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

Abstract

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 H2to produce the Mg2FeH6complex hydride, and at 11 bar of H2to produce both the complex hydride and MgH2hydride. 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 Mg2FeH6in both samples, and sample-2 also contained MgH2and 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 MgH2hydride. The improvement in sorption properties was attributed mainly to porosity and to the type of employed catalysts.

Hydrogen storage in MgAlTiFeNi high entropy alloy

“…Figure 2a presents a DSC scan where the hydrogen desorption peak can be observed at around 326 °C. Although reactive milling results in only partial hydrogenation of the alloy, it is interesting to note that the peak temperature (326 °C) and the onset temperature of 286 °C for hydrogen desorption are lower than those for commercial magnesium hydride (MgH2) which are roughly on average 426 °C and 442 °C, respectively [28][29][30][31][32][33][34][35][36]. Figure 2b displays the TG curve from which one obtained the value of 0.87 wt% of hydrogen absorbed in the alloy by reactive milling.…”