70. Sanganwar, Ganesh P.; Gupta, Ram B.; Ermoline, Alexandre; Scicolone, James V.; Dave, Rajesh N. Environmentally benign nanomixing by sonication in high-pressure carbon dioxide. Journal of Nanoparticle Research (2009), 11(2), 405-419.
Abstract
Due to the increased use of nanocomposites,
mixing at nanoscale has become important. Current mixing techniques can be classified
into: (a) dry mixing (mech. mixing), (b) wet mixing, and (c)
simultaneous prodn. of
mixed nanoparticles (when possible). Dry mixing is in general not effective in
achieving desired mixing at nanoscale,
whereas wet mixing
suffers from different disadvantages like nanomaterial
of interest should be insol., has to wet the liq., and involves addnl.
steps of
filtration and drying. This paper
examines the use of pressurized carbon dioxide having high d. and low
viscosity
to replace the liqs. (e.g.,
n-hexane,
toluene). Ultrasound is
applied to the suspension of nanopowders
in gaseous
and supercrit. carbon
dioxide where high impact collisions during sonication
help mixing and the final mixt. is
obtained by simple depressurization. The
method is tested for binary mixt. of
alumina/silica, silica/titania, MWNT (multiwalled carbon nanotubes)/silica,
and
MWNT/titania.
The effects of sonication intensity
and
pressure on the degree of mixing are studied.
Comparative study is also done with liq. n-hexane as a mixing
media. Quant. characterization (e.g.,
mean compn. std. deviation, intensity of
segregation)
of mixing of alumina/silica and silica/titania
is
done with energy-dispersive X-ray spectroscopy, and that of MWNT/silica
and MWNT/titania is done using
field-emission SEM and day-light
illumination spectrophotometry. Results show that mixing in carbon dioxide at
higher ultrasound amplitudes is as good as in liq. n-hexane, and the
final
mixed product does not contain any residual media as in the case of
liq.
n-hexane.
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