November 06, 2010

Ultra-hard graphite will be able to crack diamond

Graphite squeezed between two diamond jaws at pressures of 170,000 atmospheres managed to produce a crack in the diamond. A team modelled various crystal structures that could result when graphite is compressed, and found that bct-carbon requires the least energy to form. bct-carbon's shear strength - a measure of how difficult it is to slide the carbon layers over one another - is 17 per cent greater than that of diamond. Their findings raise the prospect of making exceptionally hard materials without extreme heating.

Computer simulations by Hui-Tian Wang at Nankai University in Tianjin, China, and colleagues have shown that the compressed material could be at least partly made of bct-carbon, which is built up from rings of four carbon atoms. Bct-carbon has attributes of both diamond, which has a cubic structure, and graphite, composed of loosely linked sheets of carbon atoms in a hexagonal lattice. In bct-carbon, layers of carbon rings are linked by strong vertical bonds.

Physics Review B- Ab initio study of the formation of transparent carbon under pressure

A body-centered tetragonal carbon (bct-carbon) allotrope has been predicted to be a transparent carbon polymorph obtained under pressure. The structural transition pathways from graphite to diamond, M-carbon, and bct-carbon are simulated and the lowest activation barrier is found for the graphite-bct transition. Furthermore, bct-carbon has a higher shear strength than diamond due to its perpendicular graphenelike structure. Our results provide a possible explanation for the formation of a transparent carbon allotrope via the cold compression of graphite. We also verify that this allotrope is hard enough to crack diamond.


Featured articles

Ocean Floor Gold and Copper
   Ocean Floor Mining Company

Форма для связи


Email *

Message *