AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
The Crystallinity and Coalescence or Sintering Mechanism of Aerosol Nanoparticles by Molecular Dynamics
Beat Buesser, SOTIRIS E. PRATSINIS, ETH Zurich
Abstract Number: 385 Working Group: Nanoparticles and Materials Synthesis
Abstract Recent computational advances have led to accelerated molecular dynamics unraveling the evolution of morphology by coalescence of nanoparticles with initial diameter 2 - 4 nm. This bridges the gap of knowledge from molecular sizes to the bulk properties of materials. That way it was shown that coalescence of titania aerosol nanoparticles proceeds by surface diffusion rather than grain boundary diffusion as it was believed from sintering of much larger particles (30-100 nm). This shift in understanding is attributed to the free surface of aerosol nanoparticles in contrast to the constrained surfaces of powder compacts that are routinely employed in materials science (1). Here sintering of Ag nanoparticles is investigated by molecular dynamics at various temperatures and arrangements. The melting temperature of these nanoparticles was reduced with decreasing particle size but converged to the bulk value of Ag for bigger particles. Sintering below these temperatures is dominated again by surface diffusion whereas a transition towards plastic flow is observed near the size-dependent melting temperature. The characteristic sintering time of straight chains of three particles is longer than that of two of the same diameter while the most compact, triangular, structure of three particles sinters even faster than two nanoparticles! Star configurations of four nanoparticles sinter nearly as fast as chains of three. Sintering by surface diffusion either increased the number of crystals by forming new grains right at the sintering neck or decreased it by consuming up smaller grains.
Buesser, B, Grohn, A, Pratsinis, SE (2011) Sintering Rate and Mechanism of TiO$_2 Nanoparticles by Molecular Dynamics. J. Phys. Chem. C 115, 11030-11035.