Nucleation and growth behaviors of hydriding and dehydriding reactions of Mg2Ni

Highlights: • Preparation of Mg₂Ni by sintering under Ar in a stainless steel crucible at 823 K. • Application of Johnson-Mehl equation for the nucleation and growth mechanism. • Reverse dependences on temperature of initial hydriding rate and quantity of H absorbed for 60 min. • Hydriding and dehydriding reactions progressed by a nucleation and growth mechanism. - Abstract: Mg₂Ni has drawn attention due to its high reaction rates, good reversibility, and possibility to be applied as a negative electrode in the Ni-MH (metal hydride) batteries. Mg₂Ni samples were prepared by sintering under Ar in a stainless-steel crucible at 823 K. Johnson-Mehl equation for nucleation and growth mechanism was applied to the behaviors of hydriding and dehydriding reactions of Mg₂Ni. At 571 K under 30 bar H₂, the activation of the Mg₂Ni sample was completed at the number of cycles of three (n = 3). At n = 3, hydrided fractions of the sample were 0.51 (1.92 wt% H) at 0.50 min and 0.90 (3.38 wt% H) at 2.00 min. Reverse temperature dependences of the initial hydriding rate and the quantity of hydrogen absorbed for 60 min appeared from 571 K to 620 K. Hydriding and dehydriding reactions progressed by the nucleation and growth mechanism and could be expressed by the Johnson-Mehl equation.