Concentration dependence of diffusion and migration of chloride ions - Part 1. Theoretical considerations

This paper series includes two parts: (1) theoretical considerations and (2 ) experimental evaluations. In Part 1, the chloride ion diffusion and migra tion processes in concentrated solutions are theoretically analyzed. The qu antitative relationship between diffusion coefficient and migration coeffic ient is established. Two important parameters that are inherent in the ceme nt based materials (i.e., ion-selective semipermeability and chloride bindi ng) are discussed. The theoretical analysis shows that the "effective" chlo ride diffusion coefficient determined from the conventional diffusion or mi gration tests is not a constant, but rather is a complicated function of co ncentration. This function contains four main factors: (1) the parameter K- tau, describing the effect of counter-electrical potential; (2) the ratio o f cation velocity to anion velocity beta(nu); (3) the friction coefficient f, which reflects the ionic interaction; and (4) the activity coefficient g amma, which is also a function of concentration. (C) 1999 Elsevier Science Ltd. All rights reserved.