Continuous cooling crystallization kinetics of a molten blast furnace slag

The crystallization characteristics and kinetics of a molten blast furnace slag during continuous cooling were investigated. Samples of molten blast furnace were continuously cooled both in tiny amounts in a differential scanning calorimetry (DSC) equipment and in bulk states in a cooling mold. The mineragraphy and morphology were investigated by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The continuous cooling crystallization kinetics were studied using different models based on DSC data. The results show that akermanite (2CaO·MgO·2SiO₂) and gehlenite (2CaO·Al₂O₃·SiO₂) are the major minerals in the continuously cooled crystalline blast furnace slag. The mechanism of crystallization of the blast furnace slag during continuous cooling is dominated by both surface nucleation and one-dimensional growth with bulk nucleation, which is significantly different to that during heating. The activation energy of crystallizations of akermanite and gehlenite was determined by Kissinger and Matusita methods. The values obtained are much higher than that yielded during heating.