Hydriding and dehydriding characteristics of mechanically alloyed mixtures Mg- xwt.%Ni ( x = 5, 10, 25 and 55)

Abstract

The kinetic characteristics of magnesium have been improved either by adding a catalyst or by using magnesium-based alloys. A comparative study of Mg 2Ni and a mechanically alloyed mixture Mg-55wt.%Ni has been recently carried out in the laboratory. The mixture presents some interesting properties and the preparation of this material is easier and less energy consuming owing to the absence of heating. However, while the hydrogen capacity (3.2 wt.%) is close to that of Mg 2Ni, it is significantly smaller than that of magnesium (7.6 wt.%). Therefore, to improve this characteristic, several compositions of mechanically alloyed mixtures Mg- xwt.%Ni with a lower nickel weight content have been studied ( x = 5, 10 and 25). It was shown that the amount of nickel has an important effect on the hydriding-dehydriding kinetics. The decrease of the particle size and the augmentation of the density of defects are because of hydriding-dehydriding cycling. These effects are enhanced by an increase in the nickel content and increase the rate of the hydriding and dehydriding reactions. In contrast, the hydrogen storage capacity diminishes as the amount of nickel increases. For these reasons, Mg-10wt.%Ni and Mg-25wt.%Ni are the most favourable compositions.