Researchers had investigated the Wurtzite structure of boron nitride (w-BN,  a repeating array of hexagons in 3-dimensional space) in the past, but it had inferior properties to the cubic structure of boron nitride mentioned above. Diamond has long been regarded as the practical and theoretical hardness champion and has found uses ranging from industrial abrasives to a girl's best friend. But cubic boron nitride is still, at best, just the world’s second hardest material with a Vickers hardness of around 50 GPa. We’re sure she’ll understand. Ad Choices. The potential for ultra-hard nanocomposites remains within reach, however. © 2020 Condé Nast. WIRED Media Group Read our affiliate link policy. This results in more complicated stresses that allow the bonds to reorder themselves into a slightly different structure; in w-BN's case, this reordering massively increased the material strength. With Valentine’s Day quickly approaching, why not consider the gift that says "This unattractive grey mineral, like my love for you, crushes puny diamonds”? That is, until researchers got their hands on an alternate crystal structure of boron nitride and … Use of and/or registration on any portion of this site constitutes acceptance of our User Agreement (updated 1/1/20) and Privacy Policy and Cookie Statement (updated 1/1/20) and Ars Technica Addendum (effective 8/21/2018). A challenger to its newly claimed hardness title quickly emerged: hexagonal diamond (called lonsdaelite), an allotrope of diamond, shares a similar structure to w-BN. There also turned out to be surprises in the mechanisms at work to generate that awesome value. You must login or create an account to comment. But using a standard hardness test, which indents the material with a small pyramid and measures the force required, researchers recently observed that the w-BN in fact easily exceeded diamond’s hardness value, 114 Gpa (16.5 million pounds/square inch), versus diamond’s 97 Gpa. Cubic boron nitride, a synthetic material, comes in at second place. Sign up or login to join the discussions! Ars may earn compensation on sales from links on this site. CNMN Collection The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Condé Nast. Lonsdaelite is a rare but naturally occurring mineral—if you consider massive meteorites impacting the Earth’s surface to generate the conditions needed for synthesis "natural." Your California Privacy Rights | Do Not Sell My Personal Information Physical Review Letters. All rights reserved. How hard is Boron Nitride? Indeed C-BN is the second hardest material next to diamond. DOI: 10.1103/PhysRevLett.102.055503. - Feb 13, 2009 6:30 pm UTC. The samples tested were small, and the researchers pointed out that the material synthesis techniques are not well-developed. The hardness value increased a whopping 78 percent in the w-BN after the bond-flipping occurred. Cubic boron nitride, a synthetic material, comes in at second place. Boron nitride exists in multiple forms that differ in the arrangement of the boron and nitrogen atoms, giving rise to varying bulk properties of the material. Its hexagonal form (w-BN) was initially reported to be even harder but these results were based upon theoretical simulations that predicted an indentation strength 18% higher than diamond. The same bond-flipping process occurred when hardness indentions were performed, and the all-carbon structure outperformed both diamond and w-BN with a strength of 152 GPa, which is 58 percent higher than regular diamond. Cubic boron nitride (C-BN) has the same structure as diamond and its properties mirror those of diamond. Unfortunately for our friend w-BN, the good times did not last. The different atomic bond orientations and planes of symmetry within the crystal give rise to different physical properties. These vaulted it above diamond for raw hardness, but it didn't wind up keeping the crown long. Join the Ars Orbital Transmission mailing list to get weekly updates delivered to your inbox. That is, until researchers got their hands on an alternate crystal structure of boron nitride and observed a unique atomic bond rearrangement under high stresses. Todd Morton The geometry of the hardness indenter dictates that the stress it puts on the material will not be limited only to one direction relative to a crystal plane in the material. C-BN was first synthesised in 1957, but it is only in the last 15 years that commercial production of C-BN has developed. Alternate crystal structures sharing the same chemical composition, called allotropes, are common in nature.

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