Pure water is an almost perfect insulator.
Yes, water found in nature conducts electricity, but that is because of the impurities in it, which dissolve into free ions that allow electrical current to flow. Pure water becomes “mineral” – electronically conductive – only at extremely high pressures, beyond our current laboratory production capabilities.
But, as researchers demonstrated for the first time in 2021, it's not just high pressures that can stimulate this mineral in pure water.
By bringing pure water into contact with an electron-sharing alkali metal – in this case an alloy of sodium and potassium – free-moving charged particles can be added, turning the water into a metal.
The resulting conductivity only lasts for a few seconds, but it is an important step toward being able to understand this phase of water by studying it directly.
“You can see the transition stage to mineral water with the naked eye!” Physicist Robert Seidel of the Helmholtz Berlin Center for Materials and Energy in Germany to explain In 2021 when the research was published.
“The silver sodium-potassium droplet covers itself with a golden glow, which is very impressive.”
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Under high enough pressures, almost any material can theoretically become a conductor.
The idea is that if you squeeze the atoms together tightly enough, the orbitals of the outermost electrons will begin to overlap, allowing them to move. For water, this pressure is about 48 megabars, just under 48 million times Earth's atmospheric pressure at sea level.
While pressures exceeding this have been generated in a laboratory setting, such experiments would not be suitable for studying mineral waters. So a team of researchers led by organic chemist Pavel Jungwirth of the Czech Academy of Sciences in the Czech Republic turned to alkali metals.
These materials release their outermost electrons very easily, which means they can induce the electron-sharing properties of pure, high-pressure water without the need for high pressures.
There's just one problem: Alkaline metals react dramatically with liquid water, sometimes to the point of exploding (there are… Really cool video below).
Drop the metal into the water and you get kaboom.
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The research team found a very cool way to solve this problem. What if water was added to the metal instead of the metal adding to the water?
In a vacuum chamber, the team began by ejecting a small drop of a sodium-potassium alloy from a nozzle, which is a liquid at room temperature, and then very carefully added a thin layer of pure water using vapor deposition.
Upon contact, electrons and metal cations (positively charged ions) flowed into the water from the alloy.
This not only gave the water a golden sheen, but made the water conductive – just as we should see in pure mineral water at high pressure.
This was confirmed using optical reflectance spectroscopy and synchrotron X-ray spectroscopy.
The two features – the golden luster and the conductive strip – occupy two different frequency bands, which allowed them to be clearly identified.
In addition to giving us a better understanding of this phase transition here on Earth, the research could also allow for a closer study of the extreme high-pressure conditions inside large planets.
In the solar system's icy planets, Neptune and Uranus, for example, liquid metallic hydrogen is thought to swirl around. Jupiter is the only planet where pressures are believed to be high enough to mineralize pure water.
The prospect of being able to replicate the conditions inside a giant planet in our solar system is truly exciting.
“Our study not only shows that mineral water can indeed be produced on Earth, but also characterizes the spectral properties associated with its beautiful golden metallic luster.” Seidel said.
The research was published in nature.
A previous version of this article was published in July 2021.
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