Phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia

The phase transformation and crystalline growth of 4 mol% yttria partially stabilized zirconia (4Y-PSZ) precursor powders have been investigated using the coprecipitation route, using zirconium oxide chloride octahydrate (ZrOCl₂·8H₂O) and yttrium nitrate (Y(NO₃)₃·6H₂O) as the initial materials. Differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), nano beam electron diffraction (NBED), and high resolution TEM (HRTEM) were utilized to characterize the behavior of phase transformation and crystalline growth of the 4Y-PSZ precursor powders after calcined. Tetragonal ZrO₂ crystallization occurred at about 718.2 K. The activation energy of tetragonal ZrO₂ crystallization was 227.0 ± 17.4 kJ/mol, obtained by a non-isothermal method. The growth morphology parameter (n) and growth mechanism index were close to 2.0, showing that tetragonal ZrO₂ had a plate-like morphology. The crystalline size of tetragonal ZrO₂ increased from 7.9 to 27.6 nm when the calcination temperature was increased from 973 to 1,273 K. The activation energies of tetragonal ZrO₂ growth were 14.97 ± 0.33 and 84.46 ± 6.65 kJ/mol when precursor powders after calcined from 723–973 and 973–1,273 K, respectively.     

Fabrication of surface: relief gratings and their laser induced damage resistance properties

This work demonstrates a promising method for fabricating ZrO₂ surface–relief gratings by photosensitive sol–gel method combining with two-beam laser interference. UV-photosensitive ZrO₂ resist with high resolution are prepared by using metal–chelate complexes as precursors. Two-beam laser interference lithography is carried out by a Kr ion laser with a wavelength of 350.7 nm and ZrO₂ gratings with the minimum line-width of 150 nm are obtained. Laser induced damage resistance properties of ZrO₂ gratings are investigated by a Q-switched solid state laser with the wavelength of 527 nm and the pulse width of 8.65 ns as the incident source. The results show that the LIDT of ZrO₂ gratings on glass substrate heated at 600 °C is about 4.59 ± 0.06 J/cm².     

A kinetic analysis of thermal decomposition of polyaniline/ZrO<Subscript>2</Subscript> composite

Synthesis, characterization and thermal analysis of polyaniline (PANI)/ZrO₂ composite and PANI was reported in our early work. In this present, the kinetic analysis of decomposition process for these two materials was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Ozawa-Flynn-Wall methods, and the possible kinetic model functions have been estimated through the multiple linear regression method. The results show that the kinetic models for the decomposition process of PANI/ZrO₂ composite and PANI are all D₃, and the corresponding function is ƒ(α)=1.5(1−α)^2/3[1−(1-α)^1/3]−1. The correlated kinetic parameters are E _a=112.7±9.2 kJ mol⁻¹, lnA=13.9 and E _a=81.8±5.6 kJ mol⁻¹, lnA=8.8 for PANI/ZrO₂ composite and PANI, respectively.     

Distribution of zirconia nanoparticles in the matrix of poly(4,4′-oxydiphenylenepyromellitimide)

Poly(4,4??-oxydiphenylenepyromellitimide) is used as a polymer matrix for incorporation of zirconia nanoparticles with different compositions (ZrO₂ and Y_0.03Zr_0.97O_1.985), sizes (20 ± 5 and 10 ± 2 nm), and morphologies (spheres, hollow spheres, rods). The nanoparticles are incorporated during the synthesis of poly(amido acid), a prepolymer of polyimide, and ZrO₂ nanoparticles are pretreated with organosilicon compounds (tetraethoxysilane, ??-aminopropyltriethoxysilane, and 3-(trimethoxysilyl)propyl methacrylate). The effect of surface modification of ZrO₂ nanoparticles on their distribution in poly(4,4??-oxydiphenylenepyromellitimide), depending on the type of the organosilicon compound as well as on the dispersity, shape, and chemical composition of particles, is studied.     

Pt||ZrO2 nanoelectrode array synthesized through the sol–gel process: evaluation of their sensing capability

Homogeneous, circular Pt||ZrO₂ nanoelectrodes have been synthesized through the sol–gel chemistry and the dip-coating process. These nanoelectrode arrays have been evaluated as a platform for electropolymerization of phenol, as model. We have shown that the microstructure of the polymer depends on the confined environment of the electrode and on the position of the –OH group of the monomer. Additionally, these nanoelectrodes have been tested as an electrochemical sensor for dihydroxybenzene isomers in aqueous medium. These Pt||ZrO ₂ nanoelectrodes exhibit a detection limit of 2?×?10^?7?M for resorcinol and 1?×?10^?6?M for catechol.     

Synthesis,Structure, and Stability of Cs4ZrO4

The colorless Cs₄ZrO₄ is obtained from the reaction of stoichiometric proportions of Cs, CsO₂, and finely divided ZrO₂ in a sealed Ag container at 400–650°C for several days. Regrinding and re-reaction provide a single phase sample. The compound is monoclinic (P2₁/c, Z = 4, a = 7.172 (1) Å, b = 19.907 (1) Å, c = 7.157 (1) Å, β = 113.1 (1)Å, R = 0.032) and isostructural with Cs₄PbO₄, with isolated ZrO₄^4? tetrahedra (d(Zr–O) = 1.97 Å). The compound decomposes to Cs₂ZrO₃ (a) in the presence of excess oxygen or CsO₂, (b) in high vacuum near 275°C, or (c) in a sealed container at about 730 ± 10°C.     

Solubility of metal oxides in molten equimolar KBr-NaBr mixture at 973 K

Solubility products (pK _s,MO, molality) are measured by potentiometric titration with a Pt(O₂)|ZrO₂(Y₂O₃) oxygen electrode in the molten KBr-NaBr equimolar mixture at 973 K for the following oxides: CaO (5.00 ± 0.3), MnO (7.85 ± 0.3), NiO (9.72 ± 0.04), PbO (5.20 ± 0.3), and SrO (3.81 ± 0.3). The correlation between pK _s,MeO and the polarization of the corresponding cations by Goldschmidt is obtained.     

Thermodynamic study of some solid solutions in the CaOZrO2 system by emf method

The thermodynamic properties of some solid solutions in the CaOZrO₂ system have been investigated by using solid electrolyte galvanic cells of the type: O₂, Pt|CaO, CaF₂|CaF₂ (t_F = 1)| δCaO(1 ? δ)ZrO₂, CaF₂|Pt, O₂. The influence of CaF₂ added in electrodes on the thermodynamic equilibrium was investigated. It was shown that the heterogeneous field with cubic solid solution reaches the composition x = 0.17 mole of CaO. The results indicate that addition of ZrO₂ to the saturated solid solution produces a significant decrease in the activity of CaO. Measured data were used to calculate thermodynamic parameters of reactions with saturated solid solutions Ca_0.17 Zr_0.83 O_1.83, ZrO₂, and CaZrO₃. At temperatures below 820°C, saturated solid solutions have a tendency to decompose into CaZrO₃ and ZrO₂. A comparison of the thermodynamic results with available data on phase relationships in the CaOZrO₂ system is presented. High thermodynamic stability of SrZrO₃ and BaZrO₃ is one of the reasons for the absence of cubic solid solutions in the system MeOZrO₂ (MeSr, Ba).     

Photodegradation of organic compounds using chromium oxide-doped nano-sulfated zirconia

ZrO₂ is considered a huge-gap semiconductor (band gap ≈ 5 eV). To improve the visible-light photocatalytic activities of ZrO₂, an efficient Cr, SO₄ ^2? co-doped ZrO₂ photocatalyst was synthesized by the simple impregnation method followed by calcination at different calcination temperatures (300, 400, 500, and 600 °C) for 3 h. The synthesized photocatalysts were characterized by x-ray diffraction, transmission electron microscopy analysis, scanning electron microscopy analysis, energy dispersive X-ray spectroscopy analysis, FT-IR spectroscopic technique, potentiometric titration and UV–Vis spectroscopy analysis. ZrO₂ co-doped with Cr and SO₄ ^2? shows more efficiency than SO₄ ^2?-doped ZrO₂ in several aspects like surface structure, decreasing electron–hole recombination and band gap energy. The photodegradation of methylene blue dye for SO₄ ^2?-doped ZrO₂ and Cr, SO₄ ^2?-co-doped ZrO₂ has been investigated. The photocatalytic reaction confirmed that the co-doped ZrO₂ photocatalyst showed higher photocatalytic activity than mono-doped ZrO₂.     

Synthesis of zirconia‐incorporated titania layer by microarc oxidation for biomedical applications

The structural features, biocompatibility, and mechanical performance of a titania (TiO₂) layer with incorporated zirconia (ZrO₂) formed by microarc oxidation on commercially pure titanium have been examined in the present study. In comparison to the ZrO₂‐free TiO₂ layer, the ZrO₂‐incorporated oxide layer was dense and contained ZrTiO₄ as a new oxide as well as ZrO₂ particles. Associated changes in the microstructure enhanced the mechanical durability of TiO₂ layer. Owing to the incorporation of identical biocompatible compounds and almost similar surface roughness, no remarkable difference in bioactivities of the ZrO₂‐free and ZrO₂‐incorporated oxide layers was detected after simulated body fluid tests. Copyright © 2015 John Wiley & Sons, Ltd.     

Planar ZrO2 Waveguides Prepared by the Sol-Gel Process: Structural and Optical Properties

ZrO₂ waveguides are prepared by the sol-gel process from a solution containing zirconiumn-propoxide and acetylacetone in propanol-2. Structural characterizations are investigated for different annealing temperatures using suitable techniques including Waveguide Raman Spectroscopy, Electron Microscopy and Atomic Force Microscopy. Films are amorphous at 300°C and the pure ZrO₂ tetragonal crystalline phase appears beyond 400°C. Crystallized films present a dense, uniform and polycrystalline structure made up by randomly oriented nanocrystallites, the diameter of which increases from 38 Å at 400°C to 53 Å at 600°C. Waveguides are at least monomode TE₀ at 632.8 nm. At this wavelength, optical losses are about, 0.8±0.2dB/cm for amorphous layers and increase up to 2.5±0.4 dB/cm for 600°C heat-treated waveguides.     

Phase Diagram at Low Temperature of the System ZrO2/Nb2O5

Various compositions of the ZrO₂/Nb₂O₅ system were synthesized and the experimental conditions for obtaining reproducible results were established. The gel was precipitated at constant pH = 10, aged at room temperature for 18 h and, after filtration, dried at 110 °C for 24 h. The phase diagram of the ZrO₂/Nb₂O₅ system was established between 600 and 1300 °C. Phase transitions of ZrO₂ and Nb₂O₅ were observed with XRD; and two ternary compounds, 6 ZrO₂ · Nb₂O₅ and 12 Nb₂O₅ · ZrO₂, were identified. The samples with a Nb₂O₅ content between approximately 10 and 40 mole% showed the greatest specific area and are thus best for use as catalyst supports.     

XPS depth profile study of porous zirconia films deposited on stainless steel by spray pyrolysis: the problem of substrate corrosion

Zirconia (ZrO₂) films of tissue‐like structure and narrow pore size distribution have been deposited by spray pyrolysis using aqueous zirconyl chloride octahydrate (ZrOCl₂·8H₂O) precursor solutions. Stainless‐steel sheets, protected or unprotected by a ZnO barrier layer, have been used as the substrate material held at 473 K. The ZnO barrier layers have been deposited on the stainless steel held at 523 K by spray pyrolysis using a zinc acetate precursor. Their property of corrosion protection to stainless steel has been proved by electrochemical polarization measurements in 0.5 M NaCl solution. A complementary study of XPS (depth profiling, mapping) and x‐ray diffraction has shown that the unprotected steel substrates were corroded during ZrO₂ film post‐annealing in air at T ≥ 773 K, whereas steel substrates protected with a compact barrier layer of crystalline ZnO before ZrO₂ film deposition did not show surface corrosion even after annealing up to 997 K. Copyright © 2004 John Wiley & Sons, Ltd.     

Strengthening of composite materials of the fluorohydroxyapatite–zirconia system by titanium nitride

Composite materials of the ZrO₂–fluorohydroxyapatite (FHA)–titanium nitride (TiN) system have been synthesized and studied. In the course of sintering even in a protective inert medium, the reaction between the components begins at 700°C to give calcium titanates, titanium oxides, and oxygen-deficient zirconia compounds. As a result of working through the procedure of synthesis of ultrafine powders and selecting sintering regimes, including the hot-pressing method, dense composite materials of the FHA–ZrO₂ system containing TiN were obtained with a bending strength of up to 273 MPa and a crack resistance of up to 3.3 MPa m^1/2.     

Fabrication of sol–gel derived ZrO2 thin film for HR coatings via rapid thermal annealing process

The properties of sol–gel derived ZrO₂ thin films heated via a novel method of rapid thermal annealing process were studied. We investigated the effects of heat-treatment schedules with different ramp rates on the refractive index and thickness of ZrO₂ thin films as well. By controlling the heating treatment parameter, the refractive index of the ZrO₂ coatings can be adjusted from 1.69 up to 1.9 continuously, which can meet different requirement for high reflectance well. The thickness of crack-free ZrO₂ coatings can be easily controlled by employing different experimental parameters. The result of X-ray diffraction shows that as-deposited film is amorphous, and it remains stable up to the heating temperature of 400 °C. However, it begins to crystallize as the temperature increases further attaining 500 °C. Meanwhile, the surface morphology was evaluated by atomic force microscopy and the result shows that the surface of the ZrO₂ coating is smooth and uniform with root means square of 0.63 nm for the measured area of 5 × 5 μm. As a typical example, ZrO₂ thin films with refractive index of 1.9 are chosen for highly reflective coatings. Nearly full reflective mirror at 1,064 nm was fabricated on fused silica substrate. The laser induced damage thresholds of 22 J/cm² (1,064 nm, 10 ns) and 14.6 J/cm² (1,064 nm, 10 ns) are obtained for ZrO₂ coating and ZrO₂/SiO₂ multilayer coatings respectively.     

Thermal properties of oxide glasses

Glasses with the composition Li₂O·2SiO₂·nTiO₂ and Li₂O·2SiO₂·nZrO₂, where n=0, 0.03, 0.062, 0.1, were prepared and the onset and peak temperatures have been determined by DTA. From these characteristic temperatures, the kinetic parameters describing the nucleation and crystal growth have been obtained by isoconversional methods. The kinetic parameters have been used for the calculation of nucleation and crystal growth times for individual glasses so determining the order of glass stability at reheating. The stability of glasses increases with the content of TiO₂ or ZrO₂ where the increase is higher for ZrO₂. Within the concentration range under study, the increase of both times with the metal oxide concentration is quadratic. It has been discussed that the crystallization kinetics does not obey the Arrhenius law and, therefore, when using the evaluation methods based on this law, the results should not be extrapolated outside the temperature range of the measurements.     

Preparation,Characterization, and Catalytic Behavior of Nanostructured Mesoporous CuO/ZrO2 Catalysts for Low-Temperature CO Oxidation

High-surface area mesoporous 20 mol% CuO/ZrO₂ catalyst was prepared by a surfactant-assisted method of nanocrystalline particle assembly, and characterized by x-ray powder diffraction (XRD), N₂ adsorption, transmission electron microscopy (TEM), H₂-TPR, TG-DTA, and x-ray photoelectron spectra (XPS) techniques. The catalytic properties of the CuO/ZrO₂ nanocatalysts calcined at different temperature were evaluated by low-temperature carbon monoxide oxidation using a CATLAB system. The results showed that these mesoporous nanostructured CuO/ZrO₂ catalysts were very active for low-temperature CO oxidation and the CuO/ZrO₂ catalyst calcined at 400°C exhibited the highest catalytic activity.     

Oxoacidic properties of potassium halide melts at 800°C

The equilibrium CO₃²⁻ = CO₂+O²⁻ (pK) in molten potassium halides (KCl, KBr and KI) and KCl-NaCl eutectic at 800°C was investigated to compare the oxoacidic properties of the melts. A potentiometric cell involving Pt(O₂)|ZrO₂(Y₂O₃) membrane oxygen electrode was used to detect the equilibrium O²⁻ molalities. The obtained pK values were 3.2±0.2 (KCl), 2.4±0.2 (KBr), 4.4±0.2 (KI) and 3.6±0.2 (KCl-NaCl) allowing arrangement of the melts studied in the following sequence: KI–KCl-NaCl–KCl–KBr with the melt acidities increasing within 2 pI units. The oxides solubilities were found to decrease sequentially from the chloride to the iodide melt.     

Ceramic membranes modified with catalytic oxide films as ensembles of catalytic nanoreactors

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO₂ ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO₂/Y₂O₃ coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu_0.03Ti_0.97O_2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P_0.03Ti_0.97O_2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ～ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.     

Novel sulfonated polyimide/ZrO2 composite membrane as a separator of vanadium redox flow battery

Sulfonated polyimide (SPI) and ZrO₂ are blended to prepare a series of novel SPI/ZrO₂ composite membranes for vanadium redox flow battery (VRFB) application. Results of atomic force microscopy and X‐ray diffraction reveal that ZrO₂ is successfully composited with SPI. All SPI/ZrO₂ membranes possess high proton conductivity (2.96–3.72 × 10^?2 S cm^?1) and low VO²⁺ permeability (2.18–4.04 × 10^?7 cm² min^?1). SPI/ZrO₂‐15% membrane is determined as the optimum one on account of its higher proton selectivity and improved chemical stability. The VRFB with SPI/ZrO₂‐15% membrane presents higher coulombic efficiency and energy efficiency than that with Nafion 117 membrane at the current density, which ranged from 20 to 80 mA cm^?2. Cycling tests indicate that the SPI/ZrO₂‐15% membrane has good operation stability in the VRFB system. Copyright © 2014 John Wiley & Sons, Ltd.