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

Abstract

Herein, a new approach for the synthesis of metal hydrides using simultaneous high‐temperature and high‐pressure reactive ball milling (HTHPRBM) 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 (RT‐400°C) and pressures up to 100 bar. A Mg and Fe (2:1) mixture was used as a substrate for Mg2FeH6 synthesis. The effects of temperature on the synthesis kinetics and their outcomes were examined. An increase in the temperature accelerated the kinetics of hydrogen absorption for MgH2, while Mg2FeH6 formation was observed only above 250°C. Increasing the reaction temperature caused magnesium particle refinement due to the hydrogenation and formation of magnesium hydrides but also led to the agglomeration of iron caused by plastification due to a lack of strain hardening. The maximum conversion to Mg2FeH6 was observed for the sample premilled at room temperature. This work 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.This article is protected by copyright. All rights reserved.