IONIC MIGRATION AND ITS RELATION TO DIFFUSION

摘要

This paper presents some theoretical considerations and experimental findings of ionic migration and its relation to diffusion. The theories of ionic transport in dilute as well as concentrated solutions are briefly reviewed and a theory based on the multi-component transport is used to describe the relationships between effective as well as apparent migration and diffusion coefficients. The theoretical equations clearly show that the effective or apparent coefficients determined from migration tests and diffusion tests are not equal. Their relations are strongly dependent on many factors, such as the effect of counter electrical potential, the ratio of cation velocity to anion velocity, the activity coefficient, and the friction factor. Under a non-steady state, the binding capacity is another factor influencing the relationship between migration and diffusion coefficients. Some experimental data are used for a quantitative evaluation of the presented relationships. The results show that the effective or apparent diffusion and migration coefficients calculated according to the theoretical equations correspond fairly well to those measured from different test methods.