Zr Amorphous Alloys Research Articles

Surface-enhanced Raman scattering (SERS) on modified amorphous Cu–Zr alloys

Partially devitrified Cu–Zr amorphous alloys with 50 at% of Cu and Zr were used as targets for in situ SERS measurements of adsorbed pyridine. We have found that large SERS signals are measured from the Cu-rich domains, whereas the intensity drops down by one order of magnitude on the Zr-rich areas. Moreover, the effect of electrode potential on the SERS signal for various surface domains (of about 1 μm 2 ) is very different one from another which suggests that the activity of various Cu clusters present at different surface sites differs accordingly, one from another. These results show that SERS, particularly if coupled with the Raman microscope, could be a useful method for studying the adsorption of molecules in Cu containing catalysts because of its high sensitivity to the physical and chemical states of the substrate.

Effect of Nb addition on glass-forming ability, strength, and hardness of Fe–B–Zr amorphous alloys

Supercooled liquid region (ΔT x), tensile fracture strength (σ f), and Vickers hardness (Hv) of Fe–B–Zr–Nb amorphous alloys were measured. The addition of Nb to the ternary Fe–B–Zr system was found to lead to significant changes in glass-forming ability (GFA), strength, and hardness. The results are discussed in the context of the three empirical rules for achievement of high GFA metallic glass and the change in packing density of the amorphous phases.

Effect of electrochemical pretreatment on SERS and catalytic activity of Cu–Zr amorphous alloys

This paper presents results of electrochemical, microscopic, spectroelectrochemical (SERS) and catalytic investigations of Cu–Zr amorphous alloy ribbons aimed at increasing their catalytic activity for the dehydrogenation reaction of aliphatic alcohols. Rapid dissolution in sulphuric acid/copper sulphate solution of partially devitrified Cu–Zr ribbons resulted in a nearly twofold enhancement of their catalytic activity for dehydrogenation of 2-propanol. However, their local SERS activity on the Cu rich areas was not distinctly altered by this electrochemical pretreatment. Yet, the SERS heterogeneity of the devitrified material vanished: the SERS intensity increased considerably outside the Cu rich areas. A tentative mechanism of the effects of various electrochemical pretreatments on the surface activity is discussed.

Effect of electrochemical pretreatment on catalytic activity of Cu–Zr amorphous alloys

This communication presents the results of electrochemical, microscopic, and catalytic investigations of 60Cu–40Zr amorphous alloy ribbons aimed at increasing their catalytic activity for dehydrogenation reaction of aliphatic alcohols. Rapid dissolution in sulphuric acid/copper sulphate solution of partially devitrified Cu–Zr ribbons, and accompanied processes, resulted in a nearly two-fold enhancement of their catalytic activity for dehydrogenation of 2-propanol.

Volume effects in Fe-rich Fe [sbnd]Zr amorphous alloys

The parameter β(x) in the temperature dependence of coercive field, H c(x,T) = H c(x,0)e −β(x)T at low temperatures is found to have a linear-type dependence on Curie points T C(x) in melt-spun Fe-rich Fe x Zr 1 − x amorphous alloys. Using a cluster model, we show that β(x) ≈ 6Γ(x)α v , where α v is the ‘volume expansion’ coefficient and Γ(x) is the ‘magnetic’ Grüneisen parameter. We estimate Γ(x) ∼ 65 and α v ∼ 2.6 × 10 −4K −1 for Fe-rich Fe-Zr amorphous alloys, and α v ∼ 8 × 10 −5K −1 for rare-earth (R)-Fe compounds.

Structural and magnetic properties of amorphous Fe/Zr multilayers

The structure and magnetic properties of rf-sputtered Fe/Zr multilayers with ultrathin layer thicknesses, in as-deposited and annealed states, have been studied using x-ray diffraction, low- angle x-ray reflectometry, conversion electron Mössbauer spectroscopy and low-temperature magnetometry. The thickness ratio of the analysed multilayers was 0.5 and the values of the bilayer thickness was varied from 9 Å to 75 Å, maintaining constant the total thickness of the samples by controlling the number of bilayers. The results obtained show that, during sputter deposition, Fe layers with thicknesses below 20 Å are alloyed forming an amorphous phase. Those multilayers with nominal Fe layer thickness below 20 Å are composed of layers of this amorphous phase, behave as a ferromagnet below the Curie temperature , and the spin structure shows a low-temperature asperomagnetic ground state with a reduced canting of the spin structure as compared with homogeneous amorphous thin films. The structural relaxation during annealing indicates that an homogeneous Fe - Zr amorphous alloy can be produced after annealing these Fe/Zr multilayer structures.

Decomposition and crystallization of the bulk amorphous Zr 11Ti 34Cu 47Ni 8 alloy studied by SANS

The microstructural evolution upon thermal annealing of the bulk amorphous alloy Zr 11Ti 34Cu 47Ni 8 was investigated by means of small-angle neutron scattering (SANS) and X-ray diffraction. The results are compared with those from the metallic glass Zr 41Ti 14Cu 12.5Ni 10Be 22.5. In both cases, inhomogeneities of about 2 nm extension have been detected upon annealing and interpreted as decomposition of the amorphous phase. In the Be-free metallic glass crystallization occurred simultaneously with the decomposition.

SERS on modified amorphous CuZr alloys

CuZr amorphous alloys with 40 at% and 60 at% Cu were used as targets for in situ SERS measurements of adsorbed pyridine. The as-quenched alloys did not produce enough enhancement for measurable SERS bands. However, a ‘modification/activation’ produced SERS active substrates. The observed SERS spectrum was shown to originate from pyridine molecules adsorbed on copper particles which form a sort of a regular grid onto a zirconia-enriched substrate. Therefore, it seems that SERS spectroscopy could be an effective and selective method for studying molecular adsorption on some activated glassy metals with catalytic properties.

Superconductivity in the metallic amorphous alloy Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5

We report an observation of the superconducting transition in the metallic amorphous alloy Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5. The resistive superconducting transition temperature is 1.1 K and the temperature gradient of the upper critical field (−d H c2/ dT) Tc is 2 T/K. Annealing of the alloy leads to a reduction of T c by 0.2 K and a decrease of H c2 to (−d H c2/ dT) Tc = 1 T/K.

Anelastic and Viscoelastic Behaviour of Amorphous Zr65Cu17.5Ni10Al7.5 in the Range of the Glass Transition

Reversible (anelasticity) and the irreversible (viscosity) relaxations in the amorphous alloy Zr 65 Cu 17.5 Ni 10 Al 7.5 have been investigated by means of creep and mechanic after-effect measurements of the shear strain, which were performed in an inverted torsion pendulum. For the evaluation of the measurements a new relaxation model is proposed which takes into account that in the range of the glass-transition temperature T g the local atomic arrangement is steadely changing. By introducing a finite mean life time τ f of local structure units we are able to trace the origin of the anelasticity and the viscosity to the same atomic relaxation processes. The temperature dependence of the viscosity η measured between 560 K and 668 K shows a jump in the activation energy at Tg = 606 K from 2.1 eV below T g to 5.6 eV above T g .

Compositional dependence of and effects of hydrogen doping on coercive fields of Fe-rich Fe - Zr amorphous alloys

Variation in low-temperature coercive fields as a function of Fe concentration x and hydrogen doping are investigated for Fe-rich amorphous alloys. The analysis is based on Fe density fluctuations in the alloys. We demonstrate a linear dependence between and . The drastic decrease in coercive field observed at low temperatures with hydrogen doping is also analysed.

Investigation of beryllium diffusion in the supercooled liquid and glassy states of the amorphous alloy Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 by high energy helium elastic backscattering

The elastic scattering cross section for 9Be(α, α) 9Be has been measured in a strongly resonant region from 6.00 to 6.50 MeV at a laboratory angle of 177°. This reaction has been used to investigate Be diffusion in the bulk metallic amorphous alloy Zr 41.2Ti 13.8Cu 12.5Ni 10Be 22.5 in the solid state (SS) as well as in the supercooled liquid state (SLS). Above the glass transition, i.e., in the SLS, a remarkable increase in the diffusivity of Be (about two orders of magnitude over a 40 K temperature interval) was observed, which can be explained with a modified Arrhenius fit, which takes into account the change in configurational entropy due to the glass transition.

Application of amorphous Cu–Zr binary alloy as a diffusion barrier in Cu/Si contact systems

Thermally stable Cu/Si contact systems using an amorphous binary alloy of Cu0.6Zr0.4 with a relatively low resistivity of ∼150 μΩ cm as a diffusion barrier have been developed. The application of the stable compound ZrN in the Zr/Cu/Cu–Zr/ZrN/Si contact system effectively suppresses the interfacial reactions up to a temperature of 550 °C, which is higher than the crystallization temperature of the Cu–Zr amorphous alloy, ∼500 °C. By designing the contact system with the Cu-containing amorphous alloy Cu–Zr and the stable barrier compound ZrN, also a compound of a constituent material of the amorphous alloy, we can obtain an effective diffusion barrier in the Cu/Si contact system.

Pressure and temperature variation of coercive field in Fe-rich FeZr amorphous alloys

A model for the variation of coercive field H c with applied pressure and temperature in Fe x Zr 1− x amorphous alloys is investigated in relation to volume changes of Fe-rich clusters having Fe density greater than a critical value ρ c . We estimate ‘volume thermal-expansion coefficients’, a v ∼ 10 −4K −1 at temperatures T < 50 K for Fe-rich alloys. Our analysis predicts a relationship between coercive field H c( T = 0 K, x) and Curie point T C( x) of the form, H c(0, x) ∝ T C −6/ n ( x) where n is a parameter which describes the variation of Fe density across an Fe-rich cluster. This result is found to be in reasonable agreement with experimental results on melt-spun and sputtered FeZr amorphous alloys.

EXAFS study of short range order in Fe[sbnd]Zr amorphous alloys

Room temperature X-ray absorption spectra on Fe K-edge have been performed in Fe100−x−yZrxBy and Fe86Zr7Cu1B6 alloys (x = 7, 7.7, 9; y = 0, 2, 4, 6). FeFe coordination number and interatomic distances do not change in any sample. However, small changes in the FeZr short range order, which could explain the evolution of the magnetic properties, have been observed.

Mossbauer and Magnetic Investigations of Iron‐Rich FeNiZr Amorphous Alloys

AbstractMössbauer, high‐field susceptibility, and thermomagnetic measurements indicate a correlation between reentrant spin glass (RSG)‐like behaviour and the presence of a broad hyperfine magnetic field distribution of Fe92−xNixZr8 glasses. The pure iron area, in which the competition between antiferromagnetic and ferromagnetic exchange takes place, is probably responsible for both. There is a transition from collinear to noncollinear magnetic structure at low temperatures for x = 0, 2, 5 due to this competition. The substitution of Ni for Fe or the hydrogenation suppresses the RSG‐like behaviour.

Effects of ambient temperature and acceleration on various mechanical alloying products: MgAlZn quasicrystals, NiZr amorphous alloys and amorphous Se

In the present work, we employed a high-energy mill which is capable of milling with intensities up to 150 G (where G is the gravity of the earth) in ambient temperatures up to 300 °C. Phase transformation diagrams were constructed as functions of milling intensity and ambient temperature for three representative systems: Mg 48Al 15Zn 37, Ni 50Zn 50 and pure Se. The ambient temperature measured on the outer wall of the vial was found to coincide well with the true “annealing” temperature which the powdered sample experiences during milling. It is shown that both the milling intensity and ambient temperature affect substantially the formation rate of a quasicrystal in the MgAlZn system and that of an amorphous phase in both NiZr and Se. By choosing appropriate conditions, we found the shortest milling times to complete the formation of MgAlZn quasicrystals, amorphous NiZr alloy and Se to be 30 min, 3 h and 20 min respectively.

Hyperfine field distribution, invar anomalies in amorphous FeZr alloys, and problems of amorphous Fe magnetism

The temperature and concentration dependence of the hyperfine field distribution in the Mössbauer spectra of Fe nuclei in FeZr amorphous alloys are studied. The relation between the low-field component and the Invar anomaly is also investigated. The nonmagnetic densities of electronic states of the model clusters Fe14 and Fe14Zr and the influence of cluster deformations simulating the interatomic distance fluctuations are calculated. The results show that the Fe atom with unstable magnetic moment causes the magneto-volume anomaly. The Fe atoms with next-nearest-neighbour Zr atoms possess unstable moments. Some Fe atoms among nearest neighbours also show a decrease of the moments with increasing temperature. These atoms have smaller interatomic distances as confirmed by the density of states calculations. [Russian Text Ignore]

Liquid-Phase Hydration of Acrylonitrile on Skeletal Copper Catalysts Prepared from Cu–Ti and Cu–Zr Amorphous Alloys

Abstract Liquid-phase hydration of acrylonitrile has been carried out on the skeletal copper catalysts which were prepared by treating pulverized amorphous Cu–Ti and Cu–Zr alloys with an HF solution. The catalysts from amorphous alloys were more effective to produce acrylamide selectively than those from crystalline alloys. This high activity was brought about by the highly homogeneous structure of the amorphous alloys.

Enthalpy relaxation and Curie temperature behavior in Fe(Ni,Co)Zr amorphous alloys

Annealing-induced changes in enthalpy relaxation and Curie temperature, T c, were examined for amorphous (Fe 0.85Ni 0.15) 90Zr 10 and (Fe 0.9Co 0.1) 90Zr 10 alloys. The compositional dependence of an endothermic reaction was also examined for amorphous (Fe 1− x Co x ) 90Zr 10 ( x = 0–1) alloys. A reversible endothermic reaction occurs above the annealing temperature, T a. The change in the magnitude of the endothermic peak, ΔC pmax , with T a shows a single stage with a peak at about T x − 400 K (i.e., the temperature that is 400 K lower than crystallization temperature). For (Fe 1− x Co x ) 90Zr 10 alloys, the endothermic reaction is the largest at x = 0.5 and disappearsat x = 0 and 1. The change in T c with T a is related to the increase in T c at T a ≌ T x − 400 K , followed by the decrease in T c at temperatures above T x − 400 K. A good correspondence was observed between the reversible endothermic enthalpy relaxation and the increase in T c and between the irreversible exothermic enthalpy relaxation and the decrease in T c. These results are explained as a consequence of the low-temperature endothermic reaction which is due to the local chemical ordering of FeNi and FeCo atoms with shorter relaxation times. The exothermic reaction is mainly due to the long-range topological change leading to the densification of amorphous structure with longer relaxation times.