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Wurtzite boron nitride is formed when volcanic eruptions generate very high temperatures and pressures

wallpapers News 2021-06-09
The rare mineral Lonsdalite is sometimes formed when meteorites containing graphite hit the Earth, while wurtzite boron nitride is formed when volcanic eruptions generate very high temperatures and pressures.
If this is confirmed, wurzite boron nitride may be the most useful of the two, as it is more stable in oxygen at higher temperatures than diamond. This makes it ideal for placing on the tips of cutting and drilling tools to operate at high temperatures, or as a corrosion-resistant film on the surface of space vehicles, for example.
Paradoxically, wurtzite boron nitride seems to derive its hardness from the flexibility of the interatomic bonds that make up it. When the material is stressed, some of the bonds are reoriented by about 90 degrees to reduce the tension.
Although diamonds go through a similar process, after that happens, something in the structure of wurtzite boron nitride makes them nearly 80 percent stronger, something they don't have, according to study co-author Changfeng Chen of the University of Nevada, Las Vegas.
Single crystal
Natalia Dubrovinskaia of the University of Heidelberg in Germany has carried out a similar study.
She told New Scientist: "This is important because any attempt to gain insight into the mechanisms that improve material properties, particularly hardness, is technically extremely important."
The more you know about the factors that affect the hardness of a material, the more likely you are to design a hard material that can be ordered, she explains.
However, she points out that in order to prove the theory, a single crystal of each material is needed. So far, there is no known way to separate or grow crystals of these two materials.
These exciting simulations have yet to be confirmed experimentally because there are not enough exotic materials to test. "Since our work in 2009, there have been no reports of large-scale synthesis of wurtzite boron nitride or hexagonal diamond," Chen said.
But research into superhard crystals continues to uncover promising candidates. Last year, Tian Yongjun of Yanshan University in Qinhuangdao, China, and his colleagues studied a cubic form of boron nitride - rather than the hexagonal form studied by Chen - which they claimed was harder than diamonds.
The experimental details of the study have been criticized, but Chen believes Tian's material is still worth investigating. "The main challenge is to understand the atomic mechanisms behind this remarkable result," Chen said.

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