Effect of Al* generated in situ in hydriding on the dehydriding properties of Mg-Al alloys prepared by hydriding combustion synthesis and mechanical milling

Abstract In this work, the effects of Al* generated in situ in hydriding on the dehydriding of Mg-Al alloys prepared by Hydriding Combustion Synthesis (HCS) and Mechanical Milling (MM) were studied. Thermal analysis showed that the peak dehydriding temperature of MgH 2 was reduced by 25 °C (or 11 °C) when 20 at% Al was added in HCS (or MM) process, even though, the same dehydriding reaction of 17MgH 2  + 12Al*/Al → Al 12 Mg 17  + 17H 2 was observed. Isothermal dehydriding at 300 °C for 3 h demonstrated that it took 81 min for HCS+MM-MgH 2 to desorb 50% of hydrogen, while only 24 min was required for HCS+MM-Mg 80 Al* 20 . The apparent activation energy for dehydriding of MgH 2 was reduced from 144.3 ± 7.19 kJ/mol for HCS+MM-MgH 2 to 118.8 ± 6.73 kJ/mol for HCS+MM-Mg 90 Al* 10 . The scanning electron microscopy/energy dispersive spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the Al* in situ generated from the hydriding of Al 12 Mg 17 in HCS would significantly decrease dehydriding temperature and improve dehydriding kinetics of the MgH 2 -Al composites because of a uniform distribution, the shortening reaction diffusion length, providing unoxidized surfaces to react with MgH 2 and the high chemical activity of Al*.