Scientists have used a new technique to synthesize diamonds at normal atmospheric pressure and without a starter gemstone, which could make growing the precious gems in the lab much easier.
Natural diamonds are formed in the earth’s mantle, the molten zone that was buried hundreds of kilometers beneath the planet’s surface. The process take place under enormous pressure of several gigapascals and scorching temperatures of over 2,700 degrees Fahrenheit (1,500 degrees Celsius).
Similar conditions are used in the method currently used to synthesize 99% of all man-made diamonds. This method, called high-pressure, high-temperature growth (HPHT), takes advantage of these extreme conditions to carbon dissolved in liquid metals such as iron to convert it into diamond around a small seed or starter diamond.
However, the high pressures and temperatures are difficult to generate and maintain. Additionally, the components involved influence the size of the diamonds, with the largest measuring about one cubic centimeter, about the size of a blueberry. Plus, HPHT takes quite a long time – a week or two – to make even these tiny gems. Another method, called chemical vapor depositioneliminates some requirements of HPHT, such as high pressures. But others remain, such as the need for seeds.
The new technique eliminates some of the disadvantages of both synthesis methods. A team led by Rodney Ruoffa physical chemist at the Institute for Basic Science in South Korea, published his results April 24 in the journal Nature.
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The diamond crucible
The novel method took a long time to develop. “For over a decade I have been thinking about new ways to grow diamonds, thinking that it could be achieved in a potentially unexpected way (from ‘conventional’ thinking),” Ruoff told Live Science by email.
First, the researchers used electrically heated gallium with some silicon in a graphite crucible. Gallium may seem like an esoteric element, but it was chosen because a previous, unrelated study showed that it can catalyze the formation of gallium Graphene from methane. Like diamond, graphene is made of pure carbon, but contains the atoms in one layer rather than in the tetrahedral orientation of the gemstone.
The researchers placed the crucible in a homemade chamber maintained at atmospheric pressure at sea level through which super-hot, carbon-rich methane gas could be flushed. Designed by co-author Won Kyung Seong, also of the Institute for Basic Science, this 2.4-gallon (9-liter) chamber could be prepared for experiments in just 15 minutes, allowing the team to quickly conduct experiments with different concentrations of metals and gases could .
Through such optimizations, the researchers concluded that a gallium-nickel-iron mixture – paired with a pinch of silicon – is optimal for catalyzing diamond growth. In fact, using this mixture, the team was able to extract diamonds from the bottom of the crucible after just 15 minutes. A more complete diamond film formed within two and a half hours. Spectroscopic analysis showed that this film was largely pure but contained some silicon atoms.
The details of the mechanism that led to the diamonds’ formation are still largely unclear, but researchers believe that a drop in temperature drives carbon from the methane to the center of the crucible, where it combines to form diamonds. Additionally, diamonds don’t form without silicon, so researchers believe silicon may act as a seed for the carbon to crystallize around.
However, the new method comes with its own challenges. One problem is that the diamonds grown using this technique are tiny; the largest are hundreds of thousands of times smaller than those grown with HPHT. This makes them too small to be used as jewelry.
Other potential uses for the diamonds synthesized using the new technique – for example in more technological applications such as polishing and drilling – are unclear. However, because the process requires low pressure, Ruoff says diamond synthesis could be significantly increased.
“In about a year or two, the world might have a clearer picture about things like possible commercial impacts,” he added.