Electrolyte interface theory characteristics

Surface Potential-pH Characteristics in the Theory of the Oxide-Electrolyte Interface... 

Bourrie, G. Trolard, F. Jaffrezic, J.-M. R.G.-A. Maitre,V. Abdelmoula, M. (1999) Iron control by equilibria between hydroxy-Green Rusts and solutions in hydromorphic soils. Geochim. Cosmochim. Acta 63 3417-3427 Bousse, L. Meindl, J.D. (1986) The importance of > /o/pH characteristics in the theory of the oxide/electrolyte interface. In Davis, J.A. Hayes, KF. (eds.) Geochemical processes... 

It can be expected from the nature of silicon/electrolyte interfaces described in the previous sections that the surface states on silicon electrodes may have different physical and chemical characteristics such as type, quantity, distribution, transfer kinetics, and so on, depending on the surface condition. Table 2.12 shows examples of measurements of surface states reported in the literature. Thus, while the energy levels in bulk silicon and electrolyte can be described by a general theory, those of surface states can only be dealt with by specific theories applicable to the specific situations. 

A predictive molecular thermodynamics approach is developed for microemulsions, to determine their structural and compositional characteristics [3.7]. The theory is built upon a molecular level model for the free energy change. For illustrative purposes, numerical calculations are performed for the system water, cyclohexane, sodium dodecyl sulfate as surfactant, pentanol as cosurfactant and NaCl as electrolyte. The droplet radius, the thickness of the surfactant layer at the interface, the number of molecules of various species in the droplets, and the distribution of the components between droplets and the continuous phase are calculated. The theory also predicts the transition from a mi-... 

For some electrolytes, the characteristic distance d, required to fit the experimental data on surface tension with Eq. (17) is smaller than the hydrated radius of the ions and might even become negative (e.g. HC1, HN03, HC104 [29]). This means that at least one component of the electrolyte is preferentially adsorbed on the interface. Therefore, dB can be regarded only as a parameter in an extremely simplified theory. 

When a conductive electrode (e.g., metallic or glassy carlxMi) is in contact with an electrolytic solution, the excess electronic charge is accumulated at the electrode surface and charge distribution occurs in the solution only. This is related to the fact that as the number of charged species increases, the space in which the redistribution of charges occurs shrinks. At a metallic electrode-solution interface, the charge redistribution in solution depends on the applied potential and is described by the Guy-Chapman-Stem theory. The characteristic thickness of the diffuse layer in nonadsorbing electrolytes varies from 0.3 nm in 1 M to 3 nm in 0.01 M aqueous electrolyte, while the thickness of the Helmholtz layer is much smaller [17]. 

The unusual nature of the silica-water system has been noted by J. A. Kitchener (7), who pointed out that the endless confusion in the literature concerning the silica-water interface has arisen because the hydration and solubility characteristics have not been understood. For example, there is the question as to why silica sols are extraordinarily stable at pH 2 where the zeta potential is zero and become increasingly sensitive to electrolytes at higher pH. where the potential is highest—in contradiction to the generally accepted electrical double layer theory. Another mystery is that crystalline quartz becomes coated with a film of amorphous silica even though the solution is undersaturated with soluble silica with respect to a surface of amorphous silica. 

The first important investigation of a liquid membrane and, at the same time, of the interface of two immiscible electrolyte solutions (ITIES) was carried out by Nemst and Riesenfeld [2] at the beginning of this century. They measured not only the electrical potential difference between both the phases but also the effect of current flow across ITIES. Their ITIES was represented by a boundary between an aqueous solution and a solution in an organic solvent. Their main interest was not, however, in the current-potential characteristics but mainly in the proportion of cations and anions carrying the charge across ITIES. On the basis of their theory they could measure experimentally the transport numbers in the organic phase. 

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