Mechanochemical hydrogenation of ZrCuAlNi based powders: Part II. Mechanical treatment intensity and kinetic behaviour

This work focuses on the details of the mechanically activated hydrogen absorption kinetics in amorphous and nanostructured Zr55Cu30Al10Ni5 powders under different and controlled regimes of mechanical treatment. Absorption follows sigmoidal-shaped trends, whose slope points out a dependence of hydriding rate on the milling conditions. The amorphous powders display a linear correlation between the reciprocal of the semi transformation period and the milling intensity. This suggests that the process is ruled by the total mechanical energy delivered to the powder, and the same mechanochemical energy is necessary to activate the absorption. The decrease of the mechanochemical yield with the milling intensity was related to the different thermal stability of the hydrogenated specimens. Finally, the key role of surface phenomena as rate determining step was evidenced by estimating the reaction rates in terms of local quantities, as absorbed H2 molecules per active sites disclosed at each collision.