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°C 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°C 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.
J. Federico Chávez Alcalá, Alejandro Cruz Ramírez and Ma. de los Ángeles Hernández Pérez
G. F. De Lima et al., "2Mg-Fe Alloy Processed by Hot Extrusion: Influence of Particle Size and Extrusion Reduction Ratio on Hydrogenation Properties", Materials Science Forum, Vol. 691, pp. 3-9, 2011