(463b) Assembly of Magnetic Microcomposites From Low pH Precursors Using a Novel Micro-Fluidic-Jet-Spray-Dryer

Spray drying is a convenient
method to produce particles in high yields within a short period of time. The
benefits include efficient energy and solvent usages, allowing for scale-up.
However, a major challenge in most conventional spray drying is the
polydispersity of the produced particles. A novel spray dryer called
micro-fluidic-jet-spray-drier (MFJSD) coupled with micro-fluidic-aerosol-nozzle
(MFAN) could generate droplets in a single trajectory pattern, to produce
monodisperse particles. The drying temperature ranges from 90-300^oC,
so that it can be used to accommodate heat sensitive materials if necessary.
Here we investigated the use of MFJSD to generate uniform magnetic
microcomposites, specifically focusing on the effects of precursor composition,
droplet size, and secondary heat treatment on the final properties of the particles.  The presence of silica nanoparticles in
the precursor was demonstrated to directly affect the morphology of the
particles. Precursor containing silica nanoparticles generated particles with
bowl-like shapes due to slower redistribution of solutes to support the
particle skeleton during drying. In the absence of silica nanoparticles, the
particles were almost perfectly spherical albeit with dimpled surfaces. After
being subjected to calcination after drying, iron oxide crystals were found on
the particle surfaces accounting for the overall magnetic property of the
microcomposites, with lower magnetisation observed for particles containing
non-magnetic silica.

SEM pictures showing (a) spray-dried particles from
precursors containing silica sol and iron chloride; (b) the particles after
calcination at 450^oC in N₂ environment; (c) iron oxide
nanocrystals (magnetite and hematite) formed on the surface after calcination