Electric fields facilitate flame synthesis of powders with
precisely controlled size and
composition. Fourier transform infrared (FTIR) spectroscopy is
used for the first time to
measure the effect of electric fields on the process temperature and
composition during
synthesis of titania powders by TiCl4 oxidation in a
premixed methane−oxygen flame; flat
electrodes apply a dc electric field to the flame. Emission and
transmission FTIR spectra
are taken at various flame heights. At each height, the FTIR
measurements reveal that
the particles and the gas have the same temperature. Electric
fields modestly increase the
flame temperature. The FTIR measured mole fractions of HCl are in
good agreement with
a mass balance indicating that all TiCl4 is converted to
TiO2 by either direct hydrolysis or
oxidation followed by hydrolysis of Cl2. The
absorption spectrum of the TiO2 indicates that
the particles scatter like a collection of ellipsoids. In the
absence of electric fields, the particle
mass concentration decreases by 20% from 0.3 to 1.3 cm above the
burner by gas dilution.
In the presence of electric fields, however, that concentration
decreases by 70% over the
same distance. Thus, FTIR spectroscopy is a powerful diagnostic
tool that can provide in
situ information of the temperature, composition, and particle
characteristics in the adverse
environment of electrically modified flames.
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