Superhard, amorphous diamond created

The Tiffany Yellow Diamond

An amorphous diamond, one that lacks the crystalline structure of diamond, but is every bit as hard, has been created by a Stanford-led team of researchers.

What good is an amorphous diamond?

“Sometimes amorphous forms of a material can have advantages over crystalline forms,” said Yu Lin, a Stanford graduate student involved in the research.

The biggest drawback with using diamond for purposes other than jewelry is that even though it is the hardest material known, its crystalline structure contains planes of weakness.

Those planes are what allow diamond cutters to cleave all the facets that help give a diamond its dazzle – 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 Wendy Mao, the Stanford mineral physicist who led the research. “But if diamond is amorphous, it may have the same strength in all directions.”

That uniform super-hardness, combined with the light weight that is characteristic of all forms of carbon, including the diamond, could open up exciting areas of application, such as cutting tools and wear-resistant parts for all kinds of transportation.

Other researchers have tried to create diamond-like amorphous carbon, but have only been able to make extremely thin films that contain impurities such as hydrogen and do not have completely diamond-like atomic bonds.

The amorphous diamond created by Mao and Lin can be made in thicker bulk forms, opening up more potential applications.

The researchers, seen here, created the new, super-hard form of carbon using a high-pressure device called a diamond anvil cell.

They did a series of experiments with tiny spheres of glassy carbon, an amorphous form of carbon which they compressed between the two diamond anvils.

The spheres were a few tens of micrometers (millionths of a meter) in diameter.

They slowly cranked up the pressure on the spheres. When the pressure exceeded 40 gigapascals, 400,000 times atmospheric pressure, 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.

The researchers detected the shift in internal bonding by probing the spheres with X-rays.

They also did experiments in which a glassy sphere was simultaneously subjected to different pressures from different directions, to further assess the strength of the new form of carbon.

While the diamonds in the anvil pressed in on the sides of the sphere with a pressure of 60 gigapascals, about 600,000 times atmospheric pressure, the pressure on the tip of the sphere reached 130 gigapascals.

To read more go to the Stanford Univeristy News Site

See 10 Legendary Diamonds and their stories here