GENERALIZED SOLUTION OF INTERDIFFUSION PROBLEM - OPTIMAL APPROACH FORMULTICOMPONENT BOUNDED SYSTEMS

Darken's phenomenological scheme for diffusion in binary systems is us ed for a description of interdiffusion in multicomponent (r greater th an or equal to 2) mixtures. The mathematical model of interdiffusion i n the bounded mixture (i.e., layer of finite thickness) showing consta nt concentration (e.g., in solid or Liquid solutions) and variable dif fusivity of the components is formulated. We derive, with the use of i dea of generalized solution, an exact expression for the evolution of components distribution. Also, we consider an asymptotic approximation of the exact expression which can be simply applied to a variety of i nitial conditions. We show, in an elementary case of interdiffusion in a two-component mixture with constant diffusion coefficients, the ana lytical results and the complete algorithm of finding the density prof iles. The experimental and theoretical results for a Cu-Ni solid solut ion are presented. (C) 1996 by John Wiley & Sons, Inc.