Co-B Alloys Research Articles

Selective hydrogenation of unsaturated nitriles to unsaturated amines over amorphous CoB and NiB alloys doped with chromium

Amorphous binary (CoB, NiB) and ternary (CoBCr, NiBCr) alloys prepared by chemical reduction with NaBH 4 were characterized by atomic absorption spectroscopy (AAS), nitrogen physisorption (BET), X-ray diffraction (XRD), temperature programmed desorption (TPD), temperature programmed reduction (TPR), hydrogen chemisorption, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) and the influence of their properties on catalytic performance in the hydrogenation of unsaturated nitriles to unsaturated amines was studied. The hydrogenation over NiB(Cr) catalysts lead to preferential hydrogenation of the C C bond, whereas the hydrogenation over CoB(Cr) catalysts occurred preferentially to the unsaturated amine. Addition of chromium dramatically increased the activity of both NiB and CoB catalysts, due to its effect on the binding energy of adsorbed hydrogen and the adsorption strength of the nitrile functional group. Amorphous cobalt borides treated with sodium hydroxide can hydrogenate unsaturated nitriles to primary unsaturated amines with medium-to-high selectivity without the presence of ammonia.

Study on the preparation and electrochemical characteristics of MgNi–CoB alloys

To improve the electrochemical performance of MgNi hydrogen storage electrode in alkaline solution, the cobalt boride powder which was prepared by mechanical alloying (MA) method was introduced. MgNi–CoB composites were prepared also by MA. The XRD patterns show they have amorphous structures. SEM photographs suggest the particle size of the composite is about 2–3 μm. It is found that the cycle stability is improved by adding small amount of CoB. The relationship of the mass ratio of MgNi:CoB and electrochemical properties was also studied. After 50 charge–discharge cycles, the discharge capacity of the MgNi–CoB composite was 29.65% higher than MgNi alloy. The cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and anticorruption test (potentiodynamic polarization) were also carried out. The results show that the cycle stability and the anticorrosion behavior of MgNi alloy in alkaline solution benefit from CoB doping.

Electroless Deposition of Thin-Film CoB alloys: The Influence of Some Bath Parameters on its Magnetic Behavior

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Evidence for polarised boron in Co-B and Fe-B alloys

By exploiting the tunability of synchrotron radiation in measurements of spin-resolved photoemission it has proved possible to obtain information on the polarisation of the valence electrons of Co-B and Fe-B amorphous magnetic alloys. Both the spin-integrated and spin-resolved energy distribution curves show a marked dependence on photon energy indicating that the p states of boron hybridise with the d states of the transition metals giving rise to mixed states in the binding energy range 1 to 5 eV. The observed polarisation and spin-resolved densities of states imply that in the above restricted energy range there is a net negative polarisation of the boron states.

Influence of small addition of Er on the magnetic properties of amorphous Co80ErxB20−x alloys

The influence of the addition of a few atomic percent of Er on the magnetic properties of amorphous Co-B alloys has been investigated. With increasing Er content (decreasing B content), the magnetic moment of the Co atom increases up to x = 4. The temperature dependence of the magnetization of the samples has been studied. Spin echo nuclear magnetic resonance measurements were carried out at 4.2 K.

The Perminvar effect in binary amorphous CoB alloys

The time-temperature dependent Perminvar effect in amorphous Co/sub 100-x/B/sub x/ (x=17-30 at%) alloys was investigated in the temperature region of 150 to 450 K for stabilization times of up to 12 hours. After stabilization of the demagnetized domain structure the AC susceptibility (permeability) dependent on the driving magnetic field H shows a constant value up to the Perminvar critical field H/sub CR/. The fact that H/sub CR/ in CoB alloys can be higher than coercive field H/sub C/ is rather curious. In the Co/sub 75/B/sub 25/ alloy H/sub CR/ reaches values of 1.5 to 56 A/m dependent on the time and temperature of the stabilization. From the relative difference between two values of H/sub CR/ measured at two times t/sub 1/ and t/sub 2/ a magnetic relaxation spectrum similar to that obtained from reluctivity have been constructed. The kinetics of the H/sub CR/ increase measured at different temperatures indicates that relaxation parameters are equal to those obtained from the magnetic reluctivity aftereffect and that both effects have the same inherent nature. >

Temperature dependence of the magnetization and of the other physical properties of rapidly quenched amorphous CoB alloys

We report here our results on magnetization study of amorphous Co/sub 100-x/B/sub x/ ribbons with 20/spl les/x/spl les/30 at.% B in the temperature range 10 K to 800 K and in applied magnetic field 5/spl middot/10/sup 3/ A/m. The thermomagnetization curve is found to obey the Bloch law, M/sub s/(T)=M/sub s/(0)(1-/spl beta/T/sup 3/2/-/spl gamma/T/sup 5/2/, spin wave stiffness constant and the range of the exchange interaction were calculated from the experimental results. We have found that the B content has a strong effect on stiffness constant D. >

無電解Ｃｏ合金皮膜の磁気特性に及ぼす熱処理の影響

Electroless films of Co-N (boron-free) alloy and three Co-B alloys having boron weight percentages of 1, 3 and 6wt% were prepared, and the effect of film composition and crystal structure on their magnetic properties was studied. It was found that in the Co-N alloy, film structure and magnetic properties were independent of heat treatment, while in the Co-B alloy films, an increase in boron weigt percentage increased the crystallization temperature under heat, treatment (1wt%: 200°C, 3wt%: 300°C, and 6wt%: 400°C) but decreased the coercive force, residual magnetic flux density and saturation magnetic flux. Maximum permeability also decreased with crystallization by heat treatment. It was also verified that the deposition of Co2 B under heat treatment affects the fine structure of the film and produces a significant increase in coercive force and residual magnetic flux density.

Electronic structure and magnetism of amorphous Co1-xBx alloys.

The electronic structure of amorphous ${\mathrm{Co}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{B}}_{\mathit{x}}$ (x=0.17, 0.23, and 0.32) alloys were calculated to clarify their magnetism and electronic specific heat. The electronic structures were calculated self-consistently, both in the spin-polarized and paramagnetic states, by employing the most-localized linear muffin-tin orbital method together with the recursion method. B s and p states split into bonding and antibonding states, and B p states, in particular, hybridize with the tails of Co d states. The exchange splitting of Co d states decreases with increasing B content mainly because of the enhancement of the hybridization. As a result, amorphous Co-B alloys become less ferromagnetic as their B content increases. The calculated magnetic moments per Co atom are proportional to the exchange splitting of Co d states, and decrease with increasing B content. They can be satisfactorily explained by the generalized Stoner model, and agree quantitatively with the experimental data. The density of states at the Fermi level rises with increasing B content, because the highest peak of the minority Co d states shifts toward the Fermi level owing to the decrease in the exchange splitting. This explains a gradual increase in the electronic specific coefficient observed in the experiment.

Structure and magnetic properties of Co(Zr, B)/Cu multilayers

Sputtered Co, CoB and CoZrB alloys in thin-film and multilayer form have been prepared using Cu as a spacer. All of the multilayers show a weak contribution to the magnetic anisotropy from the interface which favors perpendicular magnetic anisotropy and a strong contribution from the bulk which favors in-plane anisotropy. All the multilayers also show a stronger coercivity perpendicular to the film than in the plane of the film. The coercivity perpendicular to the film shows a dependence on magnetic layer thickness with the coercivity decreasing with decreasing thickness and this is discussed in terms of the magnetic domain size which is restricted by the magnetic layer thickness. CoZrB/Cu multilayers show the smallest coercivity of the above multilayer systems.

NMR investigation of 59Co-hyperfine field distributions in amorphous Co-B alloys

The hyperfine field distributions of 59Co in amorphous Co-B were measured at 4.2 K by means of spin-echo NMR in high magnetic fields. The shape of the distribution is nearly Gaussian for the amorphous material, but changes significantly during the onset of crystallization. The mean hyperfine field and the magnetic moment per Co atom decrease with increasing boron concentration. The results can be described assuming that the hyperfine field of a Co atom decreases proportional to the number of nearest B neighbours with a reduction of 3.1 T per B atom. The mean B coordination number deduced from the shape of the hyperfine field distribution is 8.5 ± 0.5 in fair agreement with results from X-ray studies.

Young's modulus in Fe-based amorphous invar alloys

The measurement of Young's modulus of Fe-B, Fe-P, Co-B and (Fe,Co,Ni)77Si10-B13 amorphous alloys has been carried out. Young's modulus measured under the saturation of magnetization Es can be arranged by the molar volume Vmol as Es∞Vmol−n (n≈2). The dependence of Es on Vmol is discussed in connection with both the arrangement of atoms and the Invar property in the amorphous alloys.

Low-temperature specific heats for amorphous Fe-B and Co-B alloys

The low-temperature specific heats for amorphous Fe-B and Co-B alloys have been measured over the temperature range 1.5–6 K. Like other physical properties for both amorphous alloys, the specific heats show marked contrast with each other.

Magnetic moments and bonding in Co-Nb-B alloys

Several new CoNbB amorphous and microcrystalline alloys have been melt quenched and their magnetic moments measured. Comparison is made with cobalt moment suppression in CoB, CoNb, CoV and other CoNbB alloys. Two issues are addressed: 1) the different rates at which Nb and V (same number of valence electrons) suppress the cobalt moment and 2) the combined effect of boron and niobium together in suppressing the cobalt moment. It is suggested that the characteristic moment variations can be accounted for by d-d hybridization in the first case and by p-d and d-d hybridization in the second case.

ＴｉＢ２‐ＴａＢ２基サーメットの機械的性質に及ぼす結合剤の影響

This paper describes, firstly, the effects of the sintering temperature on the mechanical properties of TiB2-5%TaB2-1%CoB, TiB2-5%TaB2-1%NiB, TiB2-5%TaB2-1%FeB and TiB2-5%TaB2-1%Co alloys; secondary, the effects of the amount of binders on those of TiB2-5%TaB2-CoB, TiB2-5%TaB2-NiB and TiB2-5%TaB2-FeB alloys. The results were as follows:1. CoB was the best binder for TiB2-TaB2 based cermets. The TiB2-5%TaB2-1%CoB alloys sintered at the temperature of 1700 to 1900°C for 28 min under 200 kg/mm2 in a vacuum had the transverse rupture strength of 95 kg/mm2, and scarcely had pores.2. In the cases of CoB, NiB and FeB binders, TiB2-TaB2 based cermets had a solid solution between TiB2 and TaB2. However, TiB2-5%TaB2-1%Co sintered body scarcely had the solid solution between TiB2 and TaB2.3. The binder phases of TiB2-5%TaB2-1%CoB alloy and TiB2-5%TaB2-1%FeB alloy may be CoB and FeB, respectively. The binder phases of TiB2-5%TaB2-1%NiB alloy may consist of NiB and monoclinic Ni4B3 and unknown phases. Also TiB2-5%TaB2-1% CoB alloy may have the binder phases of CoB and Co2B.

Magnetic properties of amorphous Co-B alloys

Magnetization measurements on amorphous Co-B alloys have been made in the range of B content from 19 at% to 26 at% to obtain the B concentration dependence of the magnetic moment and the spin wave stiffness constant. The magnetic moment μ per Co atom decreases linearly with the increase of the B concentration. The rate of decrease of the magnetic moment is explained by assuming that the outer electron (2S22p) of metalloid atoms are donated to the d-holes of the transition metals. Information of the exchange stiffness constant D was obtained from the temperature dependence of the magnetization using the spin wave analysis. D vs composition has a linear concentration dependence just like that of μ. From the composition dependence of D and μ, we can estimate the value of D/μ which is a quantity proportional to the average exchange integral and we obtained a result that the D/μ is almost constant against composition.