Variation of hydriding kinetic properties in massive samples of the LaAlxNi5-x system as a function of the Al content

The hydriding kinetics of the LaAlxNi5-x (0 less than or equal to x less th an or equal to 1.4) system was monitored for massive rectangular parallelep iped samples utilizing hydrogen pressures up to 70 atm and temperatures bet ween 238 and 423 K. The apparent activation energies for each composition a re derived from the temperature dependence of the reaction rate constants a t given P/P-eq ratios, where P is the applied experimental hydrogen pressur e and P-eq is the equilibrium pressure at a given temperature. The activati on energies appear to be model-independent and indicate a minimum at x=0.25 , resulting in a maximum hydriding reaction rate in the vicinity of this co mposition. This behavior correlates well with some bulk properties of the L aAlxNi5-x intermetallic system and the corresponding hydrides. (C) 2000 Els evier Science S.A. All rights reserved.