Self-diffusion and exchange diffusion kinetics were studied for a number of ions in hydrated chabazites and the corresponding diffusion coefficients were determined. Values of the self-diffusion coefficients obeyed the Arrhenius equation. The energy barriers, E, associated with each unit self-diffusion process were about 7kcal for all the ions Na+, K+, Rb+ and Cs+; for Ca2+ and Sr2+ the barriers were approximately twice this magnitude, but for Ba2+ they were 8.7kcal. The results were explained in terms of the structure of the crystals and of the possibility that the periodic variation in the intracrystalline electrostatic field determined E. Entropies of activation and also comparison with other rate processes in chabazite (self-diffusion of water, electrical conductivity and dielectric relaxation) suggested that ions and water molecules could cooperate in each unit diffusion process. In mixed (Ca,Sr)-chabazites, the self-diffusion coefficients of Ca2+ and S2+ both decreased strongly with the exchangeable cation fraction of Ca2+ and of Sr2+. Values obtained for exchange diffusion coefficients of Ca-Sr, Ca-Ba and Sr-Ba pairs were integral values over a range of cation fractions.

Ion Exchange in Porous Crystals Part I. Self- and Exchange-Diffusion of Ions in Chabazites. R.M.Barrer, R.F.Bartholomew, L.V.C.Rees: Journal of Physics and Chemistry of Solids, 1963, 24[1], 51-62