Average effective interdiffusion coefficients and the Matano plane composition

From an integration of the interdiffusion flux of a component over distance in the diffusion zone of an isothermal solid-solid diffusion couple, average effective interdiffusion coefficients can be evaluated over selected ranges of composition. An analysis is developed to inter-relate, in general, the average effective interdiffusion coefficients calculated for the composition ranges on either side of the Matano plane to the composition at the Matano plane. Characteristic depths for concentration profiles on either side of the Matano plane are employed to characterize the concentration profiles and their deviations from error function solutions. The analysis is applied to the concentration profiles of a binary Fe-C as well as a ternary Cu-Ni-Zn single-phase diffusion couple. From a knowledge of concentration profiles on one side of the Matano plane, profiles on the other side can be generated from an error function model based on the analysis.