SSnowflakes and ice crystals are among the most beautiful phenomena of nature and show an almost inexhaustible variety of forms. They are formed from the water vapor in the clouds when the temperature is below zero, but they can also be produced in the laboratory with some effort. A similar variety of forms can be observed in zinc crystals when they are grown under special conditions in the laboratory.
Australian materials researchers describe their formula in the journal Science. Jianbo Tang from the University of New South Wales in Sydney and his colleagues first placed millimeter-sized zinc spheres in a bath of liquid gallium. The mixture was then heated to several hundred degrees for around three hours until the zinc melted. Thereafter, the liquid was slowly cooled. Micrometre-sized zinc crystals gradually grew in the liquid gallium over a period of one to ten days and pressures between one and for bar.
zinc crystals
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Surprise from the gallium bath
However, the zinc stars were initially not recognizable as such. They first had to be extracted from the liquid metal solution. To insulate the zinc crystals, the researchers applied a voltage. The electric field reduced the surface tension of the gallium that separated from the solid zinc crystals. The scientists then allowed the liquid gallium to drain through a nylon membrane – the crystals remained on the membrane.
The researchers saw flat hexagonal plates, stars of various sizes with finely branched structures and filigree crystal flowers. Thin rods, columns, cubes or hexagons and octahedrons could also be fished out of the gallium bath. .
The researchers obtained similar results when they dissolved tin, bismuth, silver, nickel, manganese, copper and platinum in liquid gallium. However, the metal crystals obtained are so tiny that they can only be made visible with an electron microscope. Therefore, they cannot be used as Christmas decorations. Rather, the work of the researchers opens up new possibilities for specifically growing metallic nanoparticles with different shapes. These could be used as catalysts or electrode material in batteries.