Salt Diffusion Coefficient Research Articles

Irreversible thermodynamic parameters for isothermal transport processes in aqueous rubidium chloride

Experimentally measured conductances and salt diffusion coefficients have been combined with literature values for activities and transport numbers to provide a complete irreversible thermodynamic analysis for aqueous rubidium chloride in the range 0.25–3.0 M at 25°C. The probable effects of ion-association upon the transport parameters are discussed in a comparison with those of the other alkali chlorides.

Permeation of water and sodium chloride through cellulose acetate

AbstractThe factors contributing to the selective permeation of water and sodium chloride through cellulose acetate membranes have been examined by the use of radioactive tracers. With decreasing acetyl content both the partition coefficient (solubility) and diffusion coefficient of water increased, the latter the more sharply. The effect was even more pronounced for salt, indicating that increasing selectivity with acetyl content stems mainly from increasingly preferential restrictions on salt mobility. Trends identical with those mentioned for decreasing acetyl content were found for increasing amounts of cellulose acetate solvents that had been extracted with water to yield more highly swollen membranes. A free‐volume treatment for diffusion of small molecules below the glass transition temperature with the aid of subgroup motion in the polymer is used for both components. The water content of the membrane at (or near) saturation emerged as the predominant factor in the permeation behavior. In view of the similarity in the activation energies of water and salt diffusion the far steeper dependence of the salt diffusion coefficient on water content could not be accounted for by size differences between the diffusing species and has been attributed to confinement of salt ions to locations at which multiple water contacts are feasible.

Electrochemical Determination of Diffusion Coefficients in Clay‐Water Systems

AbstractPastes containing different concentrations of MCl (M = Li or Na) were prepared by mixing MCl olutions with M‐montmorillonites. The pastes were used in pairs in which the members differed only in NaCl activity. Initially, a Ag‐AgCl electrode and an M‐sensitive glass electrode were inserted into each paste and the emf between them was measured. Then the members of each pair were brought into contact with Ag‐AgCl electrodes inserted in them. The emf's between the latter electrodes were also measured. From the two kinds of emf measurements the transference numbers of the ions in the different pairs were calculated. These transference numbers, along with the measured electrical conductances of the pastes, were used to calculate the ionic mobilities. Finally, the calculated ionic mobilities and the known ionic concentrations were inserted in the Nernst equation to calculate the diffusion coefficients of the respective salts

The diffusion of salt in pork muscle and fat tissue.

AbstractThe diffusion coefficients of salt in pork longissirnus dorsi muscle between –2 and 25° and subcutaneous back fat at −2° have been determined and compared with coefficients calculated from reported results of other workers. The rate of salt diffusion did not depend on the muscle fibre direction. Freezing the muscle at −20° had no effect on the diffusion coefficient subsequently determined at −2°.

Transport properties of cellulose acetate osmotic membranes

AbstractDiffusion and distribution coefficients of water and sodium chloride have been measured in cellulose acetate osmotic membranes. These coefficients have been found to vary with the degree of acetylation of the cellulose ester. The diffusion coefficient of water varies from 5.7 × 10−6 to 1.3 × 10−6 cm.2/sec., and the diffusion coefficient of salt varies from 2.9 × 10−8 to 3.9 × 10−11 as the acetyl content is increased from 33.6 to 43.2 wt.‐%. A homogeneous diffusion model is proposed which describes the observations in terms of Fick's law.

Steady state material transfer through biological barriers.

A general theory of material transfer through biological barriers, based on the idea that diffusion processes obey Newton's laws of motion, is outlined. The distribution of permeant ions in the system phase α, barrier, phase ß, when the system is in a stationary state, is discussed. The theory predicts that the logarithms of the concentration ratios of ion pairs in the two phases should be nearly proportional to the flow of water through the barrier when stationary states of the first order due to steady flows of water are established. The theory further predicts that, given similar conditions, the ratio of the logarithms of the concentration ratios of two ion pairs in systems containing two or more salts should be approximately equal to the inverse ratio of the diffusion coefficients of the respective salts in water and hence quasi-invariant.

Viscosity of Water in Clay Systems

AbstractA method was devised for obtaining the activation energy for the viscous flow of a fluid through a porous medium and the method was applied to the flow of water through samples of Na-bentonite. The resulting activation energies were generally higher than the activation energy for the flow of pure water. The activation energy depended on the length of time the water was in contact with the clay and also on the particular sample. For any given sample, the water flow rate was negatively correlated with the activation energy, in accordance with theory.To help interpret these results, data are presented on the tension of water in Na-bentonite suspensions at different intervals of time after stirring. The water tension was near zero immediately after stirring but increased gradually with time. Simultaneously the suspension gelled. Data also are presented on the specific volumes of water, the activation energies for ion movement, the diffusion coefficients of chloride salts and the unfrozen water at -5°C in Li-, Na- and K-bentonite. The activation energies for ion movement and the amounts of unfrozen water were positively correlated with the specific volumes of the water, whereas the diffusion coefficients of the chloride salts were negatively correlated with the specific volumes of the water. In each clay the specific volume of the water and the activation energy for ion movement were higher than those in normal water.It is concluded that a water structure, which varies in extent with particle arrangement and the adsorbed cationic species, exists at the surface of clay particles. This structure bestows a high viscosity to the adsorbed water.