Milling effect on the microstructural and hydrogenation properties of TiFe0.9Mn0.1 alloy
Résumé
TiFe is a remarkable hydrogen storage alloy thanks to its reversibility at ambient temperature and pressure, high capacity and low cost. However, activation and sorption kinetics should be improved for practical applications. The effect of mechanical milling on the morphological, structural and hydrogen sorption properties of powdered TiFe0.9Mn0.1 alloy has been determined. Pristine alloy powder with mean particle and crystal sizes of 45 μm and 30 nm, respectively, was used as a reference. The pristine powder was ball milled for different times up to 5 h leading to significant changes in microstructural properties already observed after 0.5 h of milling. For such short milling time, the particle and crystal sizes decrease by a factor of five and three, respectively, with minor formation, if any, of amorphous phases. These microstructural changes promote a reduction of the activation time towards hydrogen absorption by a factor of five and enhance sorption kinetics. Besides, the hydrogen thermodynamic properties are slightly modified leading to sloping plateau pressures and hydride stabilization. These modifications may lead to a lowering of apparent desorption rates which should be carefully considered for the use of milled TiFe-type alloys in practical applications.