Laboratory-made hexagonal diamonds are stiffer than natural diamonds

Nature’s strongest material now has fierce competition. For the first time, researchers have hard evidence that human-made hexagonal diamonds are more rigid than common cubic diamonds found in nature and often used in jewelry.

Named for their six-sided crystal structure, hexagonal diamonds have been found at some meteorite impact sites, and others were briefly made in the lab, but they were either too small or too short to measure.

Today, scientists at Washington State University’s Institute for Shock Physics have created hexagonal diamonds large enough to measure their stiffness using sound waves. Their findings are detailed in a recent article by Physical examination B.

“Diamond is a very unique material,” said Yogendra Gupta, director of the Institute for Shock Physics and corresponding author of the study. “It is not only the strongest – it has beautiful optical properties and very high thermal conductivity. Now we have manufactured the hexagonal shape of the diamond, produced under impact compression experiments, which is significantly more rigid and stronger than ordinary gemstone diamonds. “

Researchers have long wanted to create a material that is stronger than natural diamonds, which could have a variety of uses in industry. While many have speculated that hexagonal diamonds are stronger, the WSU study provides the first experimental evidence that they are.

Lead author Travis Volz, now a postdoctoral researcher at Lawrence Livermore National Laboratory, focused his thesis work at WSU on the creation of hexagonal diamonds from graphite. For this study, Volz and Gupta used gunpowder and compressed gas to propel small, penny-sized discs of graphite at a speed of about 15,000 miles per hour over transparent material. The impact produces shock waves in the discs which very quickly transform them into hexagonal diamonds.

Immediately after the impact, the researchers produced a small sound wave and used lasers to measure its movement through the diamond. Sound travels faster through stiffer material. Previously, sound moved fastest through the cubic diamond; in hexagonal diamonds created in the lab, it moved faster.

Each process took place in several billionths of a second, or nanoseconds, but the researchers were able to take the stiffness measurements before the high-speed impact destroyed the diamond.

Stiffness is the ability of a material to resist deformation under force or pressure – for example, a rock is stiffer than rubber because rubber bends when pressed. Hardness is the resistance to scratching or other surface deformation.

Materials that are generally stiffer are also harder, Volz said. Although researchers have not been able to scratch diamonds to test hardness directly, by measuring the stiffness of diamonds, they can make inferences about their hardness.

If science advances to the point where lab-made hexagonal diamonds can be created and recovered, they could have a range of uses.

“Hard materials are useful for machining capabilities,” Volz said. “Diamond has been used for a long time in drill bits, for example. Since we have found that hexagonal diamond is likely harder than cubic diamond, it could be a superior alternative for machining, drilling, or any other type of application where cubic diamond is used. “

While the industrial benefits are obvious, Gupta said there is still a possibility that hexagonal diamonds could one day be used on engagement rings. Currently, lab-made cubic diamonds are less valuable than their natural peers, but hexagonal diamonds would likely be newer.

“If one day we can produce and polish them, I think they would be in more demand than cubic diamonds,” Gupta said. “If someone said to you, ‘Listen, I’ll give you a choice of two diamonds: one is much rarer than the other.’ Which would you choose? ”