Hydrogen Storage Properties, Metallographic Structures and Phase Transitions of Mg-Based Alloys Prepared by Super Lamina
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1128-U01-04
Hydrogen Storage Properties, Metallographic Structures and Phase Transitions of MgBased Alloys Prepared by Super Lamination Technique Nobuhiko Takeichi1, Koji Tanaka1, Hideaki Tanaka1, Nobuhiro Kuriyama1, Tamotsu T Ueda2, Makoto Tsukahara2, Hiroshi Miyamura3, and Shiomi Kikuchi3 1 National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan 2 IMRA Material R&D Co., Ltd., 5-50 Hachiken-cho, Kariya, Aichi 448-0021, JAPAN 3 The University of Shiga Prefecture, 2500 Hassaka-cho, Hikone, Shiga 522-0057, Japan ABSTRACT We have prepared Mg/Pd laminate composites with (Mg/Pd)=6, 3 and 2.5 atom ratios, by a super lamination technique. The homogeneous Mg-Pd intermetallic compounds, Mg6Pd, Mg3Pd and Mg5Pd2, are formed during the initial activation process. We investigated the hydrogen storage properties of these materials. The compounds can reversibly absorb and desorb a large amount of hydrogen, up to 1.46~0.9 H/M, at 573 K. Except for the Mg5Pd2-hydrogen system, the pressure composition-isotherms show two plateaux. The mechanism of the phase transition during hydrogenation/dehydrogenation was analyzed by in-situ XRD measurements. These intermetallic compounds absorb and desorb hydrogen through reversible multistage disproportionation and recombination processes. INTRODUCTION From the viewpoint of hydrogen storage systems, Mg [1] is a promising material because it can absorb a large amount of hydrogen up to 7.6 mass%, as MgH2. However, the hydrogen absorption/desorption kinetics is too low for practical use and requires the use of a high temperature such as 573 K. To improve the reaction kinetics and diffusion properties, reduction of the grain size and the addition of various catalysts have been investigated [2, 3]. Also, various Mg-based alloys and intermetallic compounds have been investigated to improve the rate of hydrogenation and the hydrogenation temperature [4, 5]. The Mg2Ni intermetallic compound is well known to form a Mg2NiH4 hydride, which has a hydrogen storage capacity of 3.6 mass% [5]. However, it is difficult to cast Mg-containing alloys accurately with desirable composition by conventional melt-cast methods because of the high vapor pressure of Mg, etc. In addition, single phase Mg-containing compounds cannot be obtained simply by casting, due to phase separation during solidification. Accordingly, various methods, such as mechanical alloying [6], vapor phase processing [7], and combustion synthesis [8], have been investigated. Recently, Ueda et al. have reported initial investigations on the synthesis and hydrogen storage properties of Mg-based laminate composites prepared by a super lamination technique [9]. A 67 at%Mg-33 at%Ni laminate composite was shown to transform due to a heat treatment after repetitive rolling to single phase Mg2Ni, a phase which could not be obtained simply by casting. Palladium reacts rapidly with hydrogen, even after it is placed in air, because its surface and diffusion properties provide a high catalytic a
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