It’s not the pen that’s mightier than the sword – the lead in the humble pencil contains the strongest substance on Earth.
That finding, just published by Columbia University researchers in the journal Science, could lead to ultralight, paper-thin aircraft parts, super-tough bulletproof vests and even a 23,000-mile elevator to space long dreamed of by scientists.
Pencil lead – commonly known as graphite – is made up of one-atom-thick graphene sheets squeezed together. To learn about graphene’s strength, postdoctoral researcher Changgu Lee had to figure out how to peel graphene sheets from graphite.
His low-tech solution: “We used what is called the Scotch tape method.”
Lee stuck some Scotch tape to a piece of graphite, and peeled it off. Then, he stuck the tape to a tiny piece of silicon about an inch square, and peeled it off again.
That transferred thousands of tiny flakes of graphite to the silicon, which itself had thousands of tiny holes.
At that point, Lee went high-tech. He put the silicon slice under an electron microscope and for days scanned it in hope of finding suitable one-atom thick graphene sheets over suitable holes in the silicon.
Once Lee found some defect-free graphene flakes – each 1/100th the width of a human hair – researchers tested their strength by trying to pierce them with atom-sized metal and diamond probes.
Professor Jeffrey Kysar, a mechanical engineer, explained graphene’s strength this way: Lay a graphene sheet as thick as Saran Wrap over a muffin cup, and try to pierce it with a pencil.
“The force required to push that pencil through the graphene would be equal to the weight of an elephant or a small car,” Kysar said.
“This is probably about 100 times stronger than the best steel you can buy.”
Graphite is easy to find – it’s mined all over the world. But it’ll likely be years before scientists and engineers figure out how to turn graphite into big enough quantities of graphene to make useful materials.
The researchers say they’ve proved that a 23,000-mile-long graphene ribbon could be used to build an elevator extending into space to a satellite in orbit.
Using the elevator would likely be cheaper than rockets. NASA is offering $4 million in prizes to scientists who come up with practical ideas for the project.