Reduction Behaviour of Wüstite Doped with MgO

Compacts made from pure wüstite and compacts doped with 2% MgO were annealed at 1000°C for 3 hrs in 50%CO‐CO₂ gas mixtures. The annealed samples were isothermally reduced at 800‐1100°C in H₂ gas. Selected samples were isothermally reduced at 1000°C with pure CO and 50%H₂‐CO gas mixture to investigate the effect of gas composition on the reduction processes. The oxygen weight loss resulting from the reduction of the samples was recorded as a function of time. X‐ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy and porosity measurements were used to characterize the annealed and reduced samples. Magnesio‐wüstite (MgO·FeO) phase was formed during the annealing of MgO doped wüstite. The MgO·FeO in turn decreased the porosity of the annealed doped samples compared to pure wüstite compacts. The influence of temperature, gas composition and MgO content on the reduction behaviour and the morphology of the annealed samples was investigated. The values of the apparent activation energy were calculated from Arrhenius plots and correlated with the reduction mechanism. The reduction rate increased with reaction temperature. In doped compacts, the MgO·FeO phase was not completely reduced both at lower reduction temperature (800°C) and during reduction with pure CO. From the activation energy values, the initial reaction stage was controlled by the combined effect of chemical reaction and gas diffusion while solid state diffusion controlled the final stage of reduction. Morphologically, metallic iron was formed in different shape structures under the effect of MgO addition and reduction conditions.