Synthesis by High-Energy Ball Milling of MgH<sub>2</sub>-TiFe Composites for Hydrogen Storage

Abstract

The aim of this work is to investigate the influence of some processes variables on the microstructure and hydrogen absorption kinetics of MgH2 - X wt.% TiFe composites. Samples were synthesized by high-energy ball milling in a planetary (X = 40, 50, 60) and shaker mill (X = 40) under high-purity argon atmosphere. Commercial MgH2 instead of Mg powder was used in order to reduce adherence on the vial and balls. TiFe powder was previously produced by ball milling a mixture of TiH2 and Fe powders followed by a reaction synthesis at 600oC. Milled composites samples were characterized by XRD and SEM analysis. Milling time was preliminary investigated (X = 40) in the planetary ball mill (6 to 36h). TiFe particle size reduction was shown to be difficult since they are surrounded by MgH2 matrix. Strong particle reduction was obtained by using a shaker mill only for 2 hours and adding cyclohexane as process control agent. No reaction between MgH2 and TiFe compound was observed in any milled sample. Hydrogen absorption kinetics measurements of the as-milled samples were conducted on an Sieverts' type apparatus at room temperature after hydrogen desorption at 350oC under vacuum. The best hydrogen kinetics (3 wt% at the first hour) was attained by the planetary milled sample (36 h). Higher hydrogen capacity was observed for the sample milled in the shaker mill (4.0 wt.%), but only after 13h.