Search results for " zirconia"
showing 10 items of 139 documents
The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia
2014
It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb co-doping were prepared by sol-gel method and thermally annealed to check for the impact of phase transition on luminescence properties. Phase composition and grain sizes were examined by X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison of samples with different oxygen vacancy concentrations and different Nb concentrations confirmed the known assumption that oxygen vacanc…
Comparative fracture behavior of monolithic and veneered zirconia posterior fixed dental prostheses
2017
The purpose of this study was to evaluate and to compare the fracture load and the fracture pattern of monolithic and veneered zirconia posterior fixed dental prostheses (FDPs). Twenty standardized steel dies were prepared to receive posterior 3-unit FDPs. Specimens were randomly divided into 2 groups (n=10): (1) Lava Zirconia, and (2) Lava Plus. All FDPs were cemented using glass ionomer cement and subjected to thermal and mechanical cycling at 5-55ºC with a 30-s dwell time for 120,000 masticatory cycles. All specimens were subjected to a three-point bending test until fracture. Data were statistically analyzed using Student's t test, paired t-test and Weibull statistics (α=0.05). No diffe…
Effect of Thermomechanical and Static Loading on the Load to Fracture of Metal‐Ceramic, Monolithic and Veneered Zirconia Posterior Fixed Partial Dent…
2018
PURPOSE To evaluate the influence of static (not preloaded) and thermomechanical loading on the load to fracture of metal-ceramic, monolithic and veneered zirconia computer-aided design/computer-aided manufacturing (CAD/CAM) posterior fixed partial dentures (FPDs). MATERIALS AND METHODS One hundred standardized specimens with 2 abutments screwed onto a platform were prepared from stainless steel to receive a posterior 3-unit FPD with an intermediate pontic. Specimens were randomly divided into 5 groups (n = 20): Metal-ceramic (control group), Lava Zirconia system, Vita In-Ceram YZ, IPS e.max ZirCAD, and Lava Plus. Half of the specimens of each group (n = 10) underwent no preloading, and the…
Zirconia implant abutments: A review
2009
Objectives: An increasing aesthetic demand within developed populations conducted to the fabrication of metalfree restorations and to a wide use of ceramic materials, due to its excellent characteristics of biocompatibility and aesthetics. With the incessant increase of commercial labels involved in this technological advance, a review is imposed on ceramic abutments, specifically on zirconia. We made a search of articles of peer-reviewed Journals in PubMed/ Medline, crossing the terms ?Dental Abutments?, ?Dental Porcelain? and ?Zirconia?. The review was divided by subtopics: zirconia physical and mechanical properties, precision fit in the implant-abutment interface, zirconia abutments str…
Isolated Fe(III)-O Sites Catalyze the Hydrogenation of Acetylene in Ethylene Flows under Front-End Industrial Conditions
2018
[EN] The search for simple, earth-abundant, cheap, and nontoxic metal catalysts able to perform industrial hydrogenations is a topic of interest, transversal to many catalytic processes. Here, we show that isolated FeIII¿O sites on solids are able to dissociate and chemoselectively transfer H2 to acetylene in an industrial process. For that, a novel, robust, and highly crystalline metal¿organic framework (MOF), embedding FeIII¿OH2 single sites within its pores, was prepared in multigram scale and used as an efficient catalyst for the hydrogenation of 1% acetylene in ethylene streams under front-end conditions. Cutting-edge X-ray crystallography allowed the resolution of the crystal structur…
Extraction and immediate placement of root analogue zirconia implants: an overview
2011
Dental implants constitute a well-established approach for replacement of lost teeth with titanium being the most favored material for implantation. However, titanium has its limitations in esthetically demanding cases and neither the form nor material of such implants has changed much over the past 40 years. Immediate implantation has been introduced to overcome the disadvantages of conventional implantation which in turn has many disadvantages owing to the incongruence of the implant to the extraction socket. Today, there is scientific evidence that zirconia dental implants osseointegrate well and offer many advantages over titanium implants. The successful use of zirconia ceramics in ort…
Zirconia in fixed prosthesis. A literature review
2014
Statement of problem: Evidence is limited on the efficacy of zirconia-based fixed dental prostheses. Objective: To carry out a literature review of the behavior of zirconium oxide dental restorations. Material and Methods: This literature review searched the Pubmed, Scopus, Medline and Cochrane Library databases using key search words “zirconium oxide,” “zirconia,” “non-metal restorations,” “ceramic oxides,” “veneering ceramic,” “zirconia-based fixed dental prostheses”. Both in vivo and in vitro studies into zirconia-based prosthodontic restoration behavior were included. Results: Clinical studies have revealed a high rate of fracture for porcelain-veneered zirconia-based restorations that …
Vanadium‐Doped Zircon and Zirconia Materials Prepared from Gel Precursors as Site‐Selective Electrochemical Sensors
2003
Abstract Polymer film electrodes incorporating vanadium‐doped zircon (V x ZrSiO4, 0.00 < x < 0.10) and vanadium‐doped monoclinic and tetragonal zirconias (V x ZrO2, 0.00 < x < 0.15), prepared by heat treatment of gel precursors, exhibit a significant site‐selective electrocatalytic activity towards the oxidation of amino acids, polyalcohols, and polyhydroxycarboxylic acids in alkaline media. Catalysis of the oxidation of carboxylate and alcohol groups involves a relatively slow chemical reaction between the substrate and vanadium centers, while the oxidation of thiolate in cysteine can be attributed to the oxidation of an adduct formed by vanadium centers and the substrate.
Porous zirconia and titania as packing materials for high-performance liquid chromatography
1990
Abstract Porous amorphous zirconia (ZrO 2 ) and titania (TiO 2 ) packings were synthesized as rigid microparticulate beads by means of a sol—gel process. Sufficient rigidity and desired mesoporosity of the ZrO 2 and TiO 2 particles were achieved only by a gel hardening process, followed by heat treatment. The mean pore diameter, p d , the specific surface area, a s , and the specific pore volume, ν p , were controlled by the heat treatment. Typical values were p d = 8 nm, a s = 80 m 2 /g and ν p = 0.23 ml/g. ZrO 2 - and TiO 2 -based revesed-phase packings were prepared by subjecting the native materials to a specific activation process and reaction with octadecyltrimethoxysilane. Native ZrO…
Water and carbon oxides on monoclinic zirconia: experimental and computational insights
2014
Zirconium oxide (ZrO2, zirconia) is an interesting catalytic material to be used in biomass conversion, e.g., gasification and reforming. In this work, we show that reducing and hydrating pretreatments affect the surface sites on monoclinic zirconia. The multitechnique approach comprises temperature-programmed surface reactions (TPSR) under CO and CO2 at 100-550 °C, in situ DRIFTS investigations of the surface species and density functional theory (DFT) calculations. The key findings of the work are: (1) formates are formed either directly from gas-phase CO on terminal surface hydroxyls or via the linear CO surface species that are found exclusively on the reduced zirconia without water tre…