Non-ideality could be important for H diffusion through metallic membranes at large concentrations. This was easily allowed for if the H concentration in the membrane was nearly constant, but if there was a large gradient, the degree of non-ideality will vary across the membrane. A procedure was given here for the conversion of measured concentration-dependent diffusion coefficients into concentration-independent ones when there was a significant gradient.

The Role of Non-Ideality in H Permeation through Membranes. T.B.Flanagan, D.Wang, K.L.Shanahan: Scripta Materialia, 2007, 56[4], 261-3