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.
Subscribe to Journal
Get full journal access for 1 year
only $13.33 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Hutton, A. T. Dramatic demonstration for a large audience – the formation of hydroxyl ions in the reaction of sodium with water. J. Chem. Educ. 58, 506 (1981).
Carnevali, S., Proust, C. & Soucille, M. Unsteady aspects of sodium–water–air reaction. Chem. Eng. Res. Design 91, 633–639 (2013).
Krebs, R. E. The History and Use of Our Earth's Chemical Elements (Greenwood Press, 2006).
Commander, J. C. An explosive hazard analysis of the eutectic solution of NaK and KO2 . Nucl. Sci. Abstracts 32, 21922 (1975).
Mukasyan, A. S., Khina, B. B., Reeves, R. V. & Son, S. F. Mechanical activation and gasless explosion: nanostructural aspects. Chem. Eng. J. 174, 677–686 (2011).
Bernardin, J. D. & Mudawar, I. A cavity activation and bubble growth model of the Leidenfrost point. J. Heat Transfer 124, 864–874 (2002).
Grubelnik, A., Meyer, V. R., Buetzer, P. & Schoenenberger, U. W. Potassium metal is explosive – do not use it! J. Chem. Educ. 85, 634 (2008).
Alchagirov, B. B. et al. Surface tension and adsorption of components in the sodium–potassium alloy systems: effective liquid metal coolants promising in nuclear and space power engineering. Inorg. Mater. Appl. Res. 2, 461–467 (2011).
Buchanan, D. J. & Dullforc, T. A. Mechanism for vapor explosions. Nature 245, 32–34 (1973).
Gibson, G. E. & Argo, W. L. The absorption spectra of the blue solutions of certain alkali and alkaline earth metals in liquid ammonia and in methylamine. J. Am. Chem. Soc. 40, 1327–1361 (1918).
Hart, E. J. Research potentials of hydrated electron. Acc. Chem. Res. 2, 161–167 (1969).
Christensen, H. & Sehested, K. The hydrated electron and its reactions at high temperatures. J. Phys. Chem. 90, 186–190 (1986).
Vilchiz, V. H., Kloepfer, J. A., Germaine, A. C., Lenchenkov, V. A. & Bradforth, S. E. Map for the relaxation dynamics of hot photoelectrons injected into liquid water via anion threshold photodetachment and above threshold solvent ionization. J. Phys. Chem. A 105, 1711–1723 (2001).
Elkins, M. H., Williams, H. L., Shreve, A. T. & Neumark, D. M. Relaxation mechanism of the hydrated electron. Science 342, 1496–1499 (2013).
Mundy, C. J., Hutter, J. & Parrinello, M. Microsolvation and chemical reactivity of sodium and water clusters. J. Am. Chem. Soc. 122, 4837–4838 (2000).
Mercuri, F., Mundy, C. J. & Parrinello, M. Formation of a reactive intermediate in molecular beam chemistry of sodium and water. J. Phys. Chem. A 105, 8423–8427 (2001).
de la Mora, J. F. On the outcome of the coulombic fission of a charged isolated drop. J. Colloid Interface Sci. 178, 209–218 (1996).
Duft, D., Achtzehn, T., Muller, R., Huber, B. A. & Leisner, T. Coulomb fission – Rayleigh jets from levitated microdroplets. Nature 421, 128–128 (2003).
Echt, O., Scheier, P. & Mark, T. D. Multiply charged clusters. C. R. Phys. 3, 353–364 (2002).
Last, I., Levy, Y. & Jortner, J. Beyond the Rayleigh instability limit for multicharged finite systems: from fission to coulomb explosion. Proc. Natl Acad. Sci. USA 99, 9107–9112 (2002).
Rayleigh, L. On the equilibrium of liquid conducting masses charged with electricity. Phil. Mag. 14, 184–186 (1882).
Lebedev, R. V. Measurements of interphase surface-tension of sodium–potassium alloys. Izv. Vus. Fiz. 15, 155–158 (1972).
Yu, M. & Trinkle, D. R. Accurate and efficient algorithm for Bader charge integration. J. Chem. Phys. 134, 064111 (2011).
VandeVondele, J. & Hutter, J. Gaussian basis sets for accurate calculations on molecular systems in gas and condensed phases. J. Chem. Phys. 127, 114105 (2007).
Goedecker, S., Teter, M. & Hutter, J. Separable dual-space Gaussian pseudopotentials. Phys. Rev. B 54, 1703–1710 (1996).
Becke, A. D. Density-functional exchange-energy approximation with correct asymptotic-behavior. Phys. Rev. A 38, 3098–3100 (1988).
Lee, C. T., Yang, W. T. & Parr, R. G. Development of the Colle–Salvetti correlation-energy formula into a functional of the electron-density. Phys. Rev. B 37, 785–789 (1988).
Grimme, S., Antony, J., Ehrlich, S. & Krieg, H. A consistent and accurate ab initio parametrization of density functional dispersion correction (DFT-D) for the 94 elements H–Pu. J. Chem. Phys. 132, 154104 (2010).
Genovese, L., Deutsch, T., Neelov, A., Goedecker, S. & Beylkin, G. Efficient solution of Poisson's equation with free boundary conditions. J. Chem. Phys. 125, 074105 (2006).
VandeVondele, J. et al. QUICKSTEP Fast and accurate density functional calculations using a mixed Gaussian and plane waves approach. Comp. Phys. Commun. 167, 103–128 (2005).
Jorgensen, W. L. OPLS and OPLS-AA Parameters for Organic Molecules, Ions, and Nucleic Acids (Yale Univ. 1997).
Bhansali, A. P., Bayazitoglu, Y. & Maruyama, S. Molecular dynamics simulation of an evaporating sodium droplet. Int. J. Thermal Sci. 38, 66–74 (1999).
Berendsen, H. J. C., Grigera, J. R. & Straatsma, T. P. The missing term in effective pair potentials. J. Phys. Chem. 91, 6269–6271 (1987).
Kastenholtz, M. A. & Hunenberger, P. H. Computation of methodology-independent solvation free energies from molecular simulations. II. The hydration free energy of the sodium cation. J. Chem. Phys. 124, 224501 (2006).
Krizek, T. et al. Electrophoretic mobilities of neutral analytes and electroosmotic flow markers in aqueous solutions of Hofmeister salts. Electrophoresis 35, 617–624 (2014).
Hess, B., Kutzner, C., van der Spoel, D. & Lindahl, E. GROMACS 4: algorithms for highly efficient, load-balanced, and scalable molecular simulation. J. Chem. Theor. Comput. 4, 435–447 (2008).
We thank J. Jiráček for boldly making his chemical laboratory available to us for the initial experiments in liquid ammonia. P.J. acknowledges the Czech Science Foundation (Grant P208/12/G016) for support and thanks the Academy of Sciences for the Praemium Academiae award. S.B. acknowledges support from the Deutsche Forschungsgemeinschaft (Grants BA 2176/3–2 and BA 2176/4–1). P.E.M. acknowledges support from the viewers of his YouTube popular science channel.
The authors declare no competing financial interests.
Supplementary information (PDF 344 kb)
Supplementary Movie 1 (MP4 7385 kb)
Supplementary Movie 2 (AVI 63560 kb)
Supplementary Movie 3 (AVI 20534 kb)
About this article
Cite this article
Mason, P., Uhlig, F., Vaněk, V. et al. Coulomb explosion during the early stages of the reaction of alkali metals with water. Nature Chem 7, 250–254 (2015). https://doi.org/10.1038/nchem.2161
Fire Safety Journal (2020)
Employing sodium hydroxide in desulfurization of the actual heavy crude oil: Theoretical optimization and experimental evaluation
Process Safety and Environmental Protection (2020)
Integrating Aesthetics Education into Chemistry Education: Students Perceive, Appreciate, Explore, and Create the Beauty of Chemistry in Scientific Photography Activity
Journal of Chemical Education (2020)
Journal of Nano Research (2020)
Materia Japan (2020)