The reducibility of calcio-wüstite (CW) originating from silico-ferrite of calcium and aluminum (SFCA) has been investigated from the perspectives of the morphology of SFCA and the concentration of FeO in CW. Two types of SFCA sample were prepared: columnar SFCA and acicular SFCA. The former was synthesized from reagent grade powders of Fe_(2)O_(3), CaCO_(3), SiO_(2) and Al_(2)O_(3), and contained columnar SFCA grains covered with slag. The latter was synthesized from iron ore and reagent grade CaCO_(3), and contained acicular SFCA grains, which were smaller than the columnar SFCA grains and had fine pores nearby. These samples were reduced in an XRD apparatus for high temperature use in a condition simulating a blast furnace where the oxygen partial pressure was controlled by CO–CO_(2) mixtures. The microstructures of the samples before and after reduction were observed by electron probe microanalysis (EPMA). XRD profiles indicated: (i) both SFCA samples were reduced to Fe via CW at 1000°C and (ii) acicular-SFCA-origin CW was reduced to Fe earlier than columnar-SFCA-origin CW, which suggests that the reducibility of acicular-SFCA-origin CW is higher than columnar-SFCA-origin CW. EMPA indicated: (i) most residual parts of acicular-SFCA-origin CW phase kept the morphologic feature of having fine pores as acicular SFCA during reduction as well and (ii) the FeO concentration in acicular-SFCA-origin CW was lower than that in columnar-SFCA-origin CW. Hence, it is concluded that the reducibility of SFCA-origin CW is dominated by the morphology of CW but not by the concentration/activity of FeO in CW.
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