Abstract
Ratios of the vapor concentrations of Mn to Fe have been determined for Fe-Mn binary alloys having 50 at% Mn or less at 1833K by a vapor transport method. In the present transport method, vapor saturation needs not be satisfied in order to measure vapor concentration ratios. The thermodynamic activities were calculated with the aid of the Gibbs-Duhem equation. The calculation has shown that a maximum of the Mn activity coefficient (yMn) exists near 17 at% Mn, and that negative deviation of yMn from ideality below 6 at% Mn and positive deviation above 6 at% Mn are seen. It has been shown that the experimental results are in qualitative agreement with the behaviors of other physical chemical properties such as inter-diffusivity, viscosity, and electrical resistivity. The existence of a maximum of yMn has been accounted for by considering a plausible variation of the liquid structure of Fe-Mn alloys in connection with the phase diagram. On combining the present data and other data, the most reliable values of the activities in Fe-Mn alloys at 1833K have been presented in tabular and graphical forms.
