Better than the best

Osmium metal is even harder than diamond

Published: Wednesday 15 May 2002

researchers have recently broken the myth of diamonds being the hardest substance found on Earth. Researchers from us-based Lawrence Livermore National Laboratory (llnl) have discovered that osmium, a metal, is harder than diamond. It withstands compression better than any other material.

A measure which is commonly used to study hardness of materials is the bulk modulus or the resistance to compression of a material. It is usually found that materials with higher bulk modulus are also hard. In the past, theoretical predictions about the higher bulk modulus of osmium as compared to that of diamond were not taken seriously. But now, H Cynn and his colleagues at llnl have experimentally proved the higher bulk modulus of osmium. They used a diamond anvil to put a small piece of osmium under high pressure.

A diamond anvil consists of two diamonds separated by a metal gasket with a tiny hole in the centre. Osmium powder and argon were placed in the hole and subjected to very high pressure of 600,000 atmospheres. The atomic spacing of osmium was recorded using x-ray diffraction at various pressures and then the bulk modulus was measured. The researchers found that osmium has a bulk modulus that is about five per cent higher than diamond.

The finding could lead to the development of many novel superhard materials with unique properties. Since the atoms in osmium retain their spacing under high pressure, it should be possible to incorporate other materials like carbon in it to create harder substances.

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