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There has been a lot of news about Graphene since its discovery in 2004. And as we are all told it is a revolutionary material which is very strong, conductive and transparent; even in some cases it has revolutionized especial laws of physics (see this page).

But what is it about the structure of Graphene which makes it so strong?

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If I understood what strong means, then graphene has high strength because of the 2-D layer structure of carbon atoms. The strength can also be attributed to its $sp^{2}$ hybridisation.

Any crystalline material will have a lattice structure. When we mean strength of a material its usually the ability to break apart the bond between two lattice atoms. But the observed strength is usually 2 or 3 orders lower than theoretically predicted strength due to flaws (voids, dislocations etc). But when graphene has a near flawless 2-D structure we can reach its theoretical strength. Though its is a very expensive process to actually realize "flawless". Even with flaws its strength is really high compared to steel.

So its essentially the 2-D one atom layer structure that can be responsible for its high strength.

One important thing is though graphene has high strength and elasticity (ability to get stretched) it is relatively brittle (fracture toughness ~4 MPa$\sqrt{m}$).

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Imagine carbon as some sort of wool. Graphite would be just some wool without any pressure on it. Diamond would be a wool ball with a structure and a shape. Graphene would be a textile knitted with the strings of wool.

Wool is soft, a wool ball is more durable to pressure and a textile could carry some weight.

Now imagine graphene as a canvas fabric knitted with the finest strings the wool has and all strings are equally long. The pressure would be splitted equally on each of this strings and you wouldn't have a weak point. You would carry an elephant with it.

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