1998 Volume 84 Issue 5 Pages 327-332
Dense wustite plates containing CaO have been reduced at 1273K with CO-CO2-Ar gas mixtures which have a chemical potential to form metallic iron. In the case that the samples were reduced with low Pco and high α(=PCO2/Pco) gas mixtures, only the oxygen content of the samples decreased and metallic iron was not formed in the early stage of the reduction. A mixed chemical reaction/solid state diffusion limited model was applied to this stage. The reduction rate r was expressed by r= k'·(1-α/Ks)· Pco (kg-oxygen/m2·s),
where k' and Ks are the apparent chemical reaction rate constant and the PCO2/Pco ratio in the reducing gas mixture in equilibrium with the surface wustite, respectively. The k' and inter-diffusion constant D were estimated by comparison of the iron ion concentration profile in the sample obtained from the lattice parameter measurement with that calculated from the model. The k' increased markedly with CaO content and was dependent on Ks as expressed by k'= A·Ksn (kg-oxygen/m2·s·Pa),
where A and n are CaO-dependent constants. The D was in the range of 2.86.4×10-10m2/s. The mass change of the sample during the reduction was explained reasonably by the model. Remarkable increase in the chemical reaction rate shortened the reduction time up to the metallic iron formation.
