Mechanism of Metastable Wüstite Formation in the Reduction Process of Iron Oxide below 570℃

Abstract

The possibility of metastable wüstite below 570℃ during the reduction of iron oxides was discussed. There was uncertainty regarding the formation of metastable wüstite in the reduction of hematite below 570℃. Planar disregistry (1/δ) was employed to predict the probability of metastable wüstite formation during the reduction process. The calculated results showed that the δ of wüstite/magnetite is similar to that of iron/magnetite with plain and normal structures, but less than flake and finger structures. The difference in disregistry of different geometries of interfaces was suggested to be the principal driving force for the formation of metastable wüstite. This implies that the formation of metastable wüstite always accompanies the nucleation of iron structures with high δ relative to magnetite. The latter structures form easily in supported iron, leading to the relatively common observation of metastable wüstite in an iron catalyst. The analysis showed that the temperature range for metastable wüstite formation, 400℃～500℃, was most likely to occur where it created a predominance of flake and finger structures.