Charged particles local equilibrium

In its turn, the non-monotonous behaviour of Y(r, t) results in a similar behaviour of the reaction rate K(t) in time (Fig. 6.48). The local maximum of K (f) observed at t = 101 (for a given L) for different initial concentrations likely arises due to the initial conditions used, which do not take into account peculiarities of the spatial distribution of charged particles a more adequate one would be a quasi-equilibrium pair distribution with incorporated potential screening. 

Concepts of local equilibrium and charged particle motion under - electrochemical potential gradients, and the description of high-temperature -> corrosion processes, - ambipolar conductivity, and diffusion-controlled reactions (see also -> chemical potential, -> Wagner equation, -> Wagner factor, and - Wagner enhancement factor). 

Plasmas are strongly non-equilibrium systems with hot light particles (electrons) and cold heavy particles (neutrals and ions in the bulk plasma). Charged particles can achieve kinetic energies of 100s of eV in the sheath (Fig. 11). In this respect, electrochemical systems are closer to thermal plasmas [268] for which local thermodynamic equilibrium (LTE) may be assumed (i.e., all particles are at the same temperature ), and the pressure ( 1 atm) is well above the limit of applicability of the continuum approximation. 

As remarked in Section VI the treatment of local equilibrium must be modified for charged particles, since the long-range coulomb interaction induces long-range correlations and neighboring volume elements cannot be considered to be statistically independent. We will indicate how the coulomb interaction can be taken into account by means of a self-consistent field, as in the Debye-Huckel theory. The results are then valid under the same conditions as the Debye-Hiickel theory, namely when the Debye radius is large compared to the mean interparticle separation. 

The main function of a fuel cell electrode is to convert a chemical flux of reactants into fluxes of charged particles, or vice versa, at the electrochemical interface. Electrochemical kinetics relates the local interfacial current density j to the local interfacial potential drop between metal and electrolyte phases, illustrated in Figure 1.8. A deviation of the potential drop from equilibrium corresponds to a local overpotential q at the interface, which is the driving force for the interfacial reaction. The reaction rate depends on overpotential, concentrations of active species, and temperature. For the remainder of this section, it is assumed that the metal electrode material is an ideal catalyst, that is, it does not undergo chemical transformation and serves as a sink or source of electrons. The basic question of electrochemical kinetics is how does the rate of interfacial electron transfer depend on the metal phase potential ... 

Since excited-state populations are achieved by collisions with other charged or neutral particles within the source, the population of any given excited state can be calculated if local thermodynamic equilibrium (LTE) can be assumed to exist within the source. Under LTE, the fractional population of any given excited electronic state, Nj, is given by... 

Particles dispersed in an aqueous medium invariably carry an electric charge. Thus they are surrounded by an electrical double-layer whose thickness k depends on the ionic strength of the solution. Flow causes a distortion of the local ionic atmosphere from spherical symmetry, but the Maxwell stress generated from the asymmetric electric field tends to restore the equilibrium symmetry of the double-layer. This leads to enhanced energy dissipation and hence an increased viscosity. This phenomenon was first described by Smoluchowski, and is now known as the primary electroviscous effect. For a dispersion of charged hard spheres of radius a at a concentration low enough for double-layers not to overlap (d> 8a ic ), the intrinsic viscosity defined by eqn. (5.2) increases... 

A comparison of Equation (3 14) with Equation (3.10) immediately shows that according to the definition given earlier. Eg is actually equal to the work of creation of inertial polarization corresponding to equilibrium in the final state (Ae = Ae), but with the charge localized on the particle A, i.e. corresponding to the initial state. 

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