(755d) Manufacturing of Nanostructured Particles Using Atmospheric-Pressure ALD

Core-shell nanoparticles have high potential in heterogeneous catalysis,
in energy storage, as biomarkers, and in several other applications. Currently,
such particles are mainly synthesized in the liquid phase. We think, however,
that it is advantageous to look beyond the commonly used liquid-phase approach
for the production of nanostructured particles [1]. Gas phase methods offer
several inherent advantages, such as a better potential for scaling-up and the
versatility with respect to particle material and size and structure. It will
be shown how ALD can be used to produce large amounts of these nanostructured
particles.

Nanopowders can be suspended in an upward gas phase, they can be
fluidized. In contrast to particles of say 200 mm, nanoparticles
are not fluidized individually but as agglomerates: very dilute clusters of
around 200 mm consisting of ~10¹⁰ primary
particles. The very open structure of the nanoparticle agglomerates enables the
coating of individual nanoparticles in a fluidized bed. Hakim et al. [2]
demonstrated the coating of individual nanoparticles with ALD in a fluidized
bed at rough vacuum. More recently, we demonstrated that these ultrathin
coatings on fluidized particles can also be achieved at atmospheric pressure
[3].

As an example, we
processed an amount of 100 g LiMn₂O₄ agglomerates
(diameter around 30 mm),
consisting of primary particles of 100-500 nm [3]. We coated this material
using 5 ALD cycles with alumina (see Fig. 1.) This material can be applied as
cathode material in Li-ion batteries. It will be shown that the ALD coating
strongly extends the battery lifetime.

One of the strong
points of ALD is that is can be used on many different substrates. Figure 2
gives an example of an alumina coating (5 ALD cycles) applied to Pd
nanoparticles on large BaSO₄ carrier particles, which can be used in
catalysis. In addition, a large range of materials can be deposited using ALD.
We have, for example, shown the deposition of Pt on TiO₂
nanoparticles. In the proposed paper, we will further discuss the fundamental
questions related to nanoparticle ALD, and the opportunities for practical
applications. Moreover, an outlook will be given to the continuous production
of nanostructured particles using ALD.

[1] van Ommen, J.R., Yurteri,
C.U., Ellis, N., Kelder, E.M., Particuology
8 (2010) 572-577.

[2] Hakim, L.F., Blackson,
J., George, S. M., Weimer, A. W., Chem. Vap. Dep. 11
(2005) 420-425.

[3] Beetstra, R., Lafont,
U., Nijenhuis, J., Kelder,
E.M., van Ommen, J.R., Chem. Vap. Dep. 15 (2009) 227-233.