Diamond is known as one of the hardest materials we have access to today, but even diamond has its limitations and when it isn’t enough we can always use cubic boron nitride. This is slightly harder than diamond, but also more expensive. The manufacturing requires such high pressures. The secret behind these extremely hard substances is the minimal distance between the atoms and this is something researchers at UCLA have chosen to focus on for the last few years. They started with the metal osmium, as it is known as one of the most non-compressible atoms we have, and then combine it with boron. This made it possible to reduce the distance between the atoms to 10% of pure osmium.
They didn’t stop there though, but continued working with other transition metals with similar properties and tried to find other metals where they could shrink the distance even further. Even if the osmium boron matrix was hard enough to scratch sapphire, that wasn’t enough.
They moved on to rhenium where they managed to shrink the distance to only 5% of pure rhenium by mixing it with boron. This resulted in a substance that could actually scratch diamond and had properties that made it even harder than cubic boron nitride. There’s a big different between rhenium diboronide and diamond, and cubic boron nitride, as the first doesn’t require a high pressure during the manufacturing.
The easier manufacturing will make it a better and cheaper alternative for drills and other industrial purposes, where both diamond and boron nitride is used, in lack of other alternatives. The article was published in Science vol. 316, 436-439, (20 Apr. 2007. It’s also available online.
