SCIENCE: Scientists turn pure water into metal

It is true that water, which exists in the nat­ur­al world, con­ducts elec­tric­i­ty, but that is because impu­ri­ties con­tained in it dis­solve and become free ions, allow­ing cur­rent to flow. In order for pure water to become a “met­al” that con­ducts elec­tric­i­ty, ultra-high pres­sures that are impos­si­ble to man­u­fac­ture in a lab­o­ra­to­ry are required.

But high pres­sure isn’t the only thing that can induce such metal­lic­i­ty in pure water, as researchers first showed in 2021.

By bring­ing pure water into con­tact with an elec­tron-shar­ing alka­li met­al (here, an alloy of sodi­um and potas­si­um), free-mov­ing charged par­ti­cles can be added, met­al­liz­ing the water.

As a result, the con­duc­tiv­i­ty lasts only a few sec­onds, but direct­ly exam­in­ing this phase of water is an impor­tant step towards under­stand­ing it.

When the study was pub­lished last year, physi­cist Robert Sei­del of the Helmholtz Insti­tute for Mate­ri­als and Ener­gy in Berlin explained, “You can see the phase tran­si­tion to metal­lic water with the naked eye.”

“The droplets of sil­very sodi­um and potas­si­um are cov­ered with a gold­en glow, which is very impressive.”

Any mate­r­i­al can the­o­ret­i­cal­ly become a con­duc­tor if you apply enough pres­sure to it.

If you squeeze an atom too hard, the orbitals of the out­er elec­trons begin to over­lap, allow­ing the atom to move. For water, this pres­sure is about 48 megabars, or just under 48 mil­lion times the Earth­’s pres­sure at sea level.

High­er pres­sures occur in the lab­o­ra­to­ry, but are unsat­is­fac­to­ry for metal­lic water stud­ies. So a research team led by Pavel Jung­wirth, an organ­ic chemist at the Czech Acad­e­my of Sci­ences, turned to alka­li metals.

These mate­ri­als release their out­er elec­trons so eas­i­ly that elec­tron exchange can be induced with­out using high-pres­sure pure water.

The only prob­lem is that alka­li met­als are high­ly reac­tive with liq­uid water and can some­times explode.

When met­al falls into water, it makes a thud.

The research team has found a very inge­nious way to solve this prob­lem. Instead of adding met­al to water, why not add water to metal?

Inside the vac­u­um ves­sel, a lump of sodi­um-potas­si­um alloy, which is liq­uid at room tem­per­a­ture, was first extrud­ed through a noz­zle, and a thin film of pure water was care­ful­ly added by vapor deposition.

Upon con­tact, elec­trons and met­al cations (pos­i­tive­ly charged ions) flowed from the alloy into the water.

As a result, the water not only had a gold­en glow, but became as con­duc­tive as pure metal­lic water under high pressure.

This was also con­firmed by opti­cal reflectance spec­troscopy and syn­chro­tron radi­a­tion X‑ray pho­to­elec­tron spectroscopy.

The two prop­er­ties, the gold­en glow and the con­duc­tive band, were clear­ly dis­tin­guish­able because they occu­py two dif­fer­ent fre­quen­cy bands.

The study will not only improve our under­stand­ing of phase tran­si­tions on Earth, but also allow us to bet­ter under­stand the extreme high pres­sure con­di­tions inside large planets.

For exam­ple, the icy plan­ets of the Solar Sys­tem, Nep­tune and Uranus, are thought to have swirls of liq­uid metal­lic hydro­gen. And only Jupiter is thought to have enough pres­sure to met­al­lize pure water.

I am very excit­ed to be able to repro­duce the con­di­tions inside the plan­et Colos­sus in the solar system.

“This study not only proves that metal­lic water is pro­duced on Earth, but also reveals the spec­tro­scop­ic prop­er­ties asso­ci­at­ed with its beau­ti­ful gold­en metal­lic lus­ter,” says Seidel.