The solubility of calcium and oxygen in molten iron equilibrated with CaO–Al
2O
3–ZrO
2 molten slag in CaO, Al
2O
3 or 5.5 mass% CaO-stabilized ZrO
2 crucible at 1873 K was measured by means of the slag-metal equilibrium partition method under Ar gas atmosphere. From the results by XRD and the phase diagram of CaO–Al
2O
3–ZrO
2 system, the slag in a CaO crucible was in equilibrium with CaO·ZrO
2 and CaO and the slag composition was 57.36 mass% CaO-34.86% Al
2O
3-7.78% ZrO
2. The slag in a Al
2O
3 crucible was in equilibrium with CaO·2Al
2O
3 and ZrO
2–CaO solid solution (Css) and the slag composition was 27.08 mass% CaO-53.42% Al
2O
3-19.50% ZrO
2. The slag in a CaO-stabilized ZrO
2 crucible was in equilibrium with ZrO
2–CaO solid solution (Css) and CaO·ZrO
2 and the slag composition was 30.38 mass% CaO- 51.56% Al
2O
3-18.06% ZrO
2. The average concentrations of oxygen and calcium in molten iron in equilibrium with slag and compounds were 251 ppm and 3 ppm in a CaO crucible, 33 ppm and 4 ppm in an Al
2O
3 crucible and 21 ppm and 5 ppm in a CaO-stabilized ZrO
2 crucible, respectively. The logarithm of equilibrium constant, logK, for the reaction of CaO(s) =
Ca +
O is –4.38 and the interaction parameter of e
CaO is 31.8. The value is satisfied the thermodynamic phase stability.
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