Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Cathodic Reaction

Last updated: January 9, 2018

What Does Cathodic Reaction Mean?

This is a type pf corrosion where hydrogen ions are reduced to their atoms. This process produces hydrogen gas when these ions react with electrons in the cathode. The reduction of hydrogen ions to hydrogen gas is characterized by many changes that include the reduction of the acidic nature of the electrolyte.

The acidic hydrogen ions are reduced to alkaline hydroxyl ions, a situation that disturbs the balance of the two ions. As a result, the electrolyte on the cathodic side becomes more alkaline compared to the anode side. A pH indicator can be used to demonstrate the existence of cathodic reactions in corroding metals.

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Corrosionpedia Explains Cathodic Reaction

There are several things that should be noted during the occurrence of cathodic reactions. These include the reduction of the oxidation number, a condition known as reduction, and the gain of electrons at the cathode.

Cathodic reactions can be represented using reaction equations like the following:

In hydrogen revolution: 2H+ (aq) + 2e- == H2 (g)

This is a half-cell reaction at the cathode, but the full equation contains the anodic reaction.

Other reactions are:

Acidic solutions: O2 + 4H+ 4e- == 2H2O

Neutral/basic solutions: O2 + 2H2O + 4e- == 4OH-

Metal ion reduction: Fe3+ + e- == Fe2+

Metal deposition: Cu2+ + 2e- == Cu(s)

Cathodic reactions can be prevented using cathodic protection methods. There are two major methods that can be used to prevent cathodic reactions in corrosion:

? Coupling of structures like iron with a more active metal such as magnesium or zinc. The active metal becomes the sacrificial anode and the less active becomes the cathode since electrons flow from the active metal to the less active metal. Zinc becomes the anode while the structure of iron becomes the cathode. This is a galvanic cell with zinc as the anode and iron the cathode.

? Direct current is impressed between the structure and the inert anode. Since electrons flow from the anode to the cathode, the structure is protected from destruction because there are no electrons lost in the process. The low DC voltage is then impressed in the area between the cathode and the anode, with the anode buried. The simplest method is the use of a sacrificial anode.


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