Material scientists create super-hard form of carbon

Material scientists at Stanford University have created a super-hard form of carbon akin to an amorphous diamond.

With improvements to the process, the material could find a use in cutting tools and wear-resistant parts for all kinds of transportation, according to the researchers.

Although the extreme hardness of regular diamonds makes them suitable for certain machine-tool uses, the crystalline structure actually contains planes of weakness. Those planes are what allow diamond cutters to cleave the facets — they are actually breaking the gem along weak planes, not cutting it.

‘With diamond, the strength depends on the direction a lot. It’s not a bad property, necessarily, but it is limiting,’ said project lead Prof Wendy Mao of Stanford. ‘But if diamond is amorphous, it may have the same strength in all directions.’

The researchers started with spheres of glassy carbon (an amorphous form of carbon), which were a few tens of micrometers in diameter then they compressed between two diamond anvils.

When the pressure exceeded 40 gigapascals, the arrangement of the bonds between the carbon atoms in the glassy spheres had completely shifted to a form that endowed the spheres with diamond-like strength.

One characteristic of the new material is that the hardness of the amorphous carbon is tunable; it is soft at low pressure, but the greater the pressure, the harder it gets.

Even though the amorphous diamond returned to plain glassy carbon when the pressure was released, there are still potential applications: the material could be used as a gasket in high-pressure devices where having a gasket that hardens with pressure would be beneficial.