HYDRIDING AND DEHYDRIDING KINETICS

The processes involved in the first few hydriding-dehydriding cycles, referred to as activation, are discussed. The controversial activation of TiFe is reviewed and new H//2-D//2 isotope scrambling results are presented which indicate that metallic iron does not play a catalytic role. The hydriding-dehydriding kinetics are resolved into three interacting processes: intrinsic kinetics, heat flow, and mass flow. The intrinsic kinetics are further resolved into three processes occurring simutaneously and in series: a surface process, diffusion, and phase transformation. The problem of determining the rate-limiting intrinsic process from the time-temperature-pressure (t-T-P) dependences of the different processes is discussed.