Hydrogenation behavior of Mg85Zn6Y9 crystalline alloy with long period stacking ordered structure

Abstract The hydrogenation behavior and structural change of Mg 85 Zn 6 Y 9 alloy with a long period stacking ordered (LPSO) structure are investigated. YH 2 hydride was formed in this alloy below 0.1 MPa hydrogen and the LPSO structure was destroyed. The remaining phase decomposed into MgH 2 and MgZn 2 by further hydrogenation. Finally, this alloy absorbed 1.6–1.8 (H/M) hydrogen and disproportionated into MgH 2 , YH 3 and MgZn 2 phases. Equilibrium hydrogenation at 673 and 623 K took 2 and 20 h, respectively. After dehydrogenation, 0.2–0.4 (H/M) hydrogen still remained as yttrium hydrides and hcp-based new phase was formed. However, the LPSO structure was not reformed. Hydrogen permeation was observed in this alloy under pressure differences of 0.4 and 0.1 MPa hydrogen at 623 K; however, the hydrogen permeability was 5.8 × 10 −10 (mol. H 2 m −1 s −1 Pa −0.5 ). The hydrogen diffusion coefficient of the alloy estimated from hydrogen absorption and permeability measurements was in the order of 10 −10 (m 2  s −1 ).