Kinetic study of the redox process for separating and storing hydrogen: Oxidation stage and ageing of solid

The behaviour of an iron oxide sample (Fe2O3) during successive reduction–oxidation cycles (steam–iron process) has been investigated by means of a thermobalance system acting as a differential reactor.The Johnson–Mehl–Avrami–Kolmogorov (JMAK) model, based on nucleation and growth mechanisms, has been used to describe the individual reoxidation processes as well as to predict the stability of the oxide after a high number of redox cycles.The effect of temperature, steam partial pressure and oxidation length has been discussed.The experimental results, as well as the parameters for the JMAK model, show that there is no significant effect of the temperature and the steam partial pressure used in the oxidation stages on the behaviour of the subsequent cycles (taking apart the first one). This conclusion applies also to the length of the oxidation period, if for such variable a value above a given threshold is used, which could be theoretically foreseen.