Influence of Al₂O₃ and MgO on the Viscosity and Stability of CaO–MgO–SiO₂–Al₂O₃ Slags with CaO/SiO₂ =1.0

Abstract

The viscosity of CaO–SiO₂–MgO–Al₂O₃ slags (CaO/SiO₂=1.0, 14–17 mass% Al₂O₃, 5–15 mass% MgO) was measured to analyze the effect of MgO and Al₂O₃. The infrared spectra was employed to analyze the ionic structure of the slag. The viscosity of CaO-SiO₂-MgO-17% Al₂O₃ slags decreases with the increase of MgO content which is in the range of 5%–10 mass%. However, the dependence relationship is reversed when MgO content is over 10 mass%. The viscosity of CaO-SiO₂-10 mass% MgO–Al₂O₃ slags and CaO-SiO₂-11% MgO–Al₂O₃ slags exhibits the minimum value at 16 mass% Al₂O₃, which may contribute to the amphiprotic properties of Al₂O₃. The above phenomenon can also be verified by the infrared spectra. Simultaneously, in order to make the blast furnace working smoothly, the viscosity value of the slag is below 1.0 Pa·s commonly. Thus, we define the temperature of the slag with a viscosity value of 1.0 Pa·s as "Critical Temperature (CT)". And, the effect of MgO and Al₂O₃ content on CT is also studied by the phase diagram. We can conclude that the fall of the CT can be owe to the simplified network structure at the MgO content from 5 mass% to 10 mass%, while the rise may be because of the appearance of solid phase at the MgO content from 10 mass% to 15 mass%.