Hydriding and dehydriding in air-exposed MgFe powder mixtures

MgFe mixtures, with a nominal Fe content of 3 wt.% and 6 wt.%, hereafter MgFe (3 wt.%) and MgFe (6 wt.%), were produced by ball milling and exposed to air for 12 h. After a proper activation procedure, which consisted in heating in vacuum and three hydriding/dehydriding cycles; their hydriding and dehydriding reactions were characterized by a gravimetric method. The hydrogen uptakes were 5.3 wt. %, 5.6 wt. % and 6.2 wt. % for the air-exposed Mg, MgFe (3 wt.%) and MgFe (6 wt.%) mixtures respectively at 350 °C and 30 bar. Pressure-Composition-Temperature (PCT) curves demonstrated a reduction of the hysteresis of the MgFe mixtures as compared to pure Mg. Powder X-ray diffraction of the studied materials confirmed the formation of fine mixtures of Mg and Fe, without evidence of solid solution or mixed hydride formation.