Ni Ribbons Research Articles

Compositions, magnetic properties and GMR performances of melt-spun Cu–Co–Ni ribbons

The effect of composition on the giant magnetoresistance (GMR) of melt-spun Cu–Co–Ni ribbons is investigated in this paper. The relations between GMR ratios and microstructure of the ribbons are analyzed by magnetic measurements and microstructure characterization. The results indicate that when Co and Ni are at a suitable percentage, melt-spun Cu–Co–Ni ribbons give a larger GMR ratio (8.6%, H=1.355 T) than that of Cu–Co ribbons without Ni addition. But it is noticed that if the Co and Ni percentage is not within the suitable range, the GMR ratios are smaller than that of Cu–Co ribbons. The reason is that the Ni addition restrains the liquid-phase separation of Cu–Co alloys during melt-spinning process which results in a higher supersaturation of Co(Ni) in the Cu matrix and thereafter increases the densities of fine magnetic Co-rich precipitations during annealing process.

Mechanically induced thermal changes in amorphous metallic melt-spun alloys

Melt-spun metallic Fe–Ni ribbon glasses were subjected to high-energy ball milling under different milling conditions. Thermal changes of the glassy sample during milling were characterized by means of differential scanning calorimetry (DSC) and thermogravimetry (TG). On increasing the ball to powder ball ratio or the milling intensity, the milling time necessary to obtain alloys in powdered form decreases. Furthermore, the thermal stability of the crystalline phase also decreases. A commitment between the desired powder morphology and the maintenance of the amorphous state is necessary to choose the best milling conditions. Significant oxidation was detected above the crystallization onset temperature. Furthermore, the material remains basically amorphous with an incipient crystalline phase in the more energetic conditions.

Effects of rare earth additions on GMR of melt-spun Cu–Co–Ni ribbons

The effects of Ni and rare earth (La, Ce, Nd, Dy, Tb) co-addition on GMR of the melt-spun Cu–Co alloys are investigated. The results indicate that Ni addition can increase the GMR of the melt-spun Cu–Co ribbons. The reasons are that Ni addition can restrain the liquid phase separation occurring at high temperature and increase the density of the fine magnetic Co-rich precipitates during the annealing process. Light rare earth, such as Ce and La, can further enhance GMR of the melt-spun Cu–Co–Ni ribbons. Among these elements, Ce is the most effective. However, heavy rare earth additions result in a GMR decline of the melt-spun Cu–Co–Ni ribbons. It is discovered that there exists an optimal addition quantity for Ce. Excessive Ce addition could result in a GMR decline as well. The reasons for the GMR improvement of Re addition are: role of purifying melt, promoting precipitates process and enhancing the magnetic susceptibility of the fine Co-rich precipitates.

The alloying effect of Ni on the corrosion behavior of melt-spun Mg–Ni ribbons

Four binary Mg–Ni ribbons with Ni content up to 18.3 atm% were rapidly solidified by melt-spinning. The microstructure changed from α-Mg plus intermetallic Mg 2Ni to a fully amorphous structure with increasing Ni content. Both the hydrogen evolution test and anodic potentiodynamic polarization revealed that the corrosion resistance of the amorphous ribbons was superior to that of ribbons with α-Mg plus intermetallic structure in 0.01 M NaCl solution (adjusted to pH 12 by NaOH). The reduced dissolution rate is attributed to the formation of a fully amorphous structure so that no intermetallic Mg 2Ni is present and all Ni atoms are embedded in the Mg matrix. The enhanced passivity is due to the incorporation of NiO in the surface of the passive film as a consequence of its p-type semiconducting properties, thus preventing the entry of aggressive CO 3 2− and Cl − ions into the passive film.

Conduction Mechanisms in Some Icosahedral and Amorphous Phases

Quasicrystalline icosahedral and amorphous phases prepared as thin films or bulk samples in the systems Al–Pd–Re, Al–Cu–Fe and Ti–Zr–Ni, have been investigated with respect to their temperature dependence of conductance and thermopower, in the range between 10 and 300 K. Various conduction mechanisms yield different exponent values in the power-law temperature dependence of conductance, Tζ. A semi-metal behaviour ζ ≌ 1.5) is found in the amorphous phase and in the disordered icosahedral Al–Pd–Re film and Ti–Zr–Ni ribbons, as well as in icosahedral Al–Cu–Fe films. Lower ζ values found in the quasi-perfect icosahedral Al–Pd–Re bulk sample and in two of the icosahedral Al–Cu–Fe films suggest that electron localization in a hierarchy of clusters is the main conduction mechanism in these samples. The thermopower data support the existence of a pseudo-gap at the Fermi level and suggest a similar short-range order in both amorphous and icosahedral phases. The special sensitivity of the thermopower to the DOS details at EF is responsible for the strong variation of its magnitude with the degree of icosahedral order.

Properties of rapidly solidified Al–12.5 Si–1Ni alloy

Rapidly solidified Al–12.5 Si–1 Ni ribbons were prepared by melt spinning. The Si solid solubility was extended to high values as deduced from X-ray diffraction and TEM. This high solubility of Si was found to have significant effects on the various properties of this alloy. High values of electric resistivity was observed which was about four times the fully annealed values. Furthermore rapid solidification improved the tensile strength and the toughness of this alloy as compared with its classically solidified counter part. The relaxation kinetics was followed by isothermal resistivity measurements. The relaxation follows an equation which has the Johnson-Mehl-Avrami (JMA) form. No metastable phase was observed.

Effects of composition on microstructures of rapidly solidified Ni–Al alloys

Microstructures of melt-spun Ni–Al alloys with compositions from 61–85 at% Ni were studied by means of transmission electron microscopy, X-ray diffraction analysis and optical microscopy. The microstructures of as-quenched ribbons exposed to cooling rates of the order of 106 K s-1 reflect the transition from primary β-NiAl to γ-Ni solidification with increasing nickel content. In 70 at% Ni alloy ribbons, martensitic NiAl grains were detected near the wheel-side surface contrasting with anomalous and lamellar eutectic microstructure in the top part. Directly ordered Ni3Al grains with single (or large) antiphase domains (APDs) and a minor eutectic fraction were observed in 75 at% Ni alloy ribbons. Samples containing 80 at% Ni exhibit mainly single-phase Ni3Al grains with 10–20 nm sized APDs indicating sequential ordering. Weak L12 ordering was even detected in 85 at% Ni ribbons which displayed ordered antiphase zones of 1 nm size. Disordered γ-(Ni) films on grain boundaries can be discounted for 80 at% Ni ribbons, but occurred near the top of 85 at% Ni samples. The results are explained in terms of the reassessed Ni–Al phase diagram employing recent corrections near to the Ni3Al composition and new results on phase formation in undercooled Ni–Al melts. © 1998 Kluwer Academic Publishers

Magnetic properties of melt-quenched Ni-rich amorphous and bcc Zr–Ni alloys (abstract)

It has been demonstrated recently that the structure of melt-quenched Zr–Ni ribbons in the vicinity of 90 at. % Ni was strongly dependent on the quenching rate: at the highest quenching rate, the alloys Zr10Ni90 and Zr9Ni91 could be prepared with an amorphous structure whereas at lower quenching rates the Zr9Ni91 alloy was prepared as a solid solution of Zr in Ni with a body-centered cubic (bcc) structure. In a preliminary measurement we have established a Curie point (Tc) of 66 K for the a-Zr9Ni91 ribbon which was much smaller than the value Tc=235 K reported for an a-Zr10Ni90 ribbon. This discrepancy has motivated us to perform the present detailed magnetization study in the temperature range 5 to 300 K. It was also of interest to compare the Curie point of the amorphous and bcc phase with the same chemical composition. The real component χ′ of the AC susceptibility as well as the magnetization isotherms up to H=18.5 kOe have been investigated. The measurements of χ′ yielded T=41, 66, and 70 K for a-Zr10Ni90, a-Zr9Ni91, and bcc-Zr9Ni91 ribbons, respectively. The para-ferromagnetic transitions were found to be fairly sharp although in some of these samples several transitions differing by a few degrees only could be observed. In some of the samples, however, very faint magnetic transitions indicated by a small broad peak could also be detected around 250 K. This feature can be attributed to some residual phases of either an unknown Zr–Ni intermetallic compound or of Ni(Zr) solid solution precipitates. The close coincidence of this peak with the Curie temperature reported by Kaul suggests that his value (Tc=235 K) cannot be representative of the amorphous Zr–Ni matrix but it rather may originate from ferromagnetic precipitates. The magnetization isotherms for the amorphous and bcc-Zr9Ni91 alloy indicated the development of a significant magnetization around the Tc values deduced from χ′. The saturation magnetization at the lowest temperature amounted to about 7 emu/g in both structural modifications. This value is reasonable in view of the reduction of Tc with respect to pure fcc-Ni. The present Tc data indicate that the critical concentration for the onset of magnetic ordering in the Zr–Ni system should be slightly below 90 at. % Ni. It can be concluded from this study that the magnetic behavior of Zr–Ni alloys at about 90 at. % Ni content is characteristic for very weak itinerant ferromagnets and the results will be analyzed in this framework with the help of Arrott plots.

Fiber optic magnetostrictive transducers for magnetic field sensing

A number of fiber optic magnetostrictive transducers were fabricated using various metallic glass ribbons made of Co₇₀Fe₁₀B₂₀, Co₇₆Fe₄B₂₀, Co₈₀B₂₀, Ni, Fe₇₉B₁₆Si₅, and Fe₄₀Ni₃₈Mo₄B₁₈ and were characterized by a typical optical fiber Mach-Zehnder interferometer constructed by splicing the fiber transducers to the single-mode-fiber sensing arm. The ac magnetostrictive responses for the metallic glasses measured with the fiber optic sensing system show that the dc-bias field (<i>H_p</i>) for the maximum response with a Co₇₀Fe₁₀B₂₀ ribbon is ~ 0.97 Oe, that with a Ni ribbon is 23 Oe, and with a Fe₇₉B₁₆Si₅ ribbon is 5.7 Oe. A magnetostriction function describing the magnetostrictive response of the transducer was also empirically found. The measured effective magnetostrictive parameters and saturation magnetostrictions are 1.3 x 10^-7/Oe² to 7 x 10^-7/Oe² and -4.6 x 10^-6 to 5.7 x 10^-6, respectively. The optical fiber sensors exhibit minimum detectable fields <i>H</i>_min of the order of between 10^-5 Oe(rms)/√Hz and 10^-7 Oe(rms)/√Hz above 1 kHz at their respective dc-bias fields <i>H_p</i>. The <i>H</i>_min can be much further improved by reducing the level of noises that limit the phase resolution to ~ 10^-4 rad/√Hz in the interferometer.

Electron microscopy and X-ray diffraction studies of rapidly quenched ZrNi and HfNi ribbons with about 90 at.% Ni

The structure of melt-spun ribbons of the alloys Zr9Ni91, Zr10Ni90 and Hf11Ni89 was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ribbons of the Zr9Ni91 and Zr10Ni90 alloys prepared at a high cooling rate (ribbon thickness d=11 μm) were characterized by an amorphous matrix with a few per cent of quenched-in crystallites. The ribbon of the Hf11Ni89 alloy prepared with the same thickness (i.e. at the same cooling rate) exhibited a nanocrystalline grain structure of the HfNi5 phase. Thicker ribbons of the Zr9Ni91 alloy (d=17–22 μm), for which the quench rate was correspondingly lower, were obtained as a b.c.c. Ni(Zr) solid solution phase with a grain size of nearly 1 μm. A high resolution (HR) TEM study of one of the Zr9Ni91 crystalline ribbons revealed a fine structure of the interior of the crystallites which can be attributed to an ordering on the Zr sublattice over distances of several nanometres within the b.c.c. grains.

Fabrication and tensile properties of rapidly solidified Cu-10wt.%Ni alloy

Cu-10wt.%Ni ribbons were produced by melt spinning and cut into small particles with a blade cutter mill. The powders were then hot consolidated to full density by hot pressing followed by hot extrusion. Tensile properties of the resulting pieces were measured. Cu-10wt.%Ni cast ingots were also hot extruded and mechanically tested to compare with the rapidly solidified alloy and to evaluate the possible benefits brought by the rapid solidification process.

Relationship between the catalytic properties and surface composition of a polycrystalline Fe—Ni ribbon

A polycrystalline Fe-Ni ribbon exhibits catalytic properties different from those expected in 1H 2- 2H 2 equilibration, benzene hydrogenation and 1H- 2H exchange, hydrogenation of carbon monoxide and oxidation of propene. This behaviour is explained by the composition of the surface layers, which undergo drastic changes during pretreatment and catalytic reactions.

Thermopower Study of Local Hydrogen Content in Rapidly Quenched Zr —Ni Ribbons*

Thermopower Study of Local Hydrogen Content in Rapidly Quenched Zr —Ni Ribbons*

Comparison of microstructures and solidification behaviour of melt-spun CuNi ribbons and bulk undercooled CuNi alloys

Surface morphologies and microstructures of melt-spun CuNi ribbons cast at wheel-surface velocities ranging from 5 to 40 m s −1 have been compared with bulk undercooled CuNi alloys. The application of a container-free electromagnetic levitation technique enables such investigations over a wide range of undercooling up to ΔT = 265 K. The microstructure formation will be discussed for both methods of solidification with respect to undercooling, recalescence as well as nucleation, recrystallization and changes in growth-front morphologies. Comparison of the observed microstructures and surface morphologies indicate that melt-spun ribbons crystallize only after achieving a large degree of undercooling and crystal growth rates can be assumed to be much faster than estimated from simple heat flux balances.

Surface characterization of amorphous Ni ribbons

Surface characterization of amorphous Ni ribbons

Real-Space Observation of the 2×1 Structure of Chemisorbed Oxygen on Ni(110) by Scanning Tunneling Microscopy

We present the first real-space observation of well defined single adsorbates: oxygen atoms forming the 2\ifmmode\times\else\texttimes\fi{}1 structure on Ni(110). The sawtooth model is consistent with all experimental results. The structure consists of domains, separated in the $[1\overline{1}0]$ direction by uncovered Ni ribbons 1\textonehalf{} surface unit cells wide. Such domain walls appear responsible for the $\ensuremath{\theta}=0.35$ coverage of the saturated chemisorption structure.

Highly Stable Metal Oxide Thermistors

A highly stable structure of metal oxide thermistors available for satellite telecommunication systems has been developed. The stresses which occurred at electrode joining points were analyzed. The stresses were greatly reduced by using flexible Ni ribbons as lead wires and by minimizing solder volume used to join Ni ribbons. The experimental results agreed well with the analytical results. In consequence, resistance drifts under satellite conditions were decreased to sufficiently small values, 0.3 percent for one year and 1.0 percent four five years.

Kinetics of carbon monoxide hydrogenation on a polycrystalline nickel ribbon catalyst

Ultrahigh vacuum procedures have been employed to highly purify reactant gases and to prepare a clean Ni ribbon for use as a methanation catalyst in a static reactor. The kinetics of CO-hydrogenation to produce CH 4 have been studied over a Ni catalyst temperature range of 600–740 K using 4 H 2 : 1 CO at a total pressure of 120 Torr. Under thse conditions, the reaction was found to be highly selective (less than 1% higher hydrocarbons produced). Small amounts of CO 2 were also produced continously during methanation. The initial rate of CH 4 production was used to estimate the activation energy (66 kJ mole -1 in this temperature range. Satisfactory agreement was observed between our rate measurements (turnover numbers) made on a 10 cm 2 Ni ribbon and other kinetics studies made on supported Ni catalysts of much larger surface area. A comparison of data from different laboratories suggests that the methanation activation energy falls as the Ni temperature is raised, and that raising the reaction temperature also produces enhanced selectivity towards CH 4 production.