Kenichi Yamamoto

Remarkable hydrogen storage properties in three-layered Pd/Mg/Pd thin films

We have investigated hydrogen storage and structural properties in nano-composite three-layered Pd(50 nm)/Mg(x nm)/Pd(50 nm) films with x=25, 50, 200, 400 and 800 prepared by an RF-associated magnetron sputtering method. After hydrogenation under a hydrogen gas pressure of 0.1 MPa at 373 K for 24 h, the TDS profiles indicated that the Pd layers contain only 0.15–0.30 mass% hydrogen, whereas the Mg film contains ∼5.0 mass% hydrogen for all the films. The most striking feature is that the temperature corresponding to maximum dehydrogenation rate remarkably shifts to low temperature with increasing the thickness of Mg film, which decreased from 465 K at x=25 nm to 360 K at x=800 nm. These improvements could be understood by the concept of cooperative phenomenon which hydrogen shows in nano-scale composite regions.

Optical transmission of magnesium hydride thin film with characteristic nanostructure

Abstract Optical and structural properties of rare-earth free and pure Mg thin film coated with Pd have been investigated. Optical examination indicates that the fully hydrogenated films are in a color-neutral transparent state. With increasing temperature up to 453 K in air, nontransparent scratch-like parts that correspond to dehydrogenated Mg precipitate in macroscopic scale, and their number gradually increases and grows sharply along specific orientations. The structural characterization indicates that the Mg layer is composed of epitaxial columnar grains whose widths are less than 100 nm with a c -axis preferred orientation for the Mg layer. The columnar grains are restructured to grains with 50–100 nm diameter during hydrogenation–dehydrogenation (optical switching) cycles.

Hydriding properties of the heat-treated MgNi alloys with nanostructural designed multiphase

Abstract The structural and hydriding properties have been investigated for the heat-treated MgNi alloys with nanoscale structure which consists of the Mg 2 Ni and MgNi 2 phases. The alloys were fabricated by mechanical alloying (MA) and heat treatment (HT), the so called MA/HT method. For the as-alloyed amorphous MgNi (a-MgNi) alloy, the maximum hydrogen content reaches 1.72 mass% at 473 K. The hydride, however, gradually decomposes into Mg 2 NiH 4 and MgNi 2 phases during measurement of pressure–composition isotherm. In the case of nanoscaled crystalline Mg 2 Ni (c-Mg 2 Ni)+amorphous MgNi 2 (a-MgNi 2 ) multiphase alloy, the maximum hydrogen content reaches only 0.35 mass% at 473 K. No plateau-like behavior is observed in the desorption process. In the case of nanoscaled c-Mg 2 Ni+crystalline MgNi 2 (c-MgNi 2 ) multiphase alloy, the maximum hydrogen content reaches 1.45 mass% at 473 K. A well-defined plateau region is observed of nearly 0.012 MPa at 473 K in the desorption process. Therefore, it is concluded that the hydriding properties of the nanoscaled MgNi multiphase alloy will be strongly affected by not only the structural properties of the matrix surrounding the c-Mg 2 Ni grains precipitated but also by the accumulation/release of internal stress on the precipitation process.

Influence of elemental diffusion on low temperature formation of MgH2 in TiMn1.3T0.2Mg (T = 3d-transition elements)

Abstract In order to examine the influence of the elemental diffusion from the host compound into the Mg region on low temperature formation of MgH 2 , we have investigated the hydriding properties and the microstructures of the composite materials TiMn 1.3 T 0.2 Mg (T = V, Cr, Mn, Fe, Co, Ni and Cu). MgH 2 is formed at 353 K in all composite materials. Of all the substitutions, the amount of MgH 2 is the largest in the case of the Cu substitution, which originates from the existence of the MgMg 2 Cu eutectic formed by Cu diffusion from the host compound TiMn 1.3 Cu 0.2 into the Mg region during the liquid phase sintering. In addition, the hydrogen capacity of TiMn 1.3 Cu 0.2 Mg (that is TiMn 1.3 Cu 0.1 (Mg+Mg 2 Cu) after the sintering) easily saturates in comparison with TiMn 1.5 (Mg+Mg 2 Cu) without Cu diffusion. It is concluded that Cu diffusion promotes the mobility of hydrogen atoms at the complex interface between the host compound and the Mg region.

FORMATION MECHANISM OF MGH2 AT LOW TEMPERATURES IN TI0.6ZR0.4MN0.8CRCU0.2-(MG+MG2CU)

Abstract We have investigated the hydriding properties and the microstructures of the composite materials Ti 0.6 Zr 0.4 Mn 0.8 CrCu 0.2 -(Mg + Mg 2 Cu) produced by liquid-phase sintering. The hydrogen capacities of the composite materials are larger than that of the host compound (Ti Mn-based compound), indicating that MgH 2 is formed at 353 K. The amount of MgH 2 is proportional to that of the Mg Mg 2 Cu eutectic phases in the composite material. Observations of the microstructure for the etched composite materials using scanning electron microscopy reveal that MgH 2 is formed near the interface between the host compound or Mg 2 Cu and the Mg region. Furthermore, MgH 2 is formed easily in the Mg region far from the host compound. This simply suggests that hydrogen diffuses from the host compound into the Mg region along or through the Mg 2 Cu phase.

Low temperature formation of MgH2 in Ti0.6Zr0.4Mn0.8CrCu0.2/Mg

Abstract We have investigated the hydriding properties and microstructures of the new composite material Ti 0.6 Zr 0.4 Mn 0.8 CrCu 0.2 /Mg which contains elemental Mg as a binder. The hydriding properties of the host compound are improved owing to the Mg reduction effect in the process of heat treatment. In addition, we observed that in the process of heat treatment the Cu in the host compound Ti 0.6 Zr 0.4 Mn 0.8 CrCu 0.2 diffuses into the Mg region and Mg 2 Cu is formed. After hydriding and dehydriding cycles, hydrogen in the host compound diffuses into the Mg region through the Mg 2 Cu phase. Consequently, MgH 2 is formed even at temperatures below 373 K under hydrogen pressures of less than 1 MPa.

Impact Strength Degradation of Adhesive Joints Under Heat and Moisture Environmental Conditions

The effects of environmental degradations on the deformation behavior of an epoxy resin for structural adhesive are experimentally examined using an INSTRON-type material testing machine. The effects of environmental degradations on the shear strength of adhesive joints are also examined using an INSTRON-type material testing machine and a split Hopkinson pressure bar apparatus. The results of quasi-static tensile tests for an epoxy resin for structural adhesive shows that the effect of the resistant to heat degradations tests is small on the deformation behavior, while it seems that the yield stress decreases and the elongation after the rupture increases as the degradations day increases in the resistant to moisture degradation tests. The results of quasi-static and impact shear tests for the adhesive joints shows that the effect of the resistant to heat degradations tests is small on the joint strength, while the shear strength decreases as the degradations day increases at any strain rate in the resistant to moisture degradation tests. In addition, the stress distributions at the adhesive interface of adhesive joints are examined using finite element stress analysis. From the numerical results, it is assumed that the joint strength increases as Young’s modulus of the adhesive decreases and the adhesive thickness is 0.25 mm. For verification of the FEA, the loading responses between the experimental and the numerical results are compared. A fairly good agreement is found between the experimental and the numerical results.Copyright