A. Kamegawa

Protium absorption properties of Ti–V–Cr–Mn alloys with a b.c.c. structure

The protium absorption–desorption properties of Ti–V–Cr–Mn alloys were studied by varying the contents of Mn, Ti and V in the alloys. It was found that Mn addition of <10 at% was effective in improving the slope of the plateau region without any reduction of the protium absorption–desorption capacity. For Ti–V–Cr–Mn alloys, the α-Ti phase, which does not contribute to the protium storage capacity, appeared along grain boundaries during heat treatment. The formation of the α-Ti phase was found to be suppressed by reducing the Ti content and increasing the V content. By inhibiting the appearance of the α-Ti phase along the grain boundary, the protium absorption–desorption capacity of Ti–xV–Cr–Mn (x=45, 55; Ti/Cr/Mn=24:31:10) heat-treated alloys exhibited 2.7 mass% H, the highest value reported so far.

Role of intermetallics in hydrogen storage materials

Abstract Many intermetallics such as AB5, AB2, A2B show the excellent hydrogen absorbing properties. Specially, LaNi5 compound has been extensively studied for the negative electrode of Ni–MH batteries. In todays use for the negative electrode of Ni–MH batteries, alloys must be single phase. But it is well known that it is difficult to make non-stoichiometric LaNi5 alloys as single phase because of its limited solid-solution range. The present study describes the rapid quenching effects on the solid-solution range of La(Ni, M)x (x=3–5) alloys prepared by melt spinning in discussing their hydrogen absorption properties. It is found that the single phase with CaCu5 crystal structure extends to LaNi4.65 compositional alloys. For fuel cell automobile, the alloys with high content of hydrogen must be developed. Strong candidates for this will be Vanadium based BCC alloys, which would be hard to be activated. Since it is well known that the Laves phases undergo easy activation treatment, it may be possible that the BCC phases will be easily activated if the alloys contain such Laves phases. The present study also found that Zr addition is effective on forming Laves phase as grain boundary phases in BCC phases in V–Ti–Zr–Ni alloys, and on improving the hydrogen absorbing properties. The study will be also extended to future hydrogen absorbing alloys with high capacity.

Protium absorption–desorption properties of Ti–Cr–Mo bcc solid solution alloys

Abstract We have investigated the protium absorption–desorption properties of Ti–Cr–Mo alloys of varying composition, including cycling-induced effects. The capacity of alloys with less than 10 at% Mo has an H/M ratio of 1.8 at 10 MPa hydrogen pressure, and remains almost unchanged regardless of Mo content. The 40Ti–Cr–2.5Mo alloy has the widest plateau region observed in this study. The amount of protium desorption and the mean particle size vary inversely with the logarithm of cycle number up to 300 cycles. The capacity of the alloy is drastically affected by the conditions of cycling. With longer evacuation times the capacity decreases significantly. The lattice parameter of the β protide increases with increasing cycles, and the reflection peaks in XRD studies are broadened. The reduction in capacity after several absorption–desorption cycles is somewhat restored by annealing at 673 K for 2 h under vacuum. The absorption pressure of the plateau for the 101st cycle, after annealing following the 100th cycle, recovers to that of the plateau for the first cycle, but then decreases with additional cycling.

Overlayer-induced anisotropic alignment of Nd2Fe14B nanograins

Highly anisotropic Nd2Fe14B thin film has been produced by triggering crystallization of sputter-deposited amorphous Nd–Fe–B layer by deposition of crystalline Cr overlayer. A downward growth of strongly textured Nd2Fe14B columnar grains was observed, starting from the interface between the Nd–Fe–B amorphous layer and the Cr overlayer. Cross-sectional transmission electron microscope observation results suggest that the possible mechanism of this peculiar crystallization is the heterogeneous nucleation at the surface of Nd–Fe–B amorphous layer, triggered by the crystalline Cr overlayer.

Ti–Cr–X protium absorbing alloys with high protium content for fuel-cell

Abstract The effects of additional elements to the Ti–Cr alloys on their protium absorption–desorption properties were investigated. Although Ti–Cr alloys with a b.c.c. structure is expected to exhibit a high protium content, it is difficult to obtain single b.c.c. phase quenching from the high temperature. The effects of additional elements such as V, Mo, W, Nb, Ta, Ru, Rh, Re, Os, Ir etc. on stabilizing b.c.c. phase in the alloys were investigated. Then, it was found that the additions of V, Mo, W, Ru, Rh, Re, Os, Ir effectively stabilized b.c.c. phases. But the addition of Nb and Ta preferentially formed Laves phases. Specially, the addition of Mo and Ru is effective to stabilize the b.c.c. phases with high protium content. The Ti–Cr–(1∼2.5%)Mo alloys show almost same capacity of protium as that reported in Ti–Cr–(5–7.5)V alloys. The addition of Ru to Ti–Cr alloys also shows the capacity of 3.0 mass% protium. These V-free Ti–Cr alloys will be also suitable for the future applications.

Electrical conductivity of layered compounds in SrO-La2O3-TiO2 systems prepared by the Pechini process

Abstract The electrical conductivity of layered-perovskite-type La 2 Ti 2 O 7 and Sr-doped La 2 Ti 2 O 7 has been studied. La 2 Ti 2 O 7 and (La 0.9 Sr 0.1 ) 2 Ti 2 O 7 with a layered-perovskite structure were successfully prepared by the Pechini process. The grain size of La 2 Ti 2 O 7 was found to be 41, 57, and 70 nm for a firing temperature of 700, 1000, and 1300 °C, respectively. A single phase of (La 0.9 Sr 0.1 ) 2 Ti 2 O 7 was also obtained by firing at 1000 °C for only 2 h. The electrical conductivity of the layered compounds was measured as a function of partial oxygen pressures and temperatures by a complex impedance technique. La 2 Ti 2 O 7 fired at 700 °C showed an ionic conductivity of 3.4×10 −6 S/cm at 700 °C, due to the Frenkel defects incorporated by low-temperature synthesis. As a result of the grain size refinement, the enhancement of electronic conductivity was also observed for La 2 Ti 2 O 7 . The ionic conductivity of (La 0.9 Sr 0.1 ) 2 Ti 2 O 7 was less than that of La 2 Ti 2 O 7 .

Magnetic properties and structure of Nd-Fe-B thin films with Cr and Ti underlayers

Abstract We investigated the influence of the underlayers of Cr and Ti on the structure and magnetic properties of Nd-Fe-B thin films which were produced by a conventional RF sputtering method. The thickness of the underlayer and the substrate temperature were varied from 0 to 5000 A and from room temperature to 670°C, respectively. It was found that the type and the thickness of the underlayer materials and the substrate temperature strongly influenced the crystal orientation and magnetic properties. The main crystalline phase was a Nd 2 Fe 14 B compound, whose tetragonal c -axis was aligned perpendicularly to the film plane. A high coercive force ( H c = 3.7 kOe) was achieved in the following conditions; Cr underlayer with the thickness of 500 A and the substrate temperature of 650°C.

Enhanced coercive force of Nd–Fe–B thin films by the introduction of a Cr underlayer

Abstract We investigated the influence of a Cr underlayer on the structure and magnetic properties of Nd–Fe–B thin films which were produced by a conventional rf sputtering method. The thickness of the underlayer and the substrate temperature were varied from 0 to 5000 A and from room temperature to 670°C, respectively. It was found that the thickness of the underlayer material and the substrate temperature strongly influenced the crystal orientation and magnetic properties. The main crystalline phase was Nd 2 Fe 14 B, whose tetragonal c -axis was aligned perpendicularly to the film plane. A high coercive force ( H c =3.7 kOe) was achieved using the following conditions: Cr underlayer with a thickness of 500 A and a substrate temperature of 650°C. From TEM observation, this enhanced coercive force is thought to be attributable to a modification of the columnar structure.

Oxygen Permeation and Methane Conversion Properties of CERIA-Based Composite Membranes Prepared by Tape-Casting Technique

The preparation of ceria-based composite membranes by means of tape-casting technique and their oxygen permeation and methane reforming properties have been investigated. Oxide powders comprising of Ce1−x REx O2−δ (RE = Pr and Sm) and spinel-type ferrites of MFe2 O4 (M = Mn and Co) were prepared by the citrate-based liquid-mix technique. As a result of the optimization of ceramics slurry composition, a crack-free dense membrane with dimensions of 5 cm × 5 cm and 140 μm in thickness was successfully prepared by means of doctor-blade technique. For Ce0.9 Sm0.1 O2−δ - 15 vol% MnFe2 O4 membrane with a thickness of 133 μm, an oxygen flux density of 9.5 μmol/cm2 s was attained at 1000 °C under Ar-10% CH4 (100 sccm). The methane conversion and CO selectivity were 22 and 93%, respectively. Laminated membranes comprising of Ce0.9 Sm0.1 O2−δ - 15 vol% MnFe2 O4 and Ce0.9 Sm0.1 O2−δ - 30 vol% CoFe2 O4 were also prepared. The laminated membrane with one Ce0.9 Sm0.1 O2−δ - 30 vol% CoFe2 O4 layer showed a higher oxygen flux density by a factor of 40% than that without Ce0.9 Sm0.1 O2−δ - 30 vol% CoFe2 O4 layer.Copyright