The two main requirements for ceria-zirconia hydrodeoxygenation (HDO) catalysts are the presence of defect sites to bind oxygenates and the ability to adsorb and dissociate hydrogen. Two types of sites were identified for exchange of hydrogen and deuterium. The activation energy for one type of site was associated with H2-D2 exchange through oxygen defect sites. The activation energy for the second type of site was associated with H2-D2 exchange through hydroxyl groups and correlated with crystallite size. Ceria-zirconia can convert guaiacol, a model pyrolysis oil compound, with a high selectivity to phenol, an HDO product. Ceria-zirconia catalysts had a higher conversion of guaiacol to deoxygenated products as well as a higher selectivity towards phenol than pure ceria. They did not deactivate over the course of 72 hours on stream, whereas coking or the presence of water in the feed can cause serious decay of common HDO catalysts HDO. Therefore, ceria-zirconia catalysts are promising HDO catalysts for the first step of deoxygenation. The stability of supported Ru on ZrO2 in acidic or basic environments at reaction temperature is examined. In this study, the ruthenium dispersion is greatly increased by hydrothermal treatment in acidic and basic pH without alterations to the surface area, pore volume, pore size or crystal structure. An increase in Ru dispersion showed an increase in the selectivity to propylene glycol relative to ethylene glycol. A decrease in total Lewis acid site concentration was correlated with a decrease in the ethylene glycol yield. The conclusions of this study indicate that stability of catalysts in realistic industrial environments is crucial to the design of catalysts for a reaction.

The term nanoceramics is well known in the ceramic field for at least two decades. Even though there are many reports that nanoceramics are superior in terms of mechanical and other properties, no comprehensive and conclusive study on the grain size dependent variation in mechanical properties. So this study was an attempt to study the property variation with grain size and yttria content for a well known ceramic, yttria stabilised zirconia. High solids content but low viscosity YSZ nanosuspensions have been slip cast into -52% dense, very homogeneous green bodies in sizes up to 60 mm in diameter. Sintering cycles have been optimised using both hybrid and conventional two-step heating to yield densities >99.5% of theoretical whilst retaining a mean grain size of <100 nm. The sintered samples have been characterised for hardness, toughness, strength, wear resistance and hydrothermal ageing resistance. The results have been compared with that of a submicron zirconia ceramic prepared using a commercial powder. The strength of the nanoceramics has been found to be very similar to that of conventional submicron ceramics, viz. -10Pa, although the fracture mechanism was different. Two toughness measurement approaches have been used, indentation and surface crack in flexure. The results indicate that the nano 1.5YSZ ceramics may be best viewed as crack, or damage, initiation resistant rather than crack propagation resistant; indentation toughness measurements as high as 14.5 MPa m 112 were observed. Micro-Raman mapping was demonstrated to be a very effective technique to map the phase transformations in zirconia. The wear mechanism of nanozirconia has been observed to be different compared to that in conventional, submicron YSZ and the wear rates to be lower, particularly under wet conditions. In addition, and potentially most usefully, the nan03YSZ ceramics appear to be completely immune to hydrothermal ageing for up to 2 weeks at 245°C & 7 bar; conditions that see a conventional, commercial submicron ceramic disintegrate completely within 1 hour.

Stabilised zirconias have a remarkable variety of technological and commercial applications, e.g., thermal barrier coatings, gas sensors, solid oxide fuel cells, ceramic knives and even fashion jewelry. This amazing versatility seems to originate from the creation of atomic defects (oxide ion vacancies) in the zirconia crystal. Indeed, these vacancies, and their interactions with other vacancies or cations, dramatically affect the structural, thermal, mechanical and electrical properties of zirconia. This thesis is concerned with the study of the role of the vacancy interactions on the conducting properties of these materials. This study was performed by using realistic, first-principles based molecular dynamics simulations. The first system studied in this thesis is Zr0:5 0:5xY0:5+0:25xNb0:25xO7. This has a fixed number of vacancies across the series but its conductivity changes by almost two orders of magnitude as a function of x. For this reason, Zr0:5 0:5xY0:5+0:25xNb0:25xO7 represents an ideal test-bed for the role of the cation species on the defect interactions and therefore on the ionic conductivity of these materials. Realistic inter-atomic potentials for Zr0:5 0:5xY0:5+0:25xNb0:25xO7 were developed on a purely first-principles basis. The observed trends of decreasing conductivity and increasing disorder with increasing Nb5+ content were successfully reproduced. These trends were traced to the influences of the cation charges and relative sizes and their effect on vacancy ordering by carrying out additional calculations in which, for instance, the charges of the cations were equalised. The effects of cation ordering were considered as well and their influence on the conductivity understood. The second part of this thesis deals with Sc2O3–doped (ScSZ) and Y2O3–doped (YSZ) zirconias. These systems are of great academic and technological interest as they find use in solid oxide fuel cells. Inter-atomic potentials were parametrised and used to predict the structural and conducting properties of these materials, which were found to agree very well with the experimental evidence. The simulations were then used to study the role of the vacancy interactions on the conducting properties of these materials. Two factors were found to influence the ionic conductivity in these materials: cation-vacancy and vacancy-vacancy interactions. The former is responsible for the difference in conductivity observed between YSZ and ScSZ. Vacancies, in fact, prefer to bind to the smaller Zr4+ ions in YSZ whereas there is not a strong preference in the case of ScSZ, since the cations have similar sizes in this case. This effect is observed at temperatures as high as T = 1500 K. Finally, it was found that vacancies tend to order so that they can minimise their mutual interaction and that this ordering tendency is what ultimately is responsible for the observed anomalous decrease of the ionic conductivity with increasing dopant concentration. The consequences of such a behaviour are discussed.

Objective: The goal of the present study was to investigate the effect of chairside surface treatments on biaxial flexural strength and subsurface damage of monolithic zirconia ceramics. Methods: Specimens (15x15x1.2 mm3) were prepared by sectioning from commercially available zirconia blanks (BruxZirTM) and sintering according to manufacturer's recommendations. Fully dense specimens were randomly divided into five groups (n=30) and treated as follows; 1) as-sintered (AS) 2) air abraded with 50 μm alumina fine particles (AAF), 3) air abraded with 250 μm coarse alumina particles (AAC), 4) ground (G), and 5) ground and polished (GP) to mimic chairside and dental laboratory treatments. Microstructural changes were thoroughly characterized by optical and scanning electron microscopy, surface profilometry and atomic force microscopy. Crystalline phases and their depth profile were investigated by x-ray diffraction (XRD) and grazing incidence x-ray diffraction (GIXRD). Results were analyzed by Kruskal-Wallis test and Tukey's adjustment for multiple comparisons. A 0.05 level of significance was used. Reliability was evaluated by Weibull analysis. Results: All treatment groups exhibited a significant difference in mean surface roughness (Rq) compared to the as-sintered group (p<0.05). The AAC group showed the highest surface roughness at 1.08 ± 0.17 μm, followed by the G, AAF and AS groups. The GP group exhibited the lowest surface roughness. The group air abraded with fine particles showed the highest mean biaxial flexural strength (1662.62 ± 202.58 MPa), but was not different from the ground and polished group (1567.19 ± 209.76 MPa). The groups air abraded with coarse particles or ground with diamond bur exhibited comparable mean biaxial flexural strength at 1371.37 ±147.62 MPa and 1356.98 ±196.77 MPa, respectively. The as-sintered group had the lowest mean biaxial flexural strength at 1202.29 ±141.92 MPa. The depth of compressive stress layer, measured by GIXRD was approximately 50 μm in the AAF group, followed by the AAC group with ~35 μm, ~10 μm for the ground group and ~5 μm for the ground and polished group. Deep subsurface cracks were observed in the AAC group (~80 μm in depth) and G group (~25 μm in depth), whereas shallower flaws were present in the AAF and GP groups at 10 and 3 μm, respectively. Weibull analysis represented a greater reliability in zirconia specimens treated with air abrasion groups. Conclusions: Surface treatments induced the t-m transformation in 3Y-TZP and associated development of compressive stresses to a depth that varied with the severity of the treatment performed. GIXRD revealed that AAF led to the thickest compressive stress layer, followed by AAC, G and GP. SEM revealed that subsurface damage was most severe with AAC, followed by G, AAF and GP. We propose that the flexural strength results can be explained by the difference between the depth of the compressive stress layer induced by the transformation and the depth of the subsurface flaws.

Les procédés de dépôt en phase vapeur sont particulièrement performants pour la synthèse de revêtements à propriétés contrôlées. Plus spécifiquement, ce travail de recherche porte sur l'élaboration de revêtements biocompatibles, sur alliage titane TiAl6V4, obtenus par pulvérisation magnétron en conditions réactives. Dans un premier temps, nous avons décrit les procédés de mise en forme des implants commerciaux pour pouvoir les reproduire au niveau du laboratoire. Dans un second, nous avons focalisé notre étude sur l'effet de la structure cristallographique de films de zircone sur leur caractère biocompatible à partir de cultures cellulaires de fibroblastes. Les résultats ainsi obtenus démontrent très nettement des différences de comportement entre des films de zircone monoclinique, quadratique ou cubique. Dans l'objectif d'apporter des éléments d'information permettant de discuter de ces effets, d'autres séries de revêtements céramiques ont été élaborées comme par exemple des oxydes de titane ou de zirconium amorphes, de l'oxyde d'yttrium, de l'oxyde d'aluminium ou encore du carbone amorphe. Les cultures cellulaires pratiquées sur ces échantillons ont permis de démontrer le caractère biocompatible de l'oxyde d'yttrium excluant ainsi tout effet nocif de cet élément dans les zircones dopées / The vapor deposition processes are particularly successful for the synthesis of coatings with tuneable properties. More specifically, this research deals with the development of biocompatible coatings on titanium alloys TA6V obtained by magnetron sputtering in reactive conditions. At first, we described the processes to design the commercial medical implants to be able to reproduce them within the laboratory. In the second, we focused our study on the effect of the crystallographic structure of zirconia-based coatings on their biocompatible character from cell cultures of fibroblasts. The results obtained demonstrate a significant variation of cell behavior for the three the zirconia structures: monoclinic, tetragonal or cubic. In the purpose to bring relevant information that allow discussing these effects, another series of ceramic coatings were developed as for instance amorphous oxides of titanium or zirconium, yttrium oxide,, aluminum oxide or amorphous carbon. The cell response on these samples demonstrates to the biocompatible properties of the yttrium oxide, excluding any harmful effect of this element in the doped zirconia

L’excellente biocompatibilité et les remarquables propriétés mécaniques font des biocéramiques une des meilleures options pour les prothèses totales de hanche (PTH). Jusqu’à récemment, le seul dispositif qui permettait d’estimer la durée de vie des PTH était le simulateur de marche. Les PTH ne sont pas uniquement sollicitées en fatigue mais aussi en chocs. Dans ce travail nous avons évalué la durabilité des prothèses de hanche en biocéramique testées sur une machine de chocs. Deux couples tête/cupule ont été testés : alumine/alumine et composite alumine-zircone/alumine. Les essais se sont déroulés à sec et en solution avec une inclinaison de 45° qui correspond à la position anatomique standard de cette articulation. Des bandes d’usure apparaissent sur la tête. Leur localisation et leur rugosité sont similaires à celles retrouvées ex vivo. La machine de chocs reproduit les mécanismes de dégradation des PTH in vivo. L’influence du vieillissement sur la résistance aux chocs a été étudiée. Afin de mieux comprendre la transformation de phase in vivo de la zircone, une grande série d’explants a été analysée. Aucune corrélation entre la transformation de phase et l’augmentation de la rugosité n’a été observée. La transformation de phase de la zircone serait liée aux processus de fabrication (polissage, usinage..). Ce travail constitue une base de données pour les couples zircone/UHMWPE. De la même façon, l’analyse d’explants composites permettrait de valider nos résultats in vitro pour les composites. / Because of the excellent biocompatibility and great mechanical properties, bioceramics are the best choice for total hip replacement (THR). When hip is replaced, a microseparation could appear between the head and the cup leading to a shock limiting the lifetime of ceramics. Classic tests on hip simulator partly allow estimating the lifetime of ceramics.Ceramics materials are subjected to shocks. In this work we evaluated the reliability of bioceramics for hip replacement tested in a shock machine. Two bearing surfaces were studied (head/cup): alumina/alumina and composite alumina-zirconia/alumina. Tests were carried out in dry and in solution with an inclination of 45° to respect the standard anatomical position. Femoral heads exhibited two wear stripes of similar location and roughness to those found ex vivo. Shock device reproduces in vivo degradation. The influence of aging on the shocks degradation was also studied for composites alumina-zirconia. Artificial ageing did not affect the shock-induced wear resistance. Further analysis of retrieved composite would be interesting for comparison of experimental results.Also, ex vivo analyses were made. A large number of retrieved zirconia femoral heads were analyzed in order to understand the phase transformation of zirconia in vivo. Any correlation between the phase transformation and the increase in roughness was found. We might suggest that phase transformation is activated during the fabrication process (sintering, polishing, machining) and is not accelerated in vivo.

No description available.

The objective of this study was to compare effect of surface treatment and fatigue to the retention of zirconia crowns luted to two different heights of titanium abutments. Thirty titanium base 3.5 mm (n = 15) and 5.5 mm in height (n = 15) and thirty zirconia crowns were used. Group A (n = 10), 3.5-mm-height titanium base with no surface treatment; Group B (n = 5), 3.5-mm-height titanium base with surface treatment; Group C (n = 5), 3.5-mm-height titanium base with no surface treatment with fatigue test; Group D (n = 5), 3.5-mm-height titanium base with surface treatment and fatigue test. The identical group allocation was utilized to 5.5-mm-height titanium base groups, Group E, F, G and H respectively. All zirconia crowns and titanium abutments of the groups with surface treatment were particle abraded with 50 μm alumina. All specimens were subjected to a pull-out test. Data were analyzed with ANOVA and the Tukey HSD test. Pull-out retention forces for each group were: Group A: 288 ± 97.5 N, Group B: 198.71 ± 82.94 N, Group C: 537.61 ± 80.13 N, Group D: 600.11 ± 27.23 N, Group E: 240.68 ± 54.33 N, Group F: 270.92 ± 16.43 N, Group G: 707.03 ± 32.30 N, and Group H: 831.19 ± 55.50 N. Particle abrasion of the titanium base significantly increased zirconia crown retention. The height of the titanium base had a significant influence on retention force in particle-abraded groups. The fatigue test did not decrease retention force. / 2018-09-26T00:00:00Z

Os implantes dentários representam uma opção de tratamento com alta previsibilidade de sucesso e sobrevivência. Os excelentes resultados geralmente estão relacionados à estabilidade da crista óssea e à saúde dos tecidos peri-implantares de suporte. O material utilizado para confecção do conector protético parece ter um papel importante no resultado clínico dos implantes em longo prazo. O objetivo deste estudo foi avaliar longitudinalmente parâmetros clínicos dos tecidos peri-implantares em pacientes reabilitados com próteses unitárias cimentadas sobre conectores de titânio ou zircônia. Foram selecionados 20 participantes que foram reabilitados com implantes dentários e coroas protéticas cimentadas sobre conectores de zircônia (n=10; região anterior da maxila) ou conectores de titânio (n=10; região posterior da maxila/mandíbula). Os parâmetros clínicos: profundidade de sondagem, nível clínico de inserção, recessão gengival, sangramento à sondagem e reabsorção óssea marginal foram coletados nos períodos T0 = baseline (instalação da prótese), T1 = 12 meses, T2 = 24 meses e T3 = 36 meses de função mastigatória. Nenhuma complicação clínica foi observada em ambos os conectores, com taxa de sucesso de 100%. Tanto os materiais avaliados quanto os períodos de investigação propostos apresentaram efeito relativo significante nos parâmetros clínicos avaliados (p &lt; 0,05). Não houve diferença significante em relação à reabsorção óssea marginal total, entre os dois materiais, após 36 meses. Os resultados sugerem manutenção da saúde peri-implantar ao longo do tempo, em ambos os grupos / Dental implants represent a treatment option with high success and survival predictability. The great results usually are related to bone crest stability and peri-implant supporting tissues health. The material used to produce the prosthetic connector seems to play an important role on the long term of implant clinical outcome. The objective of this study was to evaluate longitudinal clinical parameters of peri-implant tissues in patients rehabilitated with unitary prostheses cemented on titanium or zirconia connectors. Were selected twenty participants rehabilitated with dental implants and cemented crowns on zirconia connectors (n = 10, anterior maxilla) or titanium connectors (n = 10, posterior maxilla/ mandible). The clinical parameters: probing depth, connective tissue attachment level, gingival recession, bleeding on probing and marginal bone resorption, were collected in the periods of masticatory function: T0 = baseline (prosthesis installation), T1 = 12 months, T2 = 24 months and T3 = 36 months. No clinical complication was observed in both connectors, with a 100% success rate. The evaluated materials and the investigated periods had a significant relative effect on the clinical parameters evaluated (p &lt; 0.05). There was no significant difference on the total marginal bone resorption between the two materials, after 36 months. The results suggests maintenance of peri-implant health over time, in both groups

The thermal conductivity of various porous thermal barrier coating (TBC) systems used in elevated temperature for industrial applications has been evaluated using a proposed six-phase model. These porous TBC systems rely on microstructural properties and yield different types of porosity. These microstructural properties can influence the thermal conductivity of TBC systems. The purpose of this thesis is to assess the thermal conductivity of TBC systems based on microstructural attributes, particularly the effect of different types of porosity. Thus, the first component of this thesis investigates the microstructural characterization of various TBC systems using image analysis (IA) technique. In this technique, scanning electron microscopy (SEM) and light optical microscopy (LOM) micrographs were used to measure the porosity level of different TBC materials. The volumetric fraction of porosity along with orientation, shape, and morphology have a considerable impact on the total thermal conductivity of TBCs. The second component of this thesis evaluates the thermal conductivity of these porous TBC systems by taking into account the effect of the heat treatment process. The IA results reveal that as long as the porosity content increases, the thermal conductivity decreases for all of the TBC materials studied in this thesis. Further, while the content of microcracks and non-flat porosity play a crucial role in reducing the thermal conductivity of TBC materials, the other types of porosity (open randomly oriented, penny-shaped, and interlamellar) exert less impact on the thermal conductivity of TBCs. Comparing the results of the proposed six-phase model to experimental values and finite element analysis (FEA) values showed a relatively good agreement. The proposed six-phase model can predict the thermal conductivity of porous microstructure of TBC systems close to real measured values; therefore, the proposed six-phase model may be utilized to fabricate the porous microstructure of TBCs.