Discussion of “On the Boltzmann–Matano Analysis of Diffusion in a Semi-infinite Medium”

Ernst et al. analyzed the concentration-dependent diffusion of carbon in austenitic steel in the semi-infinite geometry by the Boltzmann–Matano method. They assumed that the origin of the position coordinate be at the surface, and tried to justify it from the particular nature of interstitial diffusion. We point out that their ‘assumption’ is prerequisite to applying the method to the problem, irrespective of the mechanism.