Characterisation of Mg–x wt.% FeTi (x = 5–30) and Mg–40 wt.% FeTiMn hydrogen absorbing materials prepared by mechanical alloying

Abstract

Composites based on Mg with intermetallic FeTi (up to 30wt.%) and FeTiMn (40wt.%) were prepared by mechanical alloying for evaluation of their hydrogen storage characteristics. In the first case FeTi was prepared by mechanical alloying and subsequently milled with Mg under argon in different proportions. Powders milled under argon had to be activated by remilling under hydrogen. In the second case FeTiMn prepared by melting was milled together with MgH2 under hydrogen. Hydrogen storage characteristics, pressure-composition isotherms and kinetics were investigated under different parameters. Among the FeTi composites, Mg–5wt.% FeTi had the maximum absorption capacity of 5.80wt.% at 300°C and 5.12wt.% at 200°C. At 300°C the initial desorption rate was the highest for Mg–10wt.% FeTi, but its final desorption capacity was less than that of Mg–5wt.% FeTi. None of the compositions showed any desorption at 200°C. In the case of composites with FeTiMn, absorption and desorption temperatures decreased by ball milling and higher storage capacities were achieved. In Mg–40wt.% FeTiMn, the lowest absorption and desorption temperatures were 80 and 240°C, respectively, with the material absorbing 4wt.% hydrogen even at 80°C. The kinetics improved with increasing milling time.