Fundamental Aspects of Diffusion Processes

Abstract A simple description of diffusion processes and a derivation of the general laws of diffusion are given. The distribution with time of particles according to a random‐walk process is considered and compared with results derived from a differential equation. Diffusion coefficients for and examples of diffusion processes in various media (e.g. gases, solutions, solids, and high polymers) are given. “Uphill” diffusion, i.e. diffusion against the concentration gradient is also discussed. In addition, diffusion in anisotropic systems, in systems consisting of more than one phase and in multicomponent systems is treated.