International Journal of Hydrogen Energy 31 (2006) 2266 – 2273 www.elsevier.com/locate/ijhydene Effect of the heating rate on crystallization behavior of mechanically alloyed Mg 50 Ni 50 amorphous alloy Nedret Aydinbeyli a , Osman Nuri Celik b , Hakan Gasan a , ∗ , Kerem Aybar c a Eskisehir Osmangazi University, Institute of Metallurgy, 26480 Eskisehir, Turkey b Eskisehir Osmangazi University, Engineering Faculty, Department of Mechanical Engineering, 26480 Eskisehir, Turkey c Eskisehir Osmangazi University, Engineering Faculty, Department of Metallurgical and Materials Engineering, 26480 Eskisehir, Turkey Received 23 September 2005; received in revised form 10 March 2006; accepted 20 March 2006 Available online 28 July 2006 Abstract The mechanical alloying is the most convenient method to produce Mg–Ni alloys. In this study, the effect of ball-to-powder weight ratios and the mechanical alloying time on amorphization of Mg 50 Ni 50 alloy and its thermal stabilities were investigated. Mg 50 Ni 50 alloy has been produced by using Spex 8000 D mixer/mill with different ball-to-powder weight ratios (5:1, 10:1, 20:1). Amorphization times by XRD analysis are found to be 60 h for 5:1 ball-to-powder weight ratio, 10 h for 10:1 ball-to-powder weight ratio and 5 h for 20:1 ball-to-powder weight ratio. The thermal stabilities of amorphous Mg 50 Ni 50 alloys, obtained by different ball-to-powder weight ratios, have been determined and the effect of heating rates on the crystallization temperatures have also been investigated by DSC. The heating rates employed were 5, 10, 15, 20 ◦ C/min. During the first crystallization reaction, the amorphous and Mg 2 Ni intermetallic phases occurred. DSC studies show that increase in heating rates increased the crystallization temperatures for all samples. The apparent activation energies were determined by means of the Kissinger method.  2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. Keywords: Amorphous materials; Mechanical alloying; Hydrogen storage; Crystallization 1. Introduction Mechanical alloying is a solid-state powder- processing technique that allows to synthesize mate- rials by a high-energy ball milling. This method was first developed by Benjamin and co-workers in 1966 to produce oxide dispersion-strengthened alloys [1,2]. Mechanical alloying has been used to produce various materials such as oxide dispersion-strengthened alloys, ∗ Corresponding author. Tel.: +90 222 239 37 50/3490; fax: +90 222 239 36 13. E-mail address: hgasan@ogu.edu.tr (H. Gasan). 0360-3199/$30.00  2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2006.03.013 nonequilibrium phases, intermetallics, composites, nanocrystalline and amorphous materials [1–4]. In the last decade, the mechanical alloying technique has been widely used to produce hydrogen storage materials, especially Mg-based alloys. Considering the large differences in melting points and vapor pressures between Mg and Ni, the production of Mg–Ni alloys by conventional methods is more difficult than mechanical alloying techniques [5,6]. In addition, the mechanical alloying leading to nanometer-scale structures having new clean surfaces improve the hydriding properties [3,7]. Amorphous Mg–Ni alloys, produced by mechan- ical alloying, can absorb and desorb, electrochemically, a large amount of hydrogen at room temperature [8–11]. These amorphous phases may be used as a precursor