THE HYDRIDING KINETICS OF MlNi,-II. EXPERIMENTAL RESULTS

The hydriding kinetics of MINi, before and after activation were studied experimentally and discussed in terms of the models presented in Part I. The parameters in the kinetic equations previously obtained were determined. The experimental data were in excellent agreement with the equations. The results indicate that the first hydrogenation process is a phase transformation process, in which the nucleation and growth of P-phase is the hydriding rate-controlling step. After activation, the hydriding process is governed by a mixed-controlled mechanism, with the hydridingcontrolling step varying with the applied pressure and transformed fraction. Copyright @ 1996 International Association for Hydrogen Energy NOMENCLATURE The hydrogen concentration of the /?or u-hydride equilibriating with P,, at the interface between the aand the b-phase Diffusion coefficient of hydrogen atoms in c1and b-phase Nucleation barrier Reaction rate constants Ratio of active areas to the total area of the sample surface Constant, representing the constraint in the hydrogen activity Rate constant for hydrogen transition from the surface to the matrix