Researchers in China have obtained pure samples of hexagonal diamond, also known as lonsdaleite, for the first time. This rare mineral is found in meteorites formed during the destruction of dwarf planets, but until now scientists have not been able to isolate it in its pure form. New work published in the journal Nature demonstrates that the synthetic material is superior ordinary diamond in hardness and oxidation resistance.
Natural diamond, or cubic diamond, is traditionally considered the hardest material on Earth. Its strength is due to its ordered cubic structure, in which the carbon atoms are located strictly along three axes. Hexagonal diamond has a different architecture: its atoms are arranged in hexagonal cells, reminiscent of a honeycomb.
Theoretically, the existence of this form of diamond was predicted back in 1962 by employees of the Pittsburgh Coal Research Center. The first laboratory samples of lonsdaleite were obtained in 1967, but they always contained impurities of cubic diamond, graphite and other minerals. This made it impossible to accurately measure the properties of a pure substance.
The authors of a new study have found a way to solve this problem. They subjected highly ordered graphite to a compression of 20 gigapascals – about 200 thousand times higher than normal atmospheric pressure. The experiment lasted ten hours at temperatures ranging from 1300 to 1900 degrees Celsius. As a result, we managed to get pure hexagonal diamond samples with a diameter of about one and a half millimeters – large enough for full testing.
The analysis confirmed that lonsdaleite is not only harder, but also tougher than cubic diamond. In addition, it is much more resistant to oxidation: its surface does not react with oxygen at high temperatures. This property is especially important for applications in drilling tools and other high temperature processes.
The authors of the work emphasize that their method makes it possible to obtain hexagonal diamond in bulk quantities. This opens the way to industrial use of a material that has until now remained a laboratory curiosity. Potential applications include cutting and drilling tools, abrasive coatings, and heat dissipation systems in electronics.
The study has additional value for astrophysics. The presence of lonsdaleite in meteorites can reveal the conditions of their formation and origin, shedding light on the early stages of the evolution of the solar system.
Chinese scientists not only confirmed the real existence of the material, but also showed how it can be produced on an industrial scale. Hexagonal diamond is ready to take its place as the hardest material available to man.
Source: Live Science
Image: DANIEL SLIM
