Electrochemical tests critical potential determination

Electrochemical techniques have also been used to provide a rapid test in ASTM F 746, Test Method for Pitting or Crevice Corrosion of Metallic Surgical Implant Materials. A specimen is anodically p>olarized to stimulate pitting and then returned to a less positive preset potential to determine if repassivation will occur. This is repeated at successively higher preset potentials until the final, or criticcJ potential is determined. More resistcmt materitJs display higher critical potentials. This relatively brief test does not wait for pits to initiate tmd reduces variabiUty by maintaining the potential of the specimen. 

Although ASTM tests use temperature to accelerate attack during exposures, temperature can also be used in combination with electrochemical techniques. One example of this is the determination of critical pitting temperatures (CPT) [76,37,32] for alloy development or selection, or both. An anodic potential is applied to an electrode at low temperature (room or below) in the solution of interest and the temperature slowly increases in order to determine the temperature at which initiation of localized corrosion occurs, as signified by an increase in the current above some criterion. Such a method allows a quantitative ranking of materials in terms of resistance to pitting. 

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