What is Polarization ? anodic polarization vs cathodic polarization


Polarization is a form of corrosion reaction that causes rust to appear on metal damage. By definition, polarization is the process of polarizing hydrogen ions (chemically electrically) so that hydrogen gas is formed with the help of binding electrons resulting from the metal degradation process. If a metal is not in equilibrium in a solution containing its ions, then the electrode potential of the metal is different from the free corrosion potential. The difference between the electrode potential and the free corrosion potential is called the polarization. Polarization or deviation from the equilibrium potential is the same as anode polarization of the metal and cathode polarization in its environment. Polarization is the change in potential from a stable state, for example, from an open circuit electrode potential as a result of current flow. It also refers to the change in electrode potential during electrolysis, so that the potential of an anode is higher, and that the cathode is more active than the respective potentials.

There are two kinds of polarization, namely activation polarization and concentration polarization. Polarization activation can take place by controlling the sequence of reactions of hydrogen formation on metals with contacting solutions. While the concentration of polarization occurs due to the presence of a concentrated hydroxyl concentration so that the controller is the concentration of ions.

Activation polarization

Electrochemical processes are controlled by sequential reactions on the metal-electrolyte surface. Activation polarization refers to electrochemical processes that are controlled by the sequence of reactions at the metal-electrolyte interface. this is easily illustrated by considering the hydrogen-evolution reaction on zinc during corrosion in acidic solutions.

Concentration polarization

Concentration polarization refers to a diffusion-controlled electrochemical reaction in an electrolyte. Activation polarization is usually the control factor during corrosion in media containing high concentrations of the active substance (eg, concentrated acids).

Polarization is definitively the process of turning hydrogen ions (electr0-chemical) so that hydrogen gas is formed with the help of the binding of electrons resulting from the metal degradation process. Polarization is sometimes referred to as “overvoltage” or “overpotential”. Actually there is a difference between the two terms, namely overvoltage and excess potential. The overvoltage is the difference between the actual electrode potential at which electrolysis begins and the reversible electrode potential (standard redox potential). whereas overpotential refers to the potential deviation from the potential balance in a system.

In the context of corrosion, polarization refers to the shifting potential of the open circuit potential (free corrosion potential) of a corrosion system. If the potential shifts in the “positive” direction (above Ecorr), it is called “anodic polarization”. If the potential shift is in the “negative” direction (below Ecorr), it is called “cathodic polarization”.

polarization effect on corrosion rate

With all metals and alloys in wet environments, cathodic polarization always reduces the rate of corrosion. Cathodic protection is basically the application of cathodic polarization to a corrosion system. For non-passive systems (eg steel in seawater), anodic polarization always increases the corrosion rate. For systems showing an active to passive transition, the anodic polarization will increase the corrosion rate initially and then cause a drastic decrease in the corrosion rate. Anodic protection is basically the application of anodic polarization to an environment that is undergoing a corrosion or corrosion system.

Author Since: May 31, 2021

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