Conjuring gemstones from thin air sounds like one of the alchemist’s more ambitious projects. But that is what a team of chemists from China is claiming to have achieved by making small diamonds from carbon dioxide.

“We are changing a waste gas into gems,” claims Qianwang Chen, head of the team producing the diamonds at the University of Science and Technology of China in Hefei, Anhui province.

The team claims its method could be cheaper and more efficient than some existing methods of synthesising diamonds, which require pressures of up five million atmospheres and temperatures that reach 1400 °C.

Chen and his colleagues make their diamonds by reacting CO 2 with metallic sodium in a pressurised oven at only 440 °C and 800 atmospheres. “This is the lowest temperature reported so far for diamond synthesis,” he says. After 12 hours, the grains of diamond can be separated from the sodium carbonate, graphite and unreacted CO 2 that remain.


Small gemstones

Metallic sodium is a hazardous material, as it reacts violently with water vapour. To ensure that it all gets used up, the team starts with an excess of CO 2 . “We have now undertaken the procedure more than 80 times without any safety problems,” says Chen.

In the online edition of the Journal of the American Chemical Society (DOI: 10.1021/ja035177) Chen’s team reports that the first diamonds reached diameters of about a quarter of a millimetre. While that is far too small for gems in wedding rings and necklaces, it is ideal for use in industrial cutting tools and abrasives.

But since the group’s paper was accepted by the journal, they have improved the process to the point at which it can be used to make small gemstones. “We can grow diamonds as large as 1.2 millimetres,” Chen says. “They are transparent and colourless, and so could be used as gems.”

“Horrifically nasty”

While the Chinese process works at a more reasonable temperature, 800 atmospheres is “still a horrifically nasty pressure to work at”, says Alison Mainwood at King’s College London, who chairs the UK’s Diamond Research Network.

She doubts whether the Chinese process will seriously challenge today’s industrial diamonds because the diamonds it yields are so small and gritty: “I’m sure it could be improved, but I doubt to the point where it could become a rival.”

De Beers, the largest diamond-mining company in the world, says that while it welcomes advances in the technology of diamond making, manufactured gems should be kept distinct from natural ones.

“We hope that any organisation involved in diamond synthesis would openly and transparently declare any such product as being synthetic and clearly distinct from natural gem diamond,” the company says.