Potential-time relationships

Potential-time relationships have been widely used for studying film formation and film breakdown, as indicated by an increase or decrease in the corrosion potential, respectively. May studied the corrosion of 70/30 brass and aluminium brass in sea-water and showed how scratching the surface resulted in a sudden fall in potential to a more negative value followed by a rapid rise due to re-formation of the film conversely, the pitting of stainless steel in chemical plant may be detected by a sudden decrease in potential... 

Fig. 1.1 Potential-time relationships realized by the Kalousek commutator...

Under these conditions, the four mechanisms CE, EC, catalytic (a) with total regeneration and catalytic (b) with partial regeneration, can together be described by one general expression for the potential—time relationship... 

The real power of digital simulation techniques lies in their ability to predict current-potential-time relationships when the reactants or products of an electrode reaction participate in some intervening chemical reaction. These kinetic complications often result in a fairly difficult differential equation (when combined with the conditions for diffusion or convection encountered in electrochemical problems) that resists solution by ordinary means. Through simulation, however, the effect of any number of chemical steps may be predicted. In practice, it is best to limit these predictions to cases where the reactants and products participate in one or two rate-determining steps each independent step adds another dimensionless kinetics parameter that must be varied over the range of... 

When the electrolysis process is irreversible (in a thermodynamic sense) but still limited by linear diffusion, the potential-time relationship takes a form that includes the heterogeneous electron-transfer kinetic parameters. For a cathodic process the relation is... 

Kalousek commutator — Figure. Potential-time relationships of Kalousek commutator... 

Figure 28. Chronopotentiometry potential-time relationship after application of a constant current. Ej/4 is the potential acquired by the electrode at time r/4.

Fig. II.1.3a, b Schematic drawing of a 3D plot with characteristic current-potential-time relationships for chronoamperometric and steady-state responses. The trace following the intersecting plane shows approximately the peak characteristics of a Mnear sweep voltammognun...

Unlike cyclic voltammetry, the solution of Pick s diffusion equations [Eqs. (2.34) and (2.35)] for chronopotentiometry can be obtained as an exact expression by applying appropriate boundary conditions. For a reversible reduction of an electroactive species [Eq. (2.9)], the potential-time relationship has been derived by Delahay for the case where O and R are free to diffuse to and from the electrode surface, including the case where R diffuses into a mercury electrode. 

Based on the data from entries 2 and 3, the desired function of the current density i and electrode potential is found (the polarization curve equation). Sometimes other relationships are investigated. For example, in the case of potentiostatic electrolysis one determines the rate as a function of time (chronoamperometry), and the potential does not change. Under galvanostatic conditions (i = const), kinetics of the process is described by a potential-time relationship (chronopo-tentiometry). 

Electrochemical measurements coupled with solution analysis were progressively backed up by analysis of the surface and in-depth profiling of the alloy composition in the dealloyed layer [198]. Current-voltage, current-time, and potential-time relationships, as a function of the alloy composition and of the degree of selective dissolution, are the techniques employed extensively. Contributions to the field using this kind of approach can be foimd in Ref 173, 196, 199. 

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