Search results for "Zirconi"
showing 10 items of 413 documents
High temperature reactivity of nickel aluminide diffusion coatings
2008
Abstract The high-temperature oxidation behaviour of nickel aluminides has been studied at 900 °C in air under atmospheric pressure. Yttria doped and undoped specimens of nickel were aluminised and then oxidised for 100 h under isothermal and cycling conditions. The results showed that when yttria is added by metal-organic chemical vapour deposition technique prior to the aluminisation process, it increased the oxidation rate of aluminised nickel, but improved the oxide scale adherence under cyclic conditions. The effects of yttria on the scale morphology, oxidation behaviour and scale spallation tendency are discussed based on the experimental results, using X-ray diffraction (XRD), scanni…
Influence of oxygen ion elementary diffusion jumps on the electron current through the conductive filament in yttria stabilized zirconia nanometer-si…
2021
Abstract The structure of the electron current through an individual filament of a nanometer-sized virtual memristor consisting of a contact of a conductive atomic force microscope probe to an yttria stabilized zirconia (YSZ) thin film deposited on a conductive substrate is investigated. Usually, such investigation is performed by the analysis of the waveform of this current with the aim to extract the random telegraph noise (RTN). Here, we suggest a new indirect method, which is based on the measurement of the spectrum of the low-frequency flicker noise in this current without extracting the RTN, taking into account the geometrical parameters of the filament. We propose that the flicker no…
Mechanical behavior of single-layer ceramized zirconia abutments for dental implant prosthetic rehabilitation
2013
Objectives: This study was undertaken to characterize the mechanical response of bare (as-received) and single-layer ceramized zirconia abutments with both internal and external connections that have been developed to enhanced aesthetic restorations. Material and Methods: Sixteen zirconia implant abutments (ZiReal Post®, Biomet 3i, USA) with internal and external connections have been analyzed. Half of the specimens were coated with a 0.5mm-thick layer of a low-fusing fluroapatite ceramic. Mechanical tests were carried out under static (constant cross-head speed of 1mm/min until fracture) and dynamic (between 100 and 400N at a frequency of 1Hz) loading conditions. The failure location was i…
Study of stress effects in the oxidation of Zircaloy-4
2001
Abstract The oxidation of zirconium alloy Zy-4 is due to an anionic diffusion of oxygen leading to the formation of an oxide layer of zirconia. According to the Pilling and Bedworth ratio of the Zr/ZrO 2 system, the oxide scale is under compressive stresses. This stress state may play an important role during the corrosion process, from the phases as well as from the kinetics point of view. In order to better understand the eventual relationship between oxide phases, oxidation kinetics and stresses, an experimental apparatus was developed in our laboratory. It allows the application of external tensile stresses, in situ oxidation of the sample in controlled environment and X-ray diffraction…
Large scale synthesis of nanostructured zirconia-based compounds from freeze-dried precursors
2013
Nanocrystalline zirconia powders have been obtained at the multigram scale by thermal decomposition of precursors resulting from the freeze-drying of aqueous acetic solutions. This technique has equally made possible to synthesize a variety of nanostructured yttria or scandia doped zirconia compositions. SEM images, as well as the analysis of the XRD patterns, show the nanoparticulated character of those solids obtained at low temperature, with typical particle size in the 10–15 nm range when prepared at 673 K. The presence of the monoclinic, the tetragonal or both phases depends on the temperature of the thermal treatment, the doping concentration and the nature of the dopant. In addition,…
V-containing ZrO 2 inorganic yellow nano-pigments prepared by hydrothermal approach
2017
Abstract Recent results on the preparation, characterization and color properties of the V-containing ZrO 2 inorganic yellow nano-pigment are reported. A series of monoclinic V-ZrO 2 solid solution nanocrystals (V x Zr 1-x O 2 , being x = 0, 0.1, 0.02, 0.03, 0.04, 0.05, 0.065, 0.08 and 0.1) were prepared straightforward by hydrothermal processing of mixtures of zirconyl nitrate and ammonium metavanadate in water. Interestingly, the crystalline precipitated obtained by hydrothermal processing at 140 °C for 3 d was almost entirely V-containing ZrO 2 nanocrystals with the structure of monoclinic zirconia for the whole range of compositions. Lattice parameters changes along the series of prepar…
PbS Nanodots For Ultraviolet Radiation Dosimetry
2011
Lead sulfide (PbS) nanodots in Zirconia (ZrO2) thin film matrix (ZrO2:PbS films) were investigated for UV radiation dosimetry purposes. Samples were fabricated using sol-gel technique. ZrO2:PbS films were irradiated with UV light with wavelengths 250 – 400 nm during 50 minutes. Photoelectron emission spectra of ZrO2:PbS films were recorded and band structure for nonradiated and UV irradiated samples was calculated. It was found that quantity of localized states decreased after UV irradiation while density of localized states was dependent on concentration of PbS nanodots. The observed changes in band structure of ZrO2:PbS films after UV irradiation suggest that the films may be considered a…
First-principles insight into CO hindered agglomeration of Rh and Pt single atoms on m-ZrO2
2020
In this first-principles study we evaluate the thermodynamic and kinetic stability of Rh and Pt single-atoms (SAs) and subnano clusters on the monoclinic zirconia surface with and without a CO atmosphere. To address the kinetic stability and agglomeration of SAs to clusters and nanoparticles, a non-equilibrium nanothermodynamic approach is developed and parametrised using data computed with density functional theory. The bare subnano clusters are more stable than SA and become more so with increasing size, which means the agglomeration is always favoured. CO binds strongly to the single atoms and clusters, and our atomistic thermodynamics treatment indicates that some CO will be present eve…
Pre-Stressed Sub-Surface Contribution on Bulk Diffusion in Metallic Solids
2011
Our recent modelling works and corresponding numerical simulations realized to describe the UO2 oxidation processes confirm the theory showing that an applied mechanical strain can strongly affect the local oxygen diffusion in a stressed solid. This result allows us to assume that stress field, previously applied at the surface of a metallic sample on several microns, will delay the degradation during its oxidation. Considering this hypothesis, we implemented a FEM simulation code developed in our laboratory to numerically investigate some different stress fields applied on a sample sub-surface, that might significantly modify the volume diffusion of oxygen during the oxidation process. The…
Caractérisation de poudres de zircone synthétisées par voie hydrothermale
1998
La synthese hydrothermale permet la realisation de poudres fines cristallisees et desagglomerees Ces qualites sont appropriees a l'elaboration de composites fins oxyde/oxyde par synthese simultanee des deux phases. Nous avons developpe ce protocole pour la realisation de nanocomposites ahrmine/zircone (Q). Nous presentons ici plus particulierement le travail effectue sur la zircone, Les conditions de traitement hydrothermal et d'un traitement thermique modere supplementaire sont analysees en relation avec les caracteristiques des poudres synthetisees. Differentes techniques complementaires sont utilisees pour ces poudres de zircone: diffraction des rayons X (% de la phase quadratique, taill…