Zugl.: Saarbrücken, Univ., Diss., 2007

Tübingen, Univ., Diss., 2006.

Zugl.: Magdeburg, Univ., Diss., 2010

Universiẗat, Diss., 1999--Saarbrücken. / Erscheinungsjahr auf der Haupttitels.: 1999.

University, Diss., 2002--Saarbrücken.

Universiẗat, Diss., 2003--Jena.

Η εργασία έγινε στα πλαίσια του ευρωπαϊκού προγράμματος “MULTIPROTECT”, NMP3-CT-2005-011783 με συμμετοχή 31 εργαστηρίων από την Ευρώπη. Το πρόγραμμα αυτό επεκτάθηκε για άλλα τέσσερα χρόνια με ένα νέο πρόγραμμα FP7 με σύντομο τίτλο “MUST”. Σκοπός του προγράμματος είναι η αντικατάσταση της υπάρχουσας τεχνολογίας προστασίας μεταλλικών επιστρώσεων από την διάβρωση που περιέχουν εξασθενές χρώμιο, με καινούργιες μεθόδους που χρησιμοποιούν υλικά φιλικά προς το περιβάλλον και τον άνθρωπο. Το κράμα αργιλίου 2024 – Τ3 χρησιμοποιείται σε προηγμένες τεχνολογικά εφαρμογές, όπου απαιτείται η υψηλή αντοχή και το χαμηλό βάρος, όμως λόγω των στοιχείων κραμάτωσης, όπου οφείλεται η αύξηση των μηχανικών ιδιοτήτων του, γίνεται ευάλωτο στην διάβρωση και η ανάγκη για την εξεύρεση προστατευτικών επιστρώσεων φιλικές προς το περιβάλλον είναι επιτακτική. Μια από τις εναλλακτικές τεχνολογίες που εξελίσσονται στο εργαστήριο Sol-Gel αφορά την σύνθεση sol-gel ηλεκτροχημικών και χημικών επιστρώσεων και η βελτίωση τους με προσθήκη νανοδοχείων πληρωμένων με αναστολείς διάβρωσης. Η εργασία αυτή δομείται από δύο μέρη. Αρχικά, στο θεωρητικό μέρος παρουσιάζεται το φαινόμενο της διάβρωσης και συζητούνται ζητήματα που αφορούν την ηλεκτροχημική της φύση όπως η θεωρία ηλεκτρικής διπλοστοιβάδας, τα δυναμικά των ηλεκτροδίων και η εξίσωση Butler-Volmer. Παρουσιάζονται οι ιδιότητες του αλουμινίου και των κραμάτων του και περιγράφονται τα είδη της διάβρωσης γι αυτό. Συνεχίζοντας παρουσιάζεται η μέθοδος sol-gel και αναλύονται τα στάδια της. Τελειώνοντας το θεωρητικό μέρος παρουσιάζονται οι πειραματικές τεχνικές που χρησιμοποιήθηκαν για τον χαρακτηρισμό του πειραματικού μέρους. Αυτές είναι η ηλεκτροχημική φασματοσκοπία σύνθετης αντίστασης (EIS), η ποτενσιοδυναμική πόλωση (potentiodynamic polarization), η ηλεκτρονιακή μικροσκοπία (SEM), η φασματοσκοπία ενεργειακής διασποράς ακτίνων Χ (EDX), η Θερμοβαρομετρική αναλυση (TG) και η διαφορική θερμική ανάλυση (DTA), η μέθοδος ΒΕΤ, η φασματοσκοπία υπερύθρου (FT-IR) και η φασματοσκοπία ακτίνων X (XRD). Το πειραματικό μέρος μπορεί να διακριθεί σε δύο ενότητες. Αρχικά στη σύνθεση και μελέτη νανοδοχείων Ce-Ti που εμπλουτίστηκαν με χημικές ενώσεις, οι οποίες λειτουργούν ως αναστολείς διάβρωσης. Περιγράφεται ο μηχανισμός λειτουργάς των αναστολέων διάβρωσης που επιλέχθηκαν (Νιτρικό δημήτριο, 2-Μερκαπτοβεζοθιαζόλη και 8-Υδροξυκινολίη). Η διαδικασία που ακολουθήθηκε για την σύνθεση των νανοδοχείων οξειδίου τιτανίου/δημητρίου χωρίζεται σε τρία βήματα. Αρχικά στην παρασκευή θετικά φορτισμένων νανοσφαιρών πολυστυρενίου (PS) στη συνέχεια ακολουθεί η επικάλυψη των πυρήνων αυτών και τέλος η θερμική επεξεργασία (calcination), όπου το δείγμα θερμαίνεται σε υψηλή θερμοκρασία με σκοπό την καταστροφή του υποστρώματος και την δημιουργία των νανοδοχείων. Ακολούθησε η πλήρωση των νανοδοχείων με αναστολείς διάβρωσης υπό υψηλό κενό. Μελετήθηκε η μορφολογία και η σύσταση των νανοδοχείων καθώς επίσης και απελευθέρωση των αναστολέων διάβρωσης. Η δεύτερη ενότητα του πειραματικού μέρους αφορά τη σύνθεση και μελέτη αντιδιαβρωτικών ORMOSIL επιστρώσεων. Για την σύνθεση των επιστρώσεων χρησιμοποιήθηκαν δύο μέθοδοι. Η ηλεκτροχημική μέθοδος, η οποία είναι μία καινοτόμος μέθοδος για τη δημιουργία επιστρώσεων και η μέθοδος της εμβύθισης (μία ή τέσσερις εμβυθίσεις), μία κλασική μέθοδος δημιουργίας επιστρώσεων η οποία επιλέχθηκε για σύγκριση με την πρώτη μέθοδο. Ως μόρια εκκινητές μελετήθηκαν 3-γλυσιδοξυ-προπιλ-τριμεθοξυ-σιλάνιο (GPTMS), Διαιθοξυ-διμεθυλο-σιλάνιο (DEDMOS) και τριμεθοξυ-μεθυλο-σιλάνιο (TMOMS). Το GPTMS παρέχοντας την καλύτερη αντιδιαβρωτική προστασία επιλέχθηκε για περεταίρω μελέτη. Για την βελτίωση των επιστρώσεων μελετήθηκαν διάφοροι παράμετροι όπως η συγκέντρωση του ηλεκτρολύτη, ο χρόνος ηλεκτροχημικής εναπόθεσης, ο ρυθμός αφαίρεσης από το διάλυμα κατά τις επιστρώσεις με την μέθοδο τα εμβύθισης, ο χρόνος και η θερμοκρασία ξήρανσης, η προσθήκη νανοσωματιδίων (διοξειδίου του δημητρίου, δημητρίου-μολυβδενίου, διοξειδίου του ζιρκονίου). Από τα αποτελέσματα επιλέχθηκε σαν ιδανική θερμοκρασία οι 90 οC για 24 ώρες. Σε αυτές τις επιστρώσεις προστέθηκαν τα νανοδοχεία Ce-Ti πληρωμένα με 8-HQ ή 2-MB σε διάφορες περιεκτικότητες. Η παρουσία νανοδοχείων πληρωμένα με αναστολείς διάβρωσης κατάφερε να ενισχύσει την προστασία από τα διάβρωση. Από την EIS παρατηρείται η εμφάνιση μιας ακόμη χρονικής σταθεράς που αντιστοιχεί στην προστασία φραγμού στις επιστρώσεις sol-gel. Τα νανοδοχεία που συντέθηκαν όχι μόνο ενίσχυσαν το δίκτυο της επίστρωσης αλλά απελευθέρωσαν τον αναστολέα διάβρωσης που ήταν πληρωμένα όταν ήρθαν σε συνθήκες διάβρωσης. Αυτή η παρατεταμένη απελευθέρωση παρέχει προστασία από τη διάβρωση του κράματος αλουμινίου 2024-Τ3 που διαρκεί. / This project was carried out within the European program "MULTIPROTECT", NMP3-CT-2005-011783 involving 31 laboratories from Europe. This program was extended for another four years with a new program FP7 with the short title "MUST". The program aims to replace the existing technology of metal protection against corrosion coatings containing hexavalent chromium, with new methods that use environmentally friendly materials. The aluminum alloy 2024 - T3 is used in advanced technology applications requiring high strength and low weight, but because of the alloy elements, which explains the increase in mechanical properties, is vulnerable to corrosion, so the need to find protective coatings friendly to the environment is imperative. One of the alternative technologies which are evolved in the Sol-Gel laboratory is the composition of sol-gel electrochemical and chemical coatings improved by the addition of nanocontainers loaded with corrosion inhibitor. This work is structured in two parts. The first part concerns with the theoretical presentation of corrosion and issues relating to the electrochemical nature such as the electric double-layer , the potentials of the electrodes and the Butler-Volmer equation. Moreover the properties of aluminum and its alloys and aluminium corrosion types are discussed. The sol-gel method is analyzed as well. Concluding the theoretical part, the characterization methods that were used are described. These are electrochemical impedance spectroscopy (EIS), the potentiodynamic polarization, scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDX), the Thermo-gravimetric analysis (TG) and differential thermal analysis (DTA), BET, infrared spectroscopy (FT-IR) and X-ray spectroscopy(XRD). The second part deals with the experimental procedures divided into two sections. First, the synthesis and study of Ce-To nanocontainers oxide loaded with corrosion inhibitors. The mechanism of corrosion protection of the inhibitors (cerium nitrate, 2-mercaptobenzothiazole and 8-Hydroxyquinoline) is described. The procedure followed for the synthesis of titanium/cerium oxide nanocontainers can be divided into three steps. Initially the synthesis of positively charged polystyrene (PS) then followed by coating of these spheres and finally the calcinations. After these all that remains is the loading of these nanocontainers under high vacuum. The morphology and composition of the nanocontainers as well as the release of corrosion inhibitors was studied. The second section of the experimental part is the synthesis and study of ORMOSIL coatings. These coatings were synthesized by electrodeposition, a novel technic for creating sol-gel coatings and the dip-coating method (one or four dips), a classic method of making the coatings selected in comparison with the first method. 3-Glycidoxypropyl-trimethoxysilane (GPTMS), Diethoxy-dimethylsilane (DEDMOS) and methyl-trimethoxy-silane (TMOMS) were used as precursors. As GPTMS coatings provided the best corrosion protection it was chosen for further study. To improve the coatings various parameters, such as concentration of the electrolyte, the time of electrochemical deposition, the removal speed from the solution during the dip-coating method, time and temperature of drying, the addition of nanoparticles (cerium oxide, cerium -molybdenum, zirconium oxide) were studied. The results showed that the ideal drying temperature was 90 οC for 24 hours. Ce-Ti nanocotainers loaded with 8-HQ or 2-MB were added into these coatings with different concetratoins. The presence of the nanocontainers loaded with corrosion inhibitors enforced the corrosion protection. EIS results witness the appearance of another time constant corresponding to the barrier effect of the sol-gel coatings. Nanocontainers not only enforced the sol-gel network but also released the corrosion inhibitor when corrosion starts. This continuous release provides extended protection against corrosion of aluminum alloy 2024-T3.

Made available in DSpace on 2014-08-13T14:50:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-26Bitstream added on 2014-08-13T18:00:41Z : No. of bitstreams: 1 000756517.pdf: 1734857 bytes, checksum: 281f33b4567ed911763af72805522884 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Materiais híbridos de Sílica modificados organicamente (ORMOSIL) são muito estudados devido à variedade de alcóxidos funcionalizados com moléculas orgânicas (epóxi, vinil, amina, fenil, etc). O estudo das propriedades de materiais híbridos de sílica/orgânico preparados via sol-gel dopados com nanocristais de semicondutores do tipo núcleo/casca é de grande interesse, pois possibilita que propriedades ópticas e mecânicas sejam controladas a partir da síntese, produzindo materiais multifuncionais que apresentam características híbridas da matriz sílica/orgânico aliada aos fenômenos ópticos produzidos pelo dopante. Neste trabalho foram estudadas as propriedades ópticas de matrizes de sílica/orgânico à base de 3-glicidoxipropiltrimetoxisilano (GPTS) e tetraetilortosilicato (TEOS) preparadas pelo processo sol-gel, dopadas com nanocristais de CdSe/ZnS. As matrizes híbridas dopadas foram caracterizadas por espectroscopia óptica (absorção óptica e luminescência UV/VIS) e espectroscopia termo-óptica (lente térmica). Nanocristais de CdSe/ZnS com três tamanhos diferentes de núcleos (~2 a 5 nm) e banda de emissão centrada em 525, 560 e 615 nm (verde, laranja e vermelho, respectivamente) foram estudados quando inseridos na matriz híbrida e as caracterizações foram realizadas in-situ na matriz desde o estado inicial sol e durante a cinética de gelificação. Durante a cinética de gelificação, catalisada pela adição de NH4OH, foi observado a diminuição da intensidade de luminescência dos nanocristais com mínimo no ponto de gel da matriz e subsequente desvio para o azul com acentuado aumento da intensidade de luminescência relacionada com a consolidação da matriz. Através dos espectros de densidade óptica foi possível determinar a variação da energia de gap das amostras durante a cinética de gelificação. As medidas de lente térmica foram realizadas usando laser de excitação e prova para estudar os... / Organically Modified Silicates (ORMOSIL) have been object of study due to the variety of the organically functionalized alkoxides (epoxy, vinyl, phenyl, etc). This allows the production of new hybrid silica materials with adjustable properties depending on the organic molecule linked to silica. The study of the properties of CdSe/ZnS core-shell nanocrystals embedded in GPTS/TEOS-derived organic/silica hybrids is of high interest due the optical and mechanical properties which can be controlled from the synthesis, producing multifunctional materials. This work aims the study of the optical properties measured in situ of CdSe/ZnS nanocrystals embedded in organic/silica hybrid colloids prepared by sol-gel technique derived from 3-glycidoxypropyltrimethoxysilane (GPTS) and tetraethylorthosilicate (TEOS). Doped organic/silica hybrid matrices were characterized by optical spectroscopy (absorption and photoluminescence) and thermo-optical spectroscopy (thermal lens). CdSe/ZnS nanocrystals with three different core sizes (~2 -5 nm) and emission band centered at 525, 560 and 615 nm (green, orange and red, respectively) were studied embedded in the hybrid matrix. The optical characterizations were performed in-situ in the matrix from the initial sol and during the gelation kinetics (transition from sol to gel). During the gelation kinetics started by NH4OH addition, an intensity decrease of the nanocrystals photoluminescence was observed during the sol to gel transition, achieving minimum photoluminescence intensity exactly at the matrix gel point with subsequent blue shift and accentuated photoluminescence intensity increase related to the matrix consolidation. Through the optical absorption spectra it was possible to determine the variation in the energy gap of the samples during the kinetics of gelation. TL transient measurements were performed using the mode-mismatched dual-beam configuration to study the effect of the CdSe/ZnS embedded in...

Made available in DSpace on 2014-08-13T14:50:46Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-25Bitstream added on 2014-08-13T18:00:40Z : No. of bitstreams: 1 000756776.pdf: 1247387 bytes, checksum: e43f6ca86e670c147013bebeba65e0d7 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho tem como objetivo estudar os efeitos da variação de concentração do copolímero tri-bloco (Pluronic F127) no preparo de géis de sílica a partir de hidrólise ácida do tetraetilortosilicato (TEOS), através de suas características estruturais em estágios que vão desde o saturado (géis úmidos) até os estados secos do gel (aerogéis e xerogéis). O F127 é um polímero formador de micelas utilizado como impregnador de estrutura no processo de formação de poros em espécies de sílicas, pois a estruturação micelar do F127 pode determinar a formação de poros de diferentes tamanhos durante os processos de geleificação na hidrólise e policondensação para obtenção de corpos porosos, produzindo interessantes estruturas de sílicas porosas obtidas pelo método sol-gel. Os aerogéis de Sílica foram obtidos por secagem a pressão ambiente (APD) após sililação dos géis em fase úmida. O processo de sililação foi feito nos géis úmidos utilizando 20% em volume de hexametildisilazano (HMDZ) em n-hexano. As características estruturais de aerogéis obtidos por APD com diferentes adições de F127 foram estudadas após tratamento térmico a 300, 500, 700 e 900 ºC, através de análises de adsorção de nitrogênio e espalhamento de raios-X a baixo ângulo (SAXS). Adicionalmente xerogéis com as mesmas composições de F127 foram obtidos por envelhecimento em solução de NH4OH 0,1M e APD. Os géis úmidos apresentaram uma estrutura de fractal de massa com dimensão fractal D em torno de 2.1 e o tamanho característico do domínio fractal (ξ) vai de 9.05 para o gel preparado sem adição de F127 até valores que extrapolam o limite máximo experimental de 14,2 nm com o aumento da concentração de F127. Estes géis também exibem um estrutura que permeiam o fractal, os domínios da estrutura do fractal de massa principal dos géis úmidos. A partir da adsorção de nitrogênio obteve-se a superfície... / The present work aims to study the effects of varying the concentration of the copolymer tri-block (F127 Pluronic) in the preparation of silica gels from acid hydrolysis of tetraethylorthosilicate (TEOS), through its structural features in stages ranging from the saturated (wet gels) to dry gel state (aerogels and xerogels). The F127 is a micelle forming polymer as used in the impregnator structure of the pore-forming species-process silica because the micellar structure of F127 can determine the formation of pores of different sizes during the process of gelation on hydrolysis and polycondensation to obtain porous bodies, producing interesting structures of porous silica obtained by sol-gel method. Silica aerogels were obtained by ambient pressure drying (APD) after silylation of the gels in humid phase. The process of silylation was done in the wet gels using 20% by volume of hexamethyldisilazane (HMDZ) in n-hexane. Heat treatment at 300, 500, 700 e 900 ºC was performed in order to characterize. The structure of aerogels by APD with different compositions of F127. This characterization was carried out using nitrogen adsorption and small angle X-ray scattering techiniques. Additionally xerogels having the same compositions F127 were obtained by aging in a solution of 0.1 M NH4OH and APD. The wet gels showed a mass fractal structure with fractal dimension D around 2.1 and fractal characteristic size of the domain (ξ) goes from 9.05 for gel prepared without the addition of F127 to values that exceed the maximum experimental limit of 14.2 nm with increasing concentration of F127. These gels also exhibit a fractal structure that permeate the field of fractal structure of the main mass of wet gels. Nitrogen adsorption shows a specific surface area (SBET) for APD aerogels, which presented a value of around 800 m2/g to different concentrations of F127, the volume (Vp), the average length (lp) pores of aerogels increased more or less regular...

Made available in DSpace on 2016-05-17T16:51:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-10-16. Added 1 bitstream(s) on 2016-05-17T16:55:27Z : No. of bitstreams: 1 000863489_20171010.pdf: 270564 bytes, checksum: 14ae6d49755d9bd4f1165d0581118e98 (MD5) Bitstreams deleted on 2017-10-16T12:45:42Z: 000863489_20171010.pdf,. Added 1 bitstream(s) on 2017-10-16T12:46:28Z : No. of bitstreams: 1 000863489.pdf: 2384161 bytes, checksum: 21b3016117fd918faa1b92c15a40eb86 (MD5) / A produção de aluminas com distribuição de tamanho e volume de poros controlados pela separação de fases líquido-sólido é um assunto emergente na área de cerâmicas porosas. As aluminas foram produzidas pelo processo sol-gel acompanhado de separação de fases, usando o óxido de polietileno (PEO) como agente indutor na separação de fases e o óxido de propileno para a gelatinização, para isso foram estabelecidas condições de controle cinético e termodinâmico desses eventos, através do controle do tempo de agitação e temperatura no meio reacional. Foram otimizadas rotas de síntese através do ajuste dos parâmetros de preparação variando a concentração do agente direcionador de poros PEO durante a transição sol-gel. Esta transformação foi acompanhada in-situ por SAXS revelando que o crescimento de objetos fractais com dimensionalidade de 1,7, que é característico do mecanismo e agregação controlado pela difusão. A calcinação em 700°C possibilitou a produção de aluminas da fase gama (-Al2O3) com textura porosa formada por macro e mesoporos. O uso do agente direcionador de poros PEO em proporção molar entre 0,01-0,07 mostrou-se eficiente no ajuste da macro-mesoporosidade. Entretanto quando se emprega proporções molares de PEO acima de 0,07 obtém-se apenas famílias de mesoporos com um decaimento do volume específico de poros quando a proporção molar aumenta de 0,08 para 0,1. Estas aluminas mesoporosas apresentaram maior área superficial especifica (Área BET máximo de  305 m²/g) e uma melhor relação OH/-O-Al em comparação com as macro-mesoporosas. / The production of alumina with volume and size distribution of pores controlled by phase separation induced by the addition of the polymer polyethylene oxide (PEO) during synthesis is an emerging issue in the area of functional ceramics. The aluminas were produced by the sol-gel process followed by phase separation, and the PEO as inducing agent phase separation and propylene oxide to gelation. Conditions for kinetic and thermodynamic control over these events were kept by controlling the stirring time and temperature in the reaction medium. Synthesis routes have been optimized by adjusting the preparation parameters varying the concentration of pores directing agent (PEO) during sol-gel process. This transformation was accompanied by in-situ SAXS and the results reveal the growth typical of fractal objects starting from a diluted solution, whose dimensionality in the Porod region was 1,7, characteristic of aggregation controlled by diffusion and the distances between the growing particles is around 2,95 nm. Gamma alumina (-Al2O3) with diversified porous texture and macro-mesopores was obtained with thermal treatment up to 700 ° C, being supported by several techniques. The macro-mesoporosity can be adjusted by PEO driver pores agent in a molar ratio from 0,01 to 0,07. Molar ratios of PEO above 0,07 produces only mesopores, decreasing the cumulative volume of this pores when the molar ratio increases from 0,08 to 0,1. These mesoporous aluminas had higher specific surface area (BET Area  305 m² / g) and better ratio OH/O-Al compared to the macro-mesoporous.