World’s Strongest Material
By Phil Schewe
July 28, 2008
Graphene, a two-dimensional sheet made of pure carbon, is 200 times stronger than steel.
A sheet of carbon only a single atom thick – essentially existing in only two dimensions – has claimed the title of the world's strongest material by resisting the force of a diamond-tipped needle with about 200 times the strength of steel. The unprecedentedly strong material, known as graphene, was first isolated in 2004, but its strength was only discovered in a recent experiment at Columbia University in New York.
Researchers stretched an ultrapure, ultrathin sliver of graphene across a hole drilled in a sheet of silicon. Then they lowered a diamond-tipped needle (part of an atomic force microscope) that is itself only nanometers across at its point, down into the graphene. The microscope measured the reaction force as the scientists pushed the probe tip down until the tip pierced the layer of graphene.
| Reaction force at the atomic level
The force required was significantly higher than anything measured before. Typically materials with low density, such as carbon-containing organic materials like wood and polymers, have low densities and little strength. Metals have higher densities and higher strength. Composite materials, which are used in everything from auto bodies to bulletproof vests, combine high strength with less density and weight.
On the chart the researchers used to categorize the graphene, the material showed itself to have record-high strength with only middle-level density. The promise of graphene is that it could lead to new superlight, yet super strong composite materials. The results were reported last week in Science magazine.
More than just the discovery of a new strong material, the work on graphene, and carbon in general, exemplifies the symbiotic relation between science and engineering that has filled the world with everything from airplanes to microscopes, from atom bombs to blenders. Generally scientists probe the inner workings of nature, increasingly at a microscopic level, while engineers snatch up the new basic knowledge and convert it into the sophisticated innovative products that characterize our nanotech society.
Carbon is, of course, one of the most important elements for both living and non-living things. In its myriad chemical combinations it provides the inner scaffolding for our body and for all the proteins and chemical processes that make life possible. Carbon in pure form is rarer but still noticeable. Bulk three-dimensional carbon can appear in the form of graphite, which consists of loosely bound sheets of carbon atoms (making graphite a good pencil-writing substance and a good lubricant), and diamond, the more elaborately bonded web of carbon with unequaled hardness.
In the last few decades scientists have discovered carbon with other dimensionalities. For example, buckyballs are molecules in the shape of a soccer ball and contain 60 carbon atoms. This nearly-perfectly-round molecule, whose official name, buckminsterfullerene, is practically a zero-dimensional form of carbon; that is, it resembles a point.
Then one-dimensional carbon tubes were discovered. These tubes, only nanometers wide (billionths of a meter) but microns (millionths of a meter) long, have interesting electrical, optical, heat, and mechanical properties. Engineers and scientists are trying to turn carbon nanotubes into useful elements in micro-circuitry.
Only a few years ago single-atom-thick sheets of carbon were discovered. Again, scientists and engineers are working together to explore and explit the unique properties of graphene. Carbon nanotubes are really just rolled up version of graphene.
Columbia University mechanical engineer James Hone, who was one of several scientists who conducted the graphene experiment, said that his new measurements will serve to reinforce the theories formulated by physicists in their fields of work. The result of this ongoing synergy between scientists and engineers might be even stronger materials yet to come, he noted.
|A graph of the strengths of many materials along with their densities
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