M. Jurczyk

Metal hydride electrodes prepared by mechanical alloying of ZrV2-type materials

Abstract The structural and electrochemical properties of a range of alloys, including: ZrV2 and ZrV2/Ni (10 wt% Ni), which have the cubic C15 type structure and Zr0.35Ti0.65V0.85Cr0.26Ni1.30, which has the hexagonal C14 type structure, have been investigated. These alloys have been prepared using mechanical alloying (MA) followed by annealing. The amorphous phase forms directly from the starting mixture of the elements, without other phase formation. Heating the MA samples at 1070 K for 1 h resulted in the creation of ordered ZrV2-type alloys. In mechanically alloyed, amorphous ZrV2, ZrV2/Ni materials and Zr0.35Ti0.65V0.85Cr0.26Ni1.30material discharge capacities of 0, 38 and 90 mAhg−1 were obtained, respectively. Annealed nanocrystalline powders have greater capacities than the amorphous parent materials.

Electrode characteristics of nanocrystalline TiFe-type alloys

The effect of 3d transition metals, Ni, Mo, Cr and Co, on the electrochemical properties of nanocrystalline TiFe-type hydrogen storage electrode were studied. The results show that the addition of Ni, Mo, Cr and Co to the alloy was useful in increasing the discharge capacity and cycle life of nanocrystalline TiFe electrode.

The electronic and electrochemical properties of the LaNi5, LaNi4Al and LaNi3AlCo systems

Abstract Nanocrystalline LaNi 5 -type materials have been prepared by mechanical alloying (MA) followed by annealing. The amorphous phase forms directly from the starting mixture of elements, without formation of other phases. The LaNi 5 , LaNi 4 Al and LaNi 3 AlCo systems crystallize in the hexagonal CaCu 5 type structure ( P6/mmm ). The electrochemical properties of these type of materials, in which there has been a partial substitution of Ni by Al and Al–Co, have been investigated and discharge capacity enhancement has been observed. The electronic structure has been studied by the tight binding version of the linear muffin-tin orbital method in the atomic sphere approximation (TB-LMTO ASA). Total energy calculations showed that the Al and Co impurities prefer 3g positions.

Surface analysis of polycrystalline and nanocrystalline LaNi5-type alloys

Abstract The chemical composition and the cleanness of the surface of polycrystalline and nanocrystalline LaNi 5 , LaNi 4.2 Al 0.8 , and LaNi 3 AlCo alloys were studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Results showed that the surface segregation under UHV conditions of lanthanum atoms in the mechanically alloyed nanocrystalline samples is significantly stronger compared to that of polycrystalline powders obtained from arc-melted ingots. On the other hand, the level of oxygen impurities trapped in the mechanically alloyed powder during the processing is practically the same as in the arc-melted ingots. Furthermore, we have estimated an average native oxide layer thickness of nanocrystalline LaNi 4.2 Al 0.8 as ∼5 nm. A strong segregation of the Fe impurities to the surface could be responsible for the observed slightly lower hydrogen storage capacity of the mechanically alloyed nanocrystalline LaNi 4.2 Al 0.8 compared to that of polycrystalline sample.

Mechanically alloyed MmNi5-type materials for metal hydride electrodes

Nanocrystalline MmNi5-type alloys have been prepared by mechanical alloying (MA) followed by annealing. The structural and electrochemical properties of these materials have been investigated at room temperature. The amorphous phase forms directly from the starting mixture of the elements, without other phase formation. Heating the MA powders at 1070 K for 1 h resulted in the formation of the hexagonal CaCu5-type structure. For nanocrystalline MmNi4.2Al0.8material discharge capacities of 207 mAh g−1 were obtained.

Magnetic properties of nanostructured Nd2(Fe,Co,Cr)14B/α-Fe magnets

The effect of intergrain exchange interactions on remanent magnetic polarization and intrinsic coercivity in nanostructured Nd12.6Fe67.8Co11.6Cr2B6/α-Fe magnets, with volume fractions of the soft magnetic phase of 0 and 37.5%, was studied experimentally and numerically. Epoxy bonded magnets were formed and values of 4πMr and JHc of 1.1 T and 760 kA m−1 were obtained, respectively.

Hydrogen storage properties of amorphous and nanocrystalline MmNi4.2Al0.8 alloys

Abstract The hydrogen storage properties of amorphous and nanocrystalline MmNi 4.2 Al 0.8 alloys were studied. These materials were prepared by mechanical alloying (MA). The amorphous phase forms directly from the starting mixture of the elements, without other phase formation. Heating the MA powders at 750°C for 0.5 h resulted in the formation of the hexagonal CaCu 5 -type structure. Gas-phase hydrogen sorption in an amorphous as well as a nanocrystalline MmNi 4.2 Al 0.8 alloy was also investigated. The nanocrystalline powders prepared by MA have a lower hydrogen storage capacity than powders from arc-melted ingots. The difference is mainly due to iron impurities trapped in the mechanically alloyed powders from erosion of the milling media.

Nanocomposite Nd-Fe-B type magnets

Abstract The temperature dependences of magnetic properties for nanocomposite two-phase Nd 12.6 Fe 69.8− x Co 11.6 Zr x B 6 /α-Fe ( x =0 and 0.5) hot pressed magnets, with an excess of α-Fe (10, 20, 37.5 and 50 vol.%), have been studied. These materials have been prepared by high-energy ball-milling and annealing. For example, hot pressing at 830°C of Nd 12.6 Fe 69.3 Co 11.6 Zr 0.5 B 6 /α-Fe, containing 37.5 vol.% α-Fe, resulted in isotropic magnets with J r =0.95 T, J H c =427 kA m −1 and ρ ∼7.59 g cm −3 . The temperature coefficients (from 20 to 140°C) of remanence α ( J r ) and coercivity β ( J H c ) of this magnet are: −0.07% °C −1 , −0.35% °C −1 , which are smaller than that of sintered Nd–Fe–B magnets.

Improved temperature and corrosion behaviour of nanocomposite Nd2(Fe,Co,M)14B/α-Fe magnets

Abstract The characteristics of the magnetic properties nanocomposite Nd 2 (Fe,Co,M) 14 B/α-Fe magnets obtained by high energy ball milling and powder metallurgy routes have been improved by appropriate Al–Cr, Cr, Zr additions. Using a single phase close to the stoichiometric composition, nanocomposite Nd 12.6 (Fe,Co,M) 81.4 B 6 /α-Fe magnets with better temperature stability are produced, due to the disappearance of the Nd-rich grain boundary phase in Nd 2 (Fe,Co) 14 B/α-Fe materials. If the content of the soft magnetic α-Fe phase in Nd 2 (Fe,Co,M) 14 B/α-Fe composities increases, the thermal stability of the coercivity increases, too. For a Nd 12.6 Fe 69.3 Co 11.6 Zr 0.5 B 6 /α-Fe magnet, containing 37.5 vol% α-Fe, the temperature coefficients (from 293 to 413 K) of remanence α ( J r ) and coercivity β ( J H c ) are: −0.07 and −0.35% K −1 , respectively. Nanocomposite magnets appears to be more corrosion resistant than sintered Nd–Fe–B magnets.

Electrochemical behaviour of high-energy ball-milled TiFe alloy

Abstract The effect of high-energy ball-milling (HEBM) on the electrochemical properties of TiFe electrode material has been investigated. The discharge capacity of HEBM TiFe material increased from 0 to 64 mA h g −1 (at 4 mA g −1 discharge current). HEBM is effective for the improvement in activation behaviour of TiFe electrode material, due to the reduction in the particle size and to the creation of new clean surfaces.