Physical properties of refining slags

Abstract

The paper presents results of studies of density, molar volume and surface tension of steelmaking refining slags of the systems CaO – Al₂O₃ – CaF₂ (up to 25 % CaF₂) and CaO – (SiO₂ + Al₂O₃) – Na₂O (up to 20 % Na₂O) as a function of chemical composition, temperature and the ratios of various components. In CaO – Al₂O₃ – CaF₂ slags the density decreases if calcium oxide is replaced with calcium fluoride and increases if calcium oxide or fluoride are replaced with aliminium oxide; in the latter case the content of calcium oxide in the melt has almost no effect on density at equal Al₂O₃/CaF₂ ratios. For all studied compositions the molar volume has positive deviations from additivity of about 10–12 %. Replacement of calcium oxide with calcium fluoride results in a decrease of surface tension, the greater the lower is the Al₂O₃ content. On the contrary, replacement of calcium fluoride with aluminium oxide increases the surface tension of the slag. Calcium oxide content does not affect the surface tension at equal Al₂O₃ / CaF₂ ratios. In the CaO – (SiO₂ + Al₂O₃) – Na₂O system increasing CaO / (SiO₂ + Al₂O₃) ratio at constant content of sodium oxide decreases the melt density, the more noticeable the smaller is Na₂O concentration. Increasing Na₂O content decreases density. The relative excess molar volume of the melts may be both negative and positive depending on structural changes in the slag.