Salt, diffusion

G. J. Janz and N. P. Bansal, J. Phys. Chem. Ref 11 (1982) 505 Molten Salts Diffusion Coefficients in Single and Multi-Component Salt Systems, American Chemical Society-American Institute of Physics-National Bureau of Standards, Washington, DC, 1982. 

The rate of growth of polymer-salt complexes can provide fundamentally important information that is difficult to determine otherwise. The rate of crystal growth of (PEO)3 NaSCN from its undercooled liquid was measured and used to determine values for the diffusion coefficients of Na" " and SCN (Lee, Sudarsana and Crist, 1991). Also it was shown that the rate of the salt diffusion is independent of the molecular weight of the polymer for PEO molecular weights above 10. This result is fully consistent with the concept that ion motion is due to local segmental motion of the polymer. 

Electroneutrality demands that a concentration gradient exists for both lithium and triflate near the Li electrode and that the diffusion is coupled in a similar fashion to the coupled diffusion of ions and electrons in intercalation electrodes (Chapter 8). As in that case it is the coupled diffusion of both species which is observed, i.e. the salt diffusion coefficient. This may be evaluated by fitting the low frequency region of the curve to ... 

The relationship of Ay/ to the salt diffusion coefficient of the species crossing the interface (DJ is ... 

As a result of Internal concentration polarization, the effective osmotic pressure difference across the membrane can be significantly below the osmotic pressure difference between the bulk solutions. The effective osmotic pressure can be calculated from the salt permeation coefficient and the salt diffusion resistance in the porous membrane substrate. The highest power output for a membrane is obtained at an operating pressure equal to about one half of the effective osmotic pressure. 

The solution-diffusion model (1 ) assumes that water and salt diffuse independently across the membrane and allows no convective salt transport. The reciprocal salt rejection, 1/r, is linearly related to the reciprocal volume flux, 1/q ... 

In both of these situations there was opportunity for partial reduction of disulfide bonds before polypeptide refolding and reaggregation began as the guanidine salt diffused out of the dialysis sac. 

At not too high concentrations of the outer solution, the amount of absorbed salt in the membrane in equilibrium is very low (y is very small). For this reason the diffusion of salt through a membrane is very small too. The membrane behaves as a barrier for salt diffusion. This is also favourable in electrodialysis, where high differences can occur in the salt concentrations of dialysate and concentrate. As the back-diffusion opposes the effect of the electrical desalting, its value must be as small as possible. 

As the permeability of the membrane for ions of different charge signs largely varies, salt diffusion through a membrane is accompanied by the establishment of a membrane potential. These concentration or dialysis potentials play an important part in the study of membrane phenomena. With the above described model, the phenomenon of electro-endosmosis i.e. the transport of solvent across a membrane under the influence of an electric field, can easily be explained also. 

Here, iiim is the limiting current density, bCf is the salt concentration of the diluate in the bulk solution, Az is the thickness of the laminar boundary layer, Tm and T5 are the transport numbers in the membrane and the solution, Ds is the salt diffusion coefficient in the solution, F is the Faraday constant, z is the charge number, and the subscript i refers to cation and anion. 

K = salt permeability coefficient (a function of the salt diffusivity through the membrane)... 

Physico-Chemical Properties of Salvarsan Solutions.— These solutions show the characteristic properties of colloids, dialysis through a parchment membrane showing but slight diffusion, w hiist in methyl alcohol solution diffusion takes place more readily. The disodium salt diffuses about four times as quickly as the free hydrochloride. Hie idscosity of aqueous solutions of Salvarsan increases from the moment of preparation until an approximately constant value is reached. This value is much higher than the initial value. As the concentration of the solution increases, the initial velocity of increase of scosity and the final value are affected, and the presence of acid or alkali also has a marked effect. With rise of temperature the viscosity more quickly attains its maximum value, but this value is diminished The viscosity of dilute solutions diminishes on keeping. The ps value of Salvarsan is 7-60 of the dihydrochloride, 2-41 of the monohydrochloride, 3-00 of the monosodium salt, 10-88 and of tlie disodium salt, 11 43. The presence of an isoelectric point at ps value about 3 4 is indicated. ... 

From the above equation it follows that the surface salinity of the Baltic Sea is controlled by the ratio between the freshwater surplus and the sum of the stochastic salt fluxes normalized by the salinity difference between the Kattegat and the Arkona Sea surface water, see Fig. 2.6. The turbulent salt diffusivity k is a function of the geometry of the Belt Sea in terms of the length of the channel and the sill depth as well as of the spectrum of wind fluctuations determining the sea level difference between the Kattegat and the Arkona Sea and subsequently the barotropic current fluctuations in the Belt Sea. 

This agrees with the description of the graded bar and the equilibrium states we imagined for various portions of that and the approach can clearly be used for the salt-diffusion problem, at the 4 m-wide dike. To treat pressure differences in a parallel manner, one notes that materials become less compressible when compressed the pressure-volume curve for a fixed mass is usually concave away from the origin, as a hyperbola is. Then a profile of graded pressure is like a profile of graded concentration it is intrinsically and unquestionably a nonequilibrium state at every point, but the properties of any small portion can be matched with the properties of an imagined equilibrium state. 

FIG. 2 Relaxation times of dynamic modes observed in polyelectrolyte solutions and mixtures over a broad range of experimental conditions 0 diffusion of low molecular weight salt diffusion of polyions or polyion segments in semidilute solutions 3 interaction mode in polyelectrolyte mixtures and diffusion of polyelectrolyte domains (clusters). The data are based mostly on the work on linear flexible polyelectrolytes. Relaxation times correspond to scattering at 90°. See text for more details. 

Fill a small cylindrical tube of unit sectional area with a solution of some salt (Fig. 164). Let the tube and contents be submerged in a vessel containing a great quantity of water, so that the open end of the cylindrical vessel, containing the salt solution, dips just beneath the surface of the water. Salt solution passes out of the diffusion vessel and sinks towards the bottom of the larger vessel. The upper brim of the diffusion vessel, therefore, is assumed to be always in contact with pure water. Let h denote the height of the liquid in the diffusion tube, reckoned from the bottom to the top. The salt diffuses according to Fourier s law,... 

The steel probe is sometimes embedded in an excessively salty patch. With no current applied, a macrocell current flows from the probe to the reinforcement if they are connected with an ammeter between them. As CP current is applied, the current reduces and then reverses. This is called the macrocell or null probe approach and is used to show that a very anodic area has been made cathodic. It is therefore assumed that all of the rest of the steel is cathodic too. However it is dependent upon the amount of salt added to the patch, and if the salt diffuses away then it may no longer be the most anodic area after a few years. 

Canas, A., Ariza, M.J. and Benavente, J. 2001. Characterization of active and porous sublayers of a composite reverse osmosis membrane by impedance spectroscopy, streaming and membrane potentials, salt diffusion and X-ray photoelectron spectroscopy. J. Memb. Sci. 183 135-146. 

S. Zugmann, M. Fleischmann, M. Amereller, R. M. Gschwind, M. Winter, H. J. Gores, J. Chem. Eng. Data 2011, 56, 4786-4789. Salt diffusion coefficients, concentration dependence of cell potentials, and transference numbers of lithium dilluoromono(oxalato)borate-based solutions. 

Albumin did not reduce the diffusion of salts. Diffusion in a jelly was nearly as fast as in water this was generally confirmed, but later workers (Reveil, 1868 Stefan, 1878, etc.) found that diffusion in jellies, especially with concentrated solutions, is somewhat slower. The theory of diffusion was first given by A. E. Fick, a physiologist. ... 

In kidney dialysis, toxic "middle molecules" diffuse across flie Cuprophane membrane and out of die blood, while the larger desirable species are retamed. Almost as much salt diffuses out of die blood as diffuses into the blood from die dialysate during diis procedure. A small pressure is imposed that depletes die patient of a few pounds of accumulated water over a period of hours. Such processes are considered to be primarily concentration-driven. 

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