The Elements of Innovation Discovered
The Elements of Innovation Discovered
Metal Tech News - September 2, 2024
Scientist discovers there is more to gallium's low melting point than what what was previously assumed.
Stephanie Lambie
Nicola Gaston
Gallium atoms begin to reform covalent bonds with increased temperatures.
As a metal that turns to liquid at near room temperature and has the uncanny ability to take on the catalytic properties of other metals, gallium is an enigmatic element that intrigues material scientists.
The understanding of why gallium melts at 85.6 degrees Fahrenheit (29.8 degrees Celsius), however, may have been built on a foundation as solid as this strange metal during the midday heat in the Sahara.
Nicola Gaston
"Thirty years of literature on the structure of liquid gallium has had a fundamental assumption that is evidently not true," said Nicola Gaston, professor at the University of Auckland and MacDiarmid Institute for Advanced Materials and Nanotechnology.
It has long been thought that gallium's low melting point had to do with a breaking of the metal's covalent bonds – a linkage between atoms due to the sharing of an electron between pairs of gallium atoms, a trait that is rare for metals.
When gallium turns to liquid, the bond between the pairs of atoms breaks. This led materials scientists to assume that gallium's very low melting point was due to the disappearance of the bonds at 85.6 F.
Stephanie Lambie
However, a recent investigation by Steph Lambie, a former University of Auckland PhD student and now a postdoctoral researcher at the Max-Planck Institute for Solid State Research in Germany, found that gallium atoms reform covalent bonds at higher temperatures.
"That is pretty much the opposite of what everybody always assumed," said Gaston.
This has material scientists rethinking gallium's liquid form and why this technology metal behaves so much differently than its periodic table neighbors, zinc and germanium.
"Fundamentally, when you go from one atom to the next on the periodic table, you are only changing the nuclear mass and charge, and you are adding an electron. You are not changing the structure very much," explained Gaston. "Atoms, individually, are all quite similar. What is fascinating, I think, in material science is when you start to put lots and lots of those atoms together, their interactions result in very complex structures and very strange behaviors, and a very strange range of behaviors as well."
Gallium has proven to have a broad range of strange behaviors that material scientists are leveraging for high-tech and clean energy applications-the best-known and most widely used of these properties is in semiconductors.
"The development of gallium arsenide as a direct band-gap semiconductor in the 1960s led to what are now some of the most well-known uses of gallium – in feature-rich, application-intensive, third- and fourth-generation smartphones and in data-centric networks," the U.S. Geological Survey penned in a 2018 report on critical minerals.
The most intriguing future-leaning uses of gallium leverage its liquid form to enhance the properties of other metals to create self-cleaning "super catalysts" capable of scrubbing carbon dioxide out of the atmosphere.
Traditionally, metals such as platinum, palladium, nickel, and tin have been used as catalysts for transforming molecular structures. These catalytic processes are used to create things like cheese, laundry detergent, and plastics. They are also used to break harmful molecules in exhaust into more benign elements or to produce hydrogen from water or natural gas.
Australian scientists have found that dissolving traditional catalysts in liquid gallium creates super catalysts that are sometimes 1,000 times more powerful than the catalytic metal in its solid form, while also requiring less energy.
"To keep the single atoms separated from each other, the conventional systems require solid matrices to stabilize them. I thought, why not use a liquid matrix instead and see what happens," said Arifur Rahim, a postdoctoral research fellow at the University of New South Wales.
This pondering led to combining the catalytic properties of platinum and the liquidity of gallium.
At a ratio of less than 0.0001 parts platinum to one part gallium, this new liquid metal alloy is 1,000 times more efficient than a solid-state catalyst with around 10% platinum.
The liquidity of the gallium-platinum alloy offers yet one more advantage – it is self-cleaning, much like a water fountain, which adds to its efficiency and longevity.
Adding to gallium's strangeness, the liquid metal seems to take on the catalytic abilities of the metals it is hosting.
"The platinum is actually a little bit below the surface and it's activating the gallium atoms around it," said Andrew Christofferson, an Exciton Science associate investigator who worked on the project. "So, the magic is happening on the gallium under the influence of the platinum. But without the platinum there, it doesn't happen."
Australian material scientists have found similar effects with silver nanorods, nickel, and tin dissolved in a liquid gallium matrix.
"By dissolving nickel in liquid gallium, we gained access to liquid nickel at very low temperatures – acting as a super' catalyst," said Junma Tang, a postdoctoral researcher at the University of New South Wales.
The researchers expect that gallium could be mixed with other metals to create low-temperature catalysts capable of scrubbing CO2 from the atmosphere, as well as minimizing greenhouse gas emissions due to the lower energy needed for catalytic processes.
Beyond the game-changing potential of super catalysts, scientists are leveraging gallium's low melting point and other strange attributes to create shapeshifting and self-healing robots.
In addition, Gaston, Lambie, and Krista Steenbergen, a researcher at the Victoria University of Wellington, created zinc "snowflakes" by crystalizing zinc in liquid gallium.
"Such metal snowflakes could be useful for catalyzing chemical reactions and constructing electronics," said Gaston. "Self-assembly is the way nature makes nanostructures. We're trying to learn to do the same things."
Given all the nanotechnology breakthroughs hinging on gallium's low melting point, Lambie meticulously revisited scientific literature from previous decades and compared temperature data to piece together the complete picture.
Gallium atoms begin to reform covalent bonds with increased temperatures.
This painstaking research, carried out while Lambie was still a PhD student at the University of Auckland, found that while the covalent bonds do break when gallium melts, the atoms begin to pair up again as temperatures increase.
With this observation running headlong into previous assumptions, the researchers have some new ideas. They believe that the key to understanding liquid gallium lies in a large increase in entropy – a measure of disorder – that occurs with the freeing of atoms when the bonds disappear.
"This revised understanding of structuring in the liquid has implications for the way these alloys are tailored for specific applications in the rapidly developing field of LMs (liquid metals)," Lambie penned in the abstract for "Resolving decades of debate: the surprising role of high-temperature covalency in the structure of liquid gallium," a paper on her findings published in the scientific journal Materials Horizons.
With more than 16 years of covering mining, Shane is renowned for his insights and and in-depth analysis of mining, mineral exploration and technology metals.
Reader Comments(0)