Potentiodynamic scan

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.)...

The most common electrochemical test for localized corrosion susceptibility is cyclic potentiodynamic polarization. As was discussed briefly in the section on the electrochemical phenomenology of localized corrosion, this test involves polarizing the material from its open circuit potential (or slightly below) anodically until a predetermined current density (known as the vertex current density) is achieved, at which point the potential is scanned back until the current reverses polarity, as shown in Fig. 42. The curve is generally analyzed in terms of the breakdown (Ebi) and repassivation potentials (Elf). Very often, metastable pits are apparent by transient bursts of anodic current. The peaks in current shown in Fig. 42 for a potentiodynamic scan are due to the same processes as those shown in Fig. 25 for a potentiostatic hold. 

A cathodic potentiodynamic scan will be conducted on an AISI 1020 steel rotating disk electrode (RDE) that has been polished to a 600 grit finish. The electrolyte consists of 2 liters of 0.6 M NaCl, the counterelectrode is a graphite rod, and an SCE will be used for the reference electrode. Make the connections shown below with the cell off, taking care to keep all leads away from the moving parts. Ensure that electrical contact is made between the RDE and the rotator using the DVM. 

Figure 19 shows the DBMS results when the potentiodynamic scans were started in the negative direction. The three most significant observations are ... 

Figure 6.14 The results of a potentiodynamic scan of a metal in solution.

In contrast to the Ce(N03)3/HN03 slurry, the HjOj slurry does not passivate the tungsten surface. Passivation in the H2O2 slurry is not expected because the slurry pH of 5.1 is above the pH where tungsten passivation occurs. The lack of a passivation film is suggested by the relatively high etch rates in the H2O2 slurry. In addition, the potentiodynamic scans in the static solution do not indicate passivation. Finally, the fact that abrasion does not... 

Potentiodynamic scans of tungsten during abrasion in four slurries. (From Ref, (21).)... 

X. Gao, M.J. Weaver, Nanoscale structural changes upon electro-oxidation of Au(lll) as probed by potentiodynamic scanning tunneling microscopy. J. Electroanal. Chem. 

Figure 2. Potentiodynamic scans for abraded and non-abraded A1 surface in the slurry in the absence or presence of H2Ozat pH 2. 

Figure 4. Potentiodynamic scans for abraded A1 and Ti surface in the slurry with the addition of 6 vol% H202 at pH 2 and 4, respectively.

The polarisation behaviour was determined using a GillAC potentiostat (ACM instruments) in a three-electrode cell containing 3.5 % NaCl solution. A saturated calomel electrode and a platinum electrode were used as reference and counter electrodes, respectively. Potentiodynamic scans were acquired in the region from -400 to +1200 mV at a scan rate of 1 mV/s. 

Electrochemical Studies. The mechanisms and kinetics associated with the decoupled reactions (equations 1 and 2) have been investigated by dynamic polarization of electrodes constructed from natural magnetite and ilmenite samples (16). Examples of resulting potentiodynamic scans are shown in Figure 2. The log of the absolute current density generated is plotted as a function of potential applied to the mineral electrodes relative to a calomel electrode. Increases in electrode current densities above approximately 1000 mV and below -200 mV corresponded to the respective oxidation and reduction of H2O to form O2 and H2. 

Figure 2. Potentiodynamic scans plotted as functions of applied potential E and measured current i for natural magnetite (A) and ilmenite (B) electrodes in anoxic solutions at pH 3. Inset is a detail of the current peak defining reductive dissolution of magnetite as a function of pH (adapted from ref. 16)...

Figure 5. Potentiodynamic scans for a magnetite electrode plotted as functions of applied potential and measured current for anoxic pH 3 solutions at 25°C containing variable concentrations of (A) Cr(VI) and (B) V(V) (adapted from refJO).

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