Graphene super strong but not graphite?

[TriKri]

How does it come that graphene is so strong, but not graphite? Graphite is basically just many graphene sheets stacked on top of each other so it should super duper strong.

 

[e.bar.goum]

Ah, but you should consider how they are stacked on top of each other. Graphite "slides" apart in different sheets.

 

[DaveC426913]

The reason graphite is used as a dry lubricant is because the layers slip past each other easily.

Yes, they are strong in one plane, but very weak across planes.

 

[TriKri]

Okay, so they slide on top of each other, but that is only when the graphite crystal is exposed to shearing, right, so what about when the crystal is exposed to strain along the graphene planes? Then the force the graphite would be able to take would still be the sum of the forces the graphene layers can take, which would still be super much? Or am I thinking wrong here?

 

[chrisbaird]

By the way, the lubrication properties of graphite is due to the presence of fluids between the layers, such as air and water, which are adsorbed naturally, from the environment, and not solely do to the weak inter-layer bounds. In vacuum, graphite becomes a poor lubricant. In theory, if you pulled a pure graphite crystal along the direction of its planes, it would be very strong. But you would have to have a very pure crystal stack, all lined up, and be pulling at just the right direction, and pulling all layers equally. Typical graphite, like in a pencil, or more like a spaghetti-ball of layers/fragments.