Graphite

[Nucleara]

I'm new here. Hello

I thought I got the idea of Graphite structure, but when I'm reading it again now I don't understand why the electron from each C can freely move(vertically?) between the two layers, forming the linked sheets of graphenes? And why is there the Van der waals bonding (vertically?)between the layers? Is it caused by the freely-moving electron?

http://batteryblog.ca/wp-content/upl...6/graphite.gif

Thank you so much

[Enthalpy]

Hi Nucleara, welcome here!

 

I hoped someone would provide a better answer, but here are already my 2 cents...

 

A graphite block consists of many crystals with random orientation, making it more or less isotropic. Only smaller objects like a fibre or a single crystal show a clear anisotropy. Then, graphite conducts electricity and heat far better along the planes, but does conduct across the sheets as well.

 

Van der Waals forces appear anywhere. Being what's left when chemical bonds are fulfilled, they have far fewer constraints. They are able to make liquid of absolutely any gas for instance, including noble gasses that wouldn't bind chemically. So, among graphite sheets, sure - that's easier than between dinitrogen molecules or neon atoms for instance.

 

What I've read up to now is indeed that pi electrons from graphite sheets make van der Waals forces among the sheets, and this shall explain that graphite sheets are strong (chemical bonds) but hold loosely together (van de Waals) and cleave easily. Though, this fact has been overstretched to too many explanations including the lubricating properties of graphite - pity, it doesn't lubricate in vacuum, wrong explanation.

 

An other funny observation is that benzene crystallizes with molecule rims pointing towards neighbours' faces, and not as stacks, so that sheet stacking in graphite is not the arrangement with best van der Waals' forces - it's just the only available one with graphite.

 

Transverse conductivity, from sheet to sheet: that's not very difficult anyway. Electrons can pass by tunnel effect. The distance between the sheets is bigger than would be comfortable, but still within reach. One atomic distance makes tunneling easy (this defines an atomic distance), two would only be difficult. So it doesn't formally need a chemical bond nor even a definite intermolecular bond: proximity would suffice.

[Sensei]

Transverse conductivity, from sheet to sheet: that's not very difficult anyway. Electrons can pass by tunnel effect. The distance between the sheets is bigger than would be comfortable, but still within reach. One atomic distance makes tunneling easy (this defines an atomic distance), two would only be difficult. So it doesn't formally need a chemical bond nor even a definite intermolecular bond: proximity would suffice.

 

This theory should be easy to check..

Place piece of graphite parallel and then perpendicular to applied current.

If you're right, results should differ.

 

ps. What I coincidence. I was just two hours ago checking what magnetic field lines will be created by piece of graphite through which we are passing 2 A current.

[Enthalpy]

Graphite's anisotropic conductivity, both electric and thermal, is daily observation and common knowledge, not theory. It doesn't really need to be checked once more - but can be.