Shuji Ueno1 and Yoshio Waseda2
1Research Student, Tohoku University, Sendai. Present address: Central Research Laboratory, UNITIKA Ltd., Uji
A theoretical equation for the activity coefficient of the solute at infinite dilution in metallic solutions has been described by the pseudopotential formalism coupled with the hard sphere model. The approximate equation for the pseudopotential term has also been proposed in terms of the molar heat of solution at infinite dilution, in order to allow simple estimation of the activity coefficient in various metallic solutions.
It was found from the calculation of the excess entropy of the solute at infinite dilution that the electron gas term is generally less than 5% of the hard sphere term and therefore the contribution from the electron gas appears to play an insignificant role in determining the sign and absolute values of the excess entropy or the activity coefficient of the solute at inifinite dilution. The present theory has been applied to 33 cases in non-ferrous alloys such as Al-base, Pb-base and Cu-base solutions and 15 cases in Fe-base solutions. The calculated values of the activity coefficient of the solute at infinite dilution were found to be in reasonable agreement with the experimental data in both non-ferrous and ferrous solutions. It should be, however, noticed that the present results do not explicitly include the entropy effect of 3d electrons which is likely singnificant in ferrous solutions.
activity, thermodynamics, infinite dilution, excess entropy, liquid alloys, metallic solution, theoretical equation
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