Zr Solid Solution Research Articles

Surface, structural and morphological characterization of nanocrystalline ceria–zirconia mixed oxides upon thermal aging

The effect of thermal aging on the physico-chemical properties of Ce–Zr oxides, as a function of Ce/Zr molar ratio, has been studied from the point of view of their application as catalytic nanomaterial. Homogeneous in size dimension and morphology, nanosized, single phase Ce–Zr solid solutions with various compositions were synthesized by the sol–gel like method. Upon thermal aging, important modifications of the textural and structural properties, which apparently create a strong effect on their catalytic performance, were observed. Their specific activity was found to be dependent on Ce/Zr molar ratio with the maximum observed over Ce0.75Zr0.25O2. Higher surface area, smaller particles, lower amount of particles agglomerates as well as higher amount of crystal faces, edges, and corners generate better catalytic activity, especially as long as cubic symmetry of mixed oxides was maintained.

Distribution of Additives in Single-Modified TiO2

ABSTRACTIn the present work the influence of different modifiers, calculated to B2O3, CeO2, Sb2O3, ZnO, and ZrO2, on their distribution in TiO2 is investigated. The phase composition and phase transformation of prepared rutile-TiO2 is determined by the selective leaching method, ICP-AES, XRD and FT-IR techniques. The addition of Sb2O3 to TiO2 has no influence on the anatase–rutile phase transformation, CeO2 and ZrO2 act as inhibitors of the TiO2 phase transformation and the addition of ZnO or B2O3 to TiO2 accelerates rutile formation. It is observed that boron is located in TiO2 in the form of soluble B2O3, zinc partly reacts with titanium forming co-phase TiZn2O4 and antimony addition to TiO2 presumably causing the formation of a co-phase of Sb with Ti. Cerium forms a separate phase, CeO2, and reacts partly with titanium, probably creating co-phase, CexTi(1-x)O2 (for example Ce0.8Ti0.2O2). Zirconium addition in TiO2 forms separate ZrO2 phase and solid solution of Zr with Ti.

Switchable mirror based on Mg–Zr–H thin films

A Mg–Zr thin film is prepared on a glass substrate by co-sputtering of Mg and Zr targets and in situ sputtering of a thin Pd overlayer. The structural and optical properties of Mg–Zr and Mg–Zr–H thin film are investigated induced by hydrogen absorption and/or desorption at room temperature. Optical transmission and reflection data indicated that Mg–Zr–H thin film is the color-neutral in the visible range with chromaticity coordinates of x = 0.3566 and y = 0.3430. The formation of the ternary hydride Mg 0.82Zr 0.18H 2 is confirmed in an Mg-rich Mg–Zr solid solution thin film in the hydride state. The hydrogen insertion and extraction occurs in fcc lattice structure. Because the volume change according to hydrogenation and dehydrogenation, the switching durability is much better than that of the switchable mirror using Mg–Ni alloy.

Preparation and Characterization of Single-Modified TiO2 for Pigmentary Applications

In the present work the influence of different additives, calculated to ZrO2, ZnO, and B2O3, on the anatase–rutile phase transformation was investigated. The chemical composition of prepared titania samples was determined by the selective leaching method, powder X-ray diffraction analysis, and FT-IR measurements. The effect of small amounts of additives on the optical properties, photoactivity, and surface area of rutile-phased TiO2 for pigmentary applications was examined using spectrophotometer, SEM, and BET measurements. ZrO2 acted as an inhibitor of the TiO2 phase transformation and the addition of ZnO or B2O3 to TiO2 accelerated rutile formation at 750 °C. ZrO2 addition in TiO2 could form separate ZrO2 phase and solid solution of Zr with Ti. Zinc partly reacted with titanium forming cophase TiZn2O4. Boron was located in TiO2 in the form of soluble compound, B2O3. Almost all optical properties were lower for modified TiO2 in comparison with the corresponding unmodified sample. The SBET increased with ...

Glass-forming ability and atomic-level structure of the ternary Ag–Ni–Zr metallic glasses studied by molecular dynamics simulations

Based on the recently proposed long-range empirical potential formulism, an n-body potential is constructed for the Ag–Ni–Zr ternary metal system and verified to be realistic by reproducing some important properties of the pure metals as well as of some equilibrium compounds of the system. Applied the constructed Ag–Ni–Zr potential, molecular dynamics simulations and Voronoi tessellations are then carried out to study the effect of alloying composition on glass-forming ability and atomic-level structure of the ternary Ag–Ni–Zr metallic glasses. For the Ag50−x/2 NixZr50−x/2 alloys, with increasing Ni concentration, distortion of the crystalline structure becomes significant, implying a disordering process going on, and at the same time, the number of {0, 0, 12, 0} icosahedrons increases remarkably and the {0, 0, 12, 0} icosahedrons are almost Ni-centered. When the Ni concentration is increased up to 20 atom %, the ternary Ag–Ni–Zr solid solution collapses and turns into a disordered state, suggesting that increasing the Ni concentration could enhance the glass-forming ability of the system. For the Ag30Ni40Zr30 ternary metallic glass, it is found that most of the polyhedrons with coordinate number (CN < 13) are Ni-centered, whereas most of polyhedrons with CN > 14 are either Ag or Zr centered.

Visible-light induced oxo-bridged ZrIV−O−CeIII redox centre in tetragonal ZrO2–CeO2 solid solution for degradation of organic pollutants

Tetragonal ZrO(2)-CeO(2) solid solutions with composition Zr(1-x)Ce(x)O(2) (x = 0.1, 0.2, and 0.3) were synthesized in a citrate complexation route and characterized by XRD, XPS, UV-vis diffuse reflectance and ESR measurements. The formation of the homogeneous solid solution Zr(1-x)Ce(x)O(2) constructed the oxo-bridged bimetallic Zr(IV)-O-Ce(III) linkage between two neighboring flattened tetrahedrons of the structural framework. As compared to their parent oxides, the ZrO(2)-CeO(2) solid solutions exhibited optical absorption extending to longer wavelengths in the visible region. The red shift in the absorption spectrum was demonstrated to be partially due to a metal-to-metal charge transfer (MMCT) transition of the oxo-bridged Zr(IV)-O-Ce(III) linkage. The visible-light induced MMCT transition of Zr(IV)-O-Ce(III)→ Zr(III)-O-Ce(IV) resulted in the generation of the additional Ce(IV) and superoxide anion radical formed by the interaction of Zr(III) with adsorbed O(2). Catalytic activity evaluation revealed that the photoexcitation of the MMCT over the solid solution can initiate the degradation of RhB and 2,4-DCP upon visible-light irradiation, whereby Zr(III) and Ce(IV) act as a site-specific reducing and oxidizing center, respectively. The structure of the solid solution Zr(1-x)Ce(x)O(2) and the oxidation states of Zr and Ce species are also discussed in detail.

Electron-irradiation-induced solid-state amorphization in supersaturated Ni–Zr solid solutions

Electron-irradiation-induced solid-state amorphization (SSA) in supersaturated Ni–Zr solid solution models was investigated by molecular dynamics (MD) simulations, focusing on the threshold composition for the occurrence of SSA. The threshold composition for the MeV electron irradiation-induced SSA can be estimated to be around Ni 82Zr 18. A Ni 82Zr 18 solid solution shows SSA, while a Ni 83Zr 17 solid solution can maintain its original crystalline structure against irradiation. Thermal recovery of the lattice defects introduced during electron irradiation can be seen in both Ni 83Zr 17 and Ni 82Zr 18 solid solutions. There is a significant difference between Ni 83Zr 17 and Ni 82Zr 18 in terms of changes in the number of 12-faced volonoi polyhedrons, namely, the number of constituent atoms whose coordination number is 12. A change in the combination of various volonoi polyhedrons (a change in coordination number of constituent atoms) during the introduction of lattice defects and thermal recovery precedes SSA in the Ni–Zr solid solution model.

Surface properties, thermal expansion, and segregation in the U–Zr solid solution

Atomistic simulation results of the (γU, βZr) solid solution behavior are discussed, including the behavior of the lattice parameter and coefficient of thermal expansion as a function of concentration and temperature. Output from these calculations is used to study the surface structure of U–Zr for different crystallographic orientations, determining the respective concentration profiles, surface energy, and segregation behavior. The segregation of Zr to the surface and overall composition of the near-surface region is studied as a function of concentration and temperature.

Investigation of the Precipitation in Mg-Zr Alloys

The Mg-Zr alloys with the Zr contents of 0.2%, 0.4%, 0.6% and 0.8% were prepared using induction melting, metal mold centrifugal casting process. The microstructures of the alloys were analyzed by scanning electron microscope, energy spectrum analysis, transmission electron microscope and their mechanical properties were also measured with tensile test. The results show that there are many micro- and nano-sized Zr-rich or Zr particles dispersed in Mg-Zr alloys. The nano-sized Zr-rich particle consists of a rectangle shaped Zr core and its surrounding Mg (Zr) solid solution shell with round exterior; a single Zr particle appears a coherent lattice relationship with matrix.

Microstructural analysis of as-processed U–10 wt.%Mo monolithic fuel plate in AA6061 matrix with Zr diffusion barrier

For higher U-loading in low-enriched U–10 wt.%Mo fuels, monolithic fuel plate clad in AA6061 is being developed as a part of Reduced Enrichment for Research and Test Reactor (RERTR) program. This paper reports the first characterization results from a monolithic U–10 wt.%Mo fuel plate with a Zr diffusion barrier that was fabricated as part of a plate fabrication campaign for irradiation testing in the Advanced Test Reactor (ATR). Both scanning and transmission electron microscopy (SEM and TEM) were employed for analysis. At the interface between the Zr barrier and U–10 wt.%Mo, going from Zr to U(Mo), UZr 2, γ-UZr, Zr solid-solution and Mo 2Zr phases were observed. The interface between AA6061 cladding and Zr barrier plate consisted of four layers, going from Al to Zr, (Al, Si) 2Zr, (Al, Si)Zr 3 (Al, Si) 3Zr, and AlSi 4Zr 5. Irradiation behavior of these intermetallic phases is discussed based on their constituents. Characterization of as-fabricated phase constituents and microstructure would help understand the irradiation behavior of these fuel plates, interpret post-irradiation examination, and optimize the processing parameters of monolithic fuel system.

Ternary arsenides Zr(Si As1−)As with PbCl2-type (0 ≤x≤ 0.4) and PbFCl-type (x= 0.6) structures

The ternary zirconium silicon arsenides Zr(SixAs1−x)As have been prepared through reaction of the elements at 900 °C. Extensive solubility of Si in the parent binary arsenide ZrAs2 was established in the form of the solid solution Zr(SixAs1−x)As (0 ≤ x ≤ 0.4). Single-crystal X-ray structure determination of the end-member Zr(Si0.39(1)As0.61)As (orthorhombic PbCl2-type, space group Pnma, Z = 4, a = 6.6828(8) Å, b = 3.6377(4) Å, c = 9.1131(11) Å, V = 221.54(4) Å3) revealed that the Si atoms prefer to occupy the interior sites of a four-atom-wide polyanionic ribbon. When the Si composition is increased to x = 0.6, the new ternary arsenide Zr(Si0.57(1)As0.43)As was identified (tetragonal PbFCl-type, space group P4/nmm, Z = 2, a = 3.6539(7) Å, c = 8.2399(15) Å, V = 110.01(4) Å3), in which the Si atoms prefer to occupy the sites of a denser polyanionic square net. Core-line X-ray photoelectron spectra measured on metallic, plate-shaped crystals of Zr(Si0.6As0.4)As support the presence of anionic Si and As atoms. Band structure calculations on idealized ordered models of Zr(Si0.5As0.5)As suggest that a competition between Zr-anion and anion–anion bonding interactions takes place in both structures.

Density-functional study of Zr-based actinide alloys: 2. U–Pu–Zr system

Density-functional theory, previously used to describe phase equilibria in the U–Zr alloys [A. Landa, P. Söderlind, P.E.A. Turchi, L. Vitos, A. Ruban, J. Nucl. Mater. 385 (2009) 68], is applied to study ground-state properties of the bcc U–Pu–Zr solid solutions. Calculated heats of formation of the Pu–U and Pu–Zr alloys are in a good agreement with CALPHAD assessments. We found that account for spin–orbit coupling is important for successful description of Pu-containing alloys.

Microstructure and mechanical properties of Al–Zr nanocomposite materials

Three different processing routes were explored to develop Al–Zr nanocomposite alloys using mechanical alloying and spark plasma sintering methods. Depending on the route of milling adopted, the powder in the as-milled condition consisted of either a solid solution of Zr in Al or a mixture of Al-solid solution and Al 3Zr (L1 2) phases. The alloys after sintering consisted of Al and Al 3Zr (L1 2) with grain sizes of less than 100 nm. These nanocomposite alloys exhibited a high compressive strength of 1 GPa with 10% plasticity. The high strength observed in these alloys was explained on the basis of the retention of nanometer sized grains and also the fine dispersion of the L1 2 phase. On the other hand, the good amount of plasticity was explained to be due to excellent bonding between the powder particles and the presence of coarse Al grains in the matrix.

Direct conversion of methane to synthesis gas using lattice oxygen of CeO 2–Fe 2O 3 complex oxides

Three kinds of complex oxides oxygen carriers (CeO 2–Fe 2O 3, CeO 2–ZrO 2 and ZrO 2–Fe 2O 3) were prepared and tested for the gas–solid reaction with methane in the absence of gaseous oxidant. These oxides were prepared by co-precipitation method and characterized by means of XRD, H 2-TPR and Raman. The XRD measurement shows that Fe 2O 3 particles well disperse on ZrO 2 surface and Ce–Zr solid solution forms in CeO 2–ZrO 2 sample. For CeO 2–Fe 2O 3 sample, only a small part of Fe 3+ has been incorporated into the ceria lattice to form solid solutions and the rest left on the surface of the oxides. Low reduction temperature and low lattice oxygen content are observed over ZrO 2–Fe 2O 3 and CeO 2–ZrO 2 samples, respectively by H 2-TPR experiments. On the other hand, CeO 2–Fe 2O 3 shows a rather high reduction peak ascribed to the consuming of H 2 by bulk CeO 2, indicating high lattice oxygen content in CeO 2–Fe 2O 3 complex oxides. The gas–solid reaction between methane and oxygen carriers are strongly affected by the reaction temperature and higher temperature is benefit to the methane oxidation. ZrO 2–Fe 2O 3 sample shows evident methane combustion during the reducing of Fe 2O 3, and then the methane conversion is strongly enhanced by the reduced Fe species through catalytic cracking of methane. CeO 2–ZrO 2 complex oxides present a high activity for methane oxidation due to the formation of Ce–Zr solid solution, however, the low synthesis gas selectivity due to the high density of surface defects on Ce–Zr–O surface could also be observed. The highly selective synthesis gas (with H 2/CO ratio of 2) can be obtained over CeO 2–Fe 2O 3 oxygen carrier through gas–solid reaction at 800 °C. It is proposed that the dispersed Fe 2O 3 and Ce–Fe solid solution interact to contribute to the generation of synthesis gas. The reduced oxygen carrier could be re-oxidized by air and restored its initial state. The CeO 2–Fe 2O 3 complex oxides maintained very high catalytic activity and structural stability in successive redox cycles. After a long period of successive redox cycles, there could be more solid solutions in the CeO 2–Fe 2O 3 oxygen carrier, and that may be responsible for its favorable successive redox cycles performance.

Formation of Zr(C,N)-ZrB&lt;SUB align=right&gt;2 composite powders by self-propagating high-temperature synthesis (SHS)

Zirconium carbide, nitride and diboride are ceramic materials suitable for use at high temperatures requiring resistance to wear, oxidation and corrosion. ZrC and ZrN have isotypical lattices and are completely soluble in each other forming zirconium carbonitride. In this study zirconium carbonitride-zirconium diboride composite powders were produced by self-propagating high-temperature synthesis (SHS) from zirconium, hexagonal boron nitride, carbon and boron powders. The ratio of ZrC/ZrN in the Zr(C,N) solid solutions were varied by changing the C and h-BN amount in the reactants. Reaction products were analysed by powder X-ray diffraction. Lattice parameters of ZrC-ZrN solid solutions were determined and they were seen to increase with increasing C content in the structure. Adiabatic temperatures of the reactions were calculated by the HSC software. Grain size and morphology of the reactants and products was examined by scanning electron microscopy. Partial fusion of the grains was observed in some of the products, indicating that the actual temperatures attained at the reaction front were close to the melting points of the products. The grains of the product phases had irregular shape.

Reactive Oxygen Species Scavenging Properties of ZrO 2 –CeO 2 Solid Solution Nanoparticles

The hypothesis that an increase in defects in cerium oxide (CeO(2)) nanoparticles induced by solid solutions with differences in valency and ionic radius of the solute will yield superior reactive oxygen species (ROS) scavengers at room temperature will be tested. Solid solutions of zirconium in CeO(2), that is, Ce(x)Zr(1-x)O(2) nanoparticles, were synthesized by a reverse micelle method. Their crystal structures, particle sizes and level of agglomeration were characterized. The nanoparticles' activities to scavenge ROS were tested in response to hydrogen peroxide at physiological levels and room temperature using an enzyme peroxidase-based assay. Solid solutions of Zr in CeO(2) nanoparticles enhanced ROS scavenging fourfold. The hypothesis is confirmed that more defects are formed and that the scavenging activities of Ce(x)Zr(1-x)O(2) correlate to the nanoparticles' oxygen-storage capacity. The antioxidant efficacy of CeO(2) nanoparticles can be enhanced by dissolving zirconium in the CeO(2) lattice. The Ce(x)Zr(1-x)O(2) nanoparticles act as an enhanced catalyst at room temperature that scavenges ROS. Increased efficacy will enable lower nanoparticle dosages to protect cells from ROS, thus increasing the therapeutic width of these compounds.

CHEMICAL VAPOR DEPOSITION OF ZrxHf1-xO2 THIN FILMS USING ANHYDROUS MIXED-METAL NITRATES PRECURSORS

ABSTRACT Hafnium-based dielectrics have been extensively investigated as a possible replacement for SiO2. A novel volatile anhydrous Zr/Hf mixed-metal nitrate precursor ZrxHf1-x(NO3)4(ZHN) was successfully synthesized. ZrxHf1-xO2 thin films were first prepared by the chemical vapor deposition (CVD) technique from the precursor of this mixed-metal nitrate. Differential scanning calorimetry (DSC) and infrared spectra (IR) measurements of ZHN indicated that ZHN may be mixture of single Hf(NO3)4 and a solid solution of Zr(NO3)4 and Hf(NO3)4. The ZrxHf1-xO2 thin films exhibit good dielectric properties with a moderate bandgap value of 5.6 eV and a value for k of 22. ZrxHf1-xO2 is, therefore, a promising candidate for gate-dielectric application, and the anhydrous mixed-metal nitrate can be a potential precursor for high-k materials derived from CVD.

Reactive Mechanical Alloying Synthesis of Nanocrystalline Cubic Zirconium Nitride

Zirconium nitride powders with rock salt structure (γ-ZrNx) are prepared by mechanical milling of a mixture of Zirconium and hexagonal boron nitride (h-BN) powders. The products are analysed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy (RS). The formation mechanism of γ-ZrNx by ball milling technique is investigated in detail. N atoms diffuse from amorphous BN (α-BN) into Zr to form Zr(N) solid solution alloy then the Zr(N) solid solution alloy decomposes into γ-ZrNx. No ZrB2 is observed in the as-milled samples or the samples annealed at 1050° C for 2h.

Microstructure and Hydrogen Permeability of Duplex Phase M-ZrNi (M=V, Nb, Ta) Alloys

AbstractIn order to develop non-Pd based high performance hydrogen permeation alloys, microstructure, crystal structure and hydrogen permeability of duplex phase M-ZrNi (M=V and Ta) alloys were investigated using a scanning electron microscope, an X-ray diffractometer and a gas flow meter. These results were compared with those of Nb-ZrNi ones which have been previously published. The hydrogen permeation was impossible in the V-ZrNi alloys, because they were brittle in the as-cast state. On the other hand, duplex phase alloys consisting of the bcc-(Ta, Zr) solid solution and the orthorhombic ZrNi (Cmcm) intermetallic compound were formed and hydrogen permeable in the Ta-ZrNi system. The Ta40Zr30Ni30 alloy shows the highest value of hydrogen permeability of 4.1×10-8 [molH2m-1s-1Pa-0.5] at 673 K, which is three times higher than that of pure Pd.

Synthesis, Ion Mobility, and Superionic Conductivity of (1 − x)PbF2 ⋅ xMF n (M = Li, Na, K, Rb, Cs, Zr) Solid Solutions

Ionic motion and conduction in (1 − x)PbF2 ⋅ xZrF4 and (1 − x)PbF2 ⋅ xMF (M = alkali-metal cation) solid solutions are studied by 19F and 207Pb NMR and impedance spectroscopy. The factors determining ionic motion in the solid solutions and their structure and energetics in the range 170–550 K are analyzed. The ionic conductivity of (1 − x)PbF2 ⋅ xZrF4 with x ≤ 0.4 and 0.93PbF2 ⋅ 0.07MF is shown to be 10−4 to 10−2 S/cm at temperatures above 425 K, which places these materials among superionics.