Synthesis of Mg2Ni using stoichiometric and superstoichiometric compositions for hydrogen storage applications

A Mg2Ni intermetallic compound was synthesized through a mechanochemical route using both stoichiometric and slightly superstoichiometric mixtures of Mg and Ni. The former composition was processed by mechanical alloying, followed by annealing, while the latter composition using high-energy ball milling. X-ray diffraction (XRD) and scanning electron microscopy (SEM) was used to examine the effect of the annealing temperature and holding time on the phase abundance and surface morphology. The sample with a stoichiometric ratio of Mg and Ni was ball-milled under the argon atmosphere for 20 hours. The XRD pattern for this unannealed ball-milled alloy had no evidence of Mg2Ni phase formation. Mg2Ni phase formation was obtained on subsequent heat treatment of the sample. The heat treatment parameters, such as annealing temperature and holding time, were optimized to get the maximum yield of Mg2Ni. The optimum temperature for annealing was found to be 480 degrees C, with a holding time of 1 hour, and the phase abundance under these conditions of Mg2Ni was 52.9%. The yield of Mg2Ni increased with holding time. For 10 hours of holding time, the optimal yield of Mg2Ni (66.9%) was achieved. In the superstoichiometric ratio of Mg and Ni, the Mg2Ni phase was obtained in only 5 hours using high-energy ball milling. The microstructure of alloy synthesized under an optimal set of conditions was studied using SEM.