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What do Mechanical & Methods Engineers need to know about atomic structures?

Updated: Jul 6, 2023

From a metallurgical perspective, the atomic structure subject is a requirement which helps you to understand the fundamentals of how they bond to each other forming alloys, compounds and pure elements and their chemical reactions to each other.

There are 3 parts to form an atom: protons, neutrons and electrons and each of these has specific qualities. The protons carry a positive electrical charge; neutrons are electrically neutral, and electrons carry a negative charge which is equal in magnitude to that of the proton.

As you can see in this diagram, protons and neutrons adhere to each other to form the atomic nucleus whilst the electrons orbit around the nucleus.

Understanding the Behaviour of Metals

It is a critical factor to differentiate between the elements as the number of neutrons alongside the protons in the nucleus distinguishes one isotope from another.

So, understanding the behaviour of metals and their structures has a direct relationship to the atoms and atomic structures which are formed on solidification, the quality of material in terms of physical, mechanical and metallurgical properties are all vital in the final product application. Mechanical and methods engineers don't often consider this as 'important' as they 'view' or use the macrostructure as a method of examining a specimen surface, or the effects of large crystals, or grain structures after solidification.

The mechanical engineers will make sure before the product is used by their customers, it meets specifications and standards, and the methods engineers may be interested in the solidification range, which allows the casting to be filled and therefore formed so in both cases the issue of non-conformances or internal or external defects in the final product, meet a range of requirements, being the correct quality for its usage.


Pure metal solidifies at one fixed temperature. If an alloy is used the solidification range is directly related to the alloy additions and the range of properties which originate from the atom's structure. However, to obtain recordings of temperature drop as the metal solidifies is introduced at suitable time intervals to provide a "cooling curve or series of cooling curves" is important to analyse its effect at each stage. The metal is cooled very slowly under equilibrium conditions. Below is a 10 mins training video explaining the equilibrium effect.

As the metal cools, the atoms 'arrange' themselves to 'sites' of low energy and become 'ordered and structured'; these unit cells grow into 'clusters of unit cells' forming a solid crystal or grain. These unit cells are most commonly known as Face Centred Cubic (FCC) - Aluminium; Body Centred Cubic (BCC) - Iron; Close Packed Hexagonal (CPH) - Zinc.

As these grow they form 3 dimensional arrangements called - lattices, which then as solidification continues become grains or crystals, which have a range of shapes, sizes and complexity.

So, the chemical composition provides the 'building' blocks for physical, corrosion, mechanical and metallurgical properties affecting how the metal or alloy is used.

Web-Training Courses

It is important for all engineers to understand the Atomic Structure & Unit Cells. This is definitely an area to investigate more about the transformations of macrostructures on solidification using the information on ferrous and non-ferrous metals and alloys. Take a look at our web training courses Metallurgy-Mini-WebTraining-Courses

Contact us if you are interested to learn more about atomic structures email:

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