Scientists Uncover the Mystery of Stationary Atoms in Molten Metals: A New Phase of Matter Revealed
In a groundbreaking discovery, researchers have found that not all atoms in a molten metal are in constant motion. Some atoms remain stationary even at high temperatures, significantly impacting the solidification process. This phenomenon has led to the creation of a unique state of matter known as a corralled supercooled liquid.
The solidification of materials is a critical process in various natural phenomena, such as mineralization, ice formation, and protein fibril folding. It also plays a vital role in numerous technological applications, including pharmaceuticals, aviation, construction, and electronics.
Using transmission electron microscopy, scientists from the University of Nottingham and the University of Ulm in Germany observed molten metal nano-droplets as they solidified. Their findings, published in the journal ACS Nano, shed light on the complex behavior of atoms within liquids.
Professor Andrei Khlobystov, who led the research team, emphasized the mystery surrounding liquids, stating that while the behavior of atoms in gases and solids is well-understood, liquids remain more enigmatic.
Complex Atomic Motion in Liquids
In liquids, atoms exhibit intricate and crowded movements, akin to people jostling through a busy street. They zip past each other at high speeds while maintaining interactions. This motion becomes particularly challenging to study during the critical moment when a liquid begins to solidify, as this stage determines the material's structure and functional properties.
Graphene 'Hob' Experiments and the SALVE Instrument
Dr. Christopher Leist, who conducted transmission electron microscopy experiments at Ulm using the unique low-voltage SALVE instrument, explained that they initially melted metal nanoparticles, such as platinum, gold, and palladium, deposited on an atomically thin support, graphene. They used graphene as a heating platform for the particles, and as they melted, their atoms started moving rapidly. However, to their surprise, they discovered that some atoms remained stationary.
Further analysis revealed that these stationary atoms are strongly attached to the supporting material at specific locations called point defects, maintaining this strong bonding even at high temperatures. By concentrating the electron beam on selected areas, the team could create more defects and control the number of atoms that stayed pinned in place within the liquid.
Wave-Particle Duality and a New Phase of Matter
Professor Ute Kaiser, who established the SALVE center at Ulm University, highlighted the surprising observation of wave-particle duality of electrons in the electron beam. They visualized the material using electrons as waves while electrons also behaved like particles, delivering discrete bursts of momentum that could either move or fix atoms at the edge of a liquid metal. This remarkable finding led to the discovery of a new phase of matter.
Atomic Corrals and Disrupted Crystal Growth
The research team discovered that stationary atoms play a significant role in directing the solidification process. When only a few atoms are pinned, a crystal can grow from the liquid and expand until the entire nanoparticle becomes solid. However, when many atoms are held in place, they interfere with crystal formation, blocking its creation.
Professor Andrei Khlobystov explained that the effect is particularly striking when stationary atoms create a ring that surrounds the liquid. Once trapped in this atomic corral, the liquid can remain in a liquid state even at temperatures significantly below its freezing point, which is lower than what is typically expected.
Corralled Supercooled Liquid and Unstable Amorphous Metal
As the temperature is lowered, the corralled liquid eventually solidifies, but not into a regular crystal. Instead, it becomes an amorphous solid, a form of metal without the ordered structure of a crystal. This amorphous metal is highly unstable and exists only as long as the stationary atoms continue to confine it. Once the confinement breaks down, the tension is released, and the metal rearranges into its usual crystalline form.
Hybrid Metal State and Catalysis
Dr. Jesum Alves Fernandes, an expert in catalysis at the University of Nottingham, emphasized the significance of the discovery of a new hybrid state of metal. Since platinum on carbon is a widely used catalyst, finding a confined liquid state with non-classical phase behavior could revolutionize our understanding of catalysis. This advancement may lead to the design of self-cleaning catalysts with improved activity and longevity.
Toward New Forms of Matter and Cleaner Technologies
Professor Andrei Khlobystov suggested that this achievement may lead to a new form of matter, combining the characteristics of solids and liquids within the same material. By carefully arranging the positions of pinned atoms on a surface, they may build larger and more intricate atomic corrals, potentially leading to more efficient use of rare metals in clean technologies, including energy conversion and storage.
