (15 vol.% - 60 vol.%) de la particule du renfort (SiC);• La mécanique des fluides avec des modélisations des vitesses des particules céramiques (SiC) et alliage d’aluminium (Al5056) et les simulations du comportement à la déformation de la particule;• Les caractérisations des dépôts avec des analyses de microstructure et de microdureté, de la cohésion du dépôt et de comportement en frottement des dépôts;Les résultats montrent que la température du gaz n'a aucun effet sur la teneur en SiC dans les dépôts mais provoque une amélioration du rendement de dépôt. La teneur en SiC dans les dépôts composites d’Al5056/SiCp augmente avec l’augmentation de la teneur en SiC dans les poudres initiales. L’ajout de SiC dans les dépôts d’Al5056 augmente la dureté et améliore la résistance à l'usure des dépôts, et puis l’amélioration dépend de la teneur en SiC dans les dépôts composites. La force de cohésion des dépôts augmente dans un premier temps avec l’augmentation de la teneur en SiC puis diminue à partir d’environ 26-27%. Les dépôts composites renforcés par SiC-67 et SiC-27 ont une teneur en SiC semblable dans les dépôts ; Pourtant la microdureté, la force de cohésion et la résistance à l'usure des dépôts formés par Al5056/SiC-67 sont supérieures à celles des dépôts construits par Al5056/SiC-27. Ce phénomène relève l’importance de l’énergie cinétique des particules renforts.Les résultats expérimentaux ont montré que les particules de SiC ne se déforment pas plastiquement mais qu’elles sont susceptibles de créer des cratères sur le substrat ou le revêtement déjà formé ou encore rebondir ou bien de s’insérer mécaniquement dans le revêtement déposé. Finalement, un modèle eulérien a été développé pour prédire la vitesse critique à partir de la morphologie de l’éjection de matière au moment de l’impact. Ce modèle a également été étendu au dépôt composite pour représenter le procédé d’empilement des particules pendant la projection. Les résultats calculés montrent la plus grande déformation des particules de la matrice grâce à l’impact des renforts. / In cold spraying, particles are accelerated in the gas jet to achieve a high velocity and deposit on the substrate with a solid state. One of potential and important applications of cold spray is realizing the composite coatings. The incorporated ceramic particles in the composite coating can greatly influence the microstructure and properties of the coatings. The objective of this thesis was to investigate factors influencing the reinforcement content in the coatings and especially the formation mechanism in cold spraying. Al5056/SiC composite coatings were prepared by cold spraying. The effect of particle size and the reinforcement content in the powders on the reinforcement content in the coatings and thus on the microstructure and the properties of the coatings were studied. A search on the particle deformation and the formation mechanism of the composite coating was also carried out by using software of fluent and Abaqus.The results show that the addition of the SiC particles in the coating increases the hardness and improves the wear resistance of the coatings. However, the cohesion strength of the coatings first increases with the increase of the SiC content in the coating and then at a certain fraction, it decreases. Moreover, under the condition of having a similar SiC content in the coating, larger SiC particles lead to better properties of the coatings.Finally, an eulerian model was used for predicting the critical velocity by the morphology of the material jet. This model has also been extended to the composite model to demonstrate the built-up process of the composite coating during cold spraying. The calculation results show that the matrix particles deform more greatly after being impacted by the reinforcements.

Print quality demands for coated papers are steadily growing, and achieving coating uniformity is crucial for high image sharpness, colour fidelity, and print uniformity. Coating uniformity may be divided into two scales: coating thickness uniformity and coating microstructure uniformity, the latter of which includes pigment, pore and binder distributions within the coating layer. This thesis concerns the investigation of both types of coating uniformity by using an approach of quantitative microscopy.First, coating thickness uniformity was analysed by using scanning electron microscope (SEM) images of paper cross sections, and the relationships between local coating thickness variations and the variations of underlying base sheet structures were determined. Special attention was given to the effect of length scales on the coating thickness vs. base sheet structure relationships.The experimental results showed that coating thickness had a strong correlation with surface height (profile) of base sheet at a small length scale. However, at a large length scale, it was mass density of base sheet (formation) that had the strongest correlation with coating thickness. This result explains well the discrepancies found in the literature for the relationship between coating thickness variation and base sheet structure variations. The total variance of coating thickness, however, was dominated by the surface height variation in the small scale, which explained around 50% of the variation. Autocorrelation analyses were further performed for the same data set. The autocorrelation functions showed a close resemblance of the one for a random shot process with a correlation length in the order of fibre width. All these results suggest that coating thickness variations are the result of random deposition of particles with the correlation length determined by the base sheet surface textures, such as fibre width.In order to obtain fundamental understandings of the random deposition processes on a rough surface, such as in paper, a generic particle deposition model was developed, and systematic analyses were performed for the effects of particle size, coat weight (average number of particles), levelling, and system size on coating thickness variation. The results showed that coating thickness variation3grows with coat weight, but beyond a certain coat weight, it reaches a plateau value. A scaling analysis yielded a universal relationship between coating thickness variation and the above mentioned variables. The correlation length of coating thickness was found to be determined by average coat weight and the state of underlying surfaces. For a rough surface at relatively low coat weight, the correlation length was typically in the range of fibre width, as was also observed experimentally.Non-uniformities within the coating layer, such as porosity variations and binder distributions, are investigated by using a newly developed method: field emission scanning electron microscopy (FESEM) in combination with argon ion beam milling technique. The combination of these two techniques produced extremely high quality images with very few artefacts, which are particularly suited for quantitative analyses of coating structures. A new evaluation method was also developed by using marker-controlled watershed segmentation (MCWS) of the secondary electron images (SEI).The high resolution imaging revealed that binder enrichment, a long disputed subject in the area, is present in a thin layer of a 500 nm thickness both at the coating surface and at the base sheet/coating interface. It was also found that the binders almost exclusively fill up the small pores, whereas the larger pores are mainly empty or depleted of binder.

Novel on-line methods are presented for the extraction, preconcentration and analysis of zwitterionic biomolecules using sol-gel-coated columns coupled to a conventional UV/visible detector. The presented approaches do not require any additional modification of the commercially available standard CE instrument. Extraction, stacking, and focusing techniques were used in the preconcentration procedures. The positively charged sol-gel coatings were created using N-octadecyldimethyl[3-(trimethoxysilyl) proply]ammonium chloride (C18-TMS) in the coating sol solutions. Due to the presence of a positively charged quaternary ammonium moiety in C18-TMS, the resulting sol-gel coating carried a positive charge. The negatively charged sol-gel coatings were due to the presence of sulfonate groups, which was formed from the oxidation of thiol groups in precursor mercaptopropyltrimethoxysilane (MPTMS) by hydrogen peroxide. Besides MPTMS, tetramethoxysilane (TMOS) and n-octadecyltriethoxysilane (C18-TEOS) were also used to prepare the sol solution for the creation of the negatively charged coatings. For extraction, the pH of the samples was properly adjusted to impart a net charge opposite to the sol-gel coatings. When a long plug of the sample was passed through the sol-gel-coated capillary, extraction was achieved via electrostatic interaction between the charged sol-gel coating and the charged sample molecules. The extracted analytes were then desorbed and focused via local pH change and stacking. The local pH change was accomplished by passing buffer solutions with proper pH values, while a dynamic pH junction between the sample solution and the background electrolyte was utilized to facilitate solute focusing. The developed methods showed excellent extraction and preconcentration effects on both positively and negatively charged sol-gel-coated columns. On-line preconcentration and analysis results obtained on the sol-gel coated columns were compared with those obtained on an uncoated fused silica capillary of identical dimensions using conventional sample injections. The described procedure provided a 150 000-fold enrichment effect for alanine on the positively charged sol-gel-coated column. On the negatively charged sol-gel-coated column, the presented sample preconcentration technique provided a sensitivity enhancement factor (SEF) on the order of 3 x 103 for myoglobin, and 7 x 103 for asparagines. The developed methods provided acceptable repeatability in terms of both peak height and migration time.

Carbon nanotube (CNT) forests have outstanding thermal, electrical, and mechanical properties, which have generated significant interest as thermal interface materials (TIMs). Some drawbacks to using CNTs as TIMs include poor substrate adhesion, high interface resistances inhibiting thermal transport, and lack of electrical insulation in electronic component applications. It is thus useful to be able to modify CNTs to reduce their electrical conductivity while maintaining high thermal conductivity and interface conductance, and high mechanical compliance. A recent report suggests that nanoscale oxide coatings could be applied to CNTs in forests without changing the mechanical deformation behavior of the forests. Oxide coatings could also provide environmental stability as well as better adhesion to the substrate compared to pristine CNT forests. In this study, we investigated thermal and electrical resistance of CNT forests with an oxide coating. Low-pressure chemical vapor deposition (LPCVD) was used to produce CNTs on high-conductivity Si substrates. Plasma-enhanced atomic layer deposition (PALD) was used to deposit Al2O3 on individual CNTs in forests. This process was facilitated by O2 plasma pretreatment to functionalize the surface of the CNTs and nucleate oxide growth. Several analytical techniques were used to characterize the CNT-oxide composites, including scanning electron microscopy, Raman and X-ray photoelectron spectroscopy. Thermal conductivity and thermal interface resistance were measured using a modified photoacoustic technique. The oxide coating had no significant effect on the effective thermal conductivity of the forests, in contrast to expectations of increased phonon scattering. Electrical resistivity measurements were made and a threefold increase was observed for the oxide-coated forests. This approach could emerge as a promising route to create a viable TIM for thermally conductive and electrically insulating applications.

Le carbone-suie, ou “black carbon” (BC), contribue au réchauffement climatique avec un forçage positif de l’ordre de +1.1 W m-2 dont l’incertitude reste haute (de l’ordre de 90%). Ce forçage s’effectue à travers l’interaction aérosol-radiation et l’interaction aérosols-nuage. Ces deux mécanismes sont affectés par le degré de mélange des particules du BC avec divers matériaux non-réfractaires et non-absorbants. Cependant, les estimations du forçage radiatif considèrent rarement les effets du mélange interne. Par ailleurs le rôle du BC comme noyau glaçogène qui influence l’interaction aérosol-nuage est largement inconnu. L’objectif de cette thèse est de mieux comprendre les mécanismes par lesquels le degré de mélange interne du BC influence la variabilité des propriétés optiques du BC et les propriétés d’activation des noyaux glaçogènes contenant du BC.Dans le premier chapitre de cette thèse, nous avons exploré la variabilité spatiale et saisonnière du coefficient d’absorption massique -mass absorption cross-section (MAC)- dans l’atmosphère en Europe. Les valeurs de MAC sont déterminées à partir de concentrations de carbone élémentaire et de coefficients d’absorption observée à différentes stations d’observation européenne du réseau ACTRIS (Aerosol, Cloud and Trace gases Research InfraStructure). Les résultats montrent une faible variabilité spatiale du MAC avec une moyenne de 10 ± 2.5 m2 g-1 à 637 nm de longueur d’onde qui peut être considérée comme représentative du BC en Europe. Le cycle saisonnier du MAC est probablement lié à la composition chimique de l’aérosol et son état de mélange, qui provoque une augmentation du MAC.Dans le second chapitre on s’est intéressé au lien entre l’absorption du BC et son état de mélange après transport sur longue-distance. Ce travail se base sur des mesures effectuées dans le cadre du projet CLIMSLIP (CLimate IMpact of Short-Lived Pollutants and methane in the Arctic). Une campagne de mesure a été conduite sur la station de recherche Zeppelin au Svalbard, Norvège en Avril 2012. Les données acquises avec un Single Particle Soot Photometer (SP2) révélaient que le BC est généralement présent en mélange interne dont l’épaisseur moyenne de la couche superficielle de matériel non-absorbant est de 47 nm pour des particules de BC de diamètre compris entre 170 et 280 nm. Ce mélange interne conduit à une augmentation d’absorption de 46%. Elle entraîne cependant une diminution relativement faible de l’albédo de simple diffusion, de l’ordre de 1%.Enfin, la capacité du BC à agir comme noyaux glaçogène pour la formation de cristaux de glace a été étudiée sur le site de haute altitude du Jungfraujoch (Suisse) dans le cadre du “cloud and aerosol characterization experiment” (CLACE) en 2013. Les différents éléments du nuage étaient séparé à partir d’une prise d’entrée type ice-CVI connectée au SP2. Ce dispositif permet de sélectionner uniquement les cristaux de glace et quantifier la fraction de BC activée. Une réduction de la présence de BC dans les résidus de glace a été observée. Des mesures de l’épaisseur de la couche de mélange interne des particules contentant du BC ont montré que les résidus de cristaux de glace présentaient des enrobages bien plus épais comparée à l’aérosol total.Les résultats obtenus au cours de ce travail ont permis de mieux comprendre l’impact du degré de mélange interne sur les propriétés optiques du BC et sur son rôle dans la formation de cristaux de glace. Les propriétés optiques du BC évoluent en fonction de la saison, tandis que la formation d’une couche superficielle amplifie sa capacité d’absorption du rayonnement solaire. De plus, cette étude souligne l’importance du vieillissement atmosphérique du BC sur sa capacité à servir de noyau de nucléation de la glace. Enfin, il fournit une avancée au sujet des propriétés sensibles mesurées dans l’atmosphère avec des techniques innovantes qui permettront la simulation plus précise du forçage radiatif. / Black carbon (BC) induces a warming effect (RFBC = +1.1 W m-2 ± 90%) through two main pathways: aerosol-radiation interaction (RFari) and aerosol-cloud interaction (RFaci). Both BC-radiation and BC-cloud interaction are affected by the mixing of black carbon with other non-refractory and non-absorbing matter present in the atmosphere. An estimation of the global radiative forcing of BC rarely accounts for internal mixing of BC while the net global cloud radiative forcing is sensitive to assumptions in the initiation of cloud glaciation, which is mostly unknown for black carbon particles. Within this thesis we investigated the variability of the light absorbing properties of black carbon, the mixing of black carbon, and the impact on light absorption and ice activation.In the first part of this thesis we investigated the spatial and seasonal variability of the mass absorption cross section (MAC) over Europe. MAC values were determined from ambient observations of elemental carbon mass concentrations (mEC) and absorption coefficients (σap). The data had been acquired during several years at different background ACTRIS supersites spread over Europe. Site specific MAC values were found to be spatially homogeneous, suggesting that the overall MAC average 9.5 ± 1.9 m2 g-1 at a wavelength of 637 nm might be representative of BC at European background locations. The MAC values showed a distinct seasonal cycle at every station. This seasonality might be related to chemical composition and aging. We observed that the MAC value has a linear and positive proportionality with the non-absorbing matter mass fraction.The second part of the work focuses on the coating acquisition of BC and the induced absorption enhancement after long-range transport. Within the CLIMSLIP (climate impact of short-lived pollutants and methane in the Arctic) project field experiments were conducted at the Zeppelin research site in Svalbard, Norway, during the Arctic spring. SP2 data were used to characterize the BC size distribution and mixing. BC containing particles having a core diameter between 170 and 280 nm were found to have a median coating thickness of 47 nm. The relationship between coating thickness and BC absorption was simulated. The observed coating thickness enhanced the mass absorption cross section by 46%, which led to a decrease of less than 1% in the single scattering albedo.In the final part of this work, the role of black carbon as ice nuclei in mixed phase clouds was investigated at the high elevation measuring site Jungfraujoch (Switzerland) during the cloud and aerosol characterization experiment (CLACE) held in 2013. The ice-CVI inlet and a single particle soot photometer were used to select and quantify the ice activated BC particles. According to the observations, BC containing particles were depleted in the ice residuals. The activation efficiency showed a size dependency, with larger BC containing particles being activated more efficiently compared to smaller ones. Activated BC cores having a diameter between 170 and 240 nm showed a larger coating thickness (median = 53 nm) compared to the total aerosol (median = 16 nm).The results obtained in this thesis shed new light on the effect of the mixing state on the optical properties and cloud activation of black carbon particles. Absorbing properties of BC showed a distinct seasonal pattern, while aging was found to consistently increase its absorption behavior. However, black carbon was found not to act as ice nuclei in low tropospheric mixed-phase clouds, where the coating thickness might play a role in the activation efficiency. This work provides freshly determined physical properties derived from ambient observations that will improve the accuracy of future aerosol and cloud radiative forcing estimations.