Restrictions on Friction Coefficients for Binary and Ternary Diffusion

A friction coefficient formalism provides a convenient method of relating mutual diffusion coefficients and self-diffusion coefficients. However, all of the friction coefficients cannot be eventually eliminated from the analysis unless additional equations relating the friction coefficients are proposed. Restrictions on friction coefficients are useful ways of eliminating proposed possibilities for friction coefficient relationships. In this study, we consider whether the entropy inequality and the Gibbs−Duhem equation produce useful restrictions on proposed friction coefficient relationships for binary and ternary diffusion. In addition, two practical restrictions on friction coefficients are considered, and a new set of equations is derived for the four mutual diffusion coefficients for a ternary system.