Transfer coefficient, cation

Here a is the effective cationic transfer coefficient, X is the complexing agent, and r and r are reaction orders the reaction order in cations is assumed to be one. The subscript indices in front of the chemical symbols and activity terms (a) denote electrolyte (3) and oxide (2), while (1) is reserved for the underlying metal. Another cationic reaction at the oxide solu-tion interface is the transfer of hydrogen ions... 

Table 1.1 Relative dielectric constant en anodic formation factor m, density p, band gap energy Eg, cation transfer coefficient t + f bias dependence and electronic behavior (SC = semiconductor), structure (a = amorphous, c = crystalline), texture dependence for some of the oxide systems described in this treatise (see also [20]). 

Fig. 4 Electrochemical reduction of a sulfonium cation (Scheme 6) showing the transition from the concerted to the stepwise mechanism as driving force increases upon raising the scan rate.33 The apparent transfer coefficient, a, is derived from the peak width according to equation (17).

Soils were further characterized by the determination of pH in water and potassium chloride in the proportions 1 2.5, total organic carbon (TOC) and cation exchange capacity (CEC). Transfer coefficients between soil and plant and enrichment in soils were determined. The results for Pb were represented in the form of relative enrichments for soils (Kabata-Pendias, 1985) and transfer coefficients in plants (Kovalevskii, 1979). 

Usually the electrode reaction is considered to occur when the reactant reaches the OHP thus, the rate of electrode reaction is influenced by the value of ( ohp- s) For a reduction, Ox2 + ne - Red2 n, the experimental standard rate constant, ksexp, deviates from the standard rate constant expected for ( ohp s) = 0 [curve (b)]. If the latter rate constant is expressed by ks,cori there is a relation ks,exp=ks,con-exp[(an-z)( oHp- s)F/RT], where a is the transfer coefficient. If z=+l, n = 1, a 0.5, and ( ohp- s)<0, then (a-z)( Ohp s)>0 and kSjexp>kSjCon, showing that the electrode reduction of a univalent cation is accelerated by the double-layer effect. On the other hand, if z=0, n= 1, a 0.5, and ( ohp s) <0, ks,expneutral molecule is decelerated by the double-layer effect. In the study of electrode kinetics, it is usual to get kSiCon. by correcting for the double layer effect (see Table 8.6 for an example). 

Electrical conductance, cation transference number and activity coefficient of the halide systems are discussed on page 37. 

Current-voltage tests to determine the limiting current intensity (/lim), ion transport numbers (ta, tc+), and surface resistances (ra, rc) in anionic and cationic membranes, as well as solute mass transfer coefficient (Am). 

The terms aanodic and cathodic are the transfer coefficients [Eq. (7.143)] for the anodic and cathodic components of the corrosion reaction, respectively. Their values will depend upon the reactions making up the corrosion situation. If one assumes that a hydrogen evolution rate controlled by charge transfer is the cathodic reaction, acathodic = 1/2 and if, e.g., the metal dissolution is controlled by charge transfer to form a divalent cation, aanodic = 2. Then, from (12.37), the maximum value of V - Ecorr allowable for the approximation of Eq. (12.35) is... 

Self-diffusivity, cooperatively with ionic conductivity, provides a coherent account of ionicity of ionic liquids. The PGSE-NMR method has been found to be a convenient means to independently measure the self-diffusion coefficients of the anions and the cations in the ionic liquids. Temperature dependencies of the self-diffusion coefficient, viscosity and ionic conductivity for the ionic liquids, cannot be explained simply by Arrhenius equation rather, they follow the VFT equation. There is a simple correlation of the summation of the cationic and the anionic diffusion coefficients for each ionic liquid with the inverse of the viscosity. The apparent cationic transference number in ionic liquids has also been found to have dependence on the... 

Table 17 Transfer Coefficients to Various Aromatic Compounds in Cationic Polymerization of Styrene"...

There is ample evidence that the plots of the logarithm of the apparent rate constant Tc against the potential difference (Tafel plots) for univalent ions have reciprocal slopes of about 118 mV per decade [42, 61, 124, 132, 142-144, 146]. This behavior is illustrated for several cations and anions in Fig. 13, which displays data obtained from equilibrium impedance measurements [132]. Tafel plots derived from dc or ac voltammetric measurements in a sufficiently broad potential range are usually curved [144, 145, 163]. Chronocoulometry has been claimed [124] to provide independently the rate constants for the forward and the backward ion transfer in Eq. (21) cf. also Girault s review [14]. However, this is impossible in principle, because these rate constants should always be related to each other by Eq. (22). The origin of the value of the apparent charge transfer coefficient and its variation with the potential has been always the key issue. 

Logarithmic analyses can be carried out on the neopolarogram in much the same way as with classical polarography (see Sec. V). Examples that illustrate the application of the convolution technique include reversible dimerization of radical cations [114], the study of dissociative electron transfer reactions [175,176], and investigations of the possible potential dependence of the transfer coefficient a [174,177]. 

In nonaqueous aprotic solvents, such as dimethoxyethane [25] or acetonitrile [26,27], the reduction product from tertiary nitroalkanes is the radical anion. Cyclic voltammetric data of 2-nitro-2-methylpropane showed that the electrochemical rate constant was rather low and depended on the size of the supporting electrolyte cation the electrochemical transfer coefficient a was found to be potential dependent [28]. The nitro-t-butyl radical anion is rather unstable (half-life of 0.66s) and decomposes into nitrite ion and t-butyl radical. Continued electrolysis results in the formatrion of di-t-alkyl nitroxide radical [25,27]. 

Figure 6.3 The dependence of feed-side and strip-side overall mass-transfer coefficients on feed flow velocities. Initial compositions feed 40 % H3PO4 WPA, containing 55.2 ppm Cd, 55.4 ppm Cu, and 290 ppm Zn LM 0.5 mol/kg PVSH aqueous solution strip 2.0 mol/kg HCl. Membrane barriers Tokayama Soda cation-exchange membrane CM-2. From Ref. [6] with permission.

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