Materials Advent Calendar 1 and 2: graphite and graphene

I’m late, but an interesting thing I thought I would attempt this year is to do a materials science Advent calendar (or Christmas countdown, we’ll see if I I want to do 23 or 25) and write brief blurbs about neat materials. For belated start, I figured I would start with what I work with: graphite! Yes, your pencil lead is actually a super interesting material. Graphite is an allotrope of carbon, and actually the more stable one in everyday life – your diamonds will eventually decay if they stay on Earth’s surface, but that reaction takes at least thousand if not millions of years because of how slow the atoms can move in diamond.

A microscope image of graphite, showing it’s flake structure. 

Graphite makes for a great writing material because of its layered structure. It’s really easy to slide layers past each other because the carbon atoms don’t interact between layers, so you can easily leave flakes of graphite on paper with just a light pencil press. It also turns out to make graphite a good solid lubricant – you can buy graphite powder and it can be stable for a wide range of conditions. We would use graphite powder to help lubricate the nail axles in Pinewood Derby. Weirdly though, it turns out that even though the layers don’t interact, graphite seems to require something in air to slide easily because it doesn’t lubricate in vacuum (which means you can’t use it as a lubricant for parts exposed to space). 

Three layers of atoms in graphite – the orange layer in between is stacked slightly out of sync with the blue layers

And to try to catch up and get a second material, let me talk about graphene. If you can isolate a single layer of atoms from graphite, you have graphene. (And it turns out you can do this with Scotch tape if you’re patient enough.) And graphene turns out to be the strongest and most conductive material humanity has discovered. If you want to be more technical (and some more rigorous solid-state people do), lots of thing people call “graphene” are actually a few layers, but it turns out even up to 10 layers it still behaves differently than your pencil lead. But we’re good at making few-layer graphene, and it could be an additive we put in almost anything. Seriously. People have proposed putting it in things from water filters to flexible electronics (bendable smartphones anyone?). We’re currently still figuring out how to best scale that up to compete with other established materials though. But it’s exciting to think where this could go in another decade or two. 

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