Sorption/Diffusion Prediction in Nonmetallics Using Fick’s Law

Rapid evaluation of nonmetallic materials to predict long-term absorption, diffusion, and permeation properties in corrosive service remains an elusive goal in materials engineering. A number of efforts have been reported that have used various forms of the analytical solution to the diffusion equation to make lifetime predictions from mass change measurements. This paper explores the limitations of three approaches for making these predictions. The analysis is limited to absorption with no simultaneous desorption from the nonmetallic material. Consideration of the dimensionless group Dt/l² is important in deciding on the appropriate sample thickness and test time. The results of this evaluation indicate that some results reported in the literature are incorrect.