High Temperature Thermodynamics and Applications of Rare Earth Oxides and Sulphides in Ferrous Metallurgy

The thermodynamic behavior of the rare earth metals lanthanum and cerium in liquid and steel as predicted by the high temperature (1400-1600°C) thermochemistry of their oxides, oxysulphides and sulphides, is compared to experimentally-determined thermodynamic behavior reported in the literature. The comparison of experimental results includes data from high temperature equilibrium studies and electrochemical cells. Phase stability diagrams, constructed in terms of the Henrian activities of oxygen and sulphur, are used to compare thermodynamic data bases and to determine some of the applications of lanthanum and cerium in ferrous metallurgy. M-S-O (M-Ce, La. Ca and Mg) phase stability diagrams arc used in the comparison of hot-metal desulphurization processes, and the control of graphite morphology in the production of nodular and compacted graphite iron.