A Kinetic study of the effect of ZrO₂ and CaO/Al ₂O₃ ratios on the crystallization behavior of a CaO-Al₂O₃-based slag system

The crystallization behavior of a CaO-Al₂O₃-based slag system with various ZrO₂ content (from 1 to 5 wt pct) and CaO/Al₂O₃ (C/A) ratio (from 0.8 to 1.2) has been studied by using single hot thermocouple technology (SHTT) in this article. The continuous-cooling-transformation (CCT) diagrams and time-temperature- transformation (TTT) diagrams of the above slag system were constructed for the analysis of the varying crystallization behaviors. The results suggested that Al₂O₃ tended to enhance the slag samples crystallization when the C/A ratio ranged from 0.8 to 1.2, and the critical cooling rate and crystallization temperature increased with the decrease of C/A ratio; meanwhile, the incubation time was also getting shorter with the reduction of C/A ratio. The addition of ZrO₂ would enhance the crystallization of slag samples because of the induced heterogeneous nucleation of molten slag. However, the general crystallization was determined by the balance between molten slag viscosity and heterogeneous nucleation, such that Sample 3 (C/A = 1.0, ZrO ₂ = 3 pct, B₂O₃ = 10 pct, Li₂O = 3 pct [in wt pct]) would demonstrate the strongest crystallization kinetics in a high-temperature zone. The different crystals formed during the tests were also analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).