Microstructural evolution of ball-milled MgH 2 during a complete dehydrogenation–hydrogenation cycle

Abstract

Repeated dehydriding–hydriding cycles of ball-milled nanocrystalline MgH 2 was carried out in a Sieverts’-type apparatus. In order to characterize the microstructural changes during a complete MgH 2 → Mg → MgH 2 transformation, the fourth desorption and subsequent absorption were interrupted at different hydrogenation stages. Convolutional multiple whole profile fitting procedure of the corresponding X-ray diffractograms was applied to reveal the evolution of microstructural parameters during the sorption cycle, such as average coherent domain size and crystallite size distribution. Complementary analysis of lattice parameters was also carried out. In this paper we demonstrate that analysing solely the evolution of microstructural parameters during cycling leads to similar rate-controlling mechanisms obtained by sorption kinetic measurements.