Ni Zr Research Articles

Formation of Cu–Zr–Ni amorphous powders with significant supercooled liquid region by mechanical alloying technique

The amorphous Cu–Ni–Zr alloys were successfully synthesized by mechanical alloying mixtures of pure crystalline Cu, Ni and Zr powders with SPEX high-energy ball mill. These ranges are similar to those for amorphous alloys produced by melt-spinning techniques. The structure and thermal stability of these alloys were analyzed by X-ray diffraction and differential scanning calorimeter. Several amorphous alloy samples were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T g and T x, i.e. Δ T x (= T g− T x), is 34 K for Cu 10Zr 60Ni 30, 48 K for Cu 20Zr 60Ni 20, 78 K for Cu 40Zr 55Ni 5, 81 K for Cu 50Zr 35Ni 15, 61 K for Cu 50Zr 40Ni 10 and 64 K for Cu 50Zr 45Ni 5.

Thermodynamic properties and phase equilibria in the nickel–zirconium system. The liquid to amorphous state transition

The vapour composition and the thermodynamic properties of Ni–Zr alloys in the liquid and solid states were studied by Knudsen-cell mass spectrometry over wide ranges of temperature (971–1896 K) and composition (0–99.8 mol% Zr). The accessible temperature range was enhanced by chemically generating volatile substances directly in the cell. For this purpose, the samples were mixed with powdered fluorides of magnesium, calcium, or sodium. Reduction reactions occurring in the cell produced zirconium fluorides, which were examined with the mass spectrometer. The thermodynamic functions of formation of all crystalline phases in the Ni–Zr system were determined. A representative file of experimental data was obtained for the Ni–Zr melt. It comprises about 900 values of the activities of both components at various concentrations and temperatures. The concentration and temperature dependences of the thermodynamic functions of liquid Ni–Zr alloy were described by the associated-solutions model under the assumption that NiZr, Ni2Zr and Ni3Zr associates exist in the melt. The phase equilibria computed on the basis of the obtained thermodynamic properties and the developed model are shown to agree with available experimental information. The nature of the interparticle interaction in the Ni–Zr system was analysed and the behaviour of the thermodynamic functions accompanying the process of transition of the Ni–Zr melt into the amorphous state was considered. Quantitative agreement with the independent experimental results was obtained.

Powder metallurgical processing of Ni–Ti–Zr alloys undergoing martensitic transformation: part I

Ni–Ti–Zr materials with Zr 12–25 at.% and Ni 42–50 at.% have been produced by powder metallurgy. Suitable temperatures for sintering in Ar-atmosphere Ni–Ti–Zr compacts are within the range 900–1000 °C. Sintering at temperatures above 1000 °C causes melting of the compacts with high Zr content. The presence of ZrC, ZrO 2, Zr 3O, TiO 2 and TiO of different modifications, complex oxides such as Ni 5TiO 7, Ti 0.5Zr 0.5O 0.2 and equilibrium phases after sintering at temperatures above 1000 °C in alloys with low Zr-content was derived from X-ray diffractometry. During sintering at temperatures below 1000 °C the phases belonging to the binary Ti–Ni and Ti–Zr systems were formed. Long-term sintering and slow furnace cooling allowed the precipitation of Ni 4Ti 3 and Ni 2Ti. The process of sintering is controlled by the diffusion of Ni in Ti and Zr particles during the early stages of sintering. Slow diffusion of Zr atoms in Ti 2Ni, Ti–Ni and diffusion of Ti atoms in Zr 2Ni, Ni–Zr controls the later stages of sintering.

Improvement of electrode performances of Mg 2Ni by mechanical alloying

Nanocrystalline and amorphous Mg 2Ni-based hydrogen storage alloys for Ni–MH batteries had been synthesized by mechanical alloying. The surface modification and Zr addition had also been carried out for improvement of its electrode performance. In comparison with the arc-melted polycrystalline one, the nanocystalline Mg 2Ni phase showed a higher discharge capacity. By increasing milling time from 120 to 160 h, the grain size of Mg 2Ni phase was more refined and the discharge capacity was raised from 180 to 370 mAh g −1. The discharge capacity of the 160-h milled Mg–Ni–Zr amorphous alloys also reached 530 mAh g −1. XPS (X-ray photoelectron spectroscopy) analysis showed that Mg2p spectra were shifted to lower binding energy implying the enhancement of the hydrogen diffusion and charge transfer reaction, and resulted in increasing the discharge capacity in amorphous alloys. To prevent the rapid degradation, the alloy powders were also coated with Ni and graphite by additional ball milling. The Ni and graphite protected the Mg from oxidation, and the coated powders showed a better cyclic stability. After 50 cycles, the degradation of bare electrode was 94% of maximum capacity, but that of coated electrode with Ni and graphite was 45 and 76% of maximum capacity, respectively.

The electrochemical hydriding properties of Mg–Ni–Zr amorphous alloy

The amorphous alloys of Mg–Ni–Zr were synthesized by mechanical alloying process, in which the effects of Zr addition were studied. A small shift of the broadening amorphous peak due to Zr additions was observed. The equilibrium hydriding pressure increased continuously with hydrogen contents in the amorphous alloys, while there was an obvious plateau pressure of 10 −4 MPa in the crystalline Mg 2Ni phase. The Zr addition lowered the equilibrium hydriding pressure and increased the hydrogen solubility from 1.4 wt% for Mg–Ni to 2.2 wt% for Mg–Ni–Zr. Accompanied by amorphization, the hydrogen discharge capacity increased largely, and reached 580 mA h / g for Mg–Ni–Zr alloy. The chronopotentiometric experiments were performed to investigate the hydrogen diffusion in the alloy powder in the high over-potential range. The diffusivity of hydrogen in the Zr-contained alloy was lower than the Mg–Ni binary amorphous alloy or in Mg 2Ni nanocrystalline alloy.

Thermodynamics of the NI-ZR melt: Specific features of interatomic interaction and transition into an amorphous state

Nickel–zirconium alloys have a high glass-forming ability in a wide range of concentrations and constitute the basis for a variety of bulky amorphous metallic materials [1]. However, until now, there is no information on the Gibbs energy of the Ni–Zr-melt formation. This fact hampers both the analysis of thermodynamic and kinetic parameters of the transition of the Ni–Zr liquid into an amorphous state and the understanding of the reasons why such a transition easily proceeds in a number of transition metal systems.

Soft X-ray spectroscopy study of the electronic structure of hydrogenated Ti–Ni–Zr quasicrystal

Investigation of the electronic structure of a material is useful to understand its properties. For such a purpose, it is interesting to use spectroscopic techniques that allow for direct insight into the electronic distributions of a solid. X-ray emission and photoabsorption spectroscopies are especially attractive as they probe separately occupied and unoccupied states of selected angular momentum around each component of an alloy or a compound. In the present work we used these techniques to analyze the nature of the interaction between H and Zr, Ni and Ti. We studied occupied d and unoccupied p and s, d states in hydrogenated icosahedral Zr–Ni–Ti as compared to the non-hydrogenated quasicrystal and the pure elements. We present here first results. The spectral curves for Zr 4d occupied states show additional states, induced by the hybridization with H. The same is observed for Ni 3d states although the spectroscopic signature of the H-metal interaction is of lower intensity than for Zr. In the unoccupied states, changes of the shapes of the various spectral curves for Zr as well as Ni and Ti display significant modifications which we attribute to changes in hybridizations owing to the interaction with H.

Advanced materials for global carbon dioxide recycling

CO 2 emission increase inducing global warming occurs mostly with the growth of the economic activity. Global CO 2 recycling can prevent global warming and supply abundant renewable energy. Global CO 2 recycling consists of three district: The electricity is generated by solar cells on deserts. At coasts close to the deserts, the electricity is used for hydrogen production by seawater electrolysis and hydrogen is used for methane production by the reaction with CO 2. Methane (CH 4) is liquefied and transported to energy consuming districts where after CH 4 is used as a fuel CO 2 is recovered, liquefied and transported to the coasts close to the deserts. Key materials necessary for the global CO 2 recycling are the anode and cathode for seawater electrolysis and the catalyst for CO 2 conversion. All of them have been tailored by us. Amorphous and nanocrystalline nickel alloys are active cathodes for hydrogen production in seawater electrolysis. Anodically deposited nanocrystalline Mn–Mo and Mn–W oxides are the unique substance which can evolve oxygen with 100% efficiency without evolving chlorine in seawater electrolysis. Amorphous Ni–Zr alloys are excellent precursors of catalysts for conversion of CO 2 into CH 4 by the reaction with hydrogen at 1 atm. A prototype CO 2 recycling plant to supply clean energy preventing global warming has been built on the roof of our Institute (IMR) in 1996 using these key materials and has been operating successfully.

Ni-based amorphous alloys in the Ni–Zr–Al–Y system that have high glass forming ability and large undercooled liquid regions

Ni-based amorphous alloys containing no metalloids are developed in the alloy system Ni–Zr–Al–Y. A partial replacement of Zr by Y significantly enhances the glass-forming ability and enlarges the undercooled liquid region during continuous heating of amorphous ribbons. A quaternary alloy Ni 55Zr 17Al 11Y 17 exhibits large undercooled liquid region (54 K) implying high glass-forming ability of the alloy. The glass transition and crystallization temperatures of the quaternary alloy obtained in a differential scanning calorimetry are 717 and 771 K, respectively. A fully amorphous rod (Φ1 mm) and a rod (Φ2 mm) having a high volume fraction (∼80%) of the amorphous phase can be prepared by copper mold injection casting.

Glass-forming ability of the Ni–Zr and Ni–Ti systems determined by interatomic potentials

Employing the n-body potentials of the Ni–Zr and Ni–Ti systems, we performed molecular dynamics simulation to study the relative stability of the terminal solid solutions versus the corresponding amorphous states as a function of solute concentrations. The terminal solid solutions transformed into amorphous states spontaneously when the solute concentrations were beyond the maximum allowable values; i.e., the critical solubilities were determined to be 14 at.% Zr in Ni and 25 at.% Ni in Zr for Ni–Zr system and 38 at.% Ti in Ni and 15 at.% Ni in Ti for the Ni–Ti system. The physical implication of the critical concentrations, as well as their correlation with the glass-forming abilities of the Ni–Zr and Ni–Ti systems, is discussed.

Icosahedral Ti–Zr–Ni and hydrogenated Ti–Zr–Ni quasicrystals under high pressure

We present results from the first X-ray diffraction studies under high pressure in icosahedral Ti–Ni–Zr quasicrystals (QCs). The icosahedral Ti53Zr27Ni20 phase and an icosahedral Ti45Zr38Ni17 phase that also contains 0.32 hydrogen atoms for each metal atom were investigated. The icosahedral QC structure is retained up to the highest pressures used. The six-dimensional (6D) lattice parameters were obtained as a function of pressure. The zero-pressure bulk modulus and its pressure derivative were determined for the different samples by fitting the 6D parameter change to a Murnaghan-type equation of state. It is worthwhile mentioning that the hydrogenated sample appears more compressible than the one without hydrogen.

Local atomic structure of icosahedral quasicrystals and 1/1 approximant in the Ti–Ni–Zr alloy system

Extended X-ray absorption fine-structure (EXAFS) experiments were performed above the Ti, Ni and Zr K absorption edges in the icosahedral Ti45Zr38Ni17 phase and in its 1/1 approximant, the Ti50Zr35Ni15 phase. The EXAFS spectra show a strong similarity for both samples, indicating that the local structures around the Ti, Ni and Zr atoms are similar in the icosahedral and 1/1 phases.

Prediction of amorphous phase stability in metallic alloys

The stabilization of the amorphous solid with respect to the high temperature liquid phase is modeled thermodynamically as a second order phase transformation. The model proposed in this work incorporates the thermodynamic description of the high temperature liquid phase, the glass transition temperature, and the maximum entropy of amorphization in an explicit formalism. The predicted heat of formation of the amorphous solid in the Cu–Zr and Ni–Zr systems agrees well with experimentally determined data.

Crystallization Phases of the Zr41Ti14Cu12.5Ni10Be22.5 Alloy After Slow Solidification

A systematic study was carried out on the equilibrium phases after slow solidification of the Zr41Ti14Cu12.5Ni10Be22.5 alloy. The crystalline microstructure of the slowly cooled melt of the alloy shows “polygons” and “plates” embedded in a fine-grained two-component matrix. To analyze the crystal structure of the different components, microdiffraction technique combining convergent beam electron diffraction and conventional selected-area electron diffraction were used. The stoichiometry of these phases was confirmed by field ion microscopy with atom probe and energy-dispersive x-ray analysis in a transmission electron microscope. The polygons were determined to be cubic (a = 1.185 nm) with space group Fm3m (cF116). The plates were found to be tetragonal (a = 0.37 nm, c = 1.137 nm) with space group I4/mmm (tI6). Its composition is (Cu + Ni)(Zr + Ti)2. One phase of the fine-grained two-component matrix was rich in Ti and poor in Be; the other one was rich in Be and poor in Ti. The Ti-rich phase was determined to be hexagonal (a = 0.536 nm, c = 0.888 nm) with space group P63/mmc.

Surface and electrochemical characterization of Ni–Zr intermetallic compounds

In this paper the Ni–Zr system has been considered with the aim of investigating the role of composition and structure of an early–late transition metals system on the electrocatalytic activity, for the hydrogen evolution reaction. As a matter of fact, pure Ni and Zr show low activity, while their intermetallic compounds generate a higher catalytic efficiency. Five alloys, with increasing Ni content starting from Ni 33Zr 67 up to Ni 75Zr 25, have been prepared and characterized. The alloy of composition (Ni 0.55Mn 0.30V 0.10Co 0.05) 2.1Zr has also been considered, in order to investigate the catalytic efficiency related to a Laves structure. The thickness and composition of the surface oxides have been investigated and their effect on reducing the catalytic efficiency of the as-prepared alloys has been discussed. The activity of the samples submitted to a surface activation treatment with hydrofluoric acid, that removes the oxide layer and allows to evidence the properties of the compounds, has been observed to increase significantly. The trend of the electrocatalytic efficiency with the composition of the alloys is discussed considering a synergetic effect between Ni and Zr. The Laves phase appears slightly more active than the binary intermetallic compound.

Structure and properties of Ti–Ni–Zr and Ti–Ni–Hf melt-spun ribbons

Rapidly solidified ribbons of Ti–Ni–Zr and Ti–Ni–Hf shape memory alloys for high-temperature applications have been produced using a planar flow casting technique. Calorimetric and mechanical measurements, as well as transmission electron microscopy (TEM) observations have been performed. The characteristics of martensitic transformation in the ribbons are studied and compared with those of arc-melted bulk samples. The microstructure features and their influence on the martensitic transformation are analyzed.

ChemInform Abstract: Thermodynamics of Liquid Al—Ni—Zr and Al—Cu—Ni—Zr Alloys.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Thermodynamic properties of liquid, undercooled liquid and amorphous Al–Cu–Zr and Al–Cu–Ni–Zr alloys

The heat capacity, C p( T), of undercooled liquid, amorphous and crystalline Al 7.5Cu 27.5Zr 65, the crystallization enthalpy of the amorphous state and the enthalpy of melting of crystalline Al 7.5Cu 27.5Zr 65 were measured using differential scanning calorimetry. An adiabatic calorimeter was used to measure the heat capacity of liquid Al 7.5Cu 27.5Zr 65. The association model was applied to calculate the thermodynamic functions of liquid and undercooled liquid Al–Cu–Zr, Cu–Ni–Zr and Al–Cu–Ni–Zr alloys. The measured C p( T) of liquid Al 7.5Cu 27.5Zr 65 and Al 7.5Cu 17.5Ni 10Zr 65 at the liquidus temperature is larger than that of the undercooled liquid state above the glass transition temperature. The calculated C p( T) curves exhibit a maximum for the undercooled liquid state.

Calorimetric study of liquid and undercooled liquid Al–Ni–Zr alloys

The heat capacities, Cp(T), of the liquid Ni24Zr76 and Al15Ni25Zr60 alloys are measured using an adiabatic calorimeter. An association model was applied to calculate the composition and temperature dependence of the enthalpy of mixing of liquid and undercooled liquid Al–Ni–Zr alloys. The calculated Cp(T) curve of the undercooled liquid Al15Ni25Zr60 alloy has a maximum and Cp(T) at the liquidus temperature is larger than that of the undercooled liquid state above the glass transition temperature.

Calorimetric and structural analysis of the new phase Al33Ni16Zr51 produced by direct synthesis and mechanical alloying

A new phase has been synthesized in the ternary phase diagram Al–Ni–Zr: its nominal composition is Al33Ni16Zr51. For the Al33Ni16Zr51 compound obtained by mixing the three components in suitable proportions, a study has been carried out by direct synthesis (calorimetry) and mechanical alloying in our laboratory. With the first method we know directly the enthalpy of formation of this alloy. For the amorphous alloys prepared by mechanical alloying we can determine the crystallisation enthalpy with the differential scanning calorimetry (DSC) method. So it is possible to determine a fundamental piece of information: the amorphous alloy formation enthalpy.