Natural and laboratory diamonds

Natural diamonds form in the Earth’s mantle, a molten region located hundreds of kilometers below the planet’s surface. The process takes place under enormous pressure of several gigapascals and scorching temperatures exceeding 1500 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 conditions to force carbon dissolved in liquid metals such as iron to grow into diamonds around a small seed, the starting diamond.

However, high pressures and temperatures are difficult to create and maintain, and the components involved affect the size of diamonds, the largest of which are about a cubic centimeter, or about the size of a blueberry. Additionally, HPHT takes quite a long time to produce even these small stones; a week or two.

Another method, called chemical vapor deposition, eliminates some of the requirements of HPHT, such as high pressure. But others, such as the initial need for diamonds, remain.

A new method

The innovative idea eliminates some of the disadvantages of both synthesis processes. A team led by Rodney Ruoff, a physical chemist at the South Korean Institute for Basic Sciences, described this in a paper in April.

The new method has been under development for a long time. “I have been thinking about new ways to grow diamonds for over a decade because I believe it can be achieved in unexpected (in terms of ‘conventional’ thinking) ways.”
said Ruoff.

To start, the researchers used electrically heated gallium along with a small amount of silicon in a graphite container. Gallium may seem like an exotic element, but it was chosen because previous work by other scientists showed that it could catalyze the formation of graphene from methane. Graphene is pure carbon, like diamond, but contains atoms in a single layer rather than in a tetrahedral orientation like gemstones.

The researchers placed the container in a homemade chamber with atmospheric pressure similar to atmospheric pressure at sea level, through which superheated, carbon-rich methane gas could flow. Designed by co-author Won Kyun Seon, also of the Institute of Basic Sciences, this 2.4-gallon (9-liter) chamber was ready for experiments in just 15 minutes, allowing the team to quickly conduct experiments with different concentrations of metals and gases. .

Thanks to this setup, the researchers found that the gallium-nickel-iron mixture (combined with a small piece of silicon) was best suited to catalyze the growth of diamonds. With this mixture The team retrieved the diamonds from the bottom of the container in just 15 minutes. A more complete diamond film was formed within two and a half hours. Spectroscopic analysis showed that this film was mostly pure but contained a few silicon atoms.

Diamonds made using new technology / Basic Sciences Photography Institute

The details of how diamonds form remain a mystery even to scientists, but researchers believe that the temperature difference pushes the carbon from the methane towards the center of the container, where it forms into diamonds (a process known as coalescence).

In addition, Diamonds cannot form without adding silicon to this process.Therefore, researchers believe it may serve as a seed for carbon crystallizing in its surroundings.

Cons

The new method isn’t perfect. The biggest problem is that diamonds grown using this method are very small; the largest are hundreds of thousands of times smaller than diamonds grown using HPHT. This makes them too small to be used as jewelry.

in its current form potential applications of such diamonds are unclear. But because the process involves low pressure, it can significantly increase the scale of synthesis, according to Ruoff.

Scientists are likely to continue refining their discoveries to achieve larger diamond sizes, but although they are considering commercializing the technology, they are not talking about it yet.