Probing microscale crystallization phenomena: Transforming waste slags into riches.

ABSTRACT

Metal smelting and combustion of solid fuels produce significant quantities of waste slag, leading to issues such as land occupation and environmental pollution. Understanding and controlling the microscale crystallization phenomena of these slags during thermal treatment is crucial for transforming waste slags into materials suitable for carbon capture or glass ceramics. Previous research has primarily focused on macroscopic crystallization behaviors, significantly advancing the utilization of waste slags in cement clinker production. However, macroscopic results are inadequate for precisely controlling the microscale crystallization behaviors of waste slags. Here, we employed the single hot thermocouple technique to visually explore crystal growth modes, shapes, sizes, numbers, and translational rates of the crystal growth front in a representative blast furnace slag under various isothermal temperatures. The results revealed that crystals exhibited five modes as the isothermal temperature gradually increased, including equiaxed, equiaxed & columnar, columnar, columnar & planar, and planar. Moreover, the translational rate of the crystal growth front increased from 0.011 µm·s-1 to 43.7 µm·s-1 with an increase in the isothermal temperature. Simultaneously, the number of crystals decreased from around 104 to 100 µm-2. On this basis, correlations between microscale crystallization behaviors and isothermal temperature were established to fill the current gap.