Growth kinetics of MgH2 nanocrystallites prepared by ball milling

MgH 2 is one of promising hydrogen storage materials due to its high hydrogen capacity of 7.6 wt%. However, MgH 2 nanocrystallites easily grow up during hydrogen absorption―desorption cycling, leading to deterioration of hydrogen storage properties. To clarify the growth kinetics of MgH 2 crystallites , the growth characteristics of MgH 2 nanocrystallites are investigated in this work. The growth exponents of MgH 2 nanocrystallites in pure MgH 2 and MgH 2 ―10 wt% Pr 3 Al 11 samples are evaluated to be n = 5 and n = 6, respectively. Meanwhile, their activation energies for crystallite growth are also determined to be 109.2 and 144.2 kJ/mol, respectively. The increase of growth exponent and rise of activation energy for crystallite growth in MgH 2 ―10 wt% Pr 3 Al 11 composite are ascribed to the presence of nano-sized Pr 3 Al 11 phase.