Atsunori Kamegawa

Ti-V-Cr b.c.c. alloys with high protium content

Abstract The effects of composition and heat-treatment on the protium absorption–desorption properties of Ti–V–Cr alloys were investigated. It was found that the Ti–35V–40Cr alloy shows a 2.6 mass% protium capacity. The plateau pressure of the Ti–35V–xCr alloys increased with decreasing lattice constants associated with increasing Cr content. The main phase of the as-cast Ti–xV–Cr (Cr/Ti=40/25) alloys containing more than 15%V was a b.c.c. phase. These b.c.c. alloys exhibited a 2.4 mass% protium capacity. Heat-treatment over 1673 K was effective on stabilizing the b.c.c. structure for the Ti–xV–Cr (Cr/Ti=2/3) alloys with low V content. The Ti–5V–57.5Cr alloy heat-treated at 1673 K for 1 h yields a high capacity of 2.8 mass% protium, which is the highest value at 313 K reported so far. The alloy is economically promising since it contains low amounts of expensive V metal.

New V-based alloys with high protium absorption and desorption capacity

Abstract The hydrogen absorption properties of V–Zr–Ti–M(M=Fe, Mn, Ni) alloys were examined in order to develop the alloys with high hydrogen capacity. It was found that the best composition among the studied alloys is the V–Zr–Ti–Ni system. A suitable amount of the vanadium in the V–Zr–Ti–Ni system was studied in correlation with its hydrogen absorption properties, and turned out to be around 75 at.%V. Substitution with Zr improved the hydrogen absorption properties in forming the grain boundary network phases of C14 Laves phase. Heat treating the alloys (homogenize and quench) drastically improves the plateau region of PCT curves. Zr addition also improves the properties for V–Zr–Ti–Cr alloys.

Protium absorption properties and protide formations of Ti–Cr–V alloys

Abstract Ti–Cr–V alloys are known to absorb about 3.8 mass% (H/M=2) of protium (hydrogen atom), but to desorb about 2.4 mass%. This paper aims to clarify protium absorption properties and protide formations of Ti–Cr–V alloys. It was found that higher protium desorption capacity was achieved by increasing Cr content and controlling measurement temperature in order to control the desorption plateau pressure near atmospheric pressure for the alloys with less than 40 at% V content. However, Cr-rich alloys were found to absorb up to H/M=1 because of the formation of the mono-protides. The region with higher protium desorption capacity was obtained. The lattice parameters of the alloys and the enthalpy changes for di-protide formation were estimated from the compositions of the alloys. Moreover, estimated enthalpy changes for di-protide formation and the lattice parameters of the alloys were found to be generally constant on the limited line between appearance of regions of mono- and di-protides.

Ti−V−Cr BCC alloys system with high protium content

This paper aims to study the relationship between the protium absorption properties and alloy composition of Ti−V−Cr alloys. We studied the effects of composition of the alloys and the heat-treatment on the protium absorption-desorption properties of Ti−V−Cr alloys, and found that Ti−35V−40Cr alloys show 2.6 mass% protium capacity. The plateau pressure of the alloys increased with decreasing lattice constants, resulting from increasing Cr content. The main phase of the samples containing more than 15%V was a BCC phase in the cast state. These BCC phase alloys exhibited 2.4 mass% protium. It was also found that the heat-treatment was effective in stabilizing a BCC structure in Ti−V−Cr alloys with low V content. The alloy yields the high capacity of 3.0 mass% protium capacity, which will be the highest value at 313 K reported so far. The alloy will be promising since it contains a low amount of the expensive V element.

Crystal structure of novel hydrides in a Mg-Ni-H system prepared under an ultra high pressure

The crystal structure of novel hydrides in the Mg–Ni–H system has been studied using a powder X-ray diffraction and transmission electron microscopy. A cubic-anvil-type apparatus was utilized to prepare samples. The new hydride with a chemical composition of around MgH2–60 at% Ni was synthesized at 1073 K for 2 h under a pressure as high as 5 GPa. From TGA analysis, the new hydride was found to be Mg2Ni3H3.4. Orthorhombic and monoclinic crystal systems with a primitive cell were proposed as possible symmetries of the new hydride. X-ray and electron diffraction patterns of the new hydride were indexed in an orthorhombic structure with a=0.8859(4), b=1.3740(5), c=0.4694(2) nm. Moreover, decomposition of the hydride into Mg2Ni was observed by the transmission electron microscopy.

Effect of synthesis pressure on hydride phases in Mg–M systems (M=Mn, Y)

Abstract High-pressure synthesis of the hydrides in Mg–M (M = Mn, Y) systems and the influence of applied pressures during synthesis on present phases and their crystal structures have been studied. In Mg–Mn system, it was found that the crystal structure of Mg3MnHy changed from hexagonal structure (a = 0:47107(4) nm and c = 1:0297(1) nm) to monoclinic structure (a = 0:8819(8) nm, b = 0:4658(4) nm, c = 0:4678(5) nm and b= 105:6(1)8) in a pressure range of 3–3.5 GPa. This crystal structural change was reversible with respect to pressure. The Mg3MnHy synthesized under 5 GPa was stable up to around 620 K. From thermogravimetric and fusion extraction analyses, the hydrogen content was determined as Mg3MnH5.0–5.6. In Mg–Y system, the high-pressure hydride (MgY2Hy) with yellowish color was synthesized at 1073 K for 2 h under 3 GPa or higher. This phase exhibited an FCC-type structure with a cell parameter of a = 0:516 nm. Its hydrogen content was determined to be about 3.7 mass%, corresponding to a chemical formula of MgY2H7.8. The hydride was partially dehydrogenated at around 600 K, and the amount of hydrogen partially desorbed was 1.4 mass%. The FCC-type structure was stable even after the partial dehydrogenation.

Crystal structure and protium absorption properties of La-rich La(Ni, M)x (x=3–4.7) (M=Al, Co, Mn, Si) melt-spun ribbons

Abstract The present study describes the rapid quenching effects on the solid-solution range of La(Ni, M) x ( x =3–4.7) (M=Al, Co, Mn, Si) alloys prepared by melt-spinning and discusses their protium (hydrogen atom) absorption properties. It is found that the single phase with CaCu 5 crystal structure extends to LaNi 4.65 compositional alloys. When x in LaNi 5− x becomes smaller, the alloy acquires better protium absorption properties including easier activation, better flatness of plateau region and a good hydrogen storage capacity comparable to those of LaNi 5 homogenized sample. On adopting a melt-spinning technique it is easy to form single phase of CaCu 5 type-structure for La-rich non-stoichiometric La–Ni–M alloys such as La(Ni, M) x ( x =3–4.7) (M=Al, Mn, Si) alloys. The readiness of forming a single phase CaCu 5 type-structure in melt-spun La–Ni–M alloys is in order of Al≥Si>Mn>Co.The phases formed and protium absorption properties of La-rich LaNi 4.5 M 0.2 melt-spun alloys are studied. It was found that LaNi 4.5 M 0.2 alloys had better protium absorption properties such as easier activation than the LaNi 4.65 binary alloy and as good hydrogen storage capacity as that of homogenized LaNi 5 .

Simultaneous Enhancement of Electrical Conductivities and Mechanical Properties in Cu-Ti Alloy by Hydrogenation Process

Effects of hydrogenation process of the microstructure, electrical conductivity and mechanical properties for the Cu-(1~3) mass%Ti alloys were investigated. During hydrogenation process at 350°C, 7.5 MPa for 48 h, the disproportionation reaction occurred with forming of Ti hydrides in the alloy. It is found that remarkable simultaneous improvements of mechanical strength of 1094 MPa and electrical properties of 21%IACS are obtained in the hydrogenated Cu-3mass%Ti alloy.

Hydrogen Production From Methane by Using Oxygen Permeable Ceramics

Oxygen permeable ceramics based on mixed conductors are attracting much attention for use in partial oxidation of hydrocarbons as a novel technique for syngas and pure hydrogen production. This paper describes the preparation and oxygen permeation properties including the methane reforming property of a novel member of oxygen permeable ceramics. The materials used are solid solutions of (La 0.5 Ba 0.3 Sr 0.2 )(Fe x In 1-x )O 3-δ . The single phase of perovskite-type (La 0.5 Ba 0.3 Sr 0.2 )(Fe x In 1-x )O 3-δ is obtained in the range of x=0.4 to 0.9. The highest oxygen flux densities of 2.2 and 11 μmol/cm 2 s (membrane thickness, L=0.2 mm) are attained for (La 0.5 Ba 0.3 Sr 0.2 )(Fe x In 1-x )O 3-δ (x=0.6) at 1000°C under He/air and CH 4 /air gradients, respectively. The electrical conductivity of (La 0.5 Ba 0.3 Sr 0.2 )(Fe 0.6 In 0.4 )O 3-δ is dominated by p-type conduction having a slope of 1/4 under the high P(O 2 ) region. The oxide-ion conductivity of the same sample is estimated to be 0.05 S/cm at 800 °C. Even though the oxygen flux density slightly decreases with increasing time, high CO selectivity of 90% is kept for 100 h. The oxygen flux density of the solid solution is also discussed in the context of surface exchange kinetics.

Synthesis and Crystal Structure of New Hydrides in Mg-RE Systems under High-Pressure (RE = La, Ce, Pr)

The high-pressure synthesis of new hydrides of Mg-RE-H systems, where RE = La, Ce and Pr, were conducted by using a cubic-anvil-type apparatus, and their crystal structure, thermal stabilities and hydrogen contents were investigated. In MgH2-xmol%REH (REH = LaH3, CeH2.5 and PrH3), new hydrides with primitive tetragonal structure were synthesized around x = 25 - 33 under GPa-order high pressures. The lattice constants were a = 0.8193 nm, c = 0.5028 nm, a = 0.8118 nm, c = 0.4979 nm and a = 0.8058 nm, c= 0.4970 nm at x = 25 in Mg-La, Ce and Pr systems, respectively. The hydrogen contents of the novel compounds were 4.1 mass%, 3.7 mass% and 3.9 mass% in Mg-La, Ce and Pr systems, respectively, and the chemical formulas were found to correspond to Mg3LaH9, Mg3CeH8.1 and Mg3PrH9. The new hydrides decomposed into Mg and rare-earth hydride at about 600 K (Mg3LaH9: 614 K, Mg3CeH8.1: 609 K, Mg3PrH9: 630 K) with an endothermic reaction.