Hydrogen absorption kinetics of MmNi4.7Al0.3

We present the analysis of hydrogen absorption kinetics of MmNi(4.7)Al(0.3) samples performed to identify the limiting process during the reaction. Measurements using the Sieverts technique on activated (powdered), surface-treated (Pd-covered)and intentionally oxided samples were compared to the pressure-time dependence proposed in recently published models. While intentionally-oxided samples showed a hydrogen absorption kinetics limited by surface-related processes (chemisorption and/or surface barrier), the reaction with hydrogen in untreated or surface-improved samples were dominated by hydrogen diffusion. As we show in this work, the use of the proposed expressions to fit absorption experimental data provides a simple and useful method to identify the slowest individual process. (C) 1998 International Association for Hydrogen Energy.