Aerosol wave CO2 laser, which initiates and

Aerosol technologies like spray and laser pyrolysis have
shown to be potential techniques for the direct and continuous production of
well-defined magnetic nanoparticles differing only in the final state (based on
aggregation). In spray pyrolysis technique, solution is sprayed into a series
of reactors where the aerosol droplets undergo condensation and solvent evaporates.
Condensation within the droplet is followed by drying and thermolysis of the
precipitated particle at higher temperature to obtain nanoparticles. The
resulting dried residue consists of particles whose size depends upon the
initial size of the original droplets                               (Laurent et al.,
2008).  This technique is used to produce
maghemite nanoparticles start with a Fe3+ salt and a certain organic
compound that acts as the reducing agent.  In this procedure, Fe3+ is
partially reduced to a mixture of Fe2+ and Fe3+ in the
presence of organic compounds with the formation of magnetite, which is finally
oxidized to maghemite. Without the presence of a reducing agent, hematite is
found to be formed instead of maghemite (Lu, Fan, Stump,
Ward, Rieker & Brinker, 1999).  Maghemite
particles with size ranging from 5 to         60 nm with different shapes have been
obtained using different iron precursor salts in alcoholic solution (Ali, Hira Zafar, ul Haq, Phull, Ali & Hussain,

Laser pyrolysis technique involves heating a flowing mixture of gases
with a continuous wave CO2 laser, which initiates and sustains a
chemical reaction. Above a certain pressure and laser power, a critical
concentration of nuclei is reached in the reaction zone, which leads to
homogeneous nucleation of particles that are further transported to a filter by
an inert gas. Small particle size, narrow particle size distribution, and near
absence of aggregation are amongst the salient features of this technique. The
CO2 laser pyrolysis device is used to produce pure,
well-crystallized and uniform ?-Fe2O3 nanoparticles in a
single step. In this device, a small reaction zone is defined by the overlap
between vertical reactant gas stream and horizontal laser beam. The reaction
zone is safely separated from the chamber walls. This provides an ideal
environment for the nucleation of small particles (3.5-5 nm range), with less
contamination and narrower size distribution (Tartaj, Veintemillas-Verdaguer,
& Serna, 2003).

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