Shear Rate and Crystalline Phase Effects on the Super-Cooling Degree and Crystallization Behavior of CaO–SiO2–CaF2–RO (R=Mg, or Sr) Flux Systems

In this study, the electrical capacitances of CaO–SiO2–CaF2–RO (R=Mg, or Sr) flux systems were measured under a shear rate. From the measurement results, it was observed that the capacitance decreased as the slag crystallized. The temperature when the capacitance began to decrease was defined as the crystallization temperature, and the super-cooling degree was defined as the difference between the crystallization and liquidus temperatures. The super-cooling degree of slag containing 5 mol% MgO depended on the shear rate: the higher the shear rate, the lower the super-cooling degree. On the other hand, the super-cooling degree of slag containing 10 mol% MgO had no dependence on the shear rate. Furthermore, super-cooling of slag containing 5 mol% SrO was not observed when the shear rate was varied. However, small changes were observed for the super-cooling degree of slag containing 10 mol% SrO when a high shear rate was applied. In order to better understand the factors that induce the acceleration of the crystallization process by shear rates, XRD was used to detect the primary and succeeding crystalline phases, and the crystalline phase morphology was observed with SEM. The XRD results showed that fluxes containing 5 mol% MgO and 10 mol% SrO, whose super-cooling degree was affected by the shear rate, had dicalcium silicate (2CaO-SiO2) as their primary crystalline phase. Conversely, fluxes containing 10 mol% MgO and 5 mol% SrO, whose super-cooling degree was not affected by the shear rate, had cuspidine (3CaO-2SiO2-CaF2) as their primary crystalline phase. The SEM results showed that the crystalline phase morphology were different between the samples containing MgO and SrO. Consequently, for CaO–SiO2–CaF2–RO (R=Mg, or Sr) flux systems, it was considered that the acceleration of the crystallization depended on the crystalline phase and changes in the morphology of the crystalline phase.