Effects of CaO and SiO2 on the Rate of H2 Reduction of Dense Wustite and the Morphology of Product Iron

Effects of CaO and SiO2 on the rate of H2 reduction of dense wustite were investigated in the temperature range of 6001000°C.The morphology of product iron by H2 reduction is classified into three types; dense iron with coarse pores, dense iron with few pores, and sponge iron with many fine pores. The reduction rate is closely related to the morphology of product iron. Difference of morphology of product iron was investigated in terms of the nucleation of iron, the manner of its growth and the morphology on the cross section of iron nucleus formed on the surface of wustite in the early stage of reduction.In the reduction of pure wustite, dense iron with coarse pores was obtained at higher temperature. It appears that pores in the dense iron layer were produced as a result of difference in specific volume between iron and wustite and sintering process of iron.In the reduction of wustite containing CaO, porous iron was produced inside the iron nucleus in the early stage of reduction at all the temperatures examined. From the observation of iron nuclei, it was suggested that the presence of CaO in wustite accelerated the chemical reaction between H2 and wustite surface.In the reduction of wustite cotaining SiO2, iron nuclei on the wustite surface were very small and did not show any further growth. Subsequent reduction occured only with the increase in the number of iron nuclei. The morphology of product iron layer was sponge iron with many fine pores except for the reduction at 700°C.