Physical properties of refining slags

The paper presents results of studies of density, molar volume and surface tension of steelmaking refining slags of the systems CaO - Al 2O 3 - CaF 2 (up to 25 % CaF 2) and CaO - (SiO 2 + Al 2O 3) - Na 2O (up to 20 % Na 2O) as a function of chemical composition, temperature and the ratios of various components. In CaO - Al 2O 3 - CaF 2 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 Al 2O 3/CaF 2 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 Al 2O 3 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 Al 2O 3 / CaF 2 ratios. In the CaO - (SiO 2 + Al 2O 3) - Na 2O system increasing CaO / (SiO 2 + Al 2O 3) ratio at constant content of sodium oxide decreases the melt density, the more noticeable the smaller is Na 2O concentration. Increasing Na 2O content decreases density. The relative excess molar volume of the melts may be both negative and positive depending on structural changes in the slag.