Measurement of diffusion coefficients

Abstract

For diffusion into a solid from a gas or a liquid solution, the constant-volume method of measuring the diffusion coefficient has distinct experimental advantages. The diffusion equations required are summarized in the present paper and their application is illustrated by typical experiments. To reduce the amount of computation, equations involving error functions have been derived for application to the first stages of a diffusion run. When the diffusion coefficient and/or the sorption coefficient are concentration dependent, the equations in this paper are still applicable if sorption is carried out in suitably chosen steps. When sorption takes place only at the two parallel faces of a slab (film, sheet or plug), simple and rapid methods of calculating D can be used.