L Journal of Alloys and Compounds 356–357 (2003) 626–629 www.elsevier.com / locate / jallcom Direct mechanical synthesis and characterisation of Mg Fe(Cu)H 2 6 1 * C.X. Shang, M. Bououdina , Z.X. Guo Department of Materials, Queen Mary, University of London, Mile End Road, London E14NS, UK Received 31 December 2002; received in revised form 21 January 2003; accepted 30 January 2003 Abstract Direct synthesis of Mg FeH was carried out by mechanically alloying MgH with Fe under both Ar and H atmospheres Both 2 6 2 2 . (3MgH 1Fe) and (4MgH 1Fe) mixtures were processed to improve the yield of Mg FeH . The (MgH –Fe–Cu) system was also 2 2 2 6 2 investigated to modify the properties of the synthesised compound. X-ray diffraction and Rietveld analysis were carried out to determine the phase evolution of the powder mixtures. Field emission SEM clearly showed substantial particle size reduction for the mixture milled under hydrogen. Thermogravimetry (TG) was employed to determine the dehydrogenation kinetics of the milled mixtures.  2003 Elsevier B.V. All rights reserved. Keywords: Hydrogen storage materials; Mechanical alloying; Mg-based alloy; Mg FeH 2 6 1. Introduction metric (2MgH 1Fe) under Ar atmosphere up to 60 h, 2 leading to a yield of 56 wt% of Mg FeH . Gennari et al. 2 6 Mg and Mg-based alloys are a group of attractive [4] reported that mechanically alloying the mixture of materials for hydrogen storage applications. MgH pro- (2Mg1Fe) in 5 bar of H atmosphere led to the formation 2 2 vides a high storage capacity of 7.6 wt% hydrogen. Many of Mg FeH . However, the yield after 60 h of milling was 2 6 research efforts have been devoted to modifying the Mg–H only 30 wt%. Sai Raman et al. [5] improved the conditions system in order to achieve rapid hydrogenation / dehydro- used in Ref. [4], and achieved 63 wt% Mg FeH under a 2 6 genation kinetics, cyclic stability and low desorption H pressure of |10 bar after only 20 h of high-energy 2 temperature. milling. So far this is the highest amount of Mg FeH 2 6 It is well known that the ternary hydride compound, produced via a single process of mechanical alloying. Mg FeH , shows a high hydrogen-storage capacity of 5.5 However, the previous studies on the synthesis of 2 6 wt%, it is desirable for hydrogen storage. However Mg FeH often involve the stoichiometric composition of 2 6 Mg FeH is more difficult to synthesize than the conven- (2MgH /Mg1Fe) and an unexpectedly large amount of 2 6 2 tional transition metal hydride, Mg NiH In the past, un-reacted species, e.g. Mg, Fe and / or MgH , still existed 2 4. 2 Didisheim et al. [1] showed that Mg FeH could be in the final mixture. Moreover, the sorption kinetics of the 2 6 synthesized by sintering the cylindrical pellets of Mg and Mg–Fe–H system has not been reported so far. Fe powders mixed in a 2:1 atomic ratio at around 500 8C In this study, direct synthesis of Mg FeH by me- 2 6 under 20–120 bar of H pressure. More recently, Huot et chanically alloying MgH with Fe under both Ar and H 2 2 2 al. [2] firstly reported a high yield of 65 wt% Mg FeH by atmospheres were investigated in order to optimise the 2 6 milling the mixture of (2Mg1Fe) in a planetary ball mill conditions of forming Mg FeH . Both (3MgH 1Fe) and 2 6 2 under H atmosphere for 20 h, followed by sintering at 623 (4MgH 1Fe) mixtures were selected with the aim of 2 2 K under 50 bar of H. Thereafter, Huot et al. [3] improving the yield of Mg FeH , while reducing the level 2 2 6 synthesised the hydride by direct milling of the stoichio- of un-reacted species. Furthermore, the (MgH –Fe–Cu) 2 system was also studied with an attempt to modify the hydrogen storage properties of the Mg FeH and stabilize 2 6 *Corresponding author. Tel.: 144-20-7882-5569; fax: 144-20-8981- the Mg Fe binary compounds in air before hydriding. The 2 9804. hydrogen desorption properties of the final mixtures were E-mail address: x.guo@qmul.ac.uk (Z.X. Guo). 1 studied using simultaneous thermogravimetry and differen- Present address: Department of Materials, School 4M, University of Nottingham, University Park, Nottingham NG7 2RD, UK. tial scanning calorimetry (TG / DSC). 0925-8388 / 03 / $ – see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00273-1