Confocal scanning laser microscopy investigation of crystallization behavior of hot blast furnace slag.

The isothermal and non-isothermal crystallization behavior of blast furnace (BF) slag with varying CaO/SiO 2 ratios was in-situ observed through a confocal scanning laser microscopy (CLSM). The crystallization kinetics was analyzed and precipitation of crystalline phases was discussed by theoretical analysis from FactSage 8.0 and X-ray Diffraction (XRD). The results showed that, with the increasing CaO/SiO 2 ratio from 1.0 to 1.3, the crystals morphology changed first from rectangles and squares to small-size and irregular, and further to long strip shape at the cooling rate of 100 °C/min. The onset crystallization temperature in CTT diagram was higher at a larger CaO/SiO 2 ratio due to the decrease of polymerization degree of the slag. For the isothermal crystallization process at 1250°C, the crystals morphology changed gradually from lamellar to long-trip or columnar, and the incubation period in TTT diagram became shorter with the increase of CaO/SiO 2 ratio. Avrami index n decreased from appropriately 2.3 to 1.5, and the growth mode of crystals converted from two-dimensional to one- dimensional. XRD analysis showed that only merwinite existed in four slags at 1380°C. Akermanite and gehlenite were generated at 1350°C, and their amount first increased greatly and then decreased slightly with a continuous increase of CaO/SiO 2 ratio. At the low temperature, the number of akermanite and gehlenite reduced, while that of merwinite increased obviously in the slags when CaO/SiO 2 ratio was 1.2 and 1.3, indicating that increasing CaO/SiO 2 ratio promoted the generation of merwinite. [ABSTRACT FROM AUTHOR]