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25 Feb 2020, 12:07

Disruptive Technology

Graphene. A material with so many near-magical properties, it sounds as if it could be a real incarnation of unobtainium. Ever since it was isolated in 2004 by Andre Geim and Kostya Novoselov using sticky tape (yes, really) at The University of Manchester, it has set scientists' minds racing with experiments to try on it and engineers with what you could do with it.

Graphite is made up of weakly bonded (one atom thick) layers of graphene that can easily slide over each other. However, within a layer, the strength of the carbon bonds makes graphene the strongest material ever discovered. It has a tensile strength of 130 gigapascals, compared to 400 megapascals for A36 structural steel. That is 325 times stronger yet, being only 1 atom thick, it weighs only 0.77 milligrams per square metre.

The tight, hexagonal atomic bonds make graphene impermeable to pretty much all gasses and liquids. Except for water. That it allows through, making graphene an exceptional filtration membrane. Researchers at the University of Manchester demonstrated this in the most important way possible for students: distilling water out of vodka to make even stronger sprits. For the rest of humanity, Lockheed Martin recently developed a graphene filter called “Perforene,” which could revolutionise the desalination process.

Perhaps of most interest to us is the incredible electrical properties of this material. I can remember discovering how well graphite conducts electricity, when I was around 8 years old, by putting a pencil lead across the terminals of an accumulator battery. Result: near-instant bright glow until the graphite burned up. Obviously, I had to keep repeating that experiment until my parents had no pencil refills left. For science.

Graphene is what is known as a zero-overlap semi-metal, which means that it has both 'holes' and electrons available as charge carriers. These electrons (and holes) are also extremely mobile at room temperature. What this means in practical terms is that graphene has an extremely high electrical current density (a million times that of copper), intrinsic mobility 100 times that of silicon and it has a lower resistivity than any other known material at room temperature, including silver.

Also useful in electronics: graphene is an incredible thermal conductor at over 5,000 W/m/K, making it better than carbon nanotubes, graphite, and diamond. Graphene is an isotropic conductor, meaning it conducts heat in all directions.

While all this makes graphene a super-fast and efficient conductor, it can't be readily used to make transistors as carbon does not have a bandgap; though work is afoot to introduce bandgap properties.

What it can be used for is better batteries.

Infuse a lithium-ion battery with graphene and you get something that is faster to charge, takes more charge cycles and runs at lower temperatures. California based company Real Graphene is doing just that. They have recently started manufacturing batteries that charge 3.5 times faster and are good for 1500 charge cycles, compared to the more usual 300 to 500 cycles for most phone batteries. They also generate much less heat.

At present, this is in two different capacity battery packs, but if these are successful, it won’t be long before we see this tech in phone batteries.

Silicon was discovered in 1824 but it took until 1948 before it even began to be used a serious technology. How far will graphene go in 124 years? Look how far it has come already.

One to watch in my book. And yes, I have bought one.

Mark completed his Electronic Engineering degree in 1991 and went on to work in real-time digital signal processing applications engineering, later moving into technical marketing.

25 Feb 2020, 12:07