Potentiostatic polarization curve

Fig. 11. Potentiostatic polarization curve on Co3P, measured in a droplet of DI water. The Tafel region is marked [125]. (Reprinted by permission of The Electrochemical Society).

Fig. 5.19 Potentiostatic polarization curve for pure chromium in hydrogen-saturated (deaerated) 1 N H2S04at25 °C. Dashed section is a cathodic "peak" where the hydrogen-ion reduction dominates over the passive chromium oxidation. Redrawn from Ref 9...

Fig. 4.1 Potentiostatic polarization curves (forward and reverse scan).

Potentiodynamic and potentiostatic anodic polarization curves obtained at the same sweep rate are identical. They identify corrosion properties of passivating metals and alloys and are very useful in predicting the corrosion properties of materials. Figure 4.5 shows potentiostatic polarization curve of an active-passive metal with more than one passivation potential. 

Fig. 4.4 Potentiostatic polarization curve of an active-passive metal obtained with controlled potential.

According to the results of the electrochemical impedance measurements, it can be expected that if a constant potential is imposed on the anodes and the produced current is recorded as a function of time, the chronoamperogram of the SCA should be below that for the general zone. Figure 6 shows the potentiostatic polarization curves. It is true that the current density on the general zone is ca. 10 mA/cm higher than that on SCA when a potential of 1.345 V vs MSE (1.981 V vs SHE) is used. 

Figure 6 - Potentiostatic Polarization Curve of the SCA and the General Zone of Lead-Silver Alloy Anodes in Zinc Electrolyte at 38°C and 1.345 V vs MSE...

The potentiostatic polarization curve provides considerably more information about passivity than does the galvanostatic curve. 

Figure 6.8. Potentiostatic polarization curves for 18-8 stainless steel in 0.1W NaCl showing increasingly noble values of the critical pitting potential with additions of Na2S04, 25°C.

The rate of an electrode reaction depends on the potential drop at the electrodeelectrolyte interface. According to Faraday s law (equation 1.8) the rate of reaction is proportional to the current density that flows through the electrode-electrolyte interface. By measuring the current density as a funetion of potential we can therefore get information about the kinetics of electrochemical reactions. The functional dependence between current density and potential is called polarization curve. To experimentally determine a polarization curve one can control either the potential or the current and measure the other quantity. One thus obtains a potentiostatic polarization curve, i =f[E), or agalvanostatic polarization curve, E = f(i), respectively. 

Figure 7.56 Potentiostatic polarization curves showing effect of electrolyte composition on pitting behavior of Fe-18Cr-8Ni exposed to d and SOl anions [25],...

Potentiostatic polarization curve generation is advantageous for situations where polarization is time-dependent and prediction of long-term galvanic corrosion performance is desired. This involves exposing a series of individual specimens of each material at a variety of different potentials for a duration sufficient to ensure steady-state behavior. The steady-state current at each potential is obtained, and polarization curves constructed from the potential/cmrent data pairs. 

Figure C2.8.3. A tliree-electrode electrochemical set-up used for the measurement of polarization curves. A potentiostat is used to control the potential between the working electrode and a standard reference electrode. The current is measured and adjusted between an inert counter-electrode (typically Pt) and the working electrode.

FIG. 28-8 The potentiostat apparatus and circuitry associated with controlled potential measurements of polarization curves. 

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. 

Fig. 12. Steady-state anodic polarization curves (a), and potentiostatic transient curves (b), of a mild steel hemisphere in neutral Na2S04 solution. From [15].

Figure 9 Polarization curve of carbon steel in deaerated, pH 13.5 solution at 65°C. Sample was initially held potentiostatically at —1.2 V(SCE) for 30 min before initiation of the potentiodynamic scan in the anodic direction at 0.5 m V/s. The cathodic loop results from the fact that the passive current density is only 1 pA/cm2, which is less than the diffusion-limited current density for oxygen reduction for the 0.5 ppm of dissolved oxygen present. (From Ref. 8.)...

Figure 28 Schematic Evans diagrams and polarization curves for a material in a solution containing a redox couple that acts as a chemical potentiostat. The i used in the Evans diagram for the O/R redox couple is that relevant to the material of interest. In the absence of the redox couple, the material obtains Ec, i. In the presence of the redox couple, the material obtains Econ2. If Econ2 is above the pitting potential, the material will be rapidly attacked.

Figure 34 Potentiostatic anodic polarization curves of a Fe 10% Cr 10% Ni alloy in a 1 N H2S04 solution at 25°C as a function of electrode mounting technique. (From Greene et al., France, and Wilde.)...

The test method ASTM F7464 covers the determination of the resistance to either pitting or crevice corrosion of passive metals and alloys from which surgical implants are produced. The resistance of surgical implants to localized corrosion is carried out in dilute sodium chloride solution under specific conditions of potentiodynamic test method. Typical transient decay curves under potentiostatic polarization should monitor susceptibility to localized corrosion. Alloys are ranked in terms of the critical potential for pitting, the higher (more noble) this potential, the more resistant is to passive film breakdown and to localized corrosion. (Sprowls)14... 

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