Transport properties of concentrated solutions

The analysis of mass transport processes in battery systems requires accurate values of the transport properties of electrolytic solutions. A generally valid theory of mass transport is presented and described. Mass transport properties are defined by the theory used to describe the flux of mobile species. A consistent set of transport equations are developed for dilute solutions of electrolytes. This theory breaks down, however, in concentrated solutions. In concentrated solution theory, the migration and diffusion fluxes are defined with respect to an average velocity of the fluid, and the driving force for these fluxes is the electrochemical potential. Unlike dilute solution theory, concentrated solution theory correctly defines the number of transport properties. The measurement of fringe displacements of diffusing solutions in an optical concentration cell is a method of determining diffusion coefficients. This method is described, and results for nitric acid solutions are given.