EVALUATION OF DATA OBTAINED WITH DIFFUSION COUPLES OF BINARY SINGLE-PHASE AND MULTIPHASE SYSTEMS

Data obtained with diffusion couples of binary systems 1-2 can be evaluated most conveniently with the help of equations due to Sauer and Freise in order to calculate the interdiffusion coefficient D as a function of composition. A simplified derivation of the principal equation for the calculation of D as a function of mol fraction N2 is presented. In multiphase systems with intermediate compounds which have a narrow homogeniety range, one may calculate values of the integral ∝ DdN2 extended over the homogeniety range of the various compounds. It is shown how values of these integrals are related to the parabolic rate constants for the growth of compound layers in diffusion couples under various conditions and, furthermore, to the thickness of compound layers which are formed under steady-state conditions, e.g. when iron is subject to dissolution in a well-stirred bath of liquid zinc, or when metal oxides are formed by oxidation of a metal and volatilize at a constant rate into a stream of oxygen passed over the sample. © 1969.