The Effect of Initial Activation on Microstructures of Mg/Cu Super-laminates and Hydrogen Absorption Properties
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1042-S03-08
The Effect of Initial Activation on Microstructures of Mg/Cu Super-laminates and Hydrogen Absorption Properties Koji Tanaka1, Nobuhiko Takeichi1, 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 Microstructures and hydrogen storage properties of Mg/Cu super-laminates were compared to clarify the effect of initial activation. The initial activation change micro/nanostructures of Mg/Cu super-laminates into Mg2Cu with layered structure in fine grain size of about 1 m and pores highly dispersed between layers in sub-micrometer size. Large surface area, dense defects and short diffusion distance for the reaction enable Mg/Cu super-laminates to absorb hydrogen very quickly.
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INTRODUCTION Among many kinds of hydrogen storage materials, magnesium is promising because it can store a large amount of hydrogen up to 7.6 mass%, as MgH2 [1]. However, MgH2 is too stable to release hydrogen smoothly; a practical decomposition rate is given at the temperatures above 673K, which is too high for practical applications. A reduction of the grain size into nanocrystalline dimensions can significantly improve the reaction kinetics and diffusion properties of MgH2 [2]. In addition, MgH2 with certain amount of 3d-transition metals lead to even better performance and lower hydrogen desorption temperatures than magnesium [3]. A lot of Mg-based alloys and compounds have been investigated to improve their kinetics of hydrogenation and dehydrogenation at elevated temperature [4, 5]. However, it is difficult to cast Mg-containing alloys accurately with desirable composition by conventional melt-cast methods because of a high vapor pressure of Mg, etc., and single phase Mg-containing compounds can not be obtained just by casting, due to the phase separation during solidification. Accordingly, many kinds of methods such as mechanical alloying, vapor phase process, combustion synthesis, etc., have been applied for Mg-based alloys and compounds. However, it is difficult to avoid oxidation of Mg in these methods because metal powders are used as a starting material, and therefore Mg-based alloys and compounds made by these methods do not show excellent properties. Super-laminates have been attracting attention since co-authors Ueda et al. reported that Mg/Cu super-laminates showed reversible hydrogen absorption and desorption at 473K, which was lower than reaction temperatures of conventional Mg-based materials [6]. The Mg/Cu superlaminate absorbs hydrogen at 473 K after initial activation at 573 K. It does not absorb hydrogen at 473 K without initial activation. It is considered that micro/nano-structures of Mg/Cu superlaminates lead to lower dehydrogenation temperature and bett
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