Softening and Melting Behavior of Lead Blast Furnace Slags

In this work, the characteristic temperatures (solidus and liquidus) of selected lead blast furnace slags were investigated using in situ high-temperature optical microscopy. The effects of the basicity of the slag (CaO/SiO2), the Fe/SiO2 ratio, and the Zn content were investigated. The deformation temperature associated with the rounding of the sample edges and the temperature at which 75% of the sample height decreases were experimentally considered as the solidus and liquidus temperatures, respectively. The pseudoternary phase diagrams CaO-SiO2-Fe0.63Zn0.37O and FeO-Ca0.54Si0.46O1.46-ZnO were calculated, along with the crystallization curves, using the thermodynamic software FactSage to estimate the characteristic temperatures and phase evolution during the cooling of the slag. The difference between the calculated and experimental solidus and liquidus temperatures was about 70 °C. The results of XRD, SEM, and DSC analysis at high temperatures showed that spinel (ZnFe2O4), melilite (Ca2ZnSi2O7), and andradite (Ca3Fe2Si3O12) were the base crystals for all slag samples. The liquidus temperature increases with decreasing slag basicity (CaO/SiO2), while the liquidus temperature increases with increasing Fe/SiO2 ratio or Zn content.