Molecular Dynamics of Nanoparticle Sintering

BEAT BUESSER (1), ARTO GROHN (1), SOTIRIS E. PRATSINIS (1)

(1) ETH Zurich

     Abstract Number: 226
     Last modified: April 30, 2010

Abstract
TiO$_2 particles are often made by the “chloride” or “sulfate” process. There, it is important to control the size and morphology of the nanoparticles for optimal performance and material safety. Non-sintered agglomerates, held together by weak van-der-Waals forces, dissolve the primary particles into solution, allowing them to cross cell walls more easily and cause damage. Whereas aggregates with sintered necks between the primary particles do not break apart, even under high pressure (Teleki et al., 2008).
To design and optimize aerosol reactors for nanoparticle production and to adjust the particle size, crystalinity and state of aggregation, it is important to know the dynamics of particle growth, most importantly the coagulation (Buesser et al., 2009) and sintering rate as function of temperature and particle size. Here, molecular dynamics implemented on the newest hardware allowing massive parallelization has been used to investigate the sintering kinetics of small nanoparticles until complete coalescence.
The evolution of the surface area of sintering TiO$_2 nanoparticles has been simulated and three regions of sintering could be identified. First, area decreases as the particles touch and form a small sinter-neck, followed by plateau whith nearly constant area where atoms in the contact zone have to restructure the crystal orientation. Finally, a sharp decrease leads to complete coalescence to one single nanoparticle. This surface area evolution is compared with the area evolution of the sintering model of Koch and Friedlander (1990) and different characteristic sintering times. The influence of particle size, temperature and orientation on the evolution of the surface area will be discussed.

Teleki, A. et al. (2008), Powder Technol., 181, 292-300
Buesser, B., Heine, M.C., Pratsinis, S.E (2009), J. Aerosol Sci., 40, 89-100
Koch, W. and Friedlander, S. K. (1990), J. Colloid Interface Sci., 140, 419-427