INTERDIFFUSION AND FREE-BOUNDARY PROBLEM FOR R-COMPONENT (R-GREATER-THAN-OR-EQUAL-TO-2) ONE-DIMENSIONAL MIXTURES SHOWING CONSTANT CONCENTRATION

The concept of separation of diffusional and drift hows, i.e., the pos tulate that the total mass flow is a sum of diffusion flux and transla tion only, is applied for the general case of diffusional transport in an r-component compound (process defined as interdiffusion in a one-d imensional mixture). The equations of local mass conservation (continu ity equations), the appropriate expressions describing the fluxes (dri ft flux and diffusional flux), and momentum conservation equation (equ ation of motion) allow a complete quantitative description of diffusio nal transport process (in one-dimensional mixture showing constant con centration) to be formulated. The equations describing the interdiffus ion process (mixing) in the general case where the components diffusiv ities vary with composition are derived. If certain regularity assumpt ions and a quantitative condition (concerning the diffusion coefficien ts-providing a parabolic type of the final equation) are fulfilled, th en there exists the unique solution of the interdiffusion problem. Goo d agreement between the numerical solution obtained with the use of Fa edo-Galerkin method and experimental data is shown. An effective algeb raic criterion allows us to determine the parabolic type of a particul ar problem. A condition for the ''up-hill diffusion'' in the three com ponent mixture is given and a universal example of such effect is demo nstrated. The results extend the standard Darken approach. The phenome nology allows the quantitative data on the dynamics of the processes t o be obtained within an interdiffusion zone.