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Tafel Plot

Definition - What does Tafel Plot mean?

The Tafel plot serves as a diagram or illustration of the Tafel equation. This equation is mainly used in electrochemical kinetics connecting the overpotential rate to the electrochemical reaction rate.

The Tafel plot presents the results of the equation and is used to identify information such as

  • Rate of pitting
  • Passivity
  • Corrosion susceptibility

With this technique, the corrosion current (icorr) can be identified and used to compute the rate of corrosion. The plot, together with the equation, can be very useful in depicting the lifespan of materials used in various industries.

Corrosionpedia explains Tafel Plot

By making use of the Tafel equation, functional plots can be illustrated to aid in finding the rate of corrosion. The plot that is extrapolated to zero produces coordinate sets relating to the X axis (Ecorr) and the Y axis (icorr). The value of icorr can be computed with the aid of Tafel constant values such as Ba + Bc as well as the rate of pitting (Rp). The Ba value can be identified by obtaining the anodic curve portion and the Bc value for the equivalent cathodic part.

In simple formulations, the Tafel equation can take this form:

* icorr = ecorr (ba + bc)/ Rp

By utilizing the equation as well as the Rp value, the icorr can be identified. With this, the rate of corrosion can be computed based on this value in mm/year. Another way to determine the rate of corrosion is by calculating the rate of overpotential, and this can be diagrammed using the Tafel plot as well.

There are certain points to make note of when making use of the Tafel plot:

  • The icorr values are never set at 0. Yet, the resulting net flow of current will be equivalent to 0 if the cathodic and anodic currents are equal in magnitude.
  • The signs can be omitted because their purpose is to identify the current flow direction. If the current flows the opposite direction, the signs will be reversed. Hence, dropping signs is acceptable.
  • Several step reactions can have various steps and varying stoichiometric electron numbers.
  • There is no existing universal plot standard when it comes to plotting log on the X and Y axes.
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