The full set of phenomenological coefficients was used in a derivation of the fluxes of diffusing radioisotope tracers. Both the diffusion of a single radioisotopic species and the co-diffusion of 2 tracer ions were considered; in the absence of a concentration gradient in each case. A method was presented for measuring phenomenological cross-terms and their associated cross-diffusion coefficients. The method involved the co-diffusion of radioisotopes, and was demonstrated for the case of Ag-for-Na ion exchange in a boroaluminosilicate glass system. The cross-coefficients were concentration-dependent. Thus, the magnitude of the measured Ag cross-coefficient was as high as 8.7 x 10-9cm2/s. This was almost as high as the corresponding Ag tracer coefficients, which attained the maximum value of 1.17 x 10-8cm2/s. The results demonstrated that cross-coefficients were important in the description of interdiffusion.

Measurement of Phenomenological Cross Terms by Radioactive Co-Tracer Diffusion in Glass. S.A.Poling, S.N.Houde-Walter: Journal of Non-Crystalline Solids, 1999, 255[1], 78-86