Analytical Derivation of the Sauer-Freise Flux Equation for Multicomponent Multiphase Diffusion Couples with Variable Partial Molar Volumes

The well-known Sauer-Freise flux equation is derived analytically for the general case of a multiphase, multicomponent diffusion couple with variable molar volume. Discontinuities in concentration versus distance data are specifically treated. Fluxes with respect to the local center of volume are employed if the partial molar volumes are constants. Fluxes with respect to the local center of moles are employed for the more general case of variable partial molar volumes.