Reaction mechanism of hydriding combustion synthesis of Mg₂NiH₄

A previous study suggested that the process of combustion synthesis of Mg₂NiH₄ from the compact of magnesium and nickel mixture in pressurized hydrogen cannot be expressed by a single reaction formula such as 2Mg+Ni+2H₂ = Mg₂NiH₄. In this paper, our attention is addressed to studying the reaction mechanism during the process of hydriding combustion synthesis of Mg₂NiH₄ by means of a differential scanning calorimeter (DSC) and an X-ray diffractometer (XRD). The results show that this process is consisted of seven distinguished reactions: (1) Mg+H₂→MgH₂; (2) MgH₂→Mg+H₂; (3) 2Mg+Ni→Mg₂Ni; (4) 2Mg+Ni→Mg₂Ni (L); (5) Mg₂Ni+0.15H₂→Mg₂NiH_0.3; (6) Mg₂Ni+2H₂→Mg₂NiH₄ (HT); and (7) Mg₂NiH₄ (HT)→Mg₂NiH₄ (LT).