Artificial diamonds - now available in extra large.
18:11 13 November 2008 by Catherine Brahic.
A team in the US has brought the world one step closer to cheap, mass-produced, perfect diamonds. The improvement also means there is no theoretical limit on the size of diamonds that can be grown in the lab.
A team led by Russell Hemley, of the Carnegie Institute of Washington, makes diamonds by chemical vapour deposition (CVD), where carbon atoms in a gas are deposited on a surface to produce diamond crystals.
The CVD process produces rapid diamond growth, but impurities from the gas are absorbed and the diamonds take on a brownish tint.
These defects can be purged by a costly high-pressure, high-temperature treatment called annealing. However, only relatively small diamonds can be produced this way: the largest so far being a 34-carat yellow diamond about 1 centimetre wide.
Now Hemley and his team have got around the size limit by using microwaves to "cook" their diamonds in a hydrogen plasma at 2200 °C but at low pressure. Diamond size is now limited only by the size of the microwave chamber used.
The most exciting aspect of this new annealing process is the unlimited size of the crystals that can be treated. The breakthrough will allow us to push to kilocarat diamonds of high optical quality," says Hemley's Carnegie Institute colleague Ho-kwang Mao.
The team's method 'could be routinely run in any laboratory where it is needed,' says Alexandre Zaitsev, a physicist at the City University of New York, whose work also includes diamonds. 'When considered in combination with the high-growth-rate technique of CVD diamonds, it seems to be a starting point of mass-scale production of perfect diamond material at a low price'.
Zaitsev considers low-pressure annealing at temperatures greater than 2000 °C to be a "breakthrough in diamond research and technology".
"The improving quality of synthetic diamonds threatens the natural diamond market. While 20 tonnes of natural diamonds are mined annually, some 600 tonnes of synthetic diamonds are produced each year for industrial use alone."