Transport number determinations

Farad. Boc. xiv. 10,1921) for the composition of the sols and gels of the inorganic colloidal hydroxides, e.g. zirconia produced by the hydrolysis of zirconium oxychloride. By electropotentiometric measurements of the hydrogen and chlorine ion concentrations of sols formed by hydrolysis as well as freezing point, conductivity and transport number determinations he has shown that a series of salts are formed of the types ... 

What are the requirements of a satisfactory structural model for ionic liquids in this composition range First, since transport-number determinations show that the... 

Sutija, D. P., Norby, T., Bjombom, P. (1995). Transport number determination by the concentration-ceU/open-circuit voltage method for oxides with mixed electronic, ionic and protonic conductivity. Solid State Ionics, 77, 167—174. 

Moving boundary method for transport number determination condition for sharp boundary... 

The measurement of transport numbers by the above electrochemical methods entails a significant amount of experimental effort to generate high-quality data. In addition, the methods do not appear applicable to many of the newer non-haloalu-minate ionic liquid systems. An interesting alternative to the above method utilizes the NMR-generated self-diffusion coefficient data discussed above. If both the cation (Dr+) and anion (Dx ) self-diffusion coefficients are measured, then both the cation (tR+) and anion (tx ) transport numbers can be determined by using the following Equations (3.6-6) and (3.6-7) [41, 44] ... 

For DC polarization studies, the ratio of steady-state to initial current is not the transport number but determines the limiting current fraction , the maximum fraction of the initial current which may be maintained at steady-state (in the absence of interfractional resistances). Variations... 

We express the altered concentration in terms of the adsorption excess. If all the adsorbed substance were contained to the extent of k gr. per cm.2 on a superficial layer of zero thickness and surface total mass present in the volume Y would be m = V + kto. The layer of altered concentration must, however, have a certain thickness. We will therefore imagine a plate 2 placed in front of the surface and parallel to it, and define the adsorption excess as the concentration in the included layer minus the concentration in the free liquid. That this result is independent of the arbitrarily chosen thickness is easily proved when we remember that the problem is exactly the same as that of finding the change of concentration around an electrode in the determination of the transport number of an ion by Hittorf s method. 

For obtaining internal or external mobilities, the corresponding transport numbers are usually measured. There are several methods for determining transport numbers in molten salts that is, the Kleimn method (countercurrent electromigration method or column method), the Hittorf method (disk method), the zone electromigration method (layer method), the emf method, and the moving boundary method. These are described in a comprehensive review. ... 

Various methods are available for determining the solvation number hj and (or) the radius of the primary solvation sheath (1) by comparing the values of the true and apparent ionic transport numbers, (2) by determining the Stokes radii of the ions, or (3) by measuring the compressibility of the solution [the compressibility decreases... 

The transference or transport number of an ion can be determined by (i) the analytical method (ii) the moving boundary method and (iii) the emf method. The first two methods will be dealt with here, but the third will figure in a later section. 

Based on the general scenario provided above, the analytical method to determine transference or transport numbers has been devised and is carried out in an apparatus which can essentially be regarded as an improvement over the Hittorf apparatus. This consists of two vertical tubes connected together with a U-tube in the middle all three tubes are provided with stop-cocks at the bottom. The U-tube is also provided with stop-cocks at the top by closing these, the solutions in the cathode and anode limbs can be isolated. The silver anode is sealed in a glass tube as shown, and the cathode is a piece of freshly silvered silver foil. The apparatus is filled up with a standard solution of silver nitrate and a steady current of about 0.01 ampere is passed for 2-3 hours. In order to avoid the occurrence of too large a change in concentration it is necessary to pass the current only for a short duration. The... 

The apparatus used to determine the transport number by the moving boundary method is shown in Figure 6.4. It consists of a long vertical tube of uniform cross-section which is fitted with two electrodes at the two ends. Let the electrolyte, the transport number of whose... 

Figure 6.4 Moving boundary experimental set-up for determining the transport number of E+ ions.

While the molar conductivity of strong electrolytes A0 can be measured directly, for determination of the ionic conductivities the measurable transport numbers must be used (cf. Eq. (2.4.12)). Table 2.1 lists the values of the limiting conductivities of some ions in aqueous solutions. 

Fig. 2.10 Schematic design of a cell for the determination of transport numbers from measurements of the concentration decrease in electrode compartments (Hittorf s method)...

The methods for determination of transport numbers include the Hittorf method and the concentration cell method (p. 121). 

Potentiometry is used in the determination of various physicochemical quantities and for quantitative analysis based on measurements of the EMF of galvanic cells. By means of the potentiometric method it is possible to determine activity coefficients, pH values, dissociation constants and solubility products, the standard affinities of chemical reactions, in simple cases transport numbers, etc. In analytical chemistry, potentiometry is used for titrations or for direct determination of ion activities. 

If measurements are made in thin oxide films (of thickness less than 5 nm), at highly polished Al, within a small acceptance angle (a < 5°), well-defined additional maxima and minima in excitation (PL) and emission (PL and EL) spectra appear.322 This structure has been explained as a result of interference between monochromatic electromagnetic waves passing directly through the oxide film and EM waves reflected from the Al surface. In a series of papers,318-320 this effect has been explored as a means for precise determination of anodic oxide film thickness (or growth rate), refractive index, porosity, mean range of electron avalanches, transport numbers, etc. 

The transport numbers of the ions can be determined by using a solid-state electrolyte. The cell voltage across an oxygen-conducting electrolyte subjected to an oxygen pressure gradient is given by the Nemst equation (Section 6.8.3) ... 

Thus, measurement of the total conductivity together with the cell voltage allows the transport numbers of the ions to be determined (Fig. 8.17). The results show that at lower temperatures proton conductivity is of greatest importance, at middle temperatures oxygen ion conductivity becomes dominant, and at high temperatures the material is predominantly a hole conductor. Between these temperatures, at approximately 350°C the solid is a mixed H+ and O2- conductor while at approximately 650°C it is a mixed hole and O2- conductor. 

The above procedures imply that (1) there is only a single type of site (2) binding occurs only to the transporter site (usually not the case for trace metals), and (3) the internalisation flux is negligible for the equilibration times that are employed [197,198], These conditions are rarely fulfilled for metal transporters. The interpretation of Scatchard plots is especially ambiguous in the presence of several independent sites. On the other hand, in the biomedical literature, where nonspecific adsorption is generally not a problem, values of 104 to 106 carriers per cell (ca. 10-13 to 10 11 carriers cm-2 of cell surface area), with even lower numbers determined for some receptors (e.g. haematopoetic growth factor [199]), are typically reported. 

Fuller, T. F. and Newman, J. 1992. Experimental determination of the transport number of water in Nafion-117 membrane. Journal of the Electrochemical Society 139 1332-1337. 

However, when the concentration or mobility of ion pairs is significant compared with the individual ions then the measured diffusion coefficients for both constituents approach that of the ion pairs and not the free ions and as a consequence the apparent t+, and hence t, approach 0.5. In fact it is no longer valid to apply the above equation in order to determine transport numbers. Generally, in the presence of mobile ion pairs or more complex mobile ion clusters, diffusion coefficients and t+ measurements... 

A battery is a transducer that converts chemical energy into electrical energy and vice versa. It contains an anode, a cathode, and an electrolyte. The anode, in the case of a lithium battery, is the source of lithium ions. The cathode is the sink for the lithium ions and is chosen to optimize a number of parameters, discussed below. The electrolyte provides for the separation of ionic transport and electronic transport, and in a perfect battery the lithium ion transport number will be unity in the electrolyte. The cell potential is determined by the difference between the chemical potential of the lithium in the anode and cathode, AG = —EF. 

W. Plotnikoff found the mol. conductivity of ethereal soln. diminishes with dilution, and increases with rise of temp. W. Hittorf attempted to determine the transport number of the anion in aq. soln. of normal sodium phosphate, but the salt was so much hydrolyzed that most of the current was carried by the alkali. With aq. soln. of sodium hydrophosphate, the transport number of the HP0"4-anion was 0-516 and with sodium dihydrophosphate for the H2PO 4-anion, 0-383. J. F. Daniell and W. A. Miller also made some observations with this salt. W. Hittorf found with soln. of potassium dihydrophosphate, the transport number of the H2P0,4-amon was 0-277. O. Wosnessensky measured the potential difference at the boundary of phosphoric acid and a non-aqueous solvent. P. Pascal studied the magnetic properties. J. Murray tried if he could decompose a soln. of the acid by magnetized iron. 

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