When is a fake diamond better than the real thing? Scientists have just created one of the world’s hardest substances -a synthesized, nano-sized version of lonsdaleite which is thought to be harder than diamond.
Led by researchers at the Australian National University, the team was able to crush carbon inside a diamond anvil cell (a laboratory tool which uses diamond points to compress tiny fragments under pressures similar to those found in planetary cores) at 400 degrees Celsius, half the temperature previously employed. Researchers found that after two hours of being crushed by up to 112 GPa of pressure (about a million times that of atmospheric pressure), the graphene sheets within the specimen folded into a crystal of hexagonal configuration, creating an “almost pure” version of lonsdaleite, a material so far only found in nature in the remnants of meteorite impacts.
“This new diamond is not going to be on any engagement rings,” says Jodie Bradby, professor at the Australian National University in a press release. “You’ll more likely find it on a mining site — but I still think that diamonds are a scientist’s best friend. Any time you need a super-hard material to cut something, this new diamond has the potential to do it more easily and more quickly.”
Named after famed crystallographer Dame Kathleen Lonsdale, lonsdaleite was first found at the Canyon Diablo meteorite site which created the Barringer Crater in Arizona about 50,000 years ago, and has since been used as a telltale sign of extra-terrestrial impact wherever it has been located. Lonsdaleite has also been recovered at the Sudbury Basin, in Northern Ontario, the second-largest impact crater on Earth. The laboratory version of lonsdaleite was first created in the late 1960s, but the purity of the newly synthesized lonsdaleite is the true breakthrough, says Bradby.
Fake diamond: “Smaller is stronger…”
“The hexagonal structure of this diamond’s atoms makes it much harder than regular diamonds, which have a cubic structure,” says Bradby. “We’ve been able to make it at the nanoscale and this is exciting because often with these materials ‘smaller is stronger.’”
A material’s hardness is measured in a variety of ways, the most venerable of them being the Mohs scale of mineral hardness, named after German geologist Friedrich Mohs who devised the system in 1812, although versions of the qualitative test have been recorded since the Ancient Greeks. The Mohs scale ranks minerals by the scratch test: essentially asking, can this one rock leave an indelible mark on this other rock? The top ten hardest minerals run from talc at number ten through gypsum, calcite and quartz, up to diamond, which naturally occurs in varying degrees of purity. The hardest diamonds can only be scratched by other diamonds.
Beyond the diamond are Wurtzite boron nitride, which can be produced under the high temperatures and high pressure of volcanic eruptions, and lonsdaleite. The newly created lonsdaleite was made possible by international collaboration, says study co-author Dougal McCulloch from the School of Science at RMIT University in Melbourne. “The discovery of the nano-crystalline hexagonal diamond was only made possible by close collaborative ties between leading physicists from Australia and overseas,” McCulloch states.
The new study is published in the journal Scientific Reports.