Zirconia Phase Research Articles

Development of defects in nanocrystalline zirconia: studied through photoluminescence spectroscopy

Zirconium dioxide (zirconia) nanoparticle with monoclinic structure is successfully synthesised by chemical route, i.e., pyrophoric method from aqueous solution of ZrOCl2.8H2O and triethanol amine. The structural and optical properties of the annealed samples have been investigated by using X-ray diffractometer, photoluminescence spectroscopy and UV-visible spectrometer. It is observed that the variations of annealing temperature from 650°C to 950°C do not change the structure. However, the crystallite size of zirconia varies from 18 nm to 27 nm and particle size from 10 to 70 nm by annealing the samples. The optical band gap of all the annealed zirconia samples does not vary a lot by the temperature variation in the monoclinic structural phase of zirconia because the crystallite size changes in nanoscale range. The photoluminescence studies clearly states the presence of interstitial and vacancy related defects in nanocrystalline ZrO2. This informs that point defects in form of oxygen vacancies and zirconia vacancies can be introduced in nanocrystalline ZrO2 which is necessary for making these samples efficient for sensor applications.

Development of defects in nanocrystalline zirconia: studied through photoluminescence spectroscopy

Zirconium dioxide (zirconia) nanoparticle with monoclinic structure is successfully synthesised by chemical route, i.e., pyrophoric method from aqueous solution of ZrOCl2.8H2O and triethanol amine. The structural and optical properties of the annealed samples have been investigated by using X-ray diffractometer, photoluminescence spectroscopy and UV-visible spectrometer. It is observed that the variations of annealing temperature from 650°C to 950°C do not change the structure. However, the crystallite size of zirconia varies from 18 nm to 27 nm and particle size from 10 to 70 nm by annealing the samples. The optical band gap of all the annealed zirconia samples does not vary a lot by the temperature variation in the monoclinic structural phase of zirconia because the crystallite size changes in nanoscale range. The photoluminescence studies clearly states the presence of interstitial and vacancy related defects in nanocrystalline ZrO2. This informs that point defects in form of oxygen vacancies and zirconia vacancies can be introduced in nanocrystalline ZrO2 which is necessary for making these samples efficient for sensor applications.

Synthesis and characterization of monoclinic phase of zirconia

Zirconium oxide (zirconia) powder has been synthesized by co-precipitation method. The structural characterization of prepared sample was obtained by X-ray diffraction and showed monoclinic phase. Further surface morphology was confirmed by scanning electron microscopy (SEM). The frequency dependence of dielectric constant, dielectric loss, and impedance of the sample was investigated at room temperature. The obtained results partially motivated for alternative silicon based on devices.

ScVO4 under non-hydrostatic compression: a new metastable polymorph

The high-pressure (HP) behaviour of scandium vanadate (ScVO4) is investigated under non-hydrostatic compression. The compound is studied by means of synchrotron-based powder x-ray diffraction (XRD) and optical-absorption techniques. The occurrence of a non-reversible phase transition is detected. The transition is from the zircon structure to the fergusonite-type structure and takes place around 6 GPa with nearly 10% volume discontinuity. XRD measurements on the pressure cycled sample confirm for the first time that the fergusonite-type ScVO4 can be recovered as the metastable phase at ambient conditions. Raman spectroscopic measurements verify the metastable phase to be of a fergusonite-type phase. Theoretical calculations also corroborate the experimental findings. The fergusonite phase is found to be stiffer than the ambient-pressure zircon phase, as indicated by the observed experimental and theoretical bulk moduli. The optical properties and lattice-dynamics calculation of the fergusonite ScVO4 are discussed. At ambient pressure the band gap of the zircon (fergusonite)-type ScVO4 is 2.75 eV (2.3 eV). This fact suggests that the novel metastable polymorph of ScVO4 can have applications in green technologies; for instance, it can be used as photocatalytic material for hydrogen production by water splitting.

Erosion Performance of Gadolinium Zirconate-Based Thermal Barrier Coatings Processed by Suspension Plasma Spray

7-8 wt.% Yttria-stabilized zirconia (YSZ) is the standard thermal barrier coating (TBC) material used by the gas turbines industry due to its excellent thermal and thermo-mechanical properties up to 1200 °C. The need for improvement in gas turbine efficiency has led to an increase in the turbine inlet gas temperature. However, above 1200 °C, YSZ has issues such as poor sintering resistance, poor phase stability and susceptibility to calcium magnesium alumino silicates (CMAS) degradation. Gadolinium zirconate (GZ) is considered as one of the promising top coat candidates for TBC applications at high temperatures (>1200 °C) due to its low thermal conductivity, good sintering resistance and CMAS attack resistance. Single-layer 8YSZ, double-layer GZ/YSZ and triple-layer GZdense/GZ/YSZ TBCs were deposited by suspension plasma spray (SPS) process. Microstructural analysis was carried out by scanning electron microscopy (SEM). A columnar microstructure was observed in the single-, double- and triple-layer TBCs. Phase analysis of the as-sprayed TBCs was carried out using XRD (x-ray diffraction) where a tetragonal prime phase of zirconia in the single-layer YSZ TBC and a cubic defect fluorite phase of GZ in the double and triple-layer TBCs was observed. Porosity measurements of the as-sprayed TBCs were made by water intrusion method and image analysis method. The as-sprayed GZ-based multi-layered TBCs were subjected to erosion test at room temperature, and their erosion resistance was compared with single-layer 8YSZ. It was shown that the erosion resistance of 8YSZ single-layer TBC was higher than GZ-based multi-layered TBCs. Among the multi-layered TBCs, triple-layer TBC was slightly better than double layer in terms of erosion resistance. The eroded TBCs were cold-mounted and analyzed by SEM.

ChemInform Abstract: Ba/ZrO2 Nanoparticles as Efficient Heterogeneous Base Catalyst for the Synthesis of β‐Nitro Alcohols and 2‐Amino 2‐Chromenes.

Zirconia nanoparticles were synthesized by precipitation, urea hydrolysis, amorphous citrate and combustion synthesis methods. The zirconia surface was subsequently modified by grafting Ba 2+ species. The Ba 2+ modified zirconia (Ba/ZrO 2) materials were characterized using XRD, Fourier analysis, UV-vis-DRS, FESEM and HRTEM techniques. XRD study indicated selective stabilization of the tetragonal phase of zirconia in the presence of Ba 2+ species. Fourier line profile analysis of the XRD peaks revealed that the average crystallite size of the zirconia nanoparticles is in the range of 5-15 nm. The surface area, basicity and barium content of the material depend strongly on the method of synthesis. The Ba/ZrO 2 catalyst prepared by urea hydrolysis method exhibited higher surface area and barium content compared to other samples. The catalytic activity of the Ba/ZrO 2 catalyst was evaluated for synthesis of β-nitro alcohols and 2-amino 2-chromenes. The β-nitro alcohols were synthesized by condensation of aryl aldehydes and nitromethane. Similarly, the 2-amino 2-chromenes were synthesized by condensation of arylaldehydes, α-naphthol and malononitrile. The Ba/ZrO 2 catalyst was found to be highly efficient for synthesis of both classes of compounds providing excellent yield and purity of the products.

Pressure-induced zircon to monazite phase transition in Y1–х La х PO4: First-principles calculations

Density functional theory was used to study pressure-induced phase transitions of zircon to monazite in doped yttrium orthophosphate, Y1–хLaхPO4, for х = 0, 0.0625, 0.125. The pressures of the phase transition, the elastic moduli and the universal elastic anisotropy index were calculated. It was shown that with increasing lanthanum concentration in Y1–xLaxPO4, the transition pressure increases. According to the Birch–Murnaghan equation of state, this effect is associated with a decrease in the critical volume. The increased stability of the doped zircon phase compared to YPO4 is attributed to the more significant increase in the anisotropy and distortions of REO8 polyhedra and RE–O–P chains found for the optimized structures at critical volumes.

Femtosecond laser induced nanostructuring of zirconium in liquid confined environment

The surface, structural, and mechanical properties of zirconium after irradiation with Ti: sapphire laser (800 nm, 30 fs, 1 kHz) have been investigated. The zirconium targets were exposed for a varying number of laser pulses ranging from 500 to 2000 at a fixed fluence of 3.6 J/cm2 corresponding to an intensity of 1.2×1014 W/cm2 in ambient environments of de-ionized water and propanol. A scanning electron microscope (SEM) was employed to investigate the surface morphology of the irradiated zirconium. The SEM analysis shows the formation of various kinds of features including nanoscale laser induced periodic surface structures (LIPSS), sponge like surface structure, flakes, conical structures, droplets, pores, and cavities. The energy dispersive x-ray spectroscopy (EDS) analysis exhibits the variation in chemical composition along with an enhanced diffusion of oxygen under both ambient conditions. The crystal structure and phase analyses of the exposed targets were explored by x-ray diffraction (XRD) and Raman spectroscopy techniques, respectively. The XRD analysis confirms the presence of various phases of zirconium hydride and zirconia after ablation in both de-ionized water and propanol. However, excessive hydrides are formed in the case of propanol. The Raman analysis supports the EDS and XRD results. It also reveals the presence of oxides (zirconia) after irradiation in both de-ionized water and propanol environments. The chemical reactivity of zirconium was significantly improved in the presence of liquids which were accountable for the growth of novel phases and modification in the chemical composition of the irradiated Zr. A nanohardness tester was employed to measure the nanohardness of the laser treated targets. The initial increase and then decrease in nanohardness was observed with an increase in the number of laser pulses in the de-ionized water environment. In the case of propanol, a continuous decrease in hardness was observed.

Identification of the Zirconia Phases by Means of Raman Spectroscopy for Specimens Prepared by FIB Lift-Out Technique

The zirconium–zirconia interface that developed during high-temperature corrosion of pure zirconium was investigated. Samples were oxidized at 600 °C in air at atmospheric pressure. The oxidized sample was then prepared by means of focused ion beam (FIB) lift-out technique and examined using Raman spectroscopy technique in three different oxide zones (external, internal, and close to the metal–oxide interface). Structural investigation was performed using line mode Raman analysis. Implementation of these techniques revealed complexity of the studied system and confirmed the presence of a thin tetragonal sub-layer located in the proximity of the metal. Recorded Raman band displacements of monoclinic and tetragonal phases were interpreted in terms of stoichiometry level and compressive stress in the oxide. The thin layer of tetragonal phase is most likely characterized by lower amount of oxygen than the external part of the oxide.

Synthesis of Fe3O4@ZrO2 core–shell nanoparticles through new approach and its solar light photocatalyst application

In this work, first, Fe3O4 nanoparticles were synthesized by microwave assisted method with using of hydrazine and citric acid as reducing and surfactant agent, respectively. Then, as-prepared magnetite nanoparticles were used as a core and a shell of ZrO2 nanoparticles were coated on the Fe3O4 seeds. Crystallographic and morphological characterizations of prepared samples have been carried out using X-ray diffraction and field emission scanning electron microscopy. The results indicate that the sample prepared has the structure of cubic reverse spinel of Fe3O4 in the core, shell contain the amorphous phase of zirconia and the size of as-synthesized Fe3O4@ZrO2 nanoparticles is about 35–55 nm. The UV–Vis spectra showed that the sample has good absorption ability in the wavelength range of 300–800 nm. The photocatalytic activity of as-synthesized core–shell NPs were investigated in the degradation of methyl orange (MO) solution under solar light. Results showed that MO degradation is increased in the presence of Fe3O4@ZrO2 nanoparticles and almost most of this organic dye is degraded after 240 min of irradiation by the solar light.

Effect of cation dopants in zirconia on interfacial properties in nickel/zirconia systems: an atomistic modeling study

Cation doping is often used to stabilize the cubic or tetragonal phase of zirconia for enhanced thermomechanical and electrochemical properties. In the present paper we report a combined density functional theory (DFT) and molecular dynamics study of the effect of Sc, Y, and Ce dopants on properties of Ni/ interfaces and nickel sintering. First, we develop an MD model that is based on DFT data for various nickel/zirconia interfaces. Then, we employ the model to simulate Ni nanoparticles coalescing on a zirconia surface. The results show the possibility of particle migration by means of fast sliding over the surface when the work of separation is small (<). The sliding observed for the O-terminated Ni(1 1 1)/(1 1 1) interface is not affected by dopants in zirconia because the work of separation of the doped interface stays small. The most pronounced effect of the dopants is observed for the Zr-terminated Ni(1 1 1)/(1 1 1) interface, which possesses a large work of separation () and thus restricts the sliding mechanism of Ni nanoparticle migration. DFT calculations for the interface revealed that dopants with a smaller covalent radius result in a larger energy barriers for Ni diffusion. We analyze this effect and discuss how it can be used to suppress nickel sintering by using the dopant selection.

HOT CORROSION OF YTTRIUM STABILIZED ZIRCONIA COATINGS DEPOSITED BY AIR PLASMA SPRAY ON A NICKEL-BASED SUPERALLOY

In this research, the electrochemical impedance spectroscopy (EIS) and Tafel analysis were utilized to study the hot corrosion performance at 700[Formula: see text]C of air plasma-sprayed (APS) yttria-stabilized zirconia (YSZ) coatings with a NiCrAlY bond coat grown by high velocity oxygen fuel spraying (HVOF), deposited on an INCONEL 625 substrate, in contact with corrosive solids salts as vanadium pentoxide V2O5 and sodium sulfate Na2SO4. The EIS data were interpreted based on proposed equivalent electrical circuits using a suitable fitting procedure performed with Echem AnalystTM Software. Phase transformations and microstructural development were examined using X-ray diffraction (XRD), with Rietveld refinement for quantitative phase analysis, scanning electron microscopy (SEM) was used to determinate the coating morphology and corrosion products. The XRD analysis indicated that the reaction between sodium vanadate (NaVO[Formula: see text] and yttrium oxide (Y2O[Formula: see text] produces yttrium vanadate (YVO[Formula: see text] and leads to the transformation from tetragonal to monoclinic zirconia phase.

Dry reforming of methane on grafted-supported Rh catalysts: effect of the metal-support interaction on the reaction rate

Catalysts of rhodium supported on pure oxides and modified alumina with 50, 75 and 100% of ZrO2 were prepared by the impregnation method, to be tested in the reaction of dry reforming of methane in order to study the effect of the metal-support interaction on the reaction rate. The catalysts were characterized by N2 adsorption isotherms, CO chemisorption, TEM, temperature programmed reduction, XRD and XPS. The reaction rate for CH4 conversion was measured at 500–700 °C, in the absence of transport limitation. The average Rh cluster size in catalysts with modified supports resulted similar as compared with the catalyst Rh/0%ZrO2–Al2O3, so that the modification of the support had no effect on the dispersion of Rh, which is associated with the similarity in the BET surface area of the pure and modified alumina. The Rh-support interaction is determined by the degree of coverage of alumina with zirconia and by the nature of ZrO2 phase formed in the grafted supports. The higher coverage of alumina with zirconia leads to a lower Rh-support interaction. However, the interaction of Rh with the monoclinic phase seems to be weaker than with the tetragonal phase of zirconia, the latter more abundant as the loading of ZrO2 is increased in the grafted supports. Consequently, the Rh-support interaction increases with the content of ZrO2. Despite the different Rh-support interaction, the structural sensitivity of dry reforming of methane on Rh catalysts was still evidenced, i.e., the DRM reaction rate is mainly determined by the coordination degree of Rh atoms on the catalyst surface.

Influence of nano zirconia on NiAl anodes for molten carbonate fuel cell: Characterization, cell tests and post-analysis

Abstract Anode materials in Molten Carbonate Fuel Cells should have high creep resistance and good mechanical behavior to endure in high temperature-corrosive environments. In this work, zirconia nanoparticles (1–10% wt.) are added to NiAl anodes in order to investigate their effects on mechanical properties and single cell performances. Results show that nanoparticles strongly adhere to metal particles and bending strength increases from 6.08 to 11.33 kg f cm −2 while creep strain is reduced from 7.55% to 3.25%. In the case of the anode with ZrO 2 3% wt., the stable and high output voltage of 0.81 V at 150 mA cm −2 is a promising result, compared to the literature. In addition, the solid contact angles between melted electrolyte and anode, for the NiAl reference sample and the ZrO 2 3% wt. are 37.6° and 17°, respectively, showing the improved wettability of the modified anode. However, it seems to be a limit to the effective zirconia content as the contact angle of the anode with ZrO 2 10% wt. is 58.1°, which indicates a low wetting ability. When zirconia content is too high, single cells have low performances due to high internal resistance and porosity reduction. The formation of a zirconate phase also occurs during operations.

Wear and Corrosion Resistance of Low Temperature Degradation Free ZTA for Artificial Joint

Low-temperature-degradation-free (LTD-free) zirconia-toughened alumina (ZTA) has been developed as an alternative to alumina and zirconia. It has been reported that ZTA has more beneficial mechanical characteristics than alumina, because of the stress-induced transformation and the spontaneous transformation of the zirconia phase that occurs for some ZTA in a hydrothermal environment. To achieve high-reliability artificial-joint prostheses, it is necessary to improve both the mechanical characteristics and phase stability of the joint material simultaneously. Thus, in this study, we evaluate the wear characteristics and corrosion resistance of LTD-free ZTA using a hip wear simulator, so as to confirm the long-term stability and reliability of this material in clinical use. The ZTA with advantageous mechanical characteristics used in this study has extremely high wear and corrosion resistance. Therefore, this ZTA could be quite useful as a bearing material in artificial joints for longer-term clinical use. It is also confirmed that the newly developed LTD-free ZTA is extremely stable under sliding conditions. Thus, it can be expected that the initial superior surface characteristics will be maintained through long-term clinical use.

CaO-ZrO2 nanocomposite oxide prepared by urea hydrolysis method as heterogeneous base catalyst for synthesis of chromene analogues

A series of CaO–ZrO2 nanocomposite oxides containing 2–50mol% of CaO were synthesized employing urea as a mild hydrolyzing agent. The nanocomposite systems were characterized using XRD, Fourier analysis, TPD, Raman, XPS, TGA-DSC, FESEM, HRTEM, and BET surface area measurement techniques. XRD study indicated selective stabilization of the tetragonal zirconia phase in the composite oxide. Upto 20mol% CaO, the Ca2+ ions substituted for Zr4+ ions in the zirconia lattice to form a substitutional solid solution. Beyond 20 mol% CaO, the presence of a mixed phase system consisting of the solid solution phase, CaO and nonstoichiometric Zr0.93O2 phase was observed. The composite oxides contain crystallites with size <20nm as observed from Fourier and HRTEM analysis. TPD study revealed a significant enhancement in the basicity of zirconia as a result of Ca2+ incorporation. XPS study confirmed presence of different lattice oxygen as potential basic sites. Raman spectral data indicated the presence of oxygen vacancy and distortion in oxygen sublattice due to Ca2+ incorporation to zirconia. Microscopic investigation of the composite oxide suggested a gradual morphological change from rod shape particles to flake like and subsequently to cubic morphology with increase in CaO content in the composite. The CaO–ZrO2 nanocomposite oxides were used as an efficient and recyclable heterogeneous base catalyst for synthesis of chromene analogues. Structurally diverse 2-amino-4H-chromenes and 2-amino-2-chromenes were synthesized in high yield and purity under mild condition using CaO-ZrO2 material as catalyst and multicomponent condensation approach.

Investigation of the Effect of Alumina Binder Addition to Pd/SO42––ZrO2 Catalysts during Sol–Gel Synthesis

We have incorporated alumina into palladium catalysts supported on sulfated zirconia (Pd/SZ) during sol–gel synthesis for application in a washcoat for NOx emissions control in natural gas-fired lean-burn engines. In situ incorporation of the adhesivity-enhancing “binder”, alumina, during the sol–gel synthesis of the Pd/SZ catalyst demonstrated significantly improved NOx reduction activity of the previously reported dual-catalyst bed when compared to the conventional ex situ mode of binder addition in a slurry. The effects of alumina addition during sol–gel synthesis of Pd/SZ on the structural, textural, and chemical properties of the resulting catalyst were examined in this study. The evolution of the crystal phase of zirconia during calcination of the Pd/SZ catalyst with the binder incorporated during the sol–gel process was studied using in situ XRD during calcination under air. Comparison of the crystal phase composition of the binder-free and binder-incorporated samples calcined at 700 and 900 °C dem...

Influence of the preparation method of sulfated zirconia nanoparticles for levulinic acid esterification

Zirconia nanomaterials were prepared by hydrothermal synthesis with or without template and were modified by post synthesis method with sulfate groups. The materials were thoroughly characterized by X-ray powder diffraction, TEM, N2 physisorption, FTIR spectroscopy of adsorbed pyridine TG analysis and XPS spectroscopy. The catalytic performance of nanosized ZrO2 catalysts and their sulfated modifications was studied in levulinic acid esterification with ethanol. The sulfate group’s dispersion was predetermined by the use of template during the mesoporous zirconia synthesis. A relation between sulfate groups leaching and the applied synthesis conditions (with or without template) of the zirconia nanoparticles was found. Sulfated materials showed significantly higher activity compared to non-sulfated ones. Furthermore, it has been found that the presence of template during the mesoporous ZrO2 nanoparticles preparation influences significantly the zirconia phase and catalytic performance in levulinic acid esterification.

High-pressure lattice-dynamics of NdVO4

High-pressure Raman-scattering measurements and ab initio calculations on NdVO4 have been carried out up to 30GPa. Our combined experimental and theoretical study confirms that beyond 5.9GPa NdVO4 undergoes an irreversible zircon to monazite transition. The coexistence of zircon and monazite phases is experimentally observed up to ~8GPa (which agrees with the theoretical transition pressure), stabilizing the monazite phase as a single phase around 10GPa. Calculations additionally predict the existence of a second high-pressure phase transition at 12.4GPa. This reversible phase transition has been experimentally observed beyond 18.1GPa and remains stable up to 30GPa. The post-monazite phase is predicted to have a monoclinic structure isomorphic to the BaWO4-II type structure. The calculated structure for the three polymorphs of NdVO4 is reported and the pressure dependence of their Raman modes is discussed.

Alkaline nanoparticle coatings improve resin bonding of 10-methacryloyloxydecyldihydrogenphosphate-conditioned zirconia.

Creating an alkaline environment prior to 10-methacryloyloxydecyldihydrogenphosphate (MDP) conditioning improves the resin bonding of zirconia. The present study evaluated the effects of four alkaline coatings with different water solubilities and pH values on resin bonding of MDP-conditioned zirconia. Two alkaline nanoparticle coatings were studied in particular. Thermodynamics calculations were performed to evaluate the strengths of MDP-tetragonal phase zirconia chemical bonds at different pH values. Zirconia surfaces with and without alkaline coatings were characterized by scanning electron microscope (SEM)/energy dispersive spectrometer and Fourier transform infrared spectroscopy; alkaline coatings included NaOH, Ca(OH)2, nano-MgO, and nano-Zr(OH)4. A shear bond strength (SBS) test was performed to evaluate the effects of the four alkaline coatings on bonding; the alkaline coatings were applied to the surfaces prior to conditioning the zirconia with MDP-containing primers. Gibbs free energies of the MDP-tetragonal zirconia crystal model coordination reaction in different pH environments were −583.892 (NaOH), −569.048 [Ca(OH)2], −547.393 (MgO), and −530.279 kJ/mol [Zr(OH)4]. Thermodynamic calculations indicated that the alkaline coatings improved bonding in the following order: NaOH > Ca(OH)2 > MgO > Zr(OH)4. Statistical analysis of SBS tests showed a different result. SBSs were significantly different in groups that had different alkaline coatings, but it was not influenced by different primers. All four alkaline coatings increased SBS compared to control groups. Of the four coatings, nano-Zr(OH)4 and -MgO showed higher SBS. Therefore, preparing nano-Zr(OH)4 or -MgO coatings prior to conditioning with MDP-containing primers may potentially improve resin bonding of zirconia in the clinic.