Solubility products of rare earth oxysulphides in liquid iron

Thermodynamic models were established based on the ionic two-sublattice liquid model to deduce a concentration relationship of rare earth, sulphur, and oxygen and to calculate the solubility product of rare earth oxysulphide in liquid iron at 1811–1973 K. Three interaction parameters were determined for the systems containing oxygen and/or sulphur. First, the expressions for solubility products of Y, Ce, and Nd oxides and sulphides were deduced, respectively. Subsequently, the expressions for solubility products of Y, Ce, and Nd oxysulphides were developed using approximation of Gibbs energy calculations, respectively. The obtained results were in good agreement with the experimental data. The expressions developed for solubility products are log⁡liqKY2O2S0≈19.1−60768T, log⁡liqKCe2O2S0≈−4.2−16284T, and log⁡liqKNd2O2S0≈23.2−66889T. The proposed thermodynamic model can be used to obtain solubility products of other oxysulphides in liquid metals by substituting the corresponding element with the rare earth.