Lighter than air (but still solid)

A team of scientists from Zhejiang have produced a new substance that is just twice as heavy as hydrogen. The material, known as graphene aerogel, also has a number of weighty commercially viable uses

  • By Rita Lobo | Thursday, April 25th, 2013

Graphene aerogel is seven times lighter than air, can balance on a blade of grass

Though carbon aerogels have been around for the past quarter of a century, their properties are still being discovered. Perhaps more notably a team of scientists from Zhejiang University have created the lightest and most interesting version so far. Graphene aerogel is so light that it can be placed upon a blade of grass without bending it. It is rather remarkable; a cubic centimetre of the substance has a mass of 0.16 milligrams. It is also record breaking; graphene aerogel is 12 percent lighter than the substance previously thought to be the lightest.

Aerogels are ultra-light materials derived from regular gels, but where the liquid component has been replaced with gas. As well as being extraordinarily light they also have extremely low levels of thermal conductivity; aerogels are also incredibly durable. These properties alone mean it has many useful and commercially viable applications; aerogels are used as thickening agents and are the most efficient chemical absorber which makes it useful at the sites of oil spills.

Aerogels are usually carbon or silica based. Graphene aerogel is no different. It is unique however because of its sheer weightlessness. Such small density might be hard to grasp; a cubic centimetre of aerographene weighs only twice as much as hydrogen and has only one seventh of the density of regular earth air.

Graphene, from which the aerogel is made from, is a sheet of a single layer or carbon molecules. Researchers in Zhejiang found that through a simple freeze-drying process they were able to stack graphene layers in three directions; the only limit on the size is the dimensions of the receptacle the aerogel is made in. Researchers believe that there would be no problem creating aerogel blocks in any size.

As well as lighter, graphene aerogel is also more easily produced than other, more common, aerogels. Previously, aerogels had been produced using the sol-gel method, where a gel is dehydrated until only the aerogel is left. But researchers found that by using solutions of carbon nanotubes achieved the same results. Researchers at zhejiang essentially created a solution of graphene and carbon nanotubes, and after pouring into a container, freeze-dried it. The nanotubes have a cylindrical nanostructure which holds up the layers of graphene together, forming the aerogel. The nanotubes themselves are carbon molecules arranged in hexagons forming a tube.

Graphene aerogel has been found to have superb elasticity and can recover its shape entirely after being compressed by more than 90 percent. It can also absorb over 900 times its own weight in chemicals, at a rate of 68.8 grams per second. Lead researcher Gao Chao thinks that these properties will make graphene aerogel an efficient chemical absorber, capable of mopping up oil from spills, returning the oil when squeezed, then thrown back into the spill to absorb more oil; much like a sponge in a bucket of water.

The researchers are also hopeful that graphene aerogel will be as conducive as aerographite, its predecessor. If that proves to be the case it might just prove to be a useful component for new, lighter batteries with higher energy-densities. It is also a powerful insulator; picture have shown a thing slab of aerogel shielding crayons from the blue-flame of a Bunsen burner; which would otherwise have melted the sticks in seconds. The commercial potential for this type of aerogel is very promising.