Hardest substance

The hardest substance on Earth is an aggregated diamond nanorod (ADNR). It is, in fact, a collection of nano-scale diamonds, and it is the least compressible, hardest substance known to science. It was first manufactured in 2005 by researchers at the Bayerisches Geoinstitut (Universität Bayreuth) in Bayreuth, Germany. The team tested the compressibility and density of this new material and confirmed that the X-ray density of the ADNR material is higher than that of diamond (the hardest element) by 0.2–0.4%. As well as confirming this as the densest known form of carbon, tests showed that ADNR is also 11% less compressible than diamond. The Vickers microhardness test failed to make any indentation on the surface of the ADNR, proving it to be harder than the diamond tip used in the test itself. Units are HV, or kg/mm².

ADNRs are important for machine tools in all forms of the manufacturing industry. The harder the tool, the cleaner the machining action and the longer the life of the tool head itself. This leads to better-quality manufacturing and cheaper production due to the reduced tool-replacement costs.