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<p> The room-temperature fracture behaviour of calcia partially stabilized zirconia (PSZ) was investigated. Fracture energy measurements were made using the standard stress intensity calibration and work to fracture techniques. The detailed nature of the PSZ microstructure was studied using scanning electron microscopy, qualitative X-ray analysis and T.E.M, surface replication. The grain structure was detenninod to be bimodal with small grains of pure zirconia dispersed along the boundaries of large grains. These large grains consist of a binary pure-zirconia/stabilized zirconia mixture. An attempt was made to relate the fracture properties to the nature of the inherent flaws present in the material. </p> <p> The strength of calcia partially stabilised zirconia was observed to depend on the size and distribution of the grain boundary precipitate of pure zirconia. It is postulated that this grain boundary precipitate causes decohesion and weakening of some of the grain boundaries due to the large internal stresses associated with its martensitic phase transformation. This phenomena of grain boundary decohesion leads to elastic nonlinearity and hysteresis. Crack propagation was always observed to proceed in a slow controlled fashion in this material. A model is proposed to explain theses observations based on the formation of a microcrack zone at the tip of a propagation crack. The occurrence of continued stable crack propagation is believed associated with increasing microcrack zone size with increasing crack length. Evidence supporting this model is presented. </p> / Thesis / Master of Science (MSc)

Esta pesquisa in vitro avaliou a influência do aquecimento de diferentes agentes de acoplamento na resistência de união de um cimento resinoso (Panavia F2.0®/Kuraray Noritake. Japão) e uma zircônia (Y-TZP - YZ ). Inicialmente, placas de zircônia foram silicatizadas com o sistema Rocatec (3M / ESPE). Foram aplicados os agentes de acoplamento químico: Single Bond Universal (3M/ESPE); Monobond N (Ivoclar Vivadent) e Clearfil Ceramic Primer (Kuraray Co); após, foram aquecidos em um forno resistivo em diferentes temperaturas (750C e 1000C) por 5 min, antes da cimentação resinosa de um cilindro de resina composta previamente confeccionado (diam. 0,8 mm). Os grupos controle de cada agente de acoplamento foram mantidos à temperatura ambiente (240C). Metade dos corpos-de-prova foi submetida imediatamente ao teste de microcisalhamento (0,5 mm/min) realizado com auxílio de um fio ortodôntico e a outra metade envelhecida por meio de a 2.000 ciclos térmicos (50C e 550C), seguido de armazenamento em água destilada a 370 C por 2 meses, antes do ensaio mecânico. A análise de variância de três fatores (ANOVA) e o teste de Tukey (p?0,05) mostraram que o aquecimento dos agentes químicos de acoplamento produziu maiores valores de resistência de união entre o cimento e a zircônia. A resistência de união imediata foi superior para o Monobond N (30 MPa) e Single Bond Universal (32,5 MPa). Após o envelhecimento, houve redução da resistência de união em todos os grupos e o grupo Monobond N (16,9 MPa) apresentou resistência de união superior à dos demais. A associação de um tratamento térmico simples a um agente de acoplamento é válida para produzir resistência de união superior entre o cimento resinoso e a zircônia. / This in vitro study evaluated the influence of the heating different coupling agents on microshear bond strength between zirconia (Y-TZP-YZ ) and a resin cement (Panavia F2.0® / Kuraray Noritake, Japan). Initially, the zirconia blocks were silicoated with the Rocatec system (3M / ESPE). After, the chemical coupling agents were applied: Single Bond Universal (3M / ESPE); Monobond N (Ivoclar Vivadent) and Clearfil Ceramic Primer (Kuraray Co). They were then heated in a resistive furnace at different temperatures (750C and 1000C) for 5 min prior to resin cementation of a preformed resin composite cilinder (0.8 mm diameter). Control groups were maintained at room temperature (240C). Half of the specimens were immediately submitted to the microshear test (0.5 mm/min) performed with an orthodontic wire and the other half was subjected to 2,000 thermal cycles (50C and 550C), followed by storage in distilled water at 370C for 2 months before the microshear test. 3-way ANOVA and Tukey\'s test (p<0.05) showed that the heating of the chemical coupling agents produced higher bond strength between the ceramic and resin cement. Immediate bond strength was superior for Monobond N (30 MPa) and Single Bond Universal (32,5 MPa). After aging, there was reduction of bond strength in all groups and the Monobond N group (16,9 MPa) was superior to the others. The combination of a simple heat treatment with a coupling agent is valid to produce greater bond strength.

Submitted by PPG Odontologia (odontologia-pg@pucrs.br) on 2018-05-28T13:41:25Z No. of bitstreams: 1 RAQUEL_DE_OLIVEIRA_LOPES_TES.pdf: 2230148 bytes, checksum: a749d045cae0f8098669b38fe6b648b6 (MD5) / Approved for entry into archive by Caroline Xavier (caroline.xavier@pucrs.br) on 2018-06-11T18:19:23Z (GMT) No. of bitstreams: 1 RAQUEL_DE_OLIVEIRA_LOPES_TES.pdf: 2230148 bytes, checksum: a749d045cae0f8098669b38fe6b648b6 (MD5) / Made available in DSpace on 2018-06-11T18:25:33Z (GMT). No. of bitstreams: 1 RAQUEL_DE_OLIVEIRA_LOPES_TES.pdf: 2230148 bytes, checksum: a749d045cae0f8098669b38fe6b648b6 (MD5) Previous issue date: 2018-01-17 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / (Artigo Os adesivos universais s?o t?o eficientes quanto um primer para a ades?o ? zirc?nia?) O objetivo do trabalho foi comparar a resist?ncia de uni?o ? cer?mica de zirc?nia de quatro adesivos universais e um primer para zirc?nia. Setenta e cinco amostras de zirc?nia foram confeccionadas e inclu?das em resina acr?lica. A superf?cie das amostras foi polida com lixas de carbeto de sil?cio nas granula??es 600, 800 e 1.200 e jateadas com ?xido de alum?nio 50 ?m por 5 s. As amostras foram divididas aleatoriamente em cinco grupos (n=15): G1 ? Single Bond Universal (SBU); G2 ? All Bond Universal (ABU); G3 ? Peak Universal Bond (PUB); G4 ? Ambar Universal (AU) e G5 ? Z-Prime Plus (ZP). Um cone de resina composta foi constru?do, atrav?s de uma matriz, sobre o material adesivo aplicado na superf?cie das amostras. Os corpos de prova foram armazenados em ?gua destilada a 37?C por 24 h, sendo submetidos ao teste de resist?ncia de uni?o ? tra??o em m?quina de ensaio universal EMIC com velocidade de 0,5 mm/min. Os tipos de falhas foram classificados em adesiva, coesiva ou mista. Os valores de resist?ncia de uni?o foram submetidos ? an?lise de vari?ncia (ANOVA), seguido do teste de Tukey (?=0,05). M?dias de resist?ncia de uni?o (MPa) seguidas de letras distintas diferem estatisticamente entre si: G5=21,12a, G1=20,55a, G4=19,12ab, G2=14,22b, G3=8,45c. As falhas foram predominantemente mistas no G1, G4 e G5, e predominantemente adesivas no G2 e G3. Os adesivos SBU e AU obtiveram resist?ncia de uni?o compar?vel ao ZP. / (Artigo Bond to zirconia ceramic: evaluation of different primers and a universal adhesive) The aim of the study was to evaluate the effect of a universal adhesive and different primers on the bond strength to zirconia ceramic. Seventy-five zirconia ceramic samples were obtained and divided into five groups (n=15): G1 ? Scothbond Universal (SBU); G2 ? silane + SBU; G3 - Signum Zirconia Bond; G4 - Z-Prime Plus; G5 - MZ Primer. A cone of composite resin was built. The specimens were stored in 100% relative humidity with distilled water at 37?C for 48 h, and then submitted to a tensile bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. The type of failure that occurred during the debonding procedure was analyzed. The mean results of the bond strength test (MPa) followed by the same letter represent no statistical difference by ANOVA and Tukey?s post-hoc test (p<0.05): G2=27.55a (?6.99), G4=23.71a (?5.65), G1=22.64a (?5.67), G5=13.64b (?5.49), G3=7.54c (?4.75). G2 and G4 exhibited predominantly cohesive failure in the resin composite cone. G1 and G5 had predominantly mixed failures, and G3 exhibited only adhesive failures. The SBU and Z-Prime Plus provided higher bond strength to zirconia ceramic. / (Artigo Os adesivos universais s?o t?o eficientes quanto um primer para a ades?o ? zirc?nia?) The aim of the study was to compare four universal adhesives and a primer on the bond strength to zirconia ceramic. Seventy-five zirconia ceramic samples were obtained and embedded in acrylic resin. The surface of the samples was polished with 600-, 800- and 1200-grit silicon carbide abrasive papers, and sandblasted with 50 ?m aluminum oxide particles for 5 s. The samples were divided into five groups (n=15): Single Bond Universal (SBU); G2 ? All Bond Universal (ABU); G3 ? Peak Universal Bond (PUB); G4 ? Ambar Universal (AU) e G5 ? Z-Prime Plus (ZP). A cone of composite resin was built on the adhesives and primer applied. The specimens were stored in distilled water at 37oC for 24 h, and then submitted to a tensile bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/min. The type of failure that occurred during the debonding procedure was classified as adhesive, cohesive or mixed. The values of bond strength were analyzed by analysis of variance (ANOVA) followed by Tukey?s test (?=0.05). Means of bond strength (MPa) followed by the distinct letters represent statistical difference: G5=21,12a, G1=20,55a, G4=19,12ab, G2=14,22b, G3=8,45c. The failures were predominantly mixed in G1, G4 and G5, and predominantly adhesive in G2 and G3. SBU and AU adhesives obtained bond strength comparable to ZP.

[pt] Materiais à base de zircônia apresentam excelentes propriedades mecânicas, estabilidade química e dimensional, tenacidade, juntamente com um módulo de Young na mesma ordem de grandeza de ligas de aço inoxidável. Devido à essas características, a zircônia tem sido utilizada em uma ampla gama de aplicações, incluindo a fabricação de peças protéticas. As modificações na composição da zircônia e o desenvolvimento do CAD-CAM (computer assisted design) fizeram com que as próteses à base de zircônia se tornassem um procedimento clinico frequentemente realizado na atual Odontologia restauradora. Blocos pré-sinterizados de zircônia, fabricados industrialmente, homogêneos e com falhas mínimas são usinados em um ambiente industrial controlado para receberem a forma desejada. Após a usinagem, as peças em zircônia são sinterizadas para promover sua densificação final. Este processo reduz os possíveis defeitos criados por etapas laboratoriais manuais e intermediárias na confecção de restaurações dentárias. O objetivo deste estudo foi avaliar o efeito da degradação hidrotérmica e do jateamento com óxido de alumínio nas propriedades mecânicas de três tipos de zircônia tetragonal policristalina estabilizada por ítria (ZTPI). Três tipos de zircônias contendo diferentes concentrações de ítria e grau de translucidez foram utilizadas: ZTPI com 5,2 por cento mol (Prettau Anterior Super-Translúcida da Zirkonzahn), ZTPI com 3 por cento mol de Y2O3 (VIPI Block Zirconn) e ZTPI com 3 por cento mol de Y2O3 com translucidez melhorada (VIPI Block Zirconn Translucent). Todas indicadas para uso em próteses odontológicas monolíticas. 15 corpos de prova de cada zircônia testada foram sinterizados e divididos em três grupos de acordo com otratamento de superfície e processo de degradação. No Grupo I as zircônias sofreram jateamento com óxido de alumino. No grupo II as zircônias foram lixadas e polidas. No grupo III as zircônias foram lixadas, polidas, recuperadas e degradadas em reator hidrotérmico por 5 horas a 134 graus Celsius e 2 bar. Para a caracterização microestrutural foram realizados ensaios de difração de raios-X, espectrometria Raman, densidade relativa, microdureza Vickers, rugosidade superficial e análise de tamanho médio de grão por MEV. Os resultados mostraram que a densidade de todos os grupos ficou acima de 99 por cento e que a degradação promoveu a transformação de fase monoclínica e afetou os valores de resistência à flexão. No entanto, a indicação clínica das cerâmicas não foi alterada. O tamanho médio de grão ficou entre 0,367 e 0,621 micrômetros. A dureza e tenacidade à fratura do material não sofreram alterações em função do teor de ítria ou das fases cristalinas presentes. A degradação não afetou de forma significativa os valores de rugosidade, porém, o jateamento com óxido de alumínio não só afetou os valores de flexão como alterou a indicação clínica de cerâmicas utilizadas neste trabalho. / [en] Zirconia-based materials present excellent mechanical properties, tenacity, chemical, and dimensional stability as well as their Young modulus is similar to stainless steel alloys. Due to these characteristics, zirconia has been largely applied in the fabrication of dental prostheses. Modifications in the zirconia composition and the development of CAD-CAM systems has allowed zirconia-based restorations to become a common clinical procedure in current dentistry. Fully sintered and homogeneous blocks from industry are machined at controlled environments seeking to obtain the desired geometry of the restorations. After the machining process, the restorations are sintered to improve their density. This process reduces the failures caused by manual and laboratorial manipulations during fabrication procedure. The aim of this study is to evaluate the effect of hydrothermal aging and sandblasting with aluminum oxide on the mechanical properties of three Yttria-containing tetragonal zirconia polycrystalline (Y-TZP). Three types of Y-TZP, containing different yttria dioxide, were used in the study: Y-TZP with 5,2 per cent mol Y2O3 (Prettau Anterior Super-Translúcida da Zirkonzahn), Y-TZP with 3 per cent mol de Y2O3 (VIPI Block Zirconn) and Y-TZP with 3 per cent mol Y2O3 and optimized translucency (VIPI Block Zirconn Translucent). All the zirconias are indicated for being used as monolithic restorations. 15 specimens from each zirconia tested were sintered and distributed to three groups according to the surface treatment and the aging process. In the group I, the specimens were sandblasted with aluminum oxide particles. For the group II, the zirconia specimens were abraded and polished. In the group III, the specimens were abraded, polished, recovered and aged in a reactor controller for 5 hours at 134 degrees Celsius and 2 bar. The characterization of the zirconia microstructure has been carried out by means of: X-ray diffraction, relative density, Raman spectroscopy, Vickers microhardness, superficial roughness. In addition, the average grain size analysis by scanning electron microscopy were made. The results show that the relative density values were above 99 per cent, and that the hydrothermal aging causes monoclinic phase transformation and affects flexural strength values. However, the clinical indications of materials did not change. The average grain size was between 0.367 and 0.621. The microhardness and tenacity values of materials did not change by yttria concentration or crystallographic phases. The roughness values were not significantly affected by the hydrothermal aging. On the other hand, the flexural strength values were affected by sandblasting process and clinical indication of ceramics tested was changed.

Ceramic cellular solids, mainly honeycombs and foams, are a novel class of composite materials where one phase is an interconnected network of solid struts or plates and the other one an empty phase or possibly a fluid. Honeycombs are an array of two dimensional prismatic cells whereas in foams the arrangements of cells are three dimensional polyhedral cells. Unlike solids, the properties of honeycombs are based on three major variables i.e. a) relative density (p* /p s where p* is the density of the cellular material and ps that of the solid of which it is made) b) cell wall material and c) geometry of the cells. Because of the flexibility in tailoring these variables, cellular solids can be engineered to exhibit a unique combination of mechanical and thermal properties for diversified thermostructural applications. Ceramic based honeycombs fabricated out of cordierite (2MgO.2Al2O35SiO2), mullite (3Al2O32SiO2), cordierite: mullite (2MgO.2Al2O35SiO2) with specific configurations are the leading candidates for many of the applications such as substrates for catalytic converters, molten metal filters, air heaters and heat exchangers etc. Zirconia by the virtue of its high fracture toughness and low thermal conductivity and high refractoriness is an interesting ceramic material and explored for versatile applications. However, no significant efforts have been reported to produce zirconia/alumina and their composite based honeycomb structures and also they have not been explored for their thermo-mechanical and energy absorption based applications. In the present study, looking at the possible potential applications of the honeycombs of Zirconia/alumina and their composites such as solid oxide fuel cells, high temperature filters, blast protection tiles etc., attempts are made to fabricate honeycomb structures. Chapter 1 of the thesis describes the detailed literature survey that has been carried out using advanced search packages regarding the evolution of ceramic honeycomb structures and their properties followed by the advantages of zirconia/alumina and their composites as candidate materials for targeted applications. Literature survey also covers the various processing techniques, characterization procedures with special emphasis on the thermo-mechanical properties. Chapter II describes attempts on developing an optimum scheme of processing of zirconia honeycomb which includes selection of precursor oxides, mixing of formulations, dough making based on viscosity measurements, shaping by extrusion, microwave drying, debinding and sintering to obtain the defect free monolithic structures keeping in view of the scale up possibilities. The chapter also describes a specially developed die fabrication process with innovative machining procedures. (Patent no. 198045). Sintered honeycombs were also characterized for their critical physiochemical properties. In chapter III mechanical characterization of honeycomb samples is reported after subjecting them to compression testing with varying cell channel orientation, compositions and configurations. It is observed that all honeycombs, irrespective of the composition and configuration exhibited anisotropic behavior. In addition, the anisotropy increases with the rib thickness and decreases with increase in the unit cell length. Thermal conductivity measurement studies of the honeycombs are reported in chapter IV. Two types of measurement techniques viz. laser diffraction and monotonic heating technique have confirmed the reduction of thermal conductivity of the honeycomb samples as compared to their solid counterpart. It is observed that the finer channel honeycombs offer low thermal conductivity as compared to the coarser channel when tested across the channel direction. For equivalent relative density, the thermal conductivity value for triangular channel is found to be more as compared to the square channel. Also, the thermal conductivity values were found less when measured across the channel as compared to the values when measured along the channels. The thermal conductivity value for fine channel zirconia-alumina composite honeycombs was found much less than the thermal conductivity of the alumina matrix. Chapter V summarises the implications of the study, conclusions and the target applications.

H Ζιρκόνια σταθεροποιημένη με Ύττρια (Yttria Stabilized Zirconia (YSZ)) χρησιμοποιείται σήμερα ευρέως στη βιομηχανία μηχανών για αεριωθούμενα και στη οδοντιατρική. Τα τελευταία χρόνια υπάρχει έντονο ερευνητικό ενδιαφέρον για την εφαρμογή της σε κυψελίδες καυσίμου στερεού ηλεκτρολύτη (SOFCs) μιας και παρουσιάζει αγωγιμότητα ιόντων οξυγόνου σε μεγάλο θερμοκρασιακό εύρος, διαθέτει υψηλή μηχανική αντοχή, μεγάλη σκληρότητα και χημική σταθερότητα σε συνθήκες ηλεκτρικής φόρτισης και αντίδρασης. Σκοπός της παρούσας εργασίας είναι η ανάπτυξη μεθόδου για εναπόθεση υμενίων ζιρκονίας με την βοήθεια πλάσματος. Η εναπόθεση λεπτών υμενίων YSZ με τη χρήση πλάσματος χαμηλής πίεσης παρουσιάζει μερικά σημαντικά πλεονεκτήματα όπως εναπόθεση σε χαμηλές θερμοκρασίες (<400oC) και ομοιόμορφη κάλυψη της επιφάνειας με μεγάλη πυκνότητα. Από την άλλη πλευρά η ιδιαιτερότητα της εναπόθεσης μέσω πλάσματος έγκειται στο γεγονός ότι η δομή, οι ιδιότητες και η χημική σύσταση των παραγόμενων υμενίων εξαρτώνται σημαντικά από τις παραμέτρους της διεργασίας. Στο πρώτο μέρος της εργασίας αναπτύσσεται η εναπόθεση υμενίων YSZ με τη τεχνική πλάσματος χαμηλής πίεσης από μεταλλοργανικές πρόδρομες ενώσεις υττρίου και ζιρκονίου σε δύο διαφορετικούς αντιδραστήρες πλάσματος, ενός επαγωγικά και ενός χωρητικά συζευγμένου. Μελετήθηκε η επίδραση της παρεχόμενης στο πλάσμα ισχύος, των παροχών των πρόδρομων ενώσεων, του συνολικού χρόνου της διεργασίας και της θερμοκρασίας του υποστρώματος στα μορφολογικά χαρακτηριστικά, στην δομή και τη σύσταση των παραγόμενων υμενίων. Στην συνέχεια εξετάσθηκε πως η χρήση πλάσματος αργού-οξυγόνου, σε ήδη εναποτεθειμένα υμένια ζιρκονίου και υττρίου με τις τεχνικές φυσικής εναπόθεσης (spin και spray coating), ενισχύει την κρυστάλλωση του υμενίου σε κυβική YSZ. Γίνεται σύγκριση με τα αποτελέσματα που λαμβάνονται για την κρυστάλλωση των υμενίων με τη μέθοδο της θερμικής ανόπτησης ως προς τον χρόνο αλλά και τη θερμοκρασία κρυστάλλωσης που χρειάζεται ώστε να επιτευχθεί το ίδιο αποτέλεσμα. Τα υμένια χαρακτηρίσθηκαν με μια σειρά από τεχνικές όπως: φασματοσκοπία φοτοηλεκτρονίων ακτίνων Χ (XPS), ηλεκτρονιακή μικροσκοπία σάρωσης (SEM), περίθλαση ακτίνων Χ (XRD) και μικροσκοπία ατομικών δυνάμεων (AFM). Τα αποτελέσματα των πειραμάτων έδειξαν ότι η παρεχόμενη ισχύ, ο χρόνος της διεργασίας καθώς και η θερμοκρασία του υποστρώματος παίζουν σημαντικό ρόλο στην ανάπτυξη τη δομή και τη μορφολογία των υμενίων YSZ. Για την πλήρη κρυστάλλωση σε κυβική ζιρκονία σταθεροποιημένη με ύττρια αλλά και την πλήρη απομάκρυνση του άνθρακα από το υμένιο, απαιτήθηκε ένα στάδιο ανόπτησης του υμενίου σε φούρνο υψηλής θερμοκρασίας. Αντικατάσταση αυτού του βήματος με επεξεργασία με πλάσμα, οδήγησε σε σημαντική ελάττωση του χρόνου αλλά και της θερμοκρασία κρυστάλλωσης με αποτέλεσμα η συγκεκριμένη τεχνική χημικής ανόπτησης να είναι ενεργειακά συμφέρουσα σε σχέση με την θερμική. Βελτιστοποίηση της διεργασίας χημικής ανόπτησης με πλάσμα έδειξε ότι είναι εφικτή η κρυστάλλωση των υμενίων σε πολύ μικρούς χρόνους και σε θερμοκρασίες μικρότερες από 400°C. / Nowadays Yttria stabilized Zirconia (YSZ) are widely used in the industries of jet engines and also in dentistry. In recent years a lot of effort has been given for the use of YSZ in solid oxide fuel cells (SOFCs) because of its high ionic conductivity in a wide temperature range, its high mechanical strength, high hardness and chemical stability. The purpose of this study is to develop a method for deposition of zirconia films with the use of plasma. The YSZ thin films deposition using low pressure plasma has important advantages such as deposition at low temperatures (<400oC) and uniform coverage of the surface with high density films. On the other hand, the uniqueness of the deposition by plasma is that the structure, the properties and the chemical composition of the films depends on the parameters of the process. In the first part of the thesis, the process of depositing YSZ films is been developed from organometallic precursors of yttrium and zirconium in two different plasma reactors, an inductively and a capacitively coupled plasma reactor. It has been investigated how the plasma power, the amount of the precursors, the total time of the process and the substrate’s temperature affect the morphological characteristics, the structure and composition of the films. It has been also examined how Argon-Oxygen plasma enhances the crystallization to cubic YSZ of already deposited amorphous films of zirconium and yttrium, which have been prepared by physical deposition techniques like spin coating and spray pyrolysis. The results is been compared with the results which have been obtained for the crystallization of the same films by thermal annealing regarding the annealing time temperature in order to achieve the same final crystallization results. The films were characterized by a variety of techniques such as X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The results showed that the plasma power, the process time and the temperature of the substrate play an important role in the development of the structure and the morphology of the YSZ films. In order fully crystallization to be achieved in cubic yttria stabilized zirconia and complete removal of the organic character of the “as deposited” films, a final step of annealing the films in a high-temperature furnace is needed. Replacing this step by Argon-Oxygen plasma treatment resulted a significant reduction in time and crystallization temperature so that the chemical annealing is advantageous in energy consumption compared to thermal annealing. Optimization of the chemical plasma treatment process showed that it is possible to get fully crystallized films in shorter time and for values of temperatures less than 400°C.

This diploma thesis focuses on the fabrication of ceramic fibres by electrospinning. The theoretical part of the thesis summarizes the currently available information regarding ceramic fibres, their properties, applications and fabrication. The theoretical part also describes the process of electrospinning as one of the most frequently used methods of nanofibre fabrication, as well as the parametres influencing this process. The experimental part is aimed at the fabrication of ceramic fibres based on titania, pure non-doped zirconia and yttria-doped zirconia by electrospinning and at the characterization of thus fabricated fibres. Ceramic precursors based on propoxide and polyvinylpyrrolidone were subjected to electrospinning. The experimental part of this diploma thesis also describes the influence of precursor composition, process conditions and calcination temperature on the morphology and phase composition of the fibres. Precursors were characterized by viscosity measurements. Thermogravimetric analysis (TGA), Röntgen analysis (RTG) and scanning electron microscopy (SEM) were used to describe the fibres. By performing electrospinning of precursors based on titanium propoxide and subsequent calcination at 500-1300 °C, TiO2 fibres with thickness of 100-2500 nm were fabricated. The phase composition changed with calcination temperature from 500 °C from anatase phase through rutile blend to pure rutile at 900 °C. By performing electrospinning of precursors based on zirconium propoxide and subsequent calcination at 550-1100 °C, 0 – 8 mol% Y2O3 doped ZrO2 fibres with thickness of 50-1000 nm were fabricated. An analysis of fibres based on non-doped ZrO2, calcined at 550 °C showed a composition of predominantly monoclinic phase. An analysis of 3 or 8 mol% Y2O3 doped ZrO2 fibres calcined at 900 °C showed a composition of predominantly tetragonal phase or purely cubic phase, respectively. With the increasing calcination temperature, the morphology of the fibres changed from porous nanostructure to chain-like non-porous structure consisting of micrometer grains of TiO2 or ZrO2. The ZrO2 fibres calcined at 700 °C remained flexible as well as the spun ones, while their fragility increased with the increase in calcination temperature.

Indiana University-Purdue University Indianapolis (IUPUI) / The objectives: 1. To compare the flexural strength, flexural modulus, and fracture toughness of specimens fabricated from recently marketed translucent full-contour zirconia, traditional zirconia, and lithium disilicate glass ceramic. 2. To compare the load-to-failure of crowns fabricated from recently marketed translucent full-contour zirconia, traditional zirconia, and lithium disilicate glass ceramic at their recommended tooth-reduction thickness. Methodology: Four groups of translucent zirconia (BruxZir, KDZ Bruxer, CAP FZ, Suntech zirconia), one group of traditional zirconia (CAP QZ) and IPS e.maxCAD) were tested. Twelve bars of each material were made and tested for flexural strength, and fracture toughness. Fracture patterns were imaged under SEM. Forty-eight crowns (8 from each group) were fabricated with CAD/CAM technique following manufacturers’ recommendations for the amount of tooth reduction. All the crowns were cemented to prepared epoxy resin dies with RelyX Unicem and tested for static load to failure in a universal machine. Result: In bar-shape samples, CAP QZ (traditional zirconia) showed the highest flexural strength (788.12 MPa), fracture toughness (6.85 MPa.m1/2), and fracture resistance (2489.8 N). All translucent zirconia groups show lower mechanical properties than QZ. However, there were no differences between translucent and traditional zirconia in the fracture resistance of the crown-shape samples. There was no significant difference in fracture resistance between IPS e.max crowns at recommended thickness and other zirconia crowns at recommended thickness. Conclusion: With less reduction of tooth structure, a high inherent strength and chip resistance make full-zirconia crowns a good alternative to porcelain-fused-to-metal crowns and all other ceramic crowns.

Indiana University-Purdue University Indianapolis (IUPUI)