Hard as a Rock

What’s the hardest thing you can think of? Rocks, wood and metals are seem pretty hard. They take a lot of force to break, if you can even break them at all! You might be surprised to learn that one of the hardest materials is diamond. Another very hard material is this month’s molecule, boron carbide.

Boron Carbide

The structure of boron carbide is quite complicated. However, it is formed from a combination of boron and carbon atoms into a large crystal structure and has a dark grey or black appearance. The crystal structure looks very complicated!

Boron carbide crystal structure. By Materialscientist – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=11276183

We also saw crystal structures when we looked at aluminium oxide.

Aluminium Oxide Title Image
Aluminium Oxide

Boron carbide has some very good physical properties. Firstly, it is very indeed, with only a few other substances being harder. It also has a very high melting point and boiling point. You have to heat it to over 2700°C to melt it, and up to 3500°C to boil it!

An erupting volcano
An erupting volcano probably still wouldn’t be hot enough to melt boron carbide!

A Hard History

Boron carbide was discovered in the 1800s, but its chemical structure remained unknown until the 1930s. However, even today there are still arguments about the exact chemical structure of this material. In 1899, Henri Moissan was able to make it by heating and reacting boron trioxide (B2O3) with carbon at very high temperatures producing it along with lots of carbon monoxide! You may have heard of carbon dioxide but carbon monoxide is the evil twin – while carbon dioxide causes global climate change carbon monoxide can straight up kill you!

A chemical structure for carbon dioxide
Carbon dioxide – a carbon atom with two oxygen atoms double bonded to it. We hear a lot about CO2 because of its role in climate change.

Hardly Useful or Useful Hardly

Unsurprisingly, many of the uses of boron carbide take advantage of its hardness like armor-plating for vehicles and clothes, such as bullet-proof-vests. Its extreme hardness also makes it ideal for cutting tools and abrasives. Even padlocks are made from this material!

a boron carbide bullet proof vest

A Nuclear Absorbent

Apart from its hardness, there is one other very important use. It’s very good and absorbing neutrons. Neutrons are found within the nucleus of an atom and are very similar to protons, but contain no electrical charge. In other words, they are neutral hence the name neutron.

Neutrons are important in nuclear reactors and weapons, however sometimes we need a material that can absorb neutrons to help control nuclear reactions. Such a material can also provide protection from neutrons. Boron carbide is very good at absorbing neutrons, making it an ideal material for nuclear processes.

A Hard Material

So, if you’re looking for a very hard material that can also shield you from neutrons, then boron carbide is your best choice!  



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