Effect of composition on the crystallisation behaviour of blast furnace slag using single hot thermocouple technique

When the content of glass in blast furnace slag is over 95%, it can be used as a raw material in the manufacture of cement. The critical cooling rate required for the formation of glassy slag is one of the important characteristics for molten BF slag. The crystallisation behaviour of molten BF slag has been studied by in situ observation with the single hot thermocouple technique. The isothermal and non-isothermal experiments were performed to construct time–temperature-transformation and continuous-cooling-transformation diagrams. The effect of MgO, Al₂O₃ and binary basicity (CaO/SiO₂) on the critical cooling rate of the CaO–SiO₂–MgO–Al₂O₃ slags were studied under conditions of CaO/SiO₂ = 1.1–1.4, 6–12 mass% MgO and 10–16 mass% Al₂O₃. The following finding are reported in the present paper: (i) Higher MgO content increased the critical cooling rate; higher Al₂O₃ content decreased the critical cooling rate; higher CaO/SiO₂ increased the critical cooling rate. (ii) The crystallisation temperature of molten BF slag lowers as the cooling rate increases, the slag have larger critical cooling rate, higher crystallisation temperature. The results could be used to design proper cooling path of molten BF slag for the formation of glassy.