Effect of Al2O3/SiO2 Ratio on the Viscosity and Structure of Slags

The present paper investigates how the mass ratio between Al2O3 and SiO2 (m(Al2O3)/m(SiO2)) in slag compositions influences the structure, viscosity and crystallization of the slag melts. The objective is to study the variations in viscosity and structure of slags with increasing m(Al2O3)/m(SiO2) ratio. In practice the results of the study are relevant to the significant changes in slag property caused by the changes in chemical composition during continuous casting of steels containing high amounts of dissolved aluminum. The viscosity was found to decrease slightly with increasing m(Al2O3)/m(SiO2) ratio up to 0.56. The degree of polymerization for [SiO4]-tetrahedra was found to decrease with increasing m(Al2O3)/m(SiO2) ratio based on the Fourier Transformation-Infrared Spectra (FT-IR) and Raman spectra, which could explain the observed decrease in viscosity. Atm(Al2O3)/m(SiO2) ratios above 0.56, the viscosity was found to abruptly increase which could be caused by the presence of spinel crystals. The activity coefficient was computed and it was found that the activity coefficient of alumina presents negative deviation when m(Al2O3)/m(SiO2) ratio is less than 0.35, while it shows a positive deviation when m(Al2O3)/m(SiO2) ratio exceeds 0.35. This phenomenon may be related to the change of the primary phase region correlating to the phase diagram to the slag composition.