ABSTRACT MICROWAVE SINTERING AND CHARACTERIZATION OF ALUMINA AND ALUMINA MATRIX CERAMIC NANOCOMPOSITES Kayiplar, Burcu M.S., Department of Metallurgical and Materials Engineering Supervisor: Assist. Prof. Dr. Arcan F. Dericioglu April 2010, 106 pages Efficiency of microwave heating on the sintering of ceramic materials has been investigated in comparison to conventional processing. Monolithic alumina with or without sintering additives such as MgO, CaO, Y2O3 were fabricated by both conventional and microwave sintering at temperatures ranging from 1000&deg / C to 1600&deg / C with a constant soaking time of 1 hour. Based on the densification results on monolithic alumina, nanometer-sized SiC or stabilized ZrO2 particle-dispersed alumina matrix ceramic nanocomposites were sintered by both methods at 1300&deg / C and 1500&deg / C for 1 hour. Sintered ceramic materials were characterized in terms of densification, microstructural evolution, chemical composition and mechanical properties such as hardness and indentation fracture toughness. Microwave sintering was determined to be a remarkably effective method in the production of Al2O3 ceramics at considerably low temperatures (&amp / #8804 / 1400&deg / C) compared to conventional sintering in achieving enhanced relative densities reaching to ~97% with improved microstructural characteristics and mechanical properties. Usage of sintering additives at temperatures higher than 1400&deg / C was determined to be effective in densifiying Al2O3 by both methods. Second phase particle incorporation yielded poor densification resulting in a decrease of hardness of the fabricated ceramic nanocomposites / however, their fracture toughness improved considerably caused by the crack deflection at the dispersed particles and grain boundaries reaching to ~4 MPa&middot / m1/2 in the case of SiC particledispersed nanocomposites. Compared to conventional sintering, microwave sintering is more effective in the processing of alumina and alumina matrix nanocomposites leading to similar densification values along with improved microstructural and mechanical characteristics at lower temperatures in shorter soaking periods.

Στην παρούσα Εργασία λεπτά υμένια (5 -25 nm) ZrO2 έχουν εναποτεθεί με τη μέθοδο ALD σε μη αδρανοποιημένο (100) Ge τύπου-p, με ειδική αντίσταση 0.2-0.5 Ω-cm. Η εναπόθεση του ZrO2 πραγματοποιήθηκε στους 2500C, με τη χρήση διαδοχικών παλμών H2O και Tetrakis (Dimethylamido) Zirconium που ήταν και οι πρόδρομες ενώσεις. Ο δομικός χαρακτηρισμός των υμενίων (στοιχειομετρία, σύνθεση και τραχύτητα της διεπιφάνειας, κρυσταλλογραφική φάση του διηλεκτρικού κλπ) πραγματοποιήθηκε μέσω των μεθόδων XPS και ΤΕΜ. Ο λεπτομερής ηλεκτρικός χαρακτηρισμός των υμενίων έγινε με παράμετρο τη θερμοκρασία σε δομές (πυκνωτές) MOS που έφεραν λευκόχρυσο, Pt, ως μέταλλο πύλης. Πραγματοποιήθηκαν μετρήσεις C-V, C-f με παράμετρο τη θερμοκρασία και για θερμοκρασίες από 300Κ έως 80 Κ. Σύμφωνα με τα αποτελέσματα που προέκυψαν από την παρούσα μελέτη τα υμένια με πάχος μικρότερο των 15 nm εμφανίζουν πολύ φτωχή ηλεκτρική συμπεριφορά, η οποία βελτιώνεται με την αύξηση του πάχους. Σχετικά παχιά (25 nm) υμένια ZrO2 εμφανίζουν πυκνότητα διεπιφανειακών παγίδων της τάξης των 1011 eV-1cm-2, όπως προκύπτουν από μετρήσεις που πραγματοποιήθηκαν στους 80K. Από μετρήσεις I-V με παράμετρο τη θερμοκρασία προκύπτουν οι μηχανισμοί αγωγιμότητας που διέπουν τις μελετούμενες δομές. Η επίδραση της ανόπτησης σε περιβάλλον Forming Gas μετά την εναπόθεση του μετάλλου μελετάται επίσης. Τέλος, μελετώνται οι ηλεκτρικές ιδιότητες δομών Pt/ZrO2 (25 nm)/p-Ge, σε υποστρώματα που περιέχουν ταυτόχρονα περιοχές που έχουν υποστεί ανόπτηση με Laser και περιοχές που δεν έχουν υποστεί ανόπτηση. Η ανόπτηση με Laser φαίνεται να υποβαθμίζει την ηλεκτρική συμπεριφορά της δομής. Ωστόσο, σύμφωνα με τα αποτελέσματα της παρούσας εργασίας, υπάρχουν ενδείξεις ότι οι δομές σε περιοχές που γειτνιάζουν με αυτές που έχουν υποστεί ανόπτηση με Laser εμφανίζουν βελτιωμένες ηλεκτρικές ιδιότητες ακόμη και σε σχέση με τα δείγματα αναφοράς που περιλαμβάνουν δομές που αναπτύχθηκαν σε μη ακτινοβολημένο υπόστρωμα. / In the present Thesis, thin (5 -25 nm) films of ZrO2 have been deposited by Atomic Layer Deposition (ALD) on non-passivated p-type (100) Germanium substrates with resistivity 0.2-0.5 Ω-cm. ZrO2 deposition has been performed at 2500C using a series of alternating pulses of H2O and Tetrakis(Dimethylamido) Zirconium, which were the deposition precursors. Structural characterization of the films in terms of stoichiometry, interface composition and roughness, crystallographic phase of the dielectric etc., has been performed using XPS and TEM analysis. Detailed electrical characterization [C-V, and C-f measurements] of the films as a function of temperature has been performed in MOS capacitors using Pt as gate metal. It has been observed that the electrical behaviour of the films is extremely poor in thickness range below 15 nm, while they show an improvement in higher thickness regime. Thick (25 nm) ZrO2 showed an interface trap density of the order of 1011 eV-1cm-2 extracted at 80K. The conductivity mechanisms of the structures are revealed by I-V measurement at various temperatures. Finally the effect of post-metallization annealing in Forming Gas ambient has been studied. In parallel the electrical properties of structures Pt/ZrO2 (25 nm)/p-Ge, on substrates containing simultaneously laser annealed and non-annealed areas has been studied. It has been obtained that laser annealing of the substrate deteriorates the electrical behaviour of the structure, while it seems that structures on the areas in proximity to the annealed ones revealed superior electrical properties as compared to the corresponding deposited on non-annealed (reference) samples.

Made available in DSpace on 2016-06-02T19:56:55Z (GMT). No. of bitstreams: 1 6143.pdf: 2289936 bytes, checksum: dcf4b81e424bb217ab83315f71624407 (MD5) Previous issue date: 2014-03-31 / Universidade Federal de Sao Carlos / NO, NO2 and N2O nitrogen oxides, named NOx, strongly contribute to the air pollution and to minimize their emissions are used catalytic processes. The catalytic reduction of NO with CO has the advantage to simultaneously abate both pollutants. For that reaction are used noble metal based catalysts, but due to their scarcity and high cost, many research have been established to their substitution by transition metal oxides, which have high potential to catalyze that reaction. Those new catalysts beside to be active to the NO reduction with CO, they must be highly selective to N2 formation, stable at high temperatures and especially resistant to the presence of the interfering compounds (O2, SO2 and H2O). In this work were prepared Fe2O3, CuO or Fe2O3-CuO catalysts supported on y-Al2O3, ZrO2 or ZrO2/y-Al2O3. The supports were prepared via synthesis sol-gel using metallics alkoxides as precursors and the active phases introduced by impregnation of Fe(III) or Cu(II) nitrates. The obtained solids were characterized by X-ray diffraction (XRD), nitrogen adsorption/desorption measurements, hydrogen temperature programmed reduction (H2-TPR) and their activity evaluated by the reduction of NO with CO between 100 to 600°C in the presence or absence of SO2, O2 and H2O. The synthesis via sol-gel resulted in y-Al2O3 and ZrO2/y-Al2O3 supports with high specific surface area that allowed adequately distribute the CuO and Fe2O3 oxides, which did not present X ray diffraction peaks. The catalysts were considerably active in the reduction of NO with CO, with the bimetallic ones being slightly more selective to N2 formation. In the presence of SO2, the Fe2O3/y- Al2O3 and Fe2O3/ZrO2/y-Al2O3 catalysts showed more catalytic stability. The presence of O2 led to a significantly NO conversion loss due to the direct CO oxidation by O2. In the presence of H2O or of all the interfering compounds, the NO conversion loss was more pronounced, except the CuO/ZrO2, that was more resistant in the presence of H2O. / Os óxidos de nitrogênio NO, N2O e NO2, denominados de NOx, são fortes causadores da poluição atmosférica e, para minimizar suas emissões utilizam-se processos catalíticos. A redução de NO com CO tem a vantagem de abater simultaneamente ambos poluentes. Nessa reação, são utilizados catalisadores à base de metais nobres, mas, a sua escassez e alto custo têm direcionado pesquisas para a sua substituição por óxidos de metais de transição, os que mostram potencial para essa reação. Além de ativos, esses catalisadores devem ser seletivos à produção de N2, estáveis em altas temperaturas e sobre tudo estáveis na presença dos interferentes O2, H2O e SO2. Neste trabalho foram preparados catalisadores de Fe2O3, CuO ou Fe2O3-CuO suportados em y-Al2O3, ZrO2 ou ZrO2/y-Al2O3. Os suportes foram preparados via sol-gel, utilizando alcóxidos metálicos como precursores e, a introdução das fases ativas, efetuada via impregnação utilizando nitratos de Fe(III) ou Cu(II). Os suportes e catalisadores foram caracterizados por difração de raios X (DRX), fisissorsão de nitrogênio, redução com hidrogênio à temperatura programada (RTP-H2) e a sua atividade avaliada através da redução de NO a N2 com CO, entre 100 e 600°C, na ausência ou presença de interferentes. A síntese sol-gel resultou em suportes y- Al2O3 e ZrO2/y-Al2O3 de alta área superficial, permitindo uma adequada distribuição de CuO e Fe2O3, os que não apresentaram picos de DRX. Os catalisadores foram bastante ativos na redução de NO a N2, com os bimetálicos sendo ligeiramente mais seletivos à formação de N2. Na presença de SO2 os catalisadores Fe2O3/y-Al2O3 e Fe2O3/ZrO2/y-Al2O3 foram mais estáveis. A presença de O2 provocou significativa queda na conversão de NO, favorecendo a oxidação direta do CO. Na presença de H2O ou de todos os interferentes simultaneamente, a queda da conversão de NO a N2 sobre todos os catalisadores analisados foi total, com exceção ao catalisador de CuO/ZrO2, que foi mais resistente na presença de vapor de água.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2018-03-20T16:46:40Z No. of bitstreams: 1 MarieleIaraSoaresDeMello_TESE.pdf: 16812894 bytes, checksum: 6e77a9036a1ea3feab8abf3d2004dd63 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2018-03-22T11:29:20Z (GMT) No. of bitstreams: 1 MarieleIaraSoaresDeMello_TESE.pdf: 16812894 bytes, checksum: 6e77a9036a1ea3feab8abf3d2004dd63 (MD5) / Made available in DSpace on 2018-03-22T11:29:20Z (GMT). No. of bitstreams: 1 MarieleIaraSoaresDeMello_TESE.pdf: 16812894 bytes, checksum: 6e77a9036a1ea3feab8abf3d2004dd63 (MD5) Previous issue date: 2017-03-10 / Estudos de catalisadores utilizados em rea??es para a produ??o de combust?veis alternativos, como a S?ntese de Fischer-Tropsch (SFT) e a S?ntese do Metanol via Hidrogena??o de CO2 foram realizados. O efeito da natureza qu?mica do ?xido do suporte sobre o desempenho de catalisadores de cobalto para a rea??o de Fischer-Tropsch foi investigado e uma s?rie de suportes foram sintetizados por meio de uma cobertura em monocamada da ?-Al2O3 com v?rios ?xidos representativos de uma ampla gama de car?ter ?cido-b?sico de Lewis, os quais foram caracterizados por espectroscopia de UV-Vis acoplado com adsor??o de alizarina. Foi poss?vel preparar catalisadores modelos com tamanho de part?culas de Co e porosidades semelhantes, possibilitando o estudo do efeito do suporte, sem sobreposi??o de fatores de difus?o ou tamanho de part?cula. A seletividade de hidrocarbonetos C13+ mostrou depend?ncia do tipo Volcano, com um m?ximo em um car?ter ?cido-base intermedi?rio. A localiza??o das nanopart?culas (NPs) das fases ativas no interior dos canais mesoporosos e o efeito de promo??o do ZrO2 nas propriedades e no desempenho catal?tico dos catalisadores na S?ntese de Metanol via Hidrogena??o de CO2 foi estudado. Tr?s m?todos de co-precipita??o foram empregados para estudar a inser??o das NPs no interior dos mesoporos do suporte. Os m?todos utilizados, ao contr?rio do m?todo de impregna??o a volume de poro convencional, se mostraram como uma forma simples e eficaz de localizar as nanopart?culas de Cu e dos promotores ZnO e ZrO2 nos mesoporos do suporte SBA-15, bem como um efeito positivo nos catalisadores com a incorpora??o do promotor ZrO2. De forma geral, a incorpora??o de ZrO2 mostrou-se eficaz na melhoria da dispers?o e localiza??o das nanopart?culas de Cu e, portanto, maior grau de intera??o do Cu0 com os promotores ZnO e ZrO2. Efeitos de localiza??o e de promo??o do ZrO2 contribuem para a produ??o de catalisadores mais ativos e seletivos para esta rea??o. / Several studies of catalysts used in reactions for the production of energy fuels, such as Fischer-Tropsch Synthesis (FTS) and Methanol Synthesis from CO2 were done. The chemical nature effect of the oxide support on the performance of Cobalt Fischer?Tropsch catalysts was investigated. A series of supports were synthesized via monolayer coverage of porous ?-Al2O3 with various representative oxides from a wide range of Lewis acid?base character, which were characterized by UV?VIS spectroscopy coupled to alizarin adsorption. It was possible to obtain model catalysts with Co particle size and porosity alike, allowing to study the effect of the support without overlapping diffusion factors or particle size. C13+ hydrocarbon selectivity showed volcano-type dependence, with a maximum of intermediate acid-base character. The the nanoparticles of Cu/ZnO/ZnO2 confinement and the promoter effect on the properties and ZrO2 was studied in the context of the catalysts performance in Methanol synthesis via Hydrogenation of CO2. Three co-precipitation methods were chosen to study the nanoparticles confinement in the mesopores. The methods used, unlike the conventional pore volume impregnation method, showed a simple and effective way to confine the Cu/ZnO/ZrO2 NPs in the mesopores of the supporting SBA-15, as well as a positive effect in catalytic converters with the ZrO2 promoter incorporation. In general, the ZrO2 incorporation was effective in improving the dispersion and confinement of Cu NPs and, therefore, a greater Cu0 interaction with ZnO and ZrO2 promoters. Effects of confinement and promotion contributed to the production of more active and selective catalysts for this reaction.

The topic of the Ph.D. thesis was focused on the process of sintering alumina and zirconia ceramic materials with the aim to compare kinetics of sintering sub-micro and nanoparticle systems. Zirconia ceramic powders stabilized by different amount of yttria addition in the concentration range of 0 – 8 mol% were used. The different crystal structure (secured by yttria stabilization) of zirconia, as found, did not play statistically proven role in the process of zirconia sintering. The possible influence was covered by other major factors as particle size and green body structure, which does affect sintering in general. According to the Herrings law, the formula predicting sintering temperature of materials with different particle size was defined. The predicted sintering temperatures were in good correlation with the experimental data for zirconia ceramic materials prepared from both, coarser submicrometer, and also nanometer powders. In case of alumina ceramics the predicted and experimentally observed sintering temperature values did not match very well. Mainly the nanoparticle alumina materials real sintering temperature values were markedly higher than predicted. The reason was, as shown in the work, strong agglomeration of the powders and strong irregularities of particle shape. The major role of green body microstructure in the sintering process was confirmed. The final density of ceramic materials was growing in spite of sintering temperature, which was decreasing together with pore - particle size ratio (materials with similar particle size were compared). Sintering temperature was increasing together with growing size of pores trapped in the green body structure. Clear message received from the above mentioned results was the importance of elimination of stable pores with high coordination number out off the green body microstructure during shaping ceramic green parts. Same sintering kinetics model was successfully applied on the sintering process of submicro- and also nanometer zirconia ceramics. Activation energy of nanometer zirconia was notably lower in comparison to submicrometer material. For the sintering of nanoparticle zirconia was typical so called “zero stage” of sintering, clearly visible on kinetic curves. It was found out, that processes running in zirconia “green” material during zero stage of sintering are heat activated and their activation energy was determined. Pores of submicrometer zirconia were growing in an open porosity stage of sintering just a slightly (1.3 times) compared to the nanoparticle zirconia, where the growth was much higher (5.5 times of the initial pore diameter). This difference was most probably caused by preferential sintering of agglomerates within the green bodies and by particle rearrangement processes which appears in the zero stage of sintering of nanoparticular ceramics. The technology of preparation of bulk dense ytria stabilized zirconia nanomaterial with high relative density of 99.6 % t.d. and average grain size 65nm was developed within the thesis research.

Size-selected Pd nanoparticles were synthesized by the reverse-micelle encapsulation method and deposited on a ZrO2 support for the catalytic NO reduction by H2. All of our samples were found to be highly selective, but a significant size effect was not seen for Pd nanoparticles of between 1.2 nm and 5.5 nm. Ultra-small Pd clusters of less than 1 nm were found to be much less active, and are assumed to be affected by an encapsulation effect of the support. Catalyst activity was comparable to that of literature, and is applicable to H2-SCR research.

Στην παρούσα εργασία μελετήθηκαν λεπτά υμένια οξειδίου του αλουμινίου (Al2O3) και οζειδίου του ζιρκονίου (ZrO2). Η ανάπτυξη των οξειδίων έγινε πάνω σε υπόστρωμα γερμανίου (Ge) με την τεχνική εναπόθεσης ατομικού στρώματος (Atomic Layer Deposition, ALD). Επίσης μελετήθηκαν υμένια οξειδίου του βολφραμίου (WO3), των οποίων η εναπόθεση έγινε με δυο διαφορετικές τεχνικές, πάνω σε υπόστρωμα P3HT:PCBM. Η μελέτη πραγματοποιήθηκε σε συνθήκες υπερυψηλού κενού (Ultra High Vacuum, UHV) με επιφανειακά ευαίσθητες τεχνικές. Κύριος στόχος αυτής της εργασίας, είναι για τα οξείδια αλουμινίου και ζιρκονίου η διερεύνηση της χημικής σύστασης και της ηλεκτρονιακής δομής ενώ θα γίνει μια εκτίμηση του πάχους των υμενίων καθώς και σύγκριση με την αναμενόμενη τιμή συμφωνα με την διαδικασία παρασκευής. Για οξείδια του βολφραμίου έγινε μελέτη τόσο της επιφανειακής χημικής σύστασης όσο και της ηλεκτρονιακής δομής της διεπιφάνειας του οξειδίου του βολφραμίου (WO3) με το υπόστρωμα P3HT:PCBM καθώς και μία σύγκριση των αποτελεσμάτων ανάμεσα στην εξάχνωση με δέσμη ηλεκτρονίων (Electron Beam Evaporation) και τη μέθοδο διαλύματος-πηκτώματος (Sol-Gel) τεχνικές οι οποίες χρησιμοποιήθηκαν για την εναπόθεση των υμενίων οξειδίου του βολφραμίου. / In the present work,studied thin films of aluminum oxide (Al2O3) and zirconium oxide (ZrO2) thin films. Atomic Layer Deposition technique (ALD) was used for the growth of oxide on the germanium (Ge) substrate. Also studied films of tungsten oxide (WO3), which were deposited with two different techniques, onto P3HT:PCBM substrate. The study was conducted under conditions of UHV (Ultra High Vacuum) using surface sensitive techniques. The main objective of this work was to investigate the chemical composition and electronic structure and make an estimate of the thickness of aluminum oxide and zirconium oxide thin films. The thickness was compared with the expected value according to the manufacturing process. For the tungsten oxides were studied the surface chemical composition and the electronic structure of the WO3/P3HT:PCBM interface as well as a comparison of results between the Electron Beam Evaporation and Sol-Gel method, techniques which were used for the deposition of thin films of tungsten oxide.

Afin d'améliorer les performances électriques des circuits intégrés (densité d'intégration, vitesse et fiabilité), des matériaux à permittivité élevée sont introduits dans les composants passifs, notamment les capacités " Métal-Isolant-Métal " (MIM). De nombreux diélectriques, allant d'une permittivité moyenne (SixNy, Ta2O5, HfO2, ZrO2) à très élevée (les pérovskites SrTiO3 et BaTiO3) en passant par les alliages de plusieurs éléments (HfTiO, TiTaO ou Pb(ZrxTi1-x)O3) sont largement étudiés comme candidats prometteurs. Ces composants et ces matériaux ont pour vocation de fonctionner à des fréquences de plus en plus élevées, jusqu'à plusieurs gigahertz. La permittivité complexe Er (permittivité réelle E'r et pertes E''r) des diélectriques peut varier avec la fréquence : des phénomènes de relaxation et de résonance peuvent apparaître. La caractérisation de ces matériaux et l'évaluation des performances des composants intégrant ces diélectriques deviennent nécessaires sur une très large bande de fréquence. Ce travail de thèse a pour objectifs d'obtenir les caractéristiques électriques des diélectriques sur une très large bande de fréquences, du continu à plusieurs dizaines de gigahertz, en configuration in-situ, c'est-à-dire en films minces et avec les mêmes procédés d'intégration que dans le composant MIM final. Pour cela, un outil générique, allant du développement de la technologie nécessaire à la réalisation des structures de test et aux procédures d'extraction des propriétés à hautes fréquences, a été développé, validé grâce au SixNy puis appliqué à différents diélectriques : AlN [1], TiTaO [2], HfO2 et ZrO2 [3,4]. [1] T. Bertaud et al., Microelectron. Eng. 88, 564 (2011). [2] T. Bertaud et al., J. Appl. Phys. 110, 044110 (2011). [3] T. Bertaud et al., IEEE Electr. Device L. 31 (2), 114 (2010). [4] T. Bertaud et al., IEEE T. Compon. Pack. 2 (3), 502 (2012).

Nanokristalle werden beispielsweise für eine Anwendung in Solarzellen, Lichtemittern und nichtflüchtigen Datenspeichern diskutiert. Damit diese Anwendungen funktionieren können, ist eine genaue Kontrolle der Kristallitgröße sowie der Flächendichte und Lage der Kristallite in der Matrix wichtig. Zudem sollte die Matrix amorph sein, da amorphe Matrixmaterialien die Nanokristall-Oberfläche besser passivieren und beständiger gegen Leckströme sind. In dieser Arbeit werden Ge-Nanokristalle in die Hoch-Epsilon-Dielektrika ZrO2 und TaZrOx eingebettet. Im System Ge/ZrO2 kristallisieren die Ge-Cluster und die ZrO2-Matrix bei der gleichen Temperatur. Aufgrund der kristallinen Matrix weicht die Form der Ge-Nanokristalle von einer Kugel ab, worunter unter anderem die Größenkontrolle leidet. Die Beimischung von Ta2O5 stabilisiert die amorphe Phase des ZrO2 und verhindert dadurch die gemeinsame Kristallisation. Dadurch wird es im System Ge/TaZrOx möglich, kugelförmige Ge-Nanokristalle im Größenbereich von 3 nm bis 6 nm positionskontrolliert in eine amorphe Matrix einzubetten. Für die Untersuchung einer möglichen Anwendung des Materialsystems wurden Speicherzellen eines nichtflüchtigen Datenspeichers auf Basis von Ge-Nanokristallen hergestellt. Dabei zeigte sich, dass das System Ge/TaZrOx überdurchschnittlich viele Ladungen speichert und daher für diese Anwendung vielversprechend ist. Zudem stabilisiert die Beimischung von Ta2O5 eine extrem seltene orthorhombische Modifikation des ZrO2. Für ferroelektrische Datenspeicher könnte diese Phase eine aussichtsreiche Alternative zum HfO2 sein.

Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2013-04-23T11:48:39Z No. of bitstreams: 5 Guilhermo Berrocal 5.pdf: 441982 bytes, checksum: ed6d9be182498c6b4db2d0c4a32f7ac8 (MD5) Guilhermo Berrocal 4.pdf: 1385591 bytes, checksum: c4e7c73fa8dc1eec5a3eb4d438068c56 (MD5) Guilhermo Berrocal 3.pdf: 1956923 bytes, checksum: f8dc8503637b206d198b9966a177a091 (MD5) Guilhermo Berrocal 2.pdf: 289780 bytes, checksum: 3fc530194e3c8918ac11f9c2ccdabc15 (MD5) Guilhermo Berrocal 1.pdf: 340675 bytes, checksum: 7e5ee755b290eae4c9ff083197916037 (MD5) / Made available in DSpace on 2013-04-23T11:48:39Z (GMT). No. of bitstreams: 5 Guilhermo Berrocal 5.pdf: 441982 bytes, checksum: ed6d9be182498c6b4db2d0c4a32f7ac8 (MD5) Guilhermo Berrocal 4.pdf: 1385591 bytes, checksum: c4e7c73fa8dc1eec5a3eb4d438068c56 (MD5) Guilhermo Berrocal 3.pdf: 1956923 bytes, checksum: f8dc8503637b206d198b9966a177a091 (MD5) Guilhermo Berrocal 2.pdf: 289780 bytes, checksum: 3fc530194e3c8918ac11f9c2ccdabc15 (MD5) Guilhermo Berrocal 1.pdf: 340675 bytes, checksum: 7e5ee755b290eae4c9ff083197916037 (MD5) Previous issue date: 2005 / Níquel suportado em alumina tem sido extensivamente usado para catalisar a reforma a vapor do metano, devido ao seu baixo custo, quando comparado a outros catalisadores, à base de metais nobres. Entretanto, ele não é estável durante a reação principalmente devido à transição de fase e à sinterização do suporte. Isto requer o desenvolvimento de novos catalisadores. Uma opção atrativa seria usar suportes baseados em zircônia, que possui diversas vantagens, tais como estabilidade térmica, dureza e propriedades anfotériças, mas esse sólido possui baixa área superficial específica, quando comparado a suportes catalíticos convencionais. Uma provável solução para esse problema é combinar as propriedades da alumina e da zircônia. Com este objetivo foi estudada, neste trabalho, a preparação e caracterização de catalisadores de níquel suportado em zircônia e alumina. Os suportes foram preparados por métodos de precipitação à temperatura ambiente, a partir de soluções aquosas de oxicloreto de zircônio e de nitrato de alumínio, seguido de calcinação a 500 oC. Foram obtidos sólidos com razões molares Zr/Al (molar) = 10; 5; 2; 1; 0,5; 0,2 e 0.1, além de alumina e zircônia puras. Os catalisadores foram preparados por métodos de impregnação de soluções de nitrato de níquel, seguido de calcinação a 500 oC. As amostras foram caracterizadas por energia dispersiva de raios X, termogravimetria, análise térmica diferencial, espectroscopia no infravermelho, com transformadas de Fourier, difração de raios X, redução termoprogramada, medidas de área superficial específica e porosidade e espectroscopia fotoeletrônica de raios X. O efeito da temperatura sobre a cristalização dos suportes foi estudada "in situ" por difração de raios X, usando uma câmara de aquecimento. Observou-se a presença das fases tetragonal e monoclínica na zircônia pura e g-Al2O3 na alumina pura. A adição de pequenas quantidades de alumínio estabilizou a fase tetragonal da zircônia, enquanto quantidades mais elevadas de alumínio levaram à produção de sólidos mal cristalizados. As amostras ricas em alumínio (Zr/Al= 0,1; 0,2 e 0,5) também produziram g-Al2O3. A altas temperaturas, os sólidos mal cristalizados formaram aluminato de níquel. A área superficial específica aumentou com a adição de alumínio, o que foi atribuído à presença desse metal na superfície do sólido, onde ele atua como espaçador. A amostra pobre em alumínio (Zr/Al= 0,1) mostrou a área superficial específica mais elevada. Entretanto, a área superficial específica decresceu devido à adição de níquel, provavelmente devido ao bloqueio de alguns poros por esse metal. As amostras apresentaram poros com diferentes formas e tamanhos e produziram isotermas dos Tipos II e III com "loops" de histerese, típicas de materiais mesoporosos. A adição de alumínio também afetou a redução de níquel, tornando esse processo mais difícil; este efeito aumentou com a quantidade de níquel nos sólidos. Entre as amostras à base de alumínio e zircônio, o sólido com quantidades iguais desses metais (Zr/Al (molar)= 1) apresentou o teor mais elevado de níquel na superfície. Ele apresenta área superficial específica elevada e pode ser facilmente reduzido, permitindo a formação da fase ativa do catalisador, na reforma a vapor do metano. Portanto, esse sólido é o catalisador mais promissor para essa reação. / Salvador