A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 2 2 9 aluminum hydroxide mineral on a mica surface in water. The team identified a crystallization pattern that was atypical of the classical nucleation theory. Instead of a rare event in which a cluster of atoms reaches a critical size and then grows across the surface, they saw thousands of fluctuating clusters that coalesced into an unexpected pattern, with gaps that persisted between crystalline islands. The team concluded that while certain aspects of the current theory held true, ultimately their system followed a nonclassical pathway. They attribute this to electrostatic forces from charges on the mica surface. Because many types of materials form charged surfaces in water, the researchers hypothesize that they observed a widespread phenomenon and are excited to look for other systems where this nonclassical process might occur. “Assumptions from classical nucleation theory have far-reaching implications in disciplines ranging from materials science to climate prediction,” the researchers say. “The results Monash University Professor Andy Tomkins (left) with RMIT University Ph.D. scholar Alan Salek holding a ureilite meteor sample. Courtesy of RMIT University. from our experiments can help produce more accurate simulations of such systems.” pnnl.gov, washington.edu, www. durham.ac.uk. DIAMONDS FROM OUTER SPACE A collaborative teamof researchers from Australia and the U.K. confirmed the existence of lonsdaleite, a rare hexagonal form of diamond, in ureilite meteorites from inside a dwarf planet in our solar system. According to the team, the unique diamonds may have formed shortly after the dwarf planet collided with a large asteroid about 4.5 billion years ago. The team—consisting of scientists from RMIT University, Monash University, the Australian Synchrotron, and the U.K.’s Plymouth University—says theun- usual hexagonal structure of lonsdaleite could help inform new manufacturing techniques for ultra-hard materials in mining applications. The researchers used advanced electron microscopy techniques to capture solid and intact slices from the meteorites to create snapshots of how lonsdaleite and regular diamonds formed. www.monash. edu, www.rmit.edu.au, www.ansto.gov. au, www.plymouth.ac.uk.
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