Effect of fluorine on surface tension of CaO-SiO2-Al2O3-Na2O-CaF2 mold flux

The surface tension of mold flux is an important parameter for controlling the quality of continuous billet, affected deeply by the compositions of mold flux and temperature, andclosed related with the structure of mold flux. In the present study, the effect of CaF2 and temperature on the surface tension of CaO-SiO2 -Al2 O3 -Na2 O-CaF2 mold flux melts is investigated by the pulling cylinder method; furthermore, the structure of melts is determined by FT-IR spectroscopy to analyze the change mechanism of surface tension. The results indicate that the variation of surface tension is in accord with that of structure of melts. The surface tension of melt decreases with the increase of CaF2 mass fraction, and this tendency becomes more apparent at higher temperature. The FT-IR spectra show thatboth the amount of Ob andthe degree of structural polymerization of melts decrease as the CaF2 content increases. This is because the Si-Ob bonds in the [SiO4 ]-tetrahedrons are broken by F− and transformed into Si-F bonds, and the silicon-oxygen anions with more complex structure were depolymerized into silicon-oxygen anions containing fluorine with simpler structure, resulting in an increase of Si-F saturated bonds on the melt surface, and thusreducing the surface tension of melts.