Ce. Buckley et al., STABILITY OF THE HYDROGEN ABSORPTION AND DESORPTION PLATEAUS IN LANI5-H .4. THERMAL HISTORY EFFECTS, Journal of alloys and compounds, 231(1-2), 1995, pp. 460-466
We consider the effects of elevated (uniform) temperatures on the pres
sure hysteresis of LaNi5-H, concentrating on two main aspects: (i) pro
motion of gamma-phase formation and (ii) annealing effects. Hysteresis
data taken at temperatures up to 110 degrees C and at 30 degrees C af
ter annealing at temperatures up to 400 degrees C are presented and di
scussed. A strictly ascending sequence of measuring and annealing temp
eratures was employed. From the discontinuities in the absorption and
desorption plateaux, the formation of the gamma phase at 90 degrees C
in absorption and 60 degrees C in desorption was inferred. Both these
temperatures are lower than in the original studies during an ascendin
g temperature sequence. Critical perusal of published data suggests th
at detailed thermal history, rather than measuring temperature: determ
ines the temperature at which the gamma phase appears. Hydrogen cyclin
g at 110 degrees C caused the gamma phase to also form during the imme
diately following absorption-desorption cycle executed at room tempera
ture. It is tentatively proposed that the microstructural modification
required to form the gamma phase at room temperature is an ordering o
f dislocations.