Diffusional Mechanism of Solid–Solid Mixing

Abstract

IN the mixing of participate materials it is often stated that the underlying mechanism of the process is the diffusion of the components one into another, which implies a random motion of the particles. Implicit in this assumption is that diffusion, as described by Fick's Laws, results from agitation of the particles by the rotation of the mixer. However, the mechanism whereby particle motion about the mixer axis results in diffusion along the axis has not been considered. It is important to consider this question, since previous investigations^1,2 have suggested that final intimate particle–particle contact can only proceed through diffusion. If, during the mixing process, regions of high concentration of one component remain, then such an aggregate may be too small to be segmented by the action of the mixer in a finite time, and diffusion out of the aggregate must take place before final mixing can occur.