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 than or equal to 1.4) system was monitored for massive rectangular parallelepiped samples utilizing hydrogen pressures up to 70 atm and temperatures between 238 and 423 K. The apparent activation energies for each composition are derived from the temperature dependence of the reaction rate constants at given P/P-eq ratios, where P is the applied experimental hydrogen pressure and P-eq is the equilibrium pressure at a given temperature. The activation 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 composition. This behavior correlates well with some bulk properties of the LaAlxNi5-x intermetallic system and the corresponding hydrides. (C) 2000 Elsevier Science S.A. All rights reserved.