Yoshihito Matsumura

Hydrogen absorption of nanocrystalline palladium

Abstract Thermodynamic properties of hydrogen in nanocrystalline Pd (Pd-n) were determined by pressure–composition ( P–C ) isotherms. Pd-n was prepared by repeated compression–extrusion cycles in the die cavity of a high speed forging apparatus. It was found that Pd obtained was composed of nano-sized Pd grains, i.e. ∼10 nm, which were strained in 〈111〉 and 〈100〉 by 1.3 and 2.4%, respectively. From P–C isotherm measurements over the temperatures from 298 to 373 K, it was found that the hydrogen solubility in the α phase region for Pd-n was significantly larger than that for coarser grained Pd. On the other hand, Pd-n showed lower plateau pressures than coarser grained Pd. In addition to the above, the maximum hydrogen solubility of Pd-n was almost 50% lower than that for coarser grained Pd. The differences in the hydrogen solubility and plateau pressure between Pd-n and coarser grained Pd will be discussed under the consideration of the structure of nano-sized Pd grains. The drastic reduction in the maximum hydrogen solubility for Pd-n could be related to the viewpoint of strain of the octahedron in f.c.c. Pd.

Progress in thin films of giant magnetostrictive alloys

Abstract This paper reviews recent progress in the study of thin films of giant magnetostrictive RFe2 (R: rare earths) compounds with the C15 Laves phase. Results of magnetostrictive property of the compound films formed by vacuum flash evaporation, ion plating, electron beam evaporation, ion beam sputter, and DC-magnetron sputter are described. Magnetostrictive property of a new giant magnetostrictive Fe–Pd alloy film is compared with those of the RFe2 films.

Surface acoustic waves on thin films of giant magnetostrictive alloys

Abstract Thin films of giant magnetostrictive (Tb,Dy)Fe 2 alloys were prepared and the magnetostriction and the velocity of a surface acoustic wave (SAW) were measured. This velocity depends on the mechanical constants of the material which can be changed under the influence of an applied magnetic field. The large magnetostrictions of the (Tb,Dy)Fe 2 materials can therefore be used for magnetically tunable SAW devices such as delay lines, signal converters and filters. Tb χ Dy 1− χ Fe 2 films of different concentrations were sputtered on piezoelectric LiNbO 3 substrates equipped with SAW-exciting interdigital electrodes. The influences of film composition, film thickness and magnetic field on SAW velocity and magnetostriction were investigated.

Preparation of films of (Tb,Dy)Fe2 giant magnetostrictive alloy by ion beam sputtering process and their characterization

Abstract Giant magnetostrictive (Tb,Dy)Fe2 films were prepared using an ion beam sputtering (IBS) process. In spite of an amorphous like structure of the films analyzed, significantly larger values of magnetization and magnetostriction were obtained in contrast with those of amorphous like films prepared by a flash evaporation process. The effect was caused by Ar in the films that was included during the IBS deposition process.

EFFECT OF KOH PRETREATMENT ON THE HYDRIDING PROPERTIES OF LANI2.5CO2.5 ALLOY

LaNi2.5Co2.5 hydrogen storage alloy was investigated by both electrochemical processes and gas phase reactions. A comparison of equilibrium characteristics and reaction kinetics obtained by both processes showed a good agreement. Pretreatment with KOH yielded faster reaction kinetics; on the other hand no effect on the equilibrium properties was found. From results of Auger electron spectroscopy, the phenomena were caused by the surface modification by the KOH pretreatment. The equilibrium and kinetic characteristics both in the gas phase and in the electrochemical reactions are discussed.

Photoinduced hydrophilicity of TiO2 thin film modified by Ar ion beam irradiation

Abstract TiO 2 are applied widely as photocatalytic materials. In this study, we investigated preparation of TiO 2 thin film with photoinduced hydrophilicity under weak UV light in indoor environment. TiO 2 films were prepared by rf magnetron sputtering process in an atmosphere of pure oxygen. Ar ion beam irradiation treatment of TiO 2 film was carried out using a plasma cathode ion source. O–H absorption peaks as the wavenumber regions 3300–3400 cm −1 increased with increasing of Ar ion beam irradiation time. The improvement of photoinduced hydrophilicity of the film was independent of surface area of TiO 2 film. In XPS measurements, O 1s peaks of Ar ion beam irradiated TiO 2 films shifted 0.4–0.6 eV to higher binding energy side. Oxygen vacancies were induced in surface of the film by Ar ion beam irradiation. The TiO 2 films showed photoinduced hydrophilicity under weak UV light such as indoor environment.

Effects of Oxidation and Hydroxidation on the Activations of LaNi5-xMx(M = Al,Mn,Co) Alloys by Hydrogen Gas*

The partial replacement of Ni with Al, Co and Mn in the LaNi5 based alloys reduces the incubation period of the initial activation and the reactivation of the oxidized alloy. The alloys containing Al exhibit increasing reactivities with H2 even in the progress of oxidation. Co in the alloys seems to stabilize the surface oxides-metal interfaces, resulting in the inhibition of pulverization. Prolonged oxidation of the alloys containing Mn yielded the markedly reduced the incubation time for activation. The pretreatment of the alloys in a KOH solution was found effective to accelerate the activation, and for which the excess concentrations of La and/or Ni in the surfaces seem to be responsible.

Reaction kinetics of N2 absorption by Sm2Fe17

Abstract The kinetics of N 2 absorption by Sm 2 Fe 17 were investigated using volumetric and gravimetric measurements under ultrahigh vacuum and high N 2 pressures. The kinetic results obtained suggest that the rate-controlling step in the N 2 absorption by Sm 2 Fe 17 changes from N 2 dissociation on the alloy surface during the initial stage to N diffusion in the bulk as the reaction proceeds. The activation energy for the diffusion was found to be in the range 100–163 kJ (mol N 2 ) −1 . Pretreatment of the alloy by H 2 gas decreases the initial rate, but increases the maximum amount of N absorbed in the equilibrium state.

Preparation and characterization of (Tb,Dy)Fe2 giant magnetostrictive thin films for surface acoustic wave devices

Abstract Thin films of giant magnetostrictive (Tb,Dy)Fe 2 alloys were prepared by three different deposition processes: ion beam sputtering, ion plating and flash evaporation. The flash evaporation process readily yields films with little deviation in composition from that of the source materials, while the ion-beam-sputtering process results in a composition deviation which depends on the substrate location. The ion-plating process yields a high rate of deposition but leads to a marked composition variation between source and film materials. The deposition conditions, mainly the background pressure, also have an important influence on the film characteristics.

A Samarium-Iron Nitride Magnet Fabricated by Shock-Compaction Technique

A samarium-iron nitride Sm2Fe17N3 powder was shock-consolidated by using a propellant gun with metal-plate impactor system. Disk-like magnets were consolidated under each experimental condition. At an optimum condition in this study, apparent density of shock-compacted Sm2Fe17Nx magnets was 97% of solid density, and X-ray diffraction patterns of these magnets showed no appearance of the decomposition of rhombohedral Sm2Fe17Nx structure. The highest value of the maximum energy product obtained so far was 10.5 MGOe. Microstructural analyses suggested the possibility of improving magnetic properties of the magnets.