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Corrosion Theory

Last updated: June 15, 2018

What Does Corrosion Theory Mean?

Corrosion refers to the gradual destruction of objects, typically metals, caused by environment and chemical reaction.

It accurately refers to electrochemical metal oxidation with oxygen as oxidant. One of the best examples of this phenomenon is iron oxide formation, or rusting. Corrosion may also take place in non-metal materials such as polymers and ceramics.


Corrosionpedia Explains Corrosion Theory

Corrosion theory involves four essential components:

  1. Cathode
  2. Anode
  3. Electrical connection that exists between the cathode and anode for the electron current flow
  4. Electrolyte or a conducting environment to facilitate ionic movement

Specifically, corrosion can be used to describe any process that involves the degradation or deterioration of metal elements. The best-known case is rust formation involving steel. The process is typically electrochemical, having the characteristics of a battery. When atoms of metals are exposed to an environment containing water, the metal can produce electrons. This action can be confined locally to create a crack or pit. This could extend further to the surrounding area, leading to general wastage. Confined corrosion that results in pitting is capable of producing fatigue, and corrosive agents such as seawater could result in immense growth of the crack. Corrosion also arises in a higher rate in areas involving microstructural changes, mainly due to welding.

Corrosion theory entails that the process involves an anodic reaction. This type of reaction is produced through dissolving metal, which generates electrons. This is further consumed by another process called cathodic reaction. These two processes balance the charges produced. The sites generating these processes may be found close or far apart, depending on the situation.

The electrons generated by the process need to be consumed through cathodic reaction. This should be close to the process of corrosion itself. Hydrogen ions and electrons react to build atomic hydrogen, and later, hydrogen gas. When hydrogen forms, further corrosion can be prevented through a thin gas film at the metal surface. This film serves as a polarizer, which is functional in decreasing metal-to-water contact, reducing corrosion. Thus, anything that breaks the barrier film tends to hasten the speed of corrosion.


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