Safe Processing Route for the Synthesis of Mg Based Metallic Hydrides

Metallic hydrides represent a safe way of storing hydrogen, minimising explosion and flammability risks. Nowadays there are several methods for the storage of hydrogen and the more conventional techniques are high-pressure tanks for gaseous hydrogen and cryogenic vessels for liquid hydrogen. However, there are two main drawbacks in the storage of gaseous and liquid hydrogen. First, as a fuel, hydrogen in the gaseous and liquid states is very combustible and the related law imposes strict regulations on its utilization, storage and transportation. Secondly, even under a high pressure, hydrogen gas is not dense enough for compact storage. Moreover, the gas storage at high pressure involves significant safety risks. Hydrogen storage in the metal hydrides does not have such deficiencies. Metal hydrides are safe and can be easily store and transported. For that reason, it should be stressed that metallic hydrides represent a safe way of storing hydrogen, minimising explosion and flammability risks. Among metallic hydrides, one of the most promising hydrides in terms of absorbed hydrogen content is Mg2NiH4. However, it is difficult to obtain Mg2Ni by the conventional melting method because of the large difference in vapour pressure and melting point between magnesium and nickel. This paper presents an alternative and safe method for obtaining such hydride: HCS (Hydriding Combustion Synthesis). This method presents some interesting advantages over its conventional counterpart: the process is carried out at lower reaction process, which means safer process and the alloy stoichiometry is closer to the nominal (Mg2Ni) which allow better hydrogen absorption behaviour. The aim of this work is to investigate the formation mechanism of this compound and to study some parameters of the process.