Electrode characteristics and microstructure of AB(2)-AB(5) composite hydrogen storage alloy formed by ball-milling process

For improving the electrode characteristics of the Zr-based AB(2)-type alloy, a new kind of composite hydrogen Zr0.9Ti0.1(Ni0.50Mn0.35V0.15)(2)(represented as AB(2)) with a rare storage alloy was successfully prepared by ball-milling I earth-based AB(5)-type alloy (represented as AB(5)) which worked as a surface modifier. Effects of ball-milling on the electrode characteristics and microstructure of Zr0.9Ti0.1(Ni0.50Mn0.35V0.15)(2) alloy and mixtures of AB(2) with AB(5) alloy were investigated. After milling the mixed AB(2) and AB(5) powders (9: 1 in mass ratio) for 10min, XRD and SEM analysis showed that AB(2) and AB(5) maintained their original crystalline states, respectively, some AB(5) particles were adhered onto the surface of AB(2), and some fresh surfaces were formed. It was found that the activation cycles of AB(2)-AB(5) composite alloy was shortened from 14 to 7 and the maximum discharge capacity was increased from 330mAh . g(-1) to 347mAh . g(-1) as compared with AB(2) alloy. The discharge rate capability of AB(2) alloy was also improved by ball milling AB(2) with AB(5) alloy process. The combined effect of ball-milling and mixing with AB(5) alloy is superior to that of sole treatment. It was believed that AB(5) alloy works not only as a regular hydrogen storage alloy, but also as a surface modifier to catalyze the hydriding/ dehydriding process of AB(2) alloy.

Crystallographic and electrochemical properties of ball-milled quasicrystalline Ti45Zr35Ni17Cu3 alloy with 20 mass% Ni

Icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy powder was ball-milled with 20 mass% Ni, and the effect of the ball-milling time (t) on crystallographic and electrochemical characteristics were investigated. The amounts of icosahedral quasicrystalline and Ni phases decreased when ball-milling time increased from 30 to 180 min. The powder consisted of amorphous and (Ni and Ti) phases after 360 min of ball-milling. The maximum discharge capacity of the powder electrodes first increased from 89 (t = 0 min) to 192 mAh g(-1) (t = 180 min), and then decreased to 138 mAh g(-1) (t = 360 min). The high-rate dischargeability and the discharge capacity after 15 cycles increased with increasing ball-milling time.

Mechanical alloying of Fe-Mn and Fe-Mn-Si

The ball milling of Fe-24Mn and Fe-24Mn-6Si mixed powders has been performed by the high energy ball milling technique. By employing X-ray diffraction and Mossbauer measurements, the composition evolution during the milling process has been investigated. The results indicate the formation of paramagnetic Fe-Mn or Fe-Mn-Si alloys with a metastable fee phase as final products, which imply that the Fe and Mn proceed a co-diffusion mechanism through the surface of fragmented powders. The thermal stability and composition evolution of the as-milled alloys were discussed comparing with the bulk alloy. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

Hard magnetic properties of Sm3Fe26.7VxN4 and Sm3Fe26.7VxCy

Sm3Fe26.7V2.3N4 nitrides and Sm3Fe26.7V2.3Cy carbides have been synthesized by gas-solid phase reaction. Their hard magnetic properties have been investigated by means of additional ball-milling at room temperature. The saturation magnetization of Sm3Fe26.7V2.3N4 almost decreases linearly with increasing ball-milling time t, but that of Sm3Fe26.7V2.3Cy has no obvious change when the ball-milling time increases from t = 1 to 28 h. As a preliminary result, the maximum remanence B-r of 0.94 and 0.88 T, the coercivity mu(0i)H(C) of 0.75 and 0.25 T, and the maximum energy product (BH) of 108.5 and 39.1 kJ/m(3) for their resin-bonded permanent magnets are achieved, respectively, by ball-milling at 293 K. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Thermomagnetic behavior and first order magnetization processes of Sm3Fe29-xTx and Sm3Fe29-xTxN4 (T = V and Cr)

A systematic investigation of structure and intrinsic magnetic properties of the compounds Sm3Fe29-xTx (T = V and Cr) and their nitrides has been performed. Nitrogenation resulted in remarkable improvements in the saturation magnetization and anisotropy fields at 4.2 K and room temperature. First order magnetization processes are observed at around 5.7 T for Sm3Fe26.7V2.3 and around 2.8 T for Sm3Fe24.0Cr5.0 and Sm3Fe24.0Cr5.0N4, respectively. The spin reorientation of the easy magnetization direction of Sm3Fe26.7V2.3 is observed at around 230 K. As a preliminary result, the maximum remanence B-r of 0.94 T, the coercivity mu(0)H(C) of 0.75 T, and the maximum energy product (BH) of 108.5 kJ/m(3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

Crystallographic and magnetic properties of R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Nitrogenation leads to a relative volume expansion of about 6%. The lattice constants and unit cell volume decrease with increasing rare-earth atomic number from Nd to Dy, reflecting the lanthanide contraction. On average, the Curie temperature increases due to the nitrogenation to about 200 K compared with its parent compound. Generally speaking, nitrogenation also results in a remarkable improvement of the saturation magnetization and anisotropy fields at 4.2 K and room temperature for R3Fe29-xVxN4 compared with their parent compounds. The transition temperature indicates the spin reorientations of R3Fe29-xVxN4 for R = Nd and Sm are at around 375 and 370 K which are higher than that of R3Fe29-xVx, for R = Nd and Sm 145 and 140 K, respectively. The magnetohistory effects of R3Fe29-xVxN4 (R = Ce, Nd, and Sm) are observed in low fields of 0.04 T. After nitrogenation the easy magnetization direction of Sm3Fe26.7V2.3 is changed from an easy-cone structure to the b-axis. As a preliminary result, a maximum remanence B-r of 0.94 T, an intrinsic coercivity mu(0)H(C) of 0.75 T, and a maximum energy product (B H)(max) of 108.5 kJ m(-3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

Synthesis, reactive mechanism and thermal stability of W1-xAlxC (x=0.33, 0.5, 0.75, 0.86) nanocrystalline

W1-xAlxC (x = 0.33, 0.50, 0.75, 0.86) solid solutions have been synthesized directly by ball-milling tungsten powder, aluminum powder and activated carbon. The structural development of W0.5Al0.5C phase with the milling times up to 160 h has been followed using X-ray diffraction. X-ray photoelectron spectra demonstrate that Al atom takes the place of W. High temperature annealing experiment reveals that Al is stable in hexagonal structure to 1873 K. Transmission electron microscopy image shows that the grain size of the prepared powders is about 5 nm.

Preparation of W-Al alloys by mechanical alloying

W1-xAlx (x=0-0.86) alloys were synthesized by mechanically alloying the pure metal powder mixtures at designated compositions by conventional high-energy ball milling. The W-Al alloys were stable under high pressure and high temperature. The alloys were lighter than W. The hardness and oxidation resistance of the alloys was greatly improved compared to both W and Al. (C) 2002 Elsevier Science B.V. All rights reserved.

Formation of epsilon-FeXN/BN magnetic nanocomposite and its thermodynamic and kinetic analyses

A nanocomposite of nanometer-sized magnetic granular epsilon-FeXN embedded in a nonmagnetic amorphous boron nitride matrix was prepared by ball milling mixture of alpha-Fe and hexagonal boron nitride in argon atmosphere. The grain size of the epsilon-FeXN alloy was about 10-20 nm. The nitrogen concentration in the epsilon-FeXN alloy increases with extending milling time. Both thermodynamic calculation and the present experiment show that iron and nitrogen atoms have higher alloying driving force than iron and boron atoms. Analyses of thermodynamics and kinetics about formation of the epsilon-FeXN alloy suggested that the formation of the epsilon-FeXN alloy is related to amorphization of the hexagonal boron nitride and refinement of the alpha-Fe. II was found from the present experiment that a critical grain size of the alpha-Fe reacting with nitrogen in the amorphous boron nitride is about 8 nm.

Crystallographic and electrochemical characteristics of TiZrNiCu quasicrystal ball-milled with La0.9Zr0.1Ni4.5Al0.5 alloy

Icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy was ball-milled with 30 mass% La0.9Zr0.1Ni4.5Al0.5 alloy (LaNi5 phase), the effect of the milling time on crystallographic and electrochemical characteristics of the alloy powder was investigated. The amount of amorphous phase increased with increasing milling time from 60 to 360 min, and the LaNi5 phase cannot be observed when milling time was 240 min or more. The maximum discharge capacity and high-rate dischargeability of milled alloy electrodes were obviously higher than those of the alloy electrode before milling. The cycling capacity retention rate after 40 cycles increased from 52.8% (t = 60 min) to 62.9% (t = 360 min).

Magnetohydrodynamics equilibrium of a self-confined elliptic plasma ball

A variational principle is applied to the problem of magnetohydrodynamics (MHD) equilibrium of a self-contained elliptical plasma ball, such as elliptical ball lightning. The principle is appropriate for an approximate solution of partial differential equations with arbitrary boundary shape. The method reduces the partial differential equation to a series of ordinary differential equations and is especially valuable for treating boundaries with nonlinear deformations. The calculations conclude that the pressure distribution and the poloidal current are more uniform in an oblate self-confined plasma ball than that of an elongated plasma ball. The ellipticity of the plasma ball is obviously restricted by its internal pressure, magnetic field, and ambient pressure. Qualitative evidence is presented for the absence of sighting of elongated ball lightning.

Magnetohydrodynamic equilibrium of plasma ball lightning

Thin foil observations using transmission electron microscopy reveal that the density of dislocations within the band is extremely high and the tangled arrangement of dislocations tends to align along the length of the shear band. The grains in the band were also elongated along the shear band and clearly exhibited a crystallographic nature.

Structural evolution of mechanically alloyed nanocrystalline FeAl intermetallics

Nanostructured FeAl intermetallics were prepared directly by mechanical alloying (MA) in a high-energy planetary ball-mill. The phase transformations and structural changes occurring in the studied material during mechanical alloying were investigated by X-ray diffraction (XRD). Transmission electron microscopy (TEM) was employed to examine the morphology of the powders. Thermal behavior of the milled powders was examined by differential scanning calorimetry (DSC). Disordered Fe(Al) solid solution was formed at the early stage. After 30 h of milling, Fe(Al) solid solution transformed into an ordered FeAl phase. The average crystallite size reduction down to about 12 nm was accompanied by the introduction of the average lattice strain up to 1.7%. The TEM picture showed that the size of milled powders was less than 30 nm. (c) 2007 Elsevier B.V. All rights reserved.