The effect of the additive V on the rate of hydrogen desorption from MgH2 is investigated using high-pressure differential scanning calorimetry (HP-DSC). The HP-DSC data obtained at different temperatures were analysed in terms of the nucleation and growth of the Mg phase within the hydride matrix and the subsequent movement of the phase boundary. Activation energies (EA) obtained for the different steps show that the rate determining step is very much dependent on the conditions of dehydriding. The high value of EA found (600 kJ mol−1 H) for the nucleation step suggests that the V inhibits nucleation of the α-Mg from the hydrided Mg-9.5 wt% V composite sample. This has been attributed to the precipitation of vanadium in the MgH2 matrix creating accommodation strains, leading to dislocations around the vanadium particles. These can then act as sinks for the hydrogen thereby increasing the activation energy for nucleation of hydrogen.
- vapour deposition
- thermal analysis