Theoretical aspects of ternary diffusion

Four theoretical aspects of ternary diffusion are investigated. Restrictions imposed on the ternary diffusion process by the entropy inequality are formulated, and their effect on the eigenvalues of the diffusion coefficient matrix is determined. Additional restrictions are formulated by accepting the Onsager reciprocal relations as valid postulates, yielding a relationship that can be regarded as a sufficient condition for the existence of real eigenvalues for the diffusion coefficient matrix. The stability of the ternary system with respect to the equilibrium state is investigated both with and without the Onsager reciprocal relations. The existence of negative concentrations is analyzed, and interpretations of the reasons for the appearance of such nonphysical results are proposed.