What happens inside planets like Neptune and Uranus? And what do these planets have to do with getting nanodiamonds out of plastic bottles?

To find out the answer to the first question, an international team led by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and the University of Rostock, both in Germany, and École Polytechnique, in France, conducted a new experiment.

The researchers laser bombarded a thin film of plain PET plastic and investigated what happened using intense laser pulses.

Nanodiamonds from plastic bottles

One result was that the researchers were able to confirm their previous thesis that it is indeed raining diamonds inside the ice giants on the outskirts of our solar system.

Another result was that this method could establish a new way to produce nanodiamonds from plastic bottles, which are needed, for example, for highly sensitive quantum sensors.

The group presented their findings in the journal Science Advances.

Conditions on other planets, simulated in the laboratory

The conditions inside the giant ice planets like Neptune and Uranus are extreme: temperatures reach several thousand degrees Celsius and the pressure is millions of times higher than in the Earth’s atmosphere.

However, such states can be simulated for short periods of time in the laboratory: powerful laser pulses strike a sample of film-like material, heat it up to 6,000 degrees Celsius for a fraction of a second, and generate a shock wave which compresses material for a few nanoseconds to a pressure a million times that of the Earth’s atmosphere.

“Until now, we have used hydrocarbon films for this type of experiment. And we discovered that this extreme pressure produced tiny diamonds, known as nanodiamonds,” explains Dominik Kraus, physicist at HZDR and professor at the University of Rostock.

However, using these films, it was only partially possible to simulate the interior of the planets, because the ice giants contain not only carbon and hydrogen, but also large amounts of oxygen. When searching for the right material for the film, the group came across an everyday substance: PET, the resin from which common plastic bottles are made.

How were nanodiamonds obtained from plastic bottles?

“PET has a good balance of carbon, hydrogen and oxygen to simulate activity on ice planets,” explains Kraus.

The team conducted their experiments at the SLAC National Accelerator Laboratory in California, the site of the Linac Coherent Light Source (LCLS), a powerful accelerator-based X-ray laser.

The scientists used this laser to analyze what happens when intense laser pulses hit a PET film, using two measurement methods at the same time: X-ray diffraction to determine whether nanodiamonds were produced from plastic bottles and so -called low angle scattering to see how fast and how big the diamonds grew.

“The effect of oxygen was to accelerate the splitting of carbon and hydrogen and thus encourage the formation of nanodiamonds. It meant that carbon atoms could combine more easily to form diamonds,” says Dominik Kraus.

Diamond showers, much more common than thought

The result further supports the assumption that it is literally raining diamonds inside the ice giants. The findings are likely relevant not only to Uranus and Neptune, but also to countless other planets in our galaxy. While such ice giants were once considered rarities, it now seems clear that they are probably the most common form of planet outside the Solar System. Tech Xplore.

The team also encountered clues of another kind: in combination with the diamonds, water should be produced, but in an unusual variant.

“So-called superionic water may have formed. The oxygen atoms form a crystalline lattice in which the hydrogen nuclei move freely,” says the researcher.

Because the nuclei are electrically charged, superionic water can conduct electricity and thus help create the magnetic field of the ice giants.

In their experiments, the research group has not yet been able to unequivocally demonstrate the existence of superionic water mixed with diamonds. This is planned to happen in close collaboration with the University of Rostock at the European XFEL in Hamburg, the world’s most powerful X-ray laser. There, HZDR leads the international user consortium HIBEF, which provides ideal conditions for experiments of this kind.

What can this nanodiamonds be used for?

In addition to this rather fundamental knowledge, the new experiment also opens up perspectives for a technical application: the customized production of nanometer-sized diamonds, which are already included in abrasives and polishing agents.

In the future, they are expected to be used as highly sensitive quantum sensors, medical contrast agents and efficient reaction accelerators, for splitting CO2, for example.

“Until now, diamonds of this kind have been produced mainly by detonating explosives. With the help of laser pulses, they could be manufactured much cleaner in the future,” explains Kraus.

A clear advantage

A high-performance laser fires ten pulses per second at a PET film, which is illuminated by the beam at tenth-second intervals. The nanodiamonds thus created emerge from the film and land in a collection tank filled with water.

There they are decelerated and can then be efficiently filtered and harvested. The key advantage of this method, as opposed to explosive production, is that “nanodiamonds could be custom cut to size or even doped with other atoms,” says Dominik Kraus.

“The X-ray laser means we have a laboratory tool that can precisely control diamond growth,” the researcher concluded.

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