Effects of milling time on the hydrogen storage properties of mg-based transition metals-added alloys

Abstract

In this work, Mg was employed as a starting material. Ni, Fe and Ti were selected as additives to improve hydriding and dehydriding rates of Mg. A 90 wt.% Mg + 5 wt.% Ni + 2.5 wt.% Fe + 2.5 wt.% Ti sample [named 90Mg-Ni-Fe-Ti (8 h)] was prepared by mechanical grinding under H2 atmosphere (reactive mechanical grinding) for 8 h, using a planetary ball mill. The hydrogen-storage properties of the prepared sample were then investigated and compared with those of a 90 wt.% Mg + 5 wt.% Ni + 2.5 wt.% Fe + 2.5 wt.% Ti sample previously studied by preparing via reactive mechanical grinding for 4 h [named 90Mg-Ni-Fe-Ti (4 h)]. Reactive mechanical grinding for a longer time (for 8 h), compared with that for 4 h, intensified the effects of reactive mechanical grinding. After activation, 90Mg-Ni-Fe-Ti (4 h) had higher initial hydriding and dehydriding rates and larger quantities of hydrogen absorbed and released for 60 min than 90Mg-Ni-Fe-Ti (8 h). Prolonged milling (for example, for 8 h) is considered to bring about coalescence of particles which is caused by severe plastic deformation of ductile Mg particles. The stronger effect of hydriding-dehydriding cycling and the less compact agglomeration are believed to lead to the higher initial hydriding and dehydriding rates and the larger quantities of hydrogen absorbed and released for 60 min of 90Mg-Ni-Fe-Ti (4 h) than those of 90Mg-Ni-Fe-Ti (8 h) after n = 2.