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Post Info TOPIC: Wurtzite Boron Nitride
Blobrana


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Lonsdaleite
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Nanoparticles have replaced diamonds as the worlds toughest material, but are not natural forms. Now, a new natural substance has literally stripped the diamond of its crown. This material is known as lonsdaleite. This is also a hexagonal diamond and is its close cousin.
This allotropic form of carbon has been named after the famous British crystallographer, Kathleen Lonsdale. Lonsdaleite is formed from graphite present in meteorites following their impact on earth.
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Blobrana


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RE: Wurtzite Boron Nitride
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The reputation of diamond as the hardest material around is under threat. Researchers in China and the United States recently determined that two naturally occurring substances surpass diamonds resistance to scratching and indentation. They calculated that the mineral lonsdaleite - made of carbon, like diamond - is 58 percent harder than its famous cousin. And wurtzite boron nitride beats diamonds hardness by about 18 percent after being subjected to pressure, which alters its atomic bonds.

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Blobrana


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In addition to being the traditional token of marital intent, the diamond has long provided the - ahem - gold standard for super-hard materials. But physicists at Shanghai Jiao Tong University and at the University of Nevada, Las Vegas, say that two lesser-known materials, wurtzite boron nitride and lonsdaleite, are even harder.

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Blobrana


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Harder than Diamond: Superior Indentation Strength of Wurtzite BN and Lonsdaleite
Recent indentation experiments indicate that Wurtzite BN (w-BN) exhibits surprisingly high hardness that rivals that of diamond. Here we unveil a novel two-stage shear deformation mechanism responsible for this unexpected result. We show by first-principles calculations that large normal compressive pressures under indenters can compel w-BN into a stronger structure through a volume-conserving bond-flipping structural phase transformation during indentation which produces significant enhancement in its strength, propelling it above diamond's. We further demonstrate that the same mechanism also works in lonsdaleite (hexagonal diamond) and produces superior indentation strength that is 58% higher than the corresponding value of diamond, setting a new record.

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