Turning air into metal with nitrogen, diamonds and lasers

More than three-quarters of the air around you is nitrogen gas: specifically, Ntwo molecules. Nitrogen is incredibly stable in this form – which is why it is rarely noticed. He reacts with almost nothing.

Chemists, goblin-like alchemists that they are, see nitrogen stability as a challenge.

Getting the nitrogen gas to be something other than Ntwo it takes a lot of complicated chemistry to achieve – but when successful, it can lead to the manufacture of high-density fertilizers or fuels out of thin air.

An international team of chemists has just announced a new success in the fight against nitrogen: after six years of work, they managed to make pure nitrogen not a gaseous N.two molecule. Instead, they created a larger, ring-shaped molecule with six nitrogen atoms.

The N molecule6two-, is known as a hexazine ring. It can store and release huge amounts of chemical energy within its bonds, making it an interesting candidate for high energy density materials.

And all it took to do was a pair of diamond anvils, laser heating, and air pressure over 400,000 times the pressure we feel at sea level. Oh, and some potassium.

The reason of NtwoThe stability of ‘s is its number of chemical bonds. Nitrogen can form three bonds with itself, and it tends to do so at any opportunity. Although nitrogen atoms happily form single bonds with other elements, they tend not to bond that way. Nitrogen atoms with only one bond between them are much more reactive.

“Low-order NN bonds are difficult to keep stable at low pressure,” says Yu Wang, a researcher at the Hefei Institute of Physical Sciences of the Chinese Academy of Sciences and lead author of a paper describing the research, published in Nature Chemistry.

Wang and his colleagues had already tricked Ntwo gas molecules to form a solid nitrogen crystal on a diamond anvil: a device that creates extremely high pressure. It uses two anvils made from high quality diamonds, because very little is hard enough to create the desired pressure. A laser is used to heat the materials inside.

At a pressure of 110 gigapascals (one gigapascal is approximately 9869 times normal atmospheric pressure) and a temperature of 2500 Kelvin (2227°C), the nitrogen gas solidified and formed single rather than double or triple bonds. But the material was not stable at lower temperatures or pressures.

This time, the researchers started with something a little easier: potassium azide, or KN.3, at 45 gigapascals. After a lot of trial and error, the researchers managed to convert the KN3 in Ntwo6-which they then stabilized with potassium again.

The resulting molecule, KtwoNo6contained the holy ring of single-bonded nitrogen.

The compound had a metallic luster and was still stable at the much lower pressure of 20 gigapascals — still about 200,000 times higher than the average room, but significantly lower than its precursors.

Wang says the researchers are “all very excited” about the result.



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