On reactive diffusion: 1 Kinetics, growth and diffusion, 2 equilibrium?

Abstract

Multiphase formation in diffusion couples poses a number of problems, amongst which: a) the relation of the diffusion coefficients in the different phases with the respective rates of growth, and b) the correspondence between the phases present in equilibrium according to the binary phase diagram and those observed in a diffusion couple. It is well established that at least beyond a possibly complex initial stage, multiple phases grow as a function of the square root of time. One may assume that the activation energy for the growth of a given phase corresponds to the activation energy for diffusion in the same phase. That is not necessarily so. When only two phases grow simultaneously, some formal relationships exist between the two sets of activation energies. It is also assumed that at high temperatures, the phases present correspond to those shown in the equilibrium diagram, with more or less the same composition limits as shown in this diagram. While small variations therefrom have been discussed, strong deviations due to variations of the diffusion coefficients with composition have received but scant attention. © 2001 Scitec Publications.