Activity-composition relations at 1100°C in the system calcium oxide-iron oxide-manganese oxide in contact with metallic iron

The extent of the solid miscibility gap in the system CaO−“FeO”−MnO at 1100°C has been determined termined by electron microprobe, point-counting, and X-ray diffraction analysis of coexisting phases within the miscibility gap. Activities of FeO in ternary solid solutions have been determined at 1100°C by equilibrating the solid solutions with metallic iron and a gas phase of known oxygen pressures. Activity-composition curves for CaO and MnO in the ternary system are calculated from a Gibbs-Duhem integration, and the data are extrapolated to the binary system CaO−MnO, which is shown to display a considerable positive deviation from ideality at 1100°C. NILS TIBERG, formerly Graduate Assistant, Department of metallurgy, The Pennsylvania State Univeristy, University Park, Pa.