Inside a vacuum chamber, the researchers expose a drop of sodium-potassium alloy to a small amount of water vapor, which begins to condense on its surface. The electrons liberated from the alkali metal dissolve in the layer of water on the surface faster than the chemical reaction that results in the explosion. There are a sufficient number of them to overcome the critical limit for the formation of a conduction band and thus give rise to a metallic water solution.
Philip E. Mason, H. Christian Schewe, Tillmann Buttersack, Vojtech Kostal, Marco Vitek, Ryan S. McMullen, Hebatallah Ali, Florian Trinter, Chin Lee, Daniel M. Neumark, Stephan Thürmer, Robert Seidel, Bernd Winter, Stephen E. Bradforth, and Pavel Jungwirth. Spectroscopic evidence for a gold-coloured metallic water solution. Nature 2021.