Stability investigation of the g-MgH 2 phase synthesized by high-energy ball milling Ntumba Lobo a,* , Akito Takasaki a , Kentaro Mineo a , Alicja Klimkowicz b , Kamil Goc c a Shibaura Institute of Technology, Department of Engineering Science and Mechanics, 3-7-5 Toyosu, Koto-ku, 135-8548 Tokyo, Japan b Shibaura Institute of Technology, SIT Research Laboratories, 3-7-5 Toyosu, Koto-ku, 135-8548 Tokyo, Japan c AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, Al. Mickiewicza 30, 30-059 Krak ow, Poland article info Article history: Received 28 November 2018 Received in revised form 29 January 2019 Accepted 21 February 2019 Available online xxx Keywords: Mechanical milling g-MgH 2 Hydrogen absorption/desorption XRD Thermal stability abstract Structural investigations showed that the crystal structure influences the hydrogen storage properties of MgH 2 . The crystal structure and dehydriding temperature of MgH 2 activated by high energy ball milling under an argon atmosphere were studied. The X-ray diffraction characterization showed that a small amount of tetragonal a-MgH 2 phase transforms into crystalline g-MgH 2 of an orthorhombic structure during milling, and g-MgH 2 peak intensity increased with increasing ball milling time within a certain limit, but disappeared early in the hydrogenation cycle at a temperature of 300  C. We studied the phase structure and the stability of the MgH 2 during absorption/desorption cycles as well as thermal stability in a context of sustainable use of MgH 2 . © 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Introduction Due to the growing demand for hydrogen as a new energy carrier, it is only natural for the hydrogen storage method to develop [1e5]. Currently, the most popular and conven- tional way of storage and transportation of hydrogen that are being used are by high-pressure gas tanks and liquefied hydrogen tanks [6,7]. Alternative methods of hydrogen storage in solids are gaining both scientific and industrial interest. Hydrogen storage in alloys seems to be particularly promising [8]. The reason for this is the disadvantage of hydrogen stored under high-pressure in a gas tank which requires compres- sion and preservation of the pressure up to 70 MPa [9]. Very thoughtful construction of the container is necessary to pre- vent leakage and loss of fuel over time caused by hydrogen fast diffusion (D ¼ 0.61 cm 2 /s) [10e17]. The significant merit of this system is that the hydrogen is stored in a gaseous form. Therefore, it is ready for immediate use. Because of it and despite technical challenges, this technology is already in practical use in hydrogen-fueled vehicles [18]. On the other hand, the big advantage of storage of hydrogen in liquefied form is its much higher volumetric * Corresponding author. E-mail address: estherntumba2@hotmail.fr (N. Lobo). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2019.02.191 0360-3199/© 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Lobo N et al., Stability investigation of the g-MgH 2 phase synthesized by high-energy ball milling, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2019.02.191