Carbon is the fourth-most-abundant element in the universe and comes in a wide variety of forms, called allotropes, including graphite, graphene, and the hardest natural material known to man, diamonds. Now scientists have discovered a new form of carbon that is capable of withstanding extreme pressure stresses previously only observed in diamond. Unlike crystalline forms of carbon such as diamonds, whose hardness is highly dependent upon the direction in which the crystal is formed, the new form of carbon is amorphous meaning it could be equally strong in all directions.
A team including scientists from Stanford University and the Carnegie Institution for Science started with a form of carbon called glassy carbon. Glassy carbon was first synthesized in the 1950s and was found to combine glassy and ceramic properties with those of graphite, including high temperature resistance, hardness, low density, low electrical resistance, low friction and low thermal resistance. To create the new carbon allotrope, the team compressed glassy carbon to above 400,000 times normal atmospheric pressure.
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The resultant new form of carbon was capable of withstanding the types of pressure stress that no other substance other than diamond had been able to withstand. It was able to withstand 1.3 million times normal atmospheric pressure in one direction while confined under a pressure of 600,000 times atmospheric levels in another direction.
Because, unlike diamonds, the structure of the new allotrope is not organized in repeating atomic units, it may hold potential advantages over diamonds. Whereas a diamond's hardness is highly dependent on the orientation of its crystalline structure, the new material is amorphous, meaning its structure lacks the long-range order of crystals offering the prospect that the new material could be isotropic - that is, having equally strong hardness in all directions. If this turns out to be the case, it could be better suited to certain applications than diamonds.
"These findings open up possibilities for potential applications, including super hard anvils for high-pressure research and could lead to new classes of ultradense and strong materials," said Russell Hemley, director of Carnegie's Geophysical Laboratory.
The team's discovery will be published in Physical Review Letters.