Les EPDM (Ethylène Propylène Diène Monomère) sont employés comme isolants des câbles électriques des centrales nucléaires. En raison de l’environnement radioactif, ils se dégradent plus rapidement qu’en environnement classique. La détermination de leur durée de vie est donc un enjeu industriel important. Pour y parvenir, ce travail a d’abord consisté à déterminer l’influence de la composition des EPDM sur leurs cinétiques de dégradation. Ainsi, deux EPDM de composition chimique différente ont été irradiés sous rayonnement en présence d’oxygène. Les suivis de la fraction soluble et de la densité de chaines actives en fonction de la dose, ont permis de mettre en évidence une dégradation par réticulation et coupures de chaines. A partir de modèles statistiques, les cinétiques de ces deux processus ont pu être estimées : la réticulation dépend de la proportion en ENB résiduels tandis que les coupures de chaines sont indépendantes de la composition chimique et du degré de réticulation initial. De plus, au - delà d’une certaine dose, les nœuds de réticulation semblent progressivement détruits. Nous nous sommes ensuite intéressés aux conséquences de l’irradiation sur les propriétés mécaniques et ce, d’abord à 80°C, pour s’affranchir de la présence de cristallites. Si dans tous les cas, l’irradiation conduit à une décroissance de la contrainte à la rupture, nos matériaux montrent une déformation à rupture qui augmente avec la dose contrairement aux matériaux de Planès et al. Pour s’affranchir du rôle des hétérogénéités sur l’initiation de fissure, les propriétés mécaniques d’éprouvettes entaillées ont ensuite été étudiées. L’énergie de déchirement est corrélée à l’énergie de rupture des matériaux entaillés et peut être décrite par le modèle de Lake et Thomas, à condition de prendre en compte la longueur réelle entre nœuds de réticulation des matériaux irradiés. Aussi, les propriétés en rupture de tous les matériaux sont améliorées quand ils sont étudiés à 25°C et la présence de cristallites masque les conséquences de la dégradation ; cet effet est ici très marqué en raison d’une importante chimie - cristallisation. Des EPDM chargés ATH ont alors été étudiés. Nos résultats confirment une accélération de la dégradation par les ATH, dépendant de la surface spécifique des charges. La compréhension des propriétés en rupture des composites s’avère complexe car la rupture peut être entrainée par divers processus en compétition. L’évolution des propriétés mécaniques des composites testés à 25°C est, comme pour la matrice pure, dépendante de l’évolution de la cristallinité et des propriétés de la phase amorphe. Enfin, ce travail remet en cause la pertinence des critères de durée de vie actuellement utilisés dans l’industrie. Les énergies de rupture étant plus directement corrélées aux paramètres microstructuraux, ne faudrait-il pas plutôt considérer ce paramètre comme critère? / EPDM (EThylene Propylene Diene Monomer) are used as insulation for electrical cables in nuclear plants. Because of the radiative environment, the degradation of these cables is accelerated and a strong industrial challenge consists in the prediction of the cables lifetime. To address this crucial industrial concern, we first looked into the influence of the chemical composition of EPDM on their kinetics of degradation. To do so, two EPDM with different chemical compositions have been irradiated under radiations and in the presence of oxygen. The soluble fraction and the active chain density have been monitored as a function of the irradiation dose, and revealed the degradation by cross-linking and chain scissions. Furthermore, the kinetics of these mechanisms have been estimated based on statistical models: the cross-linking kinetics depends on the residual ENB content while the chain scission kinetics vary neither with the chemical composition nor the initial cross-linking degree. Moreover, beyond an irradiation dose, the cross-links are progressively broken. The mechanical performances were then studied at 80°C to prevent crystallinity. If the irradiation induces a decrease of the stress at break, the materials show an increase of the strain at break conversely to the EPDM systems studied by Planès et al. The mechanical properties of notched samples have then been employed in order prevent heterogeneities driven crack initiation. The tearing energy measured was correlated with the failure energy of notched samples andcan be described by the Lake and Thomas model with account for the real length between cross-links. The same study has then been performed at 25°C where the properties at break are seen to improve. Such improvements despite irradiation confirm that crystallites attenuate the degradation. This effect is more pronounced for the current set of materials because of a strong chemi-crystallisation. The addition of ATH fillers has been studied as well, showing an acceleration of the matrix degradation with the specific surface of the fillers. The understanding of the mechanical properties at break of filled materials seems complex because the failure can be obtained by various competing processes. Nevertheless, the matrix chemical nature can be mentioned as an important factor since the difference between the matrix mechanical properties and the matrix-filler interface properties will trigger the creation of macro-defects at the origin of failure. As for the neat matrix, the evolution of the composites mechanical properties tested at 25°C depends on the evolutions of both the crystallinity and the amorphous phase. More generally, this work questions the relevance of the actual lifetime criterion used in the industry. The energies at break are more directly correlated to the microstructural parameters and thus could correspond to a relevant criteria for predicting these systems lifetime.

The main goal of this dissertation was to show that the principle of atomic layer deposition (ALD) can be applied to “endless” fibers. A reactor of atomic layer deposition has been designed, especially for coating depositions onto meter long bundles of fibers. Aluminum oxide (alumina), titanium oxide (titania), double layers of alumina and titania, as well as aluminium phosphate have been deposited onto bundles of carbon fibers using the home-built reactor. Scanning electron microscopic (SEM) and transmission electron microscopic (TEM) images indicate that the coatings were uniform and conformal onto fiber surface. There was a good adhesion of the coatings to the fibers. Alumina has been deposited using two separate aluminum sources (aluminum trichloride and trimethylaluminum), and water as a source of oxygen. In case of alumina deposition using aluminum trichloride and water, initial deposition temperature was 500 °C. In these conditions, a part of the fiber bundle has been damaged. Thus, the deposition temperature was decreased to 300 °C and the fibers were unaffected. In addition, during this process hydrochloric acid is formed as a byproduct which is a corrosive substance and affects the reactor and there was a chloride impurity in the coatings. Thus, aluminum trichloride precursor was replaced by trimethylalumium. Alumina deposition onto carbon fibers using trimethylaluminum and water was carried out at a temperature of 77 °C. SEM images revealed that the fibers were unaffected and the coatings were uniform and conformal. Oxidation resistance of the carbon fibers was improved slightly after alumina deposition. Oxidation onset temperature of the uncoated fibers was about 630 °C. The resistance was linearly increased with the coating thickness (up to 660 °C) and getting saturated over a thickness of 120 nm. Titania coatings have been deposited using titanium tetrachloride and water. The physical appearances of the titania coatings were similar to the alumina coatings. The oxidation onset temperature of the titania coated carbon fibers was similar to the uncoated fibers but the rate of oxidation was decreased than the uncoated fibers. Two double layer coatings were deposited, alumina followed by titania (alumina/titania), and titania followed by alumina (titania/alumina). If the fibers were coated with the double layer of alumina/titania, they had almost same oxidation onset as alumina coated fibers but the rate of oxidation was decreased significantly compared to alumina coated fibers. This feature is independent of the thickness of the titania layers, at least in the regime investigated (50 nm alumina followed by 13 nm and 40 nm titania). On the other hand, the oxidation onset temperature of fibers coated with titania/alumina (20 nm titania /30 nm alumina) was approximately 750 °C. The fibers were burned completely when temperature was further increased to 900 °C and held another 60 minutes at 900 °C. This is significantly better than any other coating used in this dissertation. ALD of titania and alumina in principle was known beforehand, this dissertation here applies this knowledge for the first time to endless fibers. Furthermore, this dissertation shows for the first time that one can deposit aluminum phosphate via ALD (planar surface as well as fibers). Aluminum phosphate might be special interest in the fiber coating because it is a rather soft material and thus might be used to obtain a weak coupling between fiber and matrix in composites. Aluminum phosphate was deposited using trimethylaluminum and triethylphosphate as precursors. Energy dispersive X-ray spectroscopy and solid state nuclear magnetic resonance spectra confirmed that the coating comprises aluminum phosphate (orthophosphate as well as other stoichiometries). Scanning electron microscopic images revealed that coatings are uniform and conformal. In cases of alumina and titania, it was observed that the coatings were delaminated from the ends of cut fibers and thus formed of clear steps. On the other hand, for aluminum phosphate coating it was observed that the border between coating and underlying fiber often being smeared out and thus formed an irregular line. It seems in case aluminum phosphate cohesion is weaker than adhesion, thus it might be act a weak interface between fiber and matrix. Alumina, titania, and double layer microtubes have been obtained after selective removal of the underlying carbon fibers. The carbon fibers were selectively removed via thermal oxidation in air at temperatures exceeding 550 °C. SEM and TEM images indicate that the inner side of the tube wall has the same morphology like the fibers. In addition, it was observed that the individual microtubes were separated from their neighbors and they had almost uniform wall thicknesses. The longest tubes had a length of 30 cm. / Das Hauptziel dieser Dissertation bestand darin nachzuweisen, dass die Atomlagenabscheidung (engl. atomic layer deposition (ALD)) auf „endlose“ Fasern angewendet werden kann. Es wurde ein Reaktor zur Atomlagenabscheidung gestaltet, der speziell für die Beschichtung meterlanger Faserbündel geeignet ist. Aluminiumoxid, Titanoxid, Doppelschichten aus Aluminiumoxid und Titanoxid sowie Aluminiumphosphat wurden mit Hilfe des selbstgebauten Reaktors auf Kohlefaserbündel abgeschieden. Rasterelektronenmikroskopische (REM) und transmissionselektronenmikroskopische (TEM) Aufnahmen zeigten, dass die Beschichtung auf den Fasern einheitlich und oberflächentreu war. Des Weiteren wurde eine gute Adhäsion zwischen Beschichtung und Fasern beobachtet. Das Prinzip der Beschichtung mit Titanoxid und Aluminiumoxid mit Hilfe der ALD war bereits vorher bekannt und im Rahmen dieser Dissertation jedoch erstmals auf "endlose" Fasern angewendet. Des Weiteren wird in dieser Dissertation erstmals gezeigt, dass es möglich ist, Aluminiumphosphat mittels ALD abzuscheiden (sowohl auf planaren Oberflächen als auch auf Fasern). Aluminiumphosphat könnte von besonderem Interesse in der Faserbeschichtung sein, da es ein relativ weiches Material ist und könnte daher als eine Art „schwacher“ Verbindung zwischen Faser und Matrix in Kompositen dienen. Die Oxidationsbeständigkeit von beschichten Kohlefasern wurde im Vergleich zu unbeschichteten Fasern bis zu einem gewissen Grad erhöht. Monoschichten von Aluminiumoxid und Titanoxid waren dafür wenig effektiv. Aluminiumphosphatbeschichtete Fasern waren deutlich besser geeignet als die beiden anderen. Eine Doppelschicht aus Titanoxid gefolgt von Aluminiumoxid verbesserte die Oxidationsbeständigkeit nochmals deutlich gegenüber allen anderen Beschichtungen, die in dieser Dissertation verwendet wurden. Mikroröhren aus Aluminiumoxid, Titanoxid und Doppelschichten wurden durch die selektive Entfernung der zugrunde liegenden Kohlefasern erhalten. Einzelne Mikroröhren waren von benachbarten Röhren getrennt und sie weisen eine nahezu einheitliche Wanddicke auf.

Die Filtration unter aggressiven Einsatzbedingungen, z.B. Einsatz in korrosiven Medien, Abgasfiltration, stellt besondere Anforderungen an das Filtermaterial. Sogenanntes "Liquid Phase Sintered Silicon Carbide" (LPS-SiC) erfüllt die Anforderungen sehr gut. Deshalb bestand das Ziel der Arbeit besteht darin, erstmals aus LPS-SiC asymmetrische keramische Membranen (grobporöses Substrat mit dünner, feinporiger Membran) herzustellen. Als Additivsystem fanden Yttriumoxid und Aluminiumoxid Verwendung. Es wurde Siliciumcarbid der Körnung F1200 auf Substrat der Körnung F500 abgeschieden. Dem Herstellungsverfahren kommt für die Qualität der Membran eine große Bedeutung zu. Daher wurden in dieser Arbeit folgende Beschichtungsmethoden untersucht, um die optimale Methode zu identifizieren: Tauchbeschichtung, elektrophoretische Abscheidung, Druckfiltration und Einsatz von Transfertapes (Transfertapes: Mischung aus Polyacrylatkleber und Pulver). Im Mittelpunkt stand dabei die Druckfiltration. Hierfür wurde eine neue Apparatur konzipiert und aufgebaut. Für die schlickerbasierten Methoden wurde ein wässriges System entwickelt, bei dem auf den Einsatz von organischen Hilfsstoffen verzichtet werden konnte. Die elektrostatische Stabilisierung konnte durch gezieltes Anlösen von Yttriumoxid, Ausfällen von feinskaligem Yttriumhydroxid und Belegung des Siliciumcarbids mit dem Yttriumhydroxid erreicht werden. Die Elektrophorese führte zu keinen befriedigenden Ergebnissen aufgrund des undefinierten spezifischen Widerstandes des Substrats (siehe Dissertation Jan Ihle, Bergakademie Freiberg 2004). Die Druckfiltration erwies sich als das geeignetste Verfahren. Mit ihr konnten ohne Einschränkungen hochwertige Membranen erzeugt werden. Druck und Zeit sind bei gegebenen Feststoffgehalt frei wählbar. Der Druck wurde zwischen 2*10E4 und 1*10E5 Pa variiert. Höherer Druck führte zu feineren Porengrößen (mittlere und maximale Porengröße). Mit der Druckfiltration konnten Membranen ohne makroskopische Defekte erzeugt werden. Sie führte im Vergleich aller Verfahren zu der geringsten Rauhtiefe der Membranen. Die Tauchbeschichtung ließ sich in diesem System nur über den Feststoffgehalt steuern. Membranen aus der Tauchbeschichtung wiesen makroskopische Fehler (große oberflächliche Poren) auf. Die Methode führte hinsichtlich Porengrößen und Rauhtiefe zu den schlechtesten Werten. Die Transfertape-Methode als neuartiger Ansatz erwies sich für das LPS-SiC System als noch nicht ausgereift. Das direkte Bekleben der Substrate war möglich. Hinsichtlich der Membrandicke sind aber Grenzen bei ca. 50 µm gesetzt. Darüber hinaus reißen die Membranen. Es wurden Schwankungen in der Entbinder- und Sinterschwindung verzeichnet. Weiterhin werden große Hohlräume im Substrat nicht von den Transfertapes abgeformt. Beide Effekte erhöhen die Spannungen beim Sintern, so dass bei geringeren Schichtdicken Risse entstehen. / Silicon Carbide (SiC) fulfills many requirements, e.g. a high robustness in terms of corrosion, which makes it a suitable Material for ceramic membranes. The aim of this work was to produce ceramic membranes out of porous liquid phase sintered Silicon Carbide (LPS-SiC). As additives Alumina and Yttria were used. The SiC based on commercial abrasive powders F1200 (Membrane) and F500 (Substrate). Different techniques of membrane formation were applied in order to find the optimum processing procedure: Dip Coating, Electrophoretic Deposition (EPD), Pressure Filtration and the usage of so called Transfer Tapes, a blend of Polyacrylate and ceramic powders). For the slip based methods a water based system was developed without the need of organic additives. A pure electrostatic stabilization was facilitated by solving Yttria with Hydrochloride Acid and precipitation, resulting in the coverage of the SiC particles with finely dispersed Yttria. The EPD was not successful due to a undefined specific resistance of the substrate. The pressure filtration turned out to be the best, most versatile method, leading to defect free membranes with the lowest measured surface roughness. The pressure ranged between 2*10E4 and 1*10E5 Pa. Higher pressure lead to finer pores. The Dip Coating was controlled only by the solids content. Membranes by Dip Coating showed macroscopic defects. As a new concept for ceramic membrane fabrication the Transfer Tapes needed further investigation. The direct gluing on the substrate was possible. The thickness of the membrane was limited to 50 microns in order to keep free of cracks. The Transfer Tapes exhibited pronounced fluctuations in the debinding and sintering shrinkage, leading to increased tension during sintering. Furthermore cavities, (e.g. big pores) were bridged. Both effects lead to increased tension during sintering.

No description available.

Κατά τις τελευταίες δεκαετίες παρατηρείται συνεχής αύξηση της έντασης του φαινομένου του θερμοκηπίου γεγονός που προκαλεί σημαντικές συνέπειες στο περιβάλλον και στη ζωή μας γενικότερα. Συνεπώς, είναι απαραίτητη η μείωση της ανθρωπογενούς εκπομπής των αερίων που συμβάλλουν στην αύξηση του φαινομένου αυτού. Η εκμετάλλευση και χρήση των δύο πιο σημαντικών θερμοκηπικών αερίων, του μεθανίου και του διοξειδίου του άνθρακα, μπορεί να επιτευχθεί με την αναμόρφωση του CH4 με CO2 ή αλλιώς ξηρή αναμόρφωση του μεθανίου (Dry Reforming of Methane-DRM). Με τη διεργασία DRM τα δύο συγκεκριμένα αέρια μετατρέπονται σε αέριο σύνθεσης (synthesis gas), το οποίο χρησιμοποιείται είτε για τη σύνθεση πληθώρας οργανικών ενώσεων, είτε για την παραγωγή Η2 για ενεργειακούς σκοπούς. Η DRM παρουσιάζει σημαντικά πλεονεκτήματα: δεν απαιτείται η χρήση ύδατος, φθηνό σχετικά κόστος εγκαταστάσεων, χρησιμοποιείται σε χημικά συστήματα μεταφοράς ενέργειας, ενώ και το αέριο σύνθεσης που παράγεται έχει ακόμα κατάλληλη αναλογία για συνθέσεις Fischer–Tropsch. Παρόλα αυτά η DRM δεν έχει εκτεταμένη βιομηχανική εφαρμογή επειδή αντιμετωπίζει ένα σημαντικό μειονέκτημα: ο καταλύτης μετά από κάποιο χρόνο λειτουργίας απενεργοποιείται λόγω του άνθρακα που αποτίθεται πάνω του. Στην παρούσα εργασία μελετήθηκε ο state of the art καταλύτης Ni/Al2O3, τον οποίο τροποποιήσαμε με βόριο σε διάφορους λόγους [Β/(B+Νi)] με κύριο στόχο τη μείωση των ανθρακούχων αποθέσεων. Οι τροποποιημένοι καταλύτες συντέθηκαν με τη μέθοδο του υγρού συνεμποτισμού και χαρακτηρίστηκαν φυσικοχημικά με διάφορες τεχνικές, ώστε να μελετήσουμε την επίδραση του βορίου στην υφή τους (ΒΕΤ, porosimetry, SEM, TEM), στη δομή τους (XRD, UV-Vis DRS) και στην αναγωγιμότητά τους (H2-TPR). Η καταλυτική συμπεριφορά τους για την αντίδραση της ξηρής αναμόρφωσης του μεθανίου αξιολογήθηκε σε αντιδραστήρα σταθερής κλίνης, για 24h, σε συνθήκες: 973Κ, 1 atm, τροφοδοσία 50%CH4-50%CO2. Ο άνθρακας που αποτέθηκε στους χρησιμοποιημένους καταλύτες μετρήθηκε με τη μέθοδο της θερμοπρογραμματισμένης υδρογόνωσης (TPH). Τα ανηγμένα και χρησιμοποιημένα στην DRM καταλυτικά δείγματα μελετήθηκαν επίσης με ηλεκτρονικό μικροσκόπιο σάρωσης (SEM με αναλυτή EDS) και ηλεκτρονικό μικροσκόπιο διαπερατότητας (ΤΕΜ). Βρέθηκε ότι η παρουσία του Β μειώνει σημαντικά την ποσότητα του αποτιθέμενου άνθρακα στους καταλύτες Ni/Al2O3, σε ποσοστό έως και 86%, χωρίς να επηρεάζει ιδιαίτερα τη δραστικότητα και την εκλεκτικότητα των καταλυτών. Σημαντικό ρόλο παίζει το ποσοστό του Β στον καταλύτη, με τον καταλύτη με λόγο Β/(B+Νi) = 0,5 να εμφανίζει τη βέλτιστη συμπεριφορά. Τα αποτελέσματα μας έδειξαν ότι η ιδιαίτερη θετική επίδραση του βορίου οφείλεται κυρίως στο γεγονός ότι ευνοεί τη διασπορά του μεταλλικού νικελίου. Τροποποίηση με βόριο, σε κατάλληλη περιοχή φορτίσεων, του καταλύτη Ni/Al2O3 μεγιστοποιεί το πλήθος των νανοσωματιδίων νικελίου με μέση διάσταση < 6.0 nm, τα οποία, ως γνωστόν, ελαχιστοποιούν την απόθεση άνθρακα. / The intensity of the greenhouse effect is constantly increasing in the last few decades with an adverse effect both on the environment and the humanity. In order to decrease the effect, human-caused emissions should be minimized. The two most important greenhouse gases, methane and carbon dioxide, can be used in the DRM (Dry Reforming of Methane) process. With this process the above mentioned gases are converted to synthesis gas, which is then used for the synthesis of a great number of organic compounds and synthetic fuels (through the Fisher-Tropsch syntheses) or for the production hydrogen to be used as a fuel (energy purposes). The DRM process presents a number of advantages, namely: no water is required, relatively low cost of process plants,it can be used as a Chemical Energy Transfer System and, finally, the produced synthesis gas has adequate CO/H2 ratio for Fisher-Tropsch syntheses. Although DRM is a promising process, its industrial application is hindered by a major drawback: the catalysts are rapidly deactivating due to coking. In the current study, the state of the art catalyst Ni/Al2O3 was studied and modified with boron, using different ratios of Β/(B+Νi). Our primary objective was to reduce coking. The modified catalysts were synthesized by wet co-impregnation and physicochemically characterized in their oxidic, reduced and used forms, using various techniques, in order to investigate the influence of boron on the texture (BET, Porosimetry, SEM, TEM), structure (XRD, UV-Vis DRS) and reducibility (H2-TPR) of the catalysts. The catalytic performance for the DRM process was studied under stable conditions (973Κ, 1 atm and 50%CH4-50%CO2 undiluted feed), for 24h, using a fixed bed reactor. Carbonaceous deposits on the used catalysts were determined by Temperature Programmed Hydrogenation (TPH). Scanning Electron Microscopy (SEM) with EDS analyser and Transmission Electron Microscopy (TEM) were also used in the study of reduced and used catalytic samples. Modifying Ni/Al2O3 catalysts with boron results in a great decrease of the deposited coke (up to 86%), without any significantly influence on the activity and selectivity of the catalysts. A major factor influencing the catalyst is the B loading, with the ratio Β/(B+Νi)=0,5 giving the best results. Boron’s positive effect was mainly attributed to its ability to increase Ni dispersion. Modification of Ni/Al2O3 catalysts, by using the appropriate boron loading, resulted to an increase of the amount of nickel nanoparticles with an average dimension under 6.0 nm, which are known to minimize coke deposition.

Les techniques de frittage ultrarapide « naturel » (sans charge) comme le frittage par micro-ondes ou par induction présentent de nombreux avantages. Toutefois, le développement de ces techniques passe par une compréhension et une maitrise des mécanismes mis en jeu. A la fois similaires et complémentaires, ces procédés de chauffage-frittage ont été étudiées par une approche expérimentale afin d’approfondir les connaissances dans le domaine du Frittage Ultrarapide Naturel (FUN). Au cours de cette thèse, l’étude du frittage par micro-ondes de composites céramiques Al2O3-(Y)ZrO2 (3 à 40%vol.) a été menée parallèlement à celle du frittage par induction d’une poudre métallique micronique de nickel. La démarche expérimentale adoptée a consisté à réaliser des expériences de frittage à vitesses de chauffage imposées (de 25 à 1000°C/min) sur ces matériaux modèles et des pièces de petites dimensions, en se référant aux comportements en frittage conventionnel tant au niveau macroscopique qu’au niveau microscopique. / The techniques of ultrafast pressureless sintering as microwave or induction sintering offer manyadvantages. However, the development of these techniques requires an understanding and a control ofthe mechanisms involved. Both similar and complementary, these processes of heating-sintering havebeen studied by an experimental approach to increase knowledge in the field of Ultrafast PressurelessSintering.In this thesis, the study of microwave sintering of Al2O3-(Y)ZrO2 composites has been conductedin parallel with induction sintering of a submicronic nickel powder. The experimental approach usedconsisted in carrying out sintering experiments at imposed heating rates (from 25 to 1000°C/min) onchosen materials and small parts, referring to conventional sintering behavior at the macroscopic andmicroscopic scale.

The ultra high barrier films for packaging find applications in a wide variety of areas where moisture and oxygen barrier is required for improved shelf-life of food/beverage products and for microbial free pharmaceutical containers. These materials also find applications in micro electro mechanical systems such as ICs, and for packaging in industrial and space electronics. Flexible and portable organic electronics like OLEDs (Organic Light Emitting Diodes), OPVDs (Organic Photo Voltaic Devices) and dye sensitized solar cells (DSSCs) have a good potential in next generation solar powered devices. In fact, organic insulators, semiconductors, and metals may be a large part of the future of electronics. However, these classes of materials are just an emerging class of materials mainly because of their life time constraints. Thus significant research is required to bring them into the forefront of electronic applications. If the degradation problems can be diminished, then these polymers could play a major role in the worldwide electronic industry. A flexible polymer film itself cannot be used as an encapsulation material owing to its high permeability. While a glass or metal substrate possesses ultra high barrier properties, it cannot be used in many electronic applications due to its brittleness and inflexibility. Polymer/ nanocomposites based hybrid materials are thus a promising class of material that can be used for device encapsulation. Chapter I summarizes some of the recent developments in the polymer/nanocomposites based materials for packaging and specifically its use in flexible as well as portable organic electronic device encapsulation. While the development of low permeable encapsulant materials is a chemistry problem, an engineering/instrumentation problem is the development of an accurate technique that can measure the low levels of permeability required for electronic application. Therefore, there is a keen interest in the development of an instrument to measure permeability at these limits. The existing techniques to measure the low permeabilities of barrier films, their importance and accuracy of measurements obtained by these instruments have been briefly discussed in this chapter. Different polymer based hybrid composite materials have been developed for the encapsulation of organic devices and their materials properties have been evaluated. Broadly, two diverse strategies have been used for the fabrication of the composites: in-situ curing and solution casting. Chapters II, III and IV discuss the fabrication of nanocomposite films based on in-situ curing while chapter V discusses fabrication based on solution casting. In chapter II, amine functionalized alumina was used as a cross-linking agent and reinforcing material for the polymer matrix in order to fabricate the composites to be used for encapsulation of devices. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy were used to elucidate the surface chemistry. Thermogravimetric and CHN analysis were used to quantify the grafting density of amine groups over the surface of the nanoparticles. Mechanical characterizations of the composites with various loadings were carried out with dynamic mechanical analyzer (DMA). It was observed that the composites have good thermal stability and mechanical flexibility, which are important for an encapsulant. The morphology of the composites was evaluated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The work presented in chapter III is a technique based on grafting between surface decorated γ-alumina nanoparticles and the polymer to make these nanocomposites. Alumina was functionalized with allyltrimethoxysilane and used to conjugate polymer molecules (hydride terminated polydimethylsiloxane) through platinum catalyzed hydrosilylation reaction. As in the previous chapter, the surface chemistry of the nanoparticles after surface modification was characterized by different techniques (FTIR, XPS and Raman). The grafting density of alkene groups over the surface of the modified nanoparticles was calculated using CHN analyzer. Thermal stability of the composites was also evaluated using thermogravimetric analysis. Nanoindentation technique was used to analyze the mechanical characteristics of the composites. The densities of the composites were evaluated using density gradient column and the morphology of composites was evaluated using SEM. All these studies reveal that the composites have good thermal stability and mechanical flexibility and thus can be potentially used for encapsulation of organic photovoltaic devices. In addition, rheological studies of the composites were carried out to investigate the curing reaction. The platinum-catalyzed hydrosilylation reaction was studied using both DSC and rheological measurements. The competitive reactions occurring in the system was also monitored in real time through DSC and rheology. Based on the curing curves obtained from these two studies, the mechanistic detail of the curing process was proposed. In addition, swelling studies and contact angle measurements of the composites were also carried out to determine the capability of these materials as encapsulants. Chapter IV deals with a thermally stable and flexible composite that has been synthesized by following a hydrosilylation coupling between silicone polymer containing internal hydrides and mesoporous silica. The results of the characterization of the composites indicates that the composites are thermally stable, hydrophobic, flexible and can be potentially used for encapsulating flexible electronic devices. Chapter V discusses the solution casting method for the development of composites. This chapter is divided into two parts: Part I discusses the synthesis and characterization of flexible and thermally stable composites using polyvinyl alcohol as the base polymer matrix and reactive zinc oxide nanoparticles as the dispersed phase. Various studies like thermal analysis, mechanical analysis, surface analysis and permeability studies were used to characterize the composite films for their possible use as a passivation material. The material was used to encapsulate Schottky structured devices and the performance of these encapsulated devices under accelerated weathering was studied. Part II of this chapter discusses the fabrication of hybrid organic/inorganic based polymer-composite films, based on polyvinylbutyral (PVB) and organically modified mesoporous silica. PVB and amine functionalized mesoporous silica were used to synthesize the composite. An additional polyol (‘tripentaerythritol’) component was also used to enhance the –OH group content in the composite matrix. The thermal, barrier and mechanical properties of these composites were investigated. The investigation of these films suggests that these can be used as a moisture barrier layer for encapsulation. Chapter VI gives the concluding remarks of the results presented. The advantages as well as disadvantages of the in-situ cured and solution casted films and the scope for future work is discussed in this chapter.

The work described in this thesis focuses on the effects that adsorption processes on catalytic surfaces pose in controlling key steps that can affect and control reaction pathways. To that, the development of Nuclear Magnetic Resonance (NMR) relaxometry methods and the comparison with traditional catalytic was performed with a series of C5 and C6 unsaturated hydrocarbons on two different alumina supports, γ- and θ-Al2O3. The developed techniques were applied in the study of liquid phase selective hydrogenation of citral on 5% Pt/SiO2. Infrared (IR) spectroscopy, volumetric adsorption isotherms, dynamic isotherms via a Tapered Element Oscillating Microbalance (TEOM), temperature programmed desorption (TPD) as well as 13C T1 NMR and 1H 2D T1-T2 relaxometry methods were employed. Energies of adsorption as a function of coverage were obtained via adsorption isotherms and the particular surface adsorbate interactions were described with IR spectroscopy. For example, 1-pentyne showed the strongest interaction with the alumina (94 kJ mol-1) while 1-pentene presented a weaker interaction (46 kJ mol-1) on θ-Al2O3. Desorption energies obtained from TPD ranged 85 – 130 kJ mol-1, irrespective of the adsorbate. Reactivity of the aluminas was captured with TPD, TEOM and NMR relaxometry. Interaction of adsorbates with hydrocarbon occurred predominantly on weak adsorption sites. 13C NMR T1 relaxometry provided in addition atom-specific adsorbate-adsorbent interaction strengths, showing the molecular geometry of adsorption, and applied in co adsorption measurements. The selective hydrogenation of citral as a model α,β-unsaturated aldehyde and the effect of different solvents on the activity and product distribution was studied at 298 and 373 K. A series of polar protic, polar aprotic and non polar solvents was investigated. Results showed higher initial reaction rates in non polar solvents but higher selectivities towards desired products on polar protic solvents. Solvent used also affected by product formation. The strong variations in reaction rates and selectivities reported were related with adsorbate catalyst interactions, as well as solvent reactant interactions. For example, adsorption isotherms showed that ethanol notably reduced the adsorption capacity of citral as compared with hexane, related with the rate differences observed. ATR-IR measurements indicated solvent citral interactions were solely present in polar protic solvents in line with higher yields of geraniol and nerol. Finally, 13C T1 NMR and 1H 2D T1-T2 correlation experiments determined that the geometry of adsorption of citral, influenced by solvent, affected product selectivity, and that product adsorption affected selectivity and deactivation.

Ce manuscrit de thèse porte sur l’élaboration de nouveaux matériaux pour la protection balistique grâce à l’apport du procédé de frittage flash. Il s’agit, en effet, d’associer deux composés possédant des températures de frittage éloignées, tels que l’alumine et l’aluminium, matériaux de référence utilisés dans la protection balistique.La première voie testée était un assemblage bi-matériau, réalisé par frittage d’une poudre d’aluminium sur un plot d’alumine préalablement fritté. Cette étude a permis d’observer la formation de la liaison alumine/aluminium par microscopie électronique à balayage et en transmission et d’optimiser les paramètres d’assemblage pour l’obtention d’un bi-matériau possédant une forte cohésion interfaciale. Des outils de caractérisation adaptés (diffraction des rayons X et indentation Vickers) ont mis en évidence des contraintes résiduelles dans la céramique qui résultent de la différence de coefficients de dilatation thermique entre les deux composés lors du refroidissement du bi-matériau. Ces assemblages ont également fait l’objet d’essais statiques (essais de traction indirects) et d’essais dynamiques (tirs balistiques). Ces essais ont démontré la très grandec ohésion des assemblages et ont permis de valider la pertinence de l’étude de matériaux de protection balistique par des essais statiques, qui sont plus faciles à mettre en oeuvre.L’autre voie envisagée était de fritter en une seule étape un matériau à gradient de composition, de l’alumine pure à l'aluminium pur avec une interphase constituée de mélanges alumine/aluminium. D’un point de vue technique, le frittage flash a démontré sa capacité à générer un gradient de température de plusieurs centaines de degrés à l’intérieur d’un échantillon de quelques millimètres de haut, grâce à l'utilisation d'un moulede forme spécifique. Malheureusement, la mauvaise mouillabilité de l’alumine par l’aluminium n’a pas permis d’abaisser la température de frittage des mélanges alumine/aluminium par rapport à l’alumine pure. Elle a au contraire conduit à augmenter la température de frittage des mélanges de ~200 °C, empêchant l’élaboration du matériau à gradient de composition. Cette voie a tout de même permis l’élaboration de composites denses (>99 %) à matrice d'alumine avec de faibles quantités d'aluminium, de l'ordre de 5 % en masse. / This dissertation describes the synthesis of new components for ballistic protection with the assistance of flash sintering. Indeed, the objective is to associate two compounds showing very different sintering temperatures – such as alumina and aluminum, two reference materials for ballistic protection applications.The first synthesis method tested was the elaboration of a bi-material via the sintering of aluminump owder on alumina bulks. This study permitted to observe the formation of the alumina/aluminum bonding by scanning and transmission electron microscopy and to optimize the assembly parameters in order to obtain a bimaterials howing a strong interfacial cohesion. Adapted characterization techniques (X-rays diffraction and Vickers indentation) revealed residual stresses inside the ceramic that stemmed from the difference of thermal expansion coefficients between the two compounds during the cooling of the bi-material. Moreover, these assemblies have been tested with static (indirect tensile) tests and dynamic (ballistic) tests. These tests evincedthe very strong cohesion of the assemblies and permitted to confirm the relevance of static tests, which are easierto set up, for the evaluation of materials for ballistic protection.The other synthesis method considered was the one step sintering of a material displaying a gradient of composition, from pure alumina to pure aluminum with an interphase constituted by alumina/aluminum combinations. From a technical point of view, the flash sintering process proved capable of generating a thermal gradient of several hundreds of degrees inside a sample a few millimeters high, thanks to the use of a specific shape die. Unfortunately, the limited wetting of alumina by aluminum prevents the sintering of the alumina/aluminum mixtures from temperatures being lower than that of pure alumina. On the contrary, this limited wetting leads to an increase in the sintering temperature of the composites of ~200 °C and prevents the preparation of a material showing a composition gradient. Nevertheless, this method permits the synthesis of dense alumina composites (<99 %) containing ~5 wt.% aluminum.

The master´s thesis focuses on high-alumina refractory materials used mainly in aluminia metallurgy. Teoretical part of this thesis is aimed at distribution of refractory materials, possibilities of its production and raw material basis. Characteristic properties are described as well as application possibilities in aluminium technology. In final part of this thesis experimental data are evaluated to obtain physical, mechanical, chemical properties of high-alumina refractory materials. Those are used for economical optimalization of raw materials.