Aggregated diamond nanotubes are the least compressible material known, with a mass modulus of 491 GPa, three times that of iron. They get their strength from the sp2 bond, making them the least compressible material, except for exotic matter inside super-dense stars.
The least compressible material known, with a mass modulus of 491 gigapascals (GPa) consists of aggregated diamond nanotubes. They’re what you get when you compress buckytubes, an allotrope of carbon, to 20 GPa, at a temperature of 2,500 Kelvin, using a 5,000-ton anvil press designed specifically for the purpose. The end result is a spaghetti of interconnected diamond nanotubes, with diameters ranging from 5 to 20 nanometers and lengths of about one micrometer each.
A bulk modulus of these nanotubes, 491 GPa, is about three times that of iron, which is 160 GPa. Conventional diamond has a mass modulus of 442 GPa. A mass modulus of 491 GPa means that a pressure increase of 49.1 GPa would be required to compress the material by a factor of 10%, a pressure increase of 98.2 GPa would be required to increase it by 20%, and so on. For comparison, the pressure at sea level (1 atmosphere) is about 100 kPa (kilopascals), and every 32.8 feet (10 meters) of descent into the ocean increases the pressure by another atmosphere. Then the lowest point in the ocean, about 6.2 km deep, experiences a pressure increase of 10 MPa at the surface, which would be enough to compress a solid sphere of aggregated diamond nanotubes by a factor of 100%.
They get their strength from the famous sp2bond, the strongest bond in all of chemistry. This is a carbon-carbon bond, also found in graphite (along 2D planes one atom thick), diamond (3D), and carbon nanotube fiber (which has been proposed as a building material for space elevators). . The sp2 bond isn’t just the strongest known chemical bond, it’s the strongest possible chemical bond, so these nanorods may not only be the least compressible material scientists currently know of, but the least compressible material, period. The one exception might be the exotic matter inside super-dense stars, sometimes called neutronium.
Surprisingly, these nanorods are even denser than pure diamond by a factor of 0.3%. Their appearance is dark with a slight rainbow-like scattering of light, resembling an oil slick on asphalt. Other substances less compressible than diamond, but more so than aggregated diamond nanotubes, include type IIa diamond and ultrahard fullerite.
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