Fig. 1. Rietveld refinements of the XRD patterns for ball milled (a) pure MgH2 and (b) MgH2―10 wt% Pr3Al11 composite.

Fig. 2. Dark field TEM images (a, b) and crystallite size distributions (c, d) for ball milled pure MgH2 sample (a, c) and MgH2―10 wt% Pr3Al11 composite (b, d).

Fig. 3. MgH2 nanocrystallite sizes (a, b) and lattice strains (c, d) of pure MgH2 sample (a, c) and MgH2―10 wt% Pr3Al11 composite (b, d) after isothermal treatments.

Fig. 4. Relationships between ln(dD/dt) and lnD for (a) pure MgH2 and (b) MgH2―10 wt% Pr3Al11 composite.

Fig. 5. Correlations between ((${{D}^{n}}-D_{0}^{n}$) and holding time t for (a) pure MgH2 and (b) MgH2―10 wt% Pr3Al11 composite.

Fig. 6. Arrhenius plots of lnk versus 1000/T for (a) pure MgH2 and (b) MgH2―10 wt% Pr3Al11 composite.

Fig. 7. (a) HRTEM image showing the inhibition role of Pr3Al11 in growth of MgH2 nanocrystallites in the MgH2―10 wt% Pr3Al11 composite isothermally treated at 400 °C for 20 h, (b) FFT pattern and (c) IFFT image corresponding to the square region in (a).

Fig. 8. Isothermal dehydrogenation curves measured at 350 °C for the (a) pure MgH2 and (b) MgH2―10 wt% Pr3Al11 samples after isothermal treatments at 300, 350 and 400 °C for 20 h.