Solid structural changes during the reduction of iron oxides

Abstract

AbstractThe changes in the solid structure, i.e., grain size, shape and pore structure, during the reduction. of reagent-grade hematite to iron by CO−CO2 mixtures at temperatures between 725 and 925°C were investigated. The reduction of hematite to wustite was found to produce little structural change. In contrast, three mechanisms of structural change occurred during the reduction of wustite to iron. These included the thermal sintering of the wustite, the growth of fibrous iron filaments from the partially reduced wustite grains, and the sintering or “coarsening” of the reduced iron. A quantitative model for the sintering of the wustite is described.The effects of the structural changes on the reduction kinetics are reviewed. The sintering of the wustite reduced the over-all rate of reduction; the growth of the fibrous iron increased the rate of reduction. The sintering of the iron had little effect on the kinetics. The interaction between the sintering of the wustite and the growth of the fibrous irons...