Pure water is an almost perfect insulator.
Yes, naturally occurring water conducts electricity – but the impurities in it dissolve into free ions that allow electricity to flow. Only pure water becomes a „metal” – electrically conductive – at very high pressures, beyond our current capabilities to produce them in a laboratory.
But, as researchers demonstrated for the first time in 2021, it's not just high pressures that can induce this metallicity in pure water.
By bringing pure water into contact with an electron-sharing alkali metal—in this case a mixture of sodium and potassium—the water can be turned into a metal, adding free-moving charged particles.
The resulting conductivity only lasts for a few seconds, but it is a significant step toward understanding this phase by directly studying it.
„We can see the phase change for metallic water with the naked eye!” Physicist Robert Seidel of the Helmholtz-Zentrum Berlin for Materials and Energy in Germany explained The study was published in 2021.
„The silver sodium-potassium droplet covers itself with a golden glow, which is very impressive.”
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Under sufficiently high pressures, any material can theoretically become conductive.
If you squeeze the atoms tight enough, the orbits of the outer electrons start to overlap, allowing them to move around. For water, this pressure is about 48 megabars – 48 million times lower than Earth's atmospheric pressure at sea level.
Even if pressures higher than this are generated in a laboratory setting, such tests would be inappropriate for testing metallurgical waters. So a team of researchers led by organic chemist Pavel Jungwirth of the Czech Academy of Sciences in the Czech Republic turned to the alkali metals.
These materials release their outer electrons very easily, meaning they can induce the electron-sharing properties of high-pressure pure water without high pressures.
There's just one problem: alkali metals are very reactive with liquid water, sometimes even to the point of explosion (there's Very nice video below)
Drop metal into water and you're going to get kaboom.
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The research team found a very nifty way to solve this problem. Instead of adding metal to water, what if water is added to the metal?
In a vacuum chamber, the team began by ejecting a small bubble of a sodium-potassium mixture, which is liquid at room temperature, from a nozzle, and very carefully added a thin film of pure water using vapor deposition.
Upon contact, electrons and metal cations (positively charged ions) flowed from the mixture into the water.
Not only did it give the water a golden sheen, but it also changed the water's conductivity – something we should see in metallic pure water at high pressure.
This was confirmed using optical reflectance spectroscopy and synchrotron X-ray photoelectron spectroscopy.
The two properties – the golden sheen and the conduction band – occupy two different frequency ranges, which allowed them to be clearly identified.
Not only will the research allow us to better understand this phase transition on Earth, but it will also allow us to closely examine the extreme high-pressure conditions inside the larger planets.
The solar system's ice planets, Neptune and Uranus, for example, are thought to revolve around liquid metallic hydrogen. Jupiter is the only planet thought to have enough pressure to metalize pure water.
The prospect of replicating conditions inside our own solar system's planet, Colossus, is truly exciting.
„Our study shows that metallic water can indeed be produced on Earth, but characterizes the spectral properties associated with its beautiful golden metallic luster.” Seidel said.
Published in Research Nature.
An earlier version of this article was published in July 2021.