free debate

July 5, 2009

Redefining "Hard as a Rock"

It's commonly thought that diamond is the hardest natural material. On the Moh's scale of hardness, with 1 being an extremely soft rock and 10 being extremely hard, diamond ranks at 10. However, there is new evidence that there are materials out there even harder than diamond.

The first of the two materials that beat diamond is called wurtzite boron nitrade (w-BN). It was compressed, changing the bonds between the atoms. This created a super-hard structure, harder than diamonds. It reached a strength of 114 billions of pascals (GPa) under these indentation conditions. Diamond, in comparison, has a strength of 97 GPa. A second material, lonsdaleite, is even stronger. Under the same indentation process, it compressed to a strength of 152 GPa, hugely stronger than diamond.

The reason why w-BN and lonsdaleite (the structure of which is in blue above) are so strong is because of slight differences between their atomic structures and that of diamond (the structure of which is in red below). When compressed, these bond become extremely strong. Lonsdaleite is the strongest because of its carbon-carbon bonds, like diamond. W-BN has a similar structure to lonsdaleite, but the boron-nitrogen bonds are not as strong. These materials, created in an indenter, can be a model for the technique creating other super-hard materials. Diamond has not completely lost its throne, however. Neither w-BN or lonsdaleite are easily produced in mass quantities. The nano amounts formed are not even enough for extensive experimentation, much less common use. Still, the materials, and more importantly their method of production, open a broad realm of opportunity. Super-hard materials can be created to be stable at high temperatures, which diamonds are not. They can also be tested as conductors and superconductors, which more common super-hard materials like diamond are not. The technological applications will be interesting to see.

And no longer is diamond the epitome of strength. It's still significantly harder than most substances, but is not the only super-hard material out there.

Source: "Scientist Discover Material Harder than Diamond"