Extra-hard hexagonal diamonds can now be grown in a lab

A harder form of diamonds that has escaped scientists for decades can now be synthesized in the laboratory and could be used to make extremely difficult cutting and drilling tools.

Diamonds as we know them have a cube arrangement of atoms in their crystal structure. But for at least 60 years, we have been aware of another form – hexagonal diamond – which is much more difficult, thanks to its crystals not having uniform shear lines along which the ruptures can spread.

The natural hexagonal diamond occurs in meteorites, where it is known as mineral lonsdaleite, but only in mixtures with cube diamond. Previous attempts to synthesize hexagonal diamonds have only produced tiny traces which are also unclean.

Now, Ho-Kwang Mao at the Center for High Pressure Science and Technology Advanced Research in Beijing and his colleagues have managed to create a relatively large sample of hexagonal diamond of 1 millimeter in diameter and 70 micrometers thick, with purity almost 100%.

While the normal diamond has been synthesized for some time, researchers Explored a range of pressures and temperatures to find an ideal place in which hexagonal diamonds have been produced. This ended up being 1400 ° C at 20 gigapascals – 200,000 times atmospheric pressure on earth.

Such material has never been manufactured before, so it should be studied in depth to determine its properties, explains Mao. “It’s incredibly precious,” he says. “But once we know how to do it, anyone can produce it. So the important thing is to get a patent and find a way to make it cheaper.”

Hexagonal diamonds should be about 60% harder than ordinary diamonds depending on their structure. The cube diamond has a hardness of around 115 gigapascals when measured in a Vickers hardness test. The hexagonal diamond created by Mao and his team measures 120 gigapascals, but they believe that they can improve it considerably when they develop their technique further.

If the hexagonal diamond can be synthesized with sufficient thicknesses, it could be used to make more difficult and more resilient tools for a range of uses in industry, such as drilling for geothermal energy, explains James Elliott at the University of Cambridge. “Obviously, the more you go deep, the more hot it becomes, [and] This could allow them to go further underground. »»