The distribution of oxygen between molten iron and silica-iron oxide slags was determined at 1560°C and the results were used to determine the activities of the components in the iron oxide-silica system.
The activity of iron oxide changes from positive deviation from ideality at low silica concentration to negative deviation beyond 0.28 mole fraction of silica.
At the silica saturated composition, a value of 0.455 for the iron oxide activity was obtained.
The activity of silica, which is calculated from GIBBS-DUHEM equation, shows considerable positive deviation from ideal behavior for any composition where silica concentration is greater than about 0.1 mole fraction.
The free energy of formation of liquid fayalite in the melt was calculated through the activity data.
These activity data give a value of -5.45 kcal/mol at 1560°C-a result which is in agreement with some other investigators'.
From the phase diagram, and the thermal data for Wustit, the activities of iron oxide in the melt were deduced over the range where the liquid is in equilibrium with solid Wustit and the results were compared with the values obtained from the slag-metal equilibrium study. It was showed that the estimated values lie close to experimental results.
The “excess stability” curve was constructed from the activity diagram. The curve has the maximum value at 2FeO·SiO₂ composition, Which is in agreement with the DARKEN'S finding for the similar system studied by SCHUHAMANN et al.
The theories on the ionic structure of the iron oxide-silica melts were discussed.