2Mg-Fe alloys processed by hot-extrusion: Influence of processing temperature and the presence of MgO and MgH2 on hydrogenation sorption properties

2Mg-Fe alloy powder produced by high-energy ball milling was processed by hot extrusion at temperatures of 200 degrees C and 300 degrees C to produce bulk samples. The alloys were hydrogenated for 24 h under hydrogen pressures of 24 bar (to produce the Mg2FeH6 phase) and 15 bar (to produce a mixture of MgH2 + Mg2FeH6 phases), respectively. After the hydrogenation treatments, the complex hydride Mg2FeH6 was identified in both conditions, while the MgH2 andMgOphases were observed only after extrusion at 200 degrees C. Desorption temperatures varied with the extrusion conditions; extrusion at 300 degrees C resulted in a desorption onset temperature about 68 degrees C lower than that of samples extruded at 200 degrees C, and about 200 degrees C lower than that of commercial MgH2. Extrusion at the lower temperature did not change the number of stored defects (point defects, dislocations, voids, stacking faults, vacancies and others) produced in the milling process and increased the preferential sites for hydride nucleation, increasing the hydrogen storage capacity. The presence of MgO produced the beneficial effect of grain boundary pinning, but delayed the onset temperature of desorption. The combined presence of MgH2 and Fe after hydrogenation at 15 bar seems to play a catalytic role that considerably hastened the Mg-H reactions and increased the desorption kinetics. However, the desorption kinetics in both conditions was still low. (C) 2010 Elsevier B.V. All rights reserved.