José Manuel Torralba, IMDEA MATERIALS

A diamond awakens a world of suggestions that can lead us, depending on our age, to a cabaret in Paris where Marilyn Monroe declares to the world that they are “a girl’s best friend” (Gentlemen Prefer Blondes, Howard Hawks, 1953); to New York’s Fifth Avenue, in front of Tiffany’s, through the drowsy image of Audrey Hepburn (Breakfast at Tiffany’s, 1961, Blake Edwards); to the Sierra Leone Mines (Blood Diamond, Edward Zwick, 2006); or to Antwerp’s diamond district (Rough Diamonds, Rotem Shamir and Yuval Yefet, 2023).

They represent a dream. It is no coincidence that they are the most expensive material that can be used to make jewelry, far surpassing gold.

Light years ahead of the value of gold

Diamonds and gold are a safe haven in the markets (their price rarely drops). A small 5-carat diamond (1 gram) can cost more than 60,000 euros (and no less than 10,000), while 1 gram of pure gold (24 karats) is worth no more than 90 euros. But we are talking about natural diamonds. For economic reasons, the growth of most synthetic diamonds is interrupted when they reach a mass of 1 carat (200 mg) to 1.5 carats (300 mg).

So scientific news related to such “brilliant” topics as diamonds raises many expectations. A recent work, published in Nature, develops a new method for making diamonds that does not require applying extreme pressure. And it is an important breakthrough.

Will we have more and better artificial diamonds? Will the price of diamonds drop dramatically? It is possible that in a few years (not too few) this could happen.

Less than 500 euros per gram in the laboratory

Artificial or synthetic diamonds have been a reality for decades and can now be made at a cost of less than 500 euros per gram. They are still a “costly” raw material, but new technologies are driving the price down. They are chemically very similar, and although their physical properties are not the same, only an expert jeweler/gemologist can tell them apart.

The French chemist Antoine-Laurent de Lavoisier discovered in 1772, by burning diamonds with sunlight, that they are made of carbon. Thus began the first attempts to reproduce nature’s work (turning carbon into diamond) in a laboratory. It was not until 1954 that General Electric’s laboratories in the U.S. succeeded.

At that time, they defined the pressure and temperature zones in which diamond growth occurs from various metals. And they converted graphite into diamond. From that moment on, there has always been greater production of artificial diamonds than natural diamonds in the market.

How they are made

There are two preferred technologies for making artificial diamonds.

The first one, in a certain way, reproduces how nature makes diamonds: high-pressure and high-temperature techniques (HPHT, high pressure-high temperature).

These technologies subject graphite simultaneously to pressure and temperature conditions where diamond is thermodynamically more stable than graphite. Pressures above 5 GPa and temperatures above 1,500⁰ C are required. From the 1950s to the present, different methods have been developed to achieve these conditions.

The second technology involves chemical vapor deposition (CVD) techniques. For this technology, a “seed” (also diamond) that is well-oriented crystallographically is needed, over which a carbon-rich gas (usually a mixture of methane and hydrogen) is circulated at relatively low pressures (around 27 kPa) to “grow” the diamond by chemical deposition.

What we gain with the new technique published

Diamonds have been made without applying pressure for decades. So, what does the new development published in Nature bring to the table?

The main novelty is that the medium used to grow a diamond seed is not a carbon-rich gas, but a liquid metal.

The diamond growth occurs at atmospheric pressure and the temperature of the liquid metal (which can be indium, tin, lead, mercury, or bismuth, all below lead’s “high” 327º C). These metals act as solvents but also as catalysts. Small amounts of gallium, nickel, iron, or silicon can help in the formation of diamonds.

The ecological dilemma of lab diamonds

Lab-grown diamonds are not guilt free. Making them consumes a very high amount of energy; they are not precisely ecological and sustainable. It is here, in this dilemma, where the new development could be an interesting advance, as it may have a better energy balance and could be one of its advantages, given that its manufacturing temperature is much lower than that required by conventional techniques.

The new technology paves the way for cheaper and less environmentally damaging lab-grown diamonds in their manufacturing process. It remains to be seen whether, without a natural origin, they will awaken that world of suggestions that multiplies their value in a luxury jewelry store.

José Manuel Torralba, Professor at the Universidad Carlos III de Madrid, IMDEA MATERIALES

This article was originally published in The Conversation. Read the original (content in Spanish).