2Mg-Fe Alloy Processed by Hot Extrusion: Influence of Particle Size and Extrusion Reduction Ratio on Hydrogenation Properties

Samples of a 2Mg-Fe (at.%) mixture were produced by high energy ball-milling (HEBM) with ball to powder ratio = 20:1, in an argon gas atmosphere, in 190 ml vials (sample-1) to produce powders and in 300 ml vials (sample-2) to produce plates. Both samples were cold-pressed into preforms. The preforms were then extruded at 300^oC at a ram speed of 1mm/min., with the following extrusion ratios: sample-1 at 3/1 to ensure porosity and sample-2 at 5/1 to increase the adhesion of the plates. The resulting bulks from samples 1 and 2 were hydrogenated for 24h in a reactor under 15 bar of H₂ to produce the Mg₂FeH₆ complex hydride, and at 11 bar of H₂ to produce both the complex hydride and MgH₂ hydride. In addition, sample-1 was severely temperature-hydrogen cycled to verify its microstructural stability and the influence of grain size on the sorption properties. XRD patterns showed Mg(hc), Fe(ccc) and Mg₂FeH₆ in both samples, and sample-2 also contained MgH₂ and MgO (attributed to processing contamination). DSC results demonstrated that the initial desorption temperature of sample-1 was lower than that of sample-2. However, sample-2 showed faster desorption kinetics, presenting a desorption peak about 73^oC below that of sample-1. This could be attributed to the activation/catalyst effect of the MgH₂ hydride. The improvement in sorption properties was attributed mainly to porosity and to the type of employed catalysts.