The role of 2CaO·SiO
2 phase on the formation of P
2O
5 condensed phase should be clarified to elucidate the microscopic dephosphorization mechanisms and to improve the hot metal dephosphorization efficiency by using CaO-based FeO
x–CaO–SiO
2–P
2O
5 multi phase flux. In the present study, solid 2CaO·SiO
2 piece was reacted with molten FeO
x–CaO–SiO
2–P
2O
5 slag for 1 to 60 s at 1673K, and the reaction interface between solid 2CaO·SiO
2 and molten FeO
x–CaO–SiO
2–P
2O
5 slag was observed and analyzed by SEM and EDS.
The dissolution of 2CaO·SiO
2 into the molten slag and the penetration of molten slag into solid 2CaO·SiO
2 simultaneously occurred. The 2CaO·SiO
2–3CaO·P
2O
5 was formed from solid 2CaO·SiO
2 and P
2O
5 in the slag. On the other hand, during the penetration of slag, the P
2O
5 in the slag reacted with 2CaO·SiO
2 to form 2CaO·SiO
2–3CaO·P
2O
5 phase. The P
2O
5 content of 2CaO·SiO
2–3CaO·P
2O
5 phase existing in solid 2CaO·SiO
2 region was lower than that observed at the 2CaO·SiO
2 saturated liquid phase region because of the lower P
2O
5 content of penetrating slag than that of 2CaO·SiO
2 saturated liquid slag. The 2CaO·SiO
2 saturated liquid slag region and the region where P
2O
5 condensed phase was observed at the interface expanded with time.
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