Ultrasonic cavitation of molten gallium: formation of micro- and nano-spheres

Pure gallium has a low melting point (29.8°C) and can be melted in warm water or organic liquids, thus forming two immiscible liquid phases. Irradiation of this system with ultrasonic energy causes cavitation and dispersion of the molten gallium as microscopic spheres. The resultant spheres were found to have radii range of 0.2-5 μm and they do not coalesce upon cessation of irradiation, although the ambient temperature is well above the m.p. of gallium. It was found that the spheres formed in water are covered with crystallites of GaO(OH), whereas those formed in organic liquids (hexane and n-dodecane) are smooth, lacking such crystallites. However, Raman spectroscopy revealed that the spheres formed in organic liquids are coated with a carbon film. The latter may be the factor preventing their coalescence at temperatures above the m.p. of gallium.