Unraveling the role of chemical composition in the critical cooling rate of high-temperature CMAS slag

Centrifugal-granulation-assisted thermal energy recovery (CAGTER) emerges as a leading technology to treat the industrial CaO-MgO-Al2O3-SiO2 melts such as blast furnace slag. However, large-scale implementation of CGATER is partly limited by the lack of a thorough understanding of the crystallization dynamics of the CMAS slag. To address this issue, we carried out a systematical experimental effort to visualize the crystallization process of sixteen CMAS slags by the hot thermocouple method and measured their temperature time histories in isothermal cooling and continuous cooling processes. The slag crystallization appears in three different modes including the point growth mode, line growth mode and line-flake growth mode. Interestingly, it was found that a larger CaO/MgO ratio promotes the crystallization and thus features a larger critical cooling rate, while a larger SiO2/Al2O3 ratio suppresses the crystallization. We also assessed the correlation between the critical cooling rate and the chemical-composition-related quantities and further proposed a quantitative relationship to estimate the critical cooling rate of the CMAS-like slags with agreeable accuracy. This study sheds light on the intricate composition-specific crystallization behavior of molten slag and also enables fast yet accurate prediction of the critical cooling rate of BF slag.