Relations between Microstructure of Mg/Cu Super-laminates and Kinetics of Hydrogen Absorption/desorption
- PDF / 5,094,161 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 217 Views
0971-Z07-06
Relations Between Microstructure of Mg/Cu Super-Laminates and Kinetics of Hydrogen Absorption/Desorption 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 University of Shiga Prefecture, 2500 Hassaka-cho, Hikone, Shiga, 522-8533, Japan
ABSTRACT Super-laminates have been attracting attention since co-authors Ueda et al. reported that Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473K. The Mg/Cu super-laminates were prepared by a repetitive fold and roll method. Initial activation at 573 K led the super-laminates to absorb hydrogen at 473K. TEM observations of micro/nanostructures in the super-laminates were performed in order to clarify the process of hydrogenation and dehydrogenation at 473K, The as-rolled Mg/Cu super-laminates have laminated structures in size of sub-micrometer thickness composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation keep laminated structure and have uniformly distributed pores with a sub-micrometer diameter. It is considered that these micro/nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics, which would contribute to achieve high performance hydrogen storage materials. INTRODUCTION Hydrogen storage materials have attracted more and more attention with the advance of R & D activities of fuel cell vehicles. Magnesium is expected as one of hydrogen storage media 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 nano-crystalline dimensions can significantly improve the reaction kinetics and diffusion properties of MgH2 [2-4]. In addition, MgH2 with certain amount of 3d-transition metals lead to even better performance and lower hydrogen desorption temperatures than magnesium [5-7]. Many Mg-based alloys and compounds have been investigated to improve their kinetics of hydrogenation and dehydrogenation at elevated temperature [8, 9]. 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 [10], vapor phase process [11], combustion synthesis [12], 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 mat
Data Loading...
