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Anodic Polarization

Last updated: January 5, 2020

What Does Anodic Polarization Mean?

Anodic polarization refers to the change of an electrode's potential in the positive direction. It is caused by current flowing across an electrode-to-electrolyte interface, such as electrode polarization associated with an electrochemical oxidation or anodic reaction. In other words, the change in the initial anode potential results from current flow effects at or near the anode surface.

Polarization is the change of potential from a stabilized state as the result of the passage of current. It also refers to the change in the potential of an electrode during electrolysis, such that the potential of an anode becomes more noble, and that of a cathode more active, than their respective reversible potentials.

Anodic polarization is used for measuring and protecting against corrosion. It can be used to determine the potential regions where materials are susceptible to rapid corrosion.


Corrosionpedia Explains Anodic Polarization

Polarization of an anode, that is, the decrease in the initial anode potential resulting from current flow, is evident at or near the anode surface. The potential becomes more noble (more positive) because of anodic polarization. The change in potential of an anode is caused by current flow.

In the context of corrosion, polarization refers to the potential shift away from the open circuit potential (free corroding potential) of a corroding system. If the potential shifts in the positive direction, it is anodic polarization. If the potential shifts in the negative direction, it is cathodic polarization.

For example, when polarization is disrupted in a passive metal at a given point, a very active anodic site forms, with resultant accelerated local corrosion, particularly if the metal was strongly anodically polarized. For a non-passive system (such as steel in seawater), anodic polarization always increases the corrosion rate. For systems showing an active-to-passive transition, anodic polarization will increase the corrosion rate initially, and then cause a drastic reduction in the corrosion rate. Anodic protection is essentially the application of anodic polarization to a corroding system.

Anodic surfaces can be polarized by formation of a thin, impervious oxide layer. With most metals, however, the film formation must be aided by the addition of such anodic corrosion inhibitors as chromate, nitrite, etc.

The long-term exposure of alloys at anodic potentials is shown to be accompanied by rapid failure, a remarkable decrease in tensile strength, significant loss of plasticity and substantial uniform or intergranular layer corrosion of the surface. Artificial aging improves the resistance of alloys to failure and corrosion.


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