(388q) The Polydispersity of Primary Particles in Aggregates Undergoing Sintering

The
Polydispersity of Primary Particles in Aggregates undergoing Sintering

Fractal-like
aggregates consist of multiple particles that are
connected by chemical (e.g. sintering) bonds. Such aggregates form by natural
and man-made processes, typically at high temperatures, like fly ash from coal
combustion as well as aerosol synthesis of ceramics (titania, fumed silica,
alumina) and metals (Ni, Fe, Ag etc.). The morphology of such particles has
critical implications in their performance. In nanoparticle synthesis by
aerosol processes the sintering of aggregates during particle formation narrows
their primary particle size distribution affecting mechanical and optical
properties. The understanding of the evolution of primary particle size
distributions during sintering is also important for the design of aerosol
reactors by computational modelling. Furthermore, the fractal dimension, D_f,
of agglomerates decreases steadily with increasing polydispersity of
constituent primary particles [1].

Here
a recently developed model for viscous sintering of amorphous [2] and crystalline (e.g. TiO₂
or Ag) [3] aggregates is used to elucidate the detailed evolution of their
primary particle distribution during sintering. This model reproduces nicely the
initial neck growth and evolution of particles center-to-center distance for
equally sized pairs of particles and is compared to the classic models [4]. So
the evolution of the radius of gyration and D_f of ensembles of
irregular particles is presented as they asymptotically approach full
compactness by sintering. It is shown that initially monodisperse primary
particles become slightly polydisperse during sintering exhibiting even a small
maximum in geometric standard deviation before converging to a fully coalesced
sphere. Initially polydisperse primary particles monotonically reduce the
breadth of their size distribution by sintering.

[1] Eggersdorfer, M.L. and Pratsinis, S.E., Aerosol
Sci. Technol. 46 (2012) 437-353.

[2] Eggersdorfer, M.L., et al., Langmuir 27
(2011) 6358-6367.

[3]
Eggersdorfer, M.L., et al., J. Aerosol Sci. 46 (2012) 7-19.

[4]
Coblenz, W.S., et al., Mat. Sci. Res. 13 (1980) 141-157.