ACTIVITY COEFFICIENTS AND CHEMICAL POTENTIALS OF SOLUTE ELEMENTS IN MOLTEN IRON
The lattice model of liquids was applied to molten iron containing some kinds of foreign elements. The theoretical expressions for chemical potentials and activity coefficients were derived, making use of an approximational method analogous to that of Bragg-Williams for the case of binary alloys.
The results are as follows;
1) If three absolute elements (1, 2and 3) are all interstitials, the activity coefficient f that denotes the extent of deviation from Herry's law which is valid for dilute solutions is given by for the first solute element, where ci is the concentration of the i'th element, φij the interaction potential between the i'th and j'th solute elements. The validity of this expression is examined by using the numerical data for Fe-O-C system.
2) If three elements (B, C and D) are all substitutional in the solvent (A), the activity coefficient γ that denotes the extent of deviation from Raoult's law for the ideal solution is given by for any one (say D) of the four elements, where ni is the molar fraction of the i's element, ΩAB, for example, the enthalpy change in the reaction A+B=AB. The validity of this expression is examined by the data for Fe-Si-Cu system.
3) If elements A1 and A2 are substitutional and elements B1 and B2 interstitial, the chemical potential of B2 is given by and that of substitutional A2 by where in the two-letter suffix to φ' the first letter denotes the kind of substitutional element and the second the kind of interstitial element. Further, FA2 denotes molar free energy of pure A2, and φ' the interaction potential between A and B, and φ" that between substitutional elements. The validity bf this expression is examined by using the data for Fe-Si-C system.