Scientists have used a new technique to synthesize diamonds at normal atmospheric pressure and without a starter gemstone, making the precious gemstones much easier to grow in the laboratory.
Natural diamonds form in the Earth’s mantle, buried the molten zone hundreds of kilometers beneath the planet’s surface. The process occurs under enormous pressure of several gigapascals and scorching temperatures of more than 2,700 degrees Fahrenheit (1,500 degrees Celsius).
Similar conditions apply to the method currently used to synthesize 99% of all artificially created diamonds. This method is called high pressure and high temperature growth (HPHT) and uses these extreme settings for coaxing carbon dissolved in liquid metals, such as iron, to convert it around a small seed or starter diamond into diamond.
However, the high pressures and temperatures are difficult to produce and maintain. Additionally, the components involved affect the size of the diamond, with the largest being about a cubic centimeter, or about the size of a blueberry. Furthermore, HPHT takes quite a long time – a week or two – to produce even these small gemstones. Another method, called chemical vapor depositioneliminates some of the requirements of HPHT, such as high pressure. But others remain, such as the need for seeds.
The new technique eliminates some disadvantages of both synthesis processes. A team led by Rodney Ruoffa physical chemist at the Institute for Basic Science in South Korea, published their findings April 24 in the journal Nature.
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The diamond melting pot
The new method had been in the making for a long time. “For more than a decade I have been thinking about new ways to grow diamonds, thinking it might be possible to achieve this in unexpected ways (per ‘conventional’ thinking),” Ruoff told Live Science by email .com.
To start, the researchers used electrically heated gallium with a little silicon in a graphite crucible. Gallium may seem like an esoteric element, but it was chosen because a previous, unrelated study found that it inhibits the formation of graphene from methane. Graphene, like diamond, is pure carbon, but contains the atoms in a single layer rather than in the tetrahedral orientation of the gemstone.
The researchers placed the crucible in a home-built chamber kept at atmospheric pressure at sea level, allowing super-hot, carbon-rich methane gas to be flushed out. Designed by co-author Won Kyung Seong, also from the Institute for Basic Science, this 9-liter chamber could be prepared for experiments in just 15 minutes, allowing the team to quickly undertake runs with different concentrations of metals and gases.
Such adjustments led the researchers to the conclusion that a gallium-nickel-iron mixture – coupled with a pinch of silicon – was optimal for catalyzing the growth of diamonds. With this blend, the team was able to extract diamonds from the bottom of the melting pot after just 15 minutes. Within two and a half hours, a more complete diamond film formed. Spectroscopic analyzes showed that this film was largely pure, but contained some silicon atoms.
The details of the mechanism that formed the diamonds are still largely obscure, but the researchers think a temperature drop drives carbon from the methane to the center of the crucible, where it coalesces into diamond. Furthermore, without silicon, diamonds are not formed, so the researchers think it could act as a seed for the carbon to crystallize around.
However, the new method has its own challenges. One problem is that the diamonds grown using this technique are small; the largest are hundreds of thousands of times smaller than those grown with HPHT. That makes them too small to use as jewelry.
Other possible uses – for example in more technological applications such as polishing and drilling – for the diamonds synthesized with the new technique are unclear. However, because the process involves low pressure, Ruoff said, it could significantly scale up diamond synthesis.
“In about a year or two, the world may have a clearer picture of things like the potential commercial impact,” he added.