Diamond and Boron Nitride Make a Super-Hard Material

Diamond and Boron Nitride Make a Super-Hard Material

Diamonds may be the hardest naturally occurring material, and they are used for a variety of cutting tasks, but they have a problem. When used for cutting through some hard metals like chromium, nickel, cobalt and iron, they tend to oxidise.

Scientists have now created a super-hard material that will outperform diamonds used in industrial cutting tools. A team headed by Duanwei Hei at the Institute of Atomic and Molecular Physics of Sichuan University, Chengdu, have designed a material that, if it can be manufactured on a large enough scale, could displace diamond as a cutting material in industrial sectors such as aerospace and construction.

The secret has been to combine diamond with boron nitride. The hope is to achieve the best of a natural product, diamond, which is super-hard, together with boron nitride, which is impervious chemically and has a stability superior to diamond’s.

 The biggest challenge has been to produce a large enough sample of the new material       that it may be tested for both cutting ability and chemical stability.

Boron Nitride combined with Diamond

Boron Nitride combined with Diamond

The resulting alloy was formed from mixing equal measures of the two substances in powdered form and subjecting them to high pressures between 100,000 to 200,000 bars and temperatures of between 1,300 and 2,600 degrees Kelvin. This produced an alloy that was about three millimetres in length and was large enough to be formed into a cutting tool.

After testing on granite and hardened steel and using computer-controlled lathes, the tool proved capable of outperforming standard commercial tools, and it remained hardened as well as inert.

The Sichuan University team wondered what the chemical reason was for these properties. They have concluded that new chemical bonds formed between carbon and boron atoms as well as between nitrogen and carbon atoms may straddle interfaces of the separate materials. However, they remain uncertain about the precise nature of these bonds.

The next challenge is to estimate if this new alloy is capable of being produced cheaply and consistently on a commercial scale, as the production process requires a very high energy input. The team is also working on a process that would synthesize lengths of the new alloy that could measure some centimetres rather than just millimetres.


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