Microstructural evolution of ball-milled Mg-Ni powder during hydrogen sorption

Ball-milling of Mg75Ni25 powder blends were carried out in a SPEX-8000 shaker mill. The morphology and microstructure of the milled powders were studied by scanning electron microscopy and X-ray diffraction, respectively. The dehydrogenation process of the sample milled for 10 h was stopped at different hydrogen contents (25, 50 and 75 percent of the maximum capacity) in a Sieverts' type apparatus, in order to achieve partially desorbed states. For comparison, the fully hydrided (100 percent) and the fully dehydrided (0 percent) states were also obtained. Convolutional multiple whole profile fitting analysis of the corresponding X-ray powder diffractograms was carried out in order to monitor the evolution of microstructural parameters during desorption, such as average coherent crystallite size and size distribution of two hydrides (Mg2NiH4 and Mg2NiH0.3) that nucleate during the hydrogenation of Mg-Ni powders. The desorption induced changes in the relative amount of the hydride phases were also quantified.