Synthesis of Mg2FeH6 by High-Temperature High-Pressure Reactive Planetary Ball Milling

Herein, a new approach for the synthesis of metal hydrides using simultaneous high-temperature and high-pressure reactive ball milling is demonstrated by preparing ternary magnesium iron hydride. The novelty and uniqueness of this technique are based on its integration of a specially designed and manufactured milling vial, allowing synthesis at controlled elevated temperatures (room temperature [RT]-400 degrees C) and pressures up to 100 bar. A Mg and Fe (2:1) mixture is used as a substrate for Mg2FeH6 synthesis. The effects of temperature on the synthesis kinetics and their outcomes are examined. An increase in the temperature accelerates the kinetics of hydrogen absorption for MgH2, while Mg2FeH6 formation is observed only above 250 degrees C. Increasing the reaction temperature not only causes magnesium particle refinement due to the hydrogenation and formation of magnesium hydrides but also leads to the agglomeration of iron caused by plastification due to a lack of strain hardening. The maximum conversion to Mg2FeH6 is observed for the sample premilled at RT. In this work, it is revealed that additional physical variables, e.g., pressure, temperature, time, and milling speed, during mechanochemical synthesis and material properties, need to be evaluated and considered to improve the reaction kinetics and yield of the synthesis.