Online ISSN : 1883-2954
Print ISSN : 0021-1575
ISSN-L : 0021-1575
Equilibrium between Fe0-MnO-SiO2 Slags and Molten Iron
Yasushi KOJIMAKokichi SANO
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1965 Volume 51 Issue 6 Pages 1122-1130


Silicon and manganese are the most important elements as the deoxydation reagent in the steelmaking practice. There have been a number of reports on the deoxydation reaction of these elements. The equilibrium constants reported, however, do not show good agreement among themselves.
The equilibrium between the molten iron and the slags containing FeO, MnO and saturated silica was studied in the Si02 crucible at 1550°C, 1600°C, and 1650°C. The results obtained are summarized as follows:
1) The equilibrium constant for the deoxydation of silicon in the molten iron containing less than 1.2% manganese is represented as
2) The effect of manganese on the activity coefficient of silicon was examined. The activity coefficient was a function of only the concentration of manganese, and not of temperature. The experimental results were represented by the equation:
log f(Mn)Si=0.281[%Mn]
3) The activity of iron oxide in the slag, FeO-MnO-Si02 system, was determined by using the relation
where (ao) obs refers to the activity of oxygen in the molten iron equilibrated with FeO-MnOSi02 slag and (ao) sa.t to the activity of oxygen equilibrated with pure wiistite. The activity of iron oxide was independent of temperature, and dependent on the concentration of iron oxide. It exhibited negative deviation from RAOULT'S law.
The activity coefficients of FeO (γFeo) in the binary slags such as FeO-saturated Si02 obtained by extrapolation to the zero concentration of manganese oxide was in good agreement with the values found in the literature.
4) The activity of manganese oxide in the ternary slags was obtained.It was defined as
where KMn -0 was the equilibrium constant of the reaction Mn+O=MnO (in silica-saturated slag).
The true equilibrium constants of Kmn-0 were calculated by using the value of Kmn=ampo/aFeo [%Mn] obtained by J. CHIPMAN. The activities of oxygen and manganese were calculated from the interaction parameter of the dissolved elements in the liquid iron.
The effects of silicon on the activity coefficient of manganese were estimated by using the WAGNER'S equation. The result was expressed as a function of silicon concentration in theliquid iron:
log f(Si)Mn=0.550[%Si]
The activity of manganese oxide was independent of temperature, and dependent on the concentration of manganese oxide in the silica saturated slag. It showed negative deviation from the RAOULT'S law as the iron oxide.

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