The mechanism and kinetics of hydride formation in Mg-10wt.%Ni and CeMg12

The proposition that the apparent differences between the reactivities of magnesium and hydrogen are partially due to a lack of appreciation of the effects of various parameters on the kinetics is developed. The results of investigations of the formation-decomposition kinetics and morphology of CeMg12 and Mg-10wt.%Ni alloys performed at pressures and temperatures where only the formation of the MgH2 hydride is reversible support the hypothesis that the high reactivity of such alloys with hydrogen is due, at least partially, to the effects of morphological parameters such as mechanical stresses and strains and incoherent grain boundaries which increase hydrogen diffusion and hydride nucleation and which are produced by the formation of finely divided precipitates of CeH3 or Mg2Ni. The decrease in the hydrogen capacity on cycling is interpreted as a consequence of the removal of defects.