Abstract:A thermodynamic model was developed for determining the surface tension of RE₂O₃-MgO-SiO₂ (RE=La, Nd, Sm, Gd and Y) melts considering the ionic radii of the components and Butler’s equation. The temperature and composition dependence of the surface tensions in molten RE₂O₃-MgO-SiO₂ slag systems was reproduced by the present model using surface tensions and molar volumes of pure oxides, as well as the anionic and cationic radii of the melt components. The iso-surface tension lines of La₂O₃-MgO-SiO₂ slag melt at 1873 K were calculated and the effects of slag composition on the surface tension were also investigated. The surface tensions of La₂O₃, Gd₂O₃, Nd₂O₃ and Y₂O₃ at 1873 K were evaluated as 686, 677, 664 and 541 mN/m, respectively. The surface tension of pure rare earth oxide melts linearly decreases with increasing cationic field strength, except for Y₂O₃ oxide, while Y₂O₃ has a much weaker surface tension. The evaluated results of the surface tension show good agreements with literature data, and the mean deviation of the present model is found to be 1.05% at 1873 K.

Key words: rare-earth oxide; surface tension; ionic radius; Butler’s equation; calculating model