The role of 2CaO · SiO 2 phase on the formation of P 2 O 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 2 O 5 multi phase flux. In the present study, solid 2CaO · SiO 2 piece was reacted with molten FeO x -CaO-SiO 2 -P 2 O 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 2 O 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 2 O 5 was formed from solid 2CaO · SiO 2 and P 2 O 5 in the slag. On the other hand, during the penetration of slag, the P 2 O 5 in the slag reacted with 2CaO · SiO 2 to form 2CaO · SiO 2 -3CaO · P 2 O 5 phase. The P 2 O 5 content of 2CaO · SiO 2 -3CaO · P 2 O 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 2 O 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 2 O 5 condensed phase was observed at the interface expanded with time.

CHINAReaction between molten oxide containing iron oxide and CO῍CO2 gas is the essential reaction in numerous metallurgical smelting processes and the refining speed depends on this reaction rate. Therefore, the mechanism and kinetics for this reaction give us important information for the analysis, simulation and control of processes, and development of new refining systems. Many investigations have been done for clarification of reaction mechanisms between molten oxide containing iron oxide and CO῍CO2 gas, however the direct measurement of oxygen exchange rate controlled by chemical reaction has not been conducted because of experimental di$culties. In the present work, oxygen exchange reaction rate between molten iron oxide and CO῍CO2 gas has been measured by means of isotope exchange technique using C 18 O2-enriched CO2 gas. Isotope exchange technique is a useful method because the chemical reaction rate between gas and liquid phases could be measured directly without any influence of mass transfer in gas or liquid phases. The e#ects of temperature and CO2/CO ratio on the exchange rate have been investigated. It was clarified that the exchange rate was determined by interfacial reactions at first, and then by di#usion of 18

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