It was recalled that self-diffusion could be studied in binary systems when suitable isotopes for both alloy constituents were available. In the case of the Fe-Al system, suitable tracers (e.g. 59Fe) were available for Fe but not for Al. Further insight into the diffusion behavior of Fe-Al could be gleaned from interdiffusion experiments, within the framework of the Boltzmann-Matano method. The interdiffusion coefficient was related, via the modified Darken equation, to the tracer diffusivities of the constituents. The thermodynamic factor in the Darken equation was proportional to the second derivative of the Gibbs free energy of the alloy with respect to the molar fraction of one of the components. These relationships could be used to deduce the tracer diffusivity of Al; provided that the tracer diffusivity of Fe, the interdiffusion coefficient and the thermodynamic factor were known. The mixing energy, which entered into the Gibbs free energy, could be calculated on the basis of thermodynamic data.

Methodological Aspects of Calculations of the Thermodynamic Factor in Interdiffusion. S.Dorfman, D.Fuks, H.Mehrer: European Physic Journal B, 1998, 3[2], 175-8