Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-01-13T18:22:43Z No. of bitstreams: 1 nataliavelosomalta.pdf: 1376730 bytes, checksum: cdeb2bd74c09e4792776e296bd5f7f42 (MD5) / Approved for entry into archive by Diamantino Mayra (mayra.diamantino@ufjf.edu.br) on 2017-01-31T10:32:11Z (GMT) No. of bitstreams: 1 nataliavelosomalta.pdf: 1376730 bytes, checksum: cdeb2bd74c09e4792776e296bd5f7f42 (MD5) / Made available in DSpace on 2017-01-31T10:32:11Z (GMT). No. of bitstreams: 1 nataliavelosomalta.pdf: 1376730 bytes, checksum: cdeb2bd74c09e4792776e296bd5f7f42 (MD5) Previous issue date: 2016-06-09 / O objetivo desse estudo foi avaliar, a influência de duas diferentes técnicas de aplicação de glaze (pincél e spray) sobre a morfologia de superfície de uma cerâmica Y-TZP (IPS e.maxR®ZirCAD (IvoclarVivadent) antes e após a aplicação do ácido fluorídrico. Foram confeccionados 20 corpos de prova a partir de 4 blocos cerâmicos de zircônia parcialmente estabilizada por ítria pré-sinterizados, que foram divididos em 5 grupos (n=4) de acordo com o tratamento de superfície recebido: C= controle (nenhum tratamento de superfície); S: glaze spray VITA AKZENT( Vita Zanhfabrik )P/L: glaze pó/líquido VITA AKZENT (Vita Zanhfabrik,) S+HF: S + condicionamento com ácido fluorídrico 10% (HF)(FGM) (1min); P/L + HF: P/L + condicionamento com HF 10% (1min). As amostras forma então submetidas ao seguintes testes: 1) goniometria, para ánalise do ângulo de contato e da energia de superfície; 2) análise dos dados de rugosidade (Ra) por meio de um perfilômetro óptico digital; 3)identificação das fases cristalinas do material pela Difratometria de Raios X; 4) análise dos elementos químicos presentes no material cerâmico por Microscopia e espectrometria por energia dispersiva (EDS); 5) análise da superfície por meio de microscopia eletrônica de varredura (MEV). Os resultados demonstraram que: 1) a superfície das amostras tratadas com o glaze pó/líquido foram as que apresentaram uma camada mais espessa de glaze, com superfícies menos rugosas; 2)o grupo que recebeu o tratamento com o glaze pó/líquido foi o que apresentou a maior energia de superfície (69,83mN/m), e os demais grupos apresentaram elevados valores de ângulos de contato; 3) o tratamento térmico de vitrificação não causou alterações de fases na estrutura da zircônia; 4)As imagens de perfilometria e MEV revelaram um padrão irregular de disposição do glaze após o condicionamento com HF 10%, e um alto conteúdo de sílica foi observado somente nos grupos P/L e P/L + HF. O estudo concluiu que a utilização do glaze pó/líquido pela técnica do pincel promoveu uma maior padronização da camada de glaze e foi método de tratamento de superfície que apresentou uma maior energia de superfície e um maior conteúdo vítreo. Pelas imagens de microscopia, pode-se observar que a aplicação do ácido fluorídrico a 10% criou microretenções sobre a camada de glaze pó-liquido que podem favorecer a adesão a esta superfície. / The present study evaluated qualitatively the influence of two different types of glaze (brush and spray) on the surface of Y-TZP ceramics (IPS e.maxR® ZirCAD (IvoclarVivadent,) before and after use of hydrofluoric acid. Twenty specimens were made from 4 zirconia ceramic blocks partially stabilized by pre-sintered yttria, which were divided into 5 groups (n=5) according to the surface treatment received: C = Zirconia (control) (no surface treatment); S: glaze spray VITA AKZENT; P/L: glaze powder/liquid VITA AKZENT, S+HF: S + etching with hidrofluoridric acid 10% (HF)(FGM) (1min); P/L + HF: P/L + etching with HF 10% (1min).Samples were then subjected to the following tests: 1) Goniometry for analysis of the contact angle and the surface energy ; 2) Analysis of roughness data (Ra) by means of a digital optical profilometer; 3) Identification of the crystalline phases of the material by X-ray diffraction;4) Analysis of the chemical elements present in the ceramic material by microscopy and energy dispersive spectrometry (EDS); 5) analysis of the surface after each surface treatment by means of scanning electron microscopy (SEM).Partial results showed that: 1) The surface of the samples treated with glaze powder/liquid showed a thicker layer of glaze with less rough surfaces; 2) the group receiving treatment with glaze powder/liquid presented higher surface energy (69,83mN/m), while the other groups showed high values of contact angles; 3) thermal treatment of vitrification did not change the phases of zirconia surface; 4) The SEM and profilometry images revealed a glaze irregular pattern layout after etching with 10% HF, and a high silica content was observed only in GP / L and GP / L + HF groups. The study concluded that use of the glaze powder / liquid by brush technique promoted a greater standardization of the glaze layer and this surface treatment method was the one that showed a higher surface energy and a higher glassy content. For microscopy images, it can be seen that the application of hydrofluoric acid 10% created micro retentions on the glaze powder-liquid layer that can promote adhesion to this surface.

Le recyclage des actinides mineurs produits en réacteur nucléaire est un point clé pour les cycles du combustible du futur. Différentes options sont ainsi envisagées : leur réintégration au sein d'un nouveau combustible « refabriqué » ou leur transmutation dans le but de réduire significativement la radiotoxicité des déchets ultimes. Dans ces deux cas de figure, la synthèse de matériaux innovants intégrant les actinides mineurs de manière homogène est nécessaire.En ce sens, les voies sol-gel présentent des avantages certains par rapport aux autres voies de synthèse (co-précipitation, métallurgie des poudres) tels que l'organisation du matériau à l'échelle colloïdale ou la création de porosité de manière contrôlée grâce à l'utilisation d'un « template ». De plus, la possibilité de travailler en milieu humide, de la solution précurseur au matériau final, permet d'éviter la formation de poudres pulvérulentes et contaminantes, point essentiel dans le cas de matériaux incorporant des éléments radioactifs. Cette thèse vise à démontrer l'adaptabilité de ce type de procédé au domaine du nucléaire. Dans un premier temps, une méthodologie de synthèse par voie sol-gel colloïdale et de caractérisation sur un système non-actif à base de zirconium a été mise en place et a permis la compréhension des mécanismes mis en jeu au cours de cette synthèse. Suite à cela, des études de mise en forme, et notamment d'insertion de porosité, ont été réalisées. Des monolithes de zircone ont de cette manière pu être obtenus grâce au couplage entre le procédé sol-gel colloïdal et la formation d'une émulsion stabilisée par des clusters de particules solides.Finalement, une transposition de ces travaux sur un système à base d'uranium a été initiée, soulevant différentes perspectives prometteuses concernant les possibilités de mise en forme du matériau final. / One of the main objectives for the future nuclear fuel cycle is the recycling of the minor actinides. Different options are considered: their integration into a new fuel for a prospect of a closed fuel cycle or their transmutation in order to significantly decrease the long-term radiotoxicity of ultimate wastes. In both cases, the synthesis of new advanced materials integrating the actinides jointly is required.Sol-gel processes allow the organization of the material at the colloidal scale or the insertion of controlled porosity using « templates ». Furthermore, the possibility to work in a « wet environment » prevents the formation of pulverulent powders which are contaminant in the case of materials incorporating radioactive elements. The main purpose of this work is to demonstrate the adaptability of this route to the nuclear field.Firstly, a methodology of synthesis from a colloidal sol-gel route was set up on a non-radioactive zirconium-based system in order to characterize and understand of the different mechanisms of this synthesis. Then, studies on shaping, including insertion of porosity, were performed. Zirconia monoliths have been obtained thanks to a coupling between a colloidal sol-gel process and the formation of an emulsion stabilized by clusters of solid particles. Finally, a transposition of this work to an uranium-based system was introduced, pointing out different promising perspectives specially concerning the possibilities of shaping of the final material.

Abstract Metal ceramic restorations have been used in fixed prosthodontics since the 1950s, but the lack of aesthetics, the inclination to use metal-free materials, possible allergic reactions to metals, and the high cost of high noble alloys have increased the use of all-ceramic materials. The ongoing development of ceramic materials led to the introduction of zirconia to fixed prosthodontics over a decade ago. The mechanical properties of zirconia have proven to be excellent, but the clinical outcome of conventional fixed zirconia restorations over the long term is unclear. This retrospective clinical study evaluated two- to seven-year outcomes, early complications during prosthetic treatment and short-term failures during the first year of use of zirconia single crowns and fixed dental prostheses (FDPs). The usefulness and durability of zirconia single crowns in abutment teeth of partial removable dental prostheses (RDPs) was also evaluated. The material consisted of 173 patients treated with zirconia single crowns or FDPs by undergraduate dental students between 2007 and 2010. Of these patients 94 were women and 79 men (mean age 55 years, range 18–79 years). Altogether 268 zirconia single crowns (mean 3 crowns, range 1–12 crowns per patient) had been fabricated for 88 patients and 120 zirconia FDPs (range 3–12 units, mean 4.5 units) for 102 patients. Seventeen patients had received both crown(s) and FDP(s). The results show that zirconia single crowns and FDPs are a suitable treatment alternative in fixed prosthodontics. Early complications during prosthetic treatment and short-term failures during the first year of use were few. The survival rate of the zirconia single crowns after 3.9 years (2–6 years) was 89% and the success rate was 80%. The survival rate of zirconia FDPs after 4.9 years (3–7 years) was 100% and the success rate was 89%. Zirconia single crowns perform well as abutment teeth of partial RDPs with a metal framework, but fractures in the veneering porcelain remain a problem. / Tiivistelmä Metallokeraamisia rakenteita on käytetty kiinteässä protetiikassa 1950-luvulta lähtien, mutta puutteet estetiikassa, pyrkimys metallittomiin materiaaleihin, mahdolliset allergiset reaktiot ja jalojen metallien korkea hinta ovat lisänneet kokokeraamisten materiaalien käyttöä. Kokokeraamisten materiaalien kehitystyö on tuonut zirkonian kiinteän protetiikan materiaaliksi. Zirkonian mekaaniset ominaisuudet ovat osoittautuneet erinomaisiksi, mutta hammaskantoisten kiinteiden zirkonia-runkoisten proteesien kliiniset pitkäaikaistulokset puuttuvat. Tämän retrospektiivisen kliinisen tutkimuksen tarkoituksena oli selvittää zirkonia-runkoisten yksittäisten kruunujen ja zirkonia-runkoisten siltojen menestymistä 2–7 vuoden aikavälillä sekä kartoittaa niiden valmistuksen aikaiset ongelmat ja varhaiset epäonnistumiset ensimmäisen vuoden aikana. Lisäksi tutkittiin zirkonia-runkoisten yksittäisten kruunujen käyttökelpoisuutta ja kestävyyttä metallirunkoisten rankaproteesien tukihampaina. Materiaali koostui 173 potilaasta, joille hammaslääketieteen opiskelijat olivat tehneet zirkonia-runkoisia yksittäisiä kruunuja tai zirkonia-runkoisia siltoja vuosina 2007–2010. Potilaista 94 oli naisia ja 79 miehiä (keski-ikä 55 vuotta, jakauma 18–79 vuotta). Kaiken kaikkiaan 268 zirkonia-kruunua (keskimäärin 3 kruunua, jakauma 1–12 kruunua potilasta kohti) oli valmistettu 88 potilaalle ja 120 siltaa (keskimäärin 4,5 yksikköä, jakauma 4,5 yksikköä) 102 potilaalle. Seitsemälletoista potilaalle oli tehty sekä kruunuja että siltoja. Tulokset osoittavat, että zirkonia-runkoiset kruunut ja sillat ovat käyttökelpoisia kiinteässä protetiikassa. Valmistuksenaikaiset ongelmat ja varhaiset epäonnistumiset ovat vähäisiä. Yksittäisten kruunujen selviytymisprosentti 3,9 vuoden jälkeen (2–6 vuotta) oli 89 % ja onnistumis-prosentti 80 %. Siltojen selviytymisprosentti 4,9 vuoden jälkeen (3–7 vuotta) oli 100 % ja onnistumisprosentti 89 %. Zirkonia-runkoiset kruunut toimivat hyvin rankojen tukihampaina, mutta niiden ongelmana ovat päällepolttoposliinin lohkeamat.

O objetivo deste estudo foi produzir por electrospinning fibras de zircônia, caracterizá-las e avaliar sua influência, como agente de carga, nas propriedades de compósitos tendo como matriz uma resina à base de metacrilatos de uso odontológico. O óxido de zircônio foi utilizado como precursor das fibras obtidas, as quais foram caracterizadas por microscopia eletrônica de varredura (MEV) e analisadas por termogravimetria (ATG). Após tratamento térmico, a morfologia das fibras foi analisada por MEV, a cristalinidade, por difração de raios X e a área superficial específica e a porosidade foram calculadas pelos métodos BET e BJH, respectivamente. Os compósitos odontológicos foram formulados a partir da adição das fibras de zircônia obtidas por electrospinning (grupo Híbrido N+F) e comparados com os formados com as partículas originais de zircônia nanométrica (grupo Nano N), e com a própria matriz sem carga (grupo Matriz). O grau de conversão (GC) foi analisado usando espectroscopia no infravermelho por transformada de Fourier (FT-IR). Os compósitos e a matriz foram submetidos ao ensaio de resistência à flexão, que também permitiu determinar o módulo de elasticidade. Os compósitos odontológicos foram submetidos ao ensaio de microdureza Vickers e tenacidade à fratura em deformação plana. Os compósitos estudados não formaram trincas radiais porque a matriz polimérica absorveu e dissipou a tensão gerada no material e por esse motivo não foi possível determinar a tenacidade à fratura. Observou-se que o GC dos compósitos odontológicos não apresentou diferença estatisticamente significativa entre os grupos N+F e N, sendo 54,2% e 55,1%, respectivamente. O GC da matriz polimérica foi de 68,1% (±0,6)%, sendo estatisticamente superior ao dos compósitos experimentais. Para os ensaios de resistência à flexão, módulo de elasticidade e microdureza Vickers não houve diferença estatisticamente significativa entre os grupos dos compósitos, sendo que o grupo matriz apresentou resultado estatisticamente inferior para a dureza e módulo de elasticidade. / This study aimed to produce zirconia ultrafine fibers through electrospinning method, characterize them and evaluate their influence as reinforcing element on properties for composites having as matrix methacrylate-based resin for dental use. Zirconium oxide was used as precursor of the fibers obtained which were characterized by scanning electron microscopy (SEM) and analyzed by thermogravimetry (TGA). After heat treatment fibers morphology was analyzed by SEM, crystallinity by X-ray diffraction and porosity and specific surface area were calculated by BET and BJH methods, respectively. The dental composites were formulated from the addition of zirconia fibers obtained by electrospinning (Hybrid group N+F) and compared with those formed with the original nanometric zirconia particles (Nano group N), and with matrix without reinforcing element (group Matriz). The degree of conversion (DC) was analyzed by Fourier transform infrared spectroscopy (FT-IR). The composites and matrix groups were submitted to flexural strength test, which also allowed determining elastic modulus. The dental composites were tested on Vickers microhardness and fracture toughness in flat deformation. The studied composites studied didn’t form radial cracks because polymer matrix absorbed and dissipated generated tension in material and for this reason it wasn’t possible to determine the fracture toughness. It was observed that dental composites DC showed no statistically significant difference between groups N+F and N, being 54.2% and 55.1%, respectively. The polymer matrix DC was 68.1% being statistically higher than experimental composites. Flexural strength, elastic modulus and Vickers microhardness showed no statistically significant difference between composite groups, and matrix group results were statistically lower for microhardness and elastic modulus.

O desgaste é responsável por um grande número de falhas em materiais, provocando a sua substituição antecipada e consequentemente diminuindo a sua vida útil. Por isso, estudos são realizados para caracterizar os limites de utilização desses materiais, evitando assim situações catastróficas. A partir das variáveis e parâmetros envolvidos no ensaio de desgaste, é possível construir mapas que tem como finalidade direcionar para uma correta escolha do material, de acordo com a aplicação desejada, além de identificar o seu comportamento frente à determinadas condições de uso. Neste contexto, este trabalho teve como objetivo conhecer o comportamento de desgaste de nanocompósitos de alumina contendo 5% de inclusões nanométricas de zircônia, visando construir um diagrama de transição de desgaste entre os limites de combinação de velocidade de deslizamento e carga aplicada. Para isso, corpos de prova conformados na forma de pinos com uma das extremidades semiesféricas foram caracterizados quanto a dureza e tenacidade à fratura, submetidos ao ensaio de desgaste do tipo pino-no-disco com temperaturas e umidades ambientes, variando os parâmetros de velocidade e carga. As velocidades de deslizamento variaram de 1,2 m/s à 0,1 m/s e as cargas variaram de 2 N à 100 N. Os valores de dureza e tenacidade a fratura obtidos foram de 14,08 ± 1,22 GPa e 3,99 ± 0,14 MPa.m1/2, respectivamente. Os resultados de desgaste mostraram que a partir da caracterização e construção do diagrama de transição de regime de desgaste, com combinações de parâmetros extrínsecos de carga e velocidade de deslizamento, foi possível definir e atingir as condições limites entre o regime de desgaste moderado e a transição para o regime severo. Esse diagrama auxilia na seleção e comparação da transição entre os limites de desgaste do material estudado com outros tipos usados na engenharia. / Wear is responsible for a large number of material failures, causing them to be replaced early and consequently shortening their life-time. Therefore, studies are conducted to characterize the limits of use of these materials, thus avoiding catastrophic situations. From the variables and parameters involved in the wear test, it is possible to construct maps that aim to direct the correct choice of material according to the desired application, as well as to identify its behavior against certain conditions of use. In this context, the objective of this work was to know the wear behavior of alumina nanocomposites containing 5% nanometric zirconia inclusions in order to construct a simplified wear transition diagram between the sliding speed and applied load combination limits. For this, test pieces shaped like pins with semi-spherical tips were characterized in terms of hardness and fracture toughness, took to the wear test of the pin-on-disk with ambient temperatures and humidity, varying the speed and load parameters. Slip velocities ranged from 1.2 m/s to 0.1 m/s and loads ranged from 2 N to 100 N. The values of hardness and fracture toughness obtained were 14.08 ± 1.22 GPa and 3.99 ± 0.14 MPa.m1/2, respectively. The results of wear showed that from the characterization and construction of the wear regime transition diagram, with combinations of extrinsic load parameters and slip speed, it was possible to define and reach the boundary conditions between the moderate wear regime and the transition for the severe regime. This diagram helps in the selection and comparison of the transition between the wear limits of the studied material with other types used in engineering.

<p><strong>Apstrakt je obrađen tehnologijama za optičko prepoznavanje teksta (OCR).</strong></p><p>Dobro je poznato da se žilavost keramičkih matrica znatno može povećati sa cirkonia česticama iz razloga &scaron;to se transformacijom tetragonalne u monokliničnu fazu cirkonie znatna količina energije može apsorbovati, a koja bi inače bila pukotini na raspolaganju za njeno napredovanje.<br />U ovom radu je primenom različitih varijanti sol-gel procesiranja menjana priroda i skala veličine polaznih alumina i cirkonia čestica u cilju dizajniranja mikrostrukture alumina-cirkonia kompozita. Ukazano je na postojanje interakcije između cirkonie i alumine, &scaron;to je i pored &scaron;irokog proučavanja alumina-cirkonia kompozita skoro nepoznata pojava. Pokazano je takođe da stepen interakcije zavisi od prirode i veličine polaznih čestica, pri čemu je najveći kod alkoksidnih matričnih kompozita sa cirkoniom dodanom u obliku veoma finih sol čestica ili cirkonjjumovih soli (na primer cirkoniju oksihlorid), a najmanji kod čestičnih matričnih kompozita kod kojih su kori&scaron;čene guste čestice (alumine-cirkonie).<br />Potvrđeno je da stepe interakcije određuje mikrostrukturni razvoj kompozita u toku zagrevanja. Uticaj interakcije na mikrostrukturni razvoj alumina-cirkonia kompozita je praćen različitim metodama karakterizacije (merenje gustine, IR spektroskopija, rentgenska difrakcija, diferencijalno termijska analiza i skening elektronska mikroskopija). Posle finalnog sinterovanja i bez toplog presovanja su dostignute gustine bliske teorijskim, a postignute mehaničke osobine merene su tvrdoća i žilavost) su razmatrane u funkciji mikorstrukturnih parametara. Utvrđeno je da je dominantan mehanizam povećanja žilavosti naponom indukovano povećanje žilavosti, a maksimalno postignuta vrednost odnosa povećanja žilavosti prema žilavosti matrice iznosi K_s/K_o = 0.69 (&scaron;to odgovara vrednosti kritičnog faktora intenziteta napona od K_c=5.4 MPa m^1/2). Na kraju treba jo&scaron; istaći da eksperimentalno dobijene vrednosti žilavosti dobro fituju izvedenu zavisnost doprinosa transformacionog povećanja žilavosti od veličine tetragonalni cirkonia čestica.</p> / <p><strong>Abstract was processed by technology for Optical character recognition (OCR).</strong></p><p>It is already known that fracture toughness of the ceramic matrices could be increased by dispersing of zirconia particles. The role of zirconia is in the absorption of a substantial amount of energy, which could be consumed by crack advansing, with the transformation from tetragonal to monoclinic simetry.<br />In the presented study the microstructure of the alumina-zirconia composites were designed by changing the nature and the size of original alumina and zirconia panicles, by using a different types of the sol-gel processing methods. It is pointed out on the mutual interaction between zirconia and alumina, which is almost unknown phenomena inspite of very intensive investigation of the alumina-zirconia composite system. The mutual interaction depends on the nature and size of the original particles. The largest interaction exists in alkoxide matrix composites with zirconia added in a form of very fine so! particles or zirconijum-salts (zirconium-oxychloride), and the smallest in the particulate matrix composites with dense panicles (alumina or zirconia). It is confirmed that interaction between zirconia and alumina determine the microstructure development of the heat treated composite samples. The influence of the interaction on the microstructure development was characterised by different method: density measurement, IR spectroscopy. X-ray diffraction, differential thermal analysis and scanning electron microscopy. After final sintering without hot pressing the density reach very high values (in some case &gt;99 % theoretical density). Mechanical properties (hardnes and fracture toughness) were studied in the function of the microstructural parameters. It was shown that the stress induced transformation toughening is a dominant mechanism in the sol-gel processed composites (with zirconia partcles less than critical size)., and the maximal value of the AKc/Ko = 0.69 corresponds to the fracture toughness of Kc = 5.4 MPa m1/2. Experimental fracture toughness data fit the analytically derived functional dependent between fracture toughness and zirconia particle sizes.</p>

27 Retrieved Yttria Stabilised Tetragonal Zirconia (Y-TZP) femoral heads were studied for the occurrence of tetragonal to monoclinic phase transformation and the effects that such transformation has on the bearing surface. The mean monoclinic percentage found is 53.6% with 25 of the samples having transformed more than 20%. This finding nullifies earlier predictions that it would take 25 to 30 years to transform to a monoclinic content of 30 to 40% inside the human body (Chevalier, Drouin&Calés 1997). It was however shown that Hot Isostatic Pressed (HIP’ed) Y-TZP femoral heads have a better, though still not adequate, resistance to phase transformation in the human body than non-HIP’ed femoral heads. Results of various investigations show that this transformation degrades the surface condition of the femoral heads, which in turn increases wear and subsequently decreases the survival rate of the prosthesis due to a greater risk of aseptic loosening. It is postulated that a great contributing factor to the phase transformation is increased temperatures inside the bearing couple, due to inadequate lubrication between the two bearing surfaces. Tetragonal to monoclinic phase transformation and its associated effects renders Y-TZP femoral heads less attractive for hip replacements. / Dissertation (MEng)--University of Pretoria, 2010. / Mechanical and Aeronautical Engineering / unrestricted

The present thesis focuses on the preparation of tetragonal zirconia doped with yttria oxide, ceric dioxide, and magnesium oxide. In its theoretical part the thesis covers the characteristics of doped ceramics, the possible methods of powders preparation and of their further processing. The experimental part describes the precipitation synthesis of zirconia in base environment and further processing for ceramics. Also studied were the influences of dopant and of the processing technique used on the phase composition and microstructure of the resulting ceramics. To describe the powder structure, the thermal, dilatometric, surface area, and x-ray analyses were performed; as well as both the scanning and transmission electron microscopy employed. Dry processed ceramics showed the average grain size of 87–94 nm and the relative density in the range of 84,0–99,3 %. In comparison, the ceramics produced of hydrothermally synthesised powders proved the average grain size of 75–85 nm and the relative density between 92,7-99,9 %. As the next step, samples were subjected to low-temperature degradation for the time of 5 and 15 hours. Samples consisting of pure tetragonal ZrO2 were resistant to 5 and 15 hours of low-temperature degradation at 180 °C.

The diploma thesis is focused on preparation of thin and highly flexible ceramic tapes from zirconia with a thickness from 70 to 200 m. The thesis is divided into two parts. The first part presents a literary research that focuses on the properties of zirconium dioxide, the preparation of thin ceramic foils and the evaluation of the mechanical properties of ceramic materials. The second part is experimental. It deals with the preparation of thin ceramic foils from colloidal ceramic suspensions produced by epoxy gel-tape casting method. The suspensions were prepared from zirconium dioxide stabilized by 2 and 3 mol.% of yttrium oxide. The maximum deflection and strength was determined on sintered foils. The maximum biaxial strength of 1806 MPa was achieved for 3Y-PC 75 foils with a thickness of 190 m. The maximum deflection of 10.5 mm at a ceramic foil thickness of 75 m was achieved in a 3-point bend with a support span of 30 mm on 3Y-PC 75 samples. At a support distance of 50 mm, the samples were pushed through the gap without damage. These results indicate excellent mechanical properties of the prepared ceramic foils.

Dans cette étude, nous nous intéressons au relâchement du carbone dans les CSD-C (Colis Standard de Déchets Compactés) par simulation atomique. Le carbone 14 peut atteindre la surface de la zircone par deux mécanismes : la migration par diffusion interstitielle et/ou la migration dans les porosités. La migration dans les porosités a été modélisée par une migration sur une surface anhydre de zircone. Le coefficient de diffusion est égal à 10⁻¹⁵ cm²/s à la température d’étude de 50 °C. Cela représente une migration de l’ordre du mm sur 100 000 ans (échelle de temps considérée). La migration interstitielle a été étudiée par les sauts au voisinage de la subsurface. L’épaisseur de la subsurface correspond aux 2 couches (0.7 nm) pour lesquelles l’énergie d’interaction du carbone est différente de celle en volume. La migration du carbone est préférentielle vers la surface dans cette zone. Nous avons également analysée l’hydratation de la surface par l’eau qui pourraient arriver dans le site de stockage. Une nouvelle configuration de la monocouche d’hydratation de la surface est proposée dont la stabilité en température a été étudiée par dynamique moléculaire. La monocouche d’hydratation reste inchangée en présence d’eau. Des mécanismes associées à la spéciation une fois que le carbone est sur la surface hydratée ont été simulés. Les conditions basiques ont été prise en compte. La désorption de CO et de CO₂ nécessite des énergies d’activation accessibles de 0.40 eV au maximum. La désorption de CH₄ semble plus difficile. Le carbone pourrait aussi être piégé sur la surface. / In this study, we are interested in the release of carbon in CSD-C (Standard Package of Compacted Waste) by atomic simulation. Carbon 14 can reach the surface of zirconia through two mechanisms: pore diffusion and/or migration in porosities. Migration in porosities was modelled by migration on an anhydrous zirconia surface. The calculated diffusion coefficient is equal to 10⁻¹⁵ cm²/s at the study temperature of 50 °C. This represents a migration in the order of mm per 100 000 years (time scale considered). Interstitial migration was studied by jumps in the vicinity of the subsurface. The thickness of the subsurface corresponds to the 2 oxide layers (0.7 nm) for which the interaction energy of carbon is different from bulk. Carbon migration is preferred towards the surface in this area. We have also analyzed the hydration of the surface with water that could arrive in the storage site. A new configuration of the surface hydration monolayer is proposed whose temperature stability has been studied by molecular dynamics. The hydration monolayer remains unchanged in the presence of water. Mechanisms associated with speciation once the carbon is on the hydrated surface have been simulated. The basic conditions have been taken into account. The desorption of CO and CO₂ requires accessible activation energies of up to 0.40 eV. Desorption of CH₄ seems more difficult. Carbon could also be trapped on the surface.