Phase Transformations and Kinetics Peculiarities on Hydrogen Desorption by Composites Based in Magnesium–Nickel Eutectic Alloy

The evolution of the phase contents and kinetic characteristics of hydrogen desorption processes by composites based on the eutectic alloy Mg89Ni11, including those with additives of graphene-like material (GLM), obtained by reactive ball-milling in hydrogen, were studied using the in situ high-temperature X-ray diffraction technique, volumetric measurements on a Sieverts setup, and approximation of the registered kinetic curves by Avrami−Erofeev equation. It was shown that at the initial stage of desorption processes at 300–360°C and 0–1 atm. H₂, the decomposition of the magnesium dihydride phase makes the main contribution to the amount of hydrogen released from the composites. The addition of GLM has a positive effect on the kinetics of hydrogen desorption processes, concurring with that of the heat-conducting phase Mg₂NiH_≤0.3, which is also present in the composite. It was found that the apparent activation energy for the hydrogen desorption by composites is within a range of 125–140 kJ/mol H₂. The correlation of the obtained values with the results of both experimental studies and quantum-chemical calculations obtained in the study of other magnesium systems is discussed.