Rock of vanity

Scientists at the Carnegie Institution?s Geophysical Laboratory, Washington DC, created a 10-carat, half-inch thick, single-crystal sparkler that grew at 100 micrometers an hour, writes Prakash Chandra.
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Updated on Oct 23, 2006 05:19 AM IST
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None | By Prakash Chandra

Researchers recently invested in a diamond and watched it grow. Scientists at the Carnegie Institution’s Geophysical Laboratory, Washington DC, created a 10-carat, half-inch thick, single-crystal sparkler that grew at 100 micrometers an hour. They used a new chemical vapour deposition (CVD) method to increase its size to five times that of commercially available diamonds produced by the standard high-pressure/high-temperature method.

A diamond is nothing more exotic than carbon or coal. But the way its molecules are tightly packed in a solid geometric fashion makes it the hardest substance known — the only thing that can scratch it is, well, another diamond! Still, to most people, diamonds mean jewellery because of their ‘brilliance’ and ‘fire’. Its high refractive index bends most of the light that enters it and radiates it as ‘brilliance’. The light is also split into the colours of the spectrum — the ‘fire’. Being excellent conductors of heat, diamonds are cold to the touch — a test for real diamonds.

Similarly, a diamond can easily scratch pretenders like rhinestones, zircons and synthetic minerals, but not vice versa. These properties make it useful for industrial purposes like cutting glass and other diamonds, drilling for oil, and coating low-friction hinges in the space shuttle and high-powered computer chips (where they rapidly dissipate heat that could otherwise cripple microprocessors).

Diamonds occur naturally 50 to 70 miles below Earth’s surface in the hot mantle, where pressures of over 55,000 atmospheres and temperatures topping 1,500 degrees C force carbon atoms into organised crystals. Studying diamonds that formed at about the same time as the continents tell us about the mantle. Although scientists can synthesise diamonds for industrial purposes in the lab, it costs more to make them than it’s worth.

In the late Nineties, physicist Tyrone Daulton at Illinois’ Argonne National Laboratory found microscopic diamonds in a chunk of uranium-rich coal that had never felt the mantle’s heat. When uranium atoms fly apart inside carbon-rich rocks, they can slam into the carbon atoms with enough energy to break their chemical bonds. Some of the new atomic bonds formed may turn out to be diamond bonds. Daulton’s team dissolved the rock in a powerful acid that left only the most resilient minerals behind, thereby removing most of the haystack from the needle. Using electron microscopy, they then identified the diamond crystals in the residue.

But wait, don’t rush to get carloads of coal into your backyard yet. It would take about a million trillion of micro-diamonds to make a single, commercial-size stone.

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