Contact charging, dispersion effect

The small number of charge carriers in the semiconductor is partially compensated for by the small size of metal particles. By using Schwab s magnetic measurements as a clue to the number of electrons transferred to the nickel across the nickel-alumina interface it can be estimated that a change of 0.05 electron per atom would produce detectable catalytic effects. By extrapolation to the small dispersed type of metal particle being considered here, it is seen that for a particle containing 2000 atoms the equivalent transfer would be produced by 100 electrons. Despite this, if one considers contact between a 2000-atom platinum particle and a 100 alumina particle (volume 4 x 10 cc) the flow of electrons to the metal would be drastically limited by the small number of charge... 

The earlier sections of this chapter discuss the mixed electrode as the interaction of anodic and cathodic reactions at respective anodic and cathodic sites on a metal surface. The mixed electrode is described in terms of the effects of the sizes and distributions of the anodic and cathodic sites on the potential measured as a function of the position of a reference electrode in the adjacent electrolyte and on the distribution of corrosion rates over the surface. For a metal with fine dispersions of anodic and cathodic reactions occurring under Tafel polarization behavior, it is shown (Fig. 4.8) that a single mixed electrode potential, Ecorr, would be measured by a reference electrode at any position in the electrolyte. The counterpart of this mixed electrode potential is the equilibrium potential, E M (or E x), associated with a single half-cell reaction such as Cu in contact with Cu2+ ions under deaerated conditions. The forms of the anodic and cathodic branches of the experimental polarization curves for a single half-cell reaction under charge-transfer control are shown in Fig. 3.11. It is emphasized that the observed experimental curves are curved near i0 and become asymptotic to E M at very low values of the external current. In this section, the experimental polarization of mixed electrodes is interpreted in terms of the polarization parameters of the individual anodic and cathodic reactions establishing the mixed electrode. The interpretation then leads to determination of the corrosion potential, Ecorr, and to determination of the corrosion current density, icorr, from which the corrosion rate can be calculated. 

When the electrolyte concentration, c, is low, while the concentration of colloidal particles, n, and their effective charge are high, i.e. when c q nleNA, the value of x is close to the initial electrolyte concentration. In the other words, under these conditions essentially all of the electrolyte should transfer into pure dispersion medium. This means that in the case of highly developed diffuse layers of ions and rather compact arrangement of particles, when the ionic atmospheres come into contact, the co-ions (Na+ in the present... 

The properties of the metal phase have been successfully described by rather simple models, most notably the jelliiun model. In many theoretical treatments of the liquid/metal interface, the hquid electrolyte in contact with the metal has been described, to first order, as an external field, acting on the jellium model (see Ref. 13 and references therein). In many simulation studies, the reverse approach is taken. The focus is on the description of the liquid phase and the effect of the metal on the aqueous phase is approximated, to first order, by an external potential acting on the ions and molecules in the liquid phase. This is done within the framework of classical mechanics and classical statistical mechanics. The models for the interparticle interactions will consist of distributed point charges in combination with soft interatomic repulsions and dispersive attractions. Some of the models can also be considered chemical models they can be regarded as a first step towards electrochemical modeling, very much in the spirit of molecular modeling . 

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