Electrolytes diffusivity

C), (cmVohm geqmv) K = Ci/R = specific conductance, (ohm cm) h C = solution concentration, (gequiv/ ) Ot = conductance cell constant (measured), (cm ) R = solution electrical resistance, which is measured (ohm) and/(C) = a complicated function of concentration. The resulting equation of the electrolyte diffusivity is... 

Under realistic conditions a balance is secured during current flow because of additional mechanisms of mass transport in the electrolyte diffusion and convection. The initial inbalance between the rates of migration and reaction brings about a change in component concentrations next to the electrode surfaces, and thus gives rise to concentration gradients. As a result, a diffusion flux develops for each component. Moreover, in liquid electrolytes, hydrodynamic flows bringing about convective fluxes Ji j of the dissolved reaction components will almost always arise. 

POTENTIALS BETWEEN SIMILAR ELECTROLYTES (DIFFUSION POTENTIALS)... 

S. Mathison and E. Bakker, Effect of transmembrane electrolyte diffusion on the detection limit of carrier-based potentiometric ion sensors. Anal. Chem. 70, 303-309 (1998). 

Principal differences between bulk media water and membrane water partition coefficients are listed in Table 2. These differences are essentially based on the several orders of magnitude difference in surface-to-volume ratio. In the liposomal system, charges built up due to sorption of charged species can be electrically neutralised by counter-ions from the electrolyte (diffuse double... 

At first sight the position of the pore tip in the electrode seems to be a badly defined parameter because its position changes while the pore is propagating. However, the pore tip is always farthest away from the bulk of the electrolyte. Diffusion thereby produces a minimal concentration of active ions and a maximum concentration of reaction products at the pore tip. This condition may already be sufficient for a passivation of the pore walls if the passivation mechanism is sensitive to ionic concentrations. 

Based on Kohlrausch s law and the relation between conductivity and diffusivity, electrolyte diffusivity at low concentrations decreases linearly with the square... 

The need for an air sampling pump can be eliminated by use of a diffusion tube having a set length to diameter (L/d) ratio in its geometry for introduction of a gas sample. Proper selection of the geometry and L/d ratio of the diffusion tube results in an electrochemical cell with a response which is independent of external gas flow rate. A schematic of a solid polymer electrolyte diffusion head sensor cell is shown in Figure 13. 

DIFFUSION POTENTIAL. When liquid junctions exist where two electrolytic solutions are in contact, as in the case of two solutions of different concentrations of the same electrolyte, diffusion of ions occurs between the solutions, and the differences in rales of diffusion of different ions set up an electrical double layer, having a difference of potential, known as Ihe diffusion potential nr liquid junction potential. 

The mechanism of ion transport is altered by the contribution of diffusion. To account for this effect, it is necessary to know the electrolyte diffusivity. The diffusion coefficient (Z>B0) at infinite dilution can be estimated via the Nernst-Haskell equation (Reid et al, 1987) ... 

In hemodialysis, blood from the patient flows on one side of a membrane and a specially prepared dialysis solution is fed to the other side. Waste material in the blood such as urea, excess acids, and electrolytes diffuse into the dialysate the blood is then returned to the patient, as shown in Fig. 48. A patient typically undergoes dialysis three times per week in sessions lasting several hours each. Modern dialysis systems combine sophisticated monitoring and control functions to ensure safe operation. Regenerated cellulose was the first material used in hemodialysis membranes because of its biocompatibility and low cost it remains the most popular choice. Subsequently, high-permeability dialysis membranes derived from cellulose esters, modified polysulfone, or polyacrylonitrile copolymers have also gained wide acceptance because of the shorter sessions they make possible. 

If Eqs. (5-200) and (5-201) are combined, the multicomponent diffusion coefficient may be assessed in terms of binary diffusion coefficients [see Eq. (5-214)]. For gases, the values Dy of this equation are approximately equal to the binary diffusivities for the ij pairs. The Stefan-Maxwell diffusion coefficients may be negative, and the method may be applied to liquids, even for electrolyte diffusion [Kraaijeveld, Wesselingh, and Kuiken, Ind. Eng. Chem. Res., 33, 750 (1994)]. Approximate solutions have been developed by linearization [Toor, H.L., AlChE J., 10,448 and 460 (1964) Stewart and Prober, Ind. Eng. Chem. Fundam., 3,224 (1964)]. Those differ in details but yield about the same accuracy. More recently, efficient algorithms for solving the equations exactly have been developed (see Taylor and Krishna, Krishnamurthy and Taylor [Chem. Eng. J., 25, 47 (1982)], and Taylor and Webb [Comput Chem. Eng., 5, 61 (1981)]. 

Electrolyte Diffusion Coefficient D in Units of 10 cm at Concentration (in molarity) s... 

For aqueous solutions at room temperature, the order of magnitude of the diffusion coefficient of most of the common simple ions (Na, iC, CIO4) is 10 cm s . Suppose now that a capillary tube containing a solution of an electrolyte is brought into contact vertically and very gently with a capillary of pure water about how far would the electrolyte diffuse into the capillary of water in 24 hr ... 

Figure 4.25. Schematic illustration of the creation of excess electroneutral electrol3he to the right, and a corresptondlng deficit to the left of the particle. Same situation as in fig. 4.24. Beyond the particle, (not shown), electroneutral electrolyte diffuses from the right to the left, around the particle. (Not to scale. The length of the arrows is Olx ) in reality mostly xa > 1.)...

The capacity of the electrolytic diffuse double layer is often ignored when Mott-Schottky plots are used to characterize semiconductor-electrol3ffe interfaces. Under what conditions is this assumption justified ... 

The total potential drop Apotential drop at the metal/oxide interface, the potential drop in the oxide, the potential drop in the Helmholtz layer and the potential drop in the electrolyte (diffuse double layer) ... 

There are many applications in chemical engineering where diffusion of charged species is involved. Examples include ion exchange, metals extraction, electrochemical reactors, and membrane separations. There is an excellent textbook in this area (Newman, 1991). Here we will be content to show that the treatment of electrolyte diffusion follows naturally from the generalized treatment of diffusion given in Section 2.3. 

Thin films of nanostructured metals and semiconductors (e.g., Pt, Sn, CdTe) can be prepared by electrodeposition of the metal ions doped into the Hi LLC phase [40,47,48]. Similar to the precipitation of CdS, these films can retain the symmetry of the LLC template during the deposition. These materials allow one to combine well-defined porous nanostructures, high specific surface areas, electrical connectivity, fast electrolyte diffusion, and good mechanical and electrochemical stability. With this approach, hexago-nally structured semiconductor films of uniform thickness can be prepared. Nanostructured thin films of this type are proposed to have relevance in catalysis, batteries, fuel cells, capacitors, and sensors. 

Certain membranes are more susceptible to damage by these impurities than others. The membrane structure thus determines the sensitivity of the films to contamination as well as its selectivity and ability to suppress free electrolyte diffusion (44). 

The electrolyte flux is naturally affected by osmosis. Namely, a strong positive osmosis carries the electrolyte from the dilute solution to the concentrated one, which is incongruous salt flux. Conversely, electrolyte diffusion is retarded when the mobility of the co-ion is faster (negative osmosis). The flux of the solvent provides the energy required to transfer the electrolyte against its chemical potential gradient. 

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