The relationship between the aluminum-oxygen and sulfur distribution ratio for molten iron and a CaO-Al 2O 3-ZrO 2 slag in equilibrium at 1 873 K was studied using an Al 2O 3 or CaO-stabilized ZrO 2 crucible. The slag and molten iron equilibrated with CaO·2Al 2O 3 and Css (cubic solid solution in CaO-ZrO 2 system) in the Al 2O 3 crucible, and with CaO·ZrO 2 and Css in the ZrO 2 crucible. These equilibrium states coincided with the phase diagram of CaO-Al 2O 3-ZrO 2. From the concentrations of aluminum and oxygen dissolved in molten iron, the Al 2O 3 activity in the slag was determined to be 0.393 in the Al 2O 3 crucible and 0.385 in the ZrO 2 crucible. These activities were compared with the data in the CaO-Al 2O 3 and CaO-ZrO 2 systems. The sulfur distribution ratio was higher a little in the ZrO 2 crucible than in the Al 2O 3 crucible and increased with aluminum content. The sulfide capacity of the fluxes was determined to be 8.77×10 -5 and 9.10×10 -5 in the Al 2O 3 and ZrO 2 crucibles, respectively.
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