Equilibrium between molten CaO-based slags and iron alloys and activities of slag components

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Calicia-based slags play an important role in the ladle deoxidation and desulfurization process, particularly in the production of clean steel. The CaO-Al_2O_3 system is one of the fundamental systems of the calcia-based slags, and there have been many reports on the thermodynamics of this system. However, a great discrepancy is apparent among these reports.Difficulties may be anticipated in the precise determination of the activities of the components in steelmaking slags at high temperature. Instead of measuring the absolute value of the activity of each component, measurement of the activity ratio may make the experiment much easier.On the other hand,one of bottle necks of the experimental study in the high temperature physical chemistry may be crucible materials. To avoid the sample contamination by crucible materials and the effect of the crucible materials on the reactions concerned, high temperature resistance inert materials are required.In the present experiment, on the contra … More ry, CaS crucibles were manufactured, and CaO-AlResearcho@>D2O<@D23@>Dag and molten iron alloy were brought into equilibrium with the crucible at 1600 c. Therefore, CaS took part in the chemical reactions.The equilibrium relation between the slag and molten iron alloy can be represented by the equation: 3CaO + 2Al + 3S = 3CaS + Al_2O_3, and the product of the activities of aluminum and sulfur in molten iron alloy (hA1^2・hs^3) has a constant value for a fixed slag composition.By application of the Gibbs-Duhem equation, integration techniques have been developed which allow the activities of CaO and Al_2O_3 in the slags to be determined from the relation between (hA1^2・hs^3) and the slag composition. In the activity calculation, any thermodynamic data are not required except the phase diagram of the CaO-Al_2O_3 system and the activity coefficients of aluminum and sulfur in molten iron, those have relatively high accuracies. Therefore, the activities of CaO and Al_2O_3 could be determined without any accumulation of inaccuracies in the use of any other thermodynamic data. Less