Microstructure and hydrogenation properties of RETMMg15 (RE= Nd, Gd; TM= Cu, Ni) alloys

Abstract

In this study, five RETMMg15 (RE = Nd and/or Gd, TM = Ni and/or Cu) alloys have been successfully synthesized by induction melting of pure elements and characterized by XRD, BSE-SEM and EDXS. Their hydrogen storage properties have been studied from kinetic and thermodynamic points of view. The synthesized alloys NdNiMg15, NdCuMg15 and GdCuMg15 were composed of a RETMMg15 main phase with lesser proportions of α-Mg phase and other ternary phases. It has been found that substituting half of the RE (or TM) element by another RE (or TM) element leads to the formation of two solid solutions with composition: Nd0.5Gd0.5CuMg15 and NdCu0.5Ni0.5Mg15. Upon first hydrogenation, all alloys decomposed into binary or ternary hydrides. Next hydrogenation cycles allowed to store reversibly around 4.5 %wt. hydrogen. All alloys presented reduced MgH2 formation enthalpies as compared to pure Mg which is explained in term of “chemical milling”.