Alkali Metals in Water – High Speed Photography


Alkali metals can react explosively with ​water and it is textbook knowledge that this vigorous behaviour results from heat release, steam formation and ignition of the ​hydrogen gas that is produced. Here we suggest that the initial process enabling the alkali metal explosion in ​water is, however, of a completely different nature. High-speed camera imaging of liquid drops of a ​sodium/potassium alloy in ​water reveals submillisecond formation of metal spikes that protrude from the surface of the drop. Molecular dynamics simulations demonstrate that on immersion in ​water there is an almost immediate release of electrons from the metal surface. The system thus quickly reaches the Rayleigh instability limit, which leads to a ‘coulomb explosion’ of the alkali metal drop. Consequently, a new metal surface in contact with ​water is formed, which explains why the reaction does not become self-quenched by its products, but can rather lead to explosive behaviour.

Text used with permission from Nature Chemistry

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