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Thanks for the memories  July 26, 2012

Graphene aerogel is the new world's lightest substance

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Michelle Starr is the tiger force at the core of all things. She also writes about cool stuff and apps as CNET Australia's Crave editor. But mostly the tiger force thing.

Graphene aerogel resting on a delicate plant.
(Credit: Zhejiang University)

Aerographite has been dethroned as the world's lightest substance, replaced by a new form of graphene aerogel.

As research into aerogel continues, scientists are discovering ever-lighter variations. First, there was carbon nanotube aerogel, with a density of 4 milligrams per cubic centimetre. Then along came silica aerogel, which weighed in at 1 milligram per cubic centimetre and garnered 15 entries in Guinness World Records. It was ousted by metallic microlattices, at 0.9 milligrams, and then aerographite, at 0.18 milligrams.

Now, a new graphene aerogel created by scientists led by professor Gao Chao at the Zhejiang University has swept past, weighing in at just 0.16 milligrams per cubic centimetre.

For reference, the density of air is 1.2 milligrams per cubic centimetre — so the new material is 7.5 times lighter than air. It's twice as heavy as hydrogen — the lightest element there is — but beats out helium, which has a density of 0.1786 milligrams per cubic centimetre.

Gao Chao's team had already been building macroscopic graphene materials in one and two dimensions; to create the new aerogel, the researchers branched out into the third dimension, using a new method of freeze drying the solutions of carbon nanotubes and graphene to create malleable carbon sponges.

PhD candidate Sun Haiyan explained, "It's somewhat like large space structures such as big stadiums, with steel bars as supports and high strength film as walls to achieve both lightness and strength. Here, carbon nanotubes are supports and graphene is the wall."

The new material is amazingly absorptive, able to suck in up to 900 times its own weight in oil at a rate of 68.8 grams per second — only oil, not water, which means it has massive potential as a cleaning material when it comes to events such as oil spills.

Then, both the graphene aerogel and the oil could be recycled.

The full results of the project can be found published in Nature, titled "Solid carbon, springy and light".


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PeterA1 posted a comment   
United States

If it were lighter than air it would be floating, which it clearly does not.

Because carbon is denser than air, any material made from carbon must necessarily be denser than air.

The only way a material denser than air could make something less dense than air is if it were combined with another item whose density was less than air, thereby bringing the average density below that of air. An example of this is a rubber balloon filled with helium -- the rubber is not less dense than air but the composite object is.

A conceivable way that a carbon based material could be made lighter than air would be if carbon nanotubes were created in in vacuum and sealed (this assumes they are airtight which I do not know).


PeterA1 posted a reply   
United States

It looks like graphene is in fact airtight. See


EanM posted a reply   

I was reading another discussion about this, and the explanation was basically thus: Though the material used is more dense than air, the pockets and gaps cause the overall density of the object itself to be lower than that of air.

If all the gaps were sealed and empty (vacuum) then the result would indeed float, since the carbon lattice is much less dense than the air around it. The effect would be like a boat, which is made of a steel lattice, but is filled with air and thus is effectively lighter than the water it displaces.

What we have instead is an unsealed lattice that allows the surrounding medium to flow through it... like a boat with no siding. The boat's average density is less than water if you measure volume/weight and only look at the boat itself, but once you allow the water to fill it up the result is a denser volume and it sinks.

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