Journal of Alloys and Compounds 479 (2009) 409–413 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Fabrication and hydrogen storage property study of nanostructured Mg–Ni–B ternary alloys Huaiyu Shao, Kohta Asano, Hirotoshi Enoki, Etsuo Akiba ∗ National Institute of Advanced Industrial Science and Technology (AIST), Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan article info Article history: Received 10 November 2008 Received in revised form 11 December 2008 Accepted 16 December 2008 Available online 25 December 2008 Keywords: Hydrogen storage materials Nanostructures Mechanical alloying X-ray diffraction Transmission electron microscopy abstract Mg–Ni–B ternary alloys with nanostructure were produced by mechanical alloying method. Alloys with various structures were obtained. X-ray diffraction was used to define the structure and phase informa- tion as well as crystalline size of the alloys. Bright-field and dark-field transmission electron microscope (TEM) technique was applied to observe the morphology of the samples. Electron diffraction was used to confirm the structure of the alloys. The hydrogen storage properties of the obtained Mg–Ni–B alloys were studied by high pressure differential scanning calorimetry (DSC) and pressure–composition isotherm (PCT) methods. Body centered cubic (BCC) structure alloys show better hydrogen absorption properties than CsCl and Mg 2 Ni type structure alloys in this work. Mg 48 Ni 48 B 4 and Mg 50 Ni 45 B 5 BCC alloys showed a hydrogen absorption content of 1.93 and 1.94mass% at 373K. Substitution or addition of a small amount of B to Mg 50 Ni 50 alloy is effective to improve hydrogen storage properties. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Since Reilly and Wiswall reported Mg–Cu–H system [1] and Mg–Ni–H system [2] as hydrogen storage materials, Mg-based alloys have been widely studied. Mg-based alloys have several important advantages for potential hydrogen storage application, such as low price, large abundance in earth’s crust and high capaci- ties of the hydrides (7.6mass% for MgH 2 , 3.6 mass% for Mg 2 NiH 4 , 4.5 mass% for Mg 2 CoH 5 and 5.5 mass% for Mg 2 FeH 6 ). However, Mg-based materials also face a severe obstacle for the application that Mg-based materials prepared by conventional melting method show quite poor hydrogen storage kinetics. Mg and Mg 2 Ni usu- ally need a hydrogen absorption temperature higher than 523K. Mechanical alloying (MA) method has been widely applied to pre- pare Mg-based alloys. MA as a high energy operation of repeated welding, fracturing and re-welding of sample powders [3], is a novel and well-known synthesis technique to prepare nanostruc- tured and non-equilibrium alloys. Recently, it has almost become the major preparation method to produce Mg-based hydrogen stor- age alloys [4–16] because the fresh surface area and defects formed during the milling process could greatly improve the hydrogen absorption properties of these Mg-based alloys. Our group has successfully obtained Mg–Co [17,18], Mg–Ti [19] and Mg–Ni [20] body centered cubic (BCC) alloys by mechanical ∗ Corresponding author. E-mail addresses: shaohuaiyu@gmail.com (H. Shao), e.akiba@aist.go.jp (E. Akiba). alloying method. Compared with face centered cubic (FCC) and hexagonal close packing (HCP) lattice, BCC lattice has lower packing density and more octahedral and tetrahedral sites per atom, which means more interstitial sites are available for hydrogen occupancy in BCC lattice. This work is about the preparation and hydrogen stor- age study of Mg–Ni–B ternary alloys (mostly with BCC structure). The purpose is to study the effect of addition/substitution of boron- the lightest non-metal solid-state element on the preparation and hydrogen storage properties of Mg–Ni alloys. 2. Experimental details Mg–Ni–B ternary alloys were produced using a Fritsch P5 planetary ball mill. Fab- rication results of some Mg–Ni alloys were used to compare with those of Mg–Ni–B ternary alloys. The detailed fabrication process of Mg–Ni binary alloys could be found here [20]. The samples are with the compositions shown in Table 1. The begin- ning samples were mixture of Mg (purity >99.9%, 100 mesh), Ni (purity >99.9%, 300 mesh) and B (purity >99.9%, 300 mesh) powders weighed according to the atomic ratio of x:y:(100-x–y) in MgxNiyB100-x–y. The mixture samples of 2 g in weight and stainless-steel milling balls of 10mm in diameter were put into the milling vials with a ball-to-powder weight ratio of 20:1. The vials were then closed with 0.1MPa argon in a hermetic way. The whole weighting process was conducted in glove box with high purity argon as protecting atmosphere. The mechanical alloying process of these alloys was carried out with a rotation speed of 200 rpm and a milling duration of 200 h. Structure and phase analysis of the obtained alloy samples was conducted using a Rigaku RINT-2500 V diffractometer with Cu K radiation at a generator voltage of 50 kV and a current of 200 mA. The diffraction data were collected at a scan rate of 0.8 ◦ /min with a scan step of 0.04 ◦ . The size distribution and morphology observation in bright-field and dark-field was carried out by transmission electron microscope (TEM) using JEOL JEM-2000FX II operating at the accelerating voltage of 200 kV. Electron diffraction technique was conducted to confirm the structure of the samples. 0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2008.12.067