Crystalline Zr Research Articles

The effect of Zr(IV) addition on the phosphate removal properties of MgAl-LDH

Recovery of phosphate from wastewater represents a sustainable alternative to phosphate rock, a limited resource. Magnesium aluminum layered double hydroxides (MgAl-LDH), are promising sorbents due to their high phosphate removal capacity by anion-exchange (26–124 mgP/g). Furthermore, an increased sorption capacity has been reported by the addition of zirconium (Zr(IV)) into the LDH lattice. However, ambiguity exists especially in relation to the incorporation of Zr and the stability of the MgAl-LDH. To understand how Zr(IV)-addition affects the phosphate sorption properties (both capacity and mechanism) on the atomic level, solid state multi-nuclear NMR spectroscopy was combined with complimentary characterization techniques to study a series of MgAl-LDH with Zr to Al ratios of 1:9 and 1:1, which had the Mg to (Al + Zr) ratio fixed at 2:1. The LDH were synthesized by coprecipitation and subsequently aged or hydrothermally treated to improve the crystallinity (particle size). No evidence of Zr(IV) incorporation in the LDH was observed, instead Zr was present as Zr(IV)-hydroxide (X-ray amorphous) and crystalline Zr(IV) oxide after aging and hydrothermal treatment, respectively. The segregation of Zr(IV) and resulting lower Al content in the MgAl-LDH decreased the phosphate sorption capacity from 45 to 54 to 16–20 mgP/g. Zr (hydr)oxide impurities removed <3 mgP/g. Moreover, 31P MAS NMR spectroscopy quantified that the MgAl-LDH contributed to <62% of the total P removal capacity.

Cs absorption capacity and selectivity of crystalline and amorphous Hf and Zr phosphates

Removal of radioactive Cs from sodium-rich solutions is a technical challenge that goes back to post World War II nuclear waste storage and treatment; and interest in this topic was reinvigorated by the Fukushima-Daiichi nuclear power plant disaster, 10 years ago. Since the 1960′s there has been considerable focus on layered Zr phosphates as robust inorganic sorbents for separation of radionuclides such as Cs. Here we present synthesis and characterization, and direct comparison of Cs sorption capacity and selectivity of four related materials: 1) crystalline α-Zr phosphate and α-Hf phosphate, and 2) amorphous analogues of these. Powder X-ray diffraction, thermogravimetry, solid-state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and compositional analysis (inductively coupled plasma optical emission spectroscopy and mass spectroscopy, ICP OES and ICP MS) provided formulae; respectively M(HPO4)2⋅1H2O and M(HPO4)2⋅4H2O (M = Hf, Zr) for crystalline and amorphous analogues. Maximum Cs loading, competitive Cs-Na selectivity and maximum Cs-Na loading followed by the above characterizations plus 133Cs MAS-NMR spectroscopy revealed that amorphous analogues are considerably better Cs-sorbents (based on maximum Cs-loading and selectivity over Na) than the well-studied crystalline Zr-analogue. Additionally, crystalline α-Hf phosphate is better Cs-sorbent than crystalline α-Zr phosphate. All these studies consistently show that Hf phosphate is less crystallize than Zr phosphate, when obtained under similar or identical synthesis conditions. We attribute this to lower solubility of Hf phosphate compared to Zr phosphate, preventing ‘defect healing’ during the synthesis process.

Use of Zirconium Phosphate-Sulphate as Acid Catalyst for Synthesis of Glycerol-Based Fuel Additives

In the present work, zirconium phosphates and mixed zirconium phosphate–sulphate acid catalysts have been investigated in the acetylation of glycerol in order to obtain acetins as fuel additives. The following catalysts with chemical composition, Zr3(PO4)4, Zr(SO4)2, Zr2(PO4)2SO4, Zr3(PO4)2(SO4)3 and Zr4(PO4)2(SO4)5 have been prepared and characterized by acid capacity measurements, BET, XRD, FT-IR, XPS. The surface chemical composition in terms of P/Zr and S/Zr atomic ratios was monitored in the fresh and used catalysts. Zr3(PO4)2(SO4)3 and Zr4(PO4)2(SO4)5 showed the highest acidity associated with the synergic effect of two main crystalline phases, Zr2(PO4)2SO4 and Zr(SO4)2·4H2O. The reactions of glycerol acetylation were carried out by using a mass ratio of catalyst/glycerol equal to 5 wt% and molar ratio acetic acid/glycerol equal to 3:1. The glycerol conversion versus time was investigated over all the prepared samples in order to identify the best performing catalysts. Over Zr3(PO4)2(SO4)3 and Zr4(PO4)2(SO4)5 full glycerol conversion was achieved in 1 h only. Slightly lower conversion values were registered for Zr3(PO4)4 and Zr2(PO4)2SO4, while Zr(SO4)2 was the worst catalyst. Zr4(PO4)2(SO4)5 was the most selective catalyst and was used for recycling experiments up to five cycles. Despite a modest loss of activity, a drastic decrease of selectivity to tri- and diacetin was observed already after the first cycle. This finding was attributed to the leaching of sulphate groups as detected by XPS analysis of the spent catalyst.

Temperature effect on the phonon dispersion stability of zirconium by machine learning driven atomistic simulations

It is well known that conventional harmonic lattice dynamics cannot be applied to energetically unstable crystals at 0 K, such as high temperature body centered cubic (BCC) phase of crystalline Zr. Predicting phonon spectra at finite temperature requires the calculation of force constants to the third, fourth and even higher orders, however, it remains challenging to determine to which order the Taylor expansion of the potential energy surface for different materials should be cut off. Molecular dynamics, on the other hand, intrinsically includes arbitrary orders of phonon anharmonicity, however, its accuracy is severely limited by the empirical potential field used. Using machine learning method, we developed an inter-atomic potential for Zirconium crystals for both the hexagonal closed-packed (HCP) phase and the body centered cubic phase. The developed potential field accurately captures energy-volume relationship, elastic constants and phonon dispersions. The instability of BCC structure is found to originate from the double-well shape of the potential energy surface where the local maxima is located in an unstable equilibrium position. The stabilization of the BCC phase at high temperature is due to the dynamical average of the low-symmetry minima of the double well due to atomic vibrations. Molecular dynamics simulations are then performed to stochastically sample the potential energy surface and to calculate the phonon dispersion at elevated temperature. The phonon renormalization in BCC-Zr is successfully captured by the molecular dynamics simulation at 1188 K.

Mass-selective neutron spectroscopy of glassy versus polycrystalline structures in binary mixtures of beryllium and zirconium

Exploiting the unique tandem of VESUVIO and TOSCA inverted geometry spectrometers at the ISIS pulsed neutron and muon source in the United Kingdom, specifically the capability of VESUVIO to measure concurrently neutron diffraction and Compton spectroscopy, we have performed a global study of the structural and dynamical origins of disorder in Zr —Be metallic glasses. To this end, a polycrystalline Zr30Be70 and an amorphous Zr40Be60 systems were investigated in a wide range of temperatures ranging from 10 to 300K. For the first time, neutron diffraction has provided clues as to the structural composition of the polycrystalline Zr30Be70. The Rietveld refinement of the diffraction data has revealed that the polycrystalline system is made up of three distinct structural phases; a hexagonal phase, Be2Zr, of the P6/mmm symmetry amounting to 87.11%, a second hexagonal phase, Be5Zr, of the P6/mmm point group symmetry, amounting to 12.89%, as well as trace amounts of a third orthorhombic phase of unspecified stoichiometry. The overall sample stoichiometry, inferred from the dissection of the diffraction data, was in excellent agreement with the Compton results, both confirming the Zr30Be70 formulation. The analysis of INS data agreed very well with the theoretical results from the recursion method. The INS data were cross-validated by the nuclear momentum distributions of both Zr and Be, obtained from the analysis of the NCS data. Systematic differences between the crystalline and amorphous Zr —Be systems were identified in the whole temperature range and attributed to low-frequency mode softening, when going from crystalline to the amorphous phase.

Comparing the atomic and macroscopic aging dynamics in an amorphous and partially crystalline Zr44Ti11Ni10Cu10Be25bulk metallic glass

Abstract

Oxidation resistance and mechanical properties of Zr–Si–N coatings with cyclic gradient concentration

Zr–Si–N coatings with cyclic gradient concentration were fabricated using reactive direct current magnetron cosputtering. The low-Si-content coatings, Zr60N40 and Zr58Si2N40, exhibited a face-centered cubic (f.c.c.) structure, accompanied with a nanohardness of 21.0–23.6GPa and a Young's modulus of 248–267GPa, whereas the medium-Si-content coatings, Zr54Si6N40 and Zr52Si8N40, exhibited a mixture of f.c.c. and near-amorphous structures, accompanied with a nanohardness of 19.7–18.4GPa and a Young's modulus of 204–207GPa. When the Si content ranged from 14 to 19at.%, the structures of Zr–Si–N coatings were X-ray amorphous; those coatings exhibited lower nanohardness levels of 13.7–10.3GPa and Young's modulus values of 196–148GPa. The high-Si-content coatings, Zr28Si24N48 and Zr22Si30N48, exhibited an amorphous structure, accompanied with a nanohardness of 13.7–16.2GPa and a Young's modulus of 196–217GPa, which were higher than those of the coatings with a Si content of 14–19at.%. Coatings formed by adding Si into the Zr–N matrix and performing annealing at 600°C in a 1% O2–99% Ar atmosphere showed notably high oxidation resistance because Si–Zr–O oxide scales formed on the surfaces. The mechanical properties of crystalline Zr–Si–N coatings declined after annealing, whereas near-amorphous Zr–Si–N coatings retained high levels of mechanical properties after annealing.

Synthesis, mechanism and ethylene polymerization catalysis of Ge(iv), Sn(ii) and Zr(iv) complexes derived from substituted β-diketiminates

Unusual X-ray characterized crystalline Sn(ii), Ge(iv) and Zr(iv) complexes have been prepared via a salt metathesis and elimination reaction.

Characterization of the products obtained from the reactions of Zircaloy-4 with an acid mixture of concentrated HNO3and dilute HF with the aim of understanding pickle salts of zirconium alloys

Pickling of zirconium alloys in nitric-hydrofluoric acid has been widely used in the nuclear materials industry. However, the pickle salts still remain a curiosity and a thorough knowledge of the products of the system Zr–(HNO3–HF) still needs to be well established. The present study investigated the products obtained from the reactions of Zircaloy-4 with an acid mixture of HNO3 (65 wt%) and HF (40 wt%) in a volume ratio of 94 : 6, similar to the one used under nuclear industry conditions. It shows that after the reactions, a gel-like solution was present. When drying it at a high relative humidity (at 25 °C and 70 ± 5% RH), an amorphous solid product formed, while in the case of at a low relative humidity (at 15/25 °C and 25 ± 5% RH), besides the amorphous solid, crystalline zirconium hydroxide nitrates Zr(OH)2(NO3)2·4.71H2O and Zr(OH)2(NO3)2·1.65H2O (possible) with low degree of crystallinity formed. These compounds were identified with the help of successfully synthesizing completely crystalline Zr(OH)2(NO3)2·4.71H2O from the gel-like solution by ultrasonication, which in itself was a breakthrough. Such a study can be expected to provide a deep understanding of pickle salts of zirconium alloys in practical use.

Structural differences of amorphous Cu65Zr35 between rapidly quenched and topologically destabilized crystalline Cu and Zr metals by molecular dynamics simulations

In this work we demonstrate, by means of molecular dynamic simulations, that the topological instability caused by successive substitutions of Zr in the Cu lattice, or Cu in the Zr lattice towards a final alloy composition of Cu65Zr35, transform the initial systems to the same amorphous structure at 300K. Such a structure, however, is composed of less ordered clusters, i.e. less icosahedral-like clusters in comparison with the same amorphous alloy produced by rapid quenching from the melt. After a short time annealing at 800K the less ordered structure evolves towards the structure of the rapidly solidified sample. From these results it comes out that no structural differences are to be expected in metallic glasses produced by mechanical alloying and by rapid quenching; any differences found in metallic glasses produced by these two different routes should be attributed to insufficient alloying treatment during the mechanical alloying procedure.

Electrical properties of (Zr,Ti)0.85(Ca,Sr)0.15O1.85 thin film grown on Pt/Ti/SiO2/Si substrate using RF magnetron sputtering

Crystalline (Zr,Ti)0.85(Ca,Sr)0.15O1.85 (ZTCS) films were grown on a Pt/Ti/SiO2/Si substrate at various temperatures by using rf-magnetron sputtering. The ZTCS films had a cubic stabilized zirconia structure. The dielectric constant (k) of the ZTCS film grown at 300°C was approximately 30.5 with a low tanδ value of 0.007 at 100kHz. Further, this film exhibited a similar k value of 30.4 and a high quality factor of 225 at 1.0GHz. Moreover, it showed a high capacitance density of 290nF/cm2 with a small TCC of −60.7ppm/°C at 100kHz. A low leakage current (1.4×10−8A/cm2 at 1.5MV/cm) with a high breakdown electric field (1.85MV/cm) was also observed in this film; the leakage current of this film was explained by Schottky emission. Therefore, it can be concluded that ZTCS films grown at low temperatures (≤300°C) are good candidates for use as embedded capacitor in printed circuit boards.

X-Ray diffraction study of the evolution of phase and structural state and macroscopic stress during annealing of soft magnetic Fe95 − x Zr5N x films prepared by ion-plasma deposition

The evolution of the phase composition, nanostructure parameters, and macroscopic stress in soft magnetic Fe95 − xZr5Nx films (prepared by ion-plasma deposition onto quartz substrates) during their annealing has been investigated by X-ray diffraction. During deposition, depending on the N content, either a mixed structure composed of an X-ray amorphous phase enriched in Zr and N and a crystalline phase (α-Fe(N) solid solution) or an X-ray amorphous phase enriched in Fe, Zr, and N is formed in the films. During annealing, depending on the temperature and nitrogen content, different combinations of crystalline phases (α-Fe(N) and Zr(N) solid solutions, α-Fe, Fe4N, Fe2N, ZrO2) are formed in the films. The large compressive stress formed in the films during deposition changes to a lower tensile stress during annealing.

A robust, catalytic metal–organic framework with open 2,2′-bipyridine sites

We report two synthetic approaches to prepare a highly crystalline Zr(IV)-based metal-organic framework (MOF) containing open 2,2'-bipyridine (bpy) chelating sites. The resulting UiO-67-bpydc readily forms complexes with PdCl2 to produce a MOF that exhibits efficient and recyclable catalytic activity for the Suzuki-Miyaura cross-coupling reaction.

Testing density functionals for structural phase transitions of solids under pressure: Si, SiO2, and Zr

We have investigated the structural phase transitions of crystalline Si (insulator-metal), SiO2 (insulator-insulator), and Zr (metal-metal) under pressure, as a test of several density functionals for the exchange-correlation energy. While meta-generalized gradient approximations (meta-GGAs) such as revTPSS (revised Tao-Perdew-Staroverov-Scuseria) are more sophisticated than GGAs such as PBE (Perdew-Burke-Ernzerhof), and are more accurate without empiricism for atomization energies of molecules, lattice constants of solids, and surface energies, we confirm that these meta-GGAs tend to give smaller and less realistic transition pressures than the PBE GGA does. But we also show that the recent functionals of the meta-GGA made simple family (MGGA_MS) behave differently, predicting larger and often more realistic transition pressures. We suggest that further refinement of the meta-GGA can lead to a functional that is more accurate for properties of molecules and solids at equilibrium or under compression. We also show that, contrary to recent suggestions but in line with older ones, an accurate fundamental gap in the noninteracting band structure is not necessary for an accurate prediction of the transition pressure. Unlike the semilocal GGAs and meta-GGAs, and unlike the local density approximation also tested here, the screened hybrid functional HSE06 (Heyd-Scuseria-Ernzerhof) is fully nonlocal and predicts more realistic fundamental gaps. HSE06 is better than the semilocal functionals for the transition pressures of Si and SiO2, but seriously overestimates the transition pressure in Zr. Besides the transition pressures, we report the transition energies and volumes, binding energy curves, and structural parameters at zero and transition pressure. Finally, we discuss how the performance of a functional can reflect its plottable exchange enhancement factor, and why the structural phase transitions are especially challenging for approximate density functionals.

Mechanism of ion transport in hybrid materials based on MF-4SC perfluorinated sulfonation-exchange membranes and acid zirconium phosphate nanoparticles

The relationship between the transport properties of various salt forms (H+, Li+, Na+, Cs+) of MF-4SC hybrid membranes containing nanoparticles of crystalline acid zirconium phosphate Zr(HPO4)2 at various relative humidities are investigated with the use of impedance studies and NMR spectroscopy. Modification of the membranes leads to a marked increase in ion mobility, and the maximum effect is observed under reduced humidity conditions. The conductivity of a modified membrane at a relative humidity of 10% is 1.6 × 10−4 Ω−1 cm−1, that is, almost 1.5 orders of magnitude greater than the conductivity of an initial membrane under the same conditions.

Mechanical properties of crystalline Cu/Zr and crystal–amorphous Cu/Cu–Zr multilayers

We compare the indentation hardness of crystal/crystal (C/C) Cu/Zr multilayers and the crystal/amorphous (C/A) Cu/Cu–Zr multilayers with equal individual layer thicknesses spanning from 1 to 200nm. Both systems show similar layer thickness dependent evolution of hardness. At smaller layer thickness the C/C multilayers show softening, while no softening is observed in the C/A multilayers. The layer thickness dependent hardness is quantitatively estimated by using dislocation models. The significance of crystalline (Zr) layer and amorphous (Cu–Zr) layer on plastic deformation mechanisms is discussed.

The Lattice Stability of Ti, Zr and Hf in an Ultra-Soft Pseudopotential Method of the First-Principles

The lattice constants, total energies and densities of states of Ti, Zr and Hf in ⅣB group with different crystalline structures have been calculated, and the results have been compared with the results of the projector augmented wave (PAW) method in first-principles, CALPHAD and experiments. It is found that the results of lattice stability in this paper agree completely with those of the PAW method in first-principles and agree well with those of CALPHAD. Further analyses of lattice stability from electronic structures show that the crystalline Ti,Zr and Hf with hcp structures have the obvious character of stable phases, but fcc and bcc structures have the character of metastable and unstable phases, agreeing with the results of total energy calculations. It is found from the analyses of atomic populations that the transiton numbers of electrons from the s state to the p and d states for the hcp, fcc and bcc crystals decrease with the increase in elemental period, and the transiton number of electrons from the s state to the p state decrease dramatically, but the transiton from the s state to the d state increase dramatically, leading to much more number of electrons in the d state than that in the s or p state, stronger cohesion or higher cohesive energy between atoms in heavy metals and accordingly the stabler lattice in these heavier metals.

Epitaxial growth and thermoelectric properties of TiNiSn and Zr 0.5Hf 0.5NiSn thin films

Due to their exceptional thermoelectric properties Half-Heusler alloys like MNiSn (M = Ti,Zr,Hf) have moved into focus. The growth of single crystalline thin film TiNiSn and Zr 0.5Hf 0.5NiSn by dc magnetron sputtering is reported. Seebeck and resistivity measurements were performed and their dependence on epitaxial quality is shown. Seebeck coefficient, specific resistivity and power factor for Zr 0.5Hf 0.5NiSn at room temperature were measured to be 63 μV K − 1 , 14.1 μΩ m and 0.28 mW K − 2 m − 1 , respectively. Multilayers of TiNiSn and Zr 0.5Hf 0.5NiSn are promising candidates to increase the thermoelectric figure-of-merit by decreasing thermal conductivity perpendicular to the interfaces. The epitaxial growth of multilayers containing TiNiSn and Zr 0.5Hf 0.5NiSn is demonstrated by measuring satellite peaks in the X-ray diffraction pattern originating from the additional symmetry perpendicular to the film surface.

The different initial oxidation kinetics of Zr(0001) and Zr(101−0) surfaces

The growth kinetics of thin (thickness &amp;lt;10 nm) oxide films on Zr(0001) and Zr(101−0) single-crystal surfaces were investigated by real-time in situ spectroscopic ellipsometry (RISE) and angle-resolved x-ray photoemission spectroscopy (AR-XPS). To this end, clean crystalline Zr(0001) and Zr(101−0) surfaces were prepared under UHV conditions by a cyclic treatment of alternating ion-sputtering and in vacuo annealing steps. The thus-obtained bare Zr surfaces were then exposed to dry O2(g) in the temperature range of 300 − 450 K (at a partial oxygen pressure of 10−4 Pa), while monitoring the growth kinetics by RISE. It was found that the less-densely packed Zr(101−0) surface oxidizes more readily than the densely packed Zr(0001) surface. A near-limiting thickness of the oxide film on both surfaces is attained only at oxidation temperatures T &amp;lt; 375 K. At T ≥ 375 K, the oxidation rate becomes controlled by the thermally activated dissolution and diffusion of oxygen in the α-Zr substrate. The higher oxidation rate of the Zr(101−0) surface for T ≥ 375 K is attributed mainly to the higher oxygen diffusivity in α-Zr along the Zr(101−0) direction than along the Zr(0001) direction.

Glass forming ability and crystallization of Zr–Cu–Ag–Al–Be bulk metallic glasses

The glass forming ability of Zr 46Cu 37.64− x Ag 8.36Al 8Be x ( x = 0, 6 and 10 at.%) bulk metallic glasses (BMGs) were significantly improved by Be addition. The critical size of amorphous rods can be over 35 mm diameter. The high GFA achieved is mainly due to the decrease of melting point and liquidus temperature, and suppression of the formation of crystalline phases during solidification from liquid state. The high stabilization with supercooled liquid regime of 115 K was found for the BMG with x = 10 at.%. Two independent exothermic events happen in x = 0 and 6 at.% BMGs, corresponding to the formation of primary crystalline phases Cu 10Zr 7 and AgZr, then transforming to final stable crystalline phases Zr 2Cu and AlCu 2Zr. However, in the x = 10 at.% BMG, the precipitation of primary phases and transformation to final stable phases are within the first exothermic event and the AlCu 2Zr phase is totally suppressed.