Results obtained with the iron oxide particles of different sizes (sub-micron, FeP, 40–80 lm and 80–160 lm) in Table 2 and Fig 4, illustrated that the highest reactivity corresponded to the commercial sub-micron powders during the first redox cycle. This suggests that if these iron oxide powders could be well dispersed into a LSF731 matrix, avoiding agglomeration and sintering, a significant increase in the reactivity of the composite material should be observed. To analyze the effect of the nominal cluster size on the reactivity several tests were performed in the TGA under the same operating conditions as experiments in Fig. 4. No clear effect of the cluster size was observed. SEM-EDX analyses of the composite OCMs demonstrated that the size of the iron oxide clusters was on the scale of 20 lm despite the initial cluster size used during
the preparation (Fig. 3). Agglomeration of the sub-micron powders
took place then during the OCM preparation. This could explain the
similarities in the reactivity tests when sub-micron iron oxide and
20–40 lm powders were used.