Development of a Unifying Framework for the Restrictions in Multi-component Diffusion Close to Equilibrium

In this work a unifying framework is developed for multi-component diffusion close to equilibrium by proposing additional restrictions for the Fickian diffusion coefficients such as the Onsager reciprocal relations. Moreover, it is shown that these additional restrictions can explain the discrepancy, reported in the literature, of calculating negative concentrations in Fickian ternary free diffusion observed even if the second thermodynamic law constraints and the phase stability criteria are satisfied. It is believed that this work could be used to further investigate multi-component diffusion.