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Aug 14, 2023

Chinese 'breakthrough' allows making alloys with diverse metals at lower temps

ktsimage/iStock By subscribing, you agree to our Terms of Use and Policies You may unsubscribe at any time. Researchers at the College of Chemistry and Molecular Sciences at Wuhan University in China

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Researchers at the College of Chemistry and Molecular Sciences at Wuhan University in China have achieved a significant 'breakthrough' in materials science that allows alloys to be made from a diverse range of metals and at much lower temperatures than conventional methods, the South China Morning Post reported. The breakthrough involves nothing more than adding the metal gallium to the mix.

Since the Bronze Age, alloys have contributed to the advancement of our civilization. Modern-day applications of alloys involve creating and manufacturing high-entropy alloys (HEAs) composed of five or more metallic elements.

HEAs are highly resistant to wear and tear and have found applications in areas such as aerospace, energy conversion and storage, and medicinal equipment. However, creating HEA is an energy-intensive affair requiring temperatures of up to 3,632 Fahrenheit (2,000 degrees Celsius). However, this does not guarantee their formation since metallic atoms can be highly non-compatible.

Conventional methods of making HEAs involve heating the component elements to temperatures of about 3,000 Fahrenheit and then rapidly cooling them before mixing them. However, the approach does not work every time since the five elements can disagree with each other and split the alloy, much like a group of five people with different natures and personalities.

A research team led by Fu Lei, a Wuhan University professor, found that adding gallium to the alloy mix can reduce the preparation temperatures to as low as 1,200 Fahrenheit (650 Celsius).

Gallium has a melting temperature of just 85 Fahrenheit (~30 Celsius). This means that the metal will simply melt if held in the palm of your hand. However, the researchers used it as a reaction medium and adhesive in an alloy preparation and found some exciting results.

The scientific world has known about gallium for centuries, and its ability to return to its original form has even inspired science fiction of self-healing liquid metal in movies like Terminator. However, the discovery made by Fu and his team was too good to believe.

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In fact, the discovery was made two years ago but was not publicized since a scientific peer review could not be completed. Even reviewers from journals like Nature found the discovery unbelievable and wanted to see more proof of the process before accepting the manuscript.

The team then conducted additional experiments and calculations to aid a more rigorous explanation of the underlying mechanism. They also found that the alloys made using the approach were no different from the ones made using conventional methods.

The researchers now explain that heating compatible metals with gallium results in the spontaneous growth of crystalline HEA nanoparticles. They were also able to synthesize alloys with a diverse range of metals that conventional approaches failed to deliver.

This is not the first time researchers from China have been the first to advance materials science. Recently, another group of researchers from Tsinghua University demonstrated a liquid metal coating that could one day be used for soft robots.

High-entropy alloy nanoparticles (HEA-NPs) show great potential as functional materials1,2,3. However, thus far, the realized high-entropy alloys have been restricted to palettes of similar elements, which greatly hinders the material design, property optimization and mechanistic exploration for different applications4,5. Herein, we discovered that liquid metal endowing negative mixing enthalpy with other elements could provide a stable thermodynamic condition and act as a desirable dynamic mixing reservoir, thus realizing the synthesis of HEA-NPs with a diverse range of metal elements in mild reaction conditions. The involved elements have a wide range of atomic radii (1.24–1.97 Å) and melting points (303–3,683 K). We also realized the precisely fabricated structures of nanoparticles via mixing enthalpy tuning. Moreover, the real-time conversion process (that is, from liquid metal to crystalline HEA-NPs) is captured in situ, which confirmed a dynamic fission–fusion behaviour during the alloying process.