Theory of <i>Do</i> for Atomic Diffusion in Metals

Abstract

The theory of the entropy of activation ΔS previously given for interstitial diffusion in metals is herein extended to self- and to chemical diffusion. It is concluded that this entropy of activation will always be positive; and it is shown that in the case of self-diffusion and of chemical diffusion at very low concentrations, the better the empirical ΔS the better does it correlate with the theoretical positive ΔS. The large negative apparent ΔS frequently found for chemical diffusion at higher concentrations must be attributed either to inaccuracies in experiments or to the presence of short circuiting diffusion paths. It is predicted that the presently reported negative values of ΔS will become positive when very small concentrations are used in large grain size specimens.