Absolutely metal: scientists capture footage of crystals growing in liquid metal

Researchers have successfully grown platinum crystals in liquid metal, using a powerful X-ray technique giving rare insight into how these delicate crystals form and grow.

More than a beautiful curiosity, liquid metal-grown crystals could be the key to creating new materials. They are potentially a vital ingredient in new technology being developed to extract hydrogen from water and in quantum computing applications.  

Published in Nature Communications, the University of Sydney led team used metallic crystals to build an electrode that can efficiently produce hydrogen from water.

Liquid metals like Gallium are curious elements. They shimmer on the surface like solid metals but can also be fluid. For instance, Gallium at room temperature resembles solid blocks of metal, but when warmed to body temperature it transforms into liquid metallic puddles.

“Witnessing the formation of crystals inside liquid metals like Gallium is a challenging task. Gallium is a very dense element whose atoms are tightly packed and is so opaque it is impossible for most microscopes to pass through a thick layer of Gallium. It was a really special moment to be able to develop a method to do this,” said Professor Kourosh Kalantar-Zadeh, from the School of Chemical and Biomolecular Engineering, University of Sydney, who led the research.

The team used X-ray computed tomography, equipment commonly used in medical imaging, to map internal organs.

The machinery revealed the internal details of the metallic crystals in 3D. It showed crystals blooming in liquid metal, revealing distinctive rod or frostlike structures developing over minutes and hours.

“To see how liquid metals can be harnessed to shape the future of smart materials and identify those that play important roles in energy sources, we need to understand their metallic and chemical properties, inside and out,” said Professor Kalantah-Zader.

“With X-ray computed tomography, we can now truly see what we are working with and design liquid metal grown crystals to grow more precisely.”

The contradictory nature of liquid metals, which contain both metallic and liquid properties, makes them desirable in the material science world. Researchers like Professor Kalantar- Zadeh have long eyed liquid metals as the future of industrial chemical processes. His research team specialises in pushing the chemical and technical boundaries of liquid metals to create new materials and ‘green’ catalysts, to make chemical reactions faster.    

“Liquid metals are also very good solvents, with a powerful ability to dissolve other metallic elements, like sugar in water,” said Professor Kalantah-Zader.  

Excess metallic elements form crystals, in the same way crystals form when there is too much sugar in water.

In this study, researchers dissolved platinum beads in Gallium or Gallium-indium liquid metal at 500 degrees Celsius, then cooled them to kickstart the crystal growing process.

X-ray computed tomography then imaged a droplet of the platinum and Gallium alloy (a material with two metals) in cross-sections, which were then stitched together to re-create a 3D image. This allowed the researchers to map the crystal formation process. While the platinum and Gallium alloy cooled, tiny crystal rods began to rapidly form.

“We observed with fascination how metallic particles of various crystal orientations grew inside liquid metals by changing the temperature and environmental conditions,” said study co-author PhD student Ms Moonika Widjajana.

“This study illustrated how X-ray computed tomography can overcome the challenge of observing crystal growth within liquid metal – an opaque material that is usually impossible to penetrate with light and electrons.” 

Current technology means the crystals observed can be imaged at low resolution only, but advancements in X-ray computed tomography mean researchers will soon be able to understand more about what happens when metallic crystals form.