Effects of SiO2 and Al2O3 on the Lattice Parameter and CO Gas Reduction of CaO-containing Dense Wustite.

Abstract

The effects of SiO2 and Al2O3 on the lattice parameter and the initial reduction rate of CaO-containing wustite were studied at 1 273 K. Wustite plates containing 0.5-2 mass% CaO, 0.2-2 mass% SiO2 and 1 mass% Al2O3 were prepared at the mass fractions of CaO/SiO2=0.5-5. The lattice parameter of CaO–SiO2- containing wustite decreased with decreasing CaO/SiO2 ratio at a constant CaO content. This corresponded to a decrease of the dissolved content of CaO in the wustite due to a formation of CaO-FeO-SiO2 compounds. Similarly, the dissolved content of CaO decreased in CaO-SiO2-Al2O3-containing wustite. The process of CO gas reduction within the wustite phase field was traced with the lattice parameter measurement of the partially reduced samples and was analyzed with a mixed-control model of chemical reaction at the surface and the solid state diffusion in the wustite. The chemical reaction rate constant, k´, decreased with increasing the amount of SiO2 addition at a constant CaO content. The dependence of k´ on SiO2 (and Al2O3) addition was in good accordance with the change in the dissolved content of CaO in the wustite owing to the formation of the compounds containing CaO. The inter-diffusion coefficient, D, tended to decrease slightly with increasing the amount of compound.