No end to new materials with super-strength

From the days of the alchemists and then the metallurgists who mixed different materials – often in the molten state – and then to the chemists we have now moved into the age when materials are designed in the lab to have desired properties. The challenge then is to synthesise the desired composition with the atomic structure required and then to devise manufacturing processes for the materials.

“A material called carbyne could be stronger even than graphene or diamond, according to researchers who have calculated its properties”, reports the BBC.

Carbyne is a chain of carbon atoms held together by double or alternating single and triple chemical bonds.

In their paper, Boris Yakobson and colleagues from Rice University in Houston show that carbyne’s tensile strength – the ability to withstand stretching – surpasses that of “any other known material” and is double that of graphene, the flat sheet of carbon atoms that is often held up as a “supermaterial”.

They also calculated that carbyne has twice the tensile stiffness of graphene and carbon nanotubes and nearly three times that of diamond.

It should display a number of other useful properties say the researchers. For example, it could be turned into a magnetic semiconductor (these are materials with electrical conductivity between that of a metal and an insulator like glass) and could be used as a sensor to detect twisting.

Some scientists have reported synthesising small amounts of carbyne in the lab, but it was thought to be extremely unstable. And some chemists have suggested that two strands coming into contact could react explosively.

“Our intention was to put it all together, to construct a complete mechanical picture of carbyne as a material,” said Vasilii Artyukhov, also from Rice University.

“The fact that it has been observed tells us it’s stable under tension, at least, because otherwise it would just fall apart.”

Mingjie Liu , Vasilii I. Artyukhov , Hoonkyung Lee ,Fangbo Xu , and Boris I. Yakobson, Carbyne From First Principles: Chain of C atoms, a Nanorod or a Nanorope,

ACS Nano,  DOI: 10.1021/nn404177r, October 5, 2013

Abstract: We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne’s mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5×10^7 N∙m/kg, requiring a force of ~10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be ‘switched on’ by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic-semiconductor state by mechanical twisting. We reconstruct the equivalent continuum-elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g. a nominal Young’s modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 3.2 to 4.4 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable, and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne–carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).

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