Scientists have used a new technique to synthesize diamonds at normal atmospheric pressure and without a starting gem, which could make it easier to grow the gemstones in the lab.
Natural diamonds form in the Earth’s mantle, a molten zone buried hundreds of miles below the planet’s surface. Process held under enormous pressures of several gigapascals and searing temperatures exceeding 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), uses these extreme settings to coax carbon dissolved in liquid metals such as iron to transform into a diamond around a small seed or starter diamond.
However, high pressures and temperatures are difficult to produce and maintain. Additionally, the components involved affect the size of diamonds, with the largest being about a cubic centimeter, or about the size of a blueberry. Besides, HPHT takes quite a while – a week or two – to produce even these little gems. Another method, the so-called chemical vapor deposition, eliminates some of the requirements of HPHT, such as high pressures. But others persist, like the need for seeds.
The new technique removes some of the disadvantages of both synthesis processes. Team under management Rodney Ruoffphysical chemist at the Institute for Basic Science in South Korea, published their findings April 24 in the journal Nature.
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Diamond cup
The new method has been in the making for a long time. “I’ve been thinking about new ways to grow diamonds for over a decade because I thought it could be done in a way that might be unexpected (according to ‘conventional’ thinking),” Ruoff told Live Science via email.
To begin with, 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 could catalyze the creation of graphene from methane. Graphene, like diamond, is pure carbon, but contains atoms in a single layer rather than the tetrahedral orientation of the gem.
The researchers placed the crucible in a home-built chamber maintained at atmospheric pressure at sea level through which superhot, carbon-rich methane 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 set up for experimentation in just 15 minutes, allowing the team to quickly perform tests with different concentrations of metals and gases. .
Through such tuning, the researchers found that the gallium-nickel-iron mixture – combined with a pinch of silicon – is optimal for catalyzing the growth of diamonds. With this mixture, the team actually recovered diamonds from the base of the crucible after only 15 minutes. Within two and a half hours, a more complete diamond film was formed. Spectroscopic analyzes showed that this film was largely pure but contained a few silicon atoms.
The hallmarks of the mechanism that created the diamonds are still largely unclear, but researchers believe that the drop in temperature drives carbon from the methane toward the center of the crucible, where it fuses into diamond. Additionally, no diamonds form without silicon, so scientists think it may act as a seed for carbon crystallization.
However, the new method has its pitfalls. One problem is that the diamonds grown with this technique are small; the largest ones are a hundred thousand times smaller than those grown with HPHT. This makes them too small to be used as jewelry.
Other potential uses—for example, in more technological applications such as polishing and drilling—for diamonds synthesized using the new technique are unclear. However, because the process involves low pressure, Ruoff said, it could greatly increase diamond synthesis.
“In about a year or two, the world might have a clearer idea of ​​things like the possible commercial impact,” he added.