Formation of microbeads during vapor explosions of Field's metal in water

We use high-speed video imaging to investigate vapor explosions during the impact of a molten Field's metal drop onto a pool of water. These explosions occur for temperatures above the Leidenfrost temperature and are observed to occur in up to three stages as the metal temperature is increased, with each explosion being more powerful that the preceding one. The Field's metal drop breaks up into numerous microbeads with an exponential size distribution, in contrast to tin droplets where the vapor explosion deforms the metal to form porous solid structures. We compare the characteristic bead size to the wavelength of the fastest growing mode of the Rayleigh-Taylor instability.

Figure 1

Schematic showing the experimental setup.

Figure 2

Images used for determining the surface tension of Field's metal, using the pendent drop method. Left shows the start of the fall, with near-vertical sides and the right side the pinch-off instant 56 ms later. The scale bar is 1 mm long.

Figure 3

Comparison between nucleate boiling for a $350{}^{\circ }\mathrm{C}$ Field's metal drop (top) and vapor explosion for a $400{}^{\circ }\mathrm{C}$ Field's metal drop (bottom), falling into a pool of water. See also Supplemental Videos SV2 and SV3 [36].

Figure 4

Vapor explosion of a $550{}^{\circ }\mathrm{C}$ Field's metal drop falling into $22{}^{\circ }\mathrm{C}$ deionized water. See also Supplemental Video SV6 [36]. The circled numbers indicate the different vapor explosions.

Figure 5

Porous debris resulting from the vapor explosion of tin.

Figure 6

Solidified debris resulting from the vapor explosion of Field's metal.

Figure 7

Transition temperature of tin and Field's metal droplets from nucleate boiling to vapor explosions while impacting a pool of deionized water.

Figure 8

Most unstable Rayleigh-Taylor wavelength on the water-vapor interface from Eq. (1), as a function of the temperature of the Field's metal. Determined with accelerations from videos such as in  [36]. The right axis shows the total number of beads produced in each explosion.

Figure 9

The normalized size distribution of the diameter of the spherical Field's metal debris, following vapor explosion in water, for different metal temperatures. (a) Field's metal at 400 and $450{}^{\circ }\mathrm{C}$; (b) Field's metal at 500 and $550{}^{\circ }\mathrm{C}$. Solid lines represent fit for exponential distributions.