Search results for "composite"
showing 10 items of 4584 documents
Vertical root fracture in endodontically treated teeth: A review of 25 cases
2001
Abstract Objective: We sought to examine the clinical conditions under which 25 endodontically treated teeth underwent vertical root fracture (VRF) and to relate this condition to the time elapsed from endodontic treatment to fracture. Study Design: This was a retrospective study in which we reviewed 25 case histories of patients with postendodontic VRF and studied the effect of various pretreatment and posttreatment factors as they related to VRF. Results And Conclusions: The mean time to VRF was 54 months; this was not significantly influenced by the presence or absence of prior restoration or by the presence or absence of a crown fitting. The use of a prefabricated, cylindrical, cemented…
Micromechanical approach of the high temperature oxidation of zirconium: study of the Zr/ZrO2 interfacial epitaxy with Bollmann's method
1997
The method of Bollmann has been used to determine the role of epitaxy in the formation of the mechanical stress field near the metal/oxide interface during the high temperature oxidation of zirconium. The strains due to epitaxy combine with those due to both oxygen diffusion in metal and thermal expansion of the metal/oxide composite in a model based on a micromechanical formalism. The calculated values are compared to experimental results and the applicability of Bollmann's method to this problem is discussed.
Study on the initial stages of water corrosion of fluorozirconate glasses
2004
Abstract The surface corrosion process associated with the hydrolysis of fluorozirconate glass, ZBLAN (53ZrF 4 , 20BaF 2 , 20NaF, 4LaF 2 , 3AlF 3 ) was investigated using X-ray photoelectron spectroscopy (XPS), grazing-incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). After a short exposure period (25 min) of the glass surface to deionized water the XPS data indicate an increase of the oxygen content accompanied by a decrease of fluorine concentration. The analysis of the chemical bonding structure identified the predominant surface reaction products as zirconium hydroxyfluoride and oxyfluoride species. The second most abundant…
Mechanical properties of aluminum, zirconium, hafnium and tantalum oxides and their nanolaminates grown by atomic layer deposition
2015
ABSTRACT The mechanical properties of two different metal oxide nanolaminates comprised of Ta 2 O 5 and Al 2 O 3 , HfO 2 or ZrO 2 , grown on soda–lime glass substrate by atomic layer deposition, were investigated. Ta 2 O 5 and Al 2 O 3 layers were amorphous, whereas ZrO 2 and HfO 2 possessed crystalline structure. Thickness of single oxide layers was varied between 2.5 and 15 nm. The total thickness of the laminate structures was in the range of 160–170 nm. The hardness values of single layer oxides on glass ranged from 6.7 GPa (Ta 2 O 5 ) to 9.5 GPa (Al 2 O 3 ). Corresponding elastic moduli were 96 GPa and 101 GPa. The hardnesses of laminates were in the range of 6.8–7.8 GPa and elastic mo…
Microstructure of Fe–ZrSiO4 solid solutions prepared from gels
2012
Abstract Microstructural changes associated with chemical and structural evolution from gels to Fe x –ZrSiO 4 solid solutions are reported. Mineralizer-free Fe x –ZrSiO 4 gels in the compositional range 0 ≤ x ≤ 0.15 were prepared by sol–gel liquid-phase route from mixtures of alkoxides of silicon and zirconium, and iron (III) acetylacetonate, and annealed at different temperatures and/or times. The first step on the whole process to the final Fe x –ZrSiO 4 solid solutions was the formation of aggregated of tetragonal Fe-doped ZrO 2 nanocrystals with diameters smaller than 50 nm. At this stage the tetragonal Fe–ZrO 2 were embedded in amorphous silica resulting nanocomposite materials. The …
Synthesis and characterization of V2O5SiO2ZrO2 pigments by sol-gel method
1992
Abstract Polymeric gels in the V2O5 SiO2 ZrO2 system were prepared from tetraethylorthosilicate (TEOS), zirconium(IV)-n-propoxide and vanadium(IV) oxyacetylacetonate, precursors. The effects of prehydrolysis time of TEOS and drying gel method on the stabilization of tetragonal zirconia in the silica amorphous matrix, nucleation and growth of the zircon (ZrSiO4) phase, and stabilization of the blue and green stains of vanadium zircon were studied. Results provide evidence that long time of prehydrolysis and fast drying do not favour zircon crystallization but stabilize the tetragonal zirconia in the amorphous matrix.
Microstructural Evolution from Praseodymium-Containing Zircon Gels to Prx-ZrSiO4 Solid Solutions
2012
Structural evolution and coupled microstructural transformations occurred on annealing mineralizer-free Pr-containing ZrSiO4 gels up to final praseodymium-doped zircon yellow pigments are reported. Gels with nominal compositions Prx-ZrSiO4, 0 ≤ x ≤ 0.125, were prepared from mixtures of zirconium and silicon alkoxides and praseodymium acetylacetonate. Crystallization pathway and microstructural changes of thermally treated dried gels were followed by infrared spectroscopy, X-ray diffraction, field emission scanning and transmission electron microscopies, respectively. Results indicated that the crystallization pathway through the whole process of final Prx-ZrSiO4 solid solutions formation di…
Synthesis and characterization of praseodymium-containing ZrSiO4 solid solutions from gels
2011
Abstract The preparation and characterization of a series of praseodymium–zircon solid solution (Prx–ZrSiO4) materials with increasing nominal amounts of Pr is reported. Pr-doped zircon gels were prepared by gelling mixtures of zirconium n-propoxide, praseodymium acetylacetonate and tetraethylorthosilicate, and annealed over the range of temperature up to the formation of Pr–zircon solid solutions. The reaction sequence was followed by X-ray powder diffraction (XRD), ultraviolet–visible diffuse reflectance (DR) and infrared spectroscopy (IR). The first crystalline phase detected on annealing gels was a tetragonal praseodymium-containing ZrO2 phase (t-Pr–ZrO2). On further annealing, the subs…
Evaluation of shear bond strength of zirconia to composite resin using different adhesive systems
2019
Background To evaluate shear bond strength of zirconia to composite resin using different universal and conventional adhesives and a zirconia primer. Material and methods Forty zirconia blocks were fabricated of zirconium ingots (10×10×5 mm) and sintered at 1530°C for 2 hours. They were then air-abraded with Al2O3 particles. The specimens were divided into 4 groups and subjected to one of the following bonding agents: Futurabond U (group 1), Clearfil Universal Bond, universal adhesives (group 2), Z-Prime Plus, zirconia primer (group 3) and Adper Single Bond 2, conventional adhesive (group 4). Composite resin was then applied in a diameter of 5 mm and in a thickness of 2 mm. All the specimen…
Prédiction du comportement mécanique et étude de l’endommagement d’un composite tressé 3D par une analyse multiéchelle. Application à la conception d…
2014
Cette étude porte sur la prédiction du comportement mécanique et l’étude de l’endommagement de composites tressés 3D, utilisés pour fabriquer des réservoirs multiformes. D’une part, on cherche à prédire les propriétés effectives du matériau homogénéisé par une approche dite d’homogénéisation multiéchelle à partir de la connaissance des propriétés des constituants, de leur fraction volumique et de leur disposition au sein d’un élément de volume représentatif du matériau hétérogène communément appelé volume élémentaire représentatif (VER). D’autre part, on cherche à avoir accès à des grandeurs locales pour mieux comprendre les mécanismes d’endommagement identifiés expérimentalement et évaluer…