Crystalline Zr Research Articles

Effects of oxygen and hydrogen on the surface segregation of amorphous and crystalline Zr alloys

Effects of oxygen and hydrogen on the surface segregation of amorphous and crystalline Zr alloys

Effect of oxygen and hydrogen on the surface segregation of amorphous and crystalline Zr alloys

The effect of oxygen and hydrogen on the surface segretation of amorphous and crystalline alloys of Zr were analyzed by means of AES, XPS, and UPS. Amorphous Cu 70 Zr 30 alloys with high oxygen content showed a very pronounced unexpected Cu enrichment at the surface after annealing at 473 K in H 2 atmosphere.

Metastable phase equilibrium during solid-state amorphization reaction of Zr-Co layers.

The crystal-glass transition of Co-Zr layers via interdiffusion has been followed by Rutherford-backscattering spectrometry and x-ray-diffraction analysis. Thin-film multilayer samples of Co and Zr were annealed at 250 \ifmmode^\circ\else\textdegree\fi{}C for different times up to 21 h. Planar growth of the amorphous layer is observed. The changes in the concentration profiles, as observed with Rutherford-backscattering spectrometry, in combination with corresponding x-ray analysis, indicate an interstitial solid solution of \ensuremath{\approxeq}3 at. % Co in crystalline Zr probably preceding the glass transition. This effect is discussed in the context of a metastable phase diagram.

Evidence for a nucleation barrier in the amorphous phase formation by solid-state reaction of Ni and single-crystal Zr

In an ultrahigh vacuum (UHV) environment, thin poly crystalline Ni films have been deposited on a Zr (112) single-crystal surface. In contrast to the case of poly crystalline Ni and Zr films, formation of amorphous Ni—Zr is not observed upon annealing at 300 °C for 11.5 h. The possible presence of an oxide or an amorphous phase diffusion barrier is ruled out and therefore the lack of a reaction must be due to a reaction barrier at the single-crystal Zr/ Ni interface. Either ion mixing of the interface with 400 keV, 5 × 1015 Xe+ /cm2, or deposition of a poly crystalline Zr layer in between the Zr single crystal and the Ni overlayer can overcome this reaction barrier. These results indicate that grain boundaries in polycrystalline Zr play an important role in amorphous Ni—Zr formation by a solid-state reaction.

Structure of solid phases in titania and zirconia gels

The goal of this study was to determine the chemistry and atomic structure of the solid component of titania and zirconia gels. These were made from both inorganic and organic sources. X-ray diffraction (XRD) and selected area electron diffraction (SAED) failed to show the presence of any crystalline Ti and Zr hydroxides, oxyhydroxides or oxides even with extensive hydroxyl bridging in the gels. Alcogels made from alkoxides were likewise determined to be truly amorphous to both XRD and SAED. Some of the non-dispersible gels made from TiCl 4 and ZrOCl 2 in NaOH contain very poorly crystalline oxides by SAED. The differences in morphology among the various gels are reported: alcogels of titania and zirconia showing porosity.

Amorphous Ni-Zr alloys as barriers for self-diffusion.

The diffusivity of Ni at 250 \ifmmode^\circ\else\textdegree\fi{}C through an amorphous ${\mathrm{Ni}}_{50}$${\mathrm{Zr}}_{50}$ alloy sandwiched between pure Ni and pure Zr is at least a factor of ${10}^{4}$ below that for Ni in crystalline Zr. This result contradicts a recently proposed diffusion model for amorphous phase formation by solid-state reactions, because the amorphous layer acts as a diffusion barrier to self-diffusion.

Solid State Reaction of Sputter Deposited Crystalline Multilayers of Ni and Zr

AbstractWe have prepared sputtered metallic films comprised of alternating layers of pure Ni and Zr to a total thickness of several microns. Due to the negative beat of mixing of crystalline Ni and Zr and a significant intermixing rate we have been able to form an amorphous Ni-Zr phase by a solid state reaction. In this work we report the conditions under which a substantial fraction of amorphous material may be formed. The extent of the reaction itself as a function of time has also been monitored.

Glass formation by a solid state reaction of crystalline ZrX phases with hydrogen and structure of glassy hydrides

The transformation of crystalline Zr 3Rh intermetallic phases into the amorphous state by hydriding at about 200°C is shown. The reaction endproduct shown no significant difference in their physical properties to a rapidly quenched hydrided sample. The transformation can be explained in terms of a “chemical frustration” effect due to the large disparity in the diffusion rates. Radial distribution functions suggest that hydrogen occupies tetrahedral sites defined by four Zr atoms. A simple statistical model is in good agreement with the observed absorption capacity for hydrogen.

Thermodynamics of hydrogen absorption in amorphous ZrNi alloys

Abstract The relative partial molar enthalpy and entropy for the absorption of hydrogen were obtained from the pressure-composition isotherms for both amorphous and crystalline ZrNi alloys. The quantities of Δ S H and Δ S H in the amorphous state show the minimum at certain hydrogen content and then remain fairly constant as the hydrogen content is further increased. The characteristic variations in Δ S H for the amorphous ZrNi alloys may be attributed to the changes in the local environmental structure around hydrogen atoms, leading to an increase in the configurational entropy.

Hydrogen mobility in crystalline and amorphous Zr 2PdH x

NMR measurements of proton rotating-frame relaxation times were made to deduce hydrogen diffusion parameters for crystalline and amorphous Zr 2PdH x. Enhanced proton mobility was observed in glassy a-Zr 2PdH 2.9 relative to diffusion behavior in any crystalline Zr 2PdH x sample. Both host crystal structure and proton site occupancy make significant contributions to the diffusion process where smaller activation energies correspond to jumps involving octahedral sites.

Superconductivity in FeZr, NiZr and CuZr amorphous metal alloys: Analysis of low temperature specific heat

Fe 100− x Zr x amorphous alloys are shown to be superconducting for x ⪸ 68 ± 2. Comparison of low temperature specific heat measurements for FeZr with previous results for NiZr and CuZr show that the composition trends of N 0( E F ) are consistent with recent theoretical models and photoemission results. Furthermore, the factor η = N 0( E F )〈 I 2〉 is composition independent and the same for all superconductors in these three alloy series. From these results we conclude that T c of pure amorphous Zr will be 5.1 K, compared with 0.55 K for crystalline Zr.

NMR studies of electronic structure in crystalline and amorphous Zr 2PdH x

The proton Knight shifts and spin-lattice relaxation times have been measured in crystalline and amorphous Zr 2PdH x . Core-polarization from the Zr d-band dominates the proton hyperfine interactions. The density of Fermi level d-electron states is reduced in the amorphous phase relative to the electron density in crystalline Zr 2PdH x .

A study of the properties and NMR spectra of amorphous and crystalline ZrPd hydrides

Results of a study of the hydrides of Zr 65Pd 35 and Zr 67Pd 33 metallic glasses are presented. It was found that these alloys absorb hydrogen at temperatures ranging from 150°C to 225°C to a final hydrogen concentration of Zr 67Pd 33H ≈95. X-ray diffraction, density measurements, and measurements of electrical resistivity and superconducting transition temperature were carried out on these samples. Results of NMR studies of amorphous Zr 67Pd 33H ≈95 alloys as well as the corresponding single-phase crystalline hydrides Zr 2PdH 1.94 and Zr 2PdH 2.90 are also reported. The amorphous hydrides exhibit enhanced hydrogen mobility, compared with the corresponding crystalline hydrides, as determined by motional line narrowing (T 2 ∗ measurements) of the NMR spectra. The apparent activation energy for diffusion in the amorphous hydride was studied by both T 2 ∗ and T 1 π measurements over an extended temperature range and found to depend strongly on temperature. Proton Knight shift and spin-lattice relaxation time measurements suggest that the electronic density of states at E F is significantly lower in the amorphous hydride than in the corresponding crystalline hydride.

Local structure of amorphous Zr 3Fe

It is shown that the chemical short-range order (CSRO) of amorphous Zr 3Fe studied by Mössbauer spectroscopy is similar to the CSRO of metastable crystalline Zr 3Fe formed during crystallization while it is quite different from the CSRO of the stable crystalline compounds (ZrFe 2, Zr 2Fe and orthorhombic Zr 3Fe).

Computer simulation of deformation of amorphous Cu 57Zr 43

A model amorphous alloy of Cu 57Zr 43 (1533 atoms) constructed using modified Lennard-Jones 4–8 potentials was deformed in computer under a periodic boundary condition. The bulk modulus calculated gave an intermediate value between those of crystalline Cu and Zr, whereas the shear modulus was considerably smaller, in agreement with experiments, than those of both elements reflecting reversible internal displacements of atoms under stress. On increasing pure shear strain a large energy relaxation occurred at a stress of about G/15 ( G: shear modulus). The relaxation was accompanied by a localized elementary plastic deformation, which is expressed roughly by a localized slip in an area of diameter of 4 ~ 5 a and with a slip vector of ~ a/3 ( a: atomic diameter). After the analysis of the atomic stress tensor, atoms in the slipped region were found to be initially subject collectively to internal stress that assisted the applied stress in surmounting a barrier to slip.

ChemInform Abstract: THE SYNTHESIS OF CRYSTALLINE ZIRCONIUM PHOSPHATE WITH LARGE PARTICLE SIZE BY THE DIRECT‐PRECIPITATION METHOD

AbstractDie Ausb. und die Kristallgröße werden als Funktion der HF‐ und der H3PO4‐Konzentration sowie der Erwärmungstemp. ermittelt.

D Band structure and alloying effects in crystalline and amorphous ZrCo and ZrNi

We study the electronic structure by photoemission of amorphous Zr 70Co 30, Zr 75 Ni 25 and crystalline Zr 2Co, Zr 2Ni. The results show that the electronic structures for the amorphous and crystalline states are quite similar. The valence bands of the amorphous alloys do not present features attributable specifically to the amorphous state. In both cases the valence band indicate a strong localization of the d levels and can be interpreted as a superposition of the Zr 4d levels in the upper part of the band, the Co or Ni 3d levels being centered in the low part of the part of the band. The present results and previous ones on ZrCu amorphous alloys show that the binding energies of the 3d levels increase with the distance between the alloying elements in the periodic table. Moreover the full width at half maximum of Co, Ni or Cu d levels is noticeably less than for pure elements. These results are considered at the light of atomic structure and theoretical models ; in particular it seems that the coordination number of the atoms plays a dominant role in the structure of the d levels.

The Synthesis of Crystalline Zirconium Phosphate with Large Particle Size by the Direct-precipitation Method

Abstract The direct-precipitation method was studied as a possible way to synthesize crystalline zirconium phosphate of a large and uniform crystal size. The yield and the crystal size were examined as functions of the initial hydrofluoric-acid and phosphoric-acid concentrations and the warming temperature. The conditions for preparing the largest crystal were: ZrOCl2·8H2O, 0.13 M; hydrofluoric acid concentration, 0.715 M; phosphoric acid concentration, 5 M; temperature, 50 °C. Those for preparing the material with uniform crystal-size distribution and a possibly large-mean crystal size were: ZrOCl2·8H2O, 0.13 M; hydrofluoric acid concentration, 0.715 M; phosphoric acid concentration, 9 M; temperature, 60 °C. The product was confirmed to be crystalline Zr(HPO4)2·H2O by means of chemical, thermal, and X-ray analyses, and by an examination of the titration curve.

The standard enthalpy of formation of anhydrous, monohydrated, and dihydrated zirconium bis(monohydrogenphosphate)

The enthalpies of solution of amorphous and crystalline Zr(HPO 4) 2 · H 2O, of Zr(HPO 4) 2, and Zr(HPO 4) 2 · 2H 2O have been measured calorimetrically and the standard enthalpies of formation derived. The results obtained are as follows: ΔH f o(s, 298.15 K)/kJ mol −1 Zr(HPO 4) 2 · H 2O(am) −3435.8 ± 4.2 Zr(HPO 4) 2 · H 2O(c) −3463.7 ± 4.1 Zr(HPO 4) 2(c) −3167.9 ± 4.1 Zr(HPO 4) 2 · 2H 2O(c) −3741.2 ± 4.1 In order to establish an unambiguous assessment of the degree of crystallinity of these exchangers, the ΔH o of other Zr(HPO 4) 2 · H 2O samples prepared by different techniques with various conditions have also been determined.

Structure and chromatographic applications of crystalline Zr(OPO 3R) 2; R = butyl, lauryl and octylphenyl

Structure and chromatographic applications of crystalline Zr(OPO 3R) 2; R = butyl, lauryl and octylphenyl