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An experiment suggested by a Ph.D. student may rewrite chemistry textbooks:
The project looked at a fundamental question: Which properties are inherent to a metal and which are incidental?
[...] The scientists cooled ammonia—normally a gas at room temperature—to minus 33 C to liquify it and then added, in separate experiments, the alkali metals lithium, sodium and potassium.
In these solutions, electrons from the alkali metal initially become trapped in the gaps between ammonia molecules. This creates what scientists call 'solvated electrons,' which are highly reactive but stabilized in the ammonia. These solutions have a characteristic blue color. But given enough solvated electrons, the whole liquid turns bronze and, in essence, becomes a metal while remaining liquid.
[...] The scientists next measured the amount of energy needed to bump the solvated electrons out of metallic ammonia using an extremely bright and focused X-ray beam based in Berlin.
In a first-ever experiment, they forced different concentrations of the metallic ammonia through a microjet, which created a stream about the width of a human hair that then passed through a hair-thin X-ray beam.
The results showed that, at low concentrations, solvated electrons were more easily dislodged from the solution by the interaction with the X-rays, giving a simple energy pattern. At higher concentrations, though, the energy pattern suddenly developed a sharp band edge, indicating the solution was behaving as a metal would.
Journal Reference:
Tillmann Buttersack, Philip E. Mason, Ryan S. McMullen, et al. Photoelectron spectra of alkali metal–ammonia microjets: From blue electrolyte to bronze metal [$], Science (DOI: 10.1126/science.aaz7607)
(Score: 2) by c0lo on Thursday June 25 2020, @11:18PM
May be true**, but in human perception/reaction time scale, the time from the first water contact 'til the final pop is as good as instantaneous. So, better piss on an alkali alloy T-1000 from a safe distance.
** the evolution of those tendrils, may not happen outside the narrow range of low temperature + saturating vapors of ammonia. The reaction of alkali with water is highly exothermic, to the point in which I suspect a chaotically oscillating boundary layer of water vapors+ hydrogen forms at the contact between the alkali and water (fast reaction => heat + the vapours layer => reaction starved of water and slowing => dissipation of the gaseous layer and back where we started but at a higher temperature; all at a max speed of the speed of sound in water).
Now, the heat developed by the reaction would surely melt away any tendrils so fast that I don't think they will have time to actually form. This said, there may be a mechanism involved in increasing the reaction area - the temperature and the variations in pressure are likely to cause expulsion of alkaly droplets from the metal surface into the water. Something similar with burning phosphorus in air [youtu.be].
https://www.youtube.com/watch?v=aoFiw2jMy-0