Potentiodynamic technique

The selective net loss of a component such as zinc, aluminium or nickel from copper-base alloys sometimes occurs when these alloys corrode. Early studies of the phenomenon were done by simple immersion. More recently, however, the potential-pH dependence of de-alloying has been examined , and it appears that this approach can provide a much more detailed understanding of the mechanism. Future experimental work is expected to include potentiostatic and potentiodynamic techniques to a much greater extent. 

Galvanostatic, potentiostatic as well as potentiodynamic techniques can be used to electropolymerize suitable monomeric species and form the corresponding film on the electrode. Provided that the maximum formation potentials for all three techniques are the same, the resulting porperties of the films will be broadly similar. The potentiodynamic experiment in particular provides useful information on the growth rate of conducting polymers. The increase in current with each cycle of a multisweep CV is a direct measure of the increase in the surface of the redoxactive polymer and, hence, a suitable measure of relative growth rates (Fig. 5). 

The electrochemical behavior of single-crystal (100) lead telluride, PbTe, has been studied in acetate buffer pH 4.9 or HCIO4 (pH 1.1) and KOH (pH 12.9) solutions by potentiodynamic techniques with an RRDE setup and compared to the properties of pure Pb and Te [203]. Preferential oxidation, reduction, growth, and dissolution processes were investigated. The composition of surface products was examined by XPS analysis. It was concluded that the use of electrochemical processes on PbTe for forming well-passivating or insulating surface layers is rather limited. 

Fig. 7 PPy variants generated by galvanostatic or potentiodynamic techniques. PPy (I) is formed in acetonitrile with 1% water. The average conjugation length is about 30 units.

Measurement Techniques. DC polarisation curves on freshly abraded mild steel in bulk paints were determined using a traditional 3-electrode potentiodynamic technique. A 50 ml cell employed a disc mild steel electrode (area 0.33 cm ), saturated calomel reference and platinum counter electrode. Polarisation curves were made at a scan rate of 2V/Hr between -950 to -450 mV vs see. 

Potentiodynamic Technique. Adsorption of methanol on Pt in acid solution was studied by Breiter and Gilman (3) using a potentiostatic technique. The anodic sweep, with a sweep rate of 800 V/s, was started at rest potential and extended to 2.0 V with respect to a hydrogen reference electrode in the same solution. As shown in Figure 10.8, the current was recorded as a function of potential (time) in the absence (curve A) and in the presence (curve B) of methanol. The increase in current in curve B is due to oxidation of the adsorbed methanol on the platinum electrode. Thus, shaded area 2 minus shaded area 1 (Fig. 10.8) yields the change 2m (C/cm ) required for oxidation of the adsorbed methanol ... 

The advances made since 1970 start with the fact that the solid/solution interface can now be studied at an atomic level. Single-crystal surfaces turn out to manifest radically different properties, depending on the orientation exposed to the solution. Potentiodynamic techniques that were raw and quasi-empirical in 1970 are now sophisticated experimental methods. The theory of interfacial electron transfer has attracted the attention of physicists, who have taken the beginnings of quantum electrochemistry due to Gurney in 1932 and brought that early initiative to a 1990 level. Much else has happened, but one thing must be said here. Since 1972, the use of semiconductors as electrodes has come into much closer focus, and this has enormously extended the realm of systems that can be treated in electrochemical terms. 

Potentiostatic techniques, 787, 1115, 1118 and impurities on electrodes. 1120 potential interval measurements, 1121 p-polarized light, 802 Potentiodynamic techniques, 1423, 1438 vs. potentiostatic techniques, 1426 Potentiostatic transients, 1414 difficulties in, 1415 double layer charging, 1416 radicals in, 1416 IR drop in, 1416 Prandtl layer, 1228... 

V (inversely—and just in bioelectrochemistiy derivatives of potentiodynamic techniques have found application—e.g., in determining on a micron scale the products produced by biological cells (Chapter 14). 

Figure 36 PARC 352 SoftCorr III Potentiodynamic technique combo box window.

Potentiodynamictechniques— are all those techniques in which a time-dependent -> potential is applied to an - electrode and the current response is measured. They form the largest and most important group of techniques used for fundamental electrochemical studies (see -> electrochemistry), -> corrosion studies, and in -> electroanalysis, -+ battery research, etc. See also the following special potentiodynamic techniques - AC voltammetry, - DC voltammetry, -> cyclic voltammetry, - linear scan voltammetry, -> polarography, -> pulse voltammetry, - reverse pulse voltammetry, -> differential pulse voltammetry, -> potentiodynamic electrochemical impedance spectroscopy, Jaradaic rectification voltammetry, - square-wave voltammetry. 

Electrochemical methods, such as potentiodynamic techniques and corrosion current measurements, can be applied [99] to simulate atmospheric contact corrosion... 

Because of the imposed potential variation, the potentiodynamic technique presents similar uncertainties as the galvanostatic method. Possible desorption of the adsorbate, owing to potential change, can complicate the results. Oxide formation in certain potential regimes may be more important in the potentiodynamic than in the galvanostatic method. Uncertainties from potential and concentration variations within porous electrocatalysts can be... 

Electrochemical polymerization is routinely carried out in an acidic aqueous solution of aniline. This low pH is required to solubilize the monomer and to generate the PAn/HA (HA = acid) emeraldine salt as the only conducting form of PAn. Constant potential (potentiostatic) or potentiodynamic techniques are generally employed because the overoxidation potential for PAn is very close to that required for monomer oxidation. 

For a particular electrochemical system, the dependence of the X-ray scattering intensity at various key reciprocal space positions (usually at points on the CTRs) would be monitored as a function of the applied electrode potential over the potential range of interest. This potentiodynamic technique, which we have termed as X-ray voltammetry (XRV) [9], is described in more detail in Sect. 4.1.2.1.4. 

Potentiodynamic technique—The potential is changed scanned) continuously at a predetermined rate (ASTM G 5). 

Cyclic potentiodynamic technique—The potential is scanned forward fi om some low vcdue to a high value juid scanned backward to a predetermined potential or current value (ASTM G 61). 

The essential difference between voltammetric and other potentiodynamic techniques, such as constant current coulometry, is that in voltammetry an electrode with a small surface area (< 10mm ) is used to monitor the current produced by the species in solution reacting at this electrode in response to the potential applied. Because the electrode used in voltammetry is so small, the amount of material reacting at the electrode can be ignored. This is in contrast to the case in coulometry where large area electrodes are used so that all of a species in the cell may be oxidized or reduced. 

Repassivation potentials are readily determined by using the galvanostatic method (Ref 59) or the constant potential-surface scratch test (Ref 59, 60). The galvanostatic method involves impressing an anodic current density of approximately 200 mA/cm (1290 mA/in. ) on the specimen for at least several minutes before measuring the repassivation potential of the sample. Reproducible, anambi-guous repassivation potentials are more difficult to derive by using reverse scan potentiodynamic techniques. 

The potentiodynamic technique is used to examine the passivation behavior of a metal or alloy in an electrochemical system. During the potentiodynamic scan, the metal surface may undergo several different electrochemical reactions, wherein the anodic current may vary over several orders of magnitude [34]. Generally, analysis of the anodic curve can provide potentials for active, passive, transpassive, and repassive zones a rough estimation of corrosion current and corrosion potential and a measure of the stability of passivity. Moreover, one can determine whether the passivation is spontaneous or needs to be polarized to induce passivation. In addition, one can determine whether the electrochemical system can induce a spontaneous transition from passive... 

---