Cyclic potentiodynamic polarization

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. 

Cyclic potentiodynamic polarization method. Electrochemical studies of pitting corrosion usually indicate that pitting occurs only within or above a critical potential or potential range. Therefore the susceptibility of passive metals to pitting corrosion is often investigated by electrochemical methods such as potentiodynamic or potentiostatic... 

Potentiostatic methods. Once the breakdown potential is determined by cyclic potentiodynamic polarization methods, polarizing individual samples at potentials above and below this value will indicate the validity of the chosen scan rate and give some kinetic data on the initiation and propagation of pits at different levels. Another possibility is to initiate pits above the pitting or breakdown potential and then shift to lower values above or below the protection potential. It is assumed that at imposed values below the protection potential, one should observe current decrease until complete repassivation. 

Fig.S Confocal laser scanning micrographs of air aged (a) 625 and (b) C22 after cyclic potentiodynamic polarization (CPP) testing at 95in pH 7.75 (100 1) electrolyte. Both...

ASTM G61-78, Standard Practice for Conduct-ing Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion, American Society for Testing and Materials, Philadelphia, Pa. 

A correlation has been between pitting potential and pitting in the field the tendency to form pits naturally at open circuit increases as the experimentally determined pitting potential decreases [51]. The difference between E-p and E, which is related to the extent of hysteresis in a cyclic potentiodynamic polarization curve, has also been considered to be a measure of the susceptibility to localized corrosion [3,52]. Issues associated with this interpretation have been reviewed [53]. 

G61-86, Conducting cyclic potentiodynamic polarization measurements for localized corrosion susceptibility of iron-, nickel-, or cobalt-based alloys, Annual Book of ASTM Standards, ASTM International, Philadelphia, Pa., 2000, p. 240, Vol. 3.02. 

Cyclic potentiodynamic polarization used in determining pitting potential consists of scanning the potential to more anodic and protection potentials during the forward and return scans and compare the behavior at different potentials under identical conditions. The polarization curve of an alloy (with or without coating showing active-passive behavior may be obtained in a chosen medium as a function of chloride concentration). E, or Ep represent pitting potential or breakdown potential,... 

ASTM G 61-86, Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys, ASTM International, West Conshohocken, PA, 2003. 

HG. 2—Representative cyclic potentiodynamic polarization curves (from ASTM G 61). 

FIG. 8—Schematic representations of experimental data for (a) a cyclic potentiodynamic polarization curve (b) galvanostatic potential-time curve for a material (c) potentiostatic current-time curve for a previously passivated surface which pits ad < Egg < Ej-, and (d) potentiostatic current-time curve for active surface. The protection potential is found as... 

Cyclic Potentiodynamic Polarization Methods to Determine Em aaiAEp, ... 

Complications with Cyclic Potentiodynamic Polarization Methods... 

As stated above, Ejj and Eprot often dejiend strongly on the method by which they are determined and, therefore, do not uniquely define intrinsic material properties. The Eprof values determined from the scanning method can be complicated by scan rate, pit size or depth, vertex potential/current, polarization curve shape, and specimen geometry [86,87]. Investigators have found more consistent Eprof values after a critical charge has passed, while others report a single critical potential [85]. Often this potential is difficult to choose from E-I data and has been taken at various points on the reverse scan of a cyclic potentiodynamic polarization curve [89]. 

F 2129 Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements to Determine the... 

RG. 4—Representative cyclic potentiodynamic polarization curves (ASTM G 61). The average Ei> was approximately -0.21 V(SCE). 

FIG. 7—Cyclic potentiodynamic polarization curve for type 316L SS showing hysteresis and crevice corrosion. 

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