Scientists have developed a new method to synthesize diamonds at atmospheric pressure without the need for a starter diamond. This breakthrough could simplify the production of these precious gems in the lab.
The diamonds produced by this new technique are largely pure but too small to be set in jewelry.
Credit: Institute for Basic Science
Natural diamonds form in the Earth's mantle under enormous pressures and extremely high temperatures. Currently, most synthetic diamonds are produced using the HPHT (high-pressure high-temperature) method, which mimics these extreme conditions. However, this technique is expensive and requires complex equipment.
Another method, known as chemical vapor deposition (CVD), avoids some of the constraints of HPHT but still requires a diamond seed.
The new technique, developed by a team led by Rodney Ruoff from the Institute for Basic Science in South Korea, overcomes these obstacles. The results were published in the journal
Nature.
The diamond crucible
This innovative method uses gallium heated with a bit of silicon in a graphite crucible. Gallium was chosen because it can catalyze the formation of graphene, a form of pure carbon. The crucible is placed in a chamber maintained at atmospheric pressure, through which a carbon-rich methane gas is injected. This chamber, designed by Won Kyung Seong, allows for quick tests with different concentrations of metals and gases.
The researchers found that a mixture of gallium, nickel, and iron with a pinch of silicon was ideal for catalyzing diamond growth. In just 15 minutes, diamonds form at the bottom of the crucible. In two and a half hours, a more complete diamond film appears. Analyses showed that this film is largely pure, with a few silicon atoms.
The exact mechanism remains to be elucidated, but it seems that a drop in temperature drives the carbon from the methane to the center of the crucible, where it crystallizes into diamond. Silicon likely acts as a seed for this crystallization.
However, this new method produces very small diamonds, much smaller than those obtained by HPHT. They are, therefore, too small to be used as jewelry. Potential applications in technological fields such as polishing and drilling remain to be explored. Nonetheless, this ambient pressure technique could significantly increase diamond production in the future. Rodney Ruoff estimates that within one or two years, we will have a better idea of the possible commercial impacts.