Jiri Cermak

Desorption Kinetics of Hydrogen in Mg2NiH4 Hydride and in Hydrogeneated Eutectic (Mg/Mg2Ni)Hx

Mg-Ni alloys are perspective hydrogen-storage materials. In the present work, kinetics of hydrogen desorption was studied in Mg2NiH4 hydride and in hydrogenated eutectic (Mg/Mg2Ni)Hx. Time dependence of desorbed hydrogen was measured in temperature interval 552 –723 K and hydrogen diffusion coefficients were evaluated from obtained desorption curves. Results were interpreted in relation to phase composition investigated parallel by XRD. It was found that microtwinned low-temperature phase LT2 slows-down considerably the hydrogen desorption rate.

Interrelation between Hydrogen Desorption Kinetics and Structure of (Mg2Ni)Hx and Hydrogenated Eutectic(Mg/Mg2Ni)Hy

Mg-rich alloys of the binary system Mg-Ni are prospective hydrogen-storage materials. In the present study, desorption characteristics of hydrided Mg2Ni intermetalic and hydrided Mg/Mg2Ni eutectic mixture were investigated. Structure of experimental materials during the hydrogenation was observed by SEM. Three modifications of (Mg2Ni)Hx (x ~ 4) were prepared differing in the ratio of two low-temperature phases f = LT2/LT1: with (i) f >1, (ii) f ~ 1 and with (iii) f <1. Evolution of the ratio f during hydrogen desorption was checked by XRD. It was found that the micro-twinned phase LT2 is not desirable in hydrogen-storage materials containing Mg2Ni intermetallic. Diffusion coefficient of hydrogen in LT2 is about 20 times lower than in LT1.