In-situ synchrotron X-ray diffraction investigation of the hydriding and dehydriding properties of a cast Mg-Ni alloy

In previous research, it has been demonstrated that the hydrogenation kinetics of Mg-Ni alloys is significantly improved by elemental Na doping. To clarify the underlying mechanisms in terms of crystallographic phase changes during the reactions, in-situ hydrogen absorption and desorption as a function of temperature under constant hydrogen atmospheres of 2 MPa and 0.2 MPa, respectively, was studied. The experiments were performed at the Powder Diffraction beamline of the Australian Synchrotron facility with a gas flow cell and a hot air blower. This study showed that the hydrogenation of Na-doped Mg-Ni alloys can be identified at a temperature as low as 260 °C via an interface-controlled nucleation and growth mechanism without any prior activation whilst the dehydrogenation occurred at about 370 °C. The sequence of phase transformations associated with these reactions as well as associated expansion properties of individual phases during hydrogen sorption reactions as provided by the high resolution X-ray diffraction data are discussed.