Effect of V, Nb, Ti and graphite additions on the hydrogen desorption temperature of magnesium hydride Hakan Gasan a, *, Osman N. Celik b , Nedret Aydinbeyli a , Yasar M. Yaman b a Eskisehir Osmangazi University, Institute of Metallurgy, 26480 Eskisehir, Turkey b Eskisehir Osmangazi University, Engineering Faculty, Department of Mechanical Engineering, 26480 Eskisehir, Turkey article info Article history: Received 10 January 2011 Received in revised form 20 April 2011 Accepted 12 May 2011 Available online 12 June 2011 Keywords: Mechanical milling Hydrogen desorption temperature Additives Magnesium hydride abstract In this study the effects of mechanical milling with 5 wt.% of additives (V, Nb, Ti and Graphite) on the hydrogen desorption temperature of the magnesium hydride (MgH 2 ) were studied. The powder mixtures were mechanically milled for 2 h. X-ray diffraction (XRD), scanning electron microscope (SEM), and optical microscope (OM) techniques were used for the structural and morphological characterization of powders. Differential scanning calorimeter (DSC) was used to investigate the effects of the mechanical milling with additives on the hydrogen desorption temperature of the magnesium hydride powder. DSC results show that the hydrogen desorption temperatures of mechanically milled MgH 2 with additives are depressed about w40e50  C compared with that of as-received MgH 2 . The particle size analysis results indicate that decrease of the particle size of powders leads to a decrease of the hydrogen desorption temperature. Moreover, increasing specific surface area can also contribute to a decrease on the hydrogen desorption temperature. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Magnesium hydride is one of the attractive hydrogen storage materials because of its hydrogen storage capacity (w7.6 wt %), low cost and lightweight. Nevertheless, high hydrogen desorption temperature (higher than 400  C) and relatively poor hydrogen absorption-desorption kinetics limit the use of Mg in practical applications [1]. During last decades many efforts have been made to overcome these barriers. These efforts involve preparing nanocrystalline powders by using high-energy ball milling [2e5] and alloying with the additives such as transition metals [6e11], metal oxides [12e18], halides [19e21] and different form of carbons [22e25]. Many of these studies have shown that there was a correlation between the structural characteristics and hydrogen desorp- tion properties. In our previous work [26], it was demonstrated that the particle size had the greatest effect on the hydrogen desorp- tion temperature of mechanically milled MgH 2 . An optimal milling time of 2 h was determined by structural and thermal characterization of powders milled for different times (0.5 h, 1 h, 2 h, 5 h, 10 h, 20 h). To further clarify the effect of structural changes on hydrogen desorption temperature of MgH 2 , MgH 2 powders * Corresponding author. Tel.: þ90 222 2393750; fax: þ90 222 2393613. E-mail address: hgasan@ogu.edu.tr (H. Gasan). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 1912 e1918 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.05.086