(Credit: Philip E. Mason)
Natural water conducts electricity because the impurities dissolve into free ions that allow an electric current to flow. However, it can become “metallic” (or electronically conductive) only at extremely high pressures, beyond what’s currently possible in a lab.
On the other hand, distilled water is a near-perfect insulator because it’s made of loosely-linked H2O molecules connected by hydrogen bonds, with valence electrons that remain bound.
The immobile electrons are key. To make a conduction band with freely moving electrons like in natural water, the liquid would have to be pressurized to such an extreme that the orbitals of the outer electrons overlap. Such pressure is present only in the core of giant planets like Jupiter.
But now, an international team of 15 scientists from 11 research institutions found another way to produce an aqueous solution with metallic properties. The phase transition involves alkali metals since they release their outer electron very easily. The experiments demonstrate for the first time that high pressures aren’t the only thing that can induce metallicity in pure water.
This study brought pure water into contact with the electron-sharing alkali metal – an alloy of sodium and potassium (Na-K) – to add free-moving charged particles and turn water metallic. The resulting conductivity is a significant step towards understanding this phase of water by allowing scientists to study it directly.
Physicist Robert Seidel of Germany’s Helmholtz-Zentrum Berlin für Materialien und Energie, said:
You can see the phase transition to metallic water with the naked eye! The silvery sodium-potassium droplet covers itself with a golden glow, which is very impressive.
Theoretically, practically any material could become conductive under high enough pressures. It goes to say that if you squeeze the material’s atoms together tightly enough, their outer electrons’ orbitals will start to overlap, allowing them to move. This pressure is around 48 megabars for water, just under 48 million times Earth’s atmospheric pressure at sea level.
Since alkali metals release their outer electrons easily, they also exhibit electron-sharing properties of highly pressurized pure water, minus the high pressures. However, they’re also very explosive when mixed with water and immediately start to burn on contact. You can see this in the video below.
To keep this violent chemistry in check, the team didn’t just throw a piece of alkali metal into water. Instead, they put a tiny bit of water on a drop of alkali metal.
In a vacuum chamber, they extruded a small blob of Na-K alloy from a nozzle and gently added a thin film of pure water using vapor deposition. Na-K alloy is liquid at room temperature. Upon contact, the electrons and positively charged ions (metal cations) flowed into the water from the alloy.
The thin layer of metallic water was shiny, gold-colored, and visible for a few seconds. Then, the team proved it was indeed metallic using synchrotron X-ray photoelectron spectroscopy and optical reflection spectroscopy. Plus, the water was conductive. The golden sheen and the conductive band are properties that occupy two different frequency ranges, so the team could identify both clearly.
Seidel said:
Our study not only shows that metallic water can indeed be produced on Earth but also characterizes the spectroscopic properties associated with its beautiful golden metallic luster.
This study can lead to a better understanding of this phase transition on Earth and provide a way for scientists to study extreme-high-pressure conditions within larger planets closely. For example, the Solar System’s ice planets Uranus and Neptune have swirls of liquid metallic hydrogen. And Jupiter may be the only planet with pressures high enough to metallicize pure water. So, the prospect of replicating such conditions here is exhilarating.
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August 09, 2021 at 03:35AM
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