Viscosity and Structure Changes of CaO-SiO2-Al2O3-CaF2 Melts with Substituting Al2O3 for SiO2

During the smelting process of the high Al steels, the reaction between SiO2 in molten slag and dissolved aluminum in liquid steel always takes place. This aluminathermic reduction reaction will lead to the substitution of 1 mol SiO2 for 2/3 mol Al2O3. Therefore, the investigations about the influence of the ratio of Al2O3 to SiO2 on viscosity and structure changes of mould flux during this process are very necessary. The viscosity variation of CaO-SiO2-Al2O3-CaF2 melts was studied by changing compositions considering the aluminathermic reduction reaction. It was found that viscosity increased monotonously with gradually increasing the substitution extent. According to the Raman analysis, the substitution of Al2O3 for SiO2 leads to the decrease of non-bridging oxygen but the increase of bridging oxygen. Therefore, degree of polymerization and viscosity increase as the substitution extent increases. By comparing the measured viscosities with the model calculated values, it was found that both the recently developed Zhang's model and Roboud model could describe the viscosity variation behavior of CaO-SiO2-Al2O3-CaF2 melts very well.