Metallic glassy Ti2Ni grain-growth inhibitor powder for enhancing the hydrogenation/dehydrogenation kinetics of MgH2.

Abstract

Because of its high thermal stability and poor hydrogenation/dehydrogenation kinetics, magnesium hydride (MgH2) requires mechanical treatment and/or doping with catalytic agents(s) to understand the decomposition temperature and accelerate the gas uptake/release kinetics. Whereas all catalytic species used for this purpose are crystalline materials, in this paper use of titanium nickel (Ti2Ni) metallic glassy (MG) nanopowders for enhancing the hydrogenation/dehydrogenation kinetics behavior of MgH2 powders is reported. In the present research, MG-Ti2Ni ribbons, prepared using a melt spinning technique were snipped into small pieces and then cryo-milled under a flow of liquid nitrogen to obtain submicron-powders (500 nm). The as-prepared MgH2 powders were doped with 10 wt% of the glassy powder and then cryo-milled for 25 h. The structural and morphological analysis indicated that the cryo-milling process succeeded in maintaining the short-range order structure of MG-Ti2Ni, and in reducing the MgH2 grain size to the nanolevel. The results showed that the as-prepared nanocomposite powders obtained after 25 h of cryo-milling decomposed at 283 °C, with an apparent activation energy of 87.3 kJ mol−1. The MgH2/10 wt% MG-Ti2Ni nanocomposite powders were cold rolled into thin strips, using a cold rolling technique. These cold rolled strips possessed excellent morphological characteristics, shown by the homogeneous distribution of the MgH2 spherical particles (10 nm in diameter) in the glassy Ti2Ni matrix. Furthermore, the hydrogenation/dehydrogenation kinetics measured at 225 °C were very fast, as indicated by the short time (400 s) required to uptake/release 5.7 wt% H2. At this temperature, the system possessed good life-time cycling performance – achieving 84 continuous cycles within 30 h without failure or degradation.