Combing role of MgO and Al2O3 on viscosity and its correlation to structure of fluorine-free mold fluxes

By using FactSage calculation, Fourier transform infrared spectroscopy (FTIR), rotational viscometers, and X-ray diffraction (XRD), the combined effect of MgO and Al2O3 on fluorine-free mold flux was confirmed. The slag viscosity at 1300oC reduced with 2-10 wt% MgO, and higher Al2O3 increased the viscosity as a whole. The trend of experiment results was consistent with Riboud and Iida models, while the FactSage calculation values were relatively higher. The slag viscosity was more affected by the Si-O network than Al(B)-O structure and the MgO has a dual effect on the slag structure. The viscosity-temperature curves changed from alkaline to acidic slag characteristics with Al2O3 increased from 8 wt% to 12 wt%, and its tendence was not regular with the addition of 2-10 wt% MgO. Both FactSage calculation and XRD patterns showed that, MgO increment promoted the growth of crystals Ca3MgSi2O8 and Ca11Si4B2O22 gradually, and Al2O3 addition inhibited the crystal precipitation.