Diffusion and the vapor transport of solids

It is shown that the general flux equations for multicomponent gas mixtures, which include the effects of "streaming" or viscous flow of the gas as a whole, reduce to the form of the simple Fick's law diffusion equation upon application of the steady state vapor transport conditions applicable to the vapor transport of solids. This justifies the use of Fick's law in theoretical treatments of the vapor transport of solids. The diffusion coefficients to be used in the Fick's law expression are shown to be simply related to the binary diffusion coefficients appropriate to binary gas mixtures. © 1962.