Scientists have used a new technique to synthesize diamonds at normal, atmospheric pressure and without a starting gem, which could make precious gems much easier to grow in the lab.
Natural diamonds form in the Earth’s mantle, the molten zone is buried hundreds of miles below the planet’s surface. The process is taking place under enormous pressures of several gigapascals and hot 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. Called High Pressure High Temperature (HPHT) growth, this method uses these extreme coaxial settings carbon dissolved in liquid metals such as iron to turn it into a diamond around a small seed or seed 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 cranberry. Also, HPHT takes quite a long time – a week or two – to produce even these little gems. Another method, the so-called chemical deposition of money, eliminates some requirements of HPHT, such as high pressure. But others persist, such as the need for seeds.
The new technique eliminates some drawbacks of both synthesis processes. A team led by Rodney Ruoffphysical chemist at the Institute of Basic Sciences in South Korea, published their findings April 24 in the journal Nature.
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The Diamond Crucible
The new method was a long time in the making. “For more than a decade, I’ve been thinking about new ways to grow diamonds because I thought it might be possible to achieve this in ways that might be unexpected (according to ‘conventional’ thinking),” Ruoff told Live Science via email.
To get started, 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 graphene from methane. Graphene, like diamond, is pure carbon, but contains the atoms in a single layer rather than the tetrahedral orientation of the gem.
The researchers place the crucible in a home-built chamber maintained at atmospheric pressure at sea level, through which superhot, carbon-rich methane gas can be blown. Designed by co-author Won Kyung Seong, also of the Institute of Basic Sciences, this 2.4-gallon (9-liter) chamber can be set up for experimentation in just 15 minutes, allowing the team to quickly undertake experiments with different concentrations of metals and gases.
Through such a setup, the researchers found that a mixture of gallium-nickel-iron—combined with a pinch of silicon—was optimal for catalyzing the growth of diamonds. Indeed, with this mixture, the team obtained diamonds from the base of the crucible after only 15 minutes. Within two and a half hours, a fuller diamond film is formed. Spectroscopic analyzes show that this film is largely pure but contains a few silicon atoms.
The details of the mechanism that forms the diamonds are still largely unclear, but the researchers believe that the drop in temperature pushes carbon from the methane toward the center of the crucible, where it fuses into diamond. Plus, diamonds don’t form without silicon, so the researchers think it could act as a seed for carbon to crystallize.
However, the new method has its challenges. One problem is that diamonds grown with this technique are small; 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 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 can greatly increase diamond synthesis.
“In about a year or two, the world may have a clearer picture of things like possible trade impact,” he added.
