Size Control of In Situ Synthesized TiB₂ Particles in Molten Aluminum

Aluminum-matrix nanocomposites offer advantageous properties over conventional aluminum alloys. However, controlling the size and size distribution of ceramic nanoparticles during in situ synthesis at high temperatures has been a long-term challenge due to a lack of effective size-control mechanisms. Here, we successfully synthesized titanium diboride (TiB₂) nanoparticles with an unprecedented narrow size distribution in molten aluminum. The average size of TiB₂ nanoparticles was tunable from 22.1 to 171.4 nm by solely controlling the reaction temperature under a diluted reactant salt solution. To uncover the mechanism of particle size control, an interface diffusion-controlled model was developed. The dilution of reactant salt was crucial to achieve a steady reaction environment while confining the growth of the particles in a shallow region. The model suggests that the average size of as-synthesized nanoparticles is mostly controlled by reaction temperature and unaffected by the titanium salt concentration in a diluted solution due to a steady diffusion of titanium and boron. Temperature controls the diffusion of reactants and nucleation rate to dictate the average size of the as-synthesized nanoparticles.