Severe Plastic Deformation and Additive Distribution in Mg-Fe to Improve Hydrogen Storage Properties

Abstract

Magnesium (Mg) is a light metal with relatively low cost. Its hydride (MgH 2 ) is interesting for the safe hydrogen storage in solid state and has a high gravimetric capacity of 7.6%. Practical application of Mg is still hampered by high reaction temperatures and slow kinetics. In order to improve it and focus on more viable industrial processing conditions, Mg plates, with or without iron (Fe) addition, in the form of wires and powders, were submitted to severe plastic deformation (SPD) in air, starting with extensive cold rolling (ECR), followed by repetitive rolling (ARB). The samples were characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning (SEM) and transmission electron microscopy (TEM). H 2 storage properties were evaluated by differential scanning calorimetry (DSC) and Sievert's volumetric method. Mg processed by ECR+ARB resulted in larger grain refinement and densities of cracks than ECR. In addition, Fe in the form of continuous wires was fragmented and resulted in a better distribution of particles than powders, which agglomerated. Thus, finally, the synergetic effect of microstructural features and Fe as catalyst and its distribution improved activation, kinetics and hydrogen storage capacity.

Effect of Cold Rolling on Metal Hydrides

“…The system Mg + 8 mol% Fe was studied by Antiqueira et al using different morphologies of iron: wires, pieces of iron wool or unwound iron wool. 12) As expected, rolling induced a (002) texture for all samples. The hydrogenation kinetics and reversible capacity were improved with addition of iron.…”

Hydrogen Storage in Mg and Mg-Based Alloys and Composites Processed by Severe Plastic Deformation

“…The same conclusions pointing out the importance of texture and fine distribution of additive elements or phases were also obtained in mixtures of MgFe containing carbon nanotubes processed by hot extrusion and cold rolling. 59) The combined processing of CR and ARB was used in MgFe mixtures 60) resulting in compacted flakes containing (002) texture, similar to CR processing. However, better hydrogen sorption properties were observed after the combined CR+ARB processing, which was associated with grain size reduction, increased density of cracks and better distribution of Fe particles.…”

Effect of Cold Rolling on Magnesium-Based Metal Hydrides

“…Leiva et al investigated the effect of adding a small amount of iron to magnesium by cold rolling. 75) The best hydrogenation kinetics were for the samples to which iron was added in the form of continuously unwound wool. The ternary hydride Mg 2 FeH 6 was prepared by Jung et al by first cold rolling powder mixture of Mg and Fe.…”