Reaction paths via a new transient phase in non-equilibrium hydrogen absorption of LaNi2Co3.

This study investigated the non-equilibrium hydrogen absorption reaction paths of the AB 5 -type LaNi 2 Co 3 alloy using time-resolved in situ synchrotron X-ray diffraction. Diffraction data were collected every second for reactions under two hydrogen loading pressures. Hydrogen absorption with a hydrogen loading of 1 MPa rapidly transformed α phase to a transient phase (estimated to be LaNi 2 Co 3 H 3.1–3.6 , named γ∗); this has not previously been observed under equilibrium processes. The γ∗ phase continuously transformed into the γ phase (LaNi 2 Co 3 H 4.5–5.0), and the β phase (LaNi 2 Co 3 H ~3.6) was not formed. When 0.18 MPa of hydrogen was loaded, initially, the γ∗ phase appeared, followed by the formation of the β phase, finally transforming into the γ phase. These results indicate that a higher loading pressure promotes the formation of the γ∗ phase and assists its continuous transformation into the γ phase by enhancing the dissolution of hydrogen into the α and γ∗ phases. Image 1 • Hydrogen absorption processes were observed every second in real time. • Reaction paths via a new transient phase were found. • Fast and slow reactions followed different reaction paths. • The lattice expansion was discussed in relation to the hydrogen distribution. [ABSTRACT FROM AUTHOR]