Effect of Vacancy Flow on Interdiffusion in the Binary Alloy System

Fick’s first law on binary interdiffusion which is given by −\ ildeD∂Ci⁄∂X becomes approximate and loses its theoretical ground when vacanncies flow. If the Kirkendall effect is observed, therefore, the inter- and intrinsic diffusion coefficients are errorneously determined. The effect of the vacancy flow on the interdiffusion coefficent is not so severe and appears to be within the limit of experimental error as long as a diffusion couple consists of one phase. On the contrary, formation and disappearance of the lattice planes at the interface between distinct phase layers in reaction diffusion affect the vacancy flow, so that the value of the interdiffusion coefficient at a given concentration should vary significantly when the magnitude of the vacancy flow in a given phase markedly depends on the experimental method applied.