Decomposition kinetics of metal hydrides: Experiments and modeling

The aim of the research was to understand decomposition of hydrides of metals and determine the most significant limiting reactions. We used functions that describe real physical processes, such as decomposition of hydride phase, desorption and diffusion of hydrogen, and morphology of phases. Dividing hydride materials to two classes depending on the type of bonding (metallic or non-metallic) allowed to explain details of kinetics of dehydriding. We show that for decomposition of non-metallic hydrides morphology of “nucleation and growth” is typical; while for metallic ones the “shrinking core” morphology is more common. In both cases hydrogen diffuses from the hydride-metal boundary to the outer surface through the metal phase rather quickly, so diffusion does not influence on the decomposition kinetics. The most probable limiting factor is the rate of hydrogen desorption from the metal phase. For the “shrinking core” morphology rate of hydride decomposition can also influence on the kinetics during the final stages of the process.