Anlagen zur Herstellung von Synthesegas (CO·H2) aus kohlenstoffhaltigen Rohstoffen werden durch hohe Temperaturen bis zu 1600 °C und Drücken bis zu 50 bar beansprucht und benötigen daher Schutz durch eine feuerfeste Ausmauerung. Zur Steigerung der Effizienz und Lebensdauer solcher Vergasungsanlagen ist die Entwicklung neuer keramischer Hochtemperaturwerkstoffe erforderlich. Solch ein Material stellt eine Al2O3-reiche Gießmasse dar, welche durch den gezielten Einsatz verschiedener ZrO2- und TiO2-Gehalte optimiert wurde. Es hat sich gezeigt, dass bereits durch die Zugabe geringer Mengen an ZrO2 bzw. TiO2 sowohl die Temperaturwechselbeständigkeit als auch die Korrosionsbeständigkeit von Al2O3 gegenüber Kohleschlacken erheblich verbessert werden kann, was auf die Ausbildung einer Spinell-Schutzschicht während des Korrosionsvorgangs zurückzuführen ist.

[pt] Cerâmicas termomióticas vem despertando interesse devido a sua propriedade de apresentar, sob aquecimento, uma expansão térmica baixa, próxima a zero ou negativa. Essa propriedade é proveniente de uma vibração transversal do ânion, que resulta numa aproximação de átomos em determinadas direções. A família A2M3O12 (A = um cátion trivalente e M = Mo6 positivo ou W6 positivo) apresenta uma transição de fase de monoclínica para ortorrômbica, sendo somente a fase ortorrômbica que apresenta o comportamento termomiótico. Essa família, especificamente, vem sendo bastante pesquisada, pois possui a vantagem de permitir uma vasta flexibilidade química, sem mudar de estrutura cristalina e por consequência, permitir ajustes no coeficiente de expansão térmica de acordo com a aplicação a qual o material se destina. A expansão térmica próxima à zero pode levar a uma promissora alta resistência ao choque térmico. Esse trabalho teve como objetivo, estudar as propriedades térmicas e mecânicas do Al2W3O12 que possui baixa expansão térmica positiva com o objetivo de determinar sua resistência ao choque térmico pela figura de mérito de Hasselman. Para isso, todas as suas propriedades térmicas (expansão térmica e condutividade) e mecânicas (módulo de elasticidade e resistência mecânica) foram obtidas experimentalmente apresentando um valor promissor de 120K (comparável ao da safira) para resistência ao choque térmico pela figura de mérito de Hasselman sob condições severas de aquecimento. A partir desse resultado foi desenvolvido uma segunda pesquisa com o objetivo de refinar a microestrutura e aumentar a densidade relativa da cerâmica maciça do Al2W3O12 e assim incrementar suas propriedades mecânicas. Uma síntese por co-precipitação, seguida de uma prensagem isostática e uma sinterização desenvolvida em três etapas foram implementadas, obtendo-se um aumento de 91 porcento para 96 porcento na densidade relativa, com aumento de 19 porcento no módulo de elasticidade e de 35 porcento na dureza vickers se comparados aos resultados obtidos pela amostra sinterizada anteriormente pelo método convencional de sinterização em uma etapa. No terceiro estágio desta tese foi estudada a expansão térmica de uma novo material (In0,5(ZrMg)0,75Mo3O12) com promissora expansão térmica próxima a zero (10-7 K-1), a partir do cálculo da regra das misturas. O material foi sintetizado por evaportação total.e seu coeficiente de expansão térmica intrínseco determinado in situ por difração de Raios-X foi de 1,6x10-7 K-1 na faixa de temperatura de 100 a 500 graus Celsius, enquanto o coeficiente de expansão térmica maciço, medido por dilatometria, foi de 6,68 x 10-7 K-1, na faixa de temperatura de 100 a 800 graus Celsius. Esse material apresenta uma transição de fase de monoclínica para ortorrômbica na temperatura de 82 graus Celsius o que limita seu uso como material termomiótico em temperaturas abaixo de 100 graus Celsius. / [en] Thermomiotic ceramics have been arousing interest due to their property of presenting a low, near or zero thermal expansion under hearing. This property comes from a transverse vibration of the anion, which results in an approximation of atoms in certain crystallographic axes. The A2M3O12 family (A = a trivalent cation and M = Mo6 positive or W6 positive) presents a phase transition from monoclinic to orthorhombic, with only the orthorhombic phase exhibiting thermomiotic behavior. This family is widely researched since it has the advantage of allowing a wide chemical flexibility without changing the crystalline structure and consequently allowing adjustments in the coefficient of thermal expansion according to the application, which the material is intended. Thermal expansion close to zero can lead to a promising high thermal shock resistance. This work aimed to study the thermal and mechanical properties of Al2W3O12 that has low thermal expansion with the goal of determining its thermal shock resistance by the Hasselman figure of merit. For this, all its thermal properties (thermal expansion and conductivity) and mechanical (Young modulus and mechanical strength) were obtained experimentally and presented a promising value of 120K (comparable to sapphire) for thermal shock resistance by the figure of merit of Hasselman under severe heating. A second research was developed with the goal of refining the microstructure and increasing the relative density of the Al2W3O12 bulk ceramics and thus increasing its mechanical properties. A synthesis by co-precipitation, folled by an isostatic pressing and a three steps sintering were carried out, obtaining an increase of 91 percent to 96 percent in the relative density, with increase of 19 percent in modulus of elasticity and 35 percent in Vickers hardness when compared to conventional sintering. The thermal expansion of a new material (In0,5(ZrMg)0,75Mo3O12) with promising thermal expansion close to zero (10-7 K1), calculated by mixing rule was studied in the third chapter of this thesis. The material was synthesized by total evaporation. Its intrinsic thermal expansion coefficient was determined in situ by X-ray diffraction and presented a value of 1.6x10-7 K-1 in the temperature range of 100 to 500 Celsius degrees, while the coefficient of expansion of the bulk obtained by dilatometry, was 6.68 x 10-7 K-1, in the temperature range of 100 to 800 Celsius degrees. This material presents a phase transition from monoclinic to orthorhombic at 82 Celsius degrees, which limits its use as thermomiothic material at temperatures above 100 Celsius degrees.

[pt] O principal objetivo deste trabalho foi estudar o sistema Al2-xGaxW3O12 (x = 0,2; 0,4; 0,5; 0,6; 0,7; 0,8; 1; 2) visando compreender os efeitos da substituição parcial de Al3+ (r = 0,67 Angstrom) por Ga3+ (r = 0,76 Angstrom) em relação ao coeficiente de expansão térmica da fase Al2W3O12. Foi determinado que o limite de solubilidade de Ga3+ no sistema é x = 0,5, as composições x maior ou igual 0,6 evidenciaram, por difração de raios-X (DRX), a presença de WO3 como fase secundária. Os difratogramas das composições 0,2 menor ou igual x menor ou igual 0,5, a temperatura ambiente, apresentaram exclusivamente linhas características do sistema monoclínico (P21/a). A transição para a fase ortorrômbica (Pbcn), foi evidenciada por DRX in situ e dilatometria e ocorre abaixo de 100 C em todos os casos. A temperatura de transição de fase, determinada por dilatometria, aumentou conforme foi aumentada a incorporação de Ga3+ na estrutura cristalina. A análise termogravimétrica das composições monofásicas revelou que essas fases não são higroscópicas. Embora Al1,5Ga0,5W3O12, seja a composição monofásica com maior teor de Ga, a fase Al1.6Ga0.4W3O12 foi a que apresentou o menor coeficiente de expansão térmica linear, alfa L= 1.14 K -1, uma redução de 25 por cento quando comparado ao coeficiente linear de expansão da fase Al2W3O12. O refinamento pelo método de Rietveld do padrão de difração de raios-X obtido a 100 C da Al1.6Ga0.4W3O12 ortorrômbica, confirmou que o Ga3+ substituiu o Al3+ na proporção descrita pela fórmula química nominal e evidenciou que as distorções poliédricas, Al(Ga)O6 e WO4, foram maiores do que as observadas em fases desta família. A espectroscopia de Raman corroborou as análises de DRX quanto ao limite de solubilidade, porém, evidenciando que quantidades mínimas, indetectáveis por DRX, de Al2O3 e WO3 podem estar presentes nas composições x menor ou igual 0,5, quando a síntese é realizada pelo método de reação no estado sólido. Os gráficos de Kubelka-Munk do sistema Al2- xGaxW3O12 indicaram que a substituição parcial de parcial de Ga3+ por Al3+ aumenta o intervalo de banda em x menor ou igual 0,4, no entanto, foi observada uma saliência de absorção dentro da região do visível presente em todas as amostras, interpretada como uma conseqüência da presença de WO3 monoclínica, observada na espectroscopia Raman. A síntese da fase Ga2W3O12, não foi bem sucedida, embora a entalpia de formação deste composto, calculada por meio da equação generalizada de Kapustinskii e pelo ciclo de Born-Haber, seja fortemente exotérmica, ΔHF= −10149,15 Kj. mol -1. / [en] The aim of this work was to study the Al2-xGaxW3O12 system (x = 0.2, 0.4, 0.5, 0.6, 0.7, 0.8, 2) in order to investigate the relationship between the partial replacement of Al3+ (r = 67 Angstrom) by Ga3+ (r = 0.76 Angstrom) and the coefficient of thermal expansion on the Al2W3O12 phase. It was determined as limit of solubility of Ga3+ in Al2-xGaxW3O12 the sample 𝑥 = 0.5, once it was identified in the diffraction patter WO3 as a secondary phase in 𝑥 bigger or equal 0.6. Unlike Al2W3O12 which is orthorhombic (Pbcn) at room temperature, the phases 0.2 less or equal 𝑥 less or equal 0.5 in the Al2- xGaxW3O12 appeared, at room temperature, in the monoclinic system (P21/a). The transition to orthorhombic phase (Pbcn), determined by XRPD in situ and dilatometry, was observed below 100 C for all compositions. The phase transition temperature increases as the Ga3+ content was increased in the crystalline structure. The thermogravimetric analysis of the monophasic samples showed that they were not hygroscopic. Although the monophasic composition with the highest Ga3+ content was Al1.5Ga0.5W3O12, the phase Al1.6Ga0.4W3O12 presented the lowest linear coefficient of thermal expansion, alpha l = 1.14 K -1, a reduction of 25 percent comparing with the linear coefficient of thermal expansion of the phase Al2W3O12. The Rietveld fit to the orthorhombic Pbcn space group, of the Al1.6Ga0.4W3O12 diffraction pattern taken at 100 C, confirms that Ga3+ was replaced by Al3+ in the same proportion described in the nominal chemical formula, and showed that its polyhedral distortion , Al(Ga)O6 and WO4, is in a higher amount than generally noticed for other phases in this crystal family. The Raman spectroscopy corroborated the analyzes regarding the solubility limit, although it showed that the compositions 𝑥 less or equal 0,5 could have a minimum quantities, undetectable by XRPD, of Al2O3 and WO3, when synthesized by the solid state reaction method. Kubelka-Munk graphics of Al2-xGaxW3O12 suggest that the partial replacement of Al3+ by Ga3+ increases the band gap in x less or equal 0,4, however, the absorption of Al2-xGaxW3O12 in the visible region increase, this behavior is apparently caused by the presence of WO3, as deduced by Raman spectroscopy. Attempts to synthesize Ga2W3O12 was not successful, although the enthalpy of formation of this compound, calculated by Generalized Kapustinskii equation and the Born-Haber cycle, presented a high exothermic value, ΔHF = −10149,15 Kj. mol -1.

Filter devices are central elements of radio units utilized for modern-day telecommunication. Leakages of radio waves and passive intermodulation are evolving more prominent as the frequency bands become crowded. The study in this thesis investigates the screw joints in the filter assembly to determine the influential parameters on the connection between the filter lid and its chassis. The clamp and release torque are vital factors in the resulting pre-load force. Besides the geometrical characteristics of the chassis andthe self-threading screw, the friction and surface roughness on the filter lid are significant contributors. Extensive testing revealed that increasing the countersink in the lead holeand applying the lubricant Molykote 1000 Paste increase the consequent clamp torque. After numerous cycles of thermal shock testing, the release torque does not show significant dissimilarities between the tested parameter combinations. A surface roughness test shows that applying a silver coating to the filter lid increases its surface roughness and thereby the friction of the screw head on the surface. In conclusion, the pre-load force will increase by changing the parameters as mentioned above, while it requires further testing to make a suggestion regarding the effect of the silver coating on the filter lid. / Filteranordningar är centrala delar i radioenheter vilka används vid nutida telekommunikation. Läckage av radiovågor och passiv intermodulation blir mer framträdande när frekvensbanden blir trånga. Studien i denna avhandling undersöker skruvförbanden i filtermonteringen för att bestämma de parametrar som har störst inverkan på anslutningen mellan filterlocket och dess chassi. Klämvrid- och lossdragningsmomentet är avgörande faktorer i den resulterande förspänningskraften. Förutom de geometriska egenskaperna hos chassit och den självgängande skruven, är friktionen och ytfinheten på filterlocket starktbidragande orsaker. Omfattande tester visade att en ökning av försänkningen i pilothålet och applicering av smörjmedlet Molykote 1000 Paste ökar det efterföljande klämvridmomentet. Efter talrika cykler av termisk chocktestning visar lossdragningsmomentet inga signifikanta skillnader mellan de testade parameterkombinationerna. Ett ytjämnhetstestvisar att applicering av en silverbeläggning på filterlocket ökar ytans strävhet och därmedfriktionen av skruvhuvudet på ytan. Sammanfattningsvis kommer förspänningskraften att öka genom att parametrarna ändras som nämnts ovan, samtidigt som det krävs ytterligare tester för att komma med ett förslag angående effekten av silverbeläggningen på filterlocket.

Les chocs thermiques provoquent, en général, l’endommagement et la fissuration des matériaux. Ces phénomènes sont observés, par exemple, dans le revêtement de barrière thermique pour les moteurs des turbines, le traitement des surfaces ou la soudure par laser etc. Plusieurs travaux de recherche ont été réalisés au cours des dernières décennies dans l’objectif d’améliorer les performances thermiques et/ou mécaniques des matériaux sous chargement thermique. L’étude des dommages et de la fissuration des matériaux provoqués par les chocs thermiques, tels que le décollement des interfaces et de décohésion de revêtements, a reçu également une attention considérable par les chercheurs. La majorité de ces travaux utilisent les théories classiques, tels que la loi de Fourier de conduction thermique et l'hypothèse de quasi-statique. Malheureusement ces théories ne sont pas adaptées dans le cas de charges extrêmes provoqués par le choc thermique et dans le cas des matériaux micro-fissurés. En conséquence, les théories conventionnelles doivent être enrichies.L'objectif de la thèse est de montrer le rôle crucial des termes non Fourier et les termes inertiels dans le cas de choc thermique sous conditions sévères et dans le cas où les fissures sont petites. Pour cela nous avons mené des études sur deux structures particulières soumises à des chocs thermiques. Chaque structure contient une fissure parallèle au bord libre de la structure située au voisinage de ce dernier. L’influence de la présence de fissure sur la conductivité thermique est prise en compte. Nous avons utilisé la théorie Hyperbolique de transfert de chaleur par conduction pour les champs thermique et mécanique à la place de la théorie traditionnelle classique de Fourier. Pour mener cette étude, nous avons utilisé les Transformées de Laplace et de Fourier aux équations de mouvement et à l’équation de transfert de chaleur. En s’intéressant en particulier aux champs de contrainte au voisinage de la pointe de fissure et aux facteurs d'intensité de contrainte dynamiques. Le problème se ramène à la résolution d’un système d'équations intégrales singulières dans l'espace de Laplace-Fourier. On utilise une méthode d'intégration numérique pour obtenir les différents champs. Nous résolvons ensuite un système d'équations algébriques linéaires. En effectuant des inversions numériques des transformées, nous obtenons les champs de contrainte de température et les facteurs d'intensité de contrainte dynamiques dans le domaine temporel.Les résultats numériques montrent que la conductivité thermique du milieu est affectée par l’ouverture de la fissure ce qui perturberait fortement le champ de température ainsi que l'amplitude des facteurs d'intensité de contrainte dynamiques. Les amplitudes sont supérieures à celles obtenues à partir de la théorie classique de Fourier ainsi que dans le cadre de l'hypothèse quasi-statique. On constate également qu’elles oscillent au cours du temps. La prise en compte simultanément de l’influence de la fissure sur la conductivité thermique, de l'effet non-Fourier ainsi que les effetsIVd'inertie induit un couplage entre les trois phénomènes qui rendrait le problème de choc thermique très complexe. L'effet de barrière thermique induit par la fissure affecte d’une manière significative les champs de température et des contraintes. Les effets d’inertie, et des termes non-Fourier joueraient également un rôle non négligeable lorsque la longueur de la fissure est petite. Comme dans de nombreux problèmes d'ingénierie, l'initiation et la propagation des micro-fissures sont des mécanismes dont il faut tenir compte dans les prévisions de la rupture des structures. Ces effets non conventionnels ne sont plus négligeables et doivent être inclus dans l'analyse de la fracture des structures soumises à des chocs thermiques. / Thermal shock problems occur in many engineering materials and elements, which are used in high temperature applications such as thermal barrier coatings (TBCs), solid propellant of rocket-engine, pulsed-laser processing of materials, and so on. The thermal shock resistance performances and the thermal shock damages of materials, especially the interface debonding and spallation of coatings, have received considerable attention in both analysis and design. Some conventional theories, such as the Fourier’s law of thermal conduction and the quasi-static assumption of the thermoelastic body, may no longer be appropriate because of the extreme loads provoked by the thermal shock. Therefore, these conventional theories need to be enriched or revised.The objective of this thesis is to develop the solutions of the transient temperature field and thermal stresses around a partially insulated crack in a thermoelastic strip under thermal shock loading. The crack lies parallel to the heated traction free surface. The thermal conductivity of the crack gap is taken into account. Hyperbolic heat conduction theory is used in solving the temperature field instead of the traditional Fourier thermal conduction theory. Equations of motion are applied to obtain the stress fields and the dynamic stress intensity factors of the crack. The Laplace and Fourier transforms are applied to solve the thermal-elastic governing equations such that the mixed boundary value problems are reduced to solving a singular integral equations system in Laplace-Fourier space. The numerical integration method is applied to get the temperature field and stress fields, respectively. The problems are then solved numerically by converting the singular integral equations to a linear algebraic equations system. Finally, numerical inversions of the Laplace transform are performed to obtain the temperature field and dynamic stress intensity factors in the time domain.Numerical results show that the thermal conductivity of the crack gap strongly affects the uniformity of the temperature field and consequently, the magnitude of the dynamic stress intensity factors of the crack. The stress intensity factors would have higher amplitude and oscillating feature comparing to those obtained under the conventional Fourier thermal conduction and quasi-static hypotheses. It is also observed that the interactions of the thermal conductivity of the crack gap, the non-Fourier effect and the inertia effects would make the dynamic thermal shock problem more complex. The magnitude of the thermal barrier, non-Fourier and inertia effects is estimated for some practical cases.

Σκοπός της συγκεκριμένης εργασίας είναι η κατασκευή, η μοντελοποίηση και η μελέτη της φυσικής και μηχανικής συμπεριφοράς συνθέτων υλικών πολυμερικής μήτρας ενισχυμένης με νανοσωλήνες άνθρακα. Πρώτος στόχος της εργασίας είναι η μελέτη των φυσικών και μηχανικών ιδιοτήτων νανοσυνθέτων υλικών εποξικής ρητίνης ενισχυμένης με νανοσωλήνες άνθρακα. Για τη μελέτη αυτή πραγματοποιήθηκαν μια σειρά διαφορετικών πειραμάτων προκειμένου να προκύψουν αξιόπιστα συμπεράσματα. Το πρώτο και βασικότερο πρόβλημα που μελετά η συγκεκριμένη εργασία είναι η κατασκευή νανοσυνθέτων υλικών εποξικής ρητίνης ενισχυμένης με νανοσωλήνες άνθρακα με τρόπους που συνδυάζεται το χαμηλό κόστος εξοπλισμού και η μικρή διάρκεια προετοιμασίας για την κατασκευή. Η κατασκευή των νανοσυνθέτων έγινε με δύο βασικές μεθόδους, με μηχανική ανάδευση και με χρήση υπερήχων. Το κύριο πρόβλημα που έπρεπε να ξεπερασθεί ήταν η ομογενής διασπορά μέσα στη ρητίνη καθώς η τάση που έχουν οι νανοσωλήνες να σχηματίζουν συσσωματώματα επιδρά αρνητικά. Από τη βιβλιογραφική και πειραματική μελέτη που έγινε προκύπτει πως ο χρόνος ανάμιξης, η μέθοδος ανάμιξης και η μεθοδολογία κατασκευής παίζουν καθοριστικό ρόλο στην επίτευξη καλής διασποράς των νανοσωλήνων μέσα στη ρητίνη. Εδώ πρέπει να σημειωθεί πως ο τύπος της ρητίνης και ο τύπος των νανοσωλήνων ανατρέπουν τη βέλτιστη μέθοδο. Για παράδειγμα στη μία ρητίνη που χρησιμοποιήθηκε, βέλτιστος χρόνος ήταν τα 10 λεπτά ενώ στην άλλη ρητίνη, βέλτιστος χρόνος ήταν τα 20 λεπτά. Για το στατικό μηχανικό χαρακτηρισμό νανοσυνθέτων υλικών εποξικής ρητίνης ενισχυμένης με νανοσωλήνες άνθρακα πραγματοποιήθηκαν πειράματα κάμψης τριών σημείων. Για πληρότητα της εργασίας χρησιμοποιήθηκαν δύο τύποι εποξικών ρητινών. Και οι δύο τύποι ρητινών ενισχύθηκαν με νανοσωλήνες άνθρακα σε διάφορες περιεκτικότητες. Από τα συγκεκριμένα πειράματα προέκυψε ότι υπάρχει μία συγκεκριμένη περιεκτικότητα σε νανοσωλήνες στην οποία το νανοσύνθετο εμφανίζει βελτιωμένες μηχανικές ιδιότητες. Συγκεκριμένα, για τον πρώτο τύπο εποξικής ρητίνης βρέθηκε πως το ποσοστό αυτό είναι το 0.3% κ.β. με ποσοστιαία αύξηση 10.6% και 2.6% σε μέτρο ελαστικότητας και αντοχής σε κάμψη. Σε ποσοστό 3% κ.β., η αύξηση στο μέτρο ελαστικότητας ήταν 14.03% αλλά η αντοχή του ήταν πολύ μικρή. Για το δεύτερο τύπο εποξικής ρητίνης βρέθηκε ότι το ποσοστό αυτό είναι το 0.2% κ.β., με ποσοστιαία αύξηση στο μέτρο ελαστικότητας σε κάμψη 22.8% και στην αντοχή σε κάμψη 29.4%. Για τον πειραματικό χαρακτηρισμό της βισκοελαστικής συμπεριφοράς (Long term testing) των υλικών που κατασκευάσθηκαν πραγματοποιήθηκαν πειράματα εφελκυστικού ερπυσμού-επανάταξης, ενώ για τον έλεγχο της βραχυπρόθεσμης βισκοελαστικής συμπεριφοράς πραγματοποιήθηκαν πειράματα κάμψης τριών σημείων σε διαφορετικούς ρυθμούς παραμόρφωσης για τα οποία έγινε μοντελοποίηση με εφαρμογή των βισκοελαστικών προτύπων του στερεού των τεσσάρων και τριών παραμέτρων, αντίστοιχα. Εξίσου σημαντική ήταν και η μελέτη των υλικών σε μη ιδανικές συνθήκες, δηλαδή σε συνθήκες όπου μπορεί να βρεθούν τα υλικά αυτά όταν αποτελέσουν μέρος μιας πραγματικής μηχανολογικής κατασκευής. Για το σκοπό αυτό έγινε μελέτη της βλάβης που εμφανίζεται σε υλικά καθαρής ρητίνης αλλά και ενισχυμένης τόσο ύστερα από κυκλικό θερμικό σοκ όσο και μετά από απορρόφηση υγρασίας. Η μελέτη που έγινε χωρίζεται σε δύο μέρη, το πειραματικό και το θεωρητικό. Όσον αφορά το πειραματικό σκέλος έγινε μηχανικός χαρακτηρισμός των υλικών με στατικά πειράματα κάμψης τριών σημείων, ενώ όσον αφορά το θεωρητικό σκέλος έγινε εξήγηση των μηχανισμών που λαμβάνουν χώρα με αποτέλεσμα την πρόκληση βλάβης. Τα αποτελέσματα που προκύπτουν στην περίπτωση της θερμικής κόπωσης είναι ενθαρρυντικά. Συγκεκριμένα για το μέτρο ελαστικότητας σε περιεκτικότητα 0.2%, όπου έχει γίνει μια επιτυχημένη κατασκευή νανοσυνθέτου με αύξηση που ξεπερνάει το 22.5%, παρατηρείται ότι η σχετική αύξηση σε πέντε κύκλους θερμικής κόπωσης ξεπερνάει το 30% (30, 40, 50, 80 και 90) και μάλιστα φτάνει το 40.2% στους 80 κύκλους. Όσον αφορά την αντοχή, αντίστοιχα είναι τα συμπεράσματα. Φαίνεται πως τα νανοσύνθετα συνεχίζουν να υπερτερούν έναντι του παρθένου υλικού με πιο χαρακτηριστική περίπτωση την αύξηση που παρατηρείται στους 40 κύκλους θερμικής κόπωσης όπου φτάνει το 46.7%. Τα αποτελέσματα που προκύπτουν μετά από απορρόφηση υγρασίας δεν είναι ενθαρρυντικά καθότι τόσο στο 0.2%κ.β. όσο και στο 0.3%κ.β. η σχετική μείωση των ιδιοτήτων είναι ιδιαίτερα υψηλή. Για το δυναμικό χαρακτηρισμό των υλικών έγιναν πειράματα δυναμικής θέρμο-μηχανικής ανάλυσης μέσω των οποίων προσδιορίσθηκε η θερμοκρασία υαλώδους μετάβασης Tg και η ικανότητα απόσβέσης των νανοσυνθέτων. Από τα πειράματα προέκυψε πως τα νανοσύνθετα έχουν Tg μεγαλύτερη από αυτή του μητρικού υλικού και συγκεκριμένα 126°C έναντι 101°C. Επίσης, η ικανότητα απόσβεσης των νανοσυνθέτων φαίνεται να είναι αισθητά μικρότερη. Τα πειραματικά αποτελέσματα ενισχύθηκαν με θεωρητική μελέτη. Για το σκοπό αυτό έγινε εφαρμογή αναλυτικών μοντέλων και αριθμητική ανάλυση με τη μέθοδο των Πεπερασμένων Στοιχείων. Το πρώτο μοντέλο που χρησιμοποιήθηκε ήταν το μοντέλο της υβριδικής ενδιάμεσης φάσης που έχει αναπτυχθεί από τον καθηγητή Γ. Παπανικολάου και την ερευνητική του ομάδα. Το μοντέλο αυτό εισάγει την έννοια του συντελεστή πρόσφυσης και της ενδιάμεσης φάσης, ως μίας φάσης που ξεκινά αμέσως μετά τη διεπιφάνεια ίνας-μήτρας και καταλήγει στη μήτρα. Κατά το πάχος της ενδιάμεσης φάσης οι ελαστικές ιδιότητες. Η ενδιάμεση φάση συμπεριφέρεται βισκοελαστικά με αποτέλεσμα το πάχος της να μεταβάλλεται με το χρόνο. Η υβριδική ενδιάμεση φάση είναι πολύ σημαντική και πρέπει να λαμβάνεται υπόψη στο σχεδιασμό από τους μηχανικούς. Η άποψη αυτή ενισχύεται από την παρατήρηση που γίνεται στη συγκεκριμένη εργασία, ότι, δηλαδή, μπορεί να προκύψει ένα σύνθετο υλικό με πλήρως τροποποιημένη μήτρα. Στην περίπτωση αυτή, το σύνθετο σε μικροσκοπική κλίμακα εμφανίζει ιδιότητες ίνας και ιδιότητες ενδιάμεσης φάσης, αλλά όχι μήτρας. Τα μοντέλα, τόσο της υβριδικής ενδιάμεσης φάσης όσο και της βισκοελαστικής ενδιάμεσης φάσης χρησιμοποιήθηκαν στη μοντελοποίηση που έγινε με τη μέθοδο των Πεπερασμένων Στοιχείων. Συγκεκριμένα, έγινε μοντελοποίηση ενός αντιπροσωπευτικού στοιχείου όγκου που συνδέει τις μακροσκοπικές με τις μικροσκοπικές ιδιότητες και στη συνέχεια μελετήθηκε η εντατική κατάσταση που αναπτύσσεται στη διεπιφάνεια. Τα αποτελέσματα συγκρίθηκαν με αναλυτικά μοντέλα που μελετούν τη διεπιφάνεια. / Nanocomposites constitute a very special category of composite materials. Only a small amount of nano-inclusions is enough to achieve unique mechanical, electrical and other properties. Carbon nanotubes have gain the scientists’ interest the last ten years due their becoming a material with many prospects. After an extended research by Iijima, S. in 1991, carbon nanotubes became a new attractive material to Nanotechnology. Thorough investigations in polymer matrix composites reinforced with carbon nanotubes are being developed in an effort to explain their properties. The aim of the present master thesis is multiple. The first step was the experimental procedure which started with the static mechanical characterization of epoxy polymer matrices reinforced with Multi Walled Carbon Nanotubes in order to define the factors that, mainly, come up during the mixing process and contribute to the final mechanical properties, namely the bending modulus and the strength. High speed shearing and ultrasonication were the two main manufacturing techniques that were applied in order to disperse the nanotubes in different volume fractions. Neat epoxy and MWCNT’s-reinforced epoxy specimens were also tested with Dynamic Thermo Mechanical Analysis bending experiments, by which the glass transition temperature, Tg, and the damping response were defined. Furthermore, three point bending tests in different strain rates and creep-recovery tests were executed for the definition of the short-term and long-term viscoelastic response, respectively. Finally, the damage that occurs after thermal shock cycling and water absorption was examined thoroughly. More specifically, the elastic properties degradation, due to damage, of the neat epoxy and of the nanocomposites was compared. Next, using the hybrid interphase concept and the viscoelastic intrphase, a theoretical investigation of the fiber-matrix interphase region was executed in an effort to compute both analytically and numerically its effect on the interfacial stress and strain fields developed in the area close to CNT’s. Analytical models that give the distribution of the normal and shear stresses were applied and the results were compared with the numerical analysis. The Finite Element Method was used for the numerical analysis. Many simplifying assumptions were necessary for both analytical and numerical technique. Experimental findings combined with analytical and numerical results gave a better understanding on the structural and mechanical performance of epoxy resin-carbon nanotubes composites. The static mechanical characterization that is being presented shows that we can achieve better mechanical properties by using a quit simple and low cost mixing process, but it needs much better techniques to achieve high performance materials. Glass transition temperature, Tg, of the nanocomposite is clearly higher from that of the neat epoxy. On the other hand, the damping of the nanocomposite is much lower, especially in higher temperatures. Finally, the nanocomposites seem to have much better response after cyclic thermal shock in contrast with the effect of water absorption, that seem to degrade the properties. The theoretical investigation showed that the third phase formatted around the inclusion is responsible for the stress and strain field developed in the area close to the nanotube. The interphase is not simply a geometrical concept but it mainly a property dependent concept, the thickness of which vary in compliance with the adhesion coefficient and time. Nanocomposites are materials that need further investigation in order to achieve things that the human brain could never imagine a few decades before.

The Industrial Revolution generated two parallel phenomena during the twentieth century: increased distribution of wealth and reduced energy costs, causing a large increase in energy consumption. With the international oil crisis in the 1970s, materials used until that time such as concrete, steel and glass, began to be seen as energy-intensive materials. Society began to seek buildings with minimal environmental impact, using materials that generate a smaller amount of energy, waste and pollution and CO2 emissions in the atmosphere and provide greater potential for reincorporation into nature. In this scenario, raw soil as a building material has become an alternative for the development of sustainable buildings, but also to improve the livability of housing for the low-income population in the country. Among various construction materials, raw soil-cement, which is cured without burning, is raw soil pressed and stabilized with Portland cement, which is already regulated by the Brazilian Technical Standards Association (ABNT) and possesses many advantages related to its manufacturing and use. To increase its acceptance and verify its efficiency as a building material for social housing, it is necessary to investigate its properties and performance. Thus, the present study aimed to evaluate the performance of an external vertical sealing system composed of soil-cement blocks without structural function for social housing, following determinations of NBR 15575 (2013), focusing on the requirements of Habitability and Sustainability. The habitability require the heat action and thermal shock test. Firstly, using the particle size analysis and liquid limit and plastic limit test, to characterize the compostion of the ground on which the block was used. The bodies-of-proof were tested in The laboratory of Structural Models and Tests (Laboratório de Ensaios e Modelos Estruturais LEME), at the Federal University of Rio Grande do Sul (UFRGS), Porto Alegre, RS, and consisted of two full scale walls. The system met limits set by standards for tightness against rainwater and heat action and thermal shock, but not for permeability to water. The vertical sealing system composed of hollow blocks of soil-cement has great potential for application in the construction of social housing, but there is still a need for more studies on the system. / A Revolução Industrial gerou, durante o século XX, dois fenômenos paralelos: a maior distribuição de riqueza e a diminuição do custo de energia, causando um grande aumento no consumo energético. Com a crise internacional do petróleo, na década de 1970, os materiais utilizados, até então, como concreto, aço e vidro, passam a ser vistos como materiais de grande consumo energético. A sociedade começa a buscar edificações com menor impacto ambiental possível, que utilizem materiais que envolvam baixo consumo energético, baixa geração de resíduos e poluentes, baixa emissão de CO2 na atmosfera e grande potencial de reincorporação na natureza. Diante desse cenário, a terra crua como material construtivo se torna uma alternativa para o desenvolvimento de edificações sustentáveis, como também, para a melhoria da habitabilidade das moradias da população de baixa renda existente no país. Das diversas técnicas de construção com a terra crua, o solo-cimento é um material curado sem queima, composto de terra crua prensada e estabilizada com cimento Portland, que já é normatizado pela Associação Brasileira de Normas Técnicas (ABNT), possuindo muitas vantagens que vão desde a fabricação até sua utilização no canteiro de obras. Para melhor aceitação e comprovação da sua eficiência como material construtivo para habitações de interesse social, é necessário que se conheça suas propriedades e seu desempenho. Dessa forma, a presente pesquisa consistiu em avaliar o desempenho de um sistema de vedação vertical externo composto por blocos de solo-cimento sem função estrutural para habitações de interesse social térreas, seguindo determinações da NBR 15575 (ABNT, 2013), focando nas exigências de Habitabilidade e Sustentabilidade. Como exigência de Habitabilidade analisou-se o fator Estanqueidade, com a realização dos ensaios de Estanqueidade à Água da Chuva e Permeabilidade à Água. E, como exigência de Sustentabilidade analisou-se os fatores Durabilidade e Manutenibilidade, com a realização do ensaio de Ação de Calor e Choque Térmico. Primeiramente, através de ensaio de análise granulométrica, limite de liquidez e limite de plasticidade, foi caracterizado o solo do qual o bloco utilizado é composto. Os corpos-de-prova foram ensaiados no Laboratório de Ensaios e Modelos Estruturais (LEME), da Universidade Federal do Rio Grande do Sul (UFRGS), em Porto Alegre, RS, e consistiram em duas paredes em escala real. O sistema atendeu aos limites estabelecidos pela norma nos ensaios de Estanqueidade à Água da Chuva e Ação de Calor e Choque Térmico, o que não ocorreu no ensaio de Permeabilidade à Água, no qual o sistema não atendeu às exigências. Através dos resultados dos ensaios verificou-se que o sistema de vedação vertical composto por blocos vazados de solo-cimento possui grande potencial para aplicação na construção, principalmente de habitações de interesse social, mas ainda há a necessidade de mais estudos sobre o sistema.

La littérature scientifique révèle que les résultats in vitro sur les matériaux dentaires ont une faible corrélation avec le comportement clinique. Les tests standardisés aux normes fournissent des informations précieuses et pertinentes sur les propriétés des matériaux dentaires, et permettent aussi de comparer les résultats de différents instituts. Cependant, le développement de nouveaux matériaux à partir de nouvelles formulations chimiques nécessite une amélioration des méthodes d'évaluation. Ce travail de recherche est réalisé dans le but d'approfondir les connaissances sur les méthodes d'évaluation des matériaux dentaires avant insertion dans la cavité buccale. Une grande importance a été donnée au choix des matériaux à tester ; nous nous sommes basés sur les dernières tendances actuelles et les derniers développements de composition de matériaux dentaires. La même importance a été donnée à des méthodes et des techniques d'essai au laboratoire ; leur corrélation avec les résultats cliniques a été mise en évidence. Les modifications apportées à la méthodologie de ces tests ont exploré davantage les aspects cachés des différentes interactions de paramètres. La caractérisation et l'évaluation des matériaux dentaires nécessitaient une meilleure compréhension de l'interaction entre les différentes propriétés pour expliquer le vieillissement des matériaux. Notre travail a consisté à combiner de nombreuses études pour répondre à ce sujet. Les études ont porté sur les propriétés mécaniques et physiques, le composite fibré et Bulk, les matériaux CAM CAD, les adhésifs dentaires, le choc thermique et le cyclage thermique, le bisphénol A. L'objectif final était de développer un simulateur oral qui permettrait la reproduction de différents paramètres chimiques, physiques et mécaniques de l'environnement buccal, permettant ainsi de combler l'écart entre les tests in vitro et in vivo de matériaux dentaires / Scientific literature reveals that in vitro results are poorly correlated to materials clinical behavior. ISO standardized testing provides valuable information about the dental materials properties, and enables result comparison between different institutes. Conversely, new materials chemistry and formulations requires improved methodology and testing methods. Throughout our studies included in this work, the main objective was to reach a more global knowledge of the way dental materials are evaluated before being inserted into the oral cavity. A great deal of emphasis was given to the choice of materials to be tested, and that it would represent the current trends in dental practice and the latest developments in material composition. Equal highlight was given to the choice of testing methodology and laboratory testing techniques and their correlation to the clinical outcome. The modifications made to the methodology of these tests explored further the concealed aspects of different parameter interactions. Dental materials characterization and assessment required more understanding about the interaction between different properties to explain material aging; our work was to combine numerous studies to answer this topic. The studies included mechanical and physical properties, bulk and fiber composite, CAD CAM block materials, dental resin adhesive, thermal shock and thermal cycling, Bisphenol A. The final objective was to develop an oral simulator that would enable the reproduction of different chemical, physical and mechanical parameters of the oral environment, thus permitting to bridge the gap between in vitro and in vivo testing of dental materials

This thesis dealt with the new refractory material calcium zirconate. The aim of this study was to investigate the synthesis of pure phase calcium zirconate in grain sizes up to 3 mm and to produce first refractory materials and examining their properties. For the synthesis the chosen solid state reaction of an equimolar mixture of monoclinic zirconium dioxide and calcium carbonate resulted in single phase calcium zirconate at temperature of at least 1200 °C. An increasing sintering temperature decreased the porosity. The first refractories based on single phase calcium zirconate were formed using the press process as well as slip casting. The thermomechanical properties were promising, which presents a starting point for the usage of refractories based on calcium zirconate in a wide field of possible applications. Remarkable were the residual strengths of about 5 MPa after five thermal shocks. However, corrosion tests with steel melt and gasifier ash showed the decomposition of CaZrO3 in presence of SiO2 which should be examined further for respective industrial usages.

Sa conductivité électronique ou encore sa transparence optique sont autant de propriétés physico-chimiques singulières du graphène qui expliquent le nombre accru de méthodes d’exfoliation de précurseurs graphitiques développées pour l’obtention de ce matériau. Pour palier à l’utilisation d’un oxyde de graphite/graphène caractérisé par une chimie de surface mal maitrisée, des graphites fluorés, de cristallinité mais aussi de concentration en fluor variables, ont été préparés par fluoration de graphite sous fluor moléculaire pur après optimisation des paramètres. Les précurseurs, que ce soit par fluoration dynamique ou statique, ainsi obtenus ont été caractérisés finement : diffraction des rayons X, spectroscopies IR et Raman et leur texture sondée par Microscopie Electronique à Balayage et à Transmission. Suite à cela, trois méthodes d’exfoliation ont été mises en place, basées sur des mécanismes différents : i) une exfoliation par choc thermique, déjà connue mais dont les mécanismes de décomposition ont été affinés dans cette étude, ii) une exfoliation en voie liquide, avec l’utilisation pour la première fois d’un graphite fluoré pour la synthèse de graphène fluoré multi feuillets par voie électrochimique pulsée, et enfin iii) une méthode originale, peu conventionnelle, basée sur l’interaction laser femtoseconde/graphite hautement fluoré pour induire des mécanismes de réduction contrôlée, et surtout d’exfoliation de la matrice. Ces méthodes ont permis de mettre en évidence l’intérêt de la présence de fluor dans la course actuelle pour la synthèse de graphène, et ont montré l’obtention de matériaux graphéniques,possédant une fonction résiduelle fluorée intéressante pour certaines applications. / Its electronic conductivity or its optical transparency are unequaled physicochemicalproperties of graphene which explain the increased number of exfoliation methods based ongraphitic precursors to obtain this material. To overcome the use of a graphite/graphene oxidecharacterized by a poorly controlled surface chemistry, graphite fluorides, with variablecrystallinity and also fluorine concentration, were prepared by fluorination of graphite under puremolecular fluorine atmosphere after optimization of the process parameters. The obtainedprecursors, whether by dynamic or static fluorination, were characterized : X-Ray diffraction, FTIRand Raman spectroscopies for the structure, and their texture probed by Scanning andTransmission Electron Microscopy. After that, three methods of exfoliation were developed, basedon different mechanisms: i) a thermal shock, already known but decomposition mechanisms wererefined in this study, ii) an exfoliation within liquid medium by pulsed electrochemical treatment,using for the first time a fluorinated graphite for the synthesis of few-layered fluorinated grapheneand finally iii) an unconventional method, based on the interaction between femtosecond laser andhighly fluorinated graphite to induce mechanisms like controlled reduction, and especially for thisstudy exfoliation of the matrix. These methods have permit to highlight the interest of fluorine inthe current race for the synthesis of graphene, and have shown the production of graphenematerials, having an interesting fluorinated residual functionalization for some applications.