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Why do metallic glasses usually require faster cooling than silicate glasses?

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The difference in cooling requirements between metallic and silicate glasses stems from their inherent glass-forming tendencies, which are determined by their atomic structures and crystallization kinetics.1

Silicate glasses possess a very high glass-forming tendency because they are characterized by a continuous random-network model. In these materials, atoms form strong, directional bonds that create a stable, interconnected network, making it difficult for the atoms to rearrange into a crystalline pattern during cooling.12

In contrast, metallic glasses have a very low glass-forming tendency. They are typically modeled by random close-packing, where atoms are packed together like marbles. Because metallic bonds lack the directional constraints of the covalent networks found in silicate glasses, the atoms can more easily shift into a crystalline arrangement. To bypass this "dangerous interval" where crystallization is likely to occur, metallic liquids must be cooled extremely rapidly—often through techniques like splat quenching—to "freeze" the atoms in their disordered state before they can organize into a crystal lattice.123