Effects of ball milling on hydrogen sorption properties and microstructure of ZrCo alloy

In the present work, the effects of ball milling on the hydrogen sorption kinetics and microstructure of ZrCo have been specifically studied. Experimental measurements show that the hydrogen absorption rate and hydrogenation amount decrease for ZrCo by increasing the ball milling time, while the hydrogen desorption rate increases. After ball milling, the disproportionation rate of ZrCo is enhanced, whereas the disproportionation extent is reduced. It is found from X-ray powder diffraction results that the lattice parameter of ZrCo gradually decreases from 3.197 angstrom to 3.188 angstrom when the ball milling time extends from 0 h to 8 h, which is mainly responsible for the disproportionation behavior. Meanwhile, scanning electron microscope and Focused Ion Beam images demonstrate that the morphology of ZrCo obviously changes after ball milling, which is closely related to the hydrogen sorption kinetics. Furthermore, the energy dispersive spectroscopy results reveal that the composition of ZrCo and distribution of Zr and Co elements play an important role in the disproportionation rate as well as the kinetic mechanism. Kinetic model analysis suggests that the disproportionation of ZrCo should be nucleation and growth process. However, the detailed rate limiting modes for nucleation and growth processes may vary according to different ball milling time. This study can provide valuable considerations for further improving the hydrogen storage properties of ZrCo on the basis of disclosed relationship between the kinetic performances and the characteristics of microstructure for ZrCo after ball milling.