Activities of SiO2 in some CaO-Al2O3-SiO2(-10%MgO) melts with low SiO2 contents at 1873K

The activity of SiO2 in the CaO-Al2O3-SiO2(-10%MgO) systems was measured at the region of %SiO2<10%. The melts were equilibrated with a reference metal of Cu in a controlled oxygen partial pressure at 1 873 K. ISo-SiO2 activity contours were drawn from the measured values. For the CaO-Al2O3-SiO2 system, the measurement result showed positive deviation from the previous data. It was also found that the SiO2 activity decreased as CaO content increased. In the CaO-Al2O3-SiO2-10%MgO system, the composition dependence of the SiO2 activity seemed to be similar as the ternary system. On the other hand, the activity values were much lower than that of the ternary system. It could be attributed to the strong basic behaviour of MgO. Based on the result of the SiO2 activity measurement, the equilibrium between the inclusions and liquid steel during ladle treatment was discussed.