ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2024 1 1 PROCESS TECHNOLOGY SYNTHESIZING DISORDERED MATERIALS Researchers from the University of British Columbia (UBC) have discovered how different synthesis methods impact the structural and functional properties of high-entropy oxides, a material used in electronic devices. These materials are promising due to their chemical flexibility and electrochemical properties. The team focused on a high- entropy oxide with a spinel crystal structure, which is a mixture of five different transition metal oxides. They prepared identical samples using five synthesis methods—solid state, high pressure, hydrothermal, molten salt, provides a deeper understanding of material strength, which could have a wide-ranging impact on materials design and manufacturing. However, it’s been difficult to study this process in real time, as atomic-scale observation typically requires electron microscopes, limiting researchers to before-and-after snapshots. To address this, the SEAS team used colloidal crystals—particles 10,000 times larger than atoms that mimic atomic systems. These crystals form similar structures, undergo comparable phase transitions, and display the same defects as atomic systems, making them ideal for studying work hardening. Despite being extremely soft—100,000 times softer than Jell-O—these crystals displayed strong work hardening, even more significant than many metals. When adjusted for particle size, they became stronger than most metals. The study revealed that the geo- metry of particles and the density of defects primarily govern work hardening. These findings provide a universal understanding of the process, generally applicable to all materials, even those that cannot be directly studied with optical microscopes. The research highlights the potential for developing stronger, more resilient materials across various fields including engineering and manufacturing. seas.harvard.edu. and combustion syntheses. Each method involves different heating and cooling processes and chemical conditions. The key difference between the synthesis methods is the driving mechanism that forms the material, says lead researcher Mario Ulises González-Rivas. In the solid-state method, metal oxides are mixed and then heated, similar to baking a cake. The high pressure method adds external pressure during heating, which can influence how the material forms. The hydrothermal method mimics mineral formation in Earth’s core by heating metal salts in water inside a pressurized vessel, creating a flow that helps crystals grow. The molten salt method uses melted metal salts, which form a thick liquid that, as it cools, allows crystals to precipitate. Lastly, the combustion method involves dissolving metal salts in water, forming a gel that ignites, rapidly producing the desired material through a quick combustion reaction. “Our results confirm that the synthesis method matters a great deal,” conclude the researchers. “We found that while the average structure is unaltered, the samples vary significantly in their local structures and their microstructures with the combustion synthesis resulting in the most homogeneous samples.” www.ubc.ca. WORK HARDENING MECHANISMS REVEALED For the first time, scientists have observed the detailed mechanisms behind work hardening using colloidal crystals. A team of researchers from Harvard University’s School of Engineering and Applied Sciences (SEAS), Cambridge, Mass., grew these crystals, composed of millions of particles, and tracked their movement with a confocal optical microscope. It’s the first time that work hardening has been observed in colloidal crystals. The team’s work Vianode, a battery materials manufacturer, opened its first full-scale anode graphite production plant called Via ONE in Heroya, Norway. The facility has four furnaces specifically designed to produce synthetic anode graphite for lithium-ion batteries, with an annual capacity of 2000 tons. vianode.com. BRIEF Metal oxides are mixed and then heated during the solid-state method. Courtesy of UBC. A snapshot of the von Mises equivalent strain, calculated for γ ≈ 0.06, after the onset of the localization of flow. Courtesy of Harvard SEAS.
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