Quasi - stationary polarization methods such as potentiodynamic polarization or stepwise increasing the potential are traditional techniques in corrosion testing. The resulting polarisation curves give insight to mechanisms. In many cases the corrosion rate in a given environment can be calculated from typical parts of the polarisation curve ("Tafel Line" evaluation or polarisation resistance). Moreover, the behaviour of materials can be checked qualitatively: passivation and loss of passivation, and onset of localised corrosion is easily interpreted from these curves.
Typically, linear polarisation curves are recorded at low scan rates from a few mV per hour to 100 mV/min. Stepwise increase is very helpful when localised corrosion is expected. The current transient above each potential step may decrease, showing passivity, or it may rise, or just be noisy, indicating onset of pitting, a growing crack or a depassivating grain boundary.
Slow galvanostatic pulse trains can be used to detect a change in the surface composition - more precise than a constant current level.
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