Phase equilibria of the Al 2 O 3 -CaF 2 -FeO n system
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Phase Equilibria of the Al2O3-CaF2-FeOn System SHIGERU UEDA and MASAFUMI MAEDA Calcium-oxide- and iron-oxide-based flux have been used to eliminate impurities in hot metal in the steelmaking process. Calcium fluoride is a convenient additive to enhance the fluidity of the flux in steelmaking. It decreases the melting point of the mixture of calcium oxide and increases reactivity of the flux with the molten iron. However, because of its negative environmental effects, reduction in the use of fluoride is also mandated. The disposal of after-use slag may result in the fluoride seeping down into the earth and into the underground water. The objective of the present study is to investigate ways of decreasing the total emission of fluoride and thus minimize its impact on the environment. Substitution of CaF2 by another oxide to reduce the use of fluorine in the process has been previously proposed by the authors.[1,2] The development of a fluorine recycling system is an alternative to reducing fluoride emissions. One possible process is: (1) concentrating the fluorine in a solid or liquid phase, (2) separating this phase from the other slag phase that is used in the steel making process, and (3) using the recycled CaF2 in the hot metal pretreatment process. The CaF2-FeOn system has a miscibility gap between fluorine-rich and oxygen-rich phases at 1673 K.[3] By using phase separation of this system, separation of fluorine from the oxy-fluoride mixture may be possible. The purpose of the present study was to determine the region of the miscibility gap and liquidus of melts saturated with FeOAl2O3 in the Al2O3-CaF2-FeOn system at 1673 and 1723 K. A silicon carbide electric resistance furnace connected to a PID controller with a Pt-6 pct Rh/Pt-30 pct Rh thermocouple was used to equilibrate the slag. The temperature of the specimen was controlled within 1 K. An iron or molybdenum crucible with an iron liner was used as a container, which held about 2 g of the Al2O3-CaF2-FeOn mixture.
SHIGERU UEDA, Research Associate, is with the Department of Materials Science and Engineering, Iwate University, Morioka 020–8551, Japan. MASAFUMI MAE
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