Modification Of ZrO2 Research Articles

PHASE EQUILIBRIA IN THE ZrO2 – Dy2O3 SYSTEM AT 1100°C

Phase equilibria in the binary ZrO2– Dy2O3system at 1100°C were studied by X-ray diffraction and petrography in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100oC. The solid solutions based on various polymorphous forms of constituent phases were observed. The boundaries of mutual solubility and concentration dependences the lattice parameters for all phases have been determined. It was established that in the ZrO2–Dy2O3 system there exist fields of solid solutions based on cubic (C) modification of Dy2O3, tetragonal (T) crystal modifications of ZrO2, cubic modification of ZrO2 with fluorite-type structure (F). The boundaries of the homogeneity fields for F-ZrO2 and C-Dy2O3 solid solutions (were determined from samples containing 85-100 mol % Dy2O3 at heat treatment (12604 h). The lattice parameter of the unit cell decreased from а = 1.0655 nm in pure ZrO2 to а= 1.0602 nm for sample containing 20 mol % ZrO2. The solubility of Dy2O3in the T-ZrO2is low and amounts to 0.5 mol%, as evidenced by XRD analysis results. The homogeneity field of F-ZrO2in the concentration range of 90-58 mol % ZrO2at 1100 °C was established. The lattice parameters of the unit cell F-ZrO2 varies from а = 0.5161 nm for sample containing 85 mol % ZrO2 to а = 0.5235 nm for sample containing 60 mol % ZrO2

Confined ZrO2 encapsulation over high capacity integrated 0.5Li[Ni0.5Mn1.5]O4·0.5[Li2MnO3·Li(Mn0.5Ni0.5)O2] cathode with enhanced electrochemical performance

Confined ZrO2 encapsulation over high capacity spinel-layer-layer structured 0.5Li[Ni0.5Mn1.5]O4·0.5 [Li2MnO3·Li(Mn0.5Ni0.5)O2] with various concentration by sol-gel process is reported. Presence of homogeneous ZrO2 layer is evident from the TEM studies. Various electrochemical studies such as optimization of ZrO2 concentration followed by rate performance, elevated temperature studies, and potential windows are also performed. Among the studies, 1wt.% ZrO2 modification is found superior in 2 − 4.9V vs. Li region compared to rest of the coating concentration and pristine compound. Cyclic voltammetry and impedance studies are also performed to understand the reaction mechanism and other electrochemical aspects.

Formation of nanocrystals in the ZrO2–H2O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO2 in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO2 due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO2 nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.

A simple and environmentally friendly method for surface modification of ZrO2 nanoparticles by biosafe citric acid as well as ascorbic acid (vitamin C) and its application for the preparation of poly(vinyl chloride) nanocomposite films

In this investigation, poly(vinyl chloride) (PVC) as one of the most important thermoplastic polymer was combined with different concentrations (4, 8, and 12 wt%) of ZrO2 nanoparticles (NPs) with the purpose of preparing novel nanocomposites (NCs). To prevent aggregation and obtain homogeneous dispersion of the NPs in the polymer matrix, surface modification of ZrO2 was performed by biosafe, biodegradable as well as biocompatible modifiers such as citric acid and ascorbic acid (vitamin C) due to their ability to form chelates with metal oxides. The effect of modified ZrO2 on the properties of the PVC was studied by different techniques. The field emission scanning electron microscopy and transmission electron microscopy results indicated that the modified NPs were dispersed homogeneously in the polymer matrix. UV–Vis spectroscopy was used to study optical behaviors of the obtained NCs. Thermogravimetric analysis indicated that the thermal stability of the polymer was enhanced after incorporation with NPs. Finally, mechanical test was revealed that the NC films were more flexible when compared with the neat polymer. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Liquidus Surface of the ZrO2–Y2O3–Eu2O3 Phase Diagram

The derivative thermal analysis in air up to 3000 °C, X-ray diffraction, petrography, and electron microscopy are employed to examine phase equilibria on the liquidus surface of the ZrO2–Y2O3–Eu2O3 phase diagram. It is established that the liquidus surface of the system is formed by four primary solidification fields of the phases: solid solutions based on hexagonal (N) and cubic (C) crystalline modifications of Y2O3, cubic ZrO2 modification with fluorite (F) structure, and high-temperature cubic modification (X) of Eu2O3. Two four-phase invariant incongruent equilibria are found in the ternary system.

High-performance polymer nanocomposites having a biosafe amino acid by incorporating modified nanozirconia with a flame-retardant coupling agent

A lot of polymeric materials are flammable, requiring modification to decrease their flammability. Nanoparticle (NP) fillers are very attractive for this purpose as they can improve both the physical and the flammable properties of the nanocomposites (NCs). Zirconium oxide (ZrO2) is one of the NPs having flame-retardant property. For the first time, ZrO2 NPs were modified using a fire-resistant modifier and then the chiral NCs were prepared via incorporating modified ZrO2-NPs into the poly(amide–imide) matrix. By decreasing the flammability of these NCs, severe aggregation of ZrO2-NPs could be reduced by surface modification. The surface modification of ZrO2 and the synthesis of NCs were performed through ultrasonic irradiations. The resulting modified ZrO2 and NPs-reinforced composites were characterized by different analyses. Field-emission scanning electron microscopy and transmission electron microscopy results proved that ZrO2-NPs were homogeneously distributed after the surface modification and successfully incorporated into the PAI matrix. The grafting of modifier on the surface of ZrO2 was confirmed by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy techniques. TGA also showed high thermally stable and flame-retardant properties of the obtained NCs.

Oxidation behavior of ZrB2 composites doped with various transition metal silicides

This paper deals with the oxidation behavior of ZrB2-based composites sintered with different additives, namely ZrSi2, MoSi2, TaSi2 and WSi2. The oxidation mechanisms were investigated between 1200 and 1800°C for 15min in a bottom loading furnace. The scope of this study is to draw a classification of goodness for the 4 composites depending on the temperature range and understand how each cation influences the oxidation behavior of ZrB2 by acting either on glass or on ZrO2 modification. MoSi2 was the best additive for improving the oxidation resistance of ZrB2, even up to 1800°C.

ZnO-modified zirconia as gold catalyst support for the low-temperature methanol steam reforming reaction

Nanoscale zirconia (ZrO2) is widely investigated both as catalyst support and catalyst. Bare ZrO2 binds gold weakly due to lack of surface defects. In this study, nanoscale ZrO2 was modified with zinc oxide (ZnO) at different amounts, and examined as support of gold catalysts for the methanol steam reforming (SRM) reaction. ZrO2 with high specific surface area serves as dispersant of ZnO to create highly dispersed ZnO clusters, which provide more anchoring sites for strong gold-metal oxide bonding. Addition of ZnO also passivates the surface acidity of ZrO2, thus blocking the direct methanol decomposition to CO and H2. To prepare the highly dispersed ZnO clusters on ZrO2, a carbon hard-template method was used, followed by calcination at 550°C to produce a highly porous mixed oxide solid. To investigate the modification of ZrO2 by ZnO, the surface acidity was probed with isopropanol in temperature-programmed desorption (TPD) mode. Adsorption of the gold precursor on the ZnO-modified ZrO2 was carried out by the anion adsorption method. Better dispersion, and better activity and stability of these gold catalysts were found than on either pure ZrO2 or ZnO. Accordingly, the light-off temperature of SRM is lower and a wider temperature window for CO-free H2 production up to moderately high temperatures (∼375°C) is found.

Effect of promoters on the structure and catalytic properties of tungstated zirconia in n-heptane isomerization

The effect of manganese and aluminum cations on the formation of the crystalline structure and catalytic properties of tungstated zirconia has been studied. It has been shown that the modification of ZrO2 with both cationic and anionic additives leads to the stabilization of its tetragonal form and the formation of substitutional solid solutions on its basis. It has been found that manganese and aluminum additives have different effects on catalytic properties in heptane isomerization.

Characteristic of mullite-zirconium ceramic obtained from powders synthesized by the hydrothermal method

The effect of the hydrothermal method of synthesis of the initial powders using chemical reagents and illite clay as the initial components on the phase composition and structure as well as some properties of mullite-zirconium ceramic was studied. It is shown that mullite and the tetragonal modification of ZrO2 predominate in the sintered ceramic material but closed pores are also present. As the firing temperature increases and especially with the addition of illite clay the degree of sintering and therefore the compression strength increase. The elastic modulus increases with temperature difference increasing to 1000/20°C, just as with the addition of illite clay, to 35 and 95 GPa, respectively, while with 500/20 it increases to 20 and 22 GPa.

Co-Ru/γ-Al2O3 Catalyst Modified With ZrO2 for Fischer-Tropsch Synthesis

Using an incipient impregnation method, a Co-Ru bimetallic catalyst was prepared. The effects of the ZrO2 modification of support on heavy hydrocarbon synthesis were investigated in a fixed-bed reactor. The results indicated that the ZrO2 modification could block defects of γ-Al2O3 crystal lattice, weaken the interaction between support and Co, and hinder or prevent the formation of cobalt aluminate. Zr reacted with Co to form the Co-Zr species, which is easily reduced under lower temperature. It caused an increase in the amount of easily reducible Co species and a decrease in the amount of uneasily reducible Co species. Then the reduction extent of cobalt-based catalyst was raised under the typical reduction condition. Meanwhile, support of γ-Al2O3 was modified with ZrO2, and the interface of Co-ZrO2 formed. The Co-ZrO2 interface led to an increase of the intensity of the bridge-form CO adsorption, which CO facilitates to be dissociated. At H2/CO molar ratio in feed 2.0, 503 K, 1.5 MPa, and 800 hr−1, the catalyst exhibited better catalytic performance. The CO conversion was 93.27%, the C5 + selectivity was 82.56%, and the chain growth factor was 0.81.

Effect of ceramic powder fineness on mullite-zirconium ceramic properties

Results are provided for a study of the development of high-temperature mullite-zirconium ceramic with use of activated ceramic powders prepared by grinding for different times with addition of illite clay, and from pure oxide powders. It is shown that increased activity and amorphicity of ground particles considerably promotes formation of mullite phase at 1200°C, and also transition of the monoclinic modification of ZrO2 to tetragonal, particularly with an increase in firing temperature. It is proposed that as a result of rapid “freezing” the structure retains the high-temperature modification of ZrO2, having a tendency with slow ceramic cooling to transform into the monoclinic modification.

Phase Relation Studies in the ZrO2-CeO2-La2O3 System at 1500°C

The phase relations in the ZrO2–CeO2–La2O3 ternary system at 1500°C were studied by X-ray diffraction (XRD), petrography, and scanning electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100° and 1500°C. The solid solutions based on various polymorphous forms of constituent phases and ordered phase of La2Zr2O7 were revealed in the system. No new phases were found. The isothermal section of the phase diagram for the ZrO2–CeO2–La2O3 system has been developed. It was established that in the ternary ZrO2–CeO2–La2O3 system there exist fields of solid solutions based on hexagonal (A) modification of La2O3, monoclinic (M), and tetragonal (T) crystal modifications of ZrO2, cubic modification of CeO2 with fluorite-type structure (F), as well as pyrochlore type ordered phase of cubic symmetry La2Zr2O7 (Py). The refined lattice parameters of the unit cells for solid solutions and microstructures of the definite field of compositions for the systems were determined.

Studies on Cobalt-Based Catalyst to Synthesize Heavy Hydrocarbons

With incipient impregnation method, cobalt-based catalysts were prepared. The effects of the ZrO2 modification of support and the addition of the second metal Ru on heavy hydrocarbon synthesis were investigated in a fixed-bed reactor. The results revealed that, in cobalt-based catalysts modified with ZrO2, cobalt species were presented in the form of Co3O4, Zr species were highly dispersed or amorphous on the surface of the catalysts. ZrO2 addition also increased the desorption amount of CO, which was correlative with the degree of reduction of cobalt species. When the catalysts modified with ZrO2, the strong interaction between Co species and γ-Al2O3 support was replaced by a weak interaction between Co species and ZrO2. The ZrO2 modification increased the amount of easily reducible Co species. It is noteworthy that addition of a small quantity of Ru promoted the reduction of cobalt species, which led to the reduction temperature decreasing. For the 15w%Co0.4w%Ru4.3w%ZrO2/γ-Al2O3, at a reaction condition as feed gas ratio n(H2):n(CO)=2.0, 483K, 1.5MPa and 800h-1, the conversion of CO was 76.98 %, the selectivity of C5+ 88.36 %, the chain growth probability 0.86, and as to 15.0%Co0.4%Ru/γ-Al2O3, the conversion of CO was 67.15%, the selectivity of C5+ 84.41% and the chain growth probability 0.84.

Equilibrium constants of interaction between zirconia and oxygen

The values of all ten equilibrium constants of interaction between zirconia and oxygen of ambient medium and, accordingly, quantitative dependences of the number of crystal lattice defects on temperature and on partial oxygen pressure are found in view of the defect structure of ZrO2 − x suggested in [1] and of available experimental data on the nonstoichiometry x and other properties of α, β, and γ modifications of ZrO2 − x; the position of x = 0 boundaries is determined.

Synthesis of a precursor for an alumina ceramic reinforced by zirconium dioxide from inorganic compounds in the presence of urea

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO2, tlm, after a thermal treatment (1250°C). The structure of samples in the system Al2O3-ZrO2 is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO2 sol particles in decomposition of urea. The coating of ZrO2 sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO2 sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al2O3-ZrO2 was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorption isotherms.

Mössbauer and X-ray Diffraction Studies of Cubic Solid Solutions of the ZrO2−Y2O3−Fe2O3 System

The effect of iron oxide on the polymorphic composition and thin structure of cubic solid solutions of the (ZrO2)0.9(Y2O3)0.1-x(Fe2O3)x system has been investigated. The maximum Fe2O3 solubility in the studied cut of the ternary system has been determined to be 2 mol %. Iron exists only as Fe3+ ions in octahedral co-ordination. Three nonequivalent positions of the Fe3+ ions, which differ in surrounding cations and anions, have been identified. It has been shown that Fe2O3 is not a stabilizer of the high-temperature modifications of ZrO2, but it promotes the stabilizing action (efficiency) of Y2O3 and structure stability in time due to the formation of the compound YFeO3 with structure isomorphic to c-ZrO2.

Dynamics of phase formation during combustion of Zr and Hf in air

The processes of phase formation taking place during combustion of Zr and Hf in air have been explored by time-resolved XRD (TRXRD) at a time resolution of 0.1 s. In case of Zr combustion, the final product was found to form in two stages: first the tetragonal high-temperature modification of ZrO2 is formed (in the combustion wave) and then the latter undergoes polymorphic transition (behind the combustion wave) into its monoclinic modification. In combustion of Hf, product formation proceeds in three stages: the low-temperature monoclinic modification of α-HfO2 is formed in the combustion wave, which is followed by its transformation into the tetragonal β-HfO2 and backward conversion of the latter into α-HfO2 behind the combustion wave. The obtained data were comparatively analyzed with those reported for combustion of Ti in air.

Monoclinic-tetragonal phase transition in zirconium and hafnium dioxides: A high-temperature raman scattering investigation

Zirconium dioxide ZrO2 and hafnium dioxide HfO2 are investigated using high-temperature Raman spectroscopy in the temperature range 300–2080 K, including the regions of the monoclinic-tetragonal phase transitions revealed in these materials. An analysis is made of the specific features observed in the evolution of the high-temperature Raman spectra of both the monoclinic (m) and tetragonal (t) modifications of ZrO2 and HfO2 with variations in the temperature. The polarized Raman spectra of the metastable tetragonal phases in solid solutions based on zirconia and hafnia are used to identify the symmetry of vibrations in the spectra of the tetragonal modifications of pure zirconium and hafnium dioxides, which exist at high temperatures.

Nanopowders and nanostructured oxides: phase transitions and surface reactivity

AbstractWe report on experimental characterizations of nanocrystalline oxides by Raman spectroscopy, which has proven to be a reference technique when the scale of the coherent domains becomes too small for X‐ray diffraction. Crystallite‐size modification of ZrO2 and WO3 phase diagrams along with surface modes, surface reactions and adsorbed species characterization on WO3 and SnO2 will be reviewed. Copyright © 2007 John Wiley & Sons, Ltd.