It normally takes a billion years of high pressure inside the Earth's mantle to produce diamonds, but a synthetic variety takes only a quarter of an hour to make.
How Are Lab-Grown Diamonds Created?
Natural diamonds are produced deep inside the Earth's mantle, the zone of molten rocks buried hundreds of miles beneath the surface. The process of forming this gem occurs under extreme pressures of several gigapascals and tremendous temperatures that exceed 2,700 degrees Fahrenheit (1,500 degrees Celsius).
The same conditions are employed in the current method used to synthesize 99% of all artificially grown diamonds. Known as high-pressure and high-temperature (HPHT) growth, this process involves extreme settings to dissolve carbon in liquid metals, like iron, and transform it into a diamond around a small seed (starter diamond).
However, it is difficult to produce and maintain high pressures and temperatures. Additionally, the components used in making the synthetic diamonds affect their size, with the largest being almost as big as a blueberry.
Another concern is that HPHT takes a long time, about a week or two, to create the tiny gems. There is another technique, called chemical vapor deposition, which removes some HPHT requirements, such as high pressures. Still, other requirements persist, like the need for a starter seed.
READ ALSO : Aside From Pressure and Temperature, Small Electric Fields Found To Affect Diamond Formation
Novel Diamond-Growing Technique
In a recent experiment, a team of researchers designed a new technique that eliminates some drawbacks of HPHT and chemical vapor deposition. The details of their study are discussed in the paper "Growth of diamond in liquid metal at 1 atm pressure."
Led by physical chemist Rodney Ruoff from the Institute for Basic Science in South Korea, the team used electrically heated gallium with a small amount of silicon in a graphite crucible. While gallium may look like an esoteric element, it was chosen because a previous study revealed that it can catalyze the formation of graphene from methane.
The crucible was contained in a home-built chamber through which carbon-rich methane gas can be flushed. Designed by co-author Won Kyung Seong, the chamber measures 2.4 gallons (9 liters) and can be prepared for experimentation in only 15 minutes. This allows the researchers to undertake runs quickly with various concentrations of metals and gases.
It was discovered that a gallium-nickel-iron mixture, combined with a pinch of silicon, is optimal for catalyzing diamond growth. With this blend, the scientists obtained diamonds from the base of the crucible after only 15 minutes. In just two and a half hours, a more complete diamond film was created.
Spectroscopy analysis indicates that the film was largely pure since it still contained a few silicon atoms. The mechanism that created the diamonds is still largely murky.
However, the researchers believe that a temperature drop drives carbon from the methane toward the center of the crucible, where it unites into a diamond.
Without silicon, no diamond will be formed. This made researchers believe that silicon may act as a seed for the crystallization of carbon.
Still, the new method has its own challenges. First, the diamonds created with this technique are tiny, with the largest ones hundreds of thousands of times smaller than the ones produced with HPHT. This makes them too small to be used as jewels.
The synthesized diamonds can still have technological applications. Since the process involves low pressure, they can significantly scale up diamond synthesis.
Check out more news and information on Diamonds in Science Times.
