CaO- (0–20 mass%) and SiO
2-containing (0–30 mass%) wüstite (‘FeO’) compacts were isothermally reduced at 1273 K under CO and H
2 gas. Prior to reduction, the phase of dicalcium ferrite (Ca
2Fe
2O
5) and fayalite (Fe
2SiO
4) was equilibrated with ‘FeO’ at 1273 K under 50%CO/50%CO
2 and identified using X-ray diffraction and scanning electron microscopy. The rate of reduction for CaO-containing ‘FeO’ compacts under both H
2 and CO increased up to the vicinity of 2.5 mass% CaO, and then decreased with higher CaO dependent on the formation of an intermediate phase of dicalcium ferrite. For SiO
2-containing ‘FeO’, the rate decreased with SiO
2 additions. When the dense fayalite is present reduction using CO was limited, while considerable reduction was observed using H
2. The reduction was affected by three distinct reduction mechanisms of interfacial chemical reaction, gaseous mass transport, solid state diffusion of oxygen or a combination of these individual mechanisms termed the mixed control. The contribution of each mechanism with the content of CaO or SiO
2 affecting the reduction behavior was determined. The compact porosity increased when CaO was added to approximately 2.5 mass% and subsequently decreased with higher CaO, but continuously decreased with SiO
2 additions. The ratio of the effective diffusivity (D
e) to molecular interdiffusivity (D) was highest at the vicinity of 2.5 mass% CaO and thus the maximum reduction rate was obtained when the porosity was highest.
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