Rhenium diboride stands up to diamond

With its milquetoast metallic appearance, rhenium diboride (ReB₂) probably won't usurp the place of diamond as a girl's best friend. But the superhard material could replace diamond in certain industrial applications, thanks to its ultra-incompressible nature and its relatively simple synthesis. Sarah H. Tolbert, Richard B. Kaner, and coworkers at UCLA prepared the metallic form of ReB₂ in bulk quantities under ambient pressure via an arc-melting procedure (Science 2007, 316, 436). The material's average measured hardness is comparable to that of other superhard materials, such as cubic BN or B₆O, which must be made at extreme pressures and temperatures. It falls short of being as hard as diamond, but Tolbert and Kaner believe their measurement represents only a lower limit of ReB₂'s hardness. Rhenium diboride can scratch the surface of natural diamond, however, indicating that it's one of the hardest materials known.