Effect of K2O on Phase Relation and Viscosity of the CaO-SiO2-ZnO-FeO-Al2O3 System Slags

The effect of K2O on phase relation and viscosity of the CaO-SiO2-25 wt % "FeO"-12 wt % ZnO-3 wt % Al2O3 slags was investigated using the rotating spindle method. Experimental results show that the slag viscosity increases with the first addition of K2O, exhibiting a maximum at K2O content of 1 wt %, followed by a decrease. The activation energy for viscous flow initially increases and then decreases with the increasing K2O content. K2O can lower the breaking temperature (T-Bk) of the slag at studied composition range. X-ray diffraction (XRD) analysis and thermodynamic calculation using Factsage(TM) 7.2 show that the melilite phase initially precipitates from the liquid phase, followed by the precipitation of olivine phase. Furthermore, Fourier transform infrared (FTIR) analysis reveals that the effect of K2O on the aluminate structure is prior to that of silicate structure. K2O first increases the degree of polymerization (DOP) of the slag by charge compensation effect, while acts as a network modifier when K2O is added to a certain value.