Abstract
The first part of this study investigates behavior of hydrogen absorption and desorption of non-equal-molar vacuum-arc-remelted as-cast CoFexMnTiyVZr (E6 alloys) based on their equal-molar counterpart by varying x (Fex alloys) and y (Tiy alloys) contents as well as measuring temperature. The second part does the same things as the first part but only changing the alloys to mechanical-alloying (MA) light-weighted AlMgNiwTiZr (E5 alloys). Experiments include XRD, SEM, EDS, DSC, PCI, and kinetics of hydrogen absorption and desorption for determination of crystal structure, microstructure, phase composition, hydrogen desorption temperature, and behavior of hydrogen absorption and desorption of E6 and E5 alloys, respectively. Primary conclusions are summarized as follows: The as-cast E6 alloys possess maximal hydrogen storage capacity of 2 wt %, plateau pressure in PCIs of 1 – 5 atm, time to 90 % of maximal capacity, t0.9, of about 100 s, values of hysteresis of less than 1, grain size before and after hydrogen absorption cycle of 17.1 nm - 50.3 nm, and 14.8 nm - 46.1 nm, respectively, volume expansion mostly of less than 3 %, crystal structure of C14 Laves phase for both before and after cycle states, elemental precipitation for excessive addition of Fe and Ti, and similar distribution as the AB2 alloys in the thermodynamic ΔH vs. (H/M)max plot. MA-E5 alloys have become alloys after 8-h MA with homogeneous distribution of composition, and possess maximal hydrogen storage capacity of 1.5 wt %, plateau pressure in PCIs of 5 – 12 atm, t0.9 of about 10,000 s, crystal structure composed of several intermetallics, property of easy amorphization for prolonged MA and for alloys containing less amount of Ni. Therefore Ni is an amorphization inhibitor in E5 alloys.