Under the right pressure and very little heat, a substance found in fossil fuels can be converted into pure diamonds.

It sounds like alchemy: take a cloud of white dust, squeeze it into a pressure chamber studded with diamonds, and explode it with a laser. I opened the room and found a new microscopic spot of pure diamond inside.

Yu Lin showed diamond-like carbon models with one, two and three cages, which can be transformed into complex pure carbon diamond lattices when subjected to extreme heat and pressure (see the larger blue model on the right) . (Image source: Andrew Broadhead)

A new study by Stanford University and the SLAC National Accelerator Laboratory reveals how this formula can produce diamonds from a type of hydrogen and carbon molecules found in crude oil and natural gas by carefully adjusting heat and pressure.

"The exciting thing about this paper is that it demonstrates a way to deceive the thermodynamics normally required to form diamonds," said Stanford geologist Rodney Ewing, a co-author of the paper, which was published on February 21 "Science Progress" magazine.

For more than 60 years, scientists have used other materials to synthesize diamonds, but this transformation usually requires too much energy, time or the addition of catalysts (usually metals), which often reduces the quality of the final product. The lead author of the study, Stanford University School of Earth, Energy and Environmental Sciences (Stanford Earth).

Understanding the mechanism of this transformation is very important for applications other than jewelry. The physical properties of diamond-extremely high hardness, optical transparency, chemical stability, and high thermal conductivity-make it a valuable material for medicine, industry, quantum computing technology and biosensing.

Yu Lin, senior scientist and research author at SLAC Stanford Institute of Materials and Energy Sciences (SIMES), said: "If you can produce even a small amount of this pure diamond, then you can dope it in a controlled manner for specific applications. ." National Accelerator Laboratory.

Natural diamonds are crystallized from carbon hundreds of miles below the surface of the earth, where temperatures reach thousands of degrees Fahrenheit. So far, most of the unearthed natural diamonds have soared in volcanic eruptions millions of years ago, carrying ancient minerals from deep inside the earth.

After squeezing the diamond samples and blasting them with a laser, the researchers used a second, cooler laser beam to help characterize the resulting diamonds. (Image source: Andrew Broadhead)

Therefore, diamonds can give us an in-depth understanding of the conditions and materials that exist inside the earth. "A diamond is a container that brings back samples from the deepest part of the earth," said Wendy Mao, a Stanford mineral physicist who led the laboratory where Parker conducted most of the research experiments.

In order to synthesize diamonds, the research team first extracted three powders from a tanker full of oil. "This is a very small number," Mao said. "We use a needle to pick a little bit and place it under the microscope for experiments."

At first glance, these odorless, slightly sticky powders resemble rock salt. But a trained eye can distinguish atoms arranged in the same spatial pattern as the atoms that make up a diamond crystal through powerful microscope observation. It is as if the intricate lattice of diamonds is cut into smaller units, consisting of one, two or three cages.

Unlike pure carbon diamond, this powder called diamond-like carbon also contains hydrogen. "Start with these building blocks," Mao said, "you can make diamonds faster and easier, and you can understand the process in a more complete and thoughtful way, instead of just imitating the high pressure and high temperature found in diamonds. The part of the earth that naturally forms diamonds."

The researchers put the diamond-like carbon sample into a plum-sized pressure chamber, called a diamond anvil, to press the powder between two polished diamonds. By simply turning the screw by hand, the device can generate the kind of pressure you might find in the center of the earth.

Next, they heated the sample with a laser, checked the results with a series of tests, and ran a computer model to help explain how the transformation unfolded. "A basic question we are trying to answer is whether the structure or number of cages will affect how diamond-like carbon is converted into diamonds," Lin said. They found that the three-cage diamond-like diamond called triamantane can recombine itself into diamonds with surprisingly low energy.

At 900 Kelvin (approximately 1160 degrees Fahrenheit, or the temperature of hot lava) and 20 gigapascals (hundreds of thousands of times greater than the Earth’s atmospheric pressure), the carbon atoms of triamantane align, and its hydrogen scatters or falls off.

The transformation unfolded in the smallest fraction of a second. This is also straightforward: atoms do not pass through another form of carbon, such as graphite, in the process of making diamonds.

Mao said that the tiny sample size inside the diamond anvil makes this method impractical when synthesizing far more diamond spots than the Stanford University team produced in the laboratory. "But now we have a better understanding of the key to making pure diamonds."

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Wendy Mao is a professor of geological sciences and photonic sciences. Rodney Ewing is the Frank Stanton Professor of Nuclear Safety and a senior researcher at the Freeman Spoli Institute of International Studies and the Precourt Institute of Energy.

Co-authors at Stanford University include Iwnetim Abate, Jin Liu, Chenxu Wang, Jeremy Dahl, Robert Carlson, Thomas Devereaux, and Chunjing Jia. Abate and Devereaux are affiliated with SIMES of the SLAC National Accelerator Laboratory and the Department of Materials Science and Engineering. Liu is affiliated with the Department of Geological Sciences of Stanford University and the Advanced Research Center for High Pressure Science and Technology in Beijing, China. Mr. Wang belongs to the Department of Geological Sciences. Dahl, Carlson and Jia belong to SIMES.

The other co-authors belong to the Advanced Research Center for High Voltage Science and Technology in Beijing, China and the Advanced Radiation Source Center of the University of Chicago.

The research was funded by the U.S. Department of Energy.

Josie Garthwaite, School of Earth, Energy and Environmental Sciences, josieg@stanford.edu, 650-497-0947

Wendy Mao, School of Earth, Energy and Environmental Sciences, wmao@stanford.edu

Sulgiye Park, School of Earth, Energy and Environmental Sciences, sulgiye@stanford.edu

Yu Lin, SLAC National Accelerator Laboratory, lyforest@stanford.edu

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