The concept of separation of diffusional and drift flows, i.e., the postulate that the total mass flow is a sum of diffusion flux and translation only, is applied for the general case of diffusional transport in an r-component compound (process defined as interdiffusion in a one-dimensional mixture). The equations of local mass conservation (continuity equations), the appropriate expressions describing the fluxes (drift flux and diffusional flux), and momentum conservation equation (equation of motion) allow a complete quantitative description of diffusional transport process (in one-dimensional mixture showing constant concentration) to be formulated. The equations describing the interdiffusion process (mixing) in the general case where the components diffusivities vary with composition are derived. If certain regularity assumptions and a quantitative condition (concerning the diffusion coefficients—providing a parabolic type of the final equation) are fulfilled, then there exists the unique solution of the interdiffusion problem. Good agreement between the numerical solution obtained with the use of Faedo-Galerkin method and experimental data is shown. An effective algebraic criterion allows us to determine the parabolic type of a particular problem. A condition for the ‘‘up-hill diffusion’’ in the three component mixture is given and a universal example of such effect is demonstrated. The results extend the standard Darken approach. The phenomenology allows the quantitative data on the dynamics of the processes to be obtained within an interdiffusion zone.

• Received 24 June 1994

DOI:https://doi.org/10.1103/PhysRevB.50.13336