Thermodynamics of iron oxide in Fe x O-dilute CaO + Al 2 O 3 + MgO + Fe x O slags at 1873 K
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(pct Fe21) 21/2 pO2 aFe
and CFe31 5
(pct Fe31) 23/4 pO2 aFe
for an MgO-saturated MgO 1 CaO 1 Al2O3 slag, two experiments were carried out at 1873 K: (1) the distribution of iron between FexO dilute slags of the system and Pt 1 Fe alloys under controlled atmosphere, and (2) the equilibrium among molten iron or iron alloys, magnesiowustite, and molten slags. Although the activity of iron and the partial pressure of oxygen in each experiment are remarkably different, the values of the ferrous and ferric ion capacities agree well with each other. The influence of the MgO:CaO:Al2O3 ratio on the values of CFe21 and CFe31 was found to be limited within the experimental composition range. Using CFe21 and CFe31, the relationship between total iron content, (pct FeT), and partial pressure of oxygen, pO2, under iron saturation was calculated. The change in log pO2 with respect to the bulk slag composition is less than 0.2 within the range of (pct FeT) , 5.
I. INTRODUCTION
TO date, only a few articles regarding the activity of FeO in dilute solution in slags at steelmaking temperatures have been published, as a result of the experimental difficulty of finding a crucible capable of simultaneously holding molten iron and slag containing FeO. In addition, measuring and controlling the low partial pressure of oxygen resulting from the equilibrium between pure Fe and a slag with 10 pct FeO is difficult. In a previous study[1] done by the present investigators, the distribution of iron between FexO-dilute CaO 1 Al2O3 1 FexO slags and Pt 1 Fe alloys was measured. The redox equilibrium of iron in this slag system under partial pressures of oxygen ( pO2), ranging from 1027 to 10 23, and the activities of iron (aFe), ranging from 1024 to 1022, were also investigated. The ferrous and ferric ion capacities for the slag and the activity coefficient of FexO relative to the liquid in equilibrium with iron were reported. Since the experimental ranges of the aFe and pO2 in the previous investigation were rather limited, it remains uncertain that these ion capacities are valid for the conditions of iron saturation. Therefore, the present study attempts to (1) experimentally confirm that the ferrous and ferric ion capacities obtained at rather high pO2 agree with those obtained under the presence of pure liquid iron, (2) determine the capacities for CaO 1 Al2O3 1 MgO ternary melts, and (3) discuss the composition dependence of the ferrous and ferric ion capacities for the CaO 1 Al2O3 binary and the CaO 1 Al2O3 1 MgO ternary melts. HIROYASU FUJIWARA, Associate Professor, and EIJI ICHISE, Professor Emeritus, are with the Graduate School of Energy Science, Kyoto University, Kyoto 606-8501, Japan. MASAHIRO KITOU, formerly Graduate Student, Graduate School of Energy Science, Kyoto University, is Engineer with Nagoya Works, Nippon Steel Corporation, Tokai 476, Japan. TAKAYUKI MATSUI, formerly Graduate Student, Graduate School of Energy Science, Kyoto University, is Engineer with Chiba Works, Kawasaki Steel Corporation, Chiba 260, Japan. Manuscrip
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