Cold rolling of MgH2 powders containing different additives

Abstract

In this study we have used cold rolling (CR) as a successful method to incorporate additives into MgH2. The mixtures of MgH2 + 2 Mol% X, with X = Fe, Nb, Fe2O3, Nb2O5, FeF3, were processed by CR using a horizontal rolling mill and then followed by a detailed microstructural characterization which includes X-ray diffraction (XRD) with Rietveld refinement, Differential Scanning Calorimetry (DSC) and kinetic measurements. The CR processing resulted in a drastic crystallite size reduction, ∼8–17 nm, strong texture and partial conversion from the β to the γ-MgH2 phase. The orthorhombic metastable NbHx phase was detected in the XRD pattern of the mixture MgH2 + Nb after CR, indicating the high energy involved in the CR processing. The samples containing Fe and FeF3 as additives presented the lowest desorption temperature ranges. All additives presented beneficial effect on the dehydrogenation kinetic measurements (measured at 623 K and 598 K) compared to pure MgH2, in especial for the samples containing Nb2O5 and FeF3.