Effect of Ca(II)-ion in Wüstite on its Reduction to Iron

Abstract

Fired compacts of hematite doped with different contents of CaO (mass fractions were 3.5, 4.0, 4.5, 5.0 %) were isothermally reduced to wustite in a CO-CO 2 gas mixture at 1173K. It was found from X-ray diffraction investigation that the lattice parameters of wustite increased with CaO content dissolved in wustite crystal. The pure wustite as well as the wustite doped with CaO were reduced at different temperature. The results showed that the reductions were promoted with increasing CaO content. The higher the content of CaO dissolved in wustite crystal was, the larger the lattice parameter and the interplanar distances of wustite became. This expansion was helpful to the migration of Fe ions and enhanced the reduction. At the early stage, the reduction of pure and doped wustite compacts was controlled by the interfacial chemical reaction step. At the latter stage, the gaseous diffusion was the rate-determining step for both sample types.