Difference Between Corrosion and Oxidation

Main Difference – Corrosion vs Oxidation

Corrosion and oxidation are two different terms express the same idea. Oxidation reaction is one of the two simultaneous reactions of redox reactions. Corrosion is a type of oxidation. Corrosion happens when the metal atoms on a metal surface get oxidized in the presence of oxygen and water. The corrosion in iron or steel can be recognized as rusting. There are methods to prevent metals from rusting. The main difference between corrosion and oxidation is that corrosion happens chiefly on metal surfaces whereas oxidation can happen anywhere.

Key Areas Covered

1. What is Corrosion
      – Definition, Explanation of Process, Prevention
2. What is Oxidation
      – Definition, Explanation
3. What is the Relationship Between Corrosion and Oxidation
4. What is the Difference Between Corrosion and Oxidation
      – Comparison of Key Differences

Key Terms: Corrosion, Electroplating, Galvanization, Humidity, Metal, Metal Alloy, Metallic Oxidation, Oxidation, Redox Reaction, Rusting

What is Corrosion

Corrosion is the deterioration of a material due to different reactions that take place on its surface when the material is exposed to the environment. This happens due to the chemical reactions that happen between the surface of the material and the components in air.

Corrosion can occur in both metal and nonmetal surfaces. The corrosion of a material affects the structure of the material surface. The most common example for corrosion is rusting. Here, the color and the quality of the steel is changed. This is caused by the chemical reaction between the metal surface and the moisture and oxygen in air. Therefore, different varieties of steel have been made in order to protect the metal from corrosion by changing the chemical composition of the metal alloy.

Corrosion can also take place in nonmetal surfaces such as table tops and skin. When some corrosive chemicals are dropped on these surfaces, deterioration of that surface may occur. Such chemicals include strong acids and strong bases.

The corrosion on metals is also known as metallic oxidation. This is because the metal atoms on the surface get oxidized by oxygen in the air in the presence of water. For example, Fe⁺² in steel can be oxidized to Fe⁺³ during corrosion of iron. The rate of corrosion depends on several factors such as the humidity of the air, the surface area of metal that is exposed to air, etc.

Figure 1: Corrosion of Iron

There are several methods for the prevention of metals from corrosion. Some of these strategies are given below.

• Environmental modifications
• Galvanization – A zinc coating can prevent iron from rusting by acting as a sacrificial anode.
• Corrosion inhibitors – These are chemicals that can avoid corrosion by interrupting the oxidation reaction on the metal surface.
• Paints – A coating of paints can avoid the initiation of corrosion.
• Electroplating – A thin layer of a metal (Ex: Nickel, Chromium) is deposited on steel surface.

Corrosion affects the microstructure of metal by changing the chemical composition; it affects mechanical properties and physical appearance of metal.

What is Oxidation

Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Since atoms are composed of an equal number of protons and electrons when they are neutral, loss of electrons gives the atoms a positive charge. The degree of oxidation is given as oxidation state. When an atom undergoes oxidation, the oxidation state of that atom increases positively. The opposite of oxidation is reduction.

There is always a reduction reaction happening parallel to the oxidation. In other words, an oxidation and a reduction reaction occur simultaneously. These two reactions are called redox reactions. One reaction alone is called a half reaction. The oxidation reaction releases electrons which are then consumed by the reduction reaction.

Figure 2: Oxidation of Magnesium

In the past, the oxidation referred to the addition of molecular oxygen to a compound. But this definition couldn’t explain the oxidation reactions that take place in the absence of molecular oxygen. Compounds that can make other compounds to get oxidized are known as oxidizing agents. The species that can get oxidized is called a reducing agent.

Relationship Between Corrosion and Oxidation

• Oxidation is the loss of electrons during a reaction by a molecule, atom or ion.
• Corrosion happens when the metal atoms on the surface undergo oxidation.

Difference Between Corrosion and Oxidation

Definition

Corrosion: Corrosion is the deterioration of a material due to different reactions taking place on its surface when the material is exposed to the environment.

Oxidation: Oxidation is the loss of electrons during a reaction by a molecule, atom or ion.

Benefits

Corrosion: Corrosion is often not a beneficial process.

Oxidation: Oxidation reactions are very helpful in different laboratory practices.

Process

Corrosion: Corrosion is an irreversible process.

Oxidation: Oxidation is a half reaction of redox reactions.

Oxygen

Corrosion: Corrosion happens in the presence of oxygen.

Oxidation: Oxidation can happen in absence or presence of oxygen.

Conclusion

Corrosion is the deterioration of metal or nonmetal surfaces. We can recognize rusting of metal surfaces as corrosion. Oxidation reactions always occur with a reduction reaction simultaneously. Oxidation is the loss of electrons from atoms, molecules or ions.  The main difference between corrosion and oxidation is that corrosion happens chiefly on metal surfaces whereas oxidation can happen anywhere.

References:

1.  Bell, Terence. “How and Why Do Metals Corrode?” The Balance, Available here.
2. Bell, Terence. “Learn About the Different Methods of Corrosion Prevention for Metals.” The Balance, Available here.
3. Helmenstine, Anne Marie. “Understand What Oxidation Means in Chemistry.” ThoughtCo, Available here.

Image Courtesy:

1. “Nandu River Iron Bridge corrosion – 03” By Anna Frodesiak – Own work (CC0) via Commons Wikimedia