Pressure and temperature dependence of hydriding kinetics in massive Zr(Al_xFe_1-x)₂ samples, x = 0.2, 0.5

The hydriding kinetics of the Zr(Al_xFe_1-x) ₂, x = 0.2, 0.5, compounds was monitored for massive rectangular parallelepiped samples utilizing hydrogen pressures up to 80 atm and temperatures between 238 and 353 K (1 atm = 101 325 Pa). The self-heating effects were sufficiently low under these conditions to enable approximately isothermal conditions for the kinetic experiments. The experimental data were fitted to a shrinking core model. The hydrogenations of some samples were observed in real time, utilizing a video camera and specially designed experimental system. The apparent activation energies, E_a, for each compound 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. Combination of the present results with a previous one for Zr(Al_0.1Fe_0.9)₂ indicates a minimum of E _a at the x = 0.2 compound. This behavior is explained in view of the atomic vibrational properties across the Zr(Al_xFe_1-x) ₂ system.