Pure water is almost a perfect insulator, although water found in nature conducts electricity due to the impurities present in it, which dissolve into free ions and allow the electric current to flow. However, researchers have recently demonstrated that the metallicity of pure water can be induced not only by high
pressures but also by bringing it into contact with an electron-sharing alkali metal like an alloy of sodium and potassium.
When pure water comes into contact with an electron-sharing alkali metal, free-moving charged particles are added, and water turns metallic. This conductivity lsasts only for a few seconds, but it is a significant step towards understanding this phase of water by studying it directly.
Researchers have generated pressures exceeding 48 megabars, which is around 48 million times Earth’s atmospheric pressure at sea level, in a laboratory setting. However, such experiments would be unsuitable for studying metallic water. Therefore, a team of researchers led by organic chemist Pavel Jungwirth of the Czech Academy of Sciences in Czechia turned to alkali metals, which release their outer electrons very easily, and induce the electron-sharing properties of highly pressurized pure water without the high pressures.
The only problem is that alkali metals are highly reactive with liquid water, sometimes even to the point of explosivity. Therefore, the research team found a very nifty way to solve this problem: water was added to the metal instead of adding the metal to water.
The team extruded a small blob of sodium-potassium alloy, which is liquid at room temperature, from a nozzle in a vacuum chamber, and very carefully added a thin film of pure water using vapor deposition. Upon contact, the metal cations and electrons flowed into the water from the alloy, giving the water a golden shine and turning it conductive, just like we should see in metallic pure water at high pressure.
This was confirmed using optical reflection spectroscopy and synchrotron X-ray photoelectron spectroscopy. The two properties, the golden sheen, and the conductive band, occupied two different frequency ranges, which allowed them both to be identified clearly.
This research not only gives us a better understanding of this phase transition on Earth, but it could also allow us to study the extreme high-pressure conditions inside large planets, such as Neptune and Uranus, where liquid metallic hydrogen is thought to swirl. Furthermore, it is only Jupiter where pressures are believed to be high enough to metallicize pure water.
The prospect of being able to replicate the conditions inside our Solar System’s planetary colossus is exciting indeed. According to physicist Robert Seidel from Helmholtz-Zentrum Berlin für Materialien und Energie in Germany, “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.”
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References:
1. Mason, P.E., Schewe, H.C., Buttersack, T. et al. Spectroscopic evidence for a gold-coloured metallic water solution. Nature 595, 673–676 (2021). https://doi.org/10.1038/s41586-021-03646-5
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4. Cavazzoni, C. et al. Superionic and metallic states of water and ammonia at giant planet conditions. Science 283, 44–46 (1999).
5. Mattsson, T. R. & Desjarlais, M. P. Phase diagram and electrical conductivity of high energy-density water from density functional theory. Phys. Rev. Lett. 97, 017801 (2006).
