The experimental work on the equilibrium between molten iron and FeO-MnO, FeO-MnO-SiO2 slags at 1 560°C was carried out in a rotating crucible furnace, thereby avoiding the slag to contact with the refractory.
From the molten slag-metal equilibrium data, it is shown that FeO-MnO system behaves ideally in liquid region, and also shown that it extends to 36 mol % MnO, which is in a fair agreement with the phase diagram.
When the composition of FeO-MnO slag, which is in equilibrium with molten iron, is in the twophase region, the solubility of oxygen in the molten iron substantially remains constant at 0.125% regardless of slag composition.
Combining those results on slag-metal equilibria with the data on heat of fusion of FeO, the heat of fusion of MnO was estimated, by assuming an ideal FeO-MnO solid solution behavior. This was found to be 12700 cal/mol.
The value of Kl′Mn (=NMnO/NFeo/[%Mn]) is fairly constant at 4.45, when the slag consists of FeO and MnO, while in the slag of FeO-MnO-SiO2, Kl′Mn varies with silica content according to the equation.
Log Kl′Mn=1.056 NS102+Log 4.45
It is shown that the similar equation can be derived by a simple regular solution equation with the interaction parameter; FeO-MnO: O, FeO-SiO:-6 700 cal/mol, and MnO-SiO: 15 600 cal/mol.
To check the values of interaction parameters thus obtained, the composition-activity relation for each end system, or along the silica liquidus are derived also according to the regular solution formula with the same interaction parameter, and are compared with the experimental data.
The agreement with experimetal data is reasonably good, except for the calculated silica activity referred to solid silica, of which the absolute level is much lower than experimental data.
In order to make the calculated silica activity, referred to solid silica, be fitted to the experimental result, the free energy for the fusion of silica should be assessed as follows;
Iso-activity diagram for the Fe0-MnO-Si02 melts and iso-consentration diagram for the molten iron in equilibrium with those slags are constructed, based on both the calculation according to the regular solution formula and the experimental data.