REDUCTION RATE OF DENSE WUSTITE WITH CO-C O2 GAS-MIXTURES

The reduction rate of dense wustite plates to iron with CO-CO2-Ar gas mixtures has been measured at 1203, 1273 and 1323K by using a thermoba lance. The effects of partial pressures of CO and CO2/CO ratios in the reducing gas on the reduction rate and the morphology of the iron for med on the wustite were investigated. The reduction proceeded in two c onsecutive stages. In the initial stage, no formation of metallic iron was observed and the reduction rate was slow. The iron ion concentrat ion at the wustite surface, estimated from the lattice parameter, incr eased with increasing reduction time and reached eventually to the con centration equilibrated with iron. In the next stage, metallic iron wa s formed and the reduction rate became markedly higher than that of th e initial stage. The reduction rate was affected by the morphology of formed iron and the deposited carbon. On the conditions that porous ir on layer was formed uniformly and carbon deposition was negligible, th e reduction rate was controlled by the chemical reaction process at th e interface. The reduction rate r (kg-oxygen/m2.s) was expressed by th e following equation, r=kc.(1 - alpha/Ke).Pco where Ke and alpha are t he equilibrium constant for the chemical reaction and Pco2/Pco ratio i n the gas phase, respectively. The temperature dependence of the appar ent chemical reaction rate constant kc (kg-oxygen/m2.s.Pa) was express ed by the following equation kc=3.84 x 10(-6).exp(-9.42 x 10(4)/RT).