Hydride decomposition characterization by means of “morphological trajectory” method—Applied to AlH3

Abstract New approach to analyse hydride decomposition kinetics operating with integral morphological parameters as well as kinetic parameters of possible rate-limiting reactions (nucleation, desorption and reaction at interface) is proposed. Morphology of new phase growth in powder particle is described in terms of specific values of new phase volume, outer surface occupied by new phase, interface area and their interrelations (“morphological trajectories”). The approach describes H-release kinetics for free-form shape of particles and growing nuclei. The applicability of the approach is limited by the requirements of fast enough H-diffusivity in metal areas of powder particles and of nucleation at the outer surface of particles. Alane powder completely meets these requirements. It was found that the rate-limiting step is the reaction at the interface with activation energy 104 kJ/mol. Morphology of the transformation depends on experiment conditions: the higher is reaction temperature, the smaller is quantity of new phase nuclei.