Effects of adding Nd on the microstructure and dehydrogenation performance of Mg90Al10 alloy

Abstract

Abstract In order to reduce the thermodynamic stability and improve the dehydrogenation kinetics of Mg hydride, a certain quantity of Nd was introduced into Mg90Al10 alloy to prepare the NdxMg90-xAl10 (x\u202f=\u202f2, 5, 8 and 10) alloys. The phase composition and distribution of the alloys identified by X-ray diffraction and scanning electron microscopy showed that there generated hydrogenation phases of Mg(Nd), Mg12Nd and Mg3Nd with increasing Nd content, which formed MgH2 and NdH3 phases during the hydrogenation through disproportionation reactions. The crystalline structure characterized by transmission electron microscopy showed that the grain size of the alloys decreases gradually with increasing Nd content after repeated hydrogenation cycles. The changes of phase composition and microstructure have significant improvement effect on the activation performance and dehydrogenation kinetics. However, Mg hydride in the alloys exhibited different thermodynamic stability. The dehydrogenation enthalpy (ΔHde) was 74.44, 82.59, 74.58 and 73.72\u202fkJ/mol H2 for the NdxMg90-xAl10 (x\u202f=\u202f2, 5, 8 and 10) alloys, respectively. Mechanism analysis showed that the existence of Mg(Nd) phase was the root cause of the increase of ΔHde for the Nd-5 alloy. For the Nd-8 and Nd-10 alloys, the formed Nd2H5 phase lowered the thermodynamic stability of MgH2 through causing the lattice deformation of Mg phase.