What is Corrosion

Corrosion is the deterioration of materials by chemical interaction with their environment. The term corrosion is sometimes also applied to the degradation of plastics, concrete and wood, but generally refers to metals. The most widely used metal is iron (usually as steel) and the following discussion is mainly related to its corrosion.

 

It results from oxidation of metal.

• First the metal releases electrons to form positive ions.
• Atmospheric water, condenses over the metallic surface dissolves oxygen.
• Oxygen + Water results in formation of OH ion. 
• OH (-) and Fe(+) combine to for iron hydroxide.
• Iron hydroxide reacts with oxygen to give iron oxide (rust)

We infer from the above steps that 

• Ions are involved and need a medium to move in (usually water)
• Oxygen is involved and needs to be supplied
• The metal has to be willing to give up electrons to start the process
• A new material is formed and this may react again or could be protective of the original metal
• A series of simple steps are involved and a driving force is needed to achieve them

To avoid corrosion read How to avoid corrosion

 

Types of Corrosion

1. Uniform Corrosion
2. Localized Corrosion 
• Galvanic Corrosion 
• Pitting Corrosion
• Selective Attack
• Stray Current Corrosion
• Microbial Corrosion
• Intergranular corrosion
• Concentration Cell Corrosion
• Thermogalvanic Corrosion
• Corrosion caused by combined action
• Corrosion Fatigue
• Fretting Corrosion
• Stress Corrosion Cracking
• Hydrogen Attack

 

 



How to avoid corrosion

In order to avoid corrosion

1. Slow down or stop the movement of electrons

• Coat the surface with a non-conducting medium such as paint, lacquer or oil
• Reduce the conductivity of the solution in contact with the metal an extreme case being to keep it dry. Wash away conductive pollutants regularly.
• Apply a current to the material (see cathodic protection).

2. Slow down or stop oxygen from reaching the surface. Difficult to do completely but coatings can help.
3.Prevent the metal from giving up electrons by using a more corrosion resistant metal higher in the electrochemical series. Use a sacrificial coating which gives up its electrons more easily than the metal being protected. Apply cathodic protection. Use inhibitors.
4.Select a metal that forms an oxide that is protective and stops the reaction.

Read more about Corrosion

What is Mechanical Engineering?

Mechanical engineering is a broad discipline that deals with the improvement and modification of mechanical components (machines) and systems. A machine is an assembly of parts that work together to perform action(s).

This discipline of engineering uses the principles of physics and maths to apply them to the field of machines/ mechanics. Mechanical engineering covers the design and implementation of these systems. Mechanical engineering is also involved with the dynamic motion of machines, fluids, heat and structures among others.
A common misconception about mechanical engineers is that..........

AEC1391 - Electrical Engineering Graduates (Fresh) Required

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ACE Consultants is a management consulting firm, offering services in areas of HRM, Training & Business strategy / operations. Currently we are looking Mechanical Engineer for our Dairy Food sector client.
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Years of Experience
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